abstract: Until the pathophysiology/etiology of rheumatoid arthritis (RA) is better understood, treatment strategies must focus on disease management. Early diagnosis and treatment with disease-modifying antirheumatic drugs (DMARDs) are necessary to reduce early joint damage, functional loss, and mortality. Several clinical trials have now clearly shown that administering appropriate DMARDs early yields better therapeutic outcomes. However, RA is a heterogeneous disease in which responses to treatment vary considerably for any given patient. Thus, choosing which patients receive combination DMARDs, and which combinations, remains one of our major challenges in treating RA patients. In many well controlled clinical trials methotrexate and other DMARDs, including the tumor necrosis factor-α inhibitors, have shown considerable efficacy in controlling the inflammatory process, but many patients continue to have active disease. Optimizing clinical response requires the use of a full spectrum of clinical agents with different therapeutic targets. Newer therapies, such as rituximab, that specifically target B cells have emerged as viable treatment options for patients with RA.
author: Larry Moreland
date: 2005
institute: 1University of Alabama at Birmingham School of Medicine, Birmingham, Alabama, USA
references:
title: Unmet needs in rheumatoid arthritis

# Introduction

Current treatment guidelines suggest that early diagnosis and initial treatment with disease-modifying antirheumatic drugs (DMARDs) are necessary to limit early joint damage and functional loss and to reduce mortality associated with rheumatoid arthritis (RA) \[1\]. The earlier use of methotrexate alone and in combination with other DMARDs is now the standard of care and has yielded better outcomes for patients with RA.

However, RA is a heterogeneous disease, and patient responses to standard treatments are variable. Most recent clinical trials of newer DMARDs alone and in combination with methotrexate have shown that ACR50 response – which includes reducing the signs and symptoms of disease by 50%, according to criteria established by the American College of Rheumatology (ACR) – was achieved in less than two-thirds of the patients \[2-5\]. That leaves at least one-third of the most seriously affected patients with RA without an effective long-term treatment strategy. Until we are able to identify which patients will respond to which treatment, the availability of a variety of agents with different therapeutic targets offers the best opportunity to optimize clinical outcomes.

Rituximab, a chimeric anti-CD20 monoclonal antibody that has emerged as a potential treatment for RA via selective targeting of B lymphocytes, has been used extensively in the treatment of B cell malignancies. There is a growing body of evidence for the pathophysiologic role of B cells. Silverman and Carson \[6\] described that B lymphocytes can present immune-complexed antigens to autoreactive T cells; express adhesion and other co-stimulatory molecules that promote T cell activation; synthesize chemokines that induce leukocyte infiltration; produce factors that initiate and sustain angiogenesis and granulation tissue formation; and release autoantibodies that are directly or indirectly destructive to tissues and maintain a memory response to autoantigens. Apart from B cells and T cells, populations of monocytes, macrophages, endothelial cells, and fibroblasts have been implicated in the ongoing inflammatory process \[7\]. The availability of a broader spectrum of agents with different targeting mechanisms will provide more effective treatment options for diverse patient populations.

# Overall picture of rheumatoid arthritis

RA affects almost 1% of the adult population worldwide \[1\]. Clinicians have reason to be concerned when they manage a chronic and debilitating condition that requires aggressive, life-long management. When one looks at large cohort populations, patients with RA exhibit increased morbidity and mortality, compounded by a dramatic impact on quality of life. Approximately 80% of affected patients are disabled after 20 years \[8\], and life expectancy is reduced by an average of 3–18 years \[9\].

The management of RA has a marked impact in terms not only of the financial burden to the health care system but also of the financial burden to individual patients and their families. It has been estimated that the disorder costs the average individual up to US\$8500 annually \[10\], with time lost from work ranging from 2.7 to 30 days \[11\].

# Treatment advances over the past decade

During the past 10 years or so, advances in the treatment of RA have underscored the role of methotrexate as a major cornerstone of therapy. However, many randomized controlled trials have demonstrated that methotrexate in combination with another DMARD is more effective than methotrexate monotherapy for many patient populations \[3-5,12\].

In a 2002 study, Kremer and colleagues \[12\] tested the hypothesis that adding leflumonide to the regimen of patients taking methotrexate alone would strengthen the clinical response. The team assigned 263 patients with RA to leflunomide plus methotrexate or methotrexate alone. At 24 weeks, 46.2% (60 of 130) of patients receiving the leflunomide–methotrexate combination had achieved an ACR20 clinical response, as compared with 19.5% of the patients who had been maintained on a methotrexate–placebo regimen (*P* \< 0.001). In addition, they reported that 26.2% of the leflunomide patients achieved an ACR50 response, as compared with 6.0% of the patients in the methotrexate–placebo arm (*P* \< 0.001). This study was one of the first to show that the combination of the two biologic agents produced statistically significant and clinically meaningful improvement in patients with active RA.

In a 2-year, randomized, double-blind, placebo-controlled trial, O'Dell and colleagues \[13\] compared the effectiveness of methotrexate in combination with either hydroxychloroquine or sulfasalazine, as well as a combination of all three drugs. After 2 years, 55% of the 58 patients in the triple therapy arm achieved an ACR50 response; 40% of patients on hydroxychloroquine and methotrexate achieved an ACR50 response; and 29% of those on sulfasalazine and methotrexate achieved an ACR50 response. The differences between triple therapy and double therapy with sulfasalazine reached statistical significance (*P* = 0.005).

# Biologic response modifiers

Efforts to develop safer and more effective treatments for RA, based on an improved understanding of the role of inflammatory mediators, have been realized through the development of the biologic response modifiers. Some biologics have been approved for use in RA by the US Food and Drug Administration and the European Medicine Evaluation Agency, including etanercept (a soluble tumor necrosis factor \[TNF\]-α type II receptor–IgG~1~ fusion protein administered subcutaneously), infliximab (a chimeric \[human and mouse\] monoclonal antibody against TNF-α), and adalimumab (a human anti-TNF monoclonal antibody). These therapies have shown the ability to change dramatically the outcomes of the disease in some RA patients.

Researchers have observed that interleukin (IL)-1, IL-6, and TNF-α are important mediators that initiate and maintain inflammation in RA, resulting in cellular infiltration of synovium and damage, and the destruction of cartilage and bone \[14\]. TNF-α, a potent cytokine that exerts diverse stimulatory effects, is produced mainly by monocytes and macrophages, but also by B cells, T cells, and fibroblasts. Newly synthesized TNF-α is expressed on the cell membrane and subsequently released through the cleavage of its membrane-anchoring domain by a serine metalloproteinase. Thus, inhibition of TNF-α secretion may represent a therapeutic target.

RA is believed to be initiated by CD4^+^ T cells, which amplify the immune response by stimulating other mononuclear cells, synovial fibroblasts, chondrocytes, and osteoclasts. Activated CD4^+^ T cells contribute to stimulation of osteoclastogenesis and activation of metalloproteinases responsible for the degradation of connective tissue, resulting in joint damage.

Clearly, there are many possible therapeutic targets, but inhibition of cytokines appears to offer an especially efficient approach to suppressing inflammation and preventing joint damage \[14\]. There are four biological therapies currently approved for RA: three TNF-α inhibitors (infliximab, etanercept, and adalimumab) and one IL-1 inhibitor (anakinra).

Abatacept, a cytotoxic T lymphocyte-associated antigen 4–IgG~1~ (CTLA4–Ig) fusion protein, known as a co-stimulation blocker, is administered in a 30 min infusion. Recent clinical trial data show that the combination of abatacept and methotrexate improves the signs and symptoms, physical functioning, and quality of life of patients with active RA \[15\].

## Etanercept

In the Trial of Etanercept and Methotrexate with Radiographic Patient Outcomes (TEMPO), Klareskog and coworkers \[16\] enrolled 685 patients with active RA in a double-blind, randomized trial to determine the safety and efficacy of treatment with etanercept or methotrexate alone or in combination versus placebo for up to 52 weeks. Patients were randomly assigned to treatment with etanercept 25 mg subcutaneously twice a week, oral methotrexate monotherapy up to 20 mg every week, or a combination of the two agents.

The researchers found that the proportions of patients achieving ACR50 and ACR70 responses were consistently higher for the combination group than either the etanercept or methotrexate treatment arms throughout the study (Fig. 1). At week 52, 69% of the patients in the combination protocol achieved an ACR50 response, as compared with 43% and 48% in the methotrexate and etanercept monotherapy groups, respectively (*P* \< 0.0001). Moreover, after a 1-year period, 43% of the patients in the combination group had an ACR70 response, as compared with 19% and 24% in the methotrexate and etanercept monotherapy patients, respectively (*P* \< 0.0001). Additionally, more than one-third of patients treated with the methotrexate–etanercept combination protocol were in remission at 52 weeks.

The number of patients reporting infection or adverse events (AEs) was similar in all groups. Overall, Klareskog and colleagues reported that the combination of etanercept and methotrexate was significantly better in reducing disease activity, improving functional disability, and retarding radiographic progression compared with methotrexate or etanercept alone.

A comparison of therapy with methotrexate and therapy with etanercept was also conducted by Bathon and colleagues \[17\]. They evaluated 632 patients with early RA who were given either twice weekly subcutaneous etanercept (10 mg or 25 mg) or weekly oral methotrexate (mean 19 mg/week) for 12 months.

Compared with patients who received methotrexate, patients taking the 25 mg dose of etanercept exhibited a more rapid rate of improvement, with significantly more patients having ACR20, ACR50, and ACR70 response improvement in disease activity during the first 6 months (*P* \< 0.05). The mean increase in the erosion score during the first 6 months was 0.30 in the group assigned to receive 25 mg etanercept and 0.68 in the methotrexate group (*P* = 0.001). The respective increases during the first 12 months were 0.47 and 1.03 (*P* = 0.002).

Among patients who received the 25 mg dose of etanercept, 72% had no increase in the erosion score, as compared with 60% of patients in the methotrexate group (*P* = 0.007). This group of patients also had fewer AEs (*P* = 0.02) and fewer infections (*P* = 0.006) than did the group treated with methotrexate. Compared with oral methotrexate, subcutaneous etanercept acted more rapidly to decrease symptoms and slow joint damage in patients with early active RA.

Bathon and colleagues observed that the patients in the study were at risk for rapidly progressive joint damage. Their disease was predicted to progress without treatment at an estimated rate of four to five points per year on the Sharp erosion subscale, and four points per year on the Sharp joint-space narrowing subscale. The rates of progression for joint-space narrowing were low. Both etanercept and methotrexate prevented joint-space narrowing. The overall rates of erosion were also low, equivalent to the occurrence of one new erosion or the erosion of 20% of one joint every year in the methotrexate group and every 2 years in the group assigned to receive 25 mg etanercept. The effects of this dose of etanercept were evident sooner than were the effects of methotrexate, but the rates of change were similar in the two groups during the latter half of the study. Over a 1-year period, treatment with etanercept halted erosions in 72% of patients, whereas treatment with methotrexate halted erosions in 60% of patients \[17\].

## Adalimumab

In a pivotal study \[18\], the combination of the biologic adalimumab and methotrexate, particularly at a higher dose of 40 mg every other week, yielded a statistically significant improvement compared with methotrexate plus placebo. In that multicenter, 52-week, double-blind, placebo-controlled study, 619 patients with active RA who had an inadequate response to methotrexate alone were randomly assigned to receive adalimumab 40 mg subcutaneously every other week (*n* = 207), adalimumab 20 mg subcutaneously every week (*n* = 212), or placebo (*n* = 200) plus concomitant treatment with methotrexate. The primary efficacy end-points were radiographic progression at week 52 (total Sharp score by a modified method); clinical response at week 24, defined as improvements that achieved at least an ACR20 response; and improvement in physical function at week 52, based on the disability index of the Health Assessment Questionnaire (HAQ). At week 52 there was statistically significantly less radiographic progression (Fig. 2), as measured by change in total Sharp score, in the patients receiving adalimumab either 40 mg every other week (change \[mean ± standard deviation\] 0.1 ± 4.8) or 20 mg weekly (0.8 ± 4.9), as compared with that in the placebo group (2.7 ± 6.8; *P* \< 0.001).

At week 52, ACR50 responses were achieved by 42% and 38% of patients taking adalimumab 40 mg every other week and 20 mg weekly, respectively, but by 10% of patients taking placebo (*P* \< 0.001). In terms of physical function at week 52, patients on combination therapy with adalimumab and methotrexate experienced statistically significant improvement (mean change in HAQ score -0.59 and -0.61, respectively, versus -0.25; *P* \< 0.001).

Adalimumab was generally well tolerated. Discontinuations occurred in 22% of adalimumab treated patients and in 30% of placebo treated patients. The rate of both serious AEs and nonserious AEs was similar between adalimumab and placebo groups. The proportion of patients reporting serious infections was higher in patients receiving adalimumab (3.8%) than in those receiving placebo (0.5%; *P* \< 0.02) and was highest in the patients receiving 40 mg every other week.

The benefits of early treatment of RA with adalimumab, either alone or in combination with methotrexate, were supported more recently by the results of the PREMIER study \[19\]. In an analysis of almost 800 patients with a disease duration of less than 3 years, adalimumab 40 mg every other week plus methotrexate (escalated rapidly to 20 mg/week) exhibited statistically significant improvement in ACR50 clinical response and amelioration of disease progression compared with either adalimumab or methotrexate alone. Of patients in the combination therapy group, 61% and 46% achieved ACR50 and ACR70 responses, respectively, as compared with 46% and 28% in the methotrexate group (*P* \< 0.001) – a statistically significant difference that was sustained for up to 2 years. The difference in clinical response was also comparable between the combination arm of the trial and patients taking adalimumab alone. Moreover, at 2 years radiographic remission (as indicated by a Disease Activity Scale \[DAS28\] score \< 2.6) was achieved by 50% of patients receiving combination therapy.

## Infliximab

Much of the recent knowledge regarding the safety and efficacy of infliximab in combination with methotrexate emerged from analysis of data from the Anti-Tumor Necrosis Factor Trial in Rheumatoid Arthritis with Concomitant Therapy (ATTRACT) trial \[20,21\], the pivotal study that led to approval of the TNF-α inhibitor infliximab in the USA and worldwide. ATTRACT demonstrated that the combination of methotrexate and infliximab, in particular, with highest doses given every 4–8 weeks, resulted in better clinical responses than methotrexate plus placebo.

In that study the investigators established that infliximab not only provided significant improvements in physical function and quality of life, but also succeeded in slowing or halting progressive joint damage and signs and symptoms of RA in patients who previously had an incomplete response to methotrexate alone.

The study included 428 patients who were randomly assigned to receive methotrexate plus placebo or infliximab at a dose of 3 mg/kg or 10 mg/kg plus methotrexate for 54 weeks, with an additional year of follow up. The protocol was later amended to allow for continued treatment during the second year.

Of 259 patients who entered the second year of treatment, 216 continued to receive infliximab plus methotrexate for 102 weeks. Ninety-four of these 259 patients experienced a gap in therapy of greater than 8 weeks before continuing therapy. Infusions were administered at baseline, week 2, and week 6, followed by treatment every 4 weeks or every 8 weeks – alternating with placebo infusions in the interim 4-week visits – at a dose of 3 mg/kg or 10 mg/kg for a total of 102 weeks, which included the gap in therapy.

The results of the study showed that the infliximab plus methotrexate regimens led to significantly greater improvement in HAQ scores (*P* = 0.006) and in the Short Form 36-Item Health Survey (SF-36) physical component summary scores (*P* = 0.011), compared with the group of patients receiving monotherapy with methotrexate. There also was stability in the SF-36 mental component summary score among patients who received the infliximab plus methotrexate regimens. The median changes from baseline to week 102 in the total radiographic score were 4.25 for patients who received the methotrexate-only regimen and 0.50 for patients who received the infliximab plus methotrexate regimen. The proportion of patients achieving an ACR50 response at week 102 varied from 20% to 21% for the infliximab plus methotrexate groups, as compared with 6% for the methotrexate-only group. These data emphasize that the combination of infliximab plus methotrexate conferred significant, clinically relevant improvement in physical function and quality of life, accompanied by inhibition of progressive joint damage and sustained improvement in the signs and symptoms of RA among patients who previously had an incomplete response to methotrexate alone.

The ASPIRE (Active controlled Study of Patients receiving Infliximab for RA of Early onset) trial \[5\] randomly assigned patients with early RA to either methotrexate alone or methotrexate plus 3 mg/kg or 6 mg/kg infliximab at weeks 0, 2, and 6, and every 8 weeks thereafter through week 46. It revealed improvement in ACR scores in both combination treatment groups compared with the methotrexate arm (38.9% and 46.7%, versus 26.4%, respectively; *P* \< 0.001 for both comparisons), significantly less radiographic progression at 6 months and 12 months, and improvement in physical function.

## Anakinra

Treatment with anakinra, the first IL-1 receptor antagonist, either alone or in combination with methotrexate, has emerged as an effective medication for patients with moderate-to-severe RA. In a study of 419 patients with active RA of duration greater than 6 months but less than 12 years \[22\], patients were randomly assigned to placebo or one of five doses of anakinra (0.04, 0.1, 0.4, 1.0 or 2.0 mg/kg) plus methotrexate. Those assigned to the five anakinra regimens exhibited statistically significant (*P* = 0.001), dose-escalating efficacy in ACR20 responses as compared with the placebo plus methotrexate group after 12 weeks. The ACR20 response rates in the anakinra 1.0 mg/kg (46%; *P* = 0.001) and 2.0 mg/kg (38%; *P* = 0.007) dose groups were significantly better than those in the placebo group (19%). ACR20 responses at 24 weeks were consistent with those at 12 weeks. Other researchers have reported similar 6-month ACR20 (and ACR50) responses, as well as in individual components (i.e. HAQ, pain, C-reactive protein level, and erythrocyte sedimentation rate) \[23\].

## Abatacept

Abatacept (CTLA4–Ig), a cytotoxic T-lymphocyte-associated antigen 4–IgG~1~ fusion protein, is the first in a new class of drugs known as co-stimulation blockers that are being evaluated for the treatment of RA. Abatacept selectively modulates the co-stimulatory signal required for full T cell activation. The agent, which binds to CD80 and CD86 on antigen-presenting cells, blocking the engagement of CD28 on T cells and thus preventing T cell activation, acts earlier in the inflammatory cascade than do other biologic therapies by directly inhibiting the activation of T cells and the secondary activation of macrophages and B cells.

The efficacy of this novel therapy was tested by Kremer and colleagues \[24\], who randomly assigned patients with active RA despite methotrexate therapy to receive 2 mg/kg CTLA4–Ig (105 patients), 10 mg/kg (115 patients), or placebo (119 patients) for 6 months. All patients also received methotrexate therapy during the study. Patients treated with 10 mg CTLA4–Ig were more likely to have an ACR20 response than were patients who received placebo (60% versus 35%; *P* \< 0.001). Significantly higher rates of ACR50 and ACR70 responses were seen in both CTLA4–Ig groups than in the placebo group \[24\]. The group given 10 mg CTLA4–Ig had clinically meaningful and statistically significant improvements in all eight subscales of the SF-36. CTLA4–Ig was well tolerated, with an overall safety profile similar to that of methotrexate \[15\].

Recently released phase III results from the Abatacept in Inadequate responders to Methotrexate (AIM) trial \[24\] found that 48.3% of patients achieved an ACR50 response after 1 year of therapy compared with 18.2% of patients who were given methotrexate injections (*P* \< 0.001). At 6 months, the number of patients on abatacept who achieved an ACR70 response was 19.8%, compared with 6.5% of patients on methotrexate. After 1 year, 28.8% of patients had reached an ACR70 response, compared with 6.1% of patients on methotrexate. Both differences were statistically significant (*P* \< 0.001).

# Tumor necrosis factor-α: potential safety issues

Although researchers, scientists, and clinicians are enthusiastic in their support of early intervention with TNF-α inhibitors for patients with RA, safety issues remain an important consideration. Although infusion reactions and other AEs are infrequent, they may be very serious in some patients, in particular when complications associated with opportunistic infections occur. There is a need to follow patients very closely and to work with primary care physicians to see that these issues are addressed first and foremost.

Rare and serious AEs include infections (bacterial, fungal, or tubercular), demyelination, infusion related events, hematologic/lymphoproliferative disorders, drug-induced systemic lupus erythematosus/vasculitis, hepatotoxicity (infliximab), and potential congestive heart failure. The development of neutralizing antibodies also can be an issue in some patients and needs further exploration. Further studies are needed to determine whether some of these reported side effects are truly related to the TNF-α inhibitor, or are a consequence of the disease itself and/or comorbid conditions and concomitant medications.

# Challenges

Typically, clinicians have reserved biologics for those patients with severe disease who have failed other therapies. However, the emerging body of evidence suggests that practitioners should be moving toward treating earlier disease with these biologic agents in an effort to prevent structural damage. In addition, because of the costs associated with biologic therapy – often more than US\$1000 per month \[25\] – and the potential risk for immune suppression, one of the key challenges that clinicians should address when considering the use of TNF-α inhibitor therapy for active RA is how to determine which patients should be receiving which agents and in what combination. Importantly, the medical community must endeavor to identify those patients who will respond over the long term to these agents and weigh the risk/benefit. Is it possible to pick out which patients are most likely to have that long-term response? There are numerous challenges and opportunities, as well as many unmet needs for patients with RA.

# Conclusion

RA is a hetereogeneous disease; there is substantial evidence that some patients respond adequately to a single DMARD, whereas others require a combination regimen. Reliable predictors of response are needed to guide therapeutic decision making, along with a firm definition of therapeutic goals. It is of equal importance to arrest the ongoing pre-existing damage or to intervene earlier to prevent damage. In addition, over the long term, as research and treatment become more aggressive, efficacy, toxicity, and costs must be balanced within the therapeutic equation to enhance the quality of life in patients with RA (Table 1).

Therapy for rheumatoid arthritis: unmet needs

| Problem | Details |
|----|----|
| Heterogeneity of the disease | Some patients respond to DMARD monotherapy |
|  | Not every patient responds to anti-TNF (mono or combination) therapy |
|  | 'Remission' rates |
|  | What is the pathology/biologic process in each individual patient? |
| Toxicities | Infections, immunogenecity, congestive heart failure, drug-induced vasculitis, etc |
| Costs | Limits availability to may patients |

DMARD, disease-modifying antirheumatic drug; TNF, tumor necrosis factor.

The next generation of therapies for RA will provide considerable opportunities. These include next generation TNF-α inhibitors, anticytokines (anti-IL-6 receptor, anti-IL-15, and anti-IL-1), angiogenesis inhibitors, antiadhesion molecules, anti-T-cell co-stimulatory blockers (e.g. abatacept), anti-B-cell therapies (i.e. rituximab and belimumab), and many others.

# Abbreviations

ACR = American College of Rheumatology; AE = adverse event; CTLA4–Ig = cytotoxic T lymphocyte-associated antigen 4–IgG~1~; DMARD = disease-modifying antirheumatic drug; HAQ = Health Assessment Questionnaire; IL = interleukin; RA = rheumatoid arthritis; SF-36 = Short Form 36-Item Health Survey; TNF = tumor necrosis factor.

# Competing interests

LM has received research grant support, and consulting and speaking fees from several companies in the past, including Abbott, Amgen, Centocor, Wyeth, Immunex, Bristol-Myers Squibb, Regeneron, Genentech, Merck, Pfizer, Boehringer Ingelheim, Roche and others.


abstract: A light-sensitive, externally powered microchip was surgically implanted subretinally near the macular region of volunteers blind from hereditary retinal dystrophy. The implant contains an array of 1500 active microphotodiodes ('chip'), each with its own amplifier and local stimulation electrode. At the implant's tip, another array of 16 wire-connected electrodes allows light-independent direct stimulation and testing of the neuron–electrode interface. Visual scenes are projected naturally through the eye's lens onto the chip under the transparent retina. The chip generates a corresponding pattern of 38 × 40 pixels, each releasing light-intensity-dependent electric stimulation pulses. Subsequently, three previously blind persons could locate bright objects on a dark table, two of whom could discern grating patterns. One of these patients was able to correctly describe and name objects like a fork or knife on a table, geometric patterns, different kinds of fruit and discern shades of grey with only 15 per cent contrast. Without a training period, the regained visual functions enabled him to localize and approach persons in a room freely and to read large letters as complete words after several years of blindness. These results demonstrate for the first time that subretinal micro-electrode arrays with 1500 photodiodes can create detailed meaningful visual perception in previously blind individuals.
author: Eberhart Zrenner; Karl Ulrich Bartz-Schmidt; Heval Benav; Dorothea Besch; Anna Bruckmann; Veit-Peter Gabel; Florian Gekeler; Udo Greppmaier; Alex Harscher; Steffen Kibbel; Johannes Koch; Akos Kusnyerik; Tobias Peters; Katarina Stingl; Helmut Sachs; Alfred Stett; Peter Szurman; Barbara Wilhelm; Robert Wilke\*Author for correspondence (<email@example.com>).
date: 2011-05-22
institute: 1Centre for Ophthalmology, University of Tübingen, Schleichstr. 12, 72076 Tübingen, Germany; 2Eye Clinic, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany; 3Retina Implant AG, Gerhard-Kindler-Str. 8, 72770 Reutlingen, Germany; 4Department of Ophthalmology, Semmelweis University, Tomo u. 25-29, 1083 Budapest, Hungary; 5Steinbeis Transfer Centre Eyetrial at the Centre for Ophthalmology, Schleichstr. 12-16, 72076 Tübingen, Germany; 6Klinikum Friedrichstadt, Friedrichstr. 41, 01067 Dresden, Germany; 7NMI Natural and Medical Sciences Institute at the University of Tübingen, Markwiesenstr. 55, 72770 Reutlingen, Germany
references:
title: Subretinal electronic chips allow blind patients to read letters and combine them to words

# Introduction

Retinitis pigmentosa (RP) and age-related macular degeneration are diseases that predominantly affect photoreceptors of the retina and cause progressive vision loss—leading eventually to blindness in over 15 million people worldwide \[1\]. Although blindness owing to photoreceptor degeneration presently remains incurable, inner retinal nerve cells may continue to function for many years despite neuronal remodelling \[2\]. While gene therapy and application of neuro-protective factors may help maintain vision in the early stages of degeneration, survival of the inner retina encouraged us \[3\] and others \[4–11\] to attempt a partial restoration of visual function using electric stimulation of the remaining retinal network.

Two fundamentally different approaches have been taken in this area: (i) implantation of electrode arrays which interface epiretinally with retinal ganglion cells that form the retinal output pathway \[6–7,11–13\], and (ii) implantation of microchips under the transparent retina to substitute the degenerated photoreceptors. The latter type of microchip senses light and generates stimulation signals simultaneously at many pixel locations, using microphotodiode arrays (MPDAs; \[3,14\]). While the first approach typically requires external image and data processing due to bypassing retinal image analysis, the second seeks to replace the function of degenerated photoreceptors directly by translating the light of the image falling onto the retina point by point into small currents that are proportional to the light stimulus. Ours is the only approach where the photodiode–amplifier–electrode set is contained within a single pixel of the MPDA such that each electrode provides an electrical stimulus to the remaining neurons nearby, thereby reflecting the visual signal that would normally be received via the corresponding, degenerated photoreceptor.

On the basis of *in vitro* measurements \[15\] and animal studies \[16\] our consortium developed a subretinal electronic implant that carefully accounts for biocompatibility \[17\], biostability, surgical feasibility by means of a transchoroidal surgical technique \[18\], safe threshold stimulation and dynamic range of stimulation and the limits of spatial resolution *in vitro* \[19\]. This report describes the results of a clinical pilot study, illustrating that subretinally implanted multi-electrode arrays restore sufficient visual function for object recognition and localization and for the performance of visual tasks essential in the daily lives of blind patients. The results of this pilot study provide strong evidence that the visual functions of patients blinded by a hereditary retinal dystrophy can, in principle, be restored to a degree sufficient for use in daily life.

# The subretinal implant

As shown in figure 1*a*, the tip of the implant consists of an MPDA with 1500 individual light-sensitive elements and a test field for direct stimulation (DS) with 4 × 4 electrodes for electrical, light-independent stimulation. Both are positioned on a thin polyimide foil (figure 1*b*, far left). For details on the control unit that provides power and wireless control signals, see figure 2*a*,*d* and electronic supplementary material, chapter 1*c*.

## The microphotodiode array

Each of the 1500 MPDA elements acts independently from its neighbours; four magnified elements (72 × 72 µm each) are shown in figure 1*g*. Each element includes a light-sensitive photodiode (15 × 30 µm) that controls a differential amplifier (circuit shown as a sketch) whose output stage is coupled to a titanium nitride (TiN) electrode (50 × 50 µm), connected to the amplifier via the contact hole (details see electronic supplementary material, chapter 1*b*). Essentially, an image is captured several times per second simultaneously by all photodiodes. Each element ('pixel') generates monophasic anodic voltage pulses at its electrode. Thus, pixelized repetitive stimulation is delivered simultaneously by all electrodes to adjacent groups of bipolar cells \[15,19\], the amount of current provided by each electrode being dependent on the brightness at each photodiode. Light levels ranging across approximately 2 log units are converted to charge pulses by each pixel with a sigmoidal relationship and the sensitivity can be shifted manually by several log units (see electronic supplementary material, chapter 1, figure S1). The chip is estimated to cover a visual angle of approximately 11° by 11° (1° approx. 288 µm on the retina). The distance between two MPDA electrodes corresponds to a visual angle of 15 min of arc.

## The 4 by 4 test field for direct stimulation (DS test field)

The DS test field consists of 4 × 4 quadruple TiN electrodes (100 × 100 µm^2^, 280 µm apart laterally and 396 µm diagonally) for light-independent electrical stimulation (see figure 1*c*). The DS test field was added for assessment of the electrode-interface characteristics and to study current injections and efficacy of pulses with different shapes and polarities other than those provided by the MPDA. In a limited spatial testing range simple patterns can be created with the DS test field as well (figure 1*d*,*e* and *f*).

Threshold voltage to elicit a percept was assessed in an up-and-down staircase procedure. Typical charge transfer of a single electrode at threshold was between 20 and 60 nC per pulse (for details, see electronic supplementary material, chapter 1*a*). The maximum charge density at the electrodes in the DS field was 600 µC cm^−2^. These values were well within commonly accepted safety limits and have been proven safe even for continuous retinal stimulation *ex vivo* \[20\].

Impedance values of single electrodes were typically 300 kΩ (at 1 kHz sinusoidal AC). Although regular impedance measurements in the patients were not conclusive, analysis of all available data showed that charge thresholds, but not voltage thresholds decreased significantly during the first days after implantation. Thereafter, both charge and voltage thresholds showed a slight tendency towards increasing values over the remaining implantation period.

# Patients

The patients (two males and one female, age 40, 44 and 38, respectively) were blind owing to hereditary retinal degeneration (patients 1 and 2: RP, patient 3: choroideraemia) but had good central vision previously. Disease onset was reported by patient 2 at age 16, by patients 1 and 3 at age 6. They had lost their reading ability at least 5 years before implantation. Bright light stimulation mediated some limited light perception without any recognition of shapes in all three patients. They reported neither general diseases nor regular medication (for details see electronic supplementary material, chapter 2*c*).

# Methods

## Surgical procedure

The implant, protected by a long steel tube, was advanced through a retroauricular incision to the lateral orbital rim and guided inside the orbit to the surface of the eyeball (\[21\]; figure 2*a*,*b*,*e*). The silicone cable (figure 2*a*) was implanted subperiostally beneath the temporal muscle. The polyimide foil was then protected by a silicone tube and guided from the lateral orbital rim, where it was fixed, to the equator of the eye. Subsequently pars plana vitrectomy was performed. A localized retinal detachment was created by saline injection in the upper temporal quadrant above the planned scleral and choroidal incision area. After preparation of a scleral flap, the implant was advanced *ab externo* transchoroidally along a guiding foil into the subretinal space until it reached the preoperatively defined position (\[22\]; see electronic supplementary material, chapter 2*d*). Although putting a chip directly under the fovea has not turned out to be a surgical problem we had abstained in initial patients from placing the chip under the macula, but asked to place the chip closer and closer to the foveola as the surgical learning curve improved. Silicone oil was then injected into the vitreous cavity to support retinal reattachment. No serious adverse events were noted during the course of the study. For post-operative observations and consideration on surgical safety see electronic supplementary material, chapter 2*f*).

## Psychophysical tests

Beginning 7 to 9 days after surgery, tests with solely electrical stimuli were performed with the DS test field. Thereafter light evoked visual functions mediated by the MPDA-array were assessed using four psychophysical tests concerning light detection, basic temporal resolution, object localization and movement detection using the 'basic light and motion test' (BaLM \[23\]) described in electronic supplementary material, chapter 2*g*.

If passed successfully, three further steps followed: tests for recognition of stripe patterns (BAGA \[24\]), localization and recognition of objects common to daily life and visual acuity assessment (Landolt-C rings presented in an up-and-down staircase procedure to estimate the visual acuity in terms of maximum likelihood by means of FrACT test \[25\]). If these tasks were completed successfully, more challenging tasks were set (figures 3*a* and 4*a*). Except for some optional tasks (indicated) well-established two- or four-alternative forced-choice methods (2AFC and 4AFC, respectively) were employed in order to test for statistical significance of a patient's performance. All tests were performed separately in two conditions: with 'Power ON' and 'Power OFF' ('baseline performance').

Maximum screen luminance was approximately 3200 cd m^−2^ (for white light), neutral density filters (Schott NG filters 0.15–4 log U) served for attenuation (for details see electronic supplementary material, chapter 2).

# Results

## Electrical stimulation for pre-testing and learning via DS test field

Pulses of varying duration, polarity and shape were applied via the DS test field (16 electrodes, as shown in figure 1*c*–*f*) in a pre-testing routine. This procedure determined voltage thresholds for perception, accustomed the patients to electrically evoked visual impressions and tested retinal excitability and spatial resolution. An overview of the results including their statistical evaluation is given in a table presented in electronic supplementary material, chapter 3*a*.

All patients detected single-electrode single-pulse stimulation (0.5–6 ms pulses, typically 20–60 nC per electrode). Patients 1 and 2 consistently reported these stimuli as whitish round dot-like percepts, patient 3 reported percepts as elongated, short whitish/yellowish lines. Upon activation of four electrodes with a single pulse, all three patients correctly distinguished vertical lines from horizontal lines within seconds and spontaneously reported them as straight. Patients 1 and 2 distinguished multiple single dots upon simultaneous activation of several electrodes in a diagonal row and reported dark areas separating the dots. Patient 3 saw diagonal lines formed by four electrodes, but not the dark areas between the dots.

Simple patterns were also presented with the DS-array by pulsing electrodes sequentially (figure 1*d*); each electrode was switched on for 3–6 ms at intervals of 208 ms. Patients 1 and 2 correctly reproduced these patterns after the first single presentation; patient 3 failed to do so. Upon presentation of a four-alternative, forced-choice (4AFC) paradigm, patients 1 and 2 reliably differentiated four different positions of the opening of the letter 'U' (73% and 88% correct responses, respectively, see electronic supplementary material, chapter 5, movie 1). Furthermore, patient 1 correctly distinguished 'U' from 'I' and even squares from triangles when only a single activated electrode differed in position (16/16 correct, figure 1*e*,*f*). Patient 2 correctly distinguished four letters individually presented randomly in 4AFC-mode (e.g. C,I,L,O (36/36), I,L,V,T (10/12)) in repetitive tests on different days (see electronic supplementary material, chapter 5, movie 2). He also distinguished sequential stimulation in clockwise versus anticlockwise direction (15 of 16 tests correct).

## Light pattern perception with the microphotodiode array

The light-sensitive MPDA chip was operated at a sampling rate of 1 to 20 Hz with a pulse duration (PD) of 1–4 ms. The patient's head was comfortably positioned on a chin-rest (set up 1, figure 3*a*), and refraction was corrected for the viewing distance of 60 cm. Chip settings were adjusted for a working range of 8–800 cd m^−2^ white light or 1.2–4.3 cd m^−2^ red light (for details see electronic supplementary material, chapter 2*g*). All standardized testing was performed using a functional baseline control, i.e. performance was also tested with the chip switched off at random intervals unknown to patient and observer, as summarized in electronic supplementary material, table ST1.

### Light perception and localization

All three patients were able to perceive light mediated by the chip. This was verified in task 1, using the BaLM-test in set up 1 (figure 3*a*):

1.  — *BaLM flash test*: in task 1, the whole screen was illuminated briefly with one or two flashes (200 ms duration with 600 ms pause) after an auditory signal. All three patients passed this test for light detection (81.3%, 100% and 100% correct, respectively) and scored well-above chance rate; (*n* = 16; ON versus OFF: *p* = 0.00005, *t*-test).

2.  — *BaLM localization test*: when testing the ability to localize large bright areas in the visual field (small triangle in relation to a central fixation point in BaLM test) only patient 2 (87.5%; *n* = 16) passed the test successfully.

3.  — *BaLM movement test*: perception of movement was tested with a random dot pattern at an angular speed of 1.11° s^−1^ moving in one of four directions (dot diameter 1.4 cm, average distance 1.5 cm (s.d. 0.26)), passed only by patient 2 (8 of 12, 4AFC, figure 3*e*).

In task 2, spatial resolution was tested using grid patterns (figure 3*b*). Bright lines of 0.6 cm width separated by 1.8 cm wide dark lines as well as bright lines of 0.8 cm width separated by 2.4 cm wide dark lines were presented at 63 cm distance. The orientation of these patterns was correctly recognized by patient 2. In terms of spatial frequency this corresponds to 0.46 cycles deg^−1^ (five of eight correct, 4AFC, *p* = 0.02) and 0.34 cycles deg^−1^ (four of four correct, 4AFC, *p* = 0.004), respectively (see electronic supplementary material, chapter 3, table ST1 and chapter 5, movie 3). Patient 3 succeeded at 0.22 cycles deg^−1^ (12 of 20, 4AFC, white light). Patient 1 had difficulty seeing the stripes, probably owing to her nystagmus, but distinguished horizontal from vertical lines projected onto her chip in a special set up using a fundus camera with comparable spatial arrangements and luminance.

As the spectral sensitivity of the chip is practically flat far into the infrared region, patients at several instances reported high sensitivity to infrared light.

### Landolt C ring

In task 3, single letters and Landolt C rings were presented on the screen in various sizes (figure 3*c*). Patients 1 and 3 discerned neither the Landolt C rings nor the letters and were accordingly not presented with tests of higher difficulty in set up 1. Patient 2, the only one with the chip placed under the macula, was quite successful and his visual performance is therefore described in greater detail below.

Optimizing his implant settings resulted in an image recording time of 0.5 ms with a 7.5 Hz repetition frequency at a target luminance of 3.4 cd m^−2^ (red light), viewed with a correction of +7.0 dpt sph., −1.50 dpt cyl. at 121°. Landolt C rings (figure 3*c*) were presented in an up-and-down staircase procedure (FrACT \[25\]; for details see electronic supplementary material, chapter 2). A maximum of 60 s was allowed for the patient to find each C-ring on the screen in his small visual field; failure to respond in time counted as mistake. Maximum visual acuity was up to 20/1000 (log MAR =1.69)—corresponding to a Landolt ring with 4.5 cm outer diameter and a gap of 9 mm, viewed at about 60 cm distance. In three other trials on different days he achieved log MAR values of 1.75, 1.94 and 1.86, respectively (see electronic supplementary material, chapter 5, movie 4).

Patient 2 reliably differentiated also the letters L,I,T,Z on a screen (22 of 24, 4AFC, figure 3*d*; 8.5 cm high, 1.7 cm line width, corresponding to a height of approximately 9° of visual angle). He reported that having once found a letter, it appeared clearly in its natural form and was visible as a complete entity—even during its first presentation.

### Recognition of objects on a table

In the fourth task, the ability to perceive more naturalistic scenes was tested by a standardized set up at a dining table, assessed by an independent, professional mobility trainer (figure 4*a*, for details see electronic supplementary material, chapter 2*g*). Patient 1 reliably localized a saucer, a square and a cup on the table; patient 3 correctly localized and differentiated a large plate from a saucer.

Patient 2 localized, and moreover recognized and correctly differentiated square-, triangle-, circle-, rectangular-, and diamond-shapes, which differed only in shape but not in area from each other (figure 4*b*, five of five correct, see electronic supplementary material, chapter 5, movie 5). Furthermore, he could localize and describe correctly a spoon, a knife, a cup (see electronic supplementary material, chapter 5, movie 6), as well as a banana and an apple (see electronic supplementary material, chapter 5, movie 7). Unlike the other dining table set ups this set up was entirely unknown to the patient and he was forced to make sense of an unfamiliar scene.

### Optional tasks with letters, clock, grey papers of varying shades

The fifth group of tasks was performed only in patients who had successfully passed previous tasks. Patient 2 was able to distinguish between 16 different letters cut from white paper (5–8 cm high, font: Tahoma), placed on the black table (see figure 4*c*, 22/36 correct). The patient read letters (LOVE, MOUSE, SUOMI, etc.) correctly (five of five), also repeatedly on several days. He noted spelling mistakes in his name MIIKKA (mentioning that one 'I' and one 'K' were missing) when he first saw this word (see electronic supplementary material, chapter 5, movie 8), i.e. he perceived both individual letters and continuous, meaningful words—a prerequisite for reading.

As an additional task, a clock face was presented with two hands (6 × 1.5 cm for the hours, 12 × 1.5 cm for the minutes, figure 4*d*). Patient 2 was asked to indicate clock times set to full quarter hours. The patient correctly recognized 11 of 12 possible settings. Patient 2 also distinguished seven out of nine contrast differences of 15 per cent among nine neighbouring cards (10 × 10 cm, presented in 2AFC mode, *p* = 0.07) with linearly scaled shades of grey varying from 3 to 35 cd m^−2^ (figure 4*e*).

All patients showed distinct learning effects which, while they could not be quantified in this first pilot study, are reported as 'spontaneous observations' in electronic supplementary material, chapter 3*d*.

### Pupillary reflexes

Pupillary constriction in response to light as an objective measure of MPDA efficacy was assessed by infrared pupillography (for methods and recordings, see electronic supplementary material, chapter 2*i*). The amplitude of pupillary constriction was clearly more pronounced when the chip was activated (see electronic supplementary material, chapter 2, figure S2). In all three patients the chip-on condition improved pupil reaction and was always accompanied by subjective light perception. An analysis of variance was calculated for the constriction amplitudes of all three patients (with chip-on or chip-off) and patient as factors (sum of squares 0.184, *F* = 6.48, *p* = 0.022).

# Discussion

## The general approaches to retinal prostheses

A number of research groups have taken up the challenge of developing a retinal prosthesis. Rizzo *et al.* \[4\] and Weiland *et al.* \[26\] have reported on first trial stimulations of the retina with single epiretinal electrodes. Chow *et al*. \[27\] were the first to subretinally implant well-tolerated multiphotodiode arrays, intending to use the energy created by incident light for neuronal stimulation directly without amplification. However, owing to insufficient energy from the small light sensors these failed to restore vision. Second Sight (Medical Products Inc., Sylmar, CA) has a multicentre study running with the epiretinal ARGUS II device with 60 electrodes; some patients were reported to recognize large single letters by scanning them with rapid head movements \[28\]. Clinical studies with epiretinal electrode arrays were also performed by Koch *et al.* \[29\] and Richard *et al.* \[30\]. Other groups developed approaches with electrodes placed between sclera and choroid \[8,10\]. These groups argue that this 'suprachoroidal' approach may have the benefit of being less invasive, therefore bearing fewer risks in terms of surgical procedures. At this time, as only limited peer-reviewed information is available from ongoing clinical trials using subretinal, epiretinal and suprachoroidal approaches, it is too early to compare the final long-term outcome of the various designs. All have inherent theoretical advantages and disadvantages; basic differences and their consequences are pointed out in the following.

*Epiretinal implants* seek to interact directly with the retinal output neurons; the image processing of the complex inner retinal network must be performed externally. The processing of camera-captured images can be more easily adjusted to account for individual electrode thresholds. However, the number of simultaneously addressed electrodes is limited by present technology. Several groups have developed externally powered, fully implantable epiretinal systems with arrays of up to 60 microelectrodes \[7,28–32\]. Although they have reported promising results, even for long term use, the low number of electrodes limit visual performance to object localization and shape perception \[33\]. Yanai *et al*. \[6\] reported no difference in patient performance when a single pixel or multiple pixels were activated using a prototype of the ARGUS I implant. In *epiretinal* implants that use head mounted cameras, eye movements are not correlated to the visually perceived scene. Such a mismatch of visual and proprioceptive information must render object localization difficult \[34\].

*Subretinal approaches*, in contrast, replace in principle only the lost function of diseased photoreceptors; thus, the remaining network of the inner retina can be used for more natural processing of the image as it is forwarded, point–by-point, several times per second to inner retinal neurons. Although the surgical procedure may be more demanding, the number of pixels can be much higher, presently limited only by the size of an implant and the spatial spread of electrical stimulation. Fixation of the chip in the subretinal space is easier and, once positioned, the chip remains in place, tightly connected to the inner retina without the need for scleral tacks as used in epiretinal approaches. Moreover, our subretinal implant (Retina Implant AG, Reutlingen, Germany) is the only one so far, where the image receiver array moves exactly with the eye. This has practical implications, outlined below, as natural eye movements can be used to find and fixate a target. On the other hand, the duration of our study was limited owing to time constraints of a transdermal cable; other studies have reported longer implantation times \[33\]. Moreover, the range of variations in online image processing is small in devices that work quasi-autonomously under the retina.

*Suprachoroidal implants*, although bearing lower surgical risks, are located further away from target cells. This may result in high stimulation thresholds, increased power consumption, and certainly loss of spatial resolution. While the surgery is easier and less invasive, the location between highly light absorbing sclera and choroid does not allow the implantation of a light sensitive array that moves with the eye.

In the following sections, the results obtained in our subretinal study are discussed in more detail.

## The spatial domain

Using simulated prosthetic vision Perez *et al*. \[35\] have shown that the precision in recognition tasks with normal sighted subjects increased with a density of pixels up to 1000 in a 10° × 7° visual field on the retina. Thus, at least several hundred electrodes should be employed to provide significant vision—a daunting technical barrier \[35\]. The present study—the first to successfully employ electronic arrays with such a large number of electrodes—presents proof-of-concept that such devices can restore useful vision in blind human subjects, even though the ultimate goal of broad clinical application will take time to develop.

The size of the visual field (11° × 11°) in our patients, although small, is sufficient for orientation and object localization, as is well established in patients with peripheral retinal dystrophies. Reading requires a field of 3 by 5 degrees according to Aulhorn \[36\].

Inter-individual variations in visual performance among the patients of this study can be assumed to result from their respective stages of degeneration \[2\], the duration of their blindness, and the retinal localization of the implant, although presently no convincing correlation can be established. Clearly spatial reorganization of the retina takes place; however, it is very slow, taking decades. As the inner retina is not dependent on choroidal perfusion, it also survives the complete loss of the choroid—as seen in our patient with choroideraemia. This also explains why blockage of choroido-retinal transport by our implant does not affect survival of the inner retina.

In our study, precise localization of the microelectrode array under the fovea appeared important for the restoration of useful percepts via spatially ordered electrical stimulation. High spatial resolution and the ability to read are restricted in normal observers to the central retina (5° × 3°), which is significantly over-represented in the visual cortex relative to more peripheral areas of the retina.

## The temporal domain and the problem of image fading

Temporal resolution was investigated over a range from 1 to 20 Hz. When applying continuous electrical stimuli via the *DS-array* at a fixed retinal location with PD of 1–4 ms, patient percepts faded after approximately 15 s when presented at a 0.3 Hz repetition rate; after approx. 2 s at 2 Hz; and after approx. 0.5 s at 10 Hz. This is in close accordance with the observations of Perez *et al*. \[37\] with *epiretinal* ARGUS II devices that an image stabilized on the retina quickly disappears; to restore the image required a movement of the image across the retina, by means of rapid head shaking. Similarly, Jensen & Rizzo \[38\] observed in rabbit retina that the retinal response to a second or third electrical pulse rapidly decreases as compared to the first pulse with increasing repetition rates; apparently inner retina neurons suffer from a prolonged inhibition if stimulated electrically under conditions where the surrounding network under the electrode is being activated as a whole. By contrast, objects like grating patterns or letters can be perceived continuously with our light sensitive *subretinal MPDA*. Patients see the image constantly as a complete entity without head movements—even on the first day of stimulation. The source of this difference can be found in involuntary eye movements controlled by the superior colliculus. Even during fixation, our eyes continuously make slight movements (slow drifts and microsaccades up to 50 min of arc and 1 to 3 Hz) that refresh the image by constantly changing the activated photoreceptor population—even during strict fixation \[39\]. Objects viewed by our patients—with the chip moving in synchronization with natural eye movement—dynamically activate a range of adjacent pixels on the chip, as eye movements and microsaccades continuously shift the 'electrical image' on the retina for about 1–3 pixels, thus preventing mechanisms of local adaptation and image fading. Details on the role and magnitude of microsaccades in relation to pixel size are outlined in electronic supplementary material, chapter 3*e* (figure S3).

## The cellular 'interface'

*In vitro* experiments have shown that subretinal stimulation, at least at threshold, preferentially stimulates bipolar cells \[15,19\]. This may be one reason for the correct retinotopic perceptions reported in this study, since local excitation of small groups of bipolar cells is recognized in the brain at the correct position in the visual field. By contrast, epiretinal stimulation of ganglion cell fibres may result in disparities between stimulation location and perceived visual field location because the axons of RGCs course across the retina on their way into the brain via the optic nerve. On the other hand, none of the different approaches has principal problems with addressing simultaneously ON and OFF neurons (see electronic supplementary material, chapter 3*c*).

## Learning and cognition

With the subretinal approach and its retinotopically correct spatial transmission, no long-term learning procedure was necessary to enable the patients to recognize shapes correctly. Even at the first trial with the DS test field or with the MPDA, patients were able to correctly perceive the complete entity of an object in the presented physical geometric form, the bright parts appearing whitish or yellowish, the dark parts as grey or black; there were no reports on colour sensations although in very rare and brief instances coloured tinges were noticed by patients.

The observation that patient 2 could readily name an object upon its first presentation to his visual field is of particular importance, and is in line with our observation of retinotopically correct perception from DS experiments and from the other patients who recognized a line and its direction clearly. This does not mean that the patients had undisturbed percepts. Patients reported some wobbling of the image, probably owing to a relatively low image capture frequency (5–7 Hz) to which they adapted quickly.

As expected, patient performance improved over time. Practising with the MPDA between 4 to 6 h daily, they had to learn to control their eye position because each object was presented within a relatively small field of vision (11° × 11°). Patient 2 reported that the two lines of the letter L were initially moving slightly independently of each other, but that they appeared connected at the corner after approximately one week. Apparently the binding of correlated motion cues can be regained quickly (see electronic supplementary material, chapter 3*d* and chapter 5, movie 9). If patients were asked to point to an object they had discovered there was clearly improvement of visuomotor abilities within a week.

## Future concepts

*Methodological and technical aspects*: our first approach was designed as a short duration study of up to several weeks in only a few patients in order to achieve a proof-of-concept for a cable bound version of a subretinal active implant. Our ongoing follow-up study is employing the next-generation system (Alpha IMS; \[40\], produced by Retina Implant AG, Reutlingen, Germany), where an encapsulated secondary coil for power and signal transmission is positioned subdermally behind the ear, with a primary coil clipped magnetically on top. We also anticipate that lateral processing in terms of mutual inhibition of pixels, as performed in centre-surround receptive field processing will improve contrast vision and spatial resolution. Penetrating three-dimensional electrodes as developed by various groups may improve the contact to the bipolar cell layer but may be more damaging to the retina.

# Conclusion

This study demonstrated that subretinal micro-electrode arrays can restore visual percepts in patients blind from hereditary retinal degenerations to such an extent that localization and recognition of objects can provide useful vision, up to reading letters. Despite all remaining biological and technical challenges, our results offer hope that restoration of vision in the blind with electronic retinal prostheses is a feasible way to help those who cannot profit from emerging gene therapy and/or the application of neuroprotective agents. The advantage of our approach is that all parts of the device can be implanted invisibly in the body, that inner retina processing can be used and that a continuous, stable image with unmatched spatial resolution is perceived. Still further development is necessary to provide long term stability, improved contrast, spatial resolution and increased field size through multiple chip implantation. Nevertheless, the present study provides proof-of-concept that electronic subretinal devices have the potential to improve visual function from a state of complete blindness to one of low vision that allows localization and recognition of objects up to reading capability.

## Acknowledgements

We are very grateful to all who contributed to the 'SUBRET' project; for names of contributors, funding organizations and disclosure of interest we refer to electronic supplementary material.

# References


date: 2018-06
title: 9 out of 10 people worldwide breathe polluted air, but more countries are taking action

2 May 2018 - WAir pollution levels remain dangerously high in many parts of the world. New data from WHO shows that 9 out of 10 people breathe air containing high levels of pollutants. Updated estimations reveal an alarming death toll of 7 million people every year caused by ambient (outdoor) and household air pollution.

"Air pollution threatens us all, but the poorest and most marginalized people bear the brunt of the burden," says Dr Tedros Adhanom Ghebreyesus, Director-General of WHO. "It is unacceptable that over 3 billion people – most of them women and children – are still breathing deadly smoke every day from using polluting stoves and fuels in their homes. If we don't take urgent action on air pollution, we will never come close to achieving sustainable development."

7 million deaths every year

WHO estimates that around 7 million people die every year from exposure to fine particles in polluted air that penetrate deep into the lungs and cardiovascular system, causing diseases including stroke, heart disease, lung cancer, chronic obstructive pulmonary diseases and respiratory infections, including pneumonia.

Ambient air pollution alone caused some 4.2 million deaths in 2016, while household air pollution from cooking with polluting fuels and technologies caused an estimated 3.8 million deaths in the same period.

More than 90% of air pollution-related deaths occur in low- and middle-income countries, mainly in Asia and Africa, followed by low- and middle-income countries of the Eastern Mediterranean region, Europe and the Americas.

Around 3 billion people – more than 40% of the world's population – still do not have access to clean cooking fuels and technologies in their homes, the main source of household air pollution. WHO has been monitoring household air pollution for more than a decade and, while the rate of access to clean fuels and technologies is increasing everywhere, improvements are not even keeping pace with population growth in many parts of the world, particularly in sub-Saharan Africa.

WHO recognizes that air pollution is a critical risk factor for noncommunicable diseases (NCDs), causing an estimated one-quarter (24%) of all adult deaths from heart disease, 25% from stroke, 43% from chronic obstructive pulmonary disease and 29% from lung cancer.

More countries taking action

More than 4300 cities in 108 countries are now included in WHO's ambient air quality database, making this the world's most comprehensive database on ambient air pollution. Since 2016, more than 1000 additional cities have been added to WHO's database which shows that more countries are measuring and taking action to reduce air pollution than ever before. The database collects annual mean concentrations of fine particulate matter (PM10 and PM2.5). PM2.5 includes pollutants, such as sulfate, nitrates and black carbon, which pose the greatest risks to human health. WHO air quality recommendations call for countries to reduce their air pollution to annual mean values of 20 µg/m3 (for PM10) and 10 µg/m3 (for PM25).

"Many of the world's megacities exceed WHO's guideline levels for air quality by more than 5 times, representing a major risk to people's health," says Dr Maria Neira, Director of the Department of Public Health, Social and Environmental Determinants of Health, at WHO. "We are seeing an acceleration of political interest in this global public health challenge. The increase in cities recording air pollution data reflects a commitment to air quality assessment and monitoring. Most of this increase has occurred in high-income countries, but we hope to see a similar scale-up of monitoring efforts worldwide."

While the latest data show ambient air pollution levels are still dangerously high in most parts of the world, they also show some positive progress. Countries are taking measures to tackle and reduce air pollution from particulate matter. For example, in just two years, India's Pradhan Mantri Ujjwala Yojana Scheme has provided some 37 million women living below the poverty line with free LPG connections to support them to switch to clean household energy use. Mexico City has committed to cleaner vehicle standards, including a move to soot-free buses and a ban on private diesel cars by 2025.

Major sources of air pollution from particulate matter include the inefficient use of energy by households, industry, the agriculture and transport sectors, and coal-fired power plants. In some regions, sand and desert dust, waste burning and deforestation are additional sources of air pollution. Air quality can also be influenced by natural elements such as geographic, meteorological and seasonal factors.

Air pollution does not recognize borders. Improving air quality demands sustained and coordinated government action at all levels. Countries need to work together on solutions for sustainable transport, more efficient and renewable energy production and use and waste management. WHO works with many sectors including transport and energy, urban planning and rural development to support countries to tackle this problem.

Key findings:

WHO estimates that around 90% of people worldwide breathe polluted air. Over the past 6 years, ambient air pollution levels have remained high and approximatively stable, with declining concentrations in some part of Europe and in the Americas.

The highest ambient air pollution levels are in the Eastern Mediterranean Region and in South-East Asia, with annual mean levels often exceeding more than 5 times WHO limits, followed by low and middle-income cities in Africa and the Western Pacific.

Africa and some of the Western Pacific have a serious lack of air pollution data. For Africa, the database now contains PM measurements for more than twice as many cities as previous versions, however data was identified for only 8 of 47 countries in the region.

Europe has the highest number of places reporting data.

In general, ambient air pollution levels are lowest in high-income countries, particularly in Europe, the Americas and the Western Pacific.In cities of high-income countries in Europe, air pollution has been shown to lower average life expectancy by anywhere between 2 and 24 months, depending on pollution levels.

"Political leaders at all levels of government, including city mayors, are now starting to pay attention and take action," adds Dr Tedros. "The good news is that we are seeing more and more governments increasing commitments to monitor and reduce air pollution as well as more global action from the health sector and other sectors like transport, housing and energy."

This year WHO will convene the first Global Conference on Air Pollution and Health (30 October – 1 November 2018) to bring governments and partners together in a global effort to improve air quality and combat climate change. <http://www.who.int/airpollution/events/conference/en/>

Available from: <http://www.who.int/news-room/detail/02-05-2018-9-out-of-10-people-worldwide-breathe-polluted-air-but-more-countries-are-taking-action>