Improving Vision in Adults With Macular Degeneration

The purpose of this study is to test whether a kind of brain stimulation called anodal transcranial direct current stimulation (a-tDCS) can improve the ability of people with age-related macular degeneration (AMD) or juvenile macular degeneration (JMD) to read words presented to them on a computer screen. In addition, secondary measures of visual acuity will also be examined to determine whether brain stimulation can allow patients to resolve finer details of an image. The proposed treatment is the application of a-tDCS onto the participant's head, with brain stimulation aimed at Primary Visual Cortex toward the occipital pole. The investigators will test the ability of participants to read words before and after the application of stimulation. The difference between the pre and post tests when receiving active stimulation will be compared to the difference when receiving sham stimulation, because sham stimulation is not expected to improve reading beyond a placebo. The aim of the study is to examine the potential of brain stimulation as an effective treatment for macular degeneration that may be used in conjunction with more traditional eye-based interventions. The investigators hypothesize that the brain stimulation will enable higher performance in the reading task and secondary measures due to an increase in the cortical excitability of the stimulated brain cells.

This study will be carried out in Ontario, Canada (University of Waterloo) and Hong Kong (The Hong Kong Polytechnic University). There are two conditions: Active brain stimulation and sham/placebo brain stimulation. This study uses a within-subjects design, such that all participants will take part in both conditions on separate sessions.

Participants will be recruited from university-affiliated clinics and local clinical practices. Following full informed consent, participants will complete baseline testing and clinical testing to confirm that they meet eligibility criteria including: a diagnosis of macular degeneration without any additional eye disease, impaired vision but with enough visual acuity that the computer monitor can still present readable word, and no contraindications for brain stimulation interventions. Eligible participants will then be randomized to either receiving the active stimulation first or the placebo stimulation first.

The primary outcome measure is verbal reading accuracy for sentences presented on a computer screen following a Rapid Serial Visual Presentation (RSVP) task in which a single word is presented on the screen at a time. Participants will freely observe the words and will indicate the words on the screen verbally. The secondary outcome measures are crowded and uncrowded visual acuity as measured by Freiburg Visual Acuity \& Contrast Test (FrACT) using the Landolt C stimulus. The "C"'s gap will be oriented randomly, and the participant will indicate the orientation of the stimulus. Crowded visual acuity will be assessed with Landolt C surrounded by a solid ring, while uncrowded visual acuity will be assessed with the Landolt C alone.

The study consists of 3 sessions:

Session 1: The first session will include the clinical evaluation. In addition, the first session will also collect the participant's individual RSVP performance threshold by presenting a variety of reading speeds and print sizes. The selected threshold will be the combination of print size and presentation speed required for a given participant to achieve roughly 55% performance accuracy.

Session 2 and 3: Brain stimulation sessions. At the start of each session, participants will perform baseline pre tests for the uncrowded and crowded visual acuity tasks as well as the RSVP task using their selected threshold from Session 1. They will then undergo a-tDCS to their primary visual cortex - this stimulation may be either active or placebo on any given day, but all participants will have been exposed to both sham and placebo by the end of Session 3. During the brain stimulation, participants will perform post tests for the primary outcome measure (RSVP) and the two secondary outcome measures (crowded and uncrowded visual acuity). Five minutes after the completion of the brain stimulation, participants will again perform all three post tests. A third set of post tests will be completed 30 minutes after the completion of the brain stimulation.

All outcome measures will be analyzed by comparing the baseline (pre test) scores to the post test scores, examining whether the active brain stimulation condition resulted in greater post test improvement relative to the placebo brain stimulation condition. The time course of the effect of brain stimulation will also be examined by comparing the effect of brain stimulation at each of the 3 post tests to one another.

Eligibility Criteria:
Inclusion Criteria:

1. Diagnosis of AMD (age 60+) or JMD (current age 18+).
2. Central vision loss and use of a peripheral preferred retinal locus (PRL) to fixate on visual objects, as confirmed by a microperimeter.
3. Visual acuity (VA); between 0.5 and 1.0 logMAR inclusive (6/18-6/60) in the better eye.
4. Best-corrected near visual acuity of 4.0M at 40 cm or better in the better eye
5. Stable vision for the previous 3 months (by patient report).

Exclusion Criteria:

1. Diagnosed dementia.
2. Not fluent in reading English (Waterloo) or Chinese characters (Hong Kong).
3. Any ocular surgery (including anti-vegF injections) within the duration of the study.
4. Ocular pathology other than JMD or AMD that can reduce central vision.
5. Severe hearing impairment.
6. Contraindications for brain stimulation