bluuebunny/crossref_metadata_2025 huggingface dataset:
Descemet’s Membrane Detachment
Authors: Kahook Malik Y.
Published: November 2020

Corneal injury resulting from glaucoma surgery has been well described. Causes of injury can range from direct mechanical manipulation to the often more subtle pharmacologically induced injuries that occur with use of antifibrotic medications. Descemet’s membrane detachment (DMD) occurs uncommonly during or after intraocular surgery and has been linked with a variety of procedures ranging from simple clear cornea cataract extraction to deep lamellar keratoplasty. The corneal endothelium, which rests upon Descemet’s membrane, functions as a pump to keep the stroma from becoming swollen. Therefore, DMD results in focal corneal edema and possibly bullous keratopathy. If detachment of Descemet’s membrane extends far enough centrally, visual acuity may become sufficiently compromised to necessitate corneal transplantation surgery (either full-thickness penetrating keratoplasty [PKP] or Descemet’s stripping with automated endothelial keratoplasty [DSAEK]). In glaucoma surgery, DMD often results from the mechanical manipulation that occurs with creation of the cornealtrabecular meshwork opening. Knowing how to accurately diagnose and treat DMD can prevent disastrous consequences and preserve vision. Mackool and Holtz proposed separating DMD into 2 categories, planar and nonplanar, depending on the distance of separation between Descemet’s membrane and the posterior corneal stroma. Planar DMD involves less than 1 mm separation of Descemet’s membrane from the corneal stroma and may be limited to the periphery or extend from the periphery to central regions. Nonplanar DMD involves greater than 1 mm separation of Descemet’s membrane from the corneal stroma and may also be categorized as limited to the periphery or extending to central regions. The significance of this classification was the belief that planar DMD was more likely to spontaneously resolve while nonplanar DMD required surgical intervention. Assia and colleagues also split DMD into 2 categories: DMD with scrolling of tissue and DMD without scrolling of tissue. They believed this classification more accurately described potential for spontaneous resolution in that nonscrolled DMD was more likely to resolve without surgical intervention, even if its location was >1mm from the posterior corneal stroma. While useful as a general guide, these classification systems are not foolproof, and each case of DMD should be viewed independently.
Early Excessive Iritis
Authors: Nagi Kundandeep S.
Published: November 2020

Inflammation in the early postoperative period after filtration surgery generally resolves quickly; however, there are certain underlying conditions that may produce more than the usual degree of iritis. Uveitis or iritis after glaucoma surgery may often be more severe and longer lasting than the minimal postoperative inflammation common after some other intraocular surgeries. Recognizing excessive inflammation may allow steps to be taken to prevent permanent adverse sequelae. Lacy vacuolization of the iris stroma and pigment epithelium is often present in diabetic patients. Manipulation of this abnormal iris may cause excessive, recalcitrant postoperative inflammation believed to be due to instability of the iris and/or iris pigment epithelium and a fragile blood aqueous barrier. Patients with diabetes are also at increased risk of developing endophthalmitis after intraocular surgery. Unless infectious in nature, this excessive iritis can generally be controlled with aggressive topical corticosteroid therapy. With prophylactic pre- and perioperative application of antibiotics, wound infections are rare, and the risk of early endophthalmitis following trabeculectomy remains small. However, bacterial endophthalmitis may develop months to years after routine trabeculectomy. A retrospective review of 988 trabeculectomies performed over 5 years reported only one case of early bleb-related endophthalmitis, due to Morganella morganii . Host flora is usually responsible for early cases, Staphylococcus epidermidis being the most common organism. Papaconstantinou and colleagues reported a case of acuteonset Lactobacillus endophthalmitis occurring 10 days after trabeculectomy with the OloGen™ ( OculusGen Biomedical Inc. Taipei, Taiwan) implant in the absence of antimetabolite. Severe iritis that represents endophthalmitis may present acutely after filtering surgery. The clinical picture is that of acute endophthalmitis, but the etiology is noninfectious. Subjective complaints of pain and decreased vision combined with objective findings of anterior and posterior inflammation are common. For more information on endophthalmitis, see Chapters 24 and 42. Excessive inflammation that is not responsive to routine therapy may represent toxic anterior segment syndrome (TASS), an acute, postoperative inflammatory disorder that may occur after anterior segment surgery. TASS is a sterile inflammatory reaction that is typically seen at the first postoperative visit.
Hypotony Maculopathy
Authors: Stamper Robert L.
Published: November 2020

Hypotony is often defined as intraocular pressure (IOP) less than 6 mm Hg. It has been reported to occur after glaucoma filtering surgery in up to 42% of cases and is usually associated with overfiltration or wound leaks. Hypotony requiring revision, however, occurs in about 4% of filtering procedures. Hypotony can follow any IOP-lowering procedure or even “simple” cataract surgery. The advent of guarded filtering surgery has reduced the rate of hypotony significantly compared to full-thickness filtering surgery. Unfortunately in the quest to increase success rates by using adjunctive antifibrotic agents, such as mitomycin-C (MMC) or 5-fluorouracil (5-FU), that prevent fibrotic wound healing, the incidence has increased again. Higher doses of and longer exposure times to MMC are associated with a greater risk of hypotony. Most cases of hypotony are transient and self-limited to a few days or weeks after surgery. Transient hypotony does not seem to have any deleterious effect on long-term visual acuity. However, persistent hypotony may result in structural changes that can become permanent. Hypotony maculopathy is one such condition manifesting from persistent hypotony that can result in permanent vision loss. Hypotony maculopathy occurs in up to 10% of filtering operations with MMC or 5-FU and in about 10% of eyes with chronic hypotony. Maculopathy associated with hypotony was first described by Dellaporta. Some years later, Gass, using fluorescein angiography, better characterized the condition. In hypotony maculopathy, the sclera and choroid develop folds in the posterior pole, which can cause significant visual disturbances. The condition is recognized by characteristic striae or folds in the macular area that do not leak or stain with fluorescein. The posterior sclera appears partially collapsed, causing the folds. The axial length of the eye may be shortened after both filtering and tube shunt surgery and more so in patients with hypotony. The loss of vision is usually gradual after the hypotony has persisted for at least a month or more. Indocyanine green angiography has revealed some vascular abnormalities including vessel tortuosity and filling defects.
Endophthalmitis
Authors: Lind John T. , Gedde Steven J.
Published: November 2020

Bleb-related endophthalmitis is one of the most visually devastating complications of glaucoma filtering surgery. Endophthalmitis associated with a functioning filtering bleb may develop months or years postoperatively. Early postoperative endophthalmitis occurs within 6 weeks following the surgery, and late endophthalmitis occurs after this 6-week window. Early detection and rapid institution of appropriate treatment is important in optimizing outcomes and preserving vision. Blebitis is defined as an infection localized to the bleb and surrounding tissues, including the anterior chamber. Blebitis lacks vitreous involvement. Ocular signs of blebitis may include hyperemia around the bleb site, focal infiltrate in the bleb, bleb purulence, and anterior chamber reaction. Bleb-related endophthalmitis encompasses the findings of blebitis with concurrent vitreous inflammation. The presence of vitreous inflammation differentiates bleb-related endophthalmitis from blebitis (Figure 24.1). Risk factors for bleb-related infections are listed in Table 24.1. Bleb morphology and the presence of a bleb leak affect the risk of blebitis or endophthalmitis. Bleb leaks have been identified as the single most important risk factor for the development of bleb-related infections. In a case-control study by Soltau et al, Seidel-positive bleb leaks increased the risk of bleb infection nearly 26-fold. A multicenter study also found that a bleb leak is a major risk factor for blebitis and endopthalmitis. In a review of 20 endophthalmitis cases, 55% of the patients (11 patients) had a Seidel-positive leak following filtering surgery, and three-quarters (15 patients) were noted to have a thin or avascular bleb. Recurrent bleb leaks were observed in over a third of the patients. Song et al found that bleb leaks occurred in 27% of eyes (13 of 49 eyes) with delayed-onset bleb-related endophthalmitis. It is recommended that the clinician routinely monitor patients for bleb leaks and make appropriate interventions to resolve the leak once it is identified. The advent of antifibrotic agents has improved the success rate of traditional filtering surgery but has also increased the incidence of bleb-related infections. Greenfield et al demonstrated that mitomycin-C (MMC) increases the risk of bleb leak.
Noncorneal Complications
Authors: Shrivastava Anurag , Singh Kuldev
Published: November 2020

Most glaucoma specialists advocate the use of 5-fluorouracil (5-FU) and mitomycin-C (MMC) in various concentrations during the intraoperative and postoperative periods to help inhibit postoperative scarring, the primary cause of filtration surgery failure. Although the increased use of antifibrotic agents as adjunctive therapy to guarded filtration surgery has improved the likelihood of operative success, there are many additional complications associated with this class of medications. It is the nature of filtration surgery as it is performed today that successful drainage of aqueous comes with a price. Any adjunct that improves the intraocular pressure (IOP)-lowering success of surgery must be assessed in light of this increased risk. A leaking bleb is one of the most common complications seen after trabeculectomy and may occur at any point postoperatively. This complication has been reported with an incidence ranging between 17% and 42% according to one review. More recent estimates have been somewhat lower, at between 8% and 14.6%. The longer the postoperative follow-up, the greater the cumulative likelihood of bleb leakage. It is imperative that the bleb be checked periodically for leaks, primarily through examination and standard Seidel testing. Use of antifibrotic therapy is associated with increased formation of thin-walled cystic blebs, which are more likely to result in both short-term and long-term complications. The timing of a bleb leak will dictate management. Many early postoperative bleb leaks resolve without intervention but can significantly decrease the likelihood of trabeculectomy success. Early postoperative bleb leaks are often attributed to surgical technique and can generally be avoided by use of appropriate blunt instruments and careful attention to surgical detail. The simple use of nontoothed forceps when handling the conjunctiva can prevent small buttonhole conjunctival tears, which often result in early postoperative bleb leaks. However, even with careful manipulation, friable conjunctival tissue can be prone to small tears. While some have advocated the use of light cautery, or even tissue adhesives to close bleb leaks, the use of such techniques has diminished in the antifibrotic era. Intraoperative suturing of buttonholes is definitive.
Needling and Revision Complications
Authors: Solish Alfred M.
Published: November 2020

Needle revision refers to a surgical procedure in which a fine gauge needle or needle-knife is used to incise scar tissue in the vicinity of a filtration opening. Initially described for temporary relief of elevated intraocular pressure (IOP) in the case of encapsulated filtering blebs, needle revision has been used to establish flow in the setting of a nonexistent bleb, enhance aqueous flow when a bleb is present, and to alter tectonic features of a filtration bleb. Among the many advantages of needle revision are rapidity, low cost (especially when performed in the office), minimal preparation, and rapid recovery. Compared to full surgical revision, needle revision involves relatively little disruption of tissue, resulting in minimal inflammation. Needle revision can be used to rearrange bleb architecture to decrease bleb height, a bleb morphology that is associated with corneal dellen and dysesthesia (see Chapters 18 and 19). Flow can be redirected using needle revision to reduce flow through bleb leaks, which may result in closure and/or prevent reformation of “overhanging” blebs. Although incision of relatively thin scar tissue with a needle establishes fluid flow, scar reformation is likely to occur without some sort of inhibition of scar formation. The introduction of antifibrotics, such as 5-fluorouracil (5-FU) and mitomycin-C (MMC), and antiangiogenics, such as bevacizumab, have enhanced our ability to prevent reformation of scar tissue. Needle revision is a useful procedure that can revise bleb architecture and redirect fluid flow with little inflammation. Understanding complications associated with this procedure is important for an ultimately successful glaucoma procedure. Needle revision can be performed in a variety of settings: the operating room, complete with the operating microscope, full preparation, and draping; the office minor procedure room using the operating microscope; or even at the slit lamp in the examination lane. Procedure time, cost, and equipment preference and availability are among other factors that may influence the choice of venue. Anesthesia methods also vary. Topical anesthesia, subconjunctival block, and retrobulbar injection can all be used. Generally, topical anesthesia with viscous lidocaine is adequate in most patients.
Tube Misdirection and Inadequate Tube Length
Authors: Piovanetti Omar
Published: November 2020

Tube misdirection and inadequate tube length are 2 problems commonly seen by glaucoma surgeons. These complications can occur at the time of surgery or develop years later. Understanding the underlying causes for these problems and techniques to prevent and manage these issues is critical for successful outcomes. Tube placed too anteriorly. During anterior chamber tube shunt implantation, a 23-gauge needle is commonly used to make entry into the anterior chamber. The tube is then inserted through this track into the space between the corneal and iris planes. For most surgeons the anterior chamber depth has been altered prior to tube insertion from shallowing caused by loss of aqueous volume during creation of a paracentesis or deepening caused by filling the chamber with viscoelastic to create enough room for placement. As the intraocular pressure (IOP) becomes lower, the postoperative anterior chamber depth is not always equal to the preoperative depth. As a result, the iris may move slightly forward, or if the shunt is to be implanted in combination with lens extraction, the iris may move more posteriorly. The unpredictability of postoperative chamber depth prevents consistent intraoperative determination of the appropriate plane of entry. Minimizing steps that affect the anterior chamber depth prior to tube insertion may help avoid these issues. However, despite limiting anterior chamber depth alterations, it is not uncommon for the tube to not end up in the desired anterior chamber plane. The correct plane is in front of the iris with just enough space to prevent iris contact. If the tube ends up too anteriorly, it may rub against the corneal endothelium and result in endothelial cell loss with chronic corneal edema. Alternatively, if the tube is placed too posteriorly, it could rub against the iris and cause chronic low-grade inflammation, worsening glaucoma along with other iritis-related issues. In either case, a new track may be made to direct the tube into the anterior chamber. Tube in iris stroma or in the posterior chamber. Occasionally the tube embeds in the iris stroma during its insertion. Careful preoperative evaluation is important for prevention of this scenario.
Vitreous Prolapse
Authors: Realini Tony , Khouri Albert S.
Published: November 2020

There are few absolutes in glaucoma surgery. Here is one: vitreous is bad. Anticipating and avoiding it are the best ways to avoid complications, but managing it is necessary when it rears its ugly head. There are several clinical settings in which vitreous anticipation is appropriate and expected. Recognizing these settings in advance will allow for a prepared surgical approach. Aphakic eyes pose perhaps the highest risk of encountering vitreous during tube shunt placement. In an aphakic eye, the natural barrier holding the vitreous back—the lens and specifically its posterior capsule—is no longer present. These eyes typically have vitreous at or only just behind the pupil, bare millimeters from where the tip of the tube will rest. If vitreous is in the anterior chamber prior to surgery, judicious use of viscoelastics will typically keep the vitreous away from the tube; however, if the vitreous has breached the pupil, it would be wise to clean it up prior to tube insertion. (See below for surgical details.) With vitreous just peeking through the pupil, it might be tempting to try to slip the tube in quickly and get out without stirring things up, with possible success in the short term. Postoperatively, however, if the eye is cursed with a bout of hypotony or as vitreous syneresis progresses, vitreous will almost certainly find its way to the tube lumen, the operation will no longer be successful, and the vitreous will have to be dealt with anyway. Vitreous occasionally presents during cataract surgery, during which time a good clean-up yields a good visual outcome. An incomplete clean-up may also permit a good visual outcome, but leaves the equivalent of a landmine for the glaucoma surgeon who might follow in the cataract surgeon’s wake. It behooves the glaucoma surgeon to review the operative reports for all pseudophakic eyes—particularly those with pseudoexfoliation that are prone to zonular dehiscence and subsequent vitreous laden complications during cataract surgery—so that any encounter with vitreous during tube shunt placement has been anticipated and planned for. The post-traumatic eye can offer a variety of unpleasant surprises for the unprepared surgeon.
Early Hypotony
Authors: Sidoti Paul A.
Published: November 2020

Ocular hypotony in the early postoperative period following tube shunt surgery is relatively common. The pressure level at which structural compromise of the eye and resultant secondary complications (e.g., shallow/ flat anterior chamber, serous and/or hemorrhagic choroidal detachment, chorioretinal folds, corneal folds) occur varies considerably. Some patients may tolerate extremely low pressures well for extended periods of time. However, an increased amount of secondary complications is often seen with intraocular pressures (IOPs) below 6 mm Hg. For the purpose of the ensuing discussion, we will adopt a definition of hypotony based solely on this pressure criterion without regard to the clinical state of the eye. An understanding of the causes of hypotony is critical to its prevention as well as its treatment. The etiologies of hypotony can be broken down into 2 broad categories: general (Table 34.1) and device-specific (Table 34.2). The device-specific causes can be further categorized into those that occur with valved devices and those that occur with non-valved devices. Aqueous flow around the tube at the scleral insertion site may result in early postoperative hypotony regardless of the type of tube shunt used. A 23-gauge needle generally creates a tight track in an area of normal sclera with little potential for excess flow around the tube. Rarely, however, the scleral entry track can be significantly wider than the external diameter of the tube, resulting in peri-tube flow and a low IOP, which are particularly likely to occur following excessive manipulation of the scleral opening as it is created or during tube insertion. The use of a 22-gauge or wider needle will increase the risk of peri-tube flow. Leak around the tube may also occur when a 23-gauge needle is used to create the fistula through an area of abnormally thin, ectatic sclera. Additionally, when 2 or more scleral openings are made in an effort to optimize tube placement, aqueous flow through an unused scleral entry site may result in overfiltration and early postoperative hypotony if the sclerostomy is not tightly closed. Aqueous hyposecretion secondary to ciliary body dysfunction may also result in transient ocular hypotony in the early postoperative period.
Encysted Bleb
Authors: Freedman Jeffrey
Published: November 2020

The formation of a true pathologic encysted bleb is characterized by intraocular pressure (IOP) elevation that generally starts around 6 weeks postoperatively. An encysted bleb has lost the ability to adequately reduce IOP in the presence of a patent tube, implying that aqueous permeability of the bleb wall has decreased (Figure 36.1). Physiologic encapsulation around the tube shunt plate differs from that of the pathologic encysted bleb. The normal postoperative encapsulation develops through several steps. Initially, edema and inflammation occur around the shunt’s plate during the first 7 days postoperatively. Next the edema subsides, and the bleb begins to become defined by a fibrous wall. The connective tissue forming this wall thickens over the next 3 weeks. During wall thickening the IOP may rise for about 4–6 weeks. This expected physiologic change is sometimes referred to as the hypertensive phase; however, not all patients will have elevated IOP. After 6 weeks the bleb typically becomes pale, thinner, and less congested, while the IOP stabilizes at a lower level over the next 6 months. Understanding why pathologic encysted blebs develop and how they are identified is important in prevention of their occurrence and in management once they do occur. Prostaglandin E2 (PGE2) and transforming growth factor-beta (TGF- β ) have been shown to be present in glaucomatous aqueous. These proinflammatory substances stimulate a tissue reaction culminating in the production of excessive amounts of collagen and other contractile proteins. Excessive collagen and proteins may result in a thick and relatively impermeable bleb wall. Various predisposing factors are suspected to potentially enhance this excessive fibrotic tissue reaction. Black patients have been identified as having a more rigorous tissue reaction to glaucoma surgical procedures and are therefore at a higher risk of developing encysted blebs. A history of keloid formation may indicate a greater tendency for a bleb to encyst due to an overly aggressive healing process. Pediatric patients are likely to have a stronger tissue response to surgery than older patients, most likely due to a stronger wound healing response.
Visual Loss
Authors: Whitson Jess T.
Published: November 2020

Tube shunt surgery use has increased significantly in recent years. Once reserved as a treatment option for more refractory types of disease, such as uveitic or neovascular glaucoma, or for eyes that had failed one or more trabeculectomies, tube shunts are now being used by some surgeons in place of trabeculectomy as a first-line surgical alternative in eyes with other less aggressive or less difficult to control forms of glaucoma. Visual loss can occur following tube shunt implantation as a result of complications during the postoperative period or from the progression of underlying disease (see Table 40.1). Although tube shunt implantation is associated with similar postoperative complications as trabeculectomy surgery, such as hypotony, hemorrhage, and failure to control IOP, there are several unique complications that may develop with the use of tube shunts, many of which may result in vision loss. Visual loss following tube shunt surgery is not uncommon. A large, systematic literature review of tube shunts by Hong and coworkers reported rates of vision loss following tube shunt surgery (defined as loss of 2 or more lines of visual acuity at last follow-up) ranging from (mean [SD]) 24 (7)% with the Ahmed™ Glaucoma Valve (New World Medical, Inc., Rancho Cucamonga, California) to 33 (18)% with the Molteno® implant (Molteno Ophthalmic Ltd., Dunedin, New Zealand). In the Tube Versus Trabeculectomy (TVT) Study, an ongoing, prospective, randomized clinical trial that is comparing the Baerveldt® 350 mm tube shunt (Abbott Medical Optics, Inc., Santa Ana, California) to trabeculectomy with mitomycin-C (MMC) in eyes with previous trabeculectomy and/or cataract surgery, vision loss (defined as loss of 2 or more lines of Snellen visual acuity) occurred in 31 of the 107 patients (29%) in the tube shunt group. The occurrence of any postoperative complication significantly increased the risk of vision loss (p < 0.001), and this risk correlated to the number of complications. Corneal decompensation has been reported to occur in up to 30% of patients during long-term follow-up after tube shunt surgery.
Endophthalmitis
Authors: Kim Won I. , Budenz Donald L.
Published: November 2020

Tube shunts have become an important part of the surgical armamentarium for controlling intraocular pressure (IOP). Once reserved for use only in refractory cases, they are rapidly gaining popularity as an effective alternative to trabeculectomy and cyclodestruction for lowering IOP in patients who are not satisfactorily controlled on medications. Although trabeculectomy remains the most commonly performed glaucoma surgery, tube shunts offer some significant advantages. One of these advantages is a theoretically reduced risk of one of the most feared complications of any penetrating ocular surgery— endophthalmitis. The incidence of late-onset infections such as blebitis and endophthalmitis after trabeculectomy with antifibrotic agents is alarmingly high compared to other penetrating intraocular surgeries, perhaps as high as 5% over 3–5 years. Trabeculectomies produce a perilimbal bleb that may be made thinner and more ischemic by the concomitant use of antifibrotics such as 5-fluorouracil and mitomycin-C (MMC). These anteriorly placed blebs are more exposed, more fragile, and more prone to become infected than the robust, thicker, and more posteriorly located blebs overlying a tube shunt plate. Gedde and associates reported a 1% (1 of 107 eyes) incidence of endophthalmitis after Baerveldt® Glaucoma Implant (BGI) placement compared to a 5% (5 out of 105 eyes) incidence after trabeculectomy with MMC after 5 years of follow-up. However, despite this potential advantage, endophthalmitis still does occur in association with shunts, and it is essential to understand the risk factors for its occurrence and the proper steps to take to prevent, recognize, and treat this potentially devastating complication. Distinguishing sterile from infectious endophthalmitis can be difficult. Signs suggestive of an infectious endophthalmitis include marked inflammation, hypopyon, fibrinoid anterior chamber reaction, corneal edema, marked conjunctival congestion, eyelid edema, vitritis, and retinal periphlebitis. Signs suggestive of a noninfectious etiology are a gradual onset of symptoms, such as pain, redness, and inflammation, in the absence of tube or plate erosion. Sterile endophthalmitis one month after discontinuation of corticosteroid therapy postoperatively has been reported. Possible causes for noninfectious (sterile) endophthalmitis include exacerbated preexisting uveitis, iris trauma, and toxicity from foreign substances introduced during surgery.
Complications Specifically Related to Trabeculotomy in Adults
Authors: Reynolds Adam C. , Fellman Ronald L.
Published: November 2020

Disruptive or ablative surgeries involving the trabecular meshwork and Schlemm’s canal, which have traditionally been applied to the developmental and congenital glaucomas, are currently receiving renewed interest in adult open-angle glaucoma because of the development of new technologies. The Trabectome® (NeoMedix Corporation, Tustin, California) procedure, canaloplasty with or without stent, direct trabecular bypass, excimer laser trabeculotomy (ELT), and other techniques in development are all based in their surgical approaches on classic trabeculotomy. Some of the proposed mechanisms of action, as well as the potential complications that occur in classic angle surgeries, are also likely quite similar. It is prudent to note that in some specific limited populations, adult trabeculotomy ab externo has long been employed. For example, in Japan trabeculotomy has been used in adult open-angle glaucoma, and even in North America there have been studies of trabeculotomy combined with cataract surgery. It is well accepted that any and all of the complications related to these procedures in congenital glaucoma can occur when applied to the adult eye, and mitigation and avoidance of them are likely very similar. Some specific complications may be more likely in adult eyes. By far the most common complication related to trabeculotomy, whether in adults or children, is hyphema. In fact it is expected, and some bleeding should be considered a sign that the procedure was done correctly rather than a complication. However, in several large clinical series from Japan, rates of clinically significant postoperative hyphema in adult trabeculotomy often approach 20%. It is thought that hyphema occurs due to disruption of the trabecular meshwork, as a barrier between retrograde flow of blood from the collector channel system into the anterior chamber is removed at least temporarily. Once the trabecular meshwork is disrupted, if the intraocular pressure (IOP) is lower than the episcleral venous pressure (EVP), retrograde flow of blood into the anterior chamber may result. One commonly employed technique to avoid significant hyphema in trabeculotomy is to temporarily “tamponade” the anterior chamber with viscoelastic.
Anatomic Basis and Differential Diagnosis of Field Defects
Authors: Wirtschafter Jonathan D. , Walsh Thomas J.
Published: November 2020

The purpose of any medical test is to confirm or rule out a diagnosis based on the clinical facts. In performing perimetry, the printout of the defect is not the end of the test. For even the most experienced reader, the test results at best tell the location of the defect. The next step is to consider the causes of such a defect in that part of the vision system. The experienced perimetrist will look at the results and suggest a differential list of causes. The primary diagnostic list is frequently aided by adding to the perimetry the medical history and other physical signs. The results of both then lead to the next step: ordering tests to confirm the cause of the field defect. It may require the ordering of a magnetic resonance (MR) image, but that may not be the proper test if the original differential diagnosis is faulty. Sedimentation rate and C-reactive protein may be more appropriate tests if the clinical facts suggest cranial arteritis. If carotid disease is suspected, a computed tomography (CT) angiogram may be more appropriate. In the following discussion of these defects, there has been a melding of a discussion explaining anatomically why these defects occur in certain areas. Because the course and relations of the primary visual sensory pathway have been frequently and well described (including in other chapters of this monograph), this chapter concentrates on the multiple anatomic substrates that may explain each particular pattern of visual field abnormality. Visual field abnormalities are represented by three categories: monocular, binocular, and junctional. Monocular field defects include those that can be caused by lesions of one eye or optic nerve. Binocular field defects include those that may result from single or multiple lesions at one or more points along the visual pathway. Junctional field defects include three types of visual field defects resulting from a lesion at the junction of the optic nerve and optic chiasm or of the optic tract and optic chiasm.
Introduction
Authors: Baldwin Peter
Published: November 2020

The Atlantic Gets Ever Wider. Not just in a physical sense, as oceans rise and coastlines recede, but also in ideological terms. Europe and America appear to be pitted against each other as never before. On one shore, capitalist markets, untempered by proper social policies, allow unbridled competition, poverty, pollution, violence, class divides, and social anomie. On the other side, Europe nurtures a social approach, a regulated labor market, and elaborate welfare networks. Possibly it has a less dynamic economy, but it is a more solidaristic and harmonious society. “Our social model,” as the voice of British left liberalism, the Guardian, describes the European way, “feral capitalism,” in the United States. With the collapse of communism, the European approach has been promoted from being the Third Way to the Second Way. The UK fl oats ambiguously between these two shores: “Janus Britain” in the phrase of the dean of transatlanticist observers, Timothy Garton Ash. It is part of Europe, says the British Left ; an Anglo-Saxon coconspirator, answer its continental counterparts. That major differences separate the United States from Europe is scarcely a new idea. But it has become more menacingly Manichaean over the last decade. Foreign policy disagreements fuel it: Iraq, Iran, Israel, North Korea. So does the more general question of what role the one remaining superpower should play while it still remains unchallenged. Robert Kagan has famously suggested that, when it comes to foreign policy, Americans and Europeans call different planets home. Americans wield hard power and face the nasty choices that follow in its wake. Europeans, sheltered from most geopolitical strife, enjoy the luxury of approaching conflict in a more conciliatory way: Martian unilateralism confronts Venusian multilateralism. But the dispute goes beyond diplomatic and military strategy. It touches on the nature of these two societies. Does having the strongest battalions change the country that possesses them? After all, America is not just militarily strong. It is also—compared to Europe—harsh, dominated by the market, crime-ridden, violent, unsolidaristic, and sharp-elbowed. Competition is an official part of the national ideology and violence the way it spills over into everyday life. Or so goes the argument: a major battle of worldviews and social practices separates America from Europe.
Acorn and Oak
Authors: Baldwin Peter
Published: November 2020

To Parse The Subtle Distinctions between Europe and America must strike observers from other parts of the globe as an exercise in the narcissism of minor differences. Like twins keen to differentiate themselves, some nations eagerly distinguish among countries that are, seen globally, much of a muchness. During the cold war, the unity of the North Atlantic nations against the Soviet empire was obvious. But after the fall of the Berlin Wall, new antagonisms emerged. Iraq, Iran, North Korea, Afghanistan, Israel: these are the immediate bones of contention. The larger issue has been the role of the United States, the one remaining superpower, as its regnum is tested by Middle Eastern wars, Russian saber rattling, and Chinese aspirations to great power status. Perhaps, as some Europeans argue, the United States has become a rogue state, unilaterally exempting itself from the strictures of mutual dependence in an increasingly interwoven world. Perhaps, as some Americans reply, Europeans live in a cloud-cuckoo land where conflict is considered ultimately to be based on misunderstandings, not real differences, and talk can therefore replace guns. These are geopolitical debates we need not enter into here. We are concerned, however, with the geopoliticians’ frequent and facile elisions between internal and external politics. Because Americans own guns, they like to go to war. Because they drive big cars, they need to secure oil supplies in the Middle East. Because they are religious, they see themselves as crusaders. Because continental Europeans do not have functioning armies and refuse to pay for any, they turn foreign policy into a talking shop. Because they spend their money on social benefits, they cannot afford to defend themselves and must therefore appease the aggressors. Because of their own traumatic past, they refuse to acknowledge the continuing reality of evil in the world. In this book, I have shown that, in almost every quantifiable respect, the United States and Western Europe approximate each other. Earlier, I have accounted for some of the ways that social scientists have tried, and failed, to typologize differences between Europe and America.
Filtration
Authors: Harrison Roger G. , Todd Paul W. , Rudge Scott R. , Petrides Demetri P.
Published: November 2020

Filtration is an operation that has found an important place in the processing of biotechnology products. In general, filtration is used to separate particulate or solute components in a fluid suspension or solution according to size by flowing under a pressure differential through a porous medium. There are two broad categories of filtration, which differ according to the direction of the fluid feed in relation to the filter medium. In conventional or dead-end filtration, the fluid flows perpendicular to the medium, which generally results in a cake of solids depositing on the filter medium. In crossflow filtration (which is also called tangential flow filtration), the fluid flows parallel to the medium to minimize buildup of solids on the medium. Conventional and crossflow filtration are illustrated schematically in Figure 4.1. Conventional filtration is typically used when a product has been secreted from cells, and the cells must be removed to obtain the product that is dissolved in the liquid. Antibiotics and steroids are often processed by using conventional filtration to remove the cells. Conventional filtration is also commonly used for sterile filtration in biopharmaceutical production. Crossflow filtration has been used in a wide variety of applications, including the separation of cells from a product that has been secreted, the concentration of cells, the removal of cell debris from cells that have been lysed, the concentration of protein solutions, the exchange or removal of a salt or salts in a protein solution, and the removal of viruses from protein solutions. Filtration often occurs in the early stages of bioproduct purification, in keeping with the process design heuristic “remove the most plentiful impurities first” (see Chapter 12, Bioprocess Design and Economics). At the start of purification, the desired bioproduct is usually present in a large volume of aqueous solution, and it is desirable to reduce the volume as soon as possible to reduce the scale and thus the cost of subsequent processing operations. Filtration, along with sedimentation and extraction (see Chapters 5 and 6), is an effective means of accomplishing volume reduction.
Millennial Hope
Authors: Orr David W.
Published: November 2020

For two centuries and longer, humankind has been on a collision course with the limits of the Earth. The inertial momentum—the scale and velocity of the human enterprise—has grown so rapidly since the mid-20th century that virtually every indicator of planetary health is in decline (McNeill, 2000). Even an otherwise self-characterized “optimistic” analysis concludes that: . . . The momentum toward an unsustainable future can be reversed, but only with great difficulty. [The reversal] assumes fundamental shifts in desired lifestyles, values and technology. Yet, even under these assumptions, it takes many decades to realign human activity with a healthy environment, make poverty obsolete, and ameliorate the deep fissures that divide people. Some climate change is irrevocable, water stress will persist in many places, extinct species will not return, and lives will be lost to deprivation. (Raskin et al., 2002, pp. 94–95) . . . Considerably less optimistic, Thomas Berry concludes that “It is already determined that our children and grandchildren will live amid the ruined infrastructures of the industrial world and amid the ruins of the natural world itself ” (2006, p. 95). James Lovelock’s view is even darker: “the acceleration of the climate change now under way will sweep away the comfortable environment to which we are adapted . . . . [There is evidence of ] an imminent shift in our climate towards one that could easily be described as Hell” (2006, pp. 7, 147; The Vanishing Face of Gaia, 2009). Given such dire predictions, theologian Jack Miles, author of A History of God (2000), suggests that we begin to ponder the possibility that “the effort to produce a sustainable society has definitively failed . . . that we are irreversibly en route to extinction.” Alan Weisman, in a striking exercise of journalistic imagination, describes in The World Without Us how our infrastructure would then crumble, collapse, and finally disappear (2007). These are only a few of the recent musings about the human prospect.
Helium and the Age of the Earth
Authors: Fisher David
Published: November 2020

Until nearly the end of the Nineteenth century, nobody was particularly interested in the age of the earth except a few theologians. In the second century A.D., the rabbi Yose ben Halafta wrote a tract known today as the Seder Olam (meaning Order of the World) in which he divided the history of the world into four parts: first, from the creation until the death of Moses; second, up to the murder of Zachariah; third, up to the destruction of the temple by Nebuchadnezzar, king of Babylon, in 586 B.C.; and finally, from then to his present day. The Bible gives the ages of the patriarchs at the time of the birth of their offspring: “This is the roll of Adam’s descendants … When Adam was a hundred and thirty years old he became the father of Seth … When Seth was a hundred and five years old he became the father of Enosh …” So by adding the ages of the people listed in the Bible, ben Halafta calculated the passage of years in each period, concluding that the world was created 3,828 years before the destruction of the Second Temple by the Romans in 68 B.C. (an event now assigned to the year 70 B.C.); that is, creation took place in the year 3896 B.C. (3898 if we include the new date for the Second Temple). There was little mention of his calculation until the Jews moved from Babylonia to Europe, and it then gradually came into use, replacing the then usual method of assigning dates as so many years after the beginning of the Seleucid era in 312 B.C. By the eleventh century it had been slightly revised so that the world was created in 3761 B.C., a date which became the basis of the Jewish calendar; as I write this (2009) we are in the year 5770 A.M., or Anno Mundi.
The Plundered Planet
Authors: Collier Paul
Published: November 2020

Paul Collier's The Bottom Billion was greeted as groundbreaking when it appeared in 2007, winning the Estoril Distinguished Book Prize, the Arthur Ross Book Award, and the Lionel Gelber Prize. Now, in The Plundered Planet, Collier builds upon his renowned work on developing countries and the world's poorest populations to confront the global mismanagement of natural resources. Proper stewardship of natural assets and liabilities is a matter of planetary urgency: natural resources have the potential either to transform the poorest countries or to tear them apart, while the carbon emissions and agricultural follies of the developed world could further impoverish them. The Plundered Planet charts a course between unchecked profiteering on the one hand and environmental romanticism on the other to offer realistic and sustainable solutions to dauntingly complex issues. Grounded in a belief in the power of informed citizens, Collier proposes a series of international standards that would help poor countries rich in natural assets better manage those resources, policy changes that would raise world food supply, and a clear-headed approach to climate change that acknowledges the benefits of industrialization while addressing the need for alternatives to carbon trading. Revealing how all of these forces interconnect, The Plundered Planet charts a way forward to avoid the mismanagement of the natural world that threatens our future.
Preparing to Teach
Authors: Hammel Alice M. , Hourigan Ryan M.
Published: November 2020

There are varying degrees of undergraduate and graduate preparation for students with special needs. Music educators may have had a general special education class or the opportunity to study topics regarding students with special needs embedded within a music methods course. The topic of students with special needs may have been included in an educational psychology course, or a teaching music to students with special needs course that was part of the curriculum (Heller, 1994, York & Reynolds, 1996). More often than not, music educators have little or no background or instruction in this area (Wilson & McCrary, 1996). Therefore, music educators must be resourceful in gaining insight into the skills, strategies, and understandings that accompany the experience of teaching a student with special needs. Music teacher educators often have little or no preparation as to how to educate future music educators regarding the inclusion of music students with disabilities or how to plan, implement, and assess lessons in self-contained and inclusive music classrooms. Oftentimes, this lack of understanding results in either glossing over the topic or ignoring it altogether. Licensure requirements can leave little room for “special” topics in the methods classroom. Fieldwork and engagement with special education faculty and staff in a variety of environments can assist music educators in finding ways to reach students with special needs. This chapter may appear to be designed for the music teacher educator. However, practicing music educators are encouraged to utilize the observation protocols and other strategies to obtain on-the-job and authentic experience through self-imposed fieldwork, observation, and discussion within the special education framework. This may be beneficial to music educators in understanding the subculture of students, parents, educators, and administrators that surround a student with special needs. This fieldwork may need to be conducted during preparation/planning time or through permission from an administrator. For music teacher educators, this chapter is designed as a guide to develop fieldwork opportunities for pre-service music educators. Included in this chapter will be strategies for engagement in self-contained classrooms, resource rooms, inclusive settings, and summer enrichment programs.