Ординатура / Офтальмология / Английские материалы / Essentials in Ophthalmology Glaucoma_Grehn, Stamper_2008

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■The most familiar classification of angle-closure glaucoma is based on the presence of symptoms. This approach fails to recognise the large number of asymptomatic patients and people at risk.

■Classification based on symptoms does not guide the ophthalmologist in devising a logical management plan and predicting prognosis.

■The term “glaucoma” is currently used indiscriminately, regardless of the presence or absence of optic neuropathy. Its use should be restricted to cases in which there is evidence of glaucomatous optic neuropathy.

■The terms anatomically narrow angle and occludable angle are used interchangeably to indicate an anatomical predisposition to pathological angleclosure. These terms have found widespread usage in epidemiological research, and are generally taken to indicate the presence of iridotrabecular contact (ITC)—the defining feature of angleclosure. ITC is now thought to be significant if the posterior (usually pigmented) trabecular meshwork is obstructed by the peripheral iris for half of its circumference or more. However, this is a conservative approach to the assessment of risk, and may underrepresent the “at risk” population and thus be revised in future.

■International expert consensus is that the classification of angle closure should describe the conceptual stage in the natural history of angle closure, ranging from iridotrabecular contact (ITC) (primary angle closure suspect), to anterior segment signs of disease, specifically raised intraocular pressure (IOP) and/or peripheral anterior synechiae (PAS), which are the defining features of angle closure in an eye with an anatomically

narrow angle (this stage is termed primary angle closure). The natural history finally culminates in glaucomatous optic neuropathy (termed primary angle closure glaucoma when it occurs in conjunction with angle closure as previously defined).

■This classification indicates the presence or absence of abnormalities requiring treatment, and specifies visually significant end organ damage (glaucomatous optic neuropathy).

■In addition to describing the stage of disease, it is important to identify the mechanism causing angle closure. This requires an additional system to be used in parallel.

■In addition to glaucomatous optic neuropathy, there are several forms of ocular tissue damage that may result in visual dysfunction as a consequence of angle closure, such as cataract, endothelial cell loss and anterior ischaemic optic neuropathy. These should be separately identified clinical management targeted at these specific processes.

■The most widely used classification of mechanism is the four-point system, which identifies obstructions to aqueous outflow at progressively more posterior levels: (a) pupil block; (b) ciliary body-induced; (c) lens-induced; (d) retrolenticular causes.

■The art of gonioscopy is indispensable to the diagnosis and management of all forms of glaucoma. The development of new anterior chamber imaging techniques in the clinical assessment of angle, such as ultrasound biomicropscopy and anterior segment OCT, are a useful supplement to clinical examination and gonioscopy, which will further improve understanding of the mechanisms responsible for angle closure.

5.1Background

Glaucoma has recently emerged as the second most common cause of blindness worldwide, and the leading cause

5of irreversible blindness [1]. Quigley has calculated that open-angle glaucoma (OAG) accounts for 75% of all

glaucomatous optic neuropathy, with approximately 60 million people affected by 2010, and some 16 million suffering primary angle-closure glaucoma (PACG). This latter figure is likely to rise to 21 million by 2020 [2]. The disease is especially prevalent in Asian people, and affects women and the elderly most often [3–6]. In addition, it is now believed that PACG is more rapidly progressive and visually destructive than primary OAG [7, 8]. Therefore, early identification and appropriate management are important for preventing loss of vision and for optimising the delivery of effective preventive/curative procedures such as laser iridotomy [9–11]. However, early diagnosis depends on an appropriate nosological framework which is relevant to the condition and based on scientific evidence.

The division of adult glaucoma cases into primary and secondary forms is used to indicate the presence of a separate, distinct pathological process responsible for raised intraocular pressure in secondary glaucoma. Secondary glaucoma is typically a unilateral disease, characterised by high intraocular pressure, and—if effective treatment is not commenced—a rapidly progressive glaucomatous optic neuropathy, often leading to blindness. Most commonly, secondary glaucoma occurs as a consequence of anterior segment neovascularisation, uveitis, trauma (in-cluding surgery, especially aphakia), the use of steroid medication, and other less common causes. Secondary glaucoma is usually classified as OAG or ACG. ACG is a group of disorders that share a common pathological pathway where contact between the iris and the trabecular meshwork occurs. “Primary” angle-closure glaucoma is in fact a secondary glaucoma, where the optic neuropathy occurs as a consequence of raised intraocular pressure (IOP) resulting from an identifiable process: iridotrabecular contact (ITC). The “primary” process in PACG is ITC, occurring as a consequence of one or more abnormalities in the relative or absolute size or position of anterior segment structures, or by abnormal forces in the posterior segment that alter the anatomy of the anterior segment.

Different approaches to classification of angle-closure have been based on combinations of the following:

■The presence or absence of additional pathology— denoting primary or secondary angle closure

■The location of the mechanism causing angle closure

■The constellation of clinical features that accompany the presentation of angle closure, including the presence or absence of symptoms and the level of IOP, either at presentation or in response to certain “provocative” tests—acute, intermittent (subacute), and chronic angle closure

■The presence or absence of peripheral anterior synechiae (PAS)—appositional angle closure vs. synechial angle closure

■The presence or absence of glaucomatous optic neuropathy

The predominant approach to classification has been that based on symptoms of raised IOP. However, research in Asia suggests that angle closure is predominantly an asymptomatic disease in the majority of sufferers (66–75% of cases) [3, 4, 12–14]. In the last decade, an increase in research activity focussing on angle closure glaucoma has highlighted the need to standardise the definition and classification of the disease. This chapter describes the current approaches to classification of angle closure, and describes the outcome of the Third AIGS (Association of International Glaucoma Societies) Consensus Meeting on angle-closure glaucoma [15].

5.2 The Purposes of Disease Classification

Classification systems provide a framework for describing the presence and severity of disease, why it occurs, and how different treatments will benefit patients. In most fields of medicine, as understanding of the disease increases, they have typically evolved from descriptions of a combination of symptoms, through an understanding of the anatomical location of abnormalities, to the aetiology and pathogenesis. For clinical purposes, it is highly desirable for a classification scheme to help to describe how and why a patient suffers from a specific disease process and how to manage the condition most effectively. Indeed, an appropriate system of classification is crucial for achieving the highest standards of clinical care. Ultimately, every patient is unique, and should be treated as such. However, it is only possible to make progress in understanding disease processes, and how best to control them, by looking for common patterns through formal study—through research.Outcomesfromclinicaltrialscannotbecompared unless the broad concepts of disease classification are uniform. The study of the prevalence and incidence of disease will only yield meaningful results if the classifications used reflect characteristics of importance. It has been suggested that there is a “dichotomy of purpose” between the clinical and research settings. Indeed, in a clinical setting, a myriad of clinical signs may be identified and be relevant to the

care of the patient. The identification and assimilation of these signs into a management plan is a complex process requiring many years of training and experience to master. The codification of such complex decision-making processes is beyond the scope of this chapter. However, since modern medical science adopts a progressively more evi- dence-based approach, the principles of management are based on systematic research. Major advantages of a standard classification scheme are the promotion of a common language used by all involved, the clarification of thought processes around disease mechanisms and disease (or pre-disease state) prognosis, and the ability to make valid comparisons between datasets.

5.3The Evolution of Classification Schemes for Angle-Closure Glaucoma

Angle-closure glaucoma was probably the first form of glaucoma to be recognised as a separate diagnostic entity from cataract. Von Graefe described surgical peripheral iridectomy as a method of treating glaucoma. Initial classifications of glaucoma evolved to identify congestive, post-congestive and absolute stages of disease, with several types of disease identified, including a symptomatic course (which includes an acute episode causing pain and inflammation) as well as an asymptomatic form (either of which could lead to total blindness). The advent of gonioscopy resulted in a quantum leap in the sophistication of diagnostic methodology and the potential for understanding the pathological mechanisms responsible for angle closure. It allowed the relationship between the iris and the trabecular meshwork to be observed directly for the first time. More recently, the advent of anterior segment imaging has allowed a clearer understanding of the mechanisms that cause the narrowing of the angle, as well as an understanding of the limitations of some clinical observations such as gonioscopy.

The most familiar and enduring classification of angle closure identified three subcategories based on the presence or absence of symptoms.

■Acute: Abrupt onset of symptomatic elevation of IOP resulting from total closure of the angle that is not self-limiting

■Sub-acute or intermittent: Abrupt onset of symptomatic elevation of IOP resulting from total closure of the angle that is self-limiting and recurrent

■Chronic: Elevated IOP resulting from angle closure that is asymptomatic

Some have also described a fourth subcategory, latent angle closure, which is evidence that angle closure is either

likely or may have occurred intermittently. Evidence includes a positive provocative test or the finding of primary peripheral anterior synechiae (PAS) in an eye that has an open but narrow angle. However, this term is no longer widely used, perhaps because PAS with or without elevated IOP is considered chronic angle closure.

The advantages of this scheme are that it is familiar to doctors and easy to understand for patients who have a symptomatic episode of angle closure. However, the implicit assumption within this system is that most angle closure is symptomatic. The scheme has evolved ad hoc from early clinical observations, and reflects a level of understanding of natural history and pathology that is less complete than the one we have today. It has no evidence base and no proven validity in predicting prognosis. The major flaws are an absence of emphasis on the presence or risk of significant loss of visual function, and the fact that it does nothing to guide the ophthalmologist in devising a logical management plan. The term glaucoma has traditionally been attached to all grades of disease regardless of the presence or absence of optic neuropathy, as a perpetuation of the idea that glaucoma is defined by an elevation of intraocular pressure. However, this idea has become outmoded in the diagnosis and management of primary OAG. The same rigorous, scientific approach to classifying angle closure is now becoming more widespread.

5.4Definition of an “Occludable” or Narrow Angle

The threshold at which angle closure is considered a possible diagnosis is not clearly defined. The concept of defining the threshold by describing the characteristics of an “occludable” angle is both logical and pragmatic. The terms “anatomically narrow angle” and “occludable angle” are generally seen as synonymous, and are used to indicate the anatomical predisposition to angle closure. However, debate surrounds the use of each, particularly as neither specifies that iridotrabecular contact (ITC, which is currently seen as the defining characteristic of pathological angle closure) is present. The epidemiological research standard used to define “occludable” angles in studies in Alaska, South Africa, Mongolia, Singapore and Bangladesh was that the posterior (usually pigmented) trabecular meshwork was hidden from view by the peripheral iris for three-quarters of its circumference or more [3, 4, 14, 16, 17]. This definition was first used by Arkell et al. for their study in Alaska, and used later in other studies for the sake of consistency to allow comparison between studies. Analysis of data from

Mongolia and Singapore has shown that around half of all participants in population studies who have “primary” PAS (i.e. no other identifiable cause) are excluded by this definition. Later, Thomas used a more liberal definition

5of 180° of trabecular meshwork hidden from view in his cross-sectional and longitudinal studies in Vellore, south-

ern India [18, 19]. This slightly more liberal threshold is still likely to exclude some people who have primary PAS or appositional angle closure. This belief is supported by the fact that Becker and Shaffer originally suggested that an iridotrabecular angle of 20° was the threshold at which angle closure should be considered a possibility [20]. This was based on nothing other than careful observation in clinical practice, but has been supported by findings from the analysis of data from population surveys in high-risk populations. The reason why signs of angle closure, such as PAS and/or post-appositional deposits of iris stromal pigment, are seen in narrow but open angles is demonstrated by a video recording of an ultrasound biomicroscopy (UBM) examination of a patient who had suffered symptomatic angle closure in the opposite eye [21]. The recording shows iridocorneal contact in the dark, which rapidly changes to an open angle of approximately 20° when the room lights are switched on. The magnitude and rapidity of this variation is striking, and underlines the importance of levels of illumination in identifying cases of angle closure. It is probably a limitation of the technique that gonioscopy (still the reference standard examination for the diagnosis of angle closure) relies on visible light, which, even in the most careful examination when light is kept away from the pupil, may affect the configuration of the angle, causing artefactual widening. One recent study comparing anterior segment optical coherence tomography (AS-OCT) with gonioscopy found that AS-OCT detected more closed angles than did gonioscopy [22]. This was interpreted as a superior diagnostic performance of AS-OCT, probably because the examinations were performed in dark-room conditions, whereas gonioscopy, even in the hands of experts, requires some light from the slit lamp.

5.5Primary Open-Angle Glaucoma is a Diagnosis of Exclusion

Nonetheless, an evidence-based assessment of the current definition of “risk” (i.e. an occludable angle) shows that the current diagnostic threshold (i.e. 180–270° of TM obscured) is probably far too stringent. As suggested above, gonioscopy using visible light probably underdetects cases where iridotrabecular contact is occurring. There is a strong case in favour of shifting the burden

of proof from the current de facto stance that requires we prove a patient has angle closure to proving that a patient does not have angle closure. As angle closure can potentially be “cured” with early detection and a single laser procedure (laser iridotomy), it may be that ophthalmologists are missing an opportunity to provide effective therapy to many with gonioscopically narrow angles that cause appositional closure, and consequently raised intraocular pressure.

5.6Classification of Angle Closure in Epidemiological Research (ISGEO Scheme)

A classification for use in prevalence surveys and other epidemiological research has been published [23]. It identifies three conceptual stages in the natural history of angle closure, from iridotrabecular contact (ITC) to anterior segment signs of disease (raised lop and/or PAS), and finally culminating in glaucomatous optic neuropathy.

(a)Primary angle-closure suspect (PACS): ITC in three or more quadrants, but normal IOP, disc and field, without evidence of PAS.

(b)Primary angle-closure (PAC): ITC in three or more quadrants with either raised IOP and/or primary PAS. Disc and field are normal.

(c)Primary angle-closure glaucoma (PACG): ITC in three or more quadrants plus evidence of glaucomatous damage to optic disc and visual field (with similar approaches to those used for POAG).

The diagnosis of glaucomatous optic neuropathy has been codified in the ISGEO scheme using three levels of evidence. Category 1 stipulates structural and functional abnormalities consistent with glaucoma. Category 2 stipulates that, in the case of advanced loss of vision where field-testing cannot be performed using automated perimetry, glaucoma can be diagnosed on the basis of advanced structural damage to the optic disc. Category 3 applies to cases where the disc cannot be seen. Glaucoma is diagnosed on the basis of visual acuity < 3/60 and either IOP > 24 mm Hg or signs of previous filtering surgery. It has been proposed that this category be expanded to include those with iris ischaemic sequelae (iris whirling, poorly reactive pupils and iridoschisis) and either an afferent pupil defect or no light perception. It is recognised that the current ISGEO scheme makes no allowance for variation in disc size, and that this is an important (previously recognised) omission.

This scheme has been employed widely in the research classification of cases. The incidence of each category is

known. In addition, it is useful to record physical signs of anterior segment ischaemia (distortion of radial iris fibres), or necrosis (subcapsular opacities in the lens— glaukomflecken). The inclusion of two sub-categories of PAC was discussed for the ISGEO scheme (i.e. ischaemic and nonischaemic), but there is no current consensus on this point.

The major deficiency with this approach is that it does not identify the mechanism responsible for angle closure, and requires an additional scheme to be used in parallel for this purpose. However, it does indicate the presence or absence of abnormalities requiring treatment, and it specifies visually significant end organ damage (glaucomatous optic neuropathy). There are several other causes of ocular tissue damage and visual dysfunction that are associated with angle closure, and should be separately identified in the clinical management and research assessments of people with this condition. Additional description of these factors adds an additional level of clinical sophistication if desired. These include:

Angle-Closure and Ocular Tissue Damage

(a)Corneal endothelial loss

(b)Trabecular meshwork damage

(c)Lens damage (glaukomflecken and nuclear sclerosis)

(d)Iris damage (dilated, unresponsive pupil, and iridoschisis, ectropion uveae).

(e)A flat pale optic disc similar in appearance to that of anterior ischaemic optic neuropathy

(f)Glaucomatous optic neuropathy

5.7Trabecular Meshwork Damage in Angle Closure

Damage to and obstruction of the trabecular meshwork is the mechanism by which rises in IOP occur in angle closure. There are different mechanisms by which trabecular obstruction or dysfunction may occur.

■Synechial closure. This is the most plausible and wellrecognised route to deteriorating outflow facility. The extent of synechial closure is associated with the degree of elevation of intraocular pressure. However, it is recognised that appositional angle closure may lead to glaucomatous optic neuropathy without PAS being present [18].

It seems most likely that all three of these processes (apposition, TM failure and PAS) are co-existent in the same eye.

5.8An Anatomical Basis for the Primary Angle Closure Mechanism

Angle closure is characterized by the presence of iridotrabecular contact (ITC), which may lead to trabecular dysfunction, peripheral anterior synechiae (PAS), elevated intraocular pressure (IOP), glaucomatous optic neuropathy, glaucomatous functional loss and possibly blindness. In angle closure, obstruction of the trabecular meshwork may be caused by forces acting at one or more of four separate anatomical sites, each progressively more posterior to the other: the iris (most commonly pupillary block), the ciliary body (most commonly plateau iris), the lens (“phacomorphic glaucoma”), and forces posterior to the lens (often referred to as “malignant” glaucoma). This classification, popularised by Ritch and colleagues [26], helps describe the various mechanisms responsible for angle closure. This in turn helps plan a logical programme of treatment. Each case will typically have one predominant location of blockage, but may have a component of obstruction at each of the levels preceding it. In some patients multiple mechanisms play a role. The appropriate treatment becomes more complex for each more posterior level of blockage, as each level may also require treatment for lower levels of blockage.

■Appositional closure causing a pre-trabecular outflow obstruction. This is the primary mechanism in symptomatic “acute” PAC. This is also the predominant mechanism in asymptomatic presentations, at least in the early stages of disease.

■Appositional closure causing a trabecular-level outflow obstruction. It is biologically plausible that longterm, low-grade contact and friction between TM and iris causes degradation of TM structure and function. A single histological study reported marked TM degeneration away from areas of PAS in asymptomatic angle closure [24]. Epidemiological data supports this finding, as higher IOP occurs in open but narrower angles [25].

5.9Classification System for Angle-Closure Glaucomas

5.9.1Level I: Iris and Pupil

Pupillary block is the most common mechanism responsible for primary angle closure [9, 26, 27]. It is a physiological phenomenon whereby a pressure gradient exists between the posterior and anterior chambers. The greater the pressure gradient, the greater the convexity of the iris profile. This in turn increases the possibility of iridotrabecular contact. Pupillary block accounts for approximately 75% of cases of angle closure. In the remaining 25% of cases, there is typically an element of pupil block [9, 27].

In East Asia, mixed mechanism angle closure is believed by some to be especially prevalent [28].

Laser iridotomy eliminates the pressure differential between anterior and posterior chambers and relieves the

5iris convexity. The iris assumes a planar configuration and the iridocorneal angle widens in most cases.

Barkan reported that the peripheral iris appears bulky, with marked circumferential folds crowding the angle

[29].Such eyes are susceptible to closure of the angle when the pupil dilates physiologically or pharmacologically. These cases would not respond to laser iridotomy, and would be considered “non-pupil-block” cases of angle closure. More recently, studies using ultrasound biomicroscopy (UBM) have helped identify particular anatomical characteristics associated with the failure of an iridotomy to successfully open a closed angle. These were (1) a very shallow axial anterior chamber, (2) a thicker iris, (3) a more anteriorly inserted iris, and (4) a smaller trabecular–ciliary process distance (often used as an indicator of plateau iris).

5.9.2Level II: Ciliary Body

Plateau iris configuration is the term given to the gonioscopic appearance in which the peripheral third of the iris rises steeply from its insertion before making an abrupt angulation towards the visual axis. The iris profile is otherwise flat. This configuration may predispose to closure of the angle. This configuration of the peripheral iris was first described by Tornquist [30]. The “syndrome” was reported by Wand [31]. In eyes with plateau iris, the anterior chamber appears to have normal axial anterior chamber depth. The chamber angle may be narrow, however, as a consequence of the more anteriorly positioned peripheral iris.

Using ultrasound biomicroscopy (UBM), the structures posterior to the iris that are hidden from clinical observation can be examined and their anatomical relationships assessed [32, 33]. This technology has enhanced the development of an anatomical classification of angle closure, and in particular has demonstrated that some cases of plateau iris have anteriorly positioned ciliary processes. This in turn causes the peripheral iris to be positioned more anteriorly, and results in the angulation of the peripheral iris. In these cases, the iridociliary sulcus is seen to be closed. Another, newer, imaging technology, anterior segment optical coherence tomography (ASOCT), allows the anterior chamber angle to be imaged without contact [34]. This is an advantage over (UBM), although UBM offers vastly superior resolution for structures posterior to the iris pigment epithelium [34, 35]. A particular advantage of both of these techniques over clinical examination is the ability to subject the images to

quantitative analyses [34, 35, 36]. In addition, AS-OCT, and to a lesser extent UBM, can be performed under dark room conditions.

Both level I and II blocks are usually classified as “primary” disease (providing no other pathological processes are identified), whereas levels III and IV are typically classified as secondary, being the result of other pathological processes, distinct from the crowding of anterior segment anatomy that characterises primary disease.

All of these factors may be sufficient to cause pathological angle closure. However, in some cases, an external trigger is required. These may be either physiological or pharmacological in nature, and may include near-work activities such as reading or sewing, or exposure to dark, for example a visit to the cinema [26]. In addition, several pharmacological agents are know to increase the risk of angle closure, as a result of either sympathomimetic or parasympatholytic actions, or from idiosyncratic reactions to medications resulting in suprachoroidal effusions [37, 38]. More recently, some serotonergic agents have been reported to precipitate angle closure in some people [39].

5.9.3Level III: Lens-Induced Angle Closure

Most cases of level I and II block are the result of lens size or position, and most cases of primary angle closure have some element of lens opacity in the form of nuclear sclerosis, or cortical opacity. However, these are not classified as lens-induced, which is the term reserved for cases characterised by a sudden change in lens thickness or position, as occurs in lens subluxation or intumescence (i.e. “phacomorphic” glaucoma) [26]. Cases typically present with symptoms of sudden increases in intraocular pressure, causing pain and blurred vision.

5.9.4Level IV: Ciliolenticular Block/Aqueous Misdirection/“Malignant Glaucoma”

These cases of angle closure are caused by forces posterior to the lens that push the lens–iris diaphragm forward. It is thought that a pressure differential is created between the vitreous and aqueous compartments, with aqueous being misdirected behind an intact anterior hyaloid face [26, 40, 41]. In other cases, the lens may be displaced anteriorly by other mechanisms, such as iatrogenic gas fills, large vitreous haemorrhages, or uveitis, causing inflammation of ciliary body [26]. One of the more common clinical scenarios is the finding of high intraocular pressure and a very shallow anterior chamber following trabeculectomy surgery.

These cases often require several interventions aimed at relieving the block at levels I, II and III. Ultimately, the management may involve complete decompartmentalisation of the eye, requiring surgical iridectomy, lens extraction, posterior capsulotomy, and in some cases pars plana vitrectomy [26, 42].

Two key clinical points to emphasise are that level I and II tend to be bilateral with anatomical features that are symmetrical, and are managed initially by constricting the pupil (usually with pilocarpine). Level III and IV blocks tend to be asymmetrical (with a shallow anterior chamber in the affected eye, and a relatively deeper AC in the other), and are managed with mydriatics (e.g. atropine).

5.10Gonioscopy

Gonioscopy remains the “reference standard” for diagnosing angle closure, and remains an essential component of the complete ocular examination. There are three widely used clinical grading systems, each with its own strengths and weaknesses. The Scheie system describes the structures seen and is simple and intuitive for nonspecialists [43]. An important weakness of this approach is that the number of structures seen can vary considerably depending on the direction of gaze and the orientation of the gonioscope. The Shaffer system is more widely preferred by glaucoma specialists [44]. It describes the geometric width of the iridocorneal angle. The Spaeth system allows the most detailed recording of angle characteristics: the geometric width of the iridotrabecular angle, the iris profile, as well as the true and apparent levels of insertion. It is helpful to avoid describing findings using derivative numbering systems (0–4, or 0–IV), but instead to describe exactly what was seen; for example, an iridotrabecular angle of 10° is a more precise description than “grade 1”. The best lens to use remains controversial. Many specialists feel that the use of a four-mir- ror lens is mandatory. Many others disagree—dynamic gonioscopy can be performed with a Goldmann oneor two-mirror gonioscope, and many closed angles can be “manipulated” open using a Goldmann lens. However a small proportion of appositionally closed angles cannot. In these cases, the use of a four-mirror lens is mandatory. For this reason, the minimum standard is to use a four-mirror lens. However, the ideal is to have both a four-mirror lens and a magnifying Goldmann lens available. The latter offers the opportunity for a more stable, clear view, and will probably give the occasional or inexperienced user more confidence in identifying important landmarks.

References 47

Summary for the Clinician

■Most angle-closure cases are asymptomatic

■Expert opinion is that anyone with 6 or more clock hours of irido-trabecular contact should

undergo prophylactic laser iridotomy

■ Classification should identify both the stage of natural history and the mechanism causing closure.

■Three conceptual stages of the disease are identified as i. anatomically narrow angles, ii. Primary angle-closure (narrow angles with raised IOP and /or peripheral anterior synechiae), iii. Narrow angles with glaucomatous optic neuropathy

■Four broad classes of mechanisms causing angleclosure are: i. pupil block, ii. Variations in shape, and position of the peripheral iris, iii. Lens associated, iv. Retro-lenticular (ciliary block, or malignant glaucoma)

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■The prevalence of ocular hypertension in patients with uveitis ranges from 7.6 to 23%. The duration and severity of uveitis are related to the development of ocular hypertension (OHT) and secondary glaucoma.

■Secondary glaucoma can occur through a variety of causes, including alterations to the composition of the aqueous humor and mechanical obstruction to outflow. Corticosteroids can also induce OHT and secondary glaucoma.

■Uveitic entities most commonly associated with OHT and secondary glaucoma include Fuchs’

heterochromic iridocyclitis, Posner–Schlossman syndrome, herpetic uveitis, juvenile inflammatory arthritis, and sarcoidosis.

■Medical treatment is often effective in controlling secondary glaucoma. Cessation of corticosteroids may require the addition of immunomodulating treatment to control inflammation. In glaucoma refractory to medical treatment, surgical options in combination with antimetabolites may be considered.

6.1Introduction

Glaucoma is a broad term that characterizes a large group of disorders that have optic neuropathy with visual field changes in common [1]. Elevated intraocular pressure is the most common risk factor for glaucomatous optic atrophy, and is a frequent complication of uveitis [1]. In this chapter, we will review current theories on the relationship between glaucoma and uveitis, and then discuss the uveitic entities most commonly associated with elevated intraocular pressure and secondary glaucoma. Finally, we will comment on the management of secondary glaucoma associated with uveitis.

6.2The Epidemiology of Uveitis-Related Ocular Hypertension (OHT)

and Secondary Glaucoma

The literature regarding the epidemiology of secondary glaucoma from uveitis frequently defines secondary glaucoma as an intraocular pressure (IOP) of greater than 21 mmHg, or IOP requiring medical treatment, without specifically commenting on damage to the optic nerve and progressive visual field loss. In this context, the term “uveitis-related ocular hypertension” is more appropriately used [2]. The distinction between secondary glaucoma and OHT will be noted whenever possible.

The prevalence of OHT in adults with uveitis ranges from 7.6 to 23% [3–9]. There are less data in the literature

regarding the true prevalence of secondary glaucoma taking into consideration optic nerve and visual field loss. Panek et al. looked retrospectively at 100 patients (161 eyes) with uveitis and found OHT (defined as intraocular pressure > 21 mmHg on more than one examination, or if the patient was receiving antiglaucoma therapy at the time of initial exam and had a well-documented increase in IOP concurrent with inflammation) in 23 patients (31 eyes) [8]. Twenty-two percent of these patients had glaucomatous field loss [8]. Takahashi et al. looked at 1,099 patients with uveitis between 1974 and 2000 and found OHT (defined as IOP > 21 at two consecutive visits needing treatment with medication) in 19.7% of patients [5]. 38.9% of these patients had an abnormal visual field related to high IOP [5]. Secondary glaucoma based on optic nerve changes and elevated IOP was detected in 10.9% of eyes in a cohort of patients with Behçet’s disease by Elgin et al. [5] Herbert et al. looked at the prevalence of OHT (defined as IOP > 21 mmHg on two separate occasions) in 257 patients (402 eyes) with uveitis seen over a threemonth period [7]. They found the prevalence of OHT to be 41.8%, with 29.8% requiring treatment (for those requiring treatment, the IOP was >30 with or without optic nerve/visual field changes, or IOP > 21 with optic nerve/visual field changes) [7]. 9.6% of the eyes in the study developed secondary glaucoma, two-thirds of which required medical treatment and one-third of which required surgical treatment [7]. Risk factors