HISTORICAL REVIEW AND CLASSIFICATIONS
The Hippocratic aphorisms include two mentions of blindness, one of which may refer to glaucoma: ‘When headache develops in cases of ophthalmia and accompanies it for a long time, there is a risk of blindness.’ Gradually the different causes of blindness were separated, with the most important distinction between cataract (which was treatable by couching) and glaucoma (which was not). Thirteenth century Syrian Salah-ad-din-ibin Yusuf al-kahal bi Hamah described a condition that he called ‘migraine of the eye’ or ‘headache of the pupil’: possibly a description of acute angle-closure glaucoma, with painful hemicrania and dilation of the pupil.
Itinerant British oculist Richard Banister published a clear description of end-stage or absolute glaucoma in which he observed that the eye was hard to palpation. Further descriptions of congestive glaucoma and the firmness of the eye were published by Platner, Guthrie, Beer, and Demours. Demours also reported halo vision in glaucoma.
In 1853, von Arlt ascribed the cause of glaucoma to the struggle for a livelihood, grief, weeping, vexation, eyestrain, and a damp dwelling. Most other scientists in the eighteenth and nineteenth centuries viewed glaucoma as a disease of the vitreous humor that was associated with iritis and arthritis. Following the development of the ophthalmoscope in 1851 by von Helmholtz, Jacobson, Jaeger, von Graefe, and Weber disproved this theory by noting glaucomatous cupping in eyes with clear vitreous bodies. The lack of vitreous involvement in glaucomatous eyes was confirmed histopathologically by Mackenzie and Muller.
Another important step in our understanding of glaucoma came from studies by Leber, Weber, and Knies of the aqueous humor circulation in animal and human eyes. The association between shallow anterior chambers and acute attacks of angle-closure glaucoma became clear in the late nineteenth century. It was during this time that von Graefe, in one of the landmark papers of ophthalmology, proposed iridectomy as a treatment for glaucoma. In the 1920s, Curran, Banziger, and Raeder independently put forth theories regarding the mechanism of pupillary block and further proposed that peripheral iridectomy cured angle-closure glaucoma by relieving this block. The efficacy of peripheral iridectomy as a treatment for glaucoma was confirmed by many physicians, including Gifford, O’Connor, Elschnig, Barkan, and Chandler. With the development of gonioscopy by Trantas, Salzmann, Koeppe, and Troncoso, the mechanism of angle closure was confirmed; and glaucoma was classified in modern terms by Barkan according to the state of the angle. Rosengren’s prescient biometric studies of the anterior segments in the ‘primary glaucomas’ distinguished the symptomatic angle-closure eyes from the asymptomatic open-angle eyes. This classification system was clinically elaborated by Sugar, and later adopted by the American Academy of Ophthalmology in 1949.
Today glaucoma continues to be classified into open-angle and angle-closure forms (see Ch. 1 ). In open-angle glaucoma, there is increased resistance to aqueous humor outflow through the trabecular meshwork–Schlemm’s canal–episcleral venous system by a variety of mechanisms which do not involve visible obstruction by the iris. In the angle-closure glaucomas there is increased resistance to outflow because of damage to, or obstruction of, the trabecular meshwork by the peripheral iris, preventing the aqueous humor from reaching the outflow channels.
CLASSIFICATIONS OF ANGLE-CLOSURE DISEASE
Historically the angle-closure glaucoma nomenclature has been confusing: conditions were sometimes classified by the time course of the disease, sometimes by the effects of the angle closure, and sometimes by the presumptive pathophysiology of the angle closure. For example, angle-closure glaucoma has been described by the adjective pairs congestive/non-congestive and compensated/uncompensated . These terms have been abandoned because they lack specificity. The congestion and corneal decompensation are usually a function of the rapidity with which the pressure rises, or reflect underlying causal phenomena such as uveitis.
Similarly the terms acute , subacute , and chronic have often been used to reflect the time course and/or presence of symptoms. Abrupt and total angle closure is acute ; recurrent and self-limiting episodes of closure with elevated intraocular pressure (IOP) are subacute ; and asymptomatic elevated IOP or peripheral anterior synechiae is chronic . Although these and similar temporal terms (e.g., ‘latent’ and ‘imminent’) have long had currency, even appearing in an elaborate contemporary classification of European and Inuit angle-closure disease based on high-resolution anterior segment imaging and clinical presentations, this complex scheme is problematic for two reasons. First, it is cumbersome for epidemiologic assessment, and often requires guesswork by the clinician – which makes standardization of diagnoses difficult. Second, these terms add little or no value to clinical strategies for patient care. Such terms explicitly presume correlated clinical signs and symptoms in the presentations of angle-closure glaucoma, with the time course of the patient’s disease retroactively designated by the clinican. Yet in one assessment of worldwide primary angle-closure glaucoma, four-fifths of patients presented entirely without symptoms. We concur with newer diagnostic definitions that discard older time-based terms, because they neither shed light on the natural history of disease progression, nor contribute to stage-specific management interventions for the disease.
In large part due to the recent appreciation of the magnitude of glaucoma blindness in the world, a disproportionate part of which occurs in Asians with primary angle-closure disease, consensus meetings among world glaucoma experts were held under the auspices of the Association of International Glaucoma Societies (AIGS) in 2006 to elaborate consistent and clinically applicable sets of definitions for angle-closure glaucoma disease (see Appendix). Based on over a decade’s attempts to develop a simplified, clinically relevant classification, this terminology has been endorsed by the American Academy of Ophthalmology, the International Society of Geography and Epidemiology of Ophthalmology (ISGEO), and the Southeast Asia Glaucoma Interest Group. Comparable schemes are now being used in numerous studies throughout the world: in Japan, Thailand, India, Mongolia, and among various Chinese populations.
This uniformity of approach has two major merits. Epidemiolog-ically, it greatly facilitates meaningful comparison among population studies, which further helps elucidate risk factors relevant to angle closure, determining clinical markers for progression of disease, distinguishing differential responses and complications of interventions, and discovering clues as to underlying pathogenic mechanisms. And for the individual patient, this scheme of the natural history of primary angle closure addresses both the prognosis for progression, and the stage-appropriate need for treatment.
TWENTY-FIRST CENTURY CONSENSUS CLASSIFICATION
The new classification of primary angle-closure (PAC) disease relies on three simple categories: IOP measurement, gonioscopy, and disc and visual field evaluation. In other words, the presenting patient’s clinical examination alone determines the staging of the disease, regardless of the presence, absence, or reliability of symptom history, alleged duration, intermittency of problems, etc.
- 1.
Primary angle closure SUSPECT (PAC suspect): greater than 270° of irido-trabecular contact plus absence of peripheral anterior synechiae (PAS) plus normal IOP, disc, and visual field . In other words, the suspect eye has normal IOPs, optic nerves and visual fields, i.e., no signs of clinical glaucoma, but whose angle before indentation gonioscopy is graded as a Shaffer grade 2 or less, without PAS on compression. The angle is at risk .
- 2.
Primary angle CLOSURE (PAC): greater than 270° of irido-trabecular contact with either elevated IOP and/or PAS plus normal disc and visual field examinations. In other words, angle closure demonstrates irido-trabecular contact in 75% of the angle, with either PAS or elevated IOPs, but without disc and visual field changes. The angle is abnormal in structure (PAS) or function (elevated IOP) .
- 3.
Primary angle-closure GLAUCOMA (PACG): greater than 270° of irido-trabecular contact plus elevated IOP plus optic nerve and visual field damage. In other words, angle-closure glaucoma manifests the criteria of closure above, plus demonstrable disc and/or visual field changes. The angle is abnormal in structure and function, with optic neuropathy.
It is important, of course, not to exclude all temporal information in this scheme: acute PACG remains a specific observable presentation category of the disease, requiring immediate recognition and intervention.
CLARIFICATIONS AND COMMENTARY
Mastery of indentation (compression) gonioscopy with such devices as the Posner or Zeiss 4-0 mirror goniolens (see Chapter 5 , Chapter 7 ) is the indispensable skill required to apply this classification. Since narrow angles are not particularly common – an estimated 2–6% of Caucasian eyes have suspiciously narrow angles (Shaffer grade 2 or less), and 0.6–1.1% have critically narrow angles (grade 1 or less) gonioscopic subtleties can only be learned by its routine practice in the clinic on every new patient, young or old. Irido-trabecular contact needs to be identified as present or absent , and then discriminated as either appositional (by indenting and revealing angle structures) or synechial , while documenting the latter’s extent (in terms of degrees or total clock hours). The use of a goniolens larger than the corneal diameter (e.g., Goldmann or Koeppe lenses) may allow better resolution of angle structures, but successful indentation to view deeper into the angle is usually not possible.
Consistent and competent gonisocopy technique is required, such as conducting all examinations in a dark room, using a small, 1-mm slit-lamp beam away from the pupil, identifying the most anterior point of iris–angle contact, and avoiding inadvertent compression. It is helpful to characterize PAS as to their height (e.g., ‘to Schwalbe’s line’), regularity (e.g., ‘symmetric, tented PAS’ or ‘broad, shaggy PAS’) and circumferential extent (e.g., ‘from 3 to 6 o’clock’). Indirect estimations of angle embarrassment, such as the van Herick method, or tangential pen-light examination, are not by themselves sufficient for screening; slit-lamp gonioscopy is indispensable, and preferably with indentation assessment ( Figs. 15-1 and 15-2 ).
The quintessential finding for a PAC suspect is that of irido-trabecular contact , a concept with greater specificity than ‘anatomically narrow angle’ or ‘occludable angle’ (although the latter term is still used in ICD-9-CM coding). A ‘narrow angle’ without contact, sometimes characterized as ‘occludable’, can imply for the clinician a predictive risk for closure which is not, in fact, substantiated by rigorous epidemiologically-derived criteria. The decision to proceed with iridotomy or surveillance requires a variety of factors to be considered: the patient’s access to care, whether the lens may soon require cataract surgery for visual reasons, the status of the fellow eye, the patient’s age and ethnicity, etc.
In the absence of iris–trabecular touch, it is imperative to estimate the angle depth. Though there are a variety of useful schemes to visually quantify the angle configuration (see Ch. 7 ), the Shaffer assessment of 20° or less of an irido-trabecular angle appears to be a robust and inclusive benchmark. It is also crucial to emphasize that gonioscopy in any PAC suspect needs to be repeated on a regular and recurrent basis as part of standard ophthalmic care.
Controversy remains regarding the extent of irido-trabecular contact in the definitions used to distinguish between ‘suspect’ and ‘closure’. At issue are the earliest effects and interplay of the two mechanisms, frequently co-existent, that are responsible for damage to the angle structures: (1) intermittent appositional abutment of iris to trabeculum, which can histologically manifest as degeneration of meshwork tissue even in sites remote from PAS; and (2) PAS, whose extent correlates with levels of IOP elevation.
The implications of precisely defining ‘suspect’ and ‘closure’ have real-world impact of great import, highlighting the eminent practicality of this classification and its flexibility for refinement over time. A ‘looser’ definition (e.g., 180° or less of touch) than the current criterion of 270° of irido-trabecular contact could classify up to 50% more eyes as diseased, requiring monitoring for PAS or immediate treatment of elevated IOPs; epidemiologically speaking, this could pose an enormous burden. Another aspect of this controversy is that using visible light – as is inherent in clinical gonioscopy – may be minimizing our perception of irido-trabecular contact, by unavoidably constricting the pupil and thus opening the angle to some degree. Hence our current instrumentation for clinically detecting the disease is underestimating the likelihood or extent of repetitive appositional iris–trabecular contact, which can cause chronic, cumulative trabecular damage.
There are those, however, who argue for the advantage of a lower threshold for characterizing PAC: by requiring less than 270° of irido-trabecular contact, detection is made more inclusive and attentive to early signs of angle embarrassment. In effect, this view prefers that the clinician be pre-emptive, and categorically assert that a patient does not have any stigmata of angle closure rather than, as is now done, tolerate findings that there is angle closure already underway. Earlier detection, so this line of thinking goes, might lead to earlier iridotomy treatment before the momentum of progressive disease occurs.
But since we do not precisely know which eyes will progress to actual glaucoma despite early manifestations of narrow angles with or without trabecular dysfunction, the oft-assumed benign nature of laser iridotomy needs to be reconsidered. The first consideration is that laser iridotomy therapy may, to some small extent, affect the lens and predispose to cataract formation. With the shunting of aqueous through a peripheral patent iridotomy, instead of its normal physiologic pathway through the pupil, there may be an adverse impact on overall lenticular metabolism. Moreover, focal tissue alterations have been seen following laser treatment. Small focal lenticular changes below the anterior capsule following yttrium-aluminum-garnet (YAG) iridotomy may predispose to long-term cataractous visual changes. Similarly, in marginally healthy corneas, the focal corneal endothelial loss sometimes seen following argon laser iridotomy may predispose to long-term focal or diffuse corneal decompensation.
Yet another consideration is that a patent iridotomy is not necessarily effective in eliminating irido-trabecular touch, with one study finding that over 60% of treated Chinese eyes were still manifesting post-iridotomy irido-trabecular contact, requiring continued glaucoma management. Moreover, after receiving a patent laser iridotomy for an acute attack, some eyes experience repeated acute angle-closure attacks. Thus it appears that the effectiveness of laser intervention may not always be either benign or curative; its effectiveness appears to be stage-specific to the disease, and dependent on underlying mechanisms other than pupillary block.
Consider the implications of the high rates of PACG found in surveys of select Chinese and Indian populations, affecting nearly 2% of individuals over the age of 40 years old: with nearly half of the world’s population living in India and China, scores of millions of people potentially require iridotomy. Because of the major public health ramifications in this context of millions of potentially affected eyes, it is imperative to determine whether laser iridotomy treatment induces even a small percentage of vision impairment when utilized prophylactically. Even a fraction of a per cent of post-iridotomy complications of cataract or corneal changes would affect enormous numbers of people with limited access to address their vision loss. Further research as to the benefits and demerits of each approach – either to recruit eyes with the earliest stigmata for consideration of treatment, or to reach a predetermined threshold or stage-specific criterion before progression – remains to be determined.
The end condition of primary angle-closure glaucoma includes the fundamental criteria for any glaucoma: damage to the optic nerve, with concomitant loss of visual field function. Hence the screening strategies for epidemiologically detecting this advanced stage of PACG are identical to those efforts for detecting primary open-angle glaucoma: optic nerve evaluation and, when feasible, perimetric assessment. In circumstances where advanced PACG disease with compromised media prohibits disc and visual field testing, for example cataract or corneal disease, a coarser definition holds for PACG whereby an IOP >24 and/or acuity of <3/60 (20/400), or a history of prior glaucoma surgery, will suffice. The stigmata of prior angle-closure attacks other than PAS – such as glaucomfleken changes in the anterior lens, patches of iris necrosis, etc. – are worth noting, but are not in themselves predictive.
PRESENTATIONS OF PRIMARY ANGLE-CLOSURE DISEASE
The manifest advantage of the simple tripartite definition of PAC disease, based solely on the findings present at the time of the exam, is essential for epidemiologic and comparative studies. But for deciding management and follow-up options, the clinician too must determine whether the presenting eye is a PAC suspect, manifests closure, or has PACG itself. This is the first step of management. Next she must then methodically distinguish among a variety of anatomical pathophysiologic mechanisms at play in the presenting eye. Hence a mechanism-based scheme complements the diagnostic definitions; together they illuminate the natural history and stage-appropriate findings which require intervention.
NEW IMAGING TECHNOLOGIES
As with optic nerve imaging, technological advances have profoundly impacted our understanding of patterns of anatomic alterations underlying angle-closure disease. There are two major devices whose contributions dominate the current clinical literature:
- 1.
Ultrasonic biomicroscopy (UBM) requires a skilled technician, a supine patient, and a water-bath coupling probe on the eye. With tissue penetration of 4 mm, a UBM’s resolution typically includes angle structures as well as imaging of the anterior lens and anterior ciliary processes; images appear as radial slices of one portion of the angle. Because UBM scans are obtained in real time on video, there are resultant advantages (e.g., dynamic capture of anterior segment responses to accommodation, or to dark or light stimulation, etc.) ( Fig. 15-3 ) and disadvantages (e.g., relatively low-resolution images, movement artifact, etc.)
Fig. 15-3
(A) Ultrasonic biomicroscopy of angle closed (star) in darkness-induced dilation. (B) Ultrasonic biomicroscopy of angle opened (star) in light-induced miosis.
Courtesy of Shan Lin, MD.
- 2.
Anterior segment ocular coherent tomography (AS-OCT) uses infrared light while examining a sitting patient without direct ocular contact; single-frame pictures can be obtained under different lighting conditions. Images comprise a 180°-diameter slice of the anterior segment ( Fig. 15-4 ), currently limited to but a few clock hours (e.g., 3–9 o’clock scan), but dramatically capture the pupil and iris–trabecular configuration in high definition. The limited penetration of the light source restricts resolution to the angles and iris only, without reliable imaging of the anterior ciliary processes or lens. Nevertheless, highly detailed calculations of such parameters as angle opening distance, angle recess area, and the trabecular–iris space area introduce new levels of precision for approaching PAC disease.
Fig. 15-4
Anterior segment ocular coherent tomography 180° image of narrow angles pre iridotomy.
Courtesy of Mingguang He, MD.
Both kinds of instruments propel investigations of subtle changes heretofore invisible to earlier investigators: correlation of gonioscopy and measurable parameters in imaging of the angle; alterations in angle configuration from laser iridotomies or cataract surgery; anomalous anatomical positioning of the ciliary processes in plateau iris, etc. Other instruments extend our abilities to meticulously assess the anterior chamber depth, such as the scanning peripheral anterior chamber (SPAC) depth analyzer and the Pentacam (Oculus Instruments) device incorporating Scheimpflug photography.
As a result of the revolutionary technologies of the UBM and AS-OCT studies in particular, specific mechanisms and parameters for comprehending PAC disease are being elaborated. When combined with the classical literature based on clinical observations of subtle variations in disease presentations, a fuller picture of the angle-closure glaucomas results.
CLASSIFICATION BY MECHANISMS IN THE ANTERIOR SEGMENT
We classify the primary angle-closure mechanisms based on three site-specific disturbances in the anterior segment. We group these mechanisms because they share important characteristics in common: (1) all three can, with clinical input, be discriminated by anterior segment imaging; (2) they clinically manifest under similar circumstances, clustering closely in the differential diagnosis of causes of PACG; and (3) they differentially respond to laser iridotomy, which helps discriminate among the underlying mechanisms ( Fig. 15.5 ). *
* Although ciliary block (‘malignant’) glaucoma has been included among the mechanisms at play in the primary angle-closure classification, we respectfully dissent and prefer to include it among the secondary angle-closure glaucomas. This is because of the rarity of ciliary block glaucoma, because its commonest presentation is postoperative, and because the target anatomical sites of vitreal–hyaloid and zonular–lens interface are not usually clarified by UBM studies (as are the three other mechanisms of PACG).
The three pathophysical mechanisms grouped in the consideration of PACG are:- 1.
pupillary block glaucoma
- 2.
plateau iris: configuration and syndrome (ciliary body anomalies)
- 3.
phacomorphic glaucoma (lens-induced obstruction).
Conditions involving forces involving the mid or posterior segments of the eye, such as ciliary block (malignant) glaucoma or cilio-choroidal detachments, are discussed in the following chapter.
1
PUPILLARY BLOCK GLAUCOMA
Pupillary block is the fundamental mechanism underlying the spectrum of PAC disease. Its pathophysiology involves: (1) lens–iris apposition at the pupil, with resultant bowing forward of the peripheral iris as aqueous pressure builds up in the posterior chamber; and (2) an anatomically predisposed eye that allows the anterior displaced peripheral iris to occlude the trabecular meshwork. The commonplace distinction between an acute attack and chronic disease remains important for clinical management decisions.
Epidemiologic studies
Epidemiologic studies address the entire spectrum of PAC disease in its three ‘suspect’, ‘closure’ and ‘glaucoma’ manifestations. The incidence and prevalence of PAC disease in a population are influenced by a number of factors, including the definitions used, and people’s age distribution, gender, racial make-up, range of refraction, and heredity.
Most individuals with narrow angles do not develop angle closure or glaucoma. As mentioned previously, anatomically narrow angles are found in 2–6% of eyes in the United States. In contrast, the prevalence of angle-closure glaucoma in the United States is probably less than 0.2% of the population. This suggests that, at most, only 1 of every 10 American whites with anatomically narrow angles will develop angle-closure glaucoma in his or her lifetime. In a population-based study in Hyderabad, India, Thomas and co-workers showed that, over a 5-year period, the risk of progressing from narrow angles (PAC suspects) to actual angle closure with either elevated IOP or synechiae (PAC) was 22%, but none of their patients actually developed optic nerve damage (PACG). But, of 337 patients from the same population with PAC followed for 5 years, the risk of progressing to actual PACG was 28%. In contrast, in one study in Olmsted County, Minnesota, the incidence of angle-closure glaucoma was 8.3 per 100 000 of the population 40 years of age and older. In this same study, 14% of participants were blind in at least one eye at the time of diagnosis and a further 4% became monocularly blind over a 5-year follow-up. Thus we see there is tremendous variability in the manifestations of this disease, many of which appear to be both population and disease-stage specific.
Primary angle-closure glaucoma with pupillary block occurs one-fourth to one-tenth as frequently as does primary open-angle glaucoma (POAG) among white individuals living in the United States and western Europe. One study states that PACG occurs in 0.1% of whites older than 40 years of age and comprises about 6% of the total glaucoma cases. Within this group, angle-closure glaucoma affects fewer individuals of Mediterranean origin than of northern European origin. Primary acute angle-closure glaucoma with pupillary block seems to occur less frequently in individuals of black African ancestry; those who are affected generally have a chronic asymptomatic form of the disease.
Acute PACG, with pupillary block, occurs rarely in some east Asian-derived populations, including Pacific islanders and American Indians, yet occurs frequently in other populations, including Eskimos (Inuit) in such diverse places as Greenland, Alaska, and northern Canada. Alsbirk reported that 10% of Eskimo women and 2.1% of Eskimo men over 40 years of age are affected by PACG. In such south Asian countries as India and Sri Lanka, the prevalence of PACG is equal to that of POAG. Primary angle-closure glaucoma appears to be relatively more common among many eastern and south-east Asian peoples, including the Chinese, Malaysian, Burmese, Filipino, and Vietnamese. Most of these cases are asymptomatic PACG (so-called ‘creeping angle-closure type’). Conversely, Japanese and Thai patients seem to have PACG less frequently than do other Asians.
In Taiwan, the prevalence of PACG in a rural population was about 3%, with an additional 2% PAC suspects. Angle-closure glaucoma is uncommon among those of Hispanic origin, averaging about 0.10%. In a study of a northern Italian population, a prevalence of PACG of 0.6% was found, but occludable angles were found in over 15%, which is higher than previous studies in Caucasian populations. In south India, there is a relatively low rate of PACG and suspects with narrow angles (0.7% and 1.4% respectively); but among the PACG eyes, plateau iris was common.
In descending order, the entire spectrum of PACG appears most prevalent among Inuit and Eskimos, then, those of south-east Asian heritage (especially Chinese, Filipino, Vietnamese), less so in those of European descent (although the prevalence varies from country to country), and least among those of African and Hispanic descent. In China and Singapore, for example, PACG is not only very prevalent – representing over one-third of the total glaucoma – but it is the most common cause of bilateral glaucoma blindness , though outnumbered 2:1 by POAG disease. Ethnicity apparently also plays a role in the severity of PACG when it clinically presents. For example, Chinese Singaporeans are twice as likely to require hospitalization for PACG than Singaporean Indians or Malaysians, although identical medical resources are available to all three groups.
This is a vast amount of information to keep track of, and is constantly evolving. It should be obvious that both PACG’s mechanisms and its natural history comprise a wide spectrum, with specific variations among different ethnic populations. A few salient summary facts are presented in Box 15-1 , which highlights key points from this new abundance of epidemiologic data on PAC disease.
- 1.
PACG is rare compared to occludable angles
For every 10 ‘occludable angles’ seen, there’s one case of PACG
Gonioscopy (our only tool!) is a POOR predictor
Most ‘occludable’ eyes do NOT get glaucoma!
Are YAG peripheral iridotomies innocuous (cf. reported focal lens changes and endothelial loss)? With a possible long-term complication rate of only 5%, prophylactic iridotomies on 40 million ‘at-risk’ Chinese and Indians could still cause >2 million potential problems
- 2.
Acute PACG is uncommon compared to chronic PACG
Expect one acute PACG for every three chronic PACGs: i.e., the majority of world glaucoma disease is comprised of both asymptomatic chronic PACG and POAG
There are two implications:
Most patients do not know they have disease
The same screening algorithms for assessing IOPs, disc changes and visual fields apply
- 3.
Ethnic variabilities of the glaucomas
POAG: moderate variable incidence among Caucasians ≈ Chinese < Hispanics < Africans
PACG: large variable incidence among Caucasians < urban Chinese < Mongolians ≈ Inuit
Hence, the ratio of POAG to PACG varies:
Euros ≈ Africans ≈ Hispanics – 5 POAG:1 PACG
Urban Chinese – 1 POAG:2 PACG
Mongolians – 1 POAG:3 PACG
- 4.
PACG is the major cause of world glaucoma blindness!
China: >90% glaucoma-blind have PACG, i.e., 10× more blindness from PACG than POAG (although their incidence ratio is near parity, with 2 POAG:3 PACG!)
Of 60 million with glaucoma in the world, >1/3 have PACG – but 25% of these patients are blind (more than twice the POAG blind)
Demographic risk factors
Age
Classic reports noted that PACG with pupillary block occurs with greatest frequency in the sixth and seventh decades of life. Several age-associated changes can include progressive relative pupillary block from a combination of increasing lens thickness, more anterior positioning of the lens, and pupillary miosis. It should be emphasized, however, that PACG with pupillary block can occur in patients of any age, and rarely even in children – though the etiologies among the young are almost always developmental or secondary.
Gender
Older studies have reported that PACG with pupillary block occurs 2–3 times more commonly in women than in men. The increased prevalence of angle closure in women probably reflects the fact that women have shallower anterior chambers; with some 10% less ocular volume than men. One exception to this observation may be in those of black African ancestry, in whom the occurrence of angle-closure glaucoma is apparently comparable among men and women.
Heredity
Most cases of PACG with pupillary block are sporadic in nature – that is, there is no family history of glaucoma. However, several pedigrees are reported to have a high prevalence of PACG, some with autosomal-dominant and some with autosomal-recessive patterns of inheritance. Shallow anterior chambers and narrow angles have been reported as more common in relatives of patients with PACG than in individuals whose relatives do not have the disorder. Similarly, a recent report observed that plateau iris configuration may aggregate in familial patterns.
Fifty years ago, Tornquist suggested that the configuration of the anterior chamber was inherited under polygenic influence, explaining the variable familial occurrence of PACG rather than a specific gene linked to the disease. The intricate developmental details now available regarding the growth of the anterior chamber and the explosive field of molecular genetics may soon elaborate upon these clinical perceptions.
Refractive error
The prevalence of PACG with pupillary block is much higher in individuals with hyperopic eyes, which typically have shallow anterior chambers and short axial lengths. Although rare, angle-closure glaucoma can occur in myopic eyes.
Miscellaneous factors
Older reports have suggested that PACG with pupillary block occurs more commonly in the winter months. This was variously attributed to low levels of illumination, increased cloudiness, changeable weather, and low sunspot activity. Central corneal thickness – a recently recognized risk factor for POAG – does not seem to have an association with PACG.
Ocular risk factors and mechanisms
Ocular risk factors cluster around a variety of findings, each of which reflects smaller ocular dimensions:
- 1.
Shallow anterior chamber both centrally and peripherally. Both Lowe and Alsbirk found angle-closure glaucoma to be uncommon in eyes with central anterior chamber depths of 2.5 mm or greater ( Table 15-1 ).
Table 15-1
Central anterior chamber depth and angle-closure glaucoma in a group of Eskimos
Prevalence of Angle-Closure Glaucoma (%)
Anterior Chamber Depth (mm)
>2.5
0
2.0–2.49
1
1.5–1.99
20
<1.5
85
Modified from Alsbirk PH: Acta Ophthalmol (Copenh) 53:89, 1975.
- 2.
Decreased anterior chamber volume.
- 3.
Short axial length of the globe.
- 4.
Small corneal diameter.
- 5.
Increased posterior corneal curvature (i.e., decreased radius of posterior corneal curvature).
- 6.
Decreased corneal height.
- 7.
Anterior position of the lens with respect to the ciliary body.
- 8.
Increased curvature of the anterior lens surface.
- 9.
Increased thickness of the lens.
- 10.
More anterior insertion of the iris into the ciliary body, giving a narrower approach to the angle recess, and possible anomalies of iris histology.
- 11.
Thinning of the ciliary body is reportedly associated with anterior movement of the lens, increased lens thickness and decreased anterior chamber depth.
Three measures in particular show particularly high correlations with angle-closure disease: (1) reduced axial anterior chamber depth and volume; (2) thicker lens; and (3) steeper radii of corneal curvature. The biometric peculiarities of eyes predisposed to angle-closure glaucoma are accentuated by three trends associated with aging. First, the lens grows in thickness throughout life. Second, the lens assumes a more anterior position with age. Third, the pupil becomes increasingly miotic with age. All of these age-associated changes increase the contact between the iris and lens, potentiate pupillary block, and reduce anterior chamber depth and volume. It is estimated that central anterior chamber depth decreases 0.01 mm/year.
Despite the elaboration of the specific ocular risk factors associated with PACG, the ‘fit’ with the demographic data is not completely congruent: to wit, population studies do not support the generalization that ethnic groupings have smaller eyes or ocular dimensions than others. Another way of integrating the data in light, for example, of the excessive burden of devastating PACG among Chinese populations, is to state that, statistically, Chinese don’t have smaller eyes – but those with small eyes (e.g., elderly women) are at greater risk for angle-closure disease. This anomaly has generated new hypotheses as to what other specific factors may be at play, such as the possible role of choroidal expansion in both angle-closure glaucoma and in ciliary block (malignant) glaucoma.
Iris bowing and lens–iris channel
Somehow the junction of the lens and iris at the pupillary plane modulates the flow of aqueous from the posterior to the anterior chamber, but it apparently is not a simple matter of direct contact between lens and iris. Part of this mechanism is thought to be due to iris structures: the iris sphincter muscle exerts a posterior vector of force that causes the central iris to ‘hug’ the anterior lens surface, with a possible contributory interplay with the dilator musculature. Preliminary studies of intra-iris collagen in acute PACG eyes suggest morphological changes may also contribute to abnormal iris mechanics. The flow capacity may also depend on the viscosity and other properties of the aqueous.
This important interface has been described as the iris–lens channel : an extremely thin (<5 microns), fluid-filled, flat, doughnut-shaped passage between the posterior iris surface and the anterior lens, circumferentially extending beyond the edges of the pupil. This dynamic and pulsatile fluid ‘structure’ provides normal resistance to aqueous flow from the posterior to anterior chambers. This thus functions as a relative one-way valve to sustain a minimally higher pressure in the posterior chamber than in the anterior chamber, hence directing anterior flow forward. Though the iris–lens channel is currently below the level of UBM resolution, the lens itself is not thought to directly contact the posterior iris, but remains a major variable in determining the configuration of the lens–iris channel, and hence its flow capacity.
The resistance to flow has classically been referred to as relative pupillary block ( Fig. 15-6 ). Under normal circumstances, this pressure differential is of little significance; however, if the pupillary block were to increase, the pressure posterior to the iris could force the peripheral iris to billow forward into the angle. (‘Like a sail full of wind’ is how this is often described to patients in explaining the salutory effect of a peripheral iridotomy’s perforation of the iris.) The increasing anterior bowing of the peripheral iris is maximized both when the anterior lens surface is progressively more anterior relative to the iris root, and when the pupil is in a mid-dilated position. A thicker iris has reduced flexibility which could increase the pressure difference between posterior and anterior chambers through the lens–iris channel.
If the peripheral iris bows forward slightly or if the anterior chamber is relatively large, the effect on IOP and anterior chamber dynamics would be inconsequential. However, if the peripheral iris bows forward enough to cover the trabecular meshwork, the normal outflow of aqueous humor from the anterior chamber would be blocked and the IOP could increase ( Fig. 15-7 ). Angle-closure disease typically occurs in eyes with small anterior segments in which even a relatively small forward bow of the peripheral iris may contact the trabecular meshwork.
Intraocular pressure and outflow facility are normal in eyes with shallow but open angles, no matter how narrow the angle appears. In contrast, when the iris is in contact with the trabecular meshwork, IOP rises and outflow facility falls in proportion to the extent of the angle closed; the resultant IOP would depend on the function (outflow facility) of the remaining unobstructed and undamaged angle.
Moderate pupillary dilation is historically the most recognizable cause of increased pupillary block, frequently due to pharmacologic dilation. It is thought that the posterior vector of force of the iris sphincter muscle reaches its maximum when the pupil is moderately dilated to a diameter of 3.0–4.5 mm. Furthermore, when the pupil is moderately dilated, the peripheral iris is under less tension and is more easily pushed forward into contact with the trabecular meshwork. Lastly, dilation may also thicken and bunch the peripheral iris in the angle. In contrast, when the pupil is widely dilated, there is little or no contact between the lens and the iris and minimum pupillary block. This fact explains why acute angle-closure glaucoma rarely occurs while the pupil is in the actual process of dilating due to mydriatic eye drops: the dilation occurs rapidly enough that pupillary block does not have time to develop. Rather, pupillary block ‘classically’ occurs as the pupil constricts over hours following dilation, presumably because the mid-dilation is prolonged as the mydriatic effect slowly reverses. Pupillary block can also be increased by marked pupillary miosis. Despite this cautionary apprehension about pharmacologic dilation precipitating acute angle closure, in reality it is quite rare in a general population.
There exists a rich, anecdotal literature of everyday life ‘triggers’ for precipitating attacks of acute PACG; reports commonly identified emotional upset (e.g., bad news, pain, fear, illness, an accident) or dim illumination (e.g., in a restaurant or theater). Emotional upset is thought to dilate the pupil through increased sympathetic tone to the iris dilator muscle, whereas dim illumination dilates the pupil through decreased cholinergic tone to the iris sphincter muscle. But why precisely an attack is precipitated under one such circumstance, but not by the countless dilations and constrictions of the pupil during a lifetime of quotidian activity and emotional reactivity, is never clear. Similarly, the forward movement of the lens, which occurs in a variety of situations such as reading, changes in body position, and miotic therapy, has been implicated as a trigger. Diurnal variations in the anterior chamber depth with parasympathetic fluctuations and pupillary diameter, and diurnal variations in aqueous secretion have also been suggested as contributory factors.
The pharamacological precipitation of acute PACG in predisposed individuals, by a variety of medications applied topically, systemically, or transdermally, is better documented. These medications include tranquilizers, bronchodilators, antidepressants, vasoconstrictors including common nasal decongestants, appetite suppressants, antiparkinsonian agents, cold preparations, antinausea agents, and antispasmodics ( Box 15-2 ). These drugs are thought to dilate the pupil through an anticholinergic effect on the iris sphincter muscle, or a sympathomimetic effect on the iris dilator muscle.
Antipsychotic agents
Phenothiazines: e.g., perphenazine (Trilafon), fluphenazine (Prolixin)
Anticonvulsants
e.g., Topiramate (Topomax)
Antidepressants
Tricyclic agents: e.g., amitriptylene (Elavil), imipramine (Tofanil)
Non-tricyclic agents: e.g., fluoxetine (Prozac), paroxetine (Paxil), venlafaxine (Effexor)
Monoamine oxidase (MAO) inhibitors
e.g., Phenylzine (Nardil), tranylcypromine (Parnate)
Antihistamines
e.g., Ethanolamines: e.g., orphenadrine (Norgesic)
Antiparkinsonian agents
e.g., Trihexyphenidryl (Artane)
Antispasmolytics
Propantheline (Pro-banthine)
Dicyclomine (Bentyl)
Antibiotics
e.g., Sulfa, quinine
Sympathomimetic agents
Adrenaline (epinephrine), ephedrine
Dipivefrin
Amfetamine, hydroxyamfetamine
Tetrahydrozoline
Naphazoline
Mydriatic agents
All : cyclopentolate, tropicamide, atropine, homatropine, scopolamine
Miotics
e.g., Echothiophate (Phospholine Iodide), pilocarpine 2–6%
Botulinum toxin
Cardiac agents
e.g., Disopyramide (Norpace)
Modified from Mandelkorn R: Drug-induced glaucoma. In: Zimmerman TJ, Kooner KS, editors: Clinical pathways in glaucoma, New York, Thieme, 2001:333–350.
Special attention needs to be drawn to the role of the parasympathomimetic drugs, which constrict the pupil and increase pupillary block. These drugs also contract the ciliary muscle, allowing the zonules to relax and the lens to move forward. Although these changes may not always have clinical relevance, the incontrovertible fact is that angle-closure glaucoma can be precipitated by miotic agents in susceptible eyes with narrow angles. (As discussed below, in considerations for managing the fellow eye after an attack of acute PACG, it is advisable to avoid miotics such as pilocarpine in the ‘prevention’ of PACG.) Because of this risk, it is important to repeat gonioscopy when initiating or changing miotic therapy. The strong miotics (e.g., cholinesterase inhibitors) are more likely to produce angle closure because they cause greater constriction of the pupil and induce vascular congestion of the uveal tract.
The proper treatment for miotic-induced angle closure is discontinuing the drug. If the angle remains exceedingly narrow after discontinuing the parasympathomimetic agent or if the patient requires miotic treatment for IOP control, laser iridotomy can be performed
Provocative tests
One goal that remains as elusive as ever has been the ability to predict which eye at risk will proceed towards disease. As recent epidemiologic assessments have demonstrated, most eyes with ‘occludable angles’ do not progress towards PACG. 43 This was an especially compelling concern before laser iridotomies were available, since surgical iridectomies were not without morbidity, particularly in terms of complications and cataract formation. 50
Some of the above-mentioned observations on the role of body position and pharmacologic effects have historically generated an array of provocative tests : to elevate IOP in conjunction with occlusion of the angle, so as to indicate which eyes ‘at risk’ merit surgical intervention. Most provocative tests were designed to resemble ‘physiologic’ situations, in the hope that the test would mimic the natural history of the condition. Fortunately, two prospective studies have been conducted, and neither validates the utility or reliability of such examinations.
A variety of testing strategies have been reported: (1) mydriatic stimulation with a weak, short-acting parasympatholytic agent such as tropicamide 0.5% or a weak sympathomimetic such as hydroxyamfetamine, to mildly dilate the pupil and either raise the IOP or demonstrate impaired tonographic outflow; (2) dark room testing to induce physiologic miosis; (3) a prone test with the head resting on one’s arms on a table, arguably shifting the lens anteriorly without dilation; and (4) complex pharmacologic provocations, such as applying a mixture of cycloplegics or mydriatics with pilocarpine.
Unfortunately, each of these ‘provocative’ tests produce enough false positives and false negatives to make them unreliable as predictors of true angle closure or angle-closure glaucoma. Most studies indicate that 10–30% of eyes with well-documented histories of angle-closure glaucoma have negative provocative tests. Furthermore, approximately 5% of eyes with angle-closure glaucoma have positive provocative tests after peripheral iridectomy. Finally, even a small percentage of normal eyes and of eyes with open-angle glaucoma develop elevated IOP without angle closure during provocative testing. This has been variously attributed to a cycloplegic effect on outflow facility or hypersecretion of aqueous humor. Therefore, the provocative tests from a previous generation of clinical techniques are of little help in predicting a patient’s likelihood of developing angle-closure glaucoma. They are no longer either clinically recommended or relevant.
Whether newer efforts integrating a variety of technologies will be more helpful remains to be seen. For example, Congdon and co-workers found that ultrasonic measurement of the anterior chamber depth combined with tonometry gave an acceptable balance between a sensitivity of 88% and a specificity of 92% in a screening to discover PAC suspects and PAC. While assessing the fellow eyes of patients who presented with acute PACG attacks, using both Scheimpflug photography and ultrasound biomicroscopy, Friedman and co-workers found shallow peripheral anterior chambers, more narrowing of the angle when going from light to dark, and greater opening of the angle after pilocarpine drops compared to controls. Whether these kinds of newer dynamic tests are any more sensitive or specific in indicating which patients are likely to develop angle closure still awaits longitudinal, prospective study.
Clinical presentations of acute PACG with pupillary block
When the outflow capacity of the angle is sufficiently compromised to elevate the IOP, possible irreversible damage to the optic nerve can subsequently ensue. Asymptomatic disease of presumably long duration is much more common than the dramatic symptoms of a precipitous closure of the angle, with rapid deterioration in optic nerve and/or corneal function. Acute PACG is a distinctive form of clinical disease, with a constellation of presenting signs and symptoms requiring urgent intervention, as well as preventive measures for the fellow eye.
Signs and symptoms
The typical patient with an acute attack of PACG from pupillary block will have a sudden onset of pain or aching on the side of the affected eye. This pain is accompanied by blurred vision or colored haloes around lights (from the refractive and diffractive changes of corneal edema); ocular congestion; and sometimes nausea, vomiting, and sweating. The pain usually occurs in the trigeminal distribution, and is locally experienced by the patient as in the eye; or it can manifest as referred pain in the orbit, head, ear, sinuses, or teeth. The discomfort may be mild to severe – so severe in fact that the glaucoma attack may masquerade as an acute intracranial process such as an aneurysm.
The eye pain appears to be related more to the rapid rate of the rise in IOP than to the absolute level of the pressure itself. The blurred vision occurs at first as a result of distortion of the corneal lamellae, and later as a result of corneal epithelial edema. The corneal edema acts as a diffraction grating that breaks white light into its component colors, causing patients to note colored haloes or rainbows around incandescent lights. During these episodes, the blue-green colors are central and the yellow-red colors are peripheral. In a study of over 5000 Taiwanese patients with angle-closure glaucoma, symptoms of angle closure were present in only 35% of patients.
Autonomic stimulation during an acute attack can result in nausea, vomiting, sweating, and bradycardia. These symptoms are sometimes confused with those caused by a flu-like illness or an acute abdomen; with systemic distress and vomiting, PACG attacks have been mistaken for acute appendicitis. Occasionally systemic symptoms such as abdominal or chest pain are predominant and may make diagnosis difficult. Acute angle-closure attacks have precipitated under conditions of intense physiological stress, such as pituitary apoplexy and childbirth.
Most attacks of angle-closure glaucoma are unilateral. However, 5–10% of the attacks may affect both eyes simultaneously. Patients who develop acute attacks of angle-closure glaucoma may relate that they have had similar but less severe episodes in the past, recalling mild episodes of discomfort or blurring that were relieved by sleep or by exposure to bright light. Such reports have been use to substantiate the terminology of ‘subacute’ or ‘intermittent’ angle closure; but they are, strictly speaking, variable and subjective reports, difficult to accurately correlate with actual ocular dysfunction.
Clinical examination
The clinical examination of an eye in acute PACG can reveal a spectrum of physical findings ( Boxes 15-3 and 15-4 ):
- 1.
Diminished visual acuity.
- 2.
Perilimbal conjunctival hyperemia (i.e., ‘ciliary flush’).
- 3.
Corneal edema, at times involving only the epithelium, but occasionally thickening the stroma and precipitating striae.
- 4.
A shallow anterior chamber both centrally and peripherally.
- 5.
Minimal-to-moderate anterior chamber reaction caused by increased aqueous humor protein concentration. Severe or prolonged attacks may produce heavy anterior chamber cell and flare – but keratic precipitates are rarely seen.
- 6.
A moderately dilated, vertically oval, sluggish, or nonreactive pupil. The high IOP causes ischemia and paresis of the pupillary sphincter. (It is important to assess for a reverse Marcus Gunn pupillary sign to gauge the extent of optic nerve damage in the symptomatic eye.)
- 7.
Markedly elevated IOP, usually in the range of 35–75 mmHg.
- 8.
A closed angle on gonioscopy, which is the critical test for diagnosing angle-closure glaucoma. It is sometimes difficult to evaluate the angle during an acute attack because of corneal edema and hazy media. In this situation, gonioscopy should be repeated after the IOP is reduced by medical treatment, which hopefully permits the cornea to clear (see ‘Treatment of acute PACG’ below). One or two drops of anhydrous glycerin can also be administered to the anesthetized eye to clear the cornea and improve the gonioscopic examination. (Other topical hyperosmotic agents, although less effective, may work if glycerin is not available: these include hypertonic salt solutions and Karo (or other brand) syrups whose sugar content is high enough to provide some osmotic effect.) As disussed below, repetitive corneal indentation at the slit lamp may burp the angle open to reduce both the pressure and corneal obscuration. If the view remains hazy, angle-depth estimation by the van Herick test and gonioscopy of the fellow eye can confirm the presence of narrow angles, albeit imprecisely. Ultrasonic biomicroscopy or AS-OCT imaging studies, if available, can be very helpful diagnostically.
- 9.
Sometimes a hyperemic, swollen optic disc. The optic disc is swollen during an attack of angle-closure glaucoma presumably from impaired axoplasmic flow. Or the optic disc may be swollen when hypotony follows an acute attack of angle-closure glaucoma. The disc does not appear pale or cupped during the acute attack unless there have been previous episodes of angle closure or concomitant glaucoma from another cause. When IOP was raised to high levels in experimental studies in monkey eyes, the optic discs appeared swollen for 4–5 days and then became pale and cupped. The appearance of the optic disc is altered if there is a concomitant central or branch vein occlusion. It is also possible for a central retinal vein occlusion to cause a transient shallowing of the anterior chamber (see Ch. 16 ).
- 10.
A normal or constricted visual field. (Visual field examinations are generally not performed during acute attacks of angle-closure glaucoma.) Following an attack, visual fields can demonstrate a variety of perimetric defects. Curiously, eyes with asymptomati c PACG may have worse visual fields than an eye after an acute attack, possibly reflecting the chronicity of the glaucomatous processes which may be unrecognized by the patient.
- 11.
Diminished tonographic outflow facility. The resistance to outflow is directly related to the extent of the angle closure. The resistance also depends on whether the open portions of the angle have been damaged by previous attacks of angle closure.
Findings during an acute attack of angle-closure glaucoma
Two of the following symptom sets:
Periorbital or ocular pain
Diminished vision
Specific history of rainbow haloes with blurred vision
IOP >21 mmHg plus three of the following findings:
Ciliary flush
Corneal edema
Shallow anterior chamber
Anterior chamber cell and flare
Mid-dilated and sluggishly reactive pupil
Closed angle on gonioscopy
Diminished outflow facility
Hyperemic and swollen optic disc
Constricted visual field
Findings suggesting previous episodes of acute angle-closure glaucoma
Peripheral anterior synechiae
Posterior synechiae to lens
Glaukomflecken
Sector or generalized iris atrophy
Optic nerve cupping and/or pallor
Visual field loss
Diminished outflow facility
Modified from Quigley H, Yamamoto T: Management of acute angle-closure crisis. In: Weinreb R, Friedman D, editors: Angle closure and angle closure glaucoma: reports of 3rd AIGS consensus meeting. Hague, 2006:21–26.
Evidence of compromised angle on gonioscopy or shallow anterior chamber
Ciliary block glaucoma (aqueous misdirection or malignant glaucoma)
Neovascular glaucoma
Iridocorneal endothelial syndrome
Plateau iris syndrome with angle closure
Secondary angle closure with pupillary block (e.g., posterior scleritis)
Cilio-choroidal detachments (bilateral)
High-pressure open-angle glaucomas masquerading as acute angle closure
Glaucomatocyclitic crisis
Herpes simplex keratouveitis
Herpes zoster uveitis
Sarcoid uveitis
Pigmentary glaucoma
Exfoliative glaucoma (may have associated angle closure)
Post-traumatic glaucoma
Phacolytic glaucoma
Steroid-induced glaucoma
Modified from Quigley H, Yamamoto T: Management of acute angle-closure crisis. In: Weinreb R, Friedman D, editors: Angle closure and angle closure glaucoma: reports of 3rd AIGS consensus meeting. Hague, 2006:21–26.
Recent clinical publications define an acute attack of PACG by the presence of: (1) at least two symptoms (such as ocular pain and nausea/vomiting); plus (2) an elevated IOP > 21 mmHg; plus (3) at least three findings from the clinical examination, e.g. corneal edema, shallow anterior chamber, goniscopic confirmation of angle closure, etc. (see Box 15-3 ). Such explicit criteria of definitions make clinical and research studies significantly more specific and comparable.
A patient examined during an acute attack of PACG with pupillary block may demonstrate stigmata of previous attacks, including PAS, posterior synechiae between the peripupillary iris and lens, anterior subcapsular lens opacities (‘glaukomflecken of Vogt’, sector or generalized atrophy of the iris, pallor and cupping of the optic disc, and visual field loss. The iris atrophy is probably ischemic in origin and is more often located superiorly than inferiorly. This process releases a considerable amount of pigment, which is then deposited on the iris surface, corneal endothelium, and trabecular meshwork. The ischemia may contribute to the severe pain during the acute attack.
Many of the above signs and symptoms could occur as a result of an abrupt and profound rise in IOP regardless of cause. The ophthalmologist must distinguish PACG with pupillary block from secondary forms of angle closure, as well as open-angle glaucoma with sudden markedly high levels of IOP. The differential diagnosis includes neovascular glaucoma, plateau iris syndrome, hypertensive iridocyclitis, aqueous misdirection, post-traumatic recessed angle, exfoliative glaucoma, pigmentary glaucoma, and glaucomatocyclitic crisis (see Box 15-4 ). A special situation exists with exfoliative syndrome, which can produce very high IOPs in the presence of an open angle. However, exfoliative syndrome is also associated with an increased prevalence of narrow angles and an increased risk of pupillary block PACG.
These non-PACG entities are usually discriminated by a careful history of the temporal course of events, a slit-lamp examination, and indentation gonioscopy of the involved and the fellow eyes. The examination also serves to detect secondary forms of angle closure that are associated with ciliary block glaucoma, ciliary body swelling, posterior segment tumors, central retinal vein occlusion, nanophthalmos, etc.
It is crucial that both eyes be examined in order to determine whether any presenting condition is bilateral, and to assess the potential for the second eye to become involved.
Treatment of acute PACG
The treatment of acute PACG with pupillary block can be divided into four stages:
- 1.
Immediate medical therapy is required for lowering the IOP, thus enhancing maximal visualization of angle structures for diagnosis and treatment, and interrupting pressure damage to the optic nerve, trabecular meshwork, and lens. Once the IOP has been lowered, and the cornea cleared as a result, a variety of laser interventions can be initiated (see below).
- 2.
Protection of the fellow eye is initiated with medical treatment to reduce the IOP, until the acute attack is resolved and a prophylactic iridotomy can be performed. For reasons elaborated below, we emphatically encourage that chronic miotics not be used to ‘prevent’ angle closure in the fellow eye .
- 3.
Laser iridotomy in both the involved and fellow eyes can often, but not always, achieve two objectives: (1) to relieve acute pupillary block and open the angle; and (2) eliminate future acute attacks of PACG ( Fig. 15-8 ). Following iridotomy, the central anterior chamber depth may not appreciably deepen by slit-lamp examination, and irido-trabecular contact can be seen to persist (as seen in approximately 60% of Chinese eyes in the Liwan study); in contrast, UBM studies usually demonstrate some opening of the angle. Clinically, iridotomies usually reduce but do not totally eliminate the possibility of future attacks of angle-closure glaucoma. Intriguing new studies that proceed directly to cataract/intraocular lens surgery following an attack of acute PACG may prove, with confirmatory research, to be an appealing alternative to laser iridotomy. Unless the fellow eye with PAC has visually significant cataract that can be expeditiously addressed, laser iridotomy – not prophylactic miotic medical therapy – is imperative. The risk of not performing a contralateral iridotomy after an acute attack in the presenting eye is formidable; nearly 50% of such eyes can go on to an acute attack, usually in the first months following the patient’s initial presentation, even with the use of pilocarpine.
Fig. 15-8
(A) Ultrasonic biomicroscopy of closed angle before peripheral laser iridotomy. (B) Ultrasonic biomicroscopy of opened angle after peripheral laser iridotomy.
Courtesy of Mingguang He, MD.
- 4.
Long-term glaucoma surveillance and IOP management of both eyes is obligatory following an attack of acute PACG. Following such an episode, the long-term prognosis for such an eye avoiding visual loss is guarded; cataract as well as the high likelihood of failed medical management frequently require surgery. The potential morbidity of PACG is not to be underestimated: in one long-term follow-up of 4–10 years, more than one out of six of acute-attack eyes were blind, and nearly half had advanced glaucomatous disc and field damage. Fellow eyes after prophylactic iridotomy fared better in two studies of 4–6 years’ follow-up, with single-digit rates of progressive glaucoma developing. In summary, every acute PACG eye and its fellow eye are automatically at risk for PACG – the most common cause of glaucomatous blindness in the world.
Medical management of acute PACG
Patient comfort and lowering of the IOP are the first priorities in addressing an acute crisis of PACG. When these aims are achieved, one can proceed to more definitive interventions with the laser, such as iridotomy, pupilloplasty, or iridoplasty. Medications to control pain and emesis should be administered as needed. If the patient presents in great physical distress, a retrobulbar anesthetic (e.g., 4 cc of a 50:50 mixture of 2% lidocaine with 0.75% bupivacaine) can be enormously helpful to both patient and physician: the analgesia and interruption of nausea and vomiting provide welcome relief to the sufferer; and the eye is stable and insensate for ocular manipulations (e.g., paracentesis) and laser treatments. Patients, of course, need to be explicitly told that the loss of vision with the retrobulbar injection is temporary; and the practitioner needs to compensate for the lost ability of the patient to cooperate with different gaze positions during gonioscopy or laser therapy.
The physician should immediately administer some combination of a topical β-adrenergic antagonist (such as timolol or levobunolol), a topical α-adrenergic agent (such as apraclonidine or brimonidine), a prostaglandin analogue, an oral or parenteral carbonic anhydrase inhibitor (e.g., acetazolamide) and, if necessary, an oral hyperosmotic agent (e.g., glycerin or isosorbide) ( Table 15-2 ). These agents will begin lowering the IOP, alleviating pain, and allowing the cornea to be cleared with a topical hyperosmotic agent for further diagnostic evaluation. Intravenous mannitol may be used if oral agents are unavailable, not tolerated, or contraindicated as in diabetes mellitus.
| Method | Drug and Administration |
|---|---|
| β-Adrenergic antagonist | Timolol or levobunolol: one drop to affected eye |
| Prostaglandin analogue | Latanoprost: one drop to affected eye |
| α-Adrenergic agonist | Apraclonidine or brimonidine: one drop to affected eye |
| Carbonic anhydrase inhibitor | Dorzolamide: one drop to affected eye; or acetazolamide (500 mg orally, or intravenously if the patient is nauseous) |
| Hyperosmotic agent | Glycerine 50% or isosorbide 45% (1.5–4 ml/kg orally); mannitol 20% (2–7 ml/kg intravenously if the patient is nauseous or unable to tolerate oral agents) |
| Limited role of pilocarpine | Pilocarpine 1%: one drop two or three times immediately preceding laser iridotomy |
| Pain and emesis control can be obviated by retrobulbar anesthesia |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
