Features

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This article is the first in a series that will provide up-to-date information on glaucoma, from disease detection and diagnosis through to management and monitoring. The aim is to provide background information to give context both for clinical examination and decision-making. The series is designed to inform everyday optometric practice, but will also be valuable for optometrists embarking on extended roles in glaucoma care. Specifically, this first article is an introduction to the glaucomas, defining the disease and explaining current theories on causality.

Defining the glaucomas

Glaucoma describes a group of diseases that share the single common feature of a characteristic, progressive optic neuropathy. All forms can lead to progressive loss of visual function if undetected, untreated or insufficiently treated, and all are therefore potentially blinding. The characteristic structural changes of the optic nerve head and retinal nerve fibre layer in glaucomatous optic neuropathy (GON) are typified by several clinical features, the mainstays of which include:

• Abnormalities of the neuroretinal rim
• Abnormalities of the peripapillary retinal nerve fibre layer
• Increasing disc excavation (‘cupping’)
• Disc haemorrhages.

These features distinguish GON from other optic neuropathies. It should be noted that other optic neuropathies can produce some components of this appearance. For example both compressive and arteritic anterior ischaemic optic neuropathies may result in cupping, but they do not produce focal rim abnormalities or splinter haemorrhages.

Many differing disease processes may contribute to GON. This pathophysiologic diversity explains the variation in both clinical signs observed among glaucoma sub-types and symptoms reported by patients. This variation will be explored here.

Glaucoma: a public health issue

As a group of diseases, the glaucomas are a leading cause of visual morbidity throughout the world. It is estimated that, globally, there will be 60.5 million cases of glaucoma by the year 2010. Furthermore it is estimated that, of these, about 8.4 million affected individuals will be bilaterally blind as a result.

Glaucoma is a leading single cause of blindness in the developed world. Data on visual impairment certification in England and Wales for 1999-2000 has recently confirmed glaucoma as the second most common cause of both blindness and partial sight registration. It ranks after degeneration conditions of the macula and posterior pole, such as age-related macular degeneration. Glaucoma accounts for 10.9 per cent of all certifications for blindness (now termed severe sight impairment), and 10.2 per cent of certifications for partial sight (now termed sight impairment). The rate of severe sight impairment due to glaucoma increases with age, with 10 registrations per 100,000 for individuals aged 65-74, and then 48 per 100,000 and 100 per 100,000 individuals of 75-84 years and 85 years and over respectively.

Because most glaucoma is age-related, the proportion of people with manifest disease at any single time point – prevalence – depends on population demographics. With ageing populations and increasing longevity, glaucoma prevalence is set to increase in coming decades.

Prevalence is the proportion of a population that is outcome-positive (ie glaucoma is present) at a given point in time, whereas incidence is the proportion of occurrences of new outcome-positive cases in the population. A risk factor refers to an aspect of personal behaviour or lifestyle, environmental exposure, or inborn or inherited characteristic, which, on the basis of epidemiologic evidence, is known to be associated with the disease. The prevalence of and risk factors for the different forms of glaucoma will be discussed below.

The other important epidemiological issue to note is the concept of the discriminatory power of a screening test, most commonly reported in terms of sensitivity and specificity. These indices, and their corresponding predictive values or likelihood ratios, are fundamental test properties, as they allow the user to determine the consequences of selecting a particular cut-off criterion for referral or for further investigative tests. Sensitivity is the proportion of diseased individuals correctly identified as diseased and specificity is the proportion of non-diseased individuals correctly identified as non-diseased. The positive predictive value (PPV) is the proportion of patients with positive screening test results who are found to have disease. The negative predictive value (NPV) is the proportion of patients with negative screening test results who are found not to have disease, based on a gold-standard. The discriminatory power of specific screening tests used in glaucoma detection will be discussed in subsequent articles.

At present, a formal screening program for glaucoma is not performed in the UK. Such a programme could be a public health service whereby all members of a defined population – who do not necessarily perceive they are at risk – are offered a test. Glaucoma cases are typically detected through case-finding by optometrists. Detection will vary across the optometric profession because criteria for using screening tests and referral criteria for cases of suspect glaucoma vary between optometrists. Also, the proportion of at-risk individuals who present for eye examinations may vary geographically. Referral refinement schemes have been shown to reduce the number of false positive referrals, in part because of the re-assessment of suspect cases but also because of the improved discriminatory power achieved through the use of all three main types of screening test.

What causes GON?

At cellular level, GON constitutes damage to retinal ganglion cell axons as they exit the eye to form the optic nerve. It has been estimated that, on average, more than 1 million ganglion cell axons make up a healthy optic nerve. With ageing, this number reduces physiologically with average loss of around 6,000 axons/year. Simplistically, GON can be considered as acceleration in this rate of loss to a pathophysiologic level. At some point, this accelerated loss of axons will exceed inbuilt redundancy in the axon population, leaving insufficient axons to support normal visual function.

The anatomical locus of axon damage in glaucoma is the lamina cribrosa, the fenestrated structure adjacent to the inner sclera through which retinal ganglion cell axons exit the eye. The lamina consists of stacked plates of highly specialised connective tissue, with aligned pores for axon bundles to pass through. Once an axon becomes damaged at the lamina, rapid degeneration of the ascending (optic nerve head to brain) portion occurs initially, followed by slower degeneration of the descending portion of axon (optic nerve head to retina) and cell body. Damage and degeneration of sufficient axons will eventually leads to clinically detectable changes.

There is still much debate about the exact pathophysiology of the death of ganglion cell axons in glaucoma. Retinal ganglion cell axon health and maintenance of function depends on continuous movement of materials along the axon, moving metabolic requirements and by-products to and fro. This axoplasmic transport is both orthograde (eye to brain) and retrograde (brain to eye) and requires energy provided by the cell body. Axonal transport blockade may lead to cell death, and can be caused by mechanical ligature, temperature change, toxicity or ischaemia. Therefore, any factor that causes axonal transport disruption, or promotes retinal ganglion death, may be a causal factor in the pathogenesis of glaucoma. The common mechanism of ganglion cell death in glaucoma is considered to be apoptosis, a programmed mechanism that removes cellular debris by phagocytosis without an associated inflammatory response.

Traditionally, two theories have become widely stated as involved in glaucoma pathogenesis, although more recently, a third hypothesis has also been proposed.

Mechanical theory of glaucoma pathogenesis

This hypothesis states that structural optic nerve head changes are the cause of GON. This theory is supported by clinical observations that:

• Raised intraocular pressure (IOP) is significantly associated with glaucoma and
• Therapeutic IOP reduction significantly reduces glaucoma development among patients with high IOP and also reduces disease progression among patient populations with glaucoma.

While it is possible that IOP may have a direct mechanical impact on nerve fibre bundles, backward bowing and distortion of the lamina plates (causing misalignment of lamina pores) and ligature of nerve fibre bundles suggest that nerve fibre damage is due to the indirect effect of IOP via morphological changes in the lamina cribrosa.

Although it is possible that IOP may be the sole causal factor, it is also possible that the primary pathology may result from increased lamina vulnerability, whereby connective tissue alterations may reduce its compliance and the structural support it provides to passing nerve fibres, a mechanism that may be IOP-independent.

Vascular theory of glaucoma pathogenesis

This hypothesis postulates that blood flow to ganglion cell axons at the optic nerve head is abnormal. The resultant effect of such a state may be hypoxia (reduced availability of tissue oxygen) and/or ischaemia (reduced tissue nutrients, including oxygen). Whether abnormally reduced blood flow is caused by a primary pathologic event or is secondary to raised IOP is debated.

There are a number of clinical observations supporting this hypothesis, including:

• The existence of large ocular hypertensive populations in whom only a small proportion convert to glaucoma
• The existence of normotensive glaucoma sufferers who exhibit clinical signs identical to those of primary open-angle glaucoma, but with IOP permanently within statistical normality
• The presence of progressive visual field defects in some optimally treated primary open-angle glaucoma sufferers
• The association between some cardiovascular conditions and glaucoma.

The blood flow into a tissue depends upon the local perfusion pressure, or force of blood entering the tissue, and factors resisting flow within supplying vessels. In the case of the eye, perfusion pressure is dependent on local arterial pressure and IOP. Both raised IOP or low blood pressure may therefore reduce blood flow. Resistance to flow depends upon factors that reduce vessel size, limiting volume of flow per unit time, such as vasospasm, impaired autoregulation or vessel lumen reduction. This vasogenic theory of glaucoma pathogenesis is supported by associations between glaucoma and migraine, Raynaud’s disease, systemic hypertension, haemodynamic crises, noctural blood pressure dips and possibly diabetes.

3 Immune-related theory of glaucoma pathogenesis

In recent years it has been hypothesised that some glaucomas may represent an autoimmune neuropathy in which an individual’s immune system is not appropriately regulated, causing a cytotoxic effect. It has been hypothesised that in some cases of glaucoma, although the immune system normally should be neuroprotective, autoimmunity resulting from a failure to properly control aberrant, stress-induced immune responses may accompany progressive glaucomatous neurodegeneration in some patients. Evidence supporting this theory comes from identification of auto-immune biomarkers in the vitreous adjacent to the optic nerve head in post-mortem glaucoma patient eyes, and also in the serum of glaucoma patient populations.

Pathogenesis summary

There is no single distinct causal pathway leading to the events of GON. For chronic sub-types of glaucoma it is most likely that the cause is multifactorial, and may be a balance between the three theories. For example, individuals with glaucoma accompanied by substantial IOP elevation are more likely to have an underlying mechanical causes for their disease, contrasted with individuals with normal tension glaucoma, in whom the disease is more likely to be of vasogenic, or autoimmune, causality, or both.

It is also likely that occurrence of glaucoma depends on the balance between the number and degree of potential causal factors and susceptibility of any given individual, with differences in these variables between individuals explaining the variety of clinical presentations of glaucoma. Indeed lack of susceptibility provides a likely explanation for why some individuals with risk factors for glaucoma disease, such as individuals with raised IOP, may never convert to manifest glaucoma.

Classification of the glaucomas

Making a correct diagnosis is critical to the care of a glaucoma patient. Correct diagnosis allows healthcare providers involved in management of each individual patient to perform appropriate examinations, adopt the relevant management strategy and discuss appropriate aspects of the disease, prognosis, treatment and expectations with each individual. Knowledge of the variety of glaucomas and how they are classified is therefore invaluable background to establishing a diagnosis and understanding disease processes.

A number of alternative and complementary methods for classification remain in use, both in clinical practice and the literature. It is useful to have a broad awareness of all classification methods, as it is likely that different clinicians will employ differing schemes. Furthermore, some classification schemes may provide more appropriate, descriptive and clinically useful diagnoses than others.

Cause-based classification

This traditional scheme divides the glaucomas into two sub-divisions on the basis of whether a known existing disease had a causal role in IOP elevation and subsequent glaucoma development. There are two main divisions:

• Primary glaucoma. This group’s characteristic is that it is unrelated to ocular or systemic disease. Primary glaucomas are usually bilateral and probably have a genetic basis
• Secondary glaucoma. This group has a known contribution from ocular or systemic disease. Secondary glaucomas may be unilateral or bilateral, with some having a genetic basis, and others being acquired.

These groups may again be sub-divided, as seen in Table 1.

Classification based on initial pathological events

The disadvantage of using the traditional cause-based classification is that it reflects current lack of understanding of the disease processes that underlie some primary glaucomas, and furthermore its historical dependence on elevated IOP does not account for individuals with glaucoma in whom IOP is, statistically, within the ‘normal range’. It has therefore been suggested that grouping according to initiating events leading to GON provides a more complete and appropriately sub-grouping of the glaucomas.

The four major sub-divisions within this scheme are:

• Open-angle glaucomas without other known ocular or systemic disorders
• Angle-closure glaucomas without other known ocular or systemic disorders
• Developmental glaucomas
• Glaucomas associated with other ocular and systemic disorders.

Further details are given in Table 2.

Mechanism-based classification

This scheme divides glaucomas on the basis of the mechanism underlying aqueous outflow obstruction that leads to elevation of IOP (Table 3).

• Open angle glaucoma. This group is characterised by anterior chamber angle structures being visible by gonioscopy, and may be sub-divided into:

– Pretrabecular causes of open-angle obstruction, such as membranes or deposits

– Clinically non-visible histopathologic changes within the trabecular meshwork

– Post-trabecular obstructions to aqueous outflow, such as pathology of Schlemm’s canal and raised episcleral venous pressure.

• Closed-angle glaucoma. This group is characterised by anterior chamber angle structures not being visible by gonioscopy due to physical obstruction of the anterior chamber angle structures by apposition of the peripheral iris to either the trabecular meshwork or cornea. Sub-divisions within this group are:

– Anterior (‘pulling’) mechanisms, where the iris is pulled towards the peripheral cornea by pathology

– Posterior (‘pushing’) mechanisms, in which the pressure behind the iris pushes it towards the peripheral cornea. This group can be again sub-divided into two groups with and without pupil block.

• Developmental glaucomas. This group is characterised by not being able to fall into either of the preceding categories.

Features of common glaucomas

Chronic open-angle glaucoma (COAG)
Diagnosis

Clinical diagnosis of this glaucoma sub-group is based on presence of a chronic, slowly progressive GON in the presence of normal, gonioscopically open anterior chamber angles. Dependent on the stage of disease, patients may have associated visual field defects.

COAG can be divided on the basis on statistical IOP elevation into ‘high’ and ‘normal’ pressure types, frequently referred to as primary open angle glaucoma (POAG) and normal tension glaucoma (NTG). Realistically, this division is arbitrary, with both types being part of a spectrum of disease resulting from multifactorial aetiology and differences in susceptibility among the population.

Occurence

COAG is the most common glaucoma sub-type, with population studies performed over the last 30 years estimating average prevalence levels between 0.9 and 2.1 per cent among predominantly white populations aged ≥ 40 years, with the five-year incidence in this age group being 0.5 per cent. Occurrence of COAG is age-related, with population studies estimating prevalence to be ~1-2 per cent in the fifth and sixth decades of life, and increasing to between 2-7 per cent beyond this age. COAG is extremely uncommon in individuals younger than 40 years. Five year incidence estimates of definite OAG increase from close to 0 per cent among individuals in the fifth decade up to 1 per cent of participants aged 80 years and older. Strictly, adult-onset glaucoma occurring at <35 years of age is defined as the primary juvenile-sub-type.

Heredity

The epidemiological observations of an increased risk of COAG development of seven to 10 times among individuals who have a first degree relative with the condition, and high concordance of glaucoma onset among monozygotic twins provides strong evidence for a genetic basis to COAG. Although a number of studies suggest that specific genomic regions may be implicated, lack of a simple pattern of inheritance means no single ‘glaucoma gene’ is causal, and it is most likely that multiple genes are implicated.

Risk factors

Knowledge of factors associated with an increased risk of glaucoma development permits identification of those in whom glaucoma is most likely to develop. These factors can be interpreted both on the basis of level of risk, and quality (or consensus) of evidence supporting them. Risk factors considered to be supported by the highest quality evidence are given in Table 4. Some investigations also suggest other parameters are associated with COAG, including diabetes, vasospasm (migraine, Raynaud’s disease), myopia and reduced central corneal thickness, although the evidence base for these to date is less well-founded.

Clinical features

Clinically, COAG is an insidious-onset condition that usually remains asymptomatic until relatively advanced, at which point severe visual field constriction may be perceived. Signs include a normal anterior segment with gonioscopically open, normal angle of normal appearance. IOP may be normal or elevated and can exhibit a variable diurnal range. The optic nerve will be characteristically excavated and retinal nerve fibre layer (RNFL) defects may be present, although they may not be observed in all individuals due to differences in ability to visualise the RNFL.

COAG is a slowly progressive disease, although information on progression rate without treatment is scant and may vary considerably between individuals. Untreated black individuals and those with higher IOP are likely to worsen more quickly. IOP lowering treatment has been shown to significantly reduce the proportion of patients with clinically significant progression, and the rate in those who continue to worsen in spite of treatment. Factors associated with blindness among COAG patients include late presentation, young age, inadequate IOP control and poor compliance.

Pigmentary glaucoma
Diagnosis

The diagnosis of pigmentary glaucoma is made on the basis of presence of the features of pigment dispersion syndrome (PDS) with secondary IOP elevation and GON. Dependent on stage of disease, there may be associated visual field defects.

Pathogenesis

This secondary open angle sub-type glaucoma is caused by elevation of IOP secondary to PDS, a condition whereby melanin granules are mechanically liberated from iris pigment epithelium by rubbing against the posteriorly juxtaposed zonules and anterior capsule during pupil movements. Liberated granules circulate with the aqueous, with the majority moving into the anterior chamber and becoming deposited in a variety of locations, including the trabecular meshwork. This deposition causes an initial physical obstruction to aqueous drainage, and also induces secondary histological changes to trabecular tissue reducing physiologic function.

Occurrence

Data on the epidemiology of both pigmentary glaucoma and PDS is scant. A population screening study that included slit-lamp examination estimated PDS prevalence at ~1.9 per cent in a mixed racial group, and 2.5 per cent of caucasians. Although thought to be more common among caucasians, it is possible that difficultly in identification of dispersed pigment and the presence of thicker iris stroma confounds PDS detection in black individuals. It has been postulated that pathologic pigment release may vary throughout life, with phagocytic removal of pigment from the trabecular meshwork and ongoing iris pigment epithelium melanosis resulting in underestimation of pigmentary glaucoma prevalence. It is possible that these subsequent secondary changes could result in pigmentary glaucoma looking clinically like COAG in older individuals.

One large study (Minnesota) found that risk of developing pigmentary glaucoma from PDS was 10 per cent at five years and 15 per cent at 15 years. Young, myopic men were most likely to have pigmentary glaucoma.

Heredity

No genetic relationship has been established for pigmentary glaucoma or PDS.

Risk factors

PDS has been found in individuals of both sexes throughout adult age ranges, but is most common among young, myopic male individuals, typically in their third or fourth decade of life. Although no data on pigmentary glaucoma incidence among PDS cases is available, it is likely that its development is IOP-dependent.

Clinical features

The principal sign of PDS constitutes deposition of pigment granules in the anterior chamber angle, with a characteristic heavy homongenous circumferential pigmentation of the trabecular meshwork being visible (Figure 1). Irregular light pigmentation on or anterior to Schwalbe’s line may be present (Sampaolesi’s line). Subtle backward bowing of the peripheral iris, areas of iris depigmentation are visible as mid-peripheral, radial transillumination defects (Figure 2), which vary considerably in angular subtense between affected individuals. Other co-existing signs include pigment deposition on the inferior central corneal endothelium (where convectional aqueous movement is slowest) sometimes forming a Kruckenberg’s spindle (Figure 3), pigment granules on the iris surface (Figure 4), zonules and posterior capsule (Sheie’s sign).

PDS can be symptomatic if substantial IOP elevations occur, which has been reported after episodes of rapid pigment release caused by exercise, blinking or even pharmacological dilatation. In these circumstances pigment may sometimes be observed circulating with aqueous convection currents. Symptoms are those associated with corneal oedema such as misty vision and/or coloured haloes around light sources, sometimes with mild discomfort.

Pseudoexfoliative glaucoma
Diagnosis

Pseudoexfoliative glaucoma (PXG) diagnosis requires the features of pseudoexfoliation syndrome (PXF) with secondary IOP elevation and GON. As with COAG and pigmentary glaucoma, associated visual field defects are dependent on disease stage.

Pathogenesis

This secondary open angle sub-type glaucoma is caused by elevation of IOP secondary to PXF, a systemic condition whereby abnormal proteinaceous ‘pseudoexfoliative’ material is secreted by epithelial tissues in the anterior segment, including that of the lens, ciliary body, iris, Sclemm’s canal and corneal endothelium. Associated iris atrophy also results in released pigment. IOP elevations in PXG are due to multiple mechanisms including physical obstruction of the trabecular meshwork, cellular responses to PXF material moving into the angle from elsewhere, and also local material production.

Occurrence

PXF is age and race dependent. Prevalence varies by country. In the UK, it has been reported to affect approximately 5 per cent of those aged older than 40. Worldwide extremes vary from 0 per cent among Alaskan Inuit populations to 38 per cent of American Navajo populations in Arizona. Within Europe, PXF prevalence appears highest in Scandinavia.

Heredity

Although some family pedigrees of PXS have been reported, no simple genetic relationship has been established for this condition.

Risk factors

It has been estimated that approximately 40 per cent of those with PXF will eventually develop PXG. Major risk factors for development of PXG in patients with PXF are age and IOP elevation. PXG is age-dependent, doubling every decade from the age of 50.

Clinical features

PXF material is usually visualised first on the anterior surface of the lens capsule following pupil dilation with a characteristic pattern of central and peripheral areas of material separated by a mid-peripheral annulus in which material has been sloughed off by pupil movement (Figure 5). There may be associated material on the pupil margin (Figure 6), and sometimes in the anterior chamber angle. It is important to remember signs of PXF material deposition are not all that is visible. For example, associated iris atrophy may be visible as stromal atrophy, irregularity of the collarette and loss of the pupillary ruff (Figure 6). Pigment liberation from iris atrophy may be deposited in the anterior chamber angle, forming a Sampaolesi line, and also on the corneal endothelium.

Although not visible on slit-lamp examination, PXF material has also been found on the ciliary processes and zonules. Associated zonular weakness may be visible as a poorly supported lens as phacodonesis, or wobbling of the lens on small eye movements.

PXG is more likely to be symptomatic than other COAG sub-types, and, in spite of the open angle, some cases can exhibit substantial IOP elevations with associated symptoms similar to those described above for PDS.

Primary angle closure

This group of conditions share the common feature of appositional or synechial closure of the anterior chamber angle due to a variety of possible mechanisms. Iridotrabecular contact causes raised IOP that can lead to GON. The resulting glaucoma is primarily mechanical in origin, being attributable to raised IOP.

Diagnosis

Primary angle closure (PAC) can be divided into four sub-groups.

• Acute angle closure (AAC). Characterised by symptomatic sudden onset IOP elevation, without disc and field damage, due to substantial circumferential appositional mechanical obstruction of anterior chamber angle by the peripheral iris. It does not resolve spontaneously.
• Acute angle-closure glaucoma (AACG). This condition is equivalent to AAC with resulting GON. Visual field defects may be present, dependent on degree of damage.
• Intermittent (sub-acute) angle-closure glaucoma (IACG). Presumed intermittent previous episode(s) of mild AAC which resolves spontaneously and has associated GON with or without GVFD.
• Chronic angle-closure glaucoma (CACG). Permanent synechial closure of any extent of the angle accompanied by a gradual IOP rise with associated GON with or without GVFD.

Pathogenesis

A number of mechanisms are implicated in PAC. In any given individual with PAC, contributions from each mechanism may vary.

• Pupil block: This mechanism results from the pressure of the iris lying on the anterior lens surface. Aqueous passing from the posterior chamber (PC) to the anterior chamber (AC) through the pupil must overcome this relative obstruction and if it does not, the PC pressure rises. The thinner peripheral iris billows forward (iris bombé) when PC pressure exceeds AC pressure. Acute IOP elevation occurs when the peripheral iris contacts the peripheral cornea sufficient for a substantial compromise of aqueous access to the trabecular meshwork. Pupil block is the most common cause of PAC and is considered to be at least partly responsible in all subtypes.
• Crystalline lens anatomy: An anatomically large and/or anteriorly placed crystalline lens can accentuate AC shallowing and angle narrowing, predisposing to pupil block.
• Peripheral anterior synechiae (PAS) and creeping angle closure: Adhesions between peripheral cornea and peripheral iris obstruct access to the drainage angle, with more extensive adhesions increasing probability of IOP elevation. These adhesions may either be due to previous sub-clinical episodes of IACG or ‘creeping’ of the iris base forward onto the trabeculum.
• Plateau iris configuration: This mechanism is the least common mechanism contributing to PAC. It consists of an anatomically flat iris front surface that extending far into the periphery of the AC, producing a narrow angle in spite of an apparently deep AC. The narrow angle limits aqueous access to the trabeculum.

Occurrence

PAC is age and race-dependent. Angle closure glaucoma is most common among Inuit people and individuals from south-east Asia with a prevalence of 2-3 per cent in those aged over 40 years. It is less common among other Asian races and least common among caucasians.

Heredity

The potential for pupil block, rather than glaucoma, is thought to be inherited. Family history of angle-closure episodes is not considered particularly useful in determining risk of a future ‘attack.’

Risk factors

Risk factors for PAC include age, hypermetropia, female gender, positive family history, ethnicity, diabetes, shorter axial length, shallow central anterior chamber and larger and more anteriorly placed lens.

Clinical features

Signs and symptoms of the PAC conditions vary according to the individual sub-type. AAC is characterised by rapid onset symptoms (hours) including pain, redness (Figure 7), blurred (misty) vision, coloured haloes, headache, nausea and vomiting. Signs include highly elevated IOP (40-80mmHg), corneal oedema, mid-dilated unresponsive pupil, conjunctival injection, shallow chamber, aqueous flare and appositionally closed angle. The fellow eye is likely to exhibit a narrow angle. Presence of GON or GVFD distinguishes between AAC and AACG. The disc may appear congested, rather than excavated during the period of acute IOP elevation.

In IACG, a history of mild and occasional self-limiting AAC-like symptoms will be present, as for AAC, with occurrences usually more frequent at night. A shallow AC (Figure 8) and gonioscopically occludable angle will be present. IOP is likely to be within the normal range between angle closure episodes. There may be signs of previous substantial elevated IOP, such as iris atrophy, spiralling and glaukomflecken (Figure 9). Characteristic glaucomatous disc changes will be present, with GVFD dependent on the degree of damage.

CACG features include varying degrees of IOP elevation with possible correlated symptoms. Higher IOPs are associated with larger circumference of PAS and/or synechial angle closure. This sub-type of PAC is typically slow onset and substantial IOP elevations can be accompanied by disproportionately mild and variable symptoms of discomfort rather than pain and haloes. Characteristic glaucomatous disc changes will be present, with GVFD dependent on the degree of damage.

Further reading

• Tezel G, Wax MB. The immune system and glaucoma. Curr Opin Ophthalmol, 2004 Apr;15(2):80-4. Review.
• RR Allingham, K Damji, S Freedman, Moroi S, G Shafranov. Shields Textbook of glaucoma. 5th edition. Published by Lippincott, Williams and Wilkins. Philadelphia. 1995. Chapters 11, 12, 15, 17.
• Lawrenson J. Chapter 3 Histoplathology and pathogenesis of glaucomatous optic neuropathy. In; Edgar D, Rudnicka A (editors). Glaucoma Identification and co-management. Butterworth Heinemann Elsevier. Edinburgh, 2007
• EJ Higginbotham, DA Lee. Clinical Guide to Glaucoma Management. Published by Butterworth Heinemann. Woodburn MA. 2004.
• Mukesh BN, McCarty CA, Rait JL, Taylor HR. Five-year incidence of open-angle glaucoma: the visual impairment project. Ophthalmology, 2002;109(6):1047-51
• Siddiqui Y, Ten Hulzen RD, Cameron JD, Hodge DO, Johnson DH. What is the risk of developing pigmentary glaucoma from pigment dispersion syndrome? Am J Ophthalmol, 2003 Jun;135(6):794-9.
• Ritch R, Steinberger D, Liebmann JM. Prevalence of pigment dispersion syndrome in a population undergoing glaucoma screening. Am J Ophthalmol, 1993 Jun 15;115(6):707-10.
• European Glaucoma Society. Terminology and Guidelines for Glaucoma. 2nd edition. Published by Dogma Publications, Savona, Italy. 2003.
• Dr Paul GD Spry is optometrist consultant at Bristol Eye Hospital

Dr Robert A Harper is optometrist consultant at Manchester Royal Eye Hospital

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