Primary Angle Closure Glaucoma
Dr. Srinivasan Kavitha
Dr.Rengaraj Venkatesh
Glaucoma Department
Aravind Eye Hospital
Pondicherry
Definition:
It is a condition in which elevation of intraocular pressure (IOP) occurs as a result of obstruction of aqueous outflow by partial or complete closure of angle by peripheral iris.
Stages:
I. Classical Classification:
1. Prodromal Stage
2. Stage of constant instability
3. Acute Congestive Stage
4. Chronic Angle Closure Stage
5. Absolute Stage
II. Newer Classification:
Recommended by American Academy of Ophthalmology (AAO) and World Glaucoma Association (WGA).
1. Primary Angle Closure Suspect
This includes any eye that has a primary, abnormally narrow angular width of the anterior-chamber-angle recess, wherein the peripheral iris is located close to, yet not touching, the posterior pigmented trabecular meshwork. Patients with primary anatomic narrow anterior-chamber angles are at risk for subsequent primary angle closure (PAC).
2. Primary Angle Closure and Primary Angle-Closure Glaucoma
Any eye that has a primary anatomic narrow anterior-chamber angle and evidence such as peripheral anterior synechiae (PAS), elevated IOP, sector iris atrophy, or glaukomflecken lens opacities, when trabecular obstruction by the peripheral iris has occurred is classified as having PAC. This entity is caused by pupillary block and can exist in an acute state or a chronic state. The fellow eye is at risk. Patients with PAC can present with either the acute or chronic state or they may have both and present with acute attacks superimposed on chronic angle closure. In PAC the eye is at risk of developing glaucomatous optic disc damage, particularly when associated with elevated IOP. In this case the eye has progressed from PAC to primary angle closure glaucoma (PACG).
A. Acute Primary Angle Closure:
If the entire circumference of the chamber angle is obstructed suddenly, the IOP will rise rapidly to high levels. This may cause pressure-induced corneal edema (experienced as blurred vision and occasionally as multicolored halos around lights) vascular congestion, eye pain, or headache. High IOP may be accompanied by nausea and vomiting. Acute attacks may be self-limited and resolve spontaneously or may occur repeatedly. Untreated, this entity may cause permanent vision loss or blindness.
B. Chronic Primary Angle Closure:
If only a portion of the angle closes with PAS, either slowly over time with or without acute attacks, or rapidly after a resolved acute attack of angle closure, the IOP may be in the normal range or only mildly elevated, and symptoms of acute PAC may be mild or absent. Continued, slowly progressive closure of the angle may ensue, eventually leading to sustained elevation of IOP and glaucomatous optic neuropathy. By nature of its chronicity and the insidious increase in IOP, chronic PAC my not have any of the findings of acute angle closure and can be mistaken for primary open angle glaucoma. Patients with asymptomatic chronic PAC may present with severe visual field loss compared with the mild to moderate defects found in patients with prior episodes of symptomatic angle closure.
3. Plateau Iris Configuration and Plateau Iris Syndrome
The definitions of these entities are included here because they are primary conditions that are often difficult to distinguish from the PAC entities resulting from pupillary block.
Plateau iris configuration is characterized by a near-normal-depth central anterior chamber, a flat iris profile, and crowding of the anterior chamber angle by the iris base. The IOP may be normal or elevated. The condition appears to be related to a forward displacement of the ciliary processes that causes anterior displacement of the peripheral iris and angle closure. Such closure occurs without a significant pupillary block component.
Plateau iris syndrome is defined as having a plateau iris configuration with a closed anterior chamber angle and usually with elevated IOP, which persists despite the elimination of any pupillary block component by a patent iridotomy. Intraocular pressure elevation that was present before iridotomy may persist; the IOP typically increases after pupil dilatation, which causes greater occlusion of the angle by the peripheral iris.
Risk Factors:
1. Hyperopia
2. Family history of glaucoma
3. Advancing age
4. Female gender
5. Asian descent
6. Shallow peripheral anterior chamber
Natural History:
If patients with unilateral acute PAC with high IOP do not receive treatment, glaucomatous optic neuropathy can occur rapidly (within days) or gradually (over years). Untreated fellow phakic eyes are at increased risk for developing acute angle closure. Following successful treatment of acute PAC, there is evidence that retinal nerve fiber layer thickness significantly decreases within 16 weeks after the attack. In one study, in the long term (4 to 10 years) following an acute PAC attack, 18% of eyes were blind, 48% of eyes developed serious glaucomatous optic neuropathy, and 58% of eyes had vision worse than 20/40. Thus, visual morbidity from the acute and chronic effects of angle closure may be significant. The natural history of acute and chronic angle-closure glaucoma is for the untreated patient to develop progressive visual loss that may result in bilateral blindness.
Theories of Mechanism:
Relative Pupillary Block:
The most common mechanism leading to angle closure glaucoma appears to be the increased resistance to aqueous flow from posterior to anterior chamber. The resultant pressure gradient between the posterior and anterior chamber causes a forward bowing of the peripheral iris so that the iris covers all (or) part of the filtering portion of trabecular meshwork (appositional angle closure).
Prolonged (or) repeated contact of peripheral iris with the trabecular meshwork (TBM) may lead to PAS and residual damage to TBM.
Diagnosis
Patients with PAC may present for care in different ways. Patients being examined in another context may be noted to have a shallow anterior-chamber angle with normal IOP. Patients may present for care who have been found to have elevated IOP or optic disc cupping and whose slit lamp biomicroscopy suggests a shallow anterior chamber that is confirmed by gonioscopy and patients may present with sudden onset of symptoms typical of PAC (such as pain, redness, congestion, corneal edema, very high IOP). The initial history and physical examination includes evaluation for both primary and secondary types of angle closure. This includes the appropriate components of the comprehensive adult medical eye evaluation, with particular attention to those aspects relevant to the various types of angle closure.
History:
- History of using topical and systemic medications that may induce angle closure.
e.g., Sulfonamides, Topiramate, Phenothiazines
- Symptoms that suggest intermittent angle closure
e.g., blurred vision, haloes around lights, aching eye or brow pain, eye redness
Physical Examination:
If acute angle closure is present, some components of the examination may be postponed. Components of the physical evaluation that are particularly relevant for the diagnosis and management of angle closure include the following.
Assessment of refractive status:
It is important to assess refractive status, since hyperopic eyes, especially in older patients have narrower anterior chamber angles and is at increase risk of PAC.
Pupil:
- Size
- Reactivity
External examination:
- Conjunctival hyperemia
- Corneal clarity
Slit-lamp biomicroscopy:
- Central and peripheral anterior-chamber depth
- Anterior-chamber inflammation suggestive of a recent or current attack
- Corneal edema
- Iris atrophy, especially sector types; posterior synechiae; or mid-dilated pupil suggestive of a recent or current attack
- Signs of previous angle-closure attacks (e.g.,PAS, segmental iris atrophy, glaukomflecken, posterior synechiae, pupillary dysfunction, irregular pupil)
Determination of IOP:
Intraocular pressure is measured in each eye, preferably using a contact applanation method (typically a Goldmann tonometer) before gonioscopy. Measuring central corneal thickness should be postponed until resolution of an acute attack.
Gonioscopy:
Gonioscopy of both eyes should be performed on all patients in whom angle closure is suspected. This is required to evaluate the angle anatomy, appositional closure, and presence of PAS. Compression (indentation) gonioscopy with a four-mirror or similar lens is particularly helpful to evaluate for appositional closure versus synechial angle closure and for extent of PAS.
