Subacute (and Chronic) Angle-Closure Glaucoma
Jeffrey R. SooHoo, MD; David L. Epstein, MD, MMM; and George Ulrich, MD, FACS
The principles underlying the pathogenesis, diagnosis, and treatment of subacute and chronic angle-closure glaucoma have been explained in the preceding 2 chapters. Certain important features will be highlighted in this chapter.
The incidence of subacute and chronic angle-closure glaucoma is probably considerably greater than the incidence of the acute type. However, just as in acute angle-closure glaucoma, the sole cause of the rise in intraocular pressure (IOP) is physical closure of the angle. When the angle is entirely open, the outflow is normal, and there is no glaucoma. The subacute type differs from the acute type in that the course may consist of less intense, intermittent attacks, usually over a long time. Symptoms are usually mild or may be absent entirely until the disease is advanced.
As discussed in Chapter 23, the term subacute implies mini-attacks of angle closure, with or without symptoms, where the whole circumference of the angle is not simultaneously involved. The term chronic, however, is used to describe many different clinical situations: to connote the residua and continuation of subacute episodes when peripheral anterior synechiae commonly form over time; to connote residual synechial angle closure after laser iridotomy; or, perhaps most commonly, to connote a totally silent progressive condition of angle closure, either appositional or synechial, that may mimic primary open-angle glaucoma (POAG). The latter entity is critically important for the clinician to diagnose and understand and is discussed elsewhere.
The term chronic is thus quite imprecise. It is better to use specific descriptive terms such as silent (appositional or synechial) angle closure, residual angle closure after iridotomy, or recurrent episodes of subacute angle closure leading to formation of synechiae.
DIAGNOSIS
As a rule, there is more variation in the width of different portions of the angle in the subacute form than in the acute form. In the subacute form, some portions of the angle are excessively narrow, while other portions may be considerably wider. The angle does not close in the whole circumference as is usually the case in the acute form. In both acute and subacute angle closure, the anterior chamber is characteristically shallow, and the iris is convex. Angle closure with a relatively flat iris plane and less axial shallowing (plateau iris; see Chapter 27) presents more frequently as subacute angle closure than acute angle closure.
In the differential diagnosis of subacute angle closure with irregular narrowing of the angle, one should also consider cysts of the iris or ciliary body that may cause irregular closure of the angle. This condition is discussed in Chapter 35. Irregular synechial closure should also make one consider uveitis, and if unilateral, one should consider essential iris atrophy. In rare cases, both open-angle and subacute or chronic angle-closure glaucoma occur in the same eye.
Intraocular Pressure Elevations in Subacute Closure
In subacute angle-closure glaucoma, the rise in IOP is proportional to the extent of closure at a given time. In some cases, during an episode of partial closure, there may be a considerable acute rise in IOP, giving symptoms of blurred vision, discomfort, or seeing colored haloes. In other cases in which the closure is less extensive or develops more gradually (chronic silent angle closure), the patient remains asymptomatic. If symptomatic episodes do occur, they tend to recur much more frequently than do the dramatic attacks typical of acute angle closure. In subacute intermittent angle-closure glaucoma, episodes of elevated IOP causing symptoms may occur every week or two, or even daily, whereas in severe acute angle-closure glaucoma, episodes giving rise to symptoms usually occur at intervals of several weeks, months, or even years. Violent acute irreversible episodes do not typically occur in the subacute type.
Chronic Silent Angle Closure and Chronic Angle Closure From Subacute Closure Events
Cases of chronic silent angle-closure glaucoma are encountered that are truly asymptomatic and that mimic chronic or primary open-angle glaucoma, a misdiagnosis for which patients are often mistakenly treated. Among referral patients, cases of undetected chronic silent angle closure are commonly found. Because this condition can be potentially cured by laser iridotomy, it is important to make this diagnosis correctly by employing the concepts already outlined in previous chapters. Making the correct diagnosis requires careful examination by gonioscopy. If there is a strong suspicion of this diagnosis in a patient with elevated IOP, laser iridotomy should be performed. In many such cases of chronic silent angle closure, the closure is more appositional rather than synechial; therefore, it is potentially reversible and curable by iridotomy.
In addition to chronic silent angle-closure glaucoma, one also continues to encounter the term chronic applied to the residua, recurrence, and continual progression of subacute angle closure. The term chronic, in general, is confusing because it is defined often by past symptoms, and it sometimes obscures the understanding of the entity of chronic silent angle-closure glaucoma that mimics POAG. Regardless, the treatment is the same: laser iridotomy. This is followed by a reassessment of the amount of peripheral anterior synechiae formation. Further treatment and follow-up might include laser gonioplasty. Once the diagnosis of subacute or chronic angle-closure glaucoma is established, treatment should be laser iridotomy in nearly all cases. However, in the early stages of this condition, when there is little or no synechial closure, the situation in the angle may not be recognized. Medical therapy for IOP elevation is applied indiscriminately and generically as though one is dealing with POAG. Moreover, the initial IOP response to medical therapy is normally satisfactory even without iridotomy, and the condition remains undiagnosed.
This creates a dangerous long-term situation. In the short term, by applying medical therapy, mostly with topical medications used in open-angle glaucoma, such as prostaglandin analogs, carbonic anhydrase inhibitors, beta-blockers, or alpha-2 agonists, IOP may be brought to normal. In most cases in which medical therapy is initiated and if iridotomy has not been performed, sooner or later more synechial closure of the angle occurs. The baseline IOP gradually rises, and additional medications are required to bring IOP temporarily to normal levels. This response to additional treatment also may give a false sense of security while synechial closure of the angle relentlessly progresses. Finally, after extensive synechial closure has occurred, IOP may remain at relatively high levels and may not be lowered by medical means. Properly performed gonioscopy, often with indentation, should allow for the appropriate diagnosis to be made early in the course, ideally prior to the initiation of medical therapy, and laser iridotomy can be applied.
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