What is Glaucoma?

Glaucoma, Acute Angle-Closure (AACG)

Introduction
Background
Glaucoma is a nonspecific term used for several ocular diseases that ultimately result in increased intraocular pressure (IOP) and decreased visual acuity. Acute angle-closure glaucoma (AACG) is an ocular emergency and receives distinction due to its acute presentation, need for immediate treatment, and well-established anatomic pathology.1 Rapid diagnosis, immediate intervention, and referral can have profound effects on patient outcome and morbidity.

The acute angle closure literature has been plagued by the lack of a uniform definition and specific diagnostic criteria. Only in recent years has there been a strong push to standardize the definitions of the various forms of angle closure disease. Primary angle closure, primary angle-closure glaucoma, acute angle closure, and acute angle-closure glaucoma were previously used interchangeable. Now, acute angle closure is defined as at least 2 of the following symptoms: ocular pain, nausea/vomiting, and a history of intermittent blurring of vision with halos; and at least 3 of the following signs: IOP greater than 21 mm Hg, conjunctival injection, corneal epithelial edema, mid-dilated nonreactive pupil, and shallower chamber in the presence of occlusion.

Primary angle closure is defined as an occludable drainage angle and features indicating that trabecular obstruction by the peripheral iris has occurred (ie, peripheral anterior synechiae, increased IOP, distortion of iris fibers [iris whorling], lens opacities, excessive trabecular pigmentation deposits). An eye in which contact between the peripheral iris and the posterior trabecular meshwork is considered possible based on ocular anatomy is termed primary angle closure suspect. The term glaucoma is added if glaucomatous optic neuropathy is present.

Pathophysiology
AACG represents the end stage of processes resulting in the compromised egress of aqueous humor circulation and the subsequent increase in IOP. Aqueous humor is produced by the ciliary body in the posterior chamber of the eye. It diffuses from the posterior chamber, through the pupil, and into the anterior chamber. From the anterior chamber, the fluid is drained into the vascular system via the trabecular meshwork and Schlemm canal contained within the angle.

Several anatomic abnormalities lead to anterior chamber crowding and predispose individuals to AACG. These include shallower anterior chambers, thinner ciliary bodies, a thinner iris, anteriorly situated thicker lens,2 and a shorter axial eye length. Recent studies have suggested that increased iris thickness and cross-sectional area are associated with increased risk.3 Of the many predisposing anatomical variations, a narrow angle has the most devastating consequences.

In the traditional model of AACG, the eye’s natural response of dilation to environmental or chemical stimuli results in a pathologic iris-lens apposition. The apposition and contact between the lens and the iris is called pupillary block. Furthermore, pupillary block describes a state in which the forward-most surface of the lens is anterior to the plane of the iris insertion into the ciliary body. As a result, aqueous flow from the posterior chamber to the anterior chamber is obstructed or altogether blocked. When pupillary block occurs in conjunction with the iris, the increasing pressure in the posterior chamber causes the pliable iris, particularly the peripheral region, to bow forward in a process termed iris bombé. Iris bombé further closes the already narrow angle and compromises aqueous drainage, thus increasing IOP.

Recent research has suggested an alternative pathophysiologic pathway for AACG. Cronemberger et al propose that acute events can be traced to an autonomic imbalance in individuals with AACG, specifically increased sympathetic tone. Furthermore, the iris dilator muscles in these individuals have been found to be more developed and stronger. In instances of increased ocular sympathetic tone, including emotional distress, low light conditions, or after sympathomimetic drug use, contraction of the iris dilator muscles leads to pupil dilatation and thickening of the middle-peripheral iris. This thickening can lead to angle closure, thereby obstructing the outflow of aqueous humor.4

Other proposed mechanisms of AACG include plateau iris, lens swelling, and ciliary block. Plateau iris is less common than pupillary block and is due to anterior insertion of the iris. The superfluous and crowded iris tissue blocks the trabecular meshwork and again leads to increased IOP.

Lens swelling and ciliary block are extremely rare. Lens swelling occurs in cases of cataracts in which hydration forces cause enlargement of the lens and subsequent crowding of the anterior chamber. Forces posterior to the lens can push the lens and iris forward causing ciliary block or vitreous pressure. This can be seen in panretinal photocoagulation, scleral buckles, and uveitis.

Frequency
United States
AACG occurs between 1 and 40 times for every 1000 Americans depending on their ethnicity.

Mortality/Morbidity
Outcome after AACG is dependent on duration from onset to treatment, underlying ocular disease, and ethnicity. The degree of IOP elevation has been shown to have less impact on future visual acuity. Studies report that as many as two thirds of individuals with AACG had no visual field loss. However, Asians appear to be more refractory to the initial medical management, and, even after definitive treatment, they experience a progressive increase in IOP and deterioration in visual acuity.5

Race
AACG occurs in 1 of 1000 whites, about 1 in 100 Asians, and as many as 2-4 of 100 Eskimos.

Sex
AACG predominately affects females because of their shallower anterior chamber.

Age
Elderly patients in their sixth and seventh decades of life are at greatest risk.

Clinical
History
Classically, patients are elderly, suffer from hyperopia, and have no history of glaucoma.

Most commonly, they present with periorbital pain and visual deficits.6 The pain is boring in nature and associated with an ipsilateral headache.
Patients note blurry vision and describe the phenomenon of “seeing halos around objects.”
Careful investigation may elucidate a precipitating factor, such as dim light or medications (eg, anticholinergics, sympathomimetics).
In a large percentage of patients, extraocular symptoms and systemic manifestations are the chief complaint.
Patients present with headache and may receive medications for migraines or an evaluation for a subarachnoid hemorrhage.
Several case reports discuss patients presenting with vomiting and abdominal pain that were misdiagnosed with gastroenteritis.7

Physical
The emergency department evaluation of the eye includes visual acuity, the external eye, visual fields, a funduscopic examination, pupils, ocular motility, and IOP. All of which tend to be affected in AACG.
Slit lamp evaluation may reveal corneal edema, synechiae, irregular pupil shape or function, or segmental iris atrophy.
Patients complain of blurred vision, and testing reveals the ability only to detect hand movements. They are unable to identify numbers and letters on distance charts or near cards.
Cornea and scleral injection and ciliary flush are present. The obviously edematous and cloudy cornea obscures the funduscopic examination.
Increased IOP (normal limit, 10-20 mm Hg) and ischemia result in pain on eye movement, a mid-dilated nonreactive pupil, and a firm globe. Clinicians must take a comprehensive history and perform a thorough physical examination to ensure that this time-sensitive diagnosis is not missed.
Causes
Shallower anterior chambers; anteriorly situated lens; shorter axial eye length; thick iris; overdeveloped iris dilator muscles; and a narrow angle lead to a higher propensity for development of AACG.
Precipitating factors include drugs (ie, sympathomimetics, anticholinergics, antidepressants [SSRIs], sulfonamides, cocaine, botulinum toxin)8,9,10 , dim light, and rapid correction of hyperglycemia.
Case reports have identified AACG associated with carotid-cavernous sinus fistula, trauma, prone surgical positioning, and giant cell arteritis.11,12,13

http://emedicine.medscape.com/article/798811-overview

Author: Andrew Aherne, MD,, Resident Physician, Department of Emergency Medicine, Kings County Hospital Center, University Hospital of Brooklyn
Coauthor(s): Richard H Sinert, DO, Associate Professor of Emergency Medicine, Clinical Assistant Professor of Medicine, Research Director, State University of New York College of Medicine; Consulting Staff, Department of Emergency Medicine, Kings County Hospital Center
Updated: Nov 10, 2010

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