Atlas of pathophysiology, 2 Edition

Part II - Disorders

Sensory Disorders

Glaucoma

Glaucoma is a group of disorders characterized by an abnormally high intraocular pressure (IOP) that damages the optic nerve and other intraocular structures. Untreated, it leads to a gradual loss of vision and, ultimately, blindness. Glaucoma occurs in several forms: chronic open-angle (primary), acute angle-closure, congenital (inherited as an autosomal recessive trait), and secondary to other causes. Chronic open-angle glaucoma is usually bilateral, with insidious onset and a slowly progressive course. Acute angle-closure glaucoma typically has a rapid onset, constituting an ophthalmic emergency. Unless treated promptly, this acute form of glaucoma causes blindness in 3 to 5 days.

Causes

Chronic open-angle glaucoma

·   Genetics

·   Hypertension

·   Diabetes mellitus

·   Aging

·   Black ethnicity

·   Severe myopia

Acute angle-closure glaucoma

·   Drug-induced mydriasis (extreme dilation of the pupil)

·   Excitement or stress, which can lead to hypertension

Secondary glaucoma

·   Uveitis

·   Trauma

·   Steroids

·   Diabetes

·   Infections

·   Surgery

Pathophysiology

Chronic open-angle glaucoma results from overproduction or obstruction of the outflow of aqueous humor through the trabecular meshwork or the canal of Schlemm, causing increased IOP and damage to the optic nerve. In secondary glaucoma, conditions such as trauma and surgery increase the risk of obstruction of intraocular fluid outflow caused by edema or other abnormal processes.

Acute angle-closure glaucoma results from obstruction to the outflow of aqueous humor. Obstruction may be caused by anatomically narrow angles between the anterior iris and the posterior corneal surface, shallow anterior chambers, a thickened iris that causes angle closure on pupil dilation, or a bulging iris that presses on the trabeculae, closing the angle (peripheral anterior synechiae). Any of these may cause IOP to increase suddenly.

Age Alert

In older patients, partial closure of the angle also may occur, so that two forms of glaucoma may coexist.

Signs and symptoms

Chronic open-angle glaucoma

·   Typically bilateral

·   Mild aching in the eyes

·   Loss of peripheral vision

·   Images of halos around lights

·   Reduced visual acuity, especially at night, not correctable with glasses

Acute angle-closure glaucoma

·   Rapid onset; usually unilateral

·   Inflammation; red, painful eye

·   Sensation of pressure over the eye

·   Moderate papillary dilation nonreactive to light

·   Cloudy cornea

·   Blurring and decreased visual acuity; halos around lights

·   Photophobia

·   Nausea and vomiting

Diagnostic test results

·   Tonometry measurement shows increased IOP.

·   Slit-lamp examination shows effects of glaucoma on anterior eye structures.

·   Gonioscopy shows the angle of the eye's anterior chamber.

·   Ophthalmoscopy aids visualization of the fundus.

·   Perimetry or visual field tests show the extent of peripheral vision loss.

·   Fundus photography shows optic disk changes.

Treatment

Chronic open-angle glaucoma

·   Beta-adrenergic blockers, such as timolol or betaxolol (a beta1-receptor antagonist)

·   Alpha agonists, such as brimonidine or apraclonidine

·   Carbonic anhydrase inhibitors, such as dorzolamide or acetazolamide

·   Epinephrine

·   Prostaglandins such as latanoprost

·   Miotic eyedrops such as pilocarpine

·   Surgical procedures if medical therapy fails to reduce IOP:

§  argon laser trabeculoplasty of the trabecular meshwork of an open angle, to produce a thermal burn that changes the surface of the meshwork and increases the outflow of aqueous humor

§  trabeculectomy, to remove scleral tissue, followed by a peripheral iridectomy, to produce an opening for aqueous outflow under the conjunctiva, creating a filtering bleb

Acute angle-closure glaucoma

·   Ocular emergency, requiring immediate intervention, including:

§  I.V. mannitol (20%) or oral glycerin (50%)

§  steroid drops

§  acetazolamide, a carbonic anhydrase inhibitor

§  pilocarpine, to constrict the pupil, forcing the iris away from the trabeculae and allowing fluid to escape

§  timolol, a beta-adrenergic blocker

§  opioid analgesics

§  laser iridotomy or surgical peripheral iridectomy

§  cycloplegic drops, such as apraclonidine, in the affected eye (only after laser peripheral iridectomy)

P.403

OPTIC DISK CHANGES IN GLAUCOMA

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