Glaucoma

Glaucoma is an optic neuropathy characterized by irreversible ganglion nerve cell damage and vision loss. The 2 most common types of glaucoma are angle-closure (closed-angle) and open-angle. Causes include elevated intraocular pressure (IOP); however, in some patients with open-angle glaucoma, IOP is normal. Symptoms vary by type; both types can cause blindness. Diagnosis is by history, IOP measurement, slit-lamp examination, visual field testing, and gonioscopy. Screening in the elderly is essential because glaucoma is common among the elderly. Treatment is with drugs to reduce intraocular pressure or laser or other surgery.

In glaucoma, ganglion nerve cells are irreversibly damaged, causing permanent vision loss. Worldwide, glaucoma is the 2nd leading cause of vision loss after cataracts. Although typically considered a disorder of elevated intraocular pressure (IOP), some patients with open-angle glaucoma (the most common form of glaucoma in the US) have IOP in the normal range. Therefore, the pathologic process may involve factors that increase ganglion cell susceptibility to damage; age and elevated IOP are 2 of probably many such factors.

Angle-Closure Glaucoma

(Closed-Angle Glaucoma, Narrow-Angle Glaucoma)

Angle-closure glaucoma is characterized by a closed or narrow anterior chamber angle, physically obstructing drainage of aqueous humor and elevating IOP, often to 50 to 60 mm Hg.

Worldwide, the most common cause of glaucoma-induced blindness is angle-closure glaucoma. Women, Chinese people, Eskimos, and people who are hyperopic (farsighted) are at greatest risk; use of drugs that dilate pupils (eg, anticholinergic drugs) further increase risk in these groups.

Angle-closure glaucoma develops when the pupil margin of the iris presses against the lens, preventing aqueous humor from entering the anterior chamber (see Figure 127-1). Fluid continuously produced by ciliary body epithelium in the posterior chamber then pushes the midportion of the iris forward, sealing off access to the trabecular meshwork, through which the fluid flows out of the eye, and elevating IOP to levels as high as 50 to 60 mm Hg (normal is < 21 mm Hg) within hours.

Angle closure may be acute or chronic; in acute cases, the trabecular meshwork becomes sealed off within hours; in chronic cases, it is sealed off over months.

Symptoms and Signs

Symptoms of the acute form are redness and pain in or around the eye, severe headache, nausea, vomiting, and blurred vision. Patients often see halos around lights as a result of corneal edema. The affected eye is tender and feels firmer than the other eye. The conjunctiva is injected, and the cornea appears hazy or steamy. As IOP continues to increase, nausea and vomiting can become severe enough to mimic an acute abdomen. If glaucoma is undiagnosed and untreated, vision is irreversibly damaged within 48 to 72 h.

Symptoms of the chronic form are vague and may include headaches and intermittent blurred vision, halos around lights, and red eyes.

Symptoms in either form usually occur in only one eye, although patients with glaucoma in one eye are at greater risk of developing it in the other eye because the anterior chamber is shallow.

Diagnosis

Diagnosis is by history, IOP measurement, and slit-lamp examination of angle structures; a gonioscope, a special corneal contact lens, is used to visualize the anterior chamber angle. A simple way to test for narrow angles is to shine a penlight across the eye from the temporal side. If the nasal iris is in shadow, the angle is narrow and angle closure is a risk.

Treatment

Acute angle-closure glaucoma is an emergency requiring immediate referral to an ophthalmologist. If an ophthalmologist is unavailable, emergency treatment is local instillation of 1 drop of 2% pilocarpine q 15 min 3 times (or 1 drop of 0.5% timolol q 15 min 2 times) with acetazolamide 5 to 10 mg/kg IV or 500 mg po. A topical -blocker, ₂-agonist, and corticosteroid (eg, 0.5% timolol, 0.2% brimonidine, and a corticosteroid drop) all used together may also be effective.

Although drugs can usually reduce IOP, laser iridotomy or iridectomy is the only cure. For these procedures, a small opening is made at the base of the iris to allow the pressure to equalize on both sides and to prevent the iris from obstructing the trabecular meshwork. Both procedures can be done in the office and take only a few minutes. If done within the first 24 h, before development of permanent adhesions between the iris and trabecular meshwork (peripheral anterior synechiae), either procedure can cure glaucoma and prevent future attacks. Because patients with an acute glaucoma attack in one eye are at higher risk of an attack in the other eye, laser iridotomy of the unaffected eye is usually done within several weeks after the first procedure.

Treatment of chronic angle-closure glaucoma is also laser iridotomy, but patients may need glaucoma drugs such as -blockers or prostaglandin analogs or intraocular surgery because they typically already have peripheral anterior synechiae and chronically elevated IOP.

Open-Angle Glaucoma

Open-angle glaucoma is characterized by an open anterior chamber angle, usually with elevated IOP.

Open-angle glaucoma accounts for about 80% of glaucoma cases in the US. Blacks have a 3 to 4 times greater risk of developing open-angle glaucoma. Other risk factors include age > 65, family history, long-term corticosteroid use, and increased optic nerve cupping (increased size of the depression in the optic nerve [the cup] relative to the whole disk area).

Open-angle glaucoma, like angle-closure glaucoma, involves resistance to outflow of aqueous humor, but the angle structures appear normal. The precise site and cause of resistance is unknown, but the site is believed to be in the trabecular meshwork.

IOP may or may not be elevated (> 21 mm Hg). In at least 50% of patients, IOP is within the normal range (called low- or normal-pressure glaucoma). However, for these patients, IOP may still be too high to tolerate. Proposed causes of normal-pressure glaucoma include an inadequate blood supply to the optic nerve (eg, due to vascular disorders) and a fragile optic nerve (eg, due to heredity or structural abnormalities).

Symptoms and Signs

Open-angle glaucoma is asymptomatic through the early stages. The primary symptom is gradual, painless loss of peripheral vision, usually in both eyes. Vision loss occurs over years and is usually unnoticed by patients until it is advanced.

Diagnosis

Diagnosis is by slit-lamp examination with gonioscopy, ophthalmoscopy, perimetry (visual field testing), and IOP measurement. Gonioscopy is used to determine whether the anterior chamber angle and outflow channels are anatomically normal and thereby distinguish open-angle from angle-closure glaucoma. Ophthalmoscopy shows characteristic optic and retinal nerve fiber layer changes, including loss or thinning of the neuroretinal rim, loss of the retinal nerve fiber layer, disk hemorrhages, peripapillary atrophy, increased optic nerve cupping, and focal notches in the neuroretinal rim. In long-standing cases, optic atrophy may manifest as increased cupping and thinning of the neuroretinal rim. Quantitative perimetry detects peripheral vision loss.

IOP is measured with an applanation tonometer after a topical anesthetic (eg, proparacaine 0.5%) is used. If IOP is normal (<= 21 mm Hg) but changes in the nerve fiber layer, visual field defects, or both are present, normal-pressure glaucoma is diagnosed. If IOP is elevated (> 21 mm Hg) but no visual field defects or optic nerve changes are present, ocular hypertension is diagnosed; in such cases, perimetry and optic nerve examination must be done at least every 12 mo to check for onset of glaucoma. There is no consensus on the need for treatment of ocular hypertension, but patients with thinner corneas and increased optic nerve cupping are at increased risk of developing glaucoma and may require treatment.

For most people > 65, IOP measurement and an ophthalmoscopic examination should be done every year. Optic nerve cup and disk size should be evaluated closely. Large disks with small cups are normal, and small disks with large cups are abnormal. Large disks with large cups may be normal, and small disks with small cups may be abnormal. Several imaging devices, such as confocal scanning ophthalmoscopy or scanning laser polarimetry, can be used to document the appearance of the optic nerve and any changes that occur over time.

Treatment

Open-angle glaucoma is a chronic disorder and cannot be cured; however, drugs to reduce IOP may help prevent irreversible optic nerve damage and loss of peripheral visual fields. Treatment begins with a topical drug (see Table 127-1). If monotherapy does not reduce IOP sufficiently, another class of drug can be substituted, or a drug with a different mechanism can be added. If topical drugs do not control IOP, systemic drugs may be added. Oral carbonic anhydrase inhibitors are effective, but adverse effects limit their use.

Topical drugs may decrease aqueous humor production, increase aqueous humor outflow, or do both.

Prostaglandin analogs or prostamides (which increase aqueous humor outflow) are used most commonly. They may be used alone or with other drugs. Prostaglandin analogs and prostamides have fewer adverse effects than -blockers.

-Blockers decrease aqueous humor production and may be used alone or with other drugs. Usually, patients who are taking a systemic -blocker should be given a topical drug from another class. Topical -blockers should not be used in patients with reactive airways disease, cardiac conduction abnormalities, or heart failure.

Carbonic anhydrase inhibitors decrease aqueous humor production by a different mechanism from that of -blockers and can be used with -blockers. A combination topical drug with a carbonic anhydrase inhibitor (dorzolamide) and a -blocker (timolol) is available. Carbonic anhydrase inhibitors are often used as adjunctive therapy but rarely as initial therapy.

₂-Agonists (most commonly, brimonidine) decrease aqueous humor production and increase aqueous humor outflow; these drugs are usually used as adjunctive therapy. They should not be used in patients taking monoamine oxidase (MAO) inhibitors.

Treatment continues indefinitely, and patient adherence is key. Glaucoma eye drops can be absorbed systemically and have adverse effects. To minimize these effects, patients can occlude their punctum by pressing on the medial aspect of the lids near the nose. IOP measurement, perimetry, and optic nerve imaging or examination are done periodically to monitor effects of treatment; frequency of monitoring depends on the patient but typically ranges from every 2 to 12 mo.

If perimetry and optic nerve imaging or examination suggest glaucoma progression, surgery is indicated to reduce IOP to a level that can slow or halt glaucoma. In laser trabeculoplasty, a laser is used to open the trabecular meshwork, so that aqueous humor can drain. In trabeculectomy, a partial thickness opening is created in the eye. Various drainage shunts can be used to drain fluid from the anterior chamber out of the eye.

Secondary Glaucoma

Secondary glaucoma accounts for about 10% of glaucoma cases in the US.

Causes include the following:

• Diabetes mellitus: Neovascularization of the iris and angle reduces filtration of the aqueous humor.
• Central retinal vein occlusion: A fibrovascular membrane may grow over and seal off the trabecular meshwork.
• Uveitis: Inflammatory cells or debris obstructs outflow channels.
• Ocular tumors: Tumor cells or direct pressure in the anterior chamber angle may obstruct outflow channels.

Patients with secondary glaucoma can present with a red, uncomfortable eye, often chronically painful and usually accompanied by decreased vision. However, some types of secondary glaucoma are asymptomatic.

Diagnosis is most often incidental during an eye examination for a primary ocular disorder or systemic disorder (eg, diabetes).

Primary treatment is to treat the underlying disorder. Drugs to reduce IOP may also be indicated (see Table 127-1). If these measures are ineffective, surgery is needed to create a new outflow pathway for aqueous humor or to reduce aqueous humor production (by destruction of the ciliary body).

This topic was last updated May 2006.