Glaucomas are a group of eye disorders characterized by progressive optic nerve damage at least partly due to increased intraocular pressure (IOP). Glaucoma is the 3rd most common cause of blindness worldwide.
Glaucomas are categorized as open-angle or closed-angle (angle-closure). The “angle” refers to the angle formed by the junction of the iris and cornea at the periphery of the anterior chamber. The angle is where > 98% of the aqueous humor exits the eye via either the trabecular meshwork and Schlemm's canal (the major pathway, particularly in the elderly) or the ciliary body face and choroidal vasculature.
Axons of retinal ganglion cells travel through the optic nerve carrying images from the eye to the brain. Damage to these axons causes ganglion cell death with resultant optic nerve atrophy and patchy vision loss. Elevated IOP (in unaffected eyes, the average range is 11 to 21 mm Hg) plays a role in axonal damage, either by direct nerve compression or diminution of blood flow.
IOP is determined by the balance of aqueous humor secretion and drainage. Elevated IOP is caused by inhibited or obstructed outflow, not oversecretion. In open-angle glaucoma, IOP is elevated because outflow is inadequate despite an angle that appears unobstructed. In angle-closure glaucoma, IOP is elevated when a physical distortion of the peripheral iris mechanically blocks outflow.
Open Angle Glaucoma
Aqueous humor drainage is inadequate, whereas production by the ciliary body is normal. Identifiable mechanisms for inadequate drainage include developmental anomalies, scarring caused by trauma or infection, and plugging of channels by detached iris pigment (ie, pigment dispersion syndrome) or abnormal protein deposits (eg, pseudoexfoliation syndrome).
Angle-closure glaucoma is glaucoma associated with a physically obstructed anterior chamber angle, which may be chronic or, rarely, acute.
Angle-closure glaucoma is caused by factors that either pull or push the iris up into the angle (ie, junction of the iris and cornea at the periphery of the anterior chamber), physically blocking drainage of aqueous humor (fluid between the lens and cornea) and raising IOP. Elevated IOP damages the optic nerve.
Angle closure may be primary (cause is unknown) or secondary to another condition and can be acute, subacute (intermittent), or chronic.
Primary angle-closure glaucoma: Narrow angles are not present in young people. As people age, the lens of the eye continues to grow. In some but not all people, this growth pushes the iris forward, narrowing the angle. Risk factors for developing narrow angles include Asian ethnicity, hyperopia, family history and advanced age.
In people with narrow angles, the distance between the pupillary iris and the lens is also very narrow. When the iris dilates, forces pull it centripetally and posteriorly causing iris–lens contact, which prevents aqueous from passing between the lens and iris into the anterior chamber (this mechanism is termed pupillary block). Pressure from the continued secretion of aqueous into the posterior chamber by the ciliary body pushes the peripheral iris anteriorly (causing a forward-bowing iris called iris bombe), closing the angle. This closure blocks aqueous outflow, resulting in rapid (within hours) and severe (> 40 mm Hg) elevation of IOP. Because of the rapid onset, this condition is called primary acute angle-closure glaucoma and is an ophthalmic emergency requiring immediate treatment.
Intermittent angle-closure glaucoma occurs if the episode of pupillary block resolves spontaneously after several hours, usually after sleeping supine.
Chronic angle-closure glaucoma occurs if the angle narrows slowly, allowing scarring between the peripheral iris and trabecular meshwork; IOP elevation is slow.
Symptoms and Signs
Acute angle-closure glaucoma: Patients have severe ocular pain and redness, decreased vision, colored halos around lights, headache, nausea, and vomiting. The systemic complaints may be so severe that patients are misdiagnosed as having a neurologic or GI problem. Examination typically reveals conjunctival hyperemia, a hazy cornea, a fixed mid-dilated pupil, and anterior chamber inflammation. Vision is decreased. IOP is usually 40 to 80 mm Hg. The optic nerve is difficult to visualize because of corneal edema, and visual field testing is not done because of discomfort.
Chronic angle-closure glaucoma: This type of glaucoma manifests similarly to open-angle glaucoma. Some patients have ocular redness, discomfort, blurred vision, or headache that lessens with sleep (perhaps because of sleep-induced miosis and posterior displacement of the lens by gravity). On gonioscopy, the angle is narrow, and peripheral anterior synechiae (PAS) may be seen. IOP may be normal but is usually higher in the affected eye.
Acute: Measurement of IOP and clinical findings
Chronic: Gonioscopy showing peripheral anterior synechiae and characteristic optic nerve and visual field abnormalities
Diagnosis of acute angle-closure glaucoma is clinical and by measurement of IOP. Gonioscopy may be difficult to do in the involved eye because of a clouded cornea with friable corneal epithelium. However, examination of the other eye reveals a narrow or occludable angle. If the other eye has a wide angle, a diagnosis other than primary angle-closure glaucoma should be considered.
Diagnosis of chronic angle-closure glaucoma is based on the presence of PAS on gonioscopy and characteristic optic nerve and visual field changes.
Acute: Timolol, pilocarpine, and apraclonidine drops and a systemic osmotic drug followed promptly by laser peripheral iridotomy
Chronic: Similar to primary open-angle glaucoma except that laser peripheral iridotomy may be done if the clinician feels that the procedure may slow mechanical closing of the angle
Acute angle-closure glaucoma: Treatment must be initiated immediately because vision can be lost quickly and permanently. The patient should receive several drugs at once. A suggested regimen is timolol 0.5% one drop q 30 min for 2 doses; pilocarpine 2 to 4% one drop q 15 min for the first 1 to 2 h; and an osmotic agent, such as mannitol 1.0 to 1.5 mg/kg IV, or isosorbide 100 g po. Response is evaluated by measuring IOP.
Definitive treatment is with laser peripheral iridotomy (LPI), which opens another pathway for fluid to pass from the posterior to the anterior chamber, breaking the pupillary block.
Chronic angle-closure glaucoma: Patients with chronic, subacute, or intermittent angle-closure glaucoma should also have LPI. Additionally, patients with a narrow angle, even in the absence of symptoms, should undergo prompt LPI to prevent angle-closure glaucoma.
The drug and surgical treatments are the same as with open-angle glaucoma. Laser trabeculoplasty is relatively contraindicated if the angle is so narrow that additional PAS may form after the laser procedure.
A 59 year old man comes to the emergency department because of a severe headache. The headache came on suddenly as he was leaving the light show at the planetarium. He also has right eye pain and nausea and he vomited twice during the car ride over to the hospital. He has no significant past medical history. He has had other headaches in the past, but has never experienced anything like this. His temperature is 36.7 C (98.0 F), blood pressure is 130/90 mm Hg, pulse is 75/min, and respirations are 18/min. Physical examination shows a tender red right eye with a partially dilated pupil, but is otherwise unremarkable. The most appropriate next step is to
A. administer glucocorticoids, intravenously
B. administer sumatriptan, intramuscularly
C. give him oxygen therapy, 100% for 15 minutes
D. measure intraocular pressure
E. order a CT scan of the head
The correct answer is D. This patient with a headache and a red eye either has acute glaucoma or a cluster headache. The partially dilated pupil is more consistent with acute glaucoma. Acute glaucoma, which is caused by increased intraocular pressure, often presents with abdominal pain, nausea, vomiting, and a headache. It is an ophthalmologic emergency that may lead to blindness, so this diagnosis should be included in your differential when a patient presents with these other symptoms. The patient usually has eye pain, but it may be overshadowed by the other symptoms. The diagnosis is established by measuring intraocular pressure. You should call for an immediate ophthalmologic consultation and possibly administer acetazolamide, topical beta blockers, mannitol, and pilocarpine. A cluster headache is an episodic headache that typically presents with a few short headaches a day for a few weeks that is associated with periorbital pain, reddening of the eye, and lacrimation.
A 45 year old woman is brought to the emergency department by her husband because of an "excruciatingly painful left eye." They were at the movies when she began to complain of blurry vision, a severe headache, and she had to run to the restroom to throw-up. The pain "settled into her eye" on the ride over to the hospital. She is now complaining of seeing "halos" around lights. Her ophthalmologic history is significant for several dendritic herpetic ulcers over the past few years. Physical examination shows conjunctival hyperemia with an edematous left eyelid. The cornea appears "steamy" and the pupil is fixed and mid-dilated. The left eye is tender and firm on palpation and tonometric testing reveals an intraocular pressure (IOP) of 67mm Hg. Immediate management would be to
A. administer mannitol, intravenously
B. order a CT scan of the head
C. perform a lumbar puncture
D. perform a peripheral iridotomy
E. treat the patient with corticosteroids, topically
The correct answer is A. This patient most likely has acute angle-closure glaucoma, which is an ocular emergency that requires immediate treatment to prevent blindness. It is characterized by a rapid increase of IOP, often occurring when the pupil is dilated (such as in a dark movie theater). The symptoms include severe eye pain, blurry vision, a headache, nausea, and vomiting. The physical examination usually shows a tender, firm eye with conjunctival hyperemia, lid edema, a hazy cornea, and a fixed, mid-dilated pupil. Immediate treatment includes mannitol (to reduce vitreous humor volume), acetazolamide and topical beta-blockers, such as timolol (to block aqueous production), and pilocarpine (to facilitate aqueous outflow). Ophthalmologic consultation should also be sought as soon as possible. A peripheral laser iridectomy is the definitive procedure and is usually performed after the IOP is controlled.