Physiology

Light passes through the cornea and then through an opening in the iris, the pupil. The iris is responsible for controlling the amount of light that enters the eye by dilating and constricting the pupil. This light then reaches the lens, which refracts the light rays onto the retina. The anterior chamber is located between the lens and the cornea and contains aqueous humor, which is produced by the ciliary body. This fluid maintains pressure and provides nutrients to the lens and cornea. It is reabsorbed from the anterior chamber into the venous system through the canal of Schlemm. The vitreous chamber, located between the retina and the lens, contains a gelatinous fluid called vitreous humor. Light rays pass through the vitreous humor before reaching the retina. The retina lines the back of the eye and contains photoreceptor cells called rods and cones. Rods help vision in dim light, whereas cones aid light and color vision. The cones are located in the center of the retina in an area called the macula. The fovea is a small depression in the center of the macula that contains the highest concentration of cones. The optic nerve is located behind the retina and is responsible for transmitting signals from the photoreceptor cells to the brain (Fig. 26.1).

Fig. 26.1 Anatomy of the eye (A) and retina (B).

The extraocular muscles (Fig. 26.2) help in stabilization of the eye. Six extraocular muscles assist in horizontal, vertical, and rotational movement. These muscles are controlled by impulses from cranial nerves III, IV, and VI, which tell the muscles to relax or contract.

Fig. 26.2 Extraocular muscles.

(Courtesy Ted Montgomery, OD. Available at www.tedmontgomery.com/the_eye/.)

Epidemiology

More than 3 million Americans suffer from glaucoma, the leading cause of preventable blindness in the United States.³ The term glaucoma refers to a group of disorders that damage the optic nerve and thereby lead to loss of vision. The two main classifications of glaucoma are open angle and angle closure. Acute angle-closure glaucoma is more common in white persons and women. Its peak incidence occurs between the ages of 55 and 70.⁴ African Americans, patients older than 65 years, and people with diabetes and ocular trauma are at increased risk for open-angle glaucoma. Differentiation between the two types of glaucoma lies in the mechanism of obstruction of outflow, as described later. Intraocular pressure (IOP) is determined by the rate of aqueous humor production relative to its outflow and removal. Normal IOP is between 10 and 20 mm Hg. This discussion focuses mainly on acute angle-closure glaucoma.

When the angle of the anterior chamber is reduced, outflow of aqueous humor is blocked, which results in elevated IOP and ultimately visual compromise. Patients with a shallow anterior chamber, hyperopic (farsighted) eyes, and eyes with lens abnormalities such as cataracts are more prone to acute angle-closure glaucoma. Pupillary dilation, caused by events such as presence in a dark room, is the most significant event that can cause an acute attack of glaucoma because the flaccid iris can be pushed against the trabecular meshwork and result in obstruction.

Presenting Signs and Symptoms

Patients with acute angle-closure glaucoma may have a sudden onset of headache or eye pain. Occasionally, nausea and vomiting from vagal stimulation can be the dominant symptoms. Shortly after the onset of pain, blurry vision or halos in the visual field may occur.

The classic physical findings are unilateral eye injection, especially at the limbus; a nonreactive, midsize pupil; shallow anterior chamber; corneal edema or haziness; and high IOP (often 60 to 90 mm Hg). If the attack has been prolonged, ischemia of the ciliary body reduces aqueous humor production with a resultant decrease in IOP. This process is especially important because the ultimate damage depends on the duration of the attack rather than the severity of the elevation in pressure.

With open-angle glaucoma, development of the disease is usually insidious, bilateral, slowly progressive, and painless.

Medical Decision Making

Visual acuity should be recorded in both eyes. Examination of the eye should include a search for the classic signs of glaucoma already described, including a middilated pupil in the affected eye and corneal haziness. A slit lamp should be used to estimate the depth of the anterior chamber. If this depth is less than one fourth the corneal thickness, the anterior chamber angle is very narrow. It is important to measure anterior chamber depth in both eyes; a shallow angle in only one eye argues against acute angle-closure glaucoma. IOP is usually measured with a tonometer; the cornea is flattened, and pressure is determined by measurement of the force needed to flatten it, as well as measurement of the area flattened.

Treatment

Acute angle-closure glaucoma is an ophthalmologic emergency. Because outcome depends on the duration of elevated IOP, treatment should be initiated promptly. Therapy is geared toward decreasing aqueous production, increasing aqueous outflow, and reducing vitreous volume to lower IOP.

Initial treatment includes a topical, nonselective beta-blocker such as 0.5% timolol to reduce aqueous production. Topical beta-blockers are absorbed and can cause systemic effects. Intravenous administration of a carbonic anhydrase inhibitor such as acetazolamide, 500 mg, will also rapidly reduce aqueous humor production. Intravenous mannitol will create an osmotic gradient between the vitreous and blood and thereby cause a reduction in vitreous volume, so it may be useful for severe cases. Tonometry can be performed frequently, even every 15 minutes, to assess progress.

Topical 2% pilocarpine is used to help reopen the angle. Miotics such as the direct-acting parasympathomimetic agent pilocarpine might be less effective at very high IOP because the iris is relatively ischemic and therefore less responsive. Sometimes pilocarpine is used after IOP has been reduced to less than 40 mm Hg. Pilocarpine will therefore be more effective as the initially high pressures are reduced with the initial beta-blocker drops and acetazolamide. Topical 1% prednisolone acetate may sometimes be added to reduce inflammation. For ongoing treatment, topical 2% pilocarpine and prednisolone acetate may be administered every 6 hours and oral acetazolamide two times per day. Sedatives and antiemetics may be administered as needed. When the inflammation has been reduced sufficiently, the patient will be taken for iridotomy by the ophthalmologist.

Disposition

Disposition of the patient is determined in conjunction with the consulting ophthalmologist. Indications for admission include intractable nausea and vomiting and need for careful monitoring to administer systemic agents.

Epidemiology

Retinal artery occlusion affects less than 1 per 100,000 persons annually.^5,6 It is most commonly caused by an embolus from the carotid artery that lodges in a distal branch of the ophthalmic artery. Central retinal artery occlusion most commonly affects elderly patients and men. Although most emboli are formed from cholesterol, they may also be calcific, fat, or bacterial from cardiac valve vegetations.

Pathophysiology

The visual complaints and deficits resulting from retinal artery disease are caused by ischemia. In addition to the embolic causes already described, low-flow states and vasospasm may have the same visual consequences.

Presenting Signs and Symptoms

Sudden, painless visual loss is the classic manifestation of central retinal artery occlusion. Sometimes patients report transient visual loss before complete compromise. The visual loss is usually profound. Examination can often elicit an afferent pupillary defect (when light is shined into the abnormal eye, the pupil of the affected eye paradoxically dilates instead of constricting). Funduscopic examination typically demonstrates a pale retina with a cherry-red spot at the fovea (Fig. 26.3). Complete evaluation involves auscultation of the carotid arteries for bruits, palpation of the temporal artery for tenderness, and cardiac auscultation and palpation of the pulse to detect atrial fibrillation.

Fig. 26.3 Central retinal artery occlusion.

(Courtesy Ted Montgomery, OD. Available at www.tedmontgomery.com/the_eye/.)

Differential Diagnosis

Sudden, painless visual loss can also result from central retinal vein occlusion, temporal arteritis, ischemic optic neuropathy, amaurosis fugax, retinal detachment, or vitreous hemorrhage. If the loss of vision is accompanied by pain, arterial dissection should be part of the differential diagnosis. The presence of a headache, temporal artery tenderness, and an elevated erythrocyte sedimentation rate (ESR) suggests temporal arteritis. Amaurosis fugax, or unilateral transient obstruction of a retinal artery, does not cause visual loss lasting longer than 15 minutes. Ischemic optic neuropathy causes optic disk pallor and elevation. Retinal detachment and vitreous hemorrhage result in visual disturbances such as floaters in addition to the loss of vision—the occurrence of which is variable with a detached retina. Vitreous hemorrhage causes absence of the normal red reflex of the fundus. A neurologic etiology such as a cerebral infarct must also beconsidered.

Treatment

Treatment must be initiated immediately because the visual loss is generally irreversible after 2 hours of ischemia. Regardless, the outcome is generally poor. Several approaches may be used. Intermittent globe massage can be performed in an effort to dislodge the clot and propel it distally: moderate pressure is applied for 5 second and then released for 5 seconds, and the cycle is repeated. The use of anterior chamber paracentesis for visual loss is based on the principle that decreased IOP allows better perfusion of the retinal artery and may propel the clot distally. Acetazolamide can be administered intravenously for the same purpose. Inhaled carbogen (mixture of 95% oxygen and 5% carbon dioxide) can be used to dilate the vasculature and thereby increase retinal PO₂.

Other treatment options are intraarterial thrombolysis and hyperbaric oxygen; however, studies have shown limited improvement in visual outcome with early administration of both these treatment modalities.^7–10 One retrospective study found that even with thrombolysis, vision did not improve to better than 20/300 in the affected eye.⁷ Another study investigated the outcomes of 32 patients with central retinal artery occlusion, 17 of whom underwent fibrinolysis.⁶ This study found that all but six of the treated patients reported improvement in their visual compromise but that only five of the untreated patients had any improvement. In this study, patients with a duration of symptoms of up to 24 hours were treated.

Patients with sudden visual loss are admitted to the hospital so that the underlying cause can be sought.

Epidemiology

Patients older than 50 years who have cardiovascular disease, hypertension, glaucoma, venous stasis, hypercoagulable conditions, collagen vascular diseases, or diabetes are at risk for central retinal vein occlusion.¹

Pathophysiology

Two types of retinal vein occlusion are distinguished, ischemic and nonischemic. The ischemic type is also known as hemorrhagic retinopathy, and the nonischemic type is also called venous stasis retinopathy. The manifestations and physical findings differ according to the type of occlusion involved.

Presenting Signs and Symptoms

Typically, patients with ischemic retinal vein occlusion report an acute and relatively profound decrease in visual acuity. Those with the nonischemic type have progressively blurry vision that is worse in the morning. An afferent pupillary defect is found in the ischemic type. Funduscopic examination shows an edematous optic disk and macular, dilated retinal veins, retinal hemorrhage, and cotton-wool spots. Sometimes these findings are called the “blood and thunder” appearance of the fundus (Fig. 26.4).

Fig. 26.4 Central retinal vein occlusion.

(From Noble J. Textbook of primary care medicine. 3rd ed. St. Louis: Mosby; 2001.)

Differential Diagnosis

The processes that must be considered when assessing a patient with possible central retinal vein occlusion are the same as those for central retinal artery occlusion. Branch retinal vein occlusion may also occur distal to an arteriovenous crossing, with hemorrhage developing distal to the occlusion site.

Medical Decision Making

No specific diagnostic test can identify central retinal vein occlusion. The diagnosis is based on the clinical history and physical examination, which exclude other processes that also cause painless visual loss.

Treatment

No effective therapeutic regimen exists for central retinal vein occlusion. The emergency physician (EP) should arrange for immediate ophthalmologic consultation. A search for a cause should be performed to protect the contralateral eye from the same problem. The prognosis largely depends on the type of retinal venous occlusion. Nonischemic vein occlusion, unless the macular involvement is extensive, offers a better outcome than the ischemic type does. Spontaneous resolution may occur in some cases.

Although no specific treatment is available, a number of interventions have been proposed and practiced.^11,12 However, these interventions have not been based on evidence of efficacy. Laser photocoagulation, for example, cauterizes leaking vessels with the aim of halting further visual loss. This procedure can be especially helpful for branch retinal vein occlusion. With nonischemic vein occlusion, attempts to reduce macular edema can be helpful. The reduction is accomplished with the administration of topical corticosteroids. Studies have been conducted to determine the benefit of steroids in treating both forms of retinal vein occlusion. Jonas et al.¹¹ conducted a prospective, comparative, nonrandomized clinical interventional study to evaluate the visual outcomes in 32 patients with central retinal vein occlusion after intravitreal administration of triamcinolone acetate. The study included patients with both the ischemic and nonischemic forms of retinal vein occlusion. These researchers found that the medication resulted in temporary (up to 3 months) improvement in visual outcome but also raised IOP. Anticoagulants are not recommended because they may propagate hemorrhage.

Epidemiology

Optic neuritis is inflammation of the optic nerve, and visual loss is due to focal demyelination of the optic nerve. Most affected patients are between 15 and 40 years of age. This disorder can be associated with numerous diseases, including sarcoidosis, systemic lupus erythematosus, measles, leukemia, syphilis, and alcoholism; however, it is most commonly associated with multiple sclerosis. In fact, in up to a third of patients with optic neuritis, multiple sclerosis is eventually diagnosed, and approximately two thirds of patients with multiple sclerosis have optic neuritis. Optic neuritis can also be idiopathic.

Pathophysiology

Optic neuritis results from an autoimmune reaction that ultimately causes demyelinating inflammation. In idiopathic and multiple sclerosis–related optic neuritis, lesions are characterized by areas of loss of the myelin sheath with preservation of axons. In acute disease, remyelination may occur. In chronic disease, because of the accumulation of scar tissue, the process becomes irreversible. The lesions in multiple sclerosis–associated optic neuritis are pathologically the same as those in the brain.

Presenting Signs and Symptoms

Symptoms of optic neuritis are generally unilateral. Patients complain of pain, especially with eye movement. Visual loss, which can range from minimal loss to complete loss of light perception, usually occurs over a number of hours or days. Patients may also experience dulling of color vision, worse vision after exertion or exposure to steam, brief light flashes, and central scotoma. An afferent pupillary defect is always present. Funduscopic examination may show disk pallor, swelling, or elevation. However, because up to two thirds of cases are retrobulbar, the fundus can appear normal.

Differential Diagnosis and Medical Decision Making

Any condition that causes visual disturbance along with eye pain must be considered in the differential diagnosis of optic neuritis. Orbital cellulitis can cause this clinical picture but does not include an afferent pupillary defect; furthermore, inspection alone should allow differentiation between the two diseases. Glaucoma can also cause the combination of ocular pain and visual impairment. Physical examination, including assessment of pupil size and reactivity, as well as corneal inspection, allows distinction between glaucoma and optic neuritis.

Unilateral ocular pain with visual compromise should always raise clinical suspicion for optic neuritis. If no afferent pupillary defect is found on physical examination, another diagnosis is almost ensured. Although imaging is usually not indicated, magnetic resonance imaging (MRI) provides adequate visualization of the optic nerve.

Treatment and Disposition

Ophthalmologic and neurologic consultation should be obtained if optic neuritis is suspected. Approximately 31% of patients with optic neuritis have a recurrence within 10 years of the initial episode.¹³ The goals of treatment are to restore visual acuity and prevent propagation of the underlying disease process. The Optic Neuritis Treatment Trial was a randomized, 15-center clinical trial involving 457 patients that was performed to evaluate both the benefit of corticosteroid treatment of optic neuritis and the relationship of this entity to multiple sclerosis. Use of intravenous steroids in conjunction with oral steroids reduced the short-term risk for the development of multiple sclerosis as determined by MRI evaluation. No long-term immunity from or benefit for multiple sclerosis was reported, however. The study concluded that although intravenous steroids have only minimal, if any effect on the patient’s ultimate visual acuity, they do expedite recovery from optic neuritis. Use of oral steroids alone is associated with a higher recurrence rate of optic neuritis. The dosage regimen recommended on the basis of the study results was methylprednisolone, 250 mg intravenously every 6 hours for 3 days, followed by prednisone, 1 mg/kg/day orally for 11 days.¹⁴

Pathophysiology and Anatomy

The retina has two layers, the inner neuronal layer and the outer pigment epithelial layer (the choroid). Retinal detachment refers to separation of the two layers. Rhegmatogenous retinal detachment, the most common of the three types, is caused by a tear or hole in the neuronal layer, which leads to extrusion of fluid from the vitreous cavity into the potential space between the two retinal layers. It is more common in patients older than 45 years and those with severe myopia. When caused by trauma, this type of detachment can affect any age group. Exudative retinal detachment is caused by leakage of fluid or blood from within the retina itself. Predisposing factors for this type include hypertension, vasculitis, and central retinal venous occlusion. Traction retinal detachment results from the formation and subsequent contraction of fibrous bands in the vitreous.

Presenting Signs and Symptoms

Retinal detachment can occasionally be asymptomatic. More commonly, patients complain of flashes of light, floaters, or fine dots or cobwebs in their visual fields. Generally, a new onset of floaters associated with flashing lights is indicative of retinal detachment unless proved otherwise. Visual acuity correlates with the extent of macular involvement and can be minimally changed to severely decreased. The loss of vision is usually sudden in onset and starts peripherally, with propagation to the central visual field. The visual loss is commonly described as a filmy, cloudy, or curtainlike appearance. Visual field cuts relate to the location of the retinal detachment, and an afferent pupillary defect occurs if the detachment is large enough. Retinal detachment is painless. On examination, the detached retina may appear gray or translucent or may seem out of focus (Fig. 26.5). Retinal folds may be seen. The visual field defects are variable, depending on the involvement of the retina and macula. Bedside ED ultrasonography has been shown to be helpful in confirming the presence of retinal detachment.¹⁵ Left untreated, all cases of retinal detachment progress to involve the macula and result in complete loss of vision in the affected eye.

Fig. 26.5 Retinal detachment.

(Courtesy Ted Montgomery, OD. Available at www.tedmontgomery.com/the_eye/.)

Differential Diagnosis and Medical Decision Making

Vitreous hemorrhage, which results from bleeding into either the preretinal space or the vitreous cavity itself, can be difficult to distinguish from retinal detachment. Complaints with this disorder range from floaters or cobwebs in the visual field to severe, painless loss of vision. Vitreous hemorrhage without concomitant retinal detachment should not, however, cause an afferent pupillary defect. Ophthalmoscopy usually demonstrates discoloration (ranging from reddish to black) with fundal structural details difficult to discern. Therapy for vitreous hemorrhage consists of bed rest with head elevation followed by possible interventional procedures such as laser photocoagulation and cryotherapy.

All macular disorders can cause painless visual loss. They are manifested as loss of central vision with preservation of peripheral vision, as well as findings of retinal abnormalities. A careful history and physical examination can exclude macular degeneration as a cause of central visual loss. Funduscopic examination in individuals with age-related macular degeneration shows the presence of drusen—small, yellow masses scattered on the retina. A gray-green subretinal neovascular membrane may also be seen. Inflammatory processes involving the retina often cause inflammatory proteins to fill the vitreous, thus making it appear cloudy.

Treatment