retinal disease

Optometrist's Guide to Retinal Diseases

As primary-care providers, it is critical to gain a clearer understanding of posterior segment disease.

BY DEEPAK GUPTA, O.D., F.A.A.O., Stamford, Conn.

As primary-care optometrists, many of us see patients with retinal disease. In this article, I'll review the essentials of the frequently encountered retinal diseases and what to do about them.

Age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of legal blindness in this country. In my practice, one of the most common questions elderly patients ask is whether they have any signs of AMD. After many decades of extensive research, we still don't know the exact etiology of AMD. Clinically, we separate this condition into two subtypes: dry (i.e., non-neovascular) and wet (i.e., neovascular). Patients with the dry form usually exhibit drusen and macular pigmentary changes in the absence of choroidal neovascularization (CNV). The presence of CNV is a common indicator for wet AMD. Although both forms may result in poor vision, wet AMD carries a poorer prognosis than dry AMD and often demonstrates a faster rate of vision loss.

AMD is technically defined as an acquired macular disorder affecting patients 50 years of age. The dry form is characterized by drusen more than 63 μm in diameter. Early clinical signs of the dry form include drusen and macular pigmentary changes.

The wet form of AMD more often demonstrates pigment epithelial and sensory retinal detachment, exudates, hemorrhage and subretinal scarring — all of which result from choroidal neovascularization. Although these signs are easy to detect in text books, they can be difficult to visualize in our patients who have AMD. In many cases, clinicians view these signs with a fundus contact lens. In recent years, it has become commonplace to order fundus photography on these patients. The high-resolution and quality of modern day cameras often aids in patient monitoring and provides a baseline for future comparisons. If you suspect CNV, refer the patient for fluorescein angiography (FA) to help confirm your diagnosis. In addition, FA also helps direct possible treatments and provides a baseline against which to monitor the clinical course.

AMD treatment

Although the end result of dry AMD can be legal blindness for many patients, we still do not have any tangible treatment options. Current management options are aimed at monitoring for the development of CNV through regular dilated fundus examinations and the use of a home monocular Amsler grid. In 2001, the Age-Related Eye Disease Study (AREDS) found that patients with dry AMD taking daily dietary supplements of vitamins A and C, beta-carotene, and zinc were 25% less likely to convert to wet AMD.¹ This study alone was sufficient for many clinicians to recommend vitamin supplements to those patients who are either at high risk for developing AMD or those who have early signs of AMD.

In 2000, a new development in the treatment of AMD was offered in the form of photodynamic therapy (PDT). This procedure featured a major advantage over others in that it reduces concomitant retinal damage. In PDT, a photosensitizing dye is injected prior to laser treatment. This dye, selectively taken up by CNV, absorbs the laser energy, which then spares the overlying retina from damage. The major problem with PDT is that it only serves to slow the progression of vision loss. Rarely is vision regained or progression halted.

Anti-VEGF treatment

The most recent innovations in wet AMD management feature Anti-VEGF (vascular endothelial growth factor) treatment. The glycoprotein VEGF is a powerful regulator of angiogenesis through its effects on vascular endothelium. By targeting this molecule, the goal of anti-VEGF treatment in AMD is to stop and reverse some of the damage. The options for anti-VEGF treatment include pegaptanib (Macugen, Pfizer), the off-label use of bevacizumab (Avastin, Genentech) and ranibizumab (Lucentis, Genentech). In clinical trials, Lucentis, a lower-molecular weight derivative of Avastin, was found to improve visual acuity at 12 months in 34% of treated patients.² This effect persisted for an additional year. Even though Avastin is not FDA-approved for AMD (it is approved as a treatment for colorectal cancer), it is still widely used in this role primarily due to cost — a single dose of Lucentis currently costs about $2,000, whereas a dose of Avastin costs about $100 to $200. The National Eye Institute is sponsoring a multicenter clinical trial to compare these two medications.³

Diabetic retinopathy

Many of our patients suffer from diabetes mellitus (DM), and some of them will develop diabetic retinopathy. In most cases, it's more common in patients with uncontrolled diabetes or in those who have long-standing diabetes. It can affect persons with either Type I or Type II DM. Almost all patients with Type 1 diabetes — Insulin dependent diabetes mellitus (IDDM) — after 20 years will develop some degree of diabetic retinopathy (DR).

The classic fundus signs of diabetic retinopathy include microaneurysms, dot-and-blot intraretinal hemorrhages and hard exudates. Many patients also demonstrate cotton-wool spots, intraretinal micro-vascular abnormalities (IRMA), neovascularization of the disc (NVD), neovascularization elsewhere (NVE) and diabetic macular edema. In most cases, the loss of visual acuity from diabetic retinopathy comes from non-resolving vitreous hemorrhage, fibrovascular tissue growth leading to traction retinal detachment, and diabetic macular edema and macular nonperfusion.

Some patients with advanced disease may develop severe non-proliferative diabetic retinopathy (NPDR), which is characterized by vascular tortuosity, intraretinal microvascular abnormalities, hemorrhage, venous beading and cotton wool spots. These patients may benefit from panretinal photocoagulation, which works by destroying the ischemic retina and preventing the onset of proliferative disease.

If left untreated, patients with NPDR can develop neovascularization of the disc and retina. Hemorrhage with eventual fibrosis and traction retinal detachment may occur. This type of disease may lead to profound vision loss.

DR treatment

As a primary-care optometrist, your underlying management is to prevent or minimize diabetic retinopathy in all diabetic patients via sufficient control of blood glucose levels and proper control of blood pressure and blood lipids. Proper interaction with the patient's primarycare physician should include a report of ocular finds at every visit.

In terms of ocular complications, proper management of diabetic retinopathy can range from periodic patient monitoring to immediate referral to a specialist for surgical intervention. The proper guidelines as to what to do with these patients is heavily dependent on the stage of the disease. Unfortunately, we do not have any means to prevent or cure diabetic retinopathy. Proper ocular examination of the diabetic patients requires careful attention to best-corrected visual acuity, pupil abnormalities, extraocular muscle movement, the presence of rubeosis iridis and any presence of cataracts. In general, all patients with diabetes mellitus should be dilated annually and undergo periodic fundus photography. They should also all be routinely monitored for the development of glaucoma, as patients who have diabetes also have a higher chance of developing glaucoma. In cases in which the blood sugar is poorly controlled or the patient exhibits signs of ocular abnormalities, more frequent examination may be necessary.

Papilledema

While the patient's vision is usually not affected by papilledema (although seconds-long graying out of vision, flickering, or blurred or double vision may occur), fundus examination will reveal bilateral swelling of the optic disc due to increased intracranial pressure. Careful examination will reveal blurred optic disc margins, microvascular congestion, retinal vein dilation and flame-shaped hemorrhages. If the intracranial pressure has been chronically elevated, the optic disc appears gray-white with constricted blood vessels. This is a condition which warrants prompt referral to a neuro-ophthalmologist to assess the etiology of increased intracranial pressure. The pressure may be caused by brain tumor, cerebral trauma or hemorrhage, arachnoidal adhesions, thrombosis, encephalitis, meningitis or idiopathic intracranial hypertension. The underlying cause of the papilledema will dictate treatment and prognosis.

Optic neuritis

The typical patient for this condition is a woman in her 30s or 40s. The chief complaint will be of decreased vision through the past couple of days or weeks. Clinical examination will reveal decreased color vision, pain on palpation or movement of the eyes, relative afferent papillary defects and visual field defects. Fundus examination will demonstrate a swollen and hyperemic optic disc. These patients should be referred to a neuro-ophthalmologist for additional testing, including an MRI. Many of these patients will be given a high-dose I.V. or retrobulbar corticosteroids, which may shorten the disease course. These patients should all be worked up for multiple sclerosis, which has a strong association with this condition.

Central retinal artery occlusion

The classic patient who has central retinal artery occlusion (CRAO) is a patient age 50 or older who complains of sudden, painless vision loss. Many of these patients confirm a history of previous, transient vision loss. During the first few hours after the event, retinal exam will demonstrate a narrowing of arterial columns and interruption of venous columns. Within hours after the event, however, the clinical appearance changes to the retina becoming opalescent with a loss of normal transparency. This so-called "cherry-red spot" of the fovea is a classic finding of CRAO. This condition is a true ocular emergency. In many cases, quick action may save a patient from total vision loss. Fast restoration of blood flow by paracentesis of the anterior chamber or ocular massage to dislodge the embolus is warranted. Do this by compressing the eye with the heel of the hand — 10 seconds on and 10 seconds off — for five minutes. These patients should be sent to the nearest retinologist at once.

Branch retinal artery occlusion

Branch retinal artery occlusion (BRAO) follows the same basic concept as CRAO except that it only involves occlusion of a branch of the central retinal artery. Thus, only part of the retina opacifies and the accompanying visual field defect is more localized. BRAO is commonly associated with an embolus and usually warrants an examination by the patient's primary medical doctor. If visual acuity is affected or an embolus is seen on fundus examination, ocular massage should be attempted and immediate consultation sought with a retinal specialist.

Central retinal vein occlusion

Dilated fundus exam of the patient who has central retinal vein occlusion (CRVO) will demonstrate a combination of disc swelling, venous engorgement, cotton wool spots and diffuse retinal hemorrhages. Vision loss from a CRVO will vary depending on the degree of associated ischemia, hemorrhage and edema. This condition is most common in elderly patients with a medical history of hypertension and arteriosclerosis. These patients need a general medical evaluation and follow-up with a retina specialist. These patients are also at high risk for developing neovascular glaucoma.

Branch retinal vein occlusion

Patients complain of sudden, unilateral vision loss in one particular part of their visual field. Retinal exam will demonstrate segmentally distributed intraretinal hemorrhage. A small percentage of patients will develop retinal neovascularization. If so, they may benefit from laser photocoagulation to the ischemic retina.

As primary care optometrists, we play an integral part of the patient's health care team. Nowhere is this more evident than in patients with retinal disease. In many cases, these patients require management with retinal specialists.

In a good percentage of patients, the patient's retinal disease is a manifestation of a systemic condition and requires coordination with their primary care physicians. In all cases, proper documentation of findings, additional testing, and interaction with other healthcare providers should be maintained. In many cases, these patients should undergo fundus photography to help monitor their condition for signs of change. OM

References available upon request.

Dr. Gupta practices in Stamford, Conn. He's also clinical director of The Center for Keratoconus at Stamford Ophthalmology. E-mail him at Deegup4919@hotmail.com.