Conditions Affecting the Retina for the Physician Assistant Exam
The retina is a multi-layered structure in the eye, with cones, rods, and blood vessels and the Physician Assistant Exam has questions to test your knowledge. A lot of things can affect the retina, including diseases, occlusions, and aging.
Diseases of the retina
Retinopathy is a general term that refers to some form of noninflammatory damage to the retina of the eye. Two of the biggest diseases that can cause retinopathy are hypertension and diabetes mellitus, although there are many others. Cytomegalovirus retinitis is an inflammation of the retina.
The retina is visible through an ophthalmoscope (fundoscope). In someone with a history of diabetes or hypertension, on clinical exam you should take a stab (ouch!) at looking into his or her eyes to check the retina and the blood vessels. With diabetic retinopathy, you see hemorrhages as well as cotton-wool exudates. As for hypertensive retinopathy, there are four stages:
Stage I: Narrowing of the arterioles, often named silver wiring
Stage II: More arteriovenous narrowing
Stage III: Hemorrhages; on an eye exam, you can see cotton-wool exudates
Stage IV: Papilledema
The stages of hypertensive retinopathy don’t always progress from I through IV. For example, someone who’s admitted to the hospital with a new onset hypertensive emergency may exhibit papilledema (Stage IV) without having the other stages.
In advanced retinopathy, blood vessels become fragile and can rupture. The treatment of choice is usually laser photocoagulation surgery.
The retina is a multi-layered structure. The retina can detach from its support network. Symptoms can include having a loss of central vision or seeing floaters (little specs of debris within the eye’s vitreous humor, which is normally transparent). Note that although floaters may be indicative of retinal detachment, often they’re not. The degree of vision loss and other symptoms depends on how much of the retina is detached.
Risk factors for retinal detachment include being nearsighted, a history of eye trauma, or cataract surgery. Inflammation of the uvea (uveitis) and conditions such as diabetic retinopathy can predispose someone to retinal detachment. Retinal detachment needs to be treated urgently.
Retinal vascular occlusions
The first of the retinal vascular occlusions is occlusion of the retinal artery, which causes vision loss. If the central retinal artery becomes acutely blocked, the person experiences a painless, total loss of vision in the affected eye.
If a branch retinal artery is blocked, the person experiences only a partial loss of vision in that eye. The eye exam will include a pupillary defect and, on fundoscopic exam, a pale fundus with a cherry red spot near the fovea.
Be aware of risk factors for this occlusion. Emboli from either a clogged carotid artery or a clot in the left atrium from atrial fibrillation are leading causes. Giant cell arteritis (also known as temporal arteritis) is another huge risk factor.
The key in treatment is looking for the underlying cause. Often an ophthamologist is consulted, but there’s no magic bullet to make retinal vascular occlusions better. Sometimes the vision loss is permanent. Panretinal photocoagulation (PRP) with an argon laser may be effective.
Not only can the retinal arteries become occluded, but so can the retinal veins. Hypertension and diabetes are risk factors. The presentation can be similar to a retinal artery occlusion: a loss of vision. The occlusion may be in a central or branch retinal vein. Here are the key points:
Experts think that atherosclerosis and a low blood flow state contribute to the formation of a small clot within the vein, more so than this being an embolic phenomenon.
When the retinal vein is blocked, the macula swells, leading to an increase in ocular pressure. A form of acute glaucoma can result due to the buildup of intraocular pressure. After all, the vein is the sole source of drainage for the retina.
Part of the workup for a central venous occlusion is looking for a hypercoagulable state, given the thrombus formation. The treatment is similar to treatment of arterial occlusion: laser photocoagulation.
Age-related macular degeneration (AMD) is the leading cause of adult blindness in industrialized countries. The main clinical symptom is loss of central vision with sparing of peripheral vision. When the macula (the central portion of the retina) degenerates, the main portion of the retina is essentially knocked out, so the person has no more central vision.
Macular degeneration may be dry or wet (exudative). The wet version is a more severe form, although it accounts for only 10 to 15 percent of cases. Both forms can lead to detachment of the retina if left untreated.
Researchers think that the pathogenesis of macular degeneration is related to significant deposition of cholesterol deposits, called drusen. You can see these yellow flecks on a fundoscopic (ophtalmoscopic) examination.
The main treatment for the wet type of macular degeneration is injections of angiogenesis inhibitors, such as bevacizumab (Avastin) and aflibercept. Effective specific therapies are intravitreous injection of a VEGF inhibitor, possibly thermal laser photocoagulation (in selected patients), and photodynamic therapy.
For the dry form, the use of antioxidants and certain minerals, including a combination of zinc, vitamin C, vitamin B6, and/or beta carotene, can be beneficial. Laser coagulation may also help improve the condition and prevent further loss of vision in someone with dry macular degeneration.