Study Notes on Retina and Macula Pathologies

Overview of the Retina and Macula

  • Basic Structure of the Eye

    • The retina is the inner layer of the eye.

    • Contains photosensitive cells: rods and cones.

    • Functions as the most critical component of the eye, converting light into visual images.

    • Other eye structures support the retina's function.

Blood Supply to the Retina

  • Choroid:

    • A vascular layer beneath the retina.

    • Problems can arise if the relationship between the choroid and retina is disrupted.

The Macula

  • Defined as an oval-shaped area near the center of the retina.

  • Fovea:

    • Located at the center of the macula.

    • Contains the highest concentration of cone cells.

    • Essential for high-resolution color vision.

  • Both retina and macula are necessary for normal vision.

Examination Techniques

  • Fundoscopy:

    • Term for examining the back of the eye, specifically the fundus (the back of the eye opposite the lens).

    • Includes inspection of the retina, optic disc, and macula.

    • A normal fundoscopic exam shows clear structures and colors.

    • USMLE Step One typically focuses on recognizing retinal and macular pathologies through fundoscopic findings.

Pathologies of the Retina and Macula

  • Retinitis Pigmentosa:

    • An inherited retinal disorder with various inheritance patterns (autosomal dominant, autosomal recessive, X-linked).

    • Visual loss begins in childhood due to loss of photoreceptors (rods and cones).

    • Symptoms:

    • Night and peripheral vision loss.

    • Progressive constriction of the visual field.

    • Prognosis: Most affected children are legally blind by age 40.

    • Fundoscopic Finding:

    • Intraretinal pigmentation seen as dark spots in a bone-spicule pattern.

  • Retinitis:

    • Actual inflammation of the retina leading to edema and necrosis.

    • Commonly associated with cytomegalovirus (CMV) infection, especially in patients with HIV/AIDS (CD4 count < 50) and immunosuppressed transplant patients.

    • Symptoms:

    • Floaters and vision loss.

    • Fundoscopic Findings:

    • Retinal hemorrhages and a whitish appearance resembling a pizza pie.

  • Diabetic Retinopathy:

    • Retinal pathology resulting from diabetes that can lead to blindness.

    • Linked to degeneration of pericytes; requires routine eye screenings for diabetic patients.

Types of Diabetic Retinopathy

  1. Non-proliferative Retinopathy:

    • Most common form, accounting for about 95% of cases (background retinopathy).

    • Early Signs:

      • Development of microaneurysms (difficult to see).

      • Dot and blot hemorrhages from damaged capillaries.

      • Cotton wool spots caused by nerve infarctions.

    • Hard Exudates and Macular Edema:

      • Yellow fatty lipid exudates; most dangerous due to risk of blindness.

  2. Proliferative Retinopathy:

    • Characterized by neovascularization due to retinal ischemia.

    • New, abnormal blood vessels can lead to detachment and macular edema.

    • Fundoscopic Findings:

      • Proliferation of blood vessels on the retina.

    • Treatment options:

      • Photocoagulation (laser treatment) to stop vessel growth.

      • Vitrectomy to remove bleeding vitreous humor.

      • Anti-VEGF injections (e.g., ranibizumab).

  • Retinal Detachment:

    • Occurs when the retina separates from the underlying choroid.

    • Symptoms:

    • Visual loss described as a curtain being drawn.

    • Surgical emergency; timely reattachment of the retina is crucial.

    • May follow a posterior vitreous membrane detachment (risk factors: myopia, eye surgeries, trauma).

  • Retinal Vein Occlusion:

    • Occurs when veins (central or branch) are obstructed, leading to visual loss.

    • Branch Retinal Vein Occlusion:

    • Caused by compression from sclerotic arterioles at crossings.

    • Central Retinal Vein Occlusion:

    • Often due to thrombotic disorders.

    • Fundoscopic Findings:

    • Engorged veins and hemorrhages with a streaky appearance.

  • Retinal Artery Occlusion:

    • Potentially leads to a cherry red spot on fundoscopy, indicative of a focal phenomenon.

    • Common causes include emboli from the carotid artery or cardiac sources (like atrial fibrillation).

    • Cherry red spots can also appear in Taylor Sachs disease.

  • Papilledema:

    • Not a retinal disorder but an important fundoscopic finding characterized by optic disc swelling due to increased intracranial pressure.

    • Usually results in bilateral effects and blurred optic disc margins.

Disorders of the Macula

  • Macular Degeneration:

    • Age-related condition leading to central vision loss due to degeneration.

    • Distortion of visual fields (metamorphopsia) and creation of central scotomas.

  • Two types:

  1. Dry Macular Degeneration:

    • Accounts for 80% of cases; gradual progression.

    • Characterized by drusen (yellow deposits) between Bruch's membrane and the retinal pigment epithelium.

    • No specific treatment; slow progressive loss of vision.

  2. Wet Macular Degeneration:

    • Occurs from a break in Bruch's membrane; rapid symptoms.

    • Results in hemorrhage under the retina, may be treated with anti-VEGF and laser therapy.