The choroid is a vital layer of blood vessels and connective tissue located between the retina and the sclera, playing a crucial role in nourishing the outer retina. Diseases affecting the choroid can significantly impact vision, ranging from benign lesions to sight-threatening tumors and genetic disorders. This comprehensive overview of choroidal diseases will explore various conditions, their symptoms, diagnosis, and management, providing a foundational understanding for students.
Understanding Choroidal Nevus: A Benign Lesion
A choroidal nevus is a common, benign pigmented lesion of the choroid, often discovered incidentally during routine eye exams. It's essentially a mole inside the eye, typically posing no threat to vision.
Epidemiology and Characteristics of Choroidal Nevus
Choroidal nevi are quite prevalent, affecting about 5% of the population. They are most common in white individuals and rarely seen in those of African American descent. These lesions typically develop during early life, with growth possible during adolescence and early adulthood. If growth occurs in adulthood, it is highly suspicious for a more serious condition like melanoma. They are usually flat or minimally elevated, never exceeding 2 millimeters in thickness.
Clinical Presentation and Associated Signs
Most choroidal nevi are asymptomatic. Their color can vary, commonly appearing greenish-gray, but also light brown, moderate brown, or even amelanotic (without pigment). Borders can be distinct or indistinct; this feature alone is not reliable for diagnosis. Overlying drusen or RPE pigment clumping are common associated findings, often indicative of a benign nevus.
Differentiating Nevus from Melanoma: Key Diagnostic Criteria
Distinguishing a choroidal nevus from a malignant melanoma is critical. Key features for diagnosis include:
- Size: Nevi typically range from 1-5 millimeters. Anything greater than 5mm is highly suspicious for melanoma.
- Thickness/Elevation: Nevi are usually 1-2 millimeters thick. Greater than 2 millimeters is suspicious.
- Location: While nevi can be anywhere, a lesion greater than 5mm adjacent to the optic nerve is 90% likely to be melanoma.
- Growth: Documented growth in adulthood is a significant indicator of melanoma.
- Associated signs: Drusen and RPE pigment clumping are characteristic of nevi. Orange pigment, subretinal fluid, or intrinsic tumor blood vessels are highly suspicious for melanoma.
Diagnostic Testing and Management of Choroidal Nevus
Various tests help confirm a nevus and differentiate it from other lesions:
- Red-green filter: A green filter does not penetrate the choroid, making choroidal lesions less visible. A red filter penetrates and shows choroidal lesions.
- Fluorescence Angiography (FA): A nevus typically appears hypofluorescent.
- B-scan Ultrasound: Shows a hyper-reflective, flat appearance with no elevation or choroidal excavation (shadowing).
- Photography: Essential for documenting size and characteristics to monitor for any changes over time.
Follow-up for a choroidal nevus is typically every 6-12 months initially, then twice yearly if stable. Any suspicious changes warrant immediate referral to an ocular oncologist.
Choroidal Melanoma: A Malignant Intraocular Tumor
Choroidal melanoma is the most common primary intraocular malignancy in adults, requiring careful diagnosis and management due to its metastatic potential.
Epidemiology and Risk Factors of Choroidal Melanoma
Melanoma has an incidence of about 1 per 2,000 population, predominantly affecting white individuals in middle to late adulthood (35-40 years and older). There is no significant gender predilection. Risk factors include excessive sun exposure (UV radiation), a history of choroidal nevus (as some melanomas can develop from pre-existing nevi), and a family or personal history of skin melanoma.
Clinical Presentation and Key Signs
Melanomas can be asymptomatic or cause decreased visual acuity (if associated with subretinal fluid or detachment) or metamorphopsia. Physical characteristics include:
- Color: Highly variable, from dark grey/green to light brown or amelanotic.
- Size and Thickness: Typically greater than 5 millimeters in size and 2 millimeters in thickness are suspicious. Can be several millimeters thick.
- Shape: Often dome-shaped, but can be flat or