nuclear cataract

**Definition:** Opacification of the central lens nucleus due to progressive sclerosis and yellow-brown discoloration. It is the most common form of age-related (senile) cataract.

**Pathophysiology:** - Lens fibers are laid down throughout life, and older cells are compacted centrally into the nucleus without being shed. - With aging, lens proteins (crystallins) undergo oxidation, cross-linking, aggregation, and glycation. This increases light scattering and produces yellow-brown chromophores (nuclear sclerosis). - Oxidative stress is the main driver. Smoking and UV exposure increase risk. - Increased nuclear refractive index causes a myopic shift (index myopia).

**Clinical features:** - Gradual, painless, bilateral (often asymmetric) vision loss. - Worse distance vision than near vision early on. - "Second sight" (improved near vision without reading glasses) from the myopic shift. - Glare, reduced contrast sensitivity, monocular diplopia, and difficulty with night driving. - Diminished or absent red reflex. On slit lamp, a yellow-brown central opacity (brunescent in advanced cases).

**Risk factors:** Age (most important), smoking, UV-B exposure, diabetes, corticosteroid use, alcohol, and a family history.

**Comparison with other cataract types (high-yield):** - **Cortical:** Spokelike peripheral opacities, causing glare. Associated with diabetes. - **Posterior subcapsular:** Causes early glare and reading difficulty, and affects vision in bright light (miosis). Associated with corticosteroids, diabetes, radiation, and uveitis. - **Diabetic ("snowflake"):** Sorbitol accumulation via aldose reductase causes osmotic swelling. - **Galactosemia:** Galactitol accumulation produces "oil droplet" cataracts. - **Congenital:** Check for rubella, galactosemia, and other causes, and test for leukocoria.

**Diagnosis:** Clinical, by dilated slit-lamp examination and a red reflex exam.

**Management:** - Early on, use updated glasses prescriptions, brighter lighting, and glare reduction. - Definitive treatment is surgery (phacoemulsification with posterior chamber intraocular lens implantation) when visual impairment affects function. - Complications of surgery include posterior capsule opacification (the most common late complication, treated with Nd:YAG laser capsulotomy), endophthalmitis, retinal detachment, and cystoid macular edema.

**Boards pearls:** The classic vignette describes an older patient with gradual blurry distance vision who now reads without glasses ("second sight"). Cataracts are the leading cause of reversible blindness worldwide.