posterior subcapsular cataract

**Definition:** Opacification of the posterior cortex of the lens, directly under the posterior capsule. Appears as a granular or plaque-like, "breadcrumb" or "bread-crumb"-like opacity on slit-lamp exam, often best seen with retroillumination.

**Pathophysiology:** Epithelial cells at the lens equator normally migrate posteriorly and differentiate into lens fibers. In PSC, these cells migrate aberrantly toward the posterior pole and undergo abnormal swelling and enlargement (Wedl cells or bladder cells). This produces light-scattering opacities. Oxidative damage and disrupted lens fiber organization contribute. Corticosteroids are thought to form covalent adducts with lens proteins and disrupt lens epithelial cell homeostasis.

**Risk factors / key associations (high-yield):** - Chronic systemic, inhaled, topical, or periocular corticosteroids (classic board association) - Diabetes mellitus - Chronic uveitis or other intraocular inflammation - Ionizing radiation (ocular or head and neck radiotherapy) - Ocular trauma - Retinitis pigmentosa - Aging (can also occur in age-related cataract) - Smoking, myopia

**Cataract type comparison:** - Nuclear sclerosis: most common type. It causes myopic shift ("second sight") and brunescence. - Cortical: spoke-like or wedge-shaped peripheral opacities. It causes glare. It is associated with diabetes. - Posterior subcapsular: steroids, diabetes, radiation, and uveitis. It progresses faster than the other types. - Others: congenital (galactosemia, rubella, and other TORCH infections), "snowflake" (diabetes), sunflower (Wilson disease, chalcosis), and "Christmas tree" (myotonic dystrophy).

**Clinical presentation:** - Glare and halos, especially at night with oncoming headlights - Marked difficulty in bright light, since miosis places the opacity directly in the visual axis - Reduced near vision (reading) is worse than distance vision, often early in the course - Relatively fast progression compared with nuclear or cortical cataracts - Painless, gradual vision loss - Decreased red reflex or a dark opacity against the red reflex

**Diagnosis:** Slit-lamp exam after pupil dilation. Visual acuity testing, with glare testing if needed.

**Management:** - Address the underlying cause when possible (minimize or taper steroids, control glucose, treat uveitis). - Early symptoms can be managed with glasses, anti-glare lenses, and better lighting. - Definitive treatment is surgery: phacoemulsification with intraocular lens (IOL) implantation when vision impairment affects function. - Complication to know: posterior capsule opacification (a "secondary cataract") can occur after surgery and is treated with Nd:YAG laser capsulotomy.

**Boards pearl:** A patient on long-term prednisone (for example, for asthma, RA, or SLE) who has trouble reading and glare in bright light likely has a posterior subcapsular cataract. Remember that steroids also cause glaucoma (raised IOP).