cortical cataract

**Definition/Morphology:** Cortical cataract is an opacity in the lens cortex, the outer layer between the capsule and the nucleus. On slit-lamp exam or retroillumination, it appears as white, wedge-shaped or radial spoke-like opacities that start at the periphery and progress centripetally toward the visual axis.

**Pathophysiology:** Disruption of lens fiber integrity and ion homeostasis leads to hydration and then denaturation of lens proteins (crystallins). Altered Na+/K+-ATPase function and membrane permeability cause an electrolyte imbalance (increased intracellular Na+ and Ca2+, decreased K+). The lens cortex swells, fibers rupture, and the lens becomes opaque. Osmotic stress contributes in diabetes: hyperglycemia increases aldose reductase conversion of glucose to sorbitol, which accumulates in lens cells and draws in water (more typical of "snowflake" cataracts in young type 1 diabetics, but chronic diabetes also increases cortical and posterior subcapsular cataracts).

**Risk factors:** Aging, diabetes mellitus, UV-B exposure, and smoking/alcohol (more associated with nuclear). Steroids (especially posterior subcapsular), trauma, uveitis, and radiation are other causes of cataract in general.

**Clinical features:** - Glare, especially with headlights at night, and light scatter - Monocular diplopia (polyopia) - Contrast sensitivity loss - Visual acuity may be well preserved until opacities reach the central axis - Painless, gradual progression

**Comparison of age-related types (high-yield):** - **Nuclear sclerosis:** Most common type. Central yellow-brown hardening. Causes myopic shift ("second sight") and trouble with distance vision. Associated with aging and smoking. - **Cortical:** Spoke-like peripheral opacities. Glare. Associated with diabetes. - **Posterior subcapsular:** Central, posterior plaque-like opacity. Early difficulty reading and in bright light, with glare/halos. Associated with corticosteroids, diabetes, radiation, and inflammation. Progresses fastest.

**Diagnosis:** Slit-lamp exam. Pupillary dilation is needed to see peripheral lens. A red reflex may show dark spokes against the red background.

**Management:** Observation and updated refraction/glare management for mild disease. Definitive treatment is surgery (phacoemulsification with intraocular lens implantation) when visual function impairs daily activities. Complications include posterior capsule opacification (most common late complication), endophthalmitis (rare but serious), and retinal detachment.

**Board pearls:** Know the three types and their associations. Monocular diplopia points to a lens problem rather than a neurologic one. Congenital cataract needs a work-up (galactosemia, rubella, and other TORCH infections), and an absent red reflex (leukocoria) in a child requires urgent evaluation.