Cataract and Lens
Concept anchors
Classify by morphology: nuclear sclerotic (yellowing, index myopia), cortical (spokes, glare) and posterior subcapsular (rapid glare and near-vision loss, associated with steroid use and diabetes). Biometry with optical methods needs a clear visual axis; use ultrasound for dense cataracts. Modern formulas (Barrett, Hill-RBF) outperform SRK/T in long and short eyes, and post-refractive eyes need prior data.
Surgery and its complications
Know the steps: incision, capsulorhexis, hydrodissection, phacoemulsification, IOL implantation. Risk factors for zonular weakness include pseudoexfoliation, trauma, Marfan syndrome and prior vitrectomy; these predict capsule complications and intraoperative floppy iris syndrome with tamsulosin. Posterior capsule rupture may drop nucleus - manage with vitrectomy and avoid phaco in the vitreous.
Traps
Toxic anterior segment syndrome gives diffuse limbus-to-limbus corneal edema within 12 to 24 hours with a sterile hypopyon; endophthalmitis typically presents 3 to 7 days postoperatively with pain and vitritis, and requires a vitreous tap and intravitreal antibiotics. Intumescent white cataract risks capsular rupture from high intralenticular pressure. Posterior polar cataract has a fragile capsule. Phacomorphic glaucoma and phacolytic glaucoma are distinct mechanisms.
Worked example
Ectopia lentis: a child with a superotemporal lens dislocation and aortic root disease has Marfan syndrome; a child with inferonasal dislocation and intellectual disability should be tested for homocystinuria, where general anesthesia carries thrombotic risk.
Also know
Congenital cataract surgery within the first 6 to 8 weeks is critical for unilateral dense cataract to avoid irreversible amblyopia; aphakia management with contact lens or IOL depends on laterality and age.