Cataract and Refractive Surgery
Core concepts
Understand cataract grading, indications for surgery (visual function, not just density), and biometry. Know the difference between axial length measurement methods and when to use immersion or optical biometry. Master IOL power calculation concepts: SRK/T for average eyes, and the traps of prior myopic LASIK (use history-based or intraoperative aberrometry because standard formulas overestimate power). Know the complications: endophthalmitis (rare, presents days after surgery with pain and hypopyon), retained lens fragments, posterior capsule opacification (treated with Nd:YAG), and cystoid macular edema. For refractive surgery, know PRK versus LASIK (flap complications in LASIK, haze in PRK), and the contraindications: unstable refraction, keratoconus, severe dry eye.
Traps
Questions test whether you know that a dense cataract can coexist with good acuity in bright light (nuclear sclerosis causes glare). Another trap: distinguishing endophthalmitis from toxic anterior segment syndrome (TASS) - TASS presents within 24 hours, is sterile, and responds to steroids, while endophthalmitis is later and needs intravitreal antibiotics. Also know that pseudoexfoliation increases risk of zonular weakness and capsular complications.
Worked example / rule of thumb
A patient with prior myopic LASIK needs cataract surgery. Standard keratometry overestimates corneal power, so standard IOL formulas underpredict IOL power and leave the patient hyperopic. Use the history method or intraoperative aberrometry. Rule of thumb: for post-refractive eyes, do not trust standard formulas; use measured or historical data.