A 40-year-old woman who underwent myopic LASIK ten years ago (pre-LASIK keratometry 44.5 D, current simulated K reading 38.0 D) is listed for cataract surgery. If the surgeon uses a standard modern generation formula with the current post-LASIK keratometry value alone, what error will result?
- A Underestimated IOL power producing a myopic surprise ✓
- B Overestimated IOL power producing a hyperopic surprise
- C Accurate result because current keratometry reflects the true corneal power
- D Error only if the patient was hyperopic before LASIK
Correct answer: A. Underestimated IOL power producing a myopic surprise
Explanation
After myopic excimer surgery the anterior corneal curvature flattens disproportionately relative to the posterior surface, and standard formulas using the altered simulated K underestimate the effective corneal power contribution, selecting too low an IOL power and leaving a myopic refractive surprise. Double-K formulas such as Barrett True-K or the Haigis-L correct this by estimating the pre-refractive K. Hyperopic LASIK produces the opposite direction of error.
Reference: Kanski's Clinical Ophthalmology, 9th ed.
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Written and medically reviewed by the StethoPrep medical team.