A 62-year-old man with dense nuclear sclerotic cataract presents for preoperative evaluation. He has no ocular comorbidities. Which investigation is most appropriate to determine the best IOL power for optimal postoperative refraction?

Explanation

## Preoperative IOL Power Calculation: Investigation of Choice ### Role of Optical Biometry **Key Point:** Optical biometry (IOLMaster or similar swept-source OCT devices) is the gold standard for IOL power calculation in cataract surgery because it provides the most accurate measurements of axial length, anterior chamber depth, and keratometry. **High-Yield:** Optical biometry is non-contact, faster, and achieves accuracy of ±0.1 mm for axial length — superior to ultrasound A-scan (±0.3 mm). ### When to Use Each Investigation | Investigation | Indication | Limitation | |---|---|---| | **Optical biometry (IOLMaster)** | Clear media, routine cases | Fails if dense cataract blocks signal | | **Ultrasound A-scan** | Dense cataract, posterior segment pathology | Less accurate (±0.3 mm), requires contact | | **Corneal topography** | Astigmatism assessment, toric IOL planning | Does not measure axial length or ACD | | **Retinoscopy** | Refractive error assessment | Does not provide biometric data for IOL calculation | ### Clinical Pearl In this patient with dense nuclear sclerosis, optical biometry may fail due to signal obstruction. The algorithm is: 1. **First attempt:** Optical biometry (IOLMaster) 2. **If fails:** Switch to ultrasound A-scan biometry 3. **Keratometry:** Automated or manual keratometry (or from topography) Since the stem specifies "no ocular comorbidities" and does not mention failure of optical biometry, the investigation of choice remains **optical biometry**. ### Why Not the Others? - **Ultrasound A-scan:** Second-line when optical biometry fails; less accurate - **Corneal topography:** Provides keratometry data only; does not measure axial length - **Retinoscopy:** Assesses refractive error clinically; not a biometric measurement tool **Mnemonic:** **IOL-MASTER** = **I**ntraocular **L**ens **M**easurement **A**ccuracy **S**uperior **T**o **E**chography **R**outinely [cite:Yanoff & Duker Ophthalmology 5e]