A 68-year-old man undergoes phacoemulsification for dense nuclear sclerotic cataract. During surgery, the posterior capsule ruptures. Which is the most common intraocular lens (IOL) power calculation formula error that occurs when posterior capsule rupture happens during cataract surgery?

Explanation

## IOL Power Calculation and Posterior Capsule Rupture ### Mechanism of Refractive Error After PCR **Key Point:** When posterior capsule rupture (PCR) occurs, the IOL is typically placed in the sulcus rather than the capsular bag. The sulcus is **anterior** to the capsular bag, meaning the actual IOL position is more anterior than the position predicted by standard IOL power formulas. **High-Yield:** Standard IOL power formulas (SRK/T, Holladay 1, Haigis, Barrett Universal II) predict the **Effective Lens Position (ELP)** assuming in-the-bag placement. When the IOL ends up in the sulcus, the formula **underestimates** the ELP (i.e., the formula predicted a more posterior position than actually occurs — but the IOL is actually placed more anteriorly, so the formula's assumed ELP is *larger* than the actual ELP). ### Effect on Refraction | Factor | Effect | |--------|--------| | **Sulcus placement (anterior to bag)** | Actual ELP is shorter than formula-predicted ELP | | **Formula underestimates actual anterior shift** | IOL behaves as if it has more effective power | | **More effective power than calculated** | **Myopic shift** postoperatively | | **Clinical outcome** | Patient becomes myopic after surgery | ### Why Underestimation of ELP Leads to Myopic Shift When the IOL sits more anteriorly than the formula assumed: 1. The formula calculated power for a more posterior (bag) position 2. The IOL actually sits closer to the cornea (sulcus) 3. A lens placed more anteriorly in the eye has a greater effective vergence-reducing effect on incoming light 4. The focal point falls **in front of** the retina → **myopia** **Clinical Pearl:** This is why surgeons reduce IOL power by **0.5–1.0 D** when sulcus placement is anticipated after PCR — to compensate for the myopic shift caused by the more anterior position (per Gimbel's adjustment and standard teaching in Kanski's Clinical Ophthalmology). **Mnemonic:** **SULCUS = SHORTER ELP = FORMULA UNDERESTIMATES ELP = MYOPIC SHIFT** ### Management - Recognize sulcus placement intraoperatively - Reduce IOL power by ~0.5–1.0 D if sulcus placement is planned - Postoperative myopia may require spectacle or contact lens correction - Consider IOL exchange if significant refractive error persists *Reference: Kanski's Clinical Ophthalmology, 9th ed.; Gimbel HV et al., sulcus IOL power adjustment guidelines.*