Refractive Surprise After Cataract Operation On An Extremely Advanced Keratoconus

We present a case of severe corneal irregularity due to advanced keratoconus and coexisting cataract in a long-term scleral lens wearer. The patient experienced a progressive visual decline, prompting the decision to proceed with cataract surgery. However, the extreme corneal steepness made IOL power calculation highly complex, ultimately leading to a significant refractive surprise postoperatively. This case underscores the challenges of cataract surgery in keratoconus and highlights the critical role of contact lens parameters in determining IOL power and postoperative visual outcomes.

ELZA Institute, Zurich, Switzerland.

A 50-year-old female with advanced keratoconus (Kmax >90 diopters) presented with bilateral cataracts. Her CDVA with scleral lenses was 0.32 and 0.40, while uncorrected vision was limited to hand motion in 1m. To determine IOL power, multiple formulas were applied, supplemented by manufacturer-assisted analysis. The selected IOLs were +10 D (OD) and +3 D (OS). Postoperatively, the patient continued to require scleral lenses for functional vision. However, due to the power of the IOLs chosen, the scleral lenses required +16.0 D of correction, making them three times thicker than her previous lenses. This increased central thickness reduced oxygen permeability, raising concerns about long-term corneal hypoxia.

The primary cause for this unexpected refractive outcome was a mismatch between the keratometric (K) values used for IOL calculations (Kmean ≈ 75 D) and the significantly flatter scleral lens base curve (6.70 mm radius, ≈ 50 D). This led to an underestimation of IOL power. In cataract surgery for keratoconus patients requiring rigid contact lenses postoperatively, incorporating the contact lens base curve into IOL power calculations is crucial. Overly steep corneal K-readings alone can cause refractive surprises. Comparing IOL calculations using both corneal and contact lens parameters helps achieve a more predictable outcome.