Specific toric IOL power formulas for keratoconus patients improve their outcomes

This retrospective case series study analyzed visual and refractive outcomes in patients with keratoconus undergoing cataract surgery with a toric IOL implantation. Investigators compared IOL prediction accuracy between newer keratoconus-adjusted formulas and several conventional formulas.

Study design

A total of 23 patients (32 eyes) with keratoconus underwent cataract surgery with toric IOL implantation at a single center in Israel during an 8-year period. Topography was used to confirm the diagnosis of keratoconus, and only eyes with a regular central pattern and high agreement of multiple astigmatism measurements were included. Postoperative refraction outcomes were compared to predictions from a range of formulas: the Barrett Universal II, Barrett True-K for keratoconus with corrected predicted posterior corneal astigmatism (PCA), Barrett True-K for keratoconus with measured PCA, Kane, Kane keratoconus, SRK/T, Haigis, Holladay 1, and Hoffer Q.

Outcomes

In this set of eyes, the Barrett True-K formulas with measured and predicted PCA were the most accurate and had the lowest standard deviations. The other formulas led to hyperopic outcomes. The Barrett True-K formula with measured PCA had the highest percentage of eyes within 0.5 D of the target, but was not statistically significantly superior to the True-K with predicted PCA. Mean subjective astigmatism declined from 2.95 D preoperatively to 0.95 D postoperatively.

Limitations

Five different toric IOL models were used, and the number of patients and eyes was small. Another potential weakness of the study design is its retrospective nature. This does address IOL cylinder power selection.

Clinical significance

Using newer, keratoconus-specific formulas can improve spherical IOL power calculation in eyes with keratoconus. The use of conventional formulas generally result in a hyperopic result.