Standard K values recommended for cataract surgery in severe keratoconus

This retrospective study found that for eyes with severe keratoconus undergoing cataract surgery, the use of standard K values should be considered since the use of actual K values can result in a large hyperopic error.

The authors reviewed the records of 64 consecutive keratoconus patients (92 eyes) who underwent cataract surgery with spherical IOL implantation at one hospital in the United Kingdom between 1996 and 2010. Thirty-five eyes had mild keratoconus (mean K < 48 D), 40 had moderate keratoconus (mean K 48 D to 55 D) and 17 had severe keratoconus (mean K > 55 D).

Actual K values were used in eyes with mild or moderate keratoconus with a target refraction of approximately −1.0 D in mild keratoconus and −1.5 D in moderate keratoconus that resulted in a mean biometry prediction error of 0.0 D and +0.3 D, respectively.

Actual K values were used in eight of the 17 eyes with severe keratoconus with a mean target refraction of −5.4 D, which resulted in a mean prediction error of +6.8 D. In the remaining nine severe keratoconic eyes, a standard K value of 43.25 D was used with a mean target refraction of −1.8 D, which resulted in a mean prediction error of +0.6 D.

They conclude that in patients with advanced keratoconus who are likely to return to wearing a rigid contact lens after cataract surgery, the use of standard K values (43.25 D) may be a better option than using the measured K values.