Optimising Intraocular Lens Power Calculations In Eyes With Zonulysis

To evaluate intraocular lens (IOL) power calculations in eyes with zonulysis where anterior chamber depth (ACD) and lens thickness (LT) may be non-physiological from lens subluxation.

Retrospective study of eyes that underwent surgery in Tan Tock Seng Hospital, Singapore.

Retrospective study of 41 eyes that underwent cataract surgery with capsular tension segment fixation. Formulae compared include Barrett Universal II (BUII), EVO, Hoffer Q, Holladay I and SRK/T. BUII and EVO were evaluated using all biometric parameters, axial length (AL) and keratometry (K), AL, K and ACD, and AL, K and arbitrary ACD of 2.5mm. Predicted refraction was subtracted from post-operative refraction to obtain prediction error (PE). Mean PE, standard deviation, mean absolute error (MAE), median absolute error (MedAE) and percentages of eyes with 0.25D, 0.50D, 0.75D and 1.00D were compared.

All formulae achieved >90% of eyes within 1.00D. BUII (all parameters), BUII (AL+K), BUII (AL+K+ACD2.5), EVO (AL+K) and EVO (AL+K+ACD2.5) achieved >70% of eyes within 0.50D. EVO (AL+K) had the lowest MAE (0.370) and MedAE (0.244). Hoffer Q had the highest MAE (0.464) and MedAE (0.428). All versions of BUII and EVO, except EVO (all parameters), had a lower MAE than traditional formulae. BUII performed best when AL+K+ACD2.5 was used. EVO performed best when AL+K was used. Both BUII and EVO showed more hyperopic results when ACD was used (all parameters or AL+K+ACD) compared to when it was not used (AL+K and AL+K+2.5ACD). When ACD was used, BUII and EVO showed a hyperopic and myopic error tendency in shallow and deep ACD respectively.

Overall, modern formulae outperformed traditional formulae in eyes with zonulysis. EVO(AL+K) followed by BUII(AL+K+ACD2.5) were the most accurate formulae. EVO performed best when with AL and K only, and was the most accurate formula overall. BUII was most accurate with AL + K and an arbitrary ACD of 2.5mm.