Outcome of adjustment of anterior corneal astigmatism values to incorporate the likely effect of posterior corneal curvature for toric IOL calculation

Session Details

Session Title: Corneal Astigmatism Assessment. Surgery Equipment

Session Date/Time: Saturday 05/09/2015 | 11:00-13:00

Paper Time: 11:32

Venue: Main Auditorium

First Author: : S.Caputo AUSTRALIA

Co Author(s): :    M. Goggin   L. van Zyl                 

Abstract Details

Purpose:

To evaluate the refractive outcome of adjustment of corneal astigmatism values to incorporate the likely effect of posterior corneal curvature for toric IOL calculation

Setting:

Publicly funded hospital and university department. The Queen Elizabeth Hospital, Adelaide, South Australia

Methods:

17 consecutive eyes underwent phacoemulsification with toric IOL powers calculated using anterior corneal curvature data adjusted by a nomogram to include the likely effect of posterior corneal curvature and were compared to a consecutive series without adjustment. The effect of posterior corneal curvature is relatively constant and influences the combined anterior and posterior corneal power according to the “rule” of the anterior corneal power. The nomogram is based on observation of outcome in eyes receiving toric IOLs calculated on anterior corneal curvature data alone and suggests a co-efficient of adjustment of 0.75 for WTR eyes and 1.41 for ATR eyes

Results:

Mean absolute error of the power of the refractive astigmatic outcome was reduced by over half from 0.48D (SD 0.43) without adjustment to 0.23D (SD 0.19) with adjustment by the above method (p<0.05).

Conclusions:

To improve outcome prediction a co-efficient of adjustment of 0.75 for WTR eyes and 1.41 for ATR eyes was applied to the corneal astigmatism power value to calculate a more appropriate IOL cylinder power than that calculated by using unadjusted anterior corneal curvature measurements. This lead to a reduction in the mean error of astigmatic power outcome that was both statistically and clinically significant.

Financial Interest:

NONE