The correlation between anterior and total corneal astigmatism and its use in toric IOL calculation

Session Details

Session Title: Pseudophakic IOLs: Toric I

Session Date/Time: Saturday 10/09/2016 | 16:00-18:00

Paper Time: 16:00

Venue: Hall C2

First Author: : K.Næser DENMARK

Co Author(s): :    G. Savini   J. Bregnhoj                 

Abstract Details

Purpose:

To measure the posterior corneal astigmatism and to establish models for describing the total corneal astigmatism from the anterior corneal astigmatism in 951 eyes, measured with a Pentacam rotating Scheimpflug camera. To examine the error of using such keratometric models, rather than total corneal astigmatism, in toric IOL calculation.

Setting:

Department of Ophthalmology, Randers Regional Department, Denmark

Methods:

We measured the anterior corneal astigmatism (using an optimized keratometric refractive index = 1.3324), the posterior corneal astigmatism, and the total corneal astigmatism in 951 normal eyes. The total corneal astigmatism was described as the meridional and torsional polar values along the steeper anterior corneal meridian. Prediction models were evaluated by the determination coefficient (r2) between the model and the measured total corneal meridional value. The error of the method was defined as the polar value difference between the measured and the predicted total corneal astigmatism.

Results:

The nominal astigmatisms for the keratometric astigmatism, the total corneal astigmatism, and the posterior corneal astigmatism averaged 1.05 (± 0.85) D, 1.05 (±0.83) D, and 0.33 (±0.17) D. The best linear regression model to predict the total corneal astigmatism was based on the keratometric astigmatism in combination with the angular direction of the steeper anterior corneal astigmatism (r2 = 0.96). The error of this method averaged zero (SD= ± 0.21; range -0.77 to 0.83 D) for the meridional, and -0.03 D (SD = ±0.20 ; range -0.89 to 0.70 D) for the torsional value.

Conclusions:

Corneal biometry prior to toric IOL insertion should preferentially be based on the total corneal power. However, the error of using only the anterior corneal astigmatism may be minimized by suitable models and optimized keratometric refractive indices.

Financial Disclosure:

NONE