Introduction of a new specular reflection technique to measure total corneal astigmatism

Session Details

Session Title: Special Cases

Session Date/Time: Sunday 14/09/2014 | 14:30-16:00

Paper Time: 15:00

Venue: Boulevard B

First Author: : S.Klijn THE NETHERLANDS

Co Author(s): :    E. Irazabal   D. de Brouwere   N. Reus   A. Sicam     

Abstract Details

Purpose:

To present measurement of specular reflections of the front and back surface of the cornea as a potential new technique to measuring total corneal astigmatism.

Setting:

The Rotterdam Eye Hospital, Rotterdam, The Netherlands

Methods:

Seven pseudophakic eyes of 6 patients were measured with the Cassini corneal topographer (i-Optics, The Hague, The Netherlands). Steepest and flattest curvatures and corresponding meridians of the corneal front surface were calculated based on specular reflection measurements of 679 colored light-emitting diodes (LEDs). Curvatures and meridians of the corneal back surface were calculated based on specular reflection measurements of 5 infrared LEDs. Total corneal astigmatism was then calculated with ray tracing using the front and back corneal measurements and the true refractive indices of cornea and aqueous (1.376 and 1.336, respectively). For comparison, we also calculated “effective” corneal astigmatism based on only the front corneal measurements and a keratometric index of 1.3375.

Results:

The magnitude of total corneal astigmatism ranged from 0.78 to 2.73 D. The magnitude of the vector difference between total corneal astigmatism and “effective” corneal astigmatism ranged from 0.30 to 0.99 D.

Conclusions:

In clinical practice, the front and back surface of the cornea can be measured with Scheimpflug technology. Knowing total corneal power may be advantageous in intraocular lens power calculations, especially after laser-refractive surgery. We have presented a new technique that uses specular reflection to obtain measurements of corneal front and back surface. A possible advantage of this technique compared to Scheimpflug imaging is that measurements of reflections are instantaneous and thus may be less susceptible to eye movements.

Financial Interest:

One or more of the authors... is employed by a forNONEprofit company with an interest in the subject of the presentation