Posters

Distribution of angle kappa in a preoperative population of myopic, hyperopic and emmetropic patients

Poster Details

First Author: E.Rowe UK

Co Author(s):    D. Reinstein   M. Gobbe   T. Archer        

Abstract Details

Purpose:

To report the distribution of angle kappa in a population of pre-refractive surgery patients

Setting:

London Vision Clinic, London, UK

Methods:

This was a retrospective study of consecutive eyes suitable for corneal laser eye surgery examined at the London Vision Clinic between January 2006 and May 2006, where a preoperative Orbscan (Bausch and Lomb) measurement was available. The eyes were divided in 3 groups based on their manifest refraction spherical equivalent (SEQ). Eyes with -0.25 ≤ SEQ ≤ +0.50D and with astigmatism ≤ 1D were included in the emmetropic group. Eyes with SEQ ≤ -0.50D and no mixed astigmatism were included in the myopic group and eyes with SEQ > +0.50D and no mixed astigmatism were included in the hyperopic group. Angle kappa was measured with the Orbscan II software using two different methods: the value of the angle kappa (in degrees) automatically output by the software was recorded and the pupil offset defined as the distance (in millimetres) in the corneal plane between the corneal vertex and the pupil centre was manually measured.

Results:

A total of 372 eyes met the inclusion criteria: 190 myopic, 108 hyperopic and 74 emmetropic eyes. The mean ± SD SEQ was -4.85±2.98 D (range: -0.88 to -14.00 D) for the myopic group, +2.62±1.67 D (range: +0.63 to +8.63 D) for the hyperopic group, and +0.19±0.24 D (range -0.25 to +0.50 D) for the emmetropic group. The mean ± SD angle kappa was 5.18±1.49° (range: 1.50-8.53°) for the myopic group, 6.27±1.16° (range: 3.28-9.04°) for the hyperopic group and 5.87±1.41° (range: 1.95-9.26°) for the emmetropic group. The mean ± SD pupil offset was 0.27±0.14 mm (range: 0.00-0.68 mm) for the myopic group, 0.40±0.13 mm (range: 0.21-0.72 mm) for the hyperopic group and 0.36±0.17 mm (range: 0.02-0.88 mm) for the emmetropic group. There were statistically significant differences between all groups (p<0.05).

Conclusions:

As expected, hyperopic eyes demonstrated the largest angle kappa, with a displacement of 0.40 mm on average between the pupil center and the corneal vertex. However, the results of this study also demonstrated the wide range of pupil offset in myopic and emmetropic patients. Therefore, if corneal vertex centration is intended then entrance pupil centration should not be the default for all eyes. FINANCIAL INTEREST: NONE