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Predicted corneal visual acuity in keratoconus as determined by ray tracing
Article first published online: 29 MAY 2003
DOI: 10.1034/j.1600-0420.2003.00061.x
Additional Information
How to Cite
Uçakhan, Ö. Ö. (2003), Predicted corneal visual acuity in keratoconus as determined by ray tracing. Acta Ophthalmologica Scandinavica, 81: 264–270. doi: 10.1034/j.1600-0420.2003.00061.x
Publication History
- Issue published online: 29 MAY 2003
- Article first published online: 29 MAY 2003
- Received on June 10th, 2002. Accepted on January 28th, 2003.
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Keywords:
- cornea;
- corneal topography;
- irregular astigmatism;
- keratoconus;
- predicted visual acuity;
- ray tracing;
- videokeratography
Abstract.
Purpose: To evaluate the optical quality of the central anterior corneal surface in normal eyes and in eyes with keratoconus, and to investigate the accuracy of the predicted corneal visual acuity (PCVA) index as determined by ray tracing analysis.
Methods: Twenty keratoconus eyes with contact lens-corrected visual acuity (VA) of 20/20 or better (11 patients, group A) and 20 eyes of 15 normal subjects (group B) were evaluated. After a detailed eye examination including measurement of pupil diameter, keratometry, topography and pachymetry, each subject eye was evaluated using ray tracing analysis with the Technomed C-scan colour ellipsoid topometer, using basic software (Technomed GmbH, Baesweiler, Germany). The PCVA was determined for each patient, and the results were analysed comparatively using two-sample t-test, regression analysis and Pearson correlation analysis.
Results: The average best spectacle-corrected VA was measured as 0.2 ± 0.2 logMAR (20/32) in group A and −0.1 ± 0.1 logMAR (20/16) in group B. The average PCVA measurements derived from ray tracing analysis for 3.0 mm, 3.5 mm and 4.0 mm pupil diameters were 0.06 ± 0.12 logMAR, 0.14 ± 0.13 logMAR and 0.21 ± 0.17 logMAR, respectively, in group A, and −0.14 ± 0.08 logMAR,−0.11 ± 0.09 logMAR and −0.09 ± 0.11 logMAR, respectively, in group B. There was good correlation between best corrected VA and PCVA in both groups for all pupil diameters measured (p < 0.007).
Conclusion: Predicted corneal visual acuity as determined by ray tracing analysis is useful for estimating best spectacle-corrected VA in normal corneas and the effect of irregular corneal astigmatism on VA in eyes with mild to moderate keratoconus. Further studies are required to evaluate the efficacy of ray tracing in evaluation of aberrations of the optical system of the eye.