Comparison for Kmean and Astigmatism for Orbscan IIz and Pentacam at Different Stages of Keratoconus - A Clinical Study

Aims: To compare results of Orbscan IIz and Pentacam at different stages of keratoconus on Kmean and Astigmatism.

Sample and Study Design: 94 keratoconus patients were included in the study, of which 52 were men and 42 women. Keratoconus patients were screened with Orbscan IIz and Pentacam before undergoing corneal collagen cross-linking. The patients were distributed according to different keratoconus stages.

Place and Duration of Study: University of West Attica Dept Biomedical Sciensce Course Optics & Optometry in collaboration with Athens “Ophthalmiatrio” Clinic during the period between October 2017 to January 2019.

Methodology: Topographic maps correlation of two types of corneal topographers Orbscan IIz and Pentacam. The Kmean values and the Astigmatism presented at different stages of keratoconus were compared.

Results: A Sample of 188 eyes were measured having, 20 eyes (10.6%) with subclinical keratoconus, the correlation coefficient r for Kmean values between Orbscan IIz and Pentacam was 0.9758 (P<0.0001), 44 eyes (23.3%) at stage 1 with the correlation coefficient r=0.8482 (P<0.0001), 33 eyes (17.6%) at stage 2 with the correlation coefficient r=0.8147 (P<0.0001), 67 eyes (35.6%) at stage 3 with the correlation coefficient r=0.797 (P<0.0001), 10 eyes (5.3%) at stage 4 with the correlation coefficient r=0.8455 (P=0.0021), 8 eyes (4.4%) with iatrogenic keratoectasia after refractive surgery having correlation coefficient r=0.928 (P=0.0009).

Conclusion: Statistical differences between Orbscan IIz and Pentacam were found for Kmean in all stages of keratoconus. The performance for Kmean measurement of the corneal topographers Orbscan IIz and Pentacam is satisfactory for both systems in various stages of keratoconus having a very strong correlation (Correlation coefficient r ranged from 0.9758 to 0.7970). Statistical differences between Orbscan IIz and Pentacam were evident also at the Astigmatism measurements at stage 3 and 4.