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Comparison of topographic indices that correlate with visual acuity in videokeratography
1Department of Ophthalmology, Osaka University Medical School, Suita, Japan.
Objective:
To evaluate the relationship between the best spectacle-corrected visual acuity (BSCVA) and two quantitative indices of the anterior corneal surface obtained by videokeratography.
Design:
Prospective, single center, comparative, observational study.
Participants:
Eighty-nine normal eyes and 52 eyes with keratoconus with contact lens-corrected visual acuity of 20/20 or better.
Intervention:
Videokeratography was performed with the TMS-2 and the CAS system 2000.
Main Outcome Measures:
The relationship between the BSCVA recorded in log minimal angle of resolution (logMAR) units, the surface regularity index (SRI), and the predicted corneal acuity (PCA) were assessed by linear regression analysis.
Results:
The BSCVAs for all eyes ranged from 0.82 to -0.30 logMAR units. BSCVA was highly correlated with the SRI (r = 0.70, P < 0.0001) and the PCA (r = -0.61, P < 0.0001). There was no statistical difference in the regression slopes and the intercepts for the estimated BSCVA using the SRI and measured BSCVA, and the estimated BSCVA using PCA and measured BSCVA.
Conclusions:
Two quantitative topographic indices, SRI and PCA, are useful for estimating the effect of irregular astigmatism on visual acuity even though both indices quantify different aspects of the anterior surface of the cornea.
