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Validation of an Objective Scoring System for Forme Fruste Keratoconus Detection and Post-LASIK Ectasia Risk
Cordelia Chan1, Marcus Ang, Alain Saad
1*Singapore National Eye Center, Singapore, Singapore; †Singapore Eye Research Institute, Singapore, Singapore; and ‡Rothschild Foundation, Paris, France.
Purpose:
To investigate the efficacy of the SCORE Analyzer (Bausch+Lomb TechnoLas, Germany) in detecting forme fruste keratoconus (FFKC) in Asian eyes and validate its usefulness as a risk assessment system for post-laser in situ keratomileusis (LASIK) keratectasia.
Methods:
We retrospectively evaluated corneal topographies with the Orbscan IIz system and independently tested them with the SCORE Analyzer through masked investigators. Eyes were classified into 2 groups: (1) The FFKC group included clinically and topographically normal eyes with definite keratoconus in the contralateral eye. (2) The control group included normal preoperative topographies of patients with LASIK performed at least 4 years before with no resultant keratectasia. The main outcome measures were accuracy indicators: sensitivity, specificity, positive, and negative predictive values. Parameters in the calculation of the SCORE including irregularity at 3 mm, thinnest pachymetry, the difference between central and thinnest pachymetry (CP - TP), vertical decentration of the thinnest point, maximum posterior elevation, and anterior elevation of the thinnest point were compared in both groups.
Results:
We analyzed 128 Orbscans of 128 Asian patients. There were 24 FFKC eyes and 104 control eyes. SCORE was negative in 7 eyes (false negative) in the FFKC group and was positive in 2 eyes in the control group (false positive). The sensitivity was 70.8%, specificity 98.1%, positive predictive value 89.5%, and negative predictive value 93.6%. Irregularity at 3 mm, thinnest pachymetry, CP - TP, thinnest point decentration, maximum posterior elevation, and anterior elevation of the thinnest point were significantly different in both groups.
Conclusions:
The SCORE Analyzer algorithm, developed and validated in eyes of white subjects, was found to be valid and consistent in Asian eyes, showing good sensitivity and specificity in FFKC detection, and to be useful in objectively identifying cases at risk of post-LASIK keratectasia.
