Correlation between Placido-disc and rotating Scheimpflug keratometric findings before and after corneal crosslinking in children with keratoconus.

ABSTRACT

PURPOSE: To evaluate correlation between Placido-disc and rotating Scheimpflug keratometric findings in children with progressive keratoconus (KC) before and after corneal crosslinking (CXL) and investigate whether these limits of agreement varied according to disease severity. SETTING: Department of Ophthalmology of São Paulo Hospital, São Paulo, Brazil. DESIGN: Prospective nonrandomized open study. METHODS: Data obtained using rotating Scheimpflug-based tomography and Placido-disc-based topography devices were collected from preoperative and last follow-up postoperative children with KC operated on using standard CXL protocol. Correlation and agreement analyses were performed between the 2 devices before and after CXL to obtain keratometric (K) findings. RESULTS: 44 eyes from 44 patients aged 8 to 16 years were analyzed at all timepoints. All parameters were found to be strongly correlated before ( r = 0.84 to 0.99, P < .001) and after ( r = 0.93 to 0.99, P < .001) CXL. The mean Scheimpflug measurements of flat K, steep K, Kmax, mean K, and corneal astigmatism were higher than Placido-disc measurements in a preoperative period. This mean difference decreased in postoperative, but, with exception of Kmax and corneal astigmatism, Scheimpflug measurements remained higher. The mean parameter measurements from both devices decreased after CXL; 95% limits of agreement between instruments were wide for all parameters and decreased in postoperative and in mild KC. CONCLUSIONS: Keratometry measurements obtained using rotating Scheimpflug and Placido-disc technology were found to be closely correlated but not interchangeable before and after CXL in pediatric patients. Agreement between devices was better after CXL and in mild KC than in advanced KC.