Multivariate analysis of refractive state in eyes with keratoconus

OBJECTIVE: To demonstrate a multivariate method of analysis of the short-term variation of refractive state in keratoconus (KC) patients. METHODS AND ANALYSIS: In this observational study, 19 eyes with KC and 19 healthy control eyes were measured. The study included both male and female participants and the mean age was 23.6 years (range 18–34 years) and 23.2 years (range 22–26 years) for KC and control participants, respectively. Forty consecutive autorefractor measurements were taken for each participant and the short-term variation thereof was analysed using multivariate methods of analysis. RESULTS AND CONCLUSION: Short-term variation of refractive state is greater in eyes with KC than in healthy control eyes and variation increases with severity of disease. A novel finding was that there was much more ortho-astigmatic and oblique-astigmatic variation seen in KC eyes than in control eyes which had predominately stigmatic variation. Refractive state is described by three components, namely, sphere, cylinder and axis. Although it is multivariate in nature, it is often analysed using univariate statistical methods. In diseases such as KC, where early diagnosis is crucial for a good prognosis, it is necessary that researchers endeavour to investigate the disease from different perspectives to fully understand the nature of the disease. This paper comprehensively demonstrates the multivariate statistical methods of analysis of refractive data. The implementation of this analysis provides insight into the short-term variation of refractive data in healthy and keratoconic eyes, and these findings have not been demonstrated before using univariate statistics.