Abstract
Objective: To determine association between central corneal power, asymmetrical astigmatism and keratoconus and dependent predictors of keratoconus in asymmetrical astigmatism and absence enantiomorphism
Methodology: This Case Control study was conducted at Amer Eye Hospital, Wah Cantt. from January to December 2017. Sample size of 60 patients with 1:1 randomization (30 patients in each group) was calculated using WHO calculator. Non probability consecutive sampling was used. Patients were randomly divided into two groups using computer generated random number table. Group A had patients with symmetrical astigmatism following enantiomorphism (Controls), while Group B had asymmetrical astigmatism or absence of enantiomorphism in patients (Cases). Videokeratography was done for measurement of dependent predictors of keratoconus. All were followed 6 months. SPSS software was used for data analysis. Chi-square and Regression analysis was done. P value ≤0.05 was considered significant.
Results: Out of 60 patients, 42(70%) were male and 18(30%) female. Mean age was 25.8±7.4 years. Keratoconus was significantly associated with central corneal power (p=0.02) and insignificantly associated with astigmatism symmetry (p=0.75). Keratoconus predictive index (KPI) was positively correlated with sim k reading, astigmatism, central corneal power and IS in asymmetrical group (p<0.05) while in symmetrical astigmatism group it is correlated with astigmatism and IS. Sim k reading [OR=0.12(95% C.I=0.0.081, p=0.04)], astigmatism [OR=0.28(95% C.I=0.17, p=0.00)], Central corneal power [OR=0.01(95% C.I-0.002, p=0.03)], IS[OR=0.10(95% C.I=0.002, p=0.00)] are significant predictors of keratoconus in a asymmetrical group while central corneal power [OR=1.2(95% C,I=0.01, p=0.03)] is only predictor of keratoconus in symmetrical group.
Conclusion: Keratoconus is more likely to develop in patients with central corneal power >47.2 diopter. However, asymmetrical astigmatism or absence of enantiomorphism is dependent predictor of keratoconus. Early referral of patients with high central corneal power to ophthalmologist from optometrist of resource limited area (where videoketaograph is unavailable) can prevent significant vision loss and leads to better visual outcomes.

Key words: Enantiomorphism, keratoconus, astigmatism.