Gas permeable contact lens fitting in keratoconus: Comparison of different guidelines to back optic zone radius...

Compare the agreement between the finally fitted back optic zone radius (BOZR) of a spherical gas permeable (GP) contact lense (CL) with those proposed by different guidelines currently available to fit GP CLs in keratoconus.

The BOZR fitted in 81 keratoconus eyes (46 patients) were recorded and compared with the BOZR calculated with ten different guidelines (identified after a literature review) proposed to calculate the first diagnostic lens BOZR to be fitted in keratoconus. Arithmetic and absolute mean difference between both BOZR were calculated (paired t-test). The success rate of each guideline (difference between both BOZR ≤0.05 mm) was calculated for different keratoconus stages (Amsler-Krumeich classification). Agreement between BOZR was evaluated using Bland-Altman analysis.

The BOZR proposed by all guidelines correlated with the final BOZR that was fitted (R² > 0.71; P < 0.01). A statistically significant difference was found between the BOZR suggested by all guidelines and the BOZR that was prescribed (P < 0.05), except for three Guidelines (P ≥ 0.11). CALCULENS.com presented the best agreement (mean difference of 0.00 ± 0.12 mm), and 50.6% of cases showed ≤0.05 mm of difference with the BOZR that was fitted. However, the worst guideline showed an agreement of -0.38 ± 0.22 mm, and just 3.8% of cases had ≤0.05 mm of difference with the final fitted BOZR.

BOZR calculated with most of the analyzed guidelines shows statistical differences with final fitted BOZR, suggesting a lack of clinical validation of these guidelines. The selection of the BOZR with CALCULENS.com could provide a better starting point for spherical GP CL fitting in keratoconus eyes.