author = {Ortiz-Toquero, Sara. and Rodriguez, Guadalupe. and de Juan, Victoria. and Martin, Raul.}, title = {{Gas permeable contact lens fitting in keratoconus: Comparison of different guidelines to back optic zone radius calculations}}, journal ={Indian Journal of Ophthalmology}, volume ={67}, number ={9}, pages = {1410-1416}, doi = {10.4103/ijo.IJO_1538_18}, year = {2019}, abstract ={ Purpose: 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. Methods: 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. Results: 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. Conclusion: 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. }, URL ={https://journals.lww.com/ijo/pages/default.aspx/article.asp?issn=0301-4738;year=2019;volume=67;issue=9;spage=1410;epage=1416;aulast=Ortiz-Toquero;t=6}, eprint ={https://journals.lww.com/ijo/pages/default.aspx/article.asp?issn=0301-4738;year=2019;volume=67;issue=9;spage=1410;epage=1416;aulast=Ortiz-Toquero;t=6} }