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Indian J Ophthalmol. 2019 Sep;67(9):1410-1416. doi: 10.4103/ijo.IJO_1538_18.

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

Author information

1
Universidad de Valladolid, Departamento de Física Teórica, Atómica y Óptica, Valladolid, España; Universidad de Valladolid, Instituto Universitario de Oftalmobiología Aplicada (IOBA), Valladolid, España; Optometry Research Group, IOBA Eye Institute, School of Optometry, University of Valladolid, Valladolid, Spain.
2
Optometry Research Group, IOBA Eye Institute, School of Optometry, University of Valladolid, Valladolid; Department of Ophthalmology, Ramón y Cajal University Hospital, Madrid, Spain.
3
Universidad de Valladolid, Departamento de Física Teórica, Atómica y Óptica, Valladolid, España; Universidad de Valladolid, Instituto Universitario de Oftalmobiología Aplicada (IOBA), Valladolid, España; Optometry Research Group, IOBA Eye Institute, School of Optometry, University of Valladolid, Valladolid, Spain; Faculty of Health and Human Sciences, Plymouth University, Plymouth, United Kingdom.

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.

KEYWORDS:

Contact lens; fitting; gas permeable; guidelines; keratoconus

PMID:
31436183
DOI:
10.4103/ijo.IJO_1538_18
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