Determination of central corneal clearance in scleral lenses with an optical biometer and agreement with subjective evaluation.

PURPOSE: To compare three methods to measure central corneal clearance (CCC) during scleral lens wear: subjective (slit lamp), image processed (ImageJ) and with an optic biometer. The optic biometer technique was validated in comparison to an OCT in the first part of the study. METHODS: Twenty-two eyes (11 subjects) with healthy corneas were recruited. Three measures of OCT with scleral lens and ten measurements of axial length (AL) with IOLMaster with and without lens were performed. For the second part, 61 eyes (35 subjects) enrolled in a clinical study were selected. Measurements of CCC were done with IOLMaster, SlitLamp and ImageJ. RESULTS: The measurements of CCC indirectly obtained with IOLMaster had a strong correlation with AS-OCT measurements (r = 0.981), showing a mean difference of 122.18 ± 46.05 µm (higher with IOLMaster). Regarding the second part, measurements of CCC were 238.66 ± 95.94 µm, 250.16 ± 124.31 µm and 263.15 ± 90.60 µm, for the IOLMaster, SlitLamp and ImageJ, respectively. The correlations were higher for ImageJ vs Subjective measure (r = 0.891) than for IOL vs Subjective (r = 0.748) and IOL vs ImageJ (r = 0.745). Analysis of differences and correlations between SlitLamp and ImageJ through time showed a mean difference of -32.28 ± 89.95 µm (r = 0.683) at V1month, 12.53 ± 59.46 µm (r = 0.850) at V6months and 11.57 ± 32.95 µm (r = 0.940) at V12months. CONCLUSIONS: It is possible to measure CCC with IOLMaster, considering AL measured with and without lens and lens thickness. The three methods tested have good correspondence, showing that IOLMaster and ImageJ could be objective techniques to measure CCC. Also, it is possible to improve the agreement of subjective measures when compared to objective measures trough time.