Scleral Lens Clearance Assessment with Biomicroscopy and Anterior Segment Optical Coherence Tomography

Abstract

Results from this study validate the ability of contact lens practitioners to observe and estimate the CCC in scleral lens fittings through the use of biomicroscopic viewing. Increasing experience with scleral lens fitting does not improve the correlation with measured CCC from digital or the AS-OCT. However, the intermediate and advanced groups display significantly less inter-observer variability compared with the novice group.

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

“…As the clinician gained more experience, it was possible to reduce the average difference between the subjective measures of CCC made with Slit Lamp and the objective measures recorded with ImageJ as well as to narrow the intervals of agreement. In addition, and according to Yeung and Sorbara [20], the overall standard deviation also decreased between V1m and V12 m, meaning that there was also a reduction in the variability of the differences. It is also observed on Figs.…”

“…One should think that this bias can be decreased as the fitter gains more experience, however there is some controversy about this. Yeung and Sorbara [20] concluded that, independently of the experience of the observers, there was an overestimation of clearance by an average of 103 μm when compared to AS-OCT measurement, with high correlations (r > 0.79).…”

“…As the observer knew the lens thickness (in microns) provided by the manufacture for each one of the lenses analyzed, a simple conversion of the CCC from pixel to micrometers was done. Previous studies already used this software to measure clearance [20] and turbidity of post-lens tear film [21].…”

“…If the postlens fluid is dyed before insertion, practitioners can observe the overall fitting and check for areas of corneal or limbal touch. To observe and estimate the thickness of CCC with biomicroscopy, an optic section can be used and compared to central contact lens thickness or central corneal thickness, if known [16,20]. Anterior segment optical coherence tomography (AS-OCT) is an objective method that has been widely used in different studies to measure clearance [16,17,21,22] and corneal swelling [21,23].…”

Optical coherence tomography and scleral contact lenses: clinical and research applications

“…On average, students significantly overestimated the extent of central corneal clearance, particularly for lower levels of corneal clearance (actual clearance about 100 μm, mean overestimation of 115 μm) than higher levels of corneal clearance (actual clearance about 340 μm, mean overestimation of 60 μm). Similarly, Yeung and Sorbara observed a mean subjective overestimation of about 100 μm for central corneal clearance (with sodium fluorescein) based on assessments of in vitro digital slitlamp images compared to OCT imaging across a range of apical clearance values (from 50 to 400 μm) and various levels of scleral lens fitting experience.…”