Agreement between extrapolated corneoscleral topographical data obtained during natural and retracted eyelid positions.

Purpose: To examine the influence of aperture size (corneoscleral data coverage) on extrapolated scleral sagittal height data generated by the Pentacam HR derived from the Corneo Scleral Profile (CSP) software, by comparing measurements obtained during natural and retracted eyelid positions.

Methods: Corneoscleral topography of the left eye of 20 young (age: 22 [3] years) healthy adults with normal corneas was measured using the Pentacam HR CSP with the eyelids in their natural primary gaze resting position and during eyelid retraction with a wire speculum. The measured and extrapolated sagittal height data were exported from the instrument and analysed over a range of chord diameters (10.0, 12.5, 15.0 and 17.5 mm) and locations (superior, inferior, nasal and temporal) using customised software.

Results: Eyelid retraction increased data coverage (% of available data points within 360°) for the 12.5 and 15.0 mm chord diameters (by 25% and 35%, respectively, p < 0.001), but by less than 10% for the 10.0 and 17.5 mm chord diameters. Significant differences in extrapolated sagittal height data were observed between the natural and retracted eyelid positions with respect to chord diameter and location (both p < 0.001), with the greatest difference observed superiorly for a 17.5 mm chord diameter (mean extrapolated sagittal height difference, retracted minus natural: -447 ± 401 μm, p < 0.0001).

Conclusions: Eyelid retraction substantially increased data coverage for the 12.5 and 15.0 mm chord diameters. Significant differences in the extrapolated sagittal height data generated from measurements obtained during natural and retracted eyelid positions were observed for the superior location (12.5, 15.0 and 17.5 mm chord diameters) and inferior and nasal locations (17.5 mm chord diameter). Extrapolated sagittal height values obtained during the natural eyelid position were typically greater than those obtained with eyelid retraction, most likely due to the amount of measured data available for extrapolation.