Study Evaluates Anterior Surface Measurement Tool

Australian researchers report clinicians can use the Eye Surface Profiler (ESP) to elicit a highly repeatable sagittal height measurement in the central cornea, making it an appropriate tool for anterior eye shape measurements in tasks such as scleral lens fitting, according to a study published in Optometry and Vision Science. The researchers add that the ESP may be less repeatable in the corneal periphery and scleral region.

Researchers investigated the repeatability of the ESP for anterior central corneal power and anterior eye surface height measurements in 45 healthy adults (mean age 24.8±4.6 years; 42% men) who underwent 2 sessions of anterior eye measurements using ESP. The sessions were separated by 20 minutes, and in each session, consecutive scans were taken.

The investigators found that the sagittal height intersessional coefficients of repeatability for central nasal (5 μm) and central temporal (7 μm) were better vs peripheral nasal (24 μm) and peripheral temporal (21 μm) regions. 

The sagittal height intrasessional coefficients of repeatability were 9 μm for the central nasal region, 8 μm for the central temporal region, 28 μm for the peripheral nasal region, and 31 μm for the peripheral temporal regions. 

The intersessional coefficients of repeatability was 0.67 D for the mean sphere, 0.22 D for the 90/180° astigmatism, and 0.13 D for the oblique astigmatism, with respective intrasessional coefficients of repeatability of 1.27 D, 0.21 D, and 0.27 D, respectively.

Findings indicate that improved intersessional and intrasessional repeatability for sagittal height measurements at the level of the central corneal regions, however repeatability was lower in the periphery.

The investigators found significant differences between the sagittal height measurement repeatability — even though the ESP applies two oppositely oriented projectors to try to control for the substantial differences between central and peripheral eye surface shapes.

“The reduction in the measurement repeatability of the ESP from the center toward the periphery could be attributed to either focusing inaccuracy when using the instrument or the greater variation in the anterior eye sagittal height and curvature in the far periphery of the anterior sclera,” investigators explain.

They suggest that small local variations in the scleral tissue could be due to the presence of small blood vessels, as well  conjunctival and tear film surface variations, which may also lead to poorer repeatability in the peripheral/scleral region vs the central corneal region.

Sagittal height is an important aspect of scleral lens fitting with regard to the determination of the initial apical clearance of scleral-lens fitting.

Limitations of this study include a small healthy cohort with normal corneal shapes. Data analysis involved only the horizontal meridian.

Reference

Niyazmand H ,Read SA, Atchison, DA. Repeatability of anterior eye surface topography parameters from an anterior eye surface profilometer. Optom Vis Sci. Published online October 21, 2021. doi:10.1097/OPX.0000000000001789