A starting point for scleral lens fitting: Ocular sagittal height measured with OCT and Scheimpflug CSP software in keratoconic and healthy eyes: A pilot study
Kristin Carter BSc OD MSc Candidate
Sorbara, L1 OD MSc Dipl FAAO FBCLA
1 University of Waterloo, School of Optometry and Vision Science
Purpose: The purpose of this pilot study was to compare the sagittal depth of the initial diagnostic scleral lens (CL-SAG) predicted by two instruments in eyes with and without keratoconus (KC). A secondary objective was to compare ocular sagittal height (OC-SAG) between groups. It was hypothesized that CL-SAG would be similar between instruments, and OC-SAG would be different between groups.
Method: Twelve participants with KC and 10 without participated in this cross-sectional case-control study. Horizontal and vertical OC-SAG were measured with Visante™ OCT (Zeiss Meditec, Dublin, CA) at 15mm, and averaged. With Oculus Pentacam HR® CSP, OC-SAG measurements given at 15mm were averaged. To predict CL-SAG, 400µm was added to Visante average OC-SAG (as per previous work), and 300µm to Pentacam measurements as per manufacturer’s recommendation.
Results: For the control group, predicted CL-SAG with OCT and Pentacam were not statistically significantly different (p=0.3326). There was a statistically significant difference in the KC group (p=0.0002), with OCT estimating on average a higher CL-SAG. There was a statistically significant difference between groups for OC-SAG for OCT (KC: 3920 [IQR 3825-4158] µm) (control: 3788 [IQR 3658-3980] µm) (p=0.0294), but not for Pentacam (KC: 3951 [SD=143 µm]) (control: 3910 [SD=251 µm]) (p=0.5242). Bland-Altman analysis showed a systematic error comparing the two devices for the KC group: at lower OC-SAG values, OCT underestimated the OC-SAG and at higher values, OCT overestimated the OC-SAG.
Conclusions: For eyes without KC, measurements of CL-SAG with two different instruments yield highly congruent results. A statistically, but not clinically significant difference was noted between instruments for eyes with KC. Although the KC group had a higher clinically and statistically significant OC-SAG compared to the control with OCT, our small sample size for this pilot study did not show statistical significance when measured with Pentacam.
1st Author Biography: Dr. Kirsten Carter is a Master’s student at the University of Waterloo, School of Optometry and Vision Science, and a recent graduate of the OD program. During her time as an OD student, as well as through Undergraduate Research Assistantships in Physics, Kirsten has carried out and assisted with research projects involving many forms of ocular imaging, including high-resolution research-grade OCT and Pentacam HR® topographical imaging of the keratoconic and non-keratoconic population. She is working under the supervision of Dr. Luigina Sorbara, Head of the Contact Lens Clinic, and Professor of the Basic and Advanced Contact Lens courses.
*Data correct at the time of submission to BCLA by NCC.