Identifying ocular surface indicators of initial performance in standard soft contact lenses

To identify ocular parameters associated with successful soft contact lens (SCL) fitting, with particular emphasis on δ-sag-the difference between ocular sagittal height (OC-SAG) and lens sagittal height (CL-SAG)-and the corneo-scleral profile (CSP). A secondary objective was to evaluate the influence of CL-SAG measured at the ISO reference temperature (20 °C) and physiological ocular temperature (34 °C) on δ-sag-based fitting outcomes.

A prospective cohort study included 86 eyes of young adults (21.4 ± 1.9 years). In randomized, double-masked sessions, five hydrogel lenses with different CL-SAG values were fitted. Lens behavior was assessed from slit-lamp videos for centration, blink-induced movement, horizontal lag, and push-up recovery using a standardized 1-to-5 clinical grading scale. Anterior segment measurements, including OC-SAG at multiple chord diameters, keratometry, tangential scleral angle, and inferior corneoscleral junction (CSJ_inf) angle, were obtained using Pentacam HR and slit-lamp biomicroscopy. δ-sag was calculated using CL-SAG values measured at both 20 °C and 34 °C.

OC-SAG differed by meridian, with greater sagittal height along the steep meridian, and increased with chord diameter (both p < 0.001). CSJinf measurements showed low agreement between techniques (ρ = 0.303; p < 0.001). Overall, 31% of fittings were unacceptable, mainly because of decentration and abnormal push-up response. Mean horizontal δ-sag in acceptable fittings decreased from 333 ± 199 μm at 20 °C to 236 ± 201 μm at 34 °C (Wilcoxon, W = 35.01; p < 0.001). Additional predictors of successful fitting included smaller TD-HVID differences (2.53 ± 1.02 mm; p < 0.001), tighter K-BC relationships (-0.48 ± 1.61 mm; p = 0.001), and a flatter tangential scleral angle along the flat meridian (37.22 ± 2.13°; p = 0.007).

Commercial SCLs were classified as unacceptable in 31% of first-fit cases. δ-sag was the strongest predictor of SCL fitting performance, while CSP geometry may further refine individualized lens selection. Accounting for temperature-induced changes in CL-SAG improves the physiological accuracy and clinical applicability of δ-sag-based fitting strategies.