ABSTRACT
PURPOSE: To investigate the differences in contact lens sagittal depth (CL-SAG), base curve (BC), and overall lens diameter (OAD) of daily disposable (DD) SCLs at room temperature (20 °C) and on-eye (34 °C) temperature. METHODS: Twelve different spherical daily SCLs were analyzed (labeled power -3.00 D) at 20 °C and 34 °C. The posterior CL-SAG, BC, and OAD were measured directly using a spectral domain OCT-based instrument (Optimec is830). RESULTS: The CL-SAG range for the daily disposable lenses measured at 20 °C was 3468-4016 µm. At 34 °C, the DD CL-SAG of all lenses individually decreased compared to 20 °C (t = 7.78, p < 0.001), ranging from 3385 to 3913 µm. On average at the higher temperature, the measured overall lens diameter was smaller (t = 8.18, p < 0.001) and the BC was marginally steeper (t = 2.11, p = 0.058). CONCLUSIONS: Soft lens parameters change when equilibrated from room temperature (20 °C) to on-eye temperature (34 °C). All lenses shrink when going to on-eye temperature (both lens diameter and CL-SAG decreases), compared to lenses measured at room temperature by ISO standards. Higher water content materials tend to have greater changes to the lens parameters compared to lower water content material lenses.
Subject(s)
Contact Lenses, Hydrophilic , Disposable Equipment , Temperature , Humans , Tomography, Optical CoherenceABSTRACT
PURPOSE: While knowledge of the ocular surface sagittal height (OC-SAG) is increasing with newer instrumentation, understanding of soft lens sag values (CL-SAG) in daily clinical practice is limited. This study aimed to report the differences in CL-SAG of a large collection of daily disposable (DD), reusable (2-week and 4-week replacement) and toric lens designs. METHODS: 12 different spherical DD and 15 reusable lens types were analysed (labelled power -3.00D); 17 different toric lens types analysed (6 DD and 11 reusable) in -3.00D =C 0.75 × 180. Posterior CL-SAG was measured directly using a spectral domain OCT-based instrument (Optimec is830). RESULTS: The range in CL-SAG for DDs was 3,398-3,912 microns, for reusable lenses 3,372-4,004 microns and for toric lenses 3,536-4,157 microns. Lens diameter and BC together influence CL-SAG values. For lenses with the same labelled base curve (BC), the maximum difference in the DD group was 264 microns, in the reusable group 418 microns and in the toric group 345 microns. Three lens designs within the DD group and five in the reusable group offer two BCs, with an average variation (±SD) in CL-SAG of 276 ± 39 microns; one toric lens with two BCs showed a 377-micron difference. CONCLUSIONS: Marked differences in CL-SAG values were found in this study, also between lenses of the same BC. While ECPs should be aware that diameter and BC together influence CL-SAG, this also indicates that lens substitution based on BC alone could result in substantial differences in CL-SAG, with a potential impact on lens fit. Lens designs offering two BCs showed a somewhat narrow band in absolute terms in CL-SAG, and switching from a spherical to a toric lens of the same lens manufacturer could result in a significant change in CL-SAG.