Ocular effects of exposure to low-humidity environment with contact lens wear: A pilot study.

PURPOSE: To compare the ocular effects of exposure to a low-humidity environment with and without contact lens (CL) wear using various non-invasive tests. METHODS: Fourteen habitual soft CL wearers were exposed to controlled low humidity (5% relative humidity [RH]) in an environmental chamber for 90 min on two separate occasions. First, when wearing their habitual spectacles and then, on a separate visit, when wearing silicone hydrogel CLs that were fitted specifically for this purpose. All participants had adapted to the new CL prior to data collection. Three non-invasive objective measurements were taken at each visit: blinking rate, objective ocular scatter (measured using the objective scatter index) and ocular surface cooling rate (measured using a long-wave infrared thermal camera). At each visit, measurements were taken before the exposure in comfortable environmental conditions (RH: 45%), and after exposure to environmental stress (low humidity, RH: 5%). RESULTS: CL wearers showed increased blinking rate (p < 0.005) and ocular scatter (p = 0.03) but similar cooling rate of the ocular surface (p = 0.08) when compared with spectacle wear in comfortable environmental conditions. The exposure to low humidity increased the blinking rate significantly with both types of corrections (p = 0.01). Interestingly, ocular scatter (p = 0.96) and cooling rate (p = 0.73) were not significantly different before and after exposure to low humidity. There were no significant two-way interactions between correction and exposure in any of the measurements. CONCLUSIONS: CLs significantly increased the blinking rate, which prevented a quick degradation of the tear film integrity as it was refreshed more regularly. It is hypothesised that the increased blinking rate in CL wearers aids in maintaining ocular scatter quality and cooling rate when exposed to a low-humidity environment. These results highlight the importance of blinking in maintaining tear film stability.

Optical characterisation of two novel myopia control spectacle lenses.

PURPOSE: To quantify the amount of myopic defocus, contrast modulation and other optical characteristics of two novel spectacle lenses (MiYOSMART by Hoya and Stellest by Essilor) with the inclusion of lenslets in their designs were investigated computationally and experimentally. This paper examined the hypothesis that despite the non-coaxial nature of the optics, image degradation will exist due to the fragmented nature of the base optic when imaging through the lens regions populated by lenslets. METHODS: Optical power was evaluated by computing wavefront vergence and curvature from wavefront slope measured with the Optocraft aberrometer within 1.0 and 6.0 mm apertures across MiYOSMART hexagons and Stellest rings. Point-spread functions (PSFs) were computed using physical (wave) optics and geometrical ray optics principles, and compared with experimental measurements using a 4f optical system. Simulated retinal images and modulation transfer functions (MTFs) were computed from PSF-derived optical transfer functions (OTFs). RESULTS: Mean lenslet power in MiYOSMART was +3.95 ± 0.10 D through the hexagons and +6.00 ± 0.15 D in Stellest in rings 1-5 and decreased by 0.42 D/ring reaching 3.50 D in the final one. Stellest lenslets included up to -0.015 microns of primary spherical aberration. PSFs and retinal images revealed simultaneous contributions of the base optic and lenslets. MTFs showed a decrease in contrast at low (1-10 c/deg) spatial frequencies (SFs) comparable to 0.25 D of defocus, and retention of diminished levels of contrast at higher SFs. CONCLUSIONS: Varying sagittal power and consistent curvature power across the lenslets is an identifying signature of the novel non-coaxial lens design included in both spectacle lenses. Lenslet array structure itself plays a significant role in determining image characteristics. For both lenses, the blur created by the fragmented base optic contributes to the image quality. The reduced MTFs over a wide range of spatial frequencies result in lowered image contrast.