Lens centration and retinal defocus generated by a dual focus myopia control contact lens in a hydrogel and a silicone hydrogel material

Paul Chamberlain¹, Dawn Meyer², Lee Hall¹, Ryan Webster², Arthur Bradley¹, Pete Kollbaum^2
1CooperVision Inc., ²Indiana University School of Optometry
Sponsored by CooperVision Inc.

Purpose
Compare lens centration and optical defocus generated by a dual-focus (DF) myopia control soft contact lens (SCL) fabricated in hydrogel and silicone hydrogel materials.

Methods
SCLs containing the same DF optic were fabricated in hydrogel (Hy, omafilcon A) and silicone hydrogel (SiHy, stenfilcon A) materials. A crossover study of young myopes (8-18 years, mean(SD) 15.6(2.4)) measured lens centration and resulting refractive distributions across the un-dilated pupils of habitual SCL wearers. Wavefront measurements of the right eye were acquired along the primary line of sight while DF lens-corrected subjects binocularly fixated a high contrast letter (6/12) at 4m. Wavefront slopes were used to compute refractive error for each zone of the DF lenses. Defocus was calculated by subtracting the target vergence from the measured refractive state. Centration of the lens was derived from the location of the annular zones relative to the pupil centre.

Results
Both lenses positioned inferior temporal with mean(SD) decentrations of 0.68(0.16)mm (SiHy) and 0.74(0.27)mm (Hy). Average refractive states over the optical center zone were -0.09(0.41)D (SiHy) and -0.06D(0.39)D (Hy), and  -1.80(0.51)D (SiHy) and -1.81(0.46)D (Hy) of myopic defocus in the inner treatment ring. The percentages of the pupil area exhibiting well-focused and myopically defocused light were 29.6% focused, 65.8% myopically defocused (SiHy) and 30.2% focused and 66.1% defocused (Hy). None of the small differences in mean values for SiHy and Hy were statistically significant (p>0.05). 

Conclusions
No statistically significant differences were observed in refractive impact or lens positioning of DF myopia control SCLs designed with matching optics and zone geometries and fabricated in either hydrogel or silicone hydrogel materials. Center zones were well-focused annular treatment zone produced matching levels of myopic defocus. Therefore, the demonstrated myopia control effects of DF Hy lenses will be mirrored with SiHy lenses containing the same concentric design myopia control optics.