Accommodative behaviour and retinal defocus in highly myopic eyes fitted with a dual focus myopia control contact lens

Purpose: To evaluate the myopic and hyperopic defocus delivered to the retina by a dual focus (DF) myopia control contact lens when myopia exceeds 6.00 D.

Methods: Individuals with high myopia were fitted bilaterally with high-powered DF lenses containing power profiles matching a Coopervision MiSight 1 day contact lens (omafilcon A) and a Coopervision Proclear 1 day single vision (SV) lens. Wavefront measurements along the primary line of sight and across the central ±20° of the horizontal retina were acquired using a pyramidal aberrometer, while subjects accommodated to high-contrast letter stimuli (6/12 equivalent) at six target vergences (-0.25 and -1.00 to -5.00 D). Linear mixed-effects regression models explored the relationship between the spherical equivalent refractive error (SERE) and induced defocus.

Results: Thirteen teenagers and young adults (ages 13-32 years, mean [standard deviation, SD] age = 22.8 [4.9] years) with high myopia (SERE -6.50 to -9.25 D) were tested. The treatment optic zone of the DF lens shifted retinal defocus by the expected -2.00 D, with a mean (SD) difference (DF-SV) of -2.21 (0.18) D for the inner treatment ring. Inclusion of the treatment optic had no significant impact on accommodative accuracy (p = 0.51). Accommodative lags were larger at the nearer viewing distances, with lag increasing by approximately 0.30 D for every additional dioptre of SERE. Measured retinal defocus within the annular treatment zone was approximately -2.00 D at the foveal centre, 10° nasal and temporal and 20° nasal and reduced to -1.90 (0.57) D at 20° temporal.

Conclusions: Relative to eyes with lower levels of myopia, the increased accommodative lags and more prolate retinas of highly myopic eyes reduced the myopic retinal defocus from the DF myopia control lens, while the treatment optical zones generated the combined effect of reducing hyperopic and introducing myopic retinal defocus relative to an SV correction.