Young adults with myopia commonly experience accommodative lags at close viewing distance, according to a study published in Ophthalmic and Physiological Optics. The research also found that hyper defocus was replaced with myopic defocus in the annular treatment zones when fitted with dual-focus (DF) myopia control contact lenses (CLs).
Researchers associated with Indiana University examined the refractive effect of DF myopia control CLs on compliant young adults with myopia. In phase 1 of the study, accommodative accuracy was evaluated in 40 participants (mean age: 21.85 years). In phase 2 of the study, 4 participants who demonstrated accurate accommodation and 6 participants who were chronically under accommodated were fitted with single vision and center-distance DF myopia control CLs, which contained an additional +2.00 D power.
The participants binocularly viewed high-contrast characters at 4.00, 1.00, 0.50, 0.33, 0.25 and 0.20 meters. The investigators measured at ±10˚, 20˚ and 30° across the central retina. They pooled local refractive errors for each area of the pupil covered by the central distance or first annular defocus zone of the DF CLs.
In the initial screening of 40 participants, accommodative lags at close viewing distances (0.50 m-0.20 m) were frequent (94% of all measurements) with a mean of +0.34±0.40 D, +0.37±0.44 D, +0.52±0.58 D and +0.71±0.60 D, respectively.
Researchers noted that accommodative lags were generally absent in the “good” accommodating participants, except at the closet viewing distance. The mean ± SD accommodative errors for the “good” accommodating participants was -0.09±0.22 D, -0.12±0.26 D, -0.05±0.37 D and +0.38±0.54 D, respectively. The mean accommodative errors for the “poor” accommodating participants was +0.81±0.21 D, +0.97±0.27 D, +1.18±0.39 D and +1.47±0.55 D, respectively.
When fitted with the DF CLs, hyperopic defocus seen in the region of the pupil covered by the first annular zone was replaced with myopic defocus. Myopic defocus generated via the first annular region was present across the central 30° of the retina, according to the study.
The zone-specific analysis approach represents a potential limitation of this research.
“Although the successful introduction of myopic defocus in young adult myopes even in the presence of significant accommodative lag is clearly shown here, it is important that these experiments be replicated in children who are undergoing myopia progression and myopia treatment,” the study says. “Collectively, these results also indicate potential clinical utility in measuring accommodative lag, pupil size and ocular aberrations when implementing myopia control treatment.”
Singh NK, Meyer D, Jaskulski M, Kollbaum P. Retinal defocus in myopes wearing dual-focus zonal contact lenses. Ophthalmic Physiol Opt. Published online October 23, 2021. doi:10.1111/opo.12903