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Basal Altoaimi, Meznah S Almutairi, Arthur Bradley; Accommodative behavior of young eyes fit with multifocal contact lenses. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6237. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Hyperopic defocus is implicated in the development of myopia, and multifocal contact lenses (CLs) have been proposed for removing this hyperopic growth stimulus. We examined the effectiveness of such CLs for removing hyperopic defocus while accommodating.
Ocular wavefront errors and pupil sizes were measured with a high resolution Shack-Hartmann aberrometer as 20/40 characters were viewed at distances from 2m to 20 cm by young adult subjects (n=8), who were instructed to keep the target as clear as possible and tested both monocularly and binocularly with single vision (SV), center-distance (CD) and center near (CN) +2.00D add multifocal CLs. Accommodation stimulus/response curves were sampled at 0.25 diopter increments, and dynamic accommodative responses were measured as stimuli jumped from the distance to the near optics’ retinal conjugate planes.
Average pupil size (unaccommodated) and near pupil miosis were 3.9 mm and -0.14 mm/diopter, respectively. Elevated levels for spherical aberration contributed by concentric bifocals (e.g. mean/SD C40 and C60 are 0.24±0.18μm and -0.08±0.1μm, for CD lenses with 5mm pupils) resulted in paraxial Rx being 2.1D less myopic than minRMS refractive state. As target distance was reduced in 0.25D steps, four subjects accommodated monocularly and binocularly in order to focus the distance optic, while four others failed to accommodate until the target distance was closer than the near optic far point. At -2.5 D, two subjects switched from focusing the distant optic to the near optic (they relaxed their accommodation to a nearer target) when viewing monocularly. However, these subjects continued to focus the distant optic when viewing binocularly. Mean/SD accommodative gain for paraxial Rx was 1.06±0.11, 0.99±0.09, 1.04±0.11 with SV, CD, and CN lenses, respectively. When stepping from the distant to the near retinal conjugate planes, most subjects did not accommodate when viewing monocularly, but they accommodated with typical latency and dynamics when viewing binocularly.
By introducing a bifocal optic into the visual path, one image plane (created by the near optic) will exist in front of the retina as long as the subject accommodates to focus the distant optic. However, some young subjects focus with the near optic to reduce accommodative effort, and thus create hyperopic defocus with the distance optic while viewing at near.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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