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Geethika Muralidharan, Judith Birkenfeld, Maria Vinas, Andrea Curatolo, Eduardo Martinez-Enriquez, Alberto De Castro, Susana Marcos; Crystalline lens accommodation through multifocal corrections. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1803.
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© ARVO (1962-2015); The Authors (2016-present)
Multifocal contact lenses have been shown to slow the progression of myopia by mechanisms related to the increase of peripheral defocus or reduction of accommodative error. We evaluated the effect of multifocal designs on the accommodative response of myopes by measuring changes in the crystalline lens geometry.
A custom-developed 3-D spectral Optical Coherence Tomography (sOCT) system, provided with automatic quantification and distortion correction algorithms was used to characterize the anterior eye segment of myopic subjects (n=4, age=26.8±2.87 SE:-0.75 to -2.75D). A Badal optometer allowed refraction correction and accommodation stimulation (0, 2 and 4 D) to an E-letter stimulus. Free-form lathed bifocal phase-plates (6-mm pupil, 50 far/50 near, +3 D add) were incorporated to the system by a relay of lenses and inserted onto the pupil plane. Two multifocal designs were tested: (1) concentric center distance (CCD), and (2) asymmetric upper distance (AUD). Changes in lens thickness (LT) and radius of curvature (for anterior Ra and posterior Rp lens) and pupil diameter (Pd) were evaluated for different accommodative effort (AE) without (Nat) and with multifocal designs
The crystalline lens underwent accommodative changes in all conditions: under Nat, LT increased by 0.28±0.06 mm, Pd decreased by -1.51±0.95 mm, and Ra and Rp decreased -3.1±1.6 mm and -0.63±0.27 mm, over 4 D AE range. Changes over 0-2 D AE were consistently higher than in 2-4 D (by 39% in LT & 167% in Ra). Accommodative changes in the crystalline lens LT were higher for Nat (0.065 mm/D) than for CCD (0.031 mm/D) and AUD (0.04 mm/D), in the 2-4 D, and changes in Ra were higher in Nat (-0.77 mm/D) than for CCD (-0.70 mm/D) and AUD (-0.69 mm/D), in 0-4D range.
Changes in crystalline lens morphology provide a direct assessment of the response to an accommodative effort. Bifocal lenses with various near/far pupillary distributions do not prevent young subjects to stop accommodating. However, reduced rates of change in lens thickness and curvature suggest that subjects make use of near add for near vision, to some extent, with the effect likely influenced by the specific distribution of near/distance zones.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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