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Brett A Davis, Michael J Collins, Fan Yi, Xu Cheng, Noel A Brennan; The impact on eye length and vision performance for a range of positive defocus levels in two-zone bifocal contact lens adaptive optics simulations. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2914.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate short term changes of axial length (AxL), visual acuity (VA), contrast sensitivity (CS) and halo size with simulated 2-zone centre distance bifocal contact lens designs, with positive (+ve) defocus of different magnitudes, produced with adaptive optics (AO).
An AO system allowed subjects to view a micro-display through the simulated optical designs while AxL and vision performance were measured. 16 young subjects had AxL measured by a Lenstar before and after 40 mins of watching a movie on the micro-display through five AO induced optical designs (control, +3 DS and three 2-zone bifocal designs) (Figure 1). 8 subjects participated in the VA study, 4 in the CS study and 5 in the halo study. For VA, CS and halo tests, a 2-zone bifocal was used with a central distance zone of 2.5 mm and peripheral plus ranging from +1 to +10 D. For VA, high-contrast tumbling E letters were displayed on the AO system micro-display. The E letter for CS tests had three sizes of 0.3, 0.4 and 0.65 logMAR. Halo size measurements for the bifocal designs were performed through a split channel setup in the AO system.
Greatest AxL reductions occurred for +3 D defocus and the bifocal design with peripheral +6 D (both p < 0.005). The +6 D periphery design also produced greater shortening of AxL compared to the +3 D periphery (p < 0.001). Increasing +ve defocus in the periphery caused a loss of VA (F = 14.11, p < 0.005) (Figure 2). However, the peak loss of VA occurred at about +2 D peripheral defocus and improved slightly for higher levels of defocus. The effect of increasing peripheral defocus on CS varied with the size of the test letter (F = 57.84, p < 0.005). For the largest letter, the effect of increasing +ve defocus was minimal, whereas for smaller letters, increasing peripheral +ve defocus continued to decrease CS. When the clear central zone size was fixed, higher plus power in the periphery was found to produce a larger halo.
Increasing peripheral plus power in a 2-zone simulated bifocal caused a greater reduction in short-term AxL. The peak loss of high contrast VA occurred at relatively low levels of peripheral defocus, whereas the loss of CS increased for smaller letter targets, as the defocus increased. Halo size increased with increasing peripheral plus defocus.
This is a 2021 ARVO Annual Meeting abstract.
Figure 1. AxL change.
Figure 2. VA and CS change.
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