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K. M. Rocha, L. Vabre, N. Chateau, J. Ramos-Esteban, R. R. Krueger; High Order Aberrations Effect on the Eye’s Depth of Focus Evaluated by Using an Adaptive Optics Visual Simulator. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2421. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the impact of applying individual Zernike coefficients (spherical aberration, coma and trefoil) on depth of focus.
The ocular aberrations of 10 normal subjects were measured up to the 10th Zernike order using a crx1 Adaptive Optics Visual Simulator (Imagine Eyes, France) based on a Shack-Hartmann wavefront sensor and an electromagnetic deformable mirror functioning with a closed-loop feedback algorithm throughout the experiment to control the wavefront shape. Subjects’ eyes were dilated with 1% Tropicamide to inhibit accommodation and the accommodative response was checked using the same device 15 minutes after the drops were inserted. The crx1 was used to introduce varying degrees of pure Zernike aberrations, including coma (Z(3,-1)), trefoil (Z(3,-3)) at magnitudes of +/-0.3 and spherical aberrations (Z(4,0)) at magnitudes of +/-0.3,+/-0.6 and +/-0.9µm through a fixed 6-mm pupil diameter. Depth of focus curves were plotted for each simulated aberration using measurements obtained by displaying 10 Sloan letter optotypes. Each subject’s depth of focus was assessed by plotting the number of read letters as a function of the induced defocus.
The obtained results show that applying pure spherical aberration coefficients linearly shifts the best point of focus by 1.3 D for each 0.5µm of spherical aberration in the direction of its sign. Simulating spherical aberration equally increased the depth of focus value up to 2D, depending on the sign and the value of its coefficient. This increase reached a maximum before decreasing in the presence of strong spherical aberration values (0.9µm). Trefoil and coma did not appear to shift the best focus point and only slightly changed the depth of focus value.
By using adaptive optics based technology for vision simulation, we were able to draw quantitative results on the effects of higher-order aberrations on the depth of focus. Simulating both positive and negative spherical aberrations significantly improved subjects’ Visual Depth of Focus (VDoF) when compared to the effects on VDoF observed when introducing coma and trefoil. Spherical aberrations equally appear to increase subjects’ best focus point. Our results suggest that spherical aberration should be further studied and incorporated into the design of optical corrections for presbyopia. This has the clinical potential for both in-office patient simulations and for the implementation of adaptive optics into refractive surgery techniques.
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