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Sofia C. Peixoto-de-Matos, Norberto Lopez-Gil, Jose Manuel Gonzalez-Meijome; Effect of Spherical Aberration in Accommodation and Subjective Focus under Normal and Reverse Contrast Stimulus. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2117.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effects of induced positive and negative spherical aberration (SA) on objective refraction and subjective focus for regular contrast (black letters on white background) and reverse contrast (white letters on dark background).
Five eyes from five volunteers (age 24 to 45 years of age) were evaluated in this experiment. The experimental setup consisted of a badal system mounted on top of an open field autorefractometer (WAM 5500, Grand Seiko, Japan) at a distance of 3.6 meters from an ETDRS transilluminated eye chart. Normal and reverse contrast logMAR visual acuity charts were used and the subject was asked to adjust the badal system to find the sharpest image for a 0.0 logMAR visual acuity line of letters. For each chart 5 different conditions were evaluated: naked eye and phase plates with Seidel C4,0 +0.30, +0.15, -0.15 and -0.30 microns Seidel SA for a 5 mm pupil. Phase plates and a 5 mm diaphragm were always placed in the focal plane of the mobile lens in the badal system. Three repeated adjustments were made for each condition and the subjective focus in the badal system was recorded as well as the objective refraction measured with the autorefractometer, under phenyliphrine pupil dilatation first and under cycloplegia with tropicamide at a later stage.
Under phenyliphrine, the subjective focus shifted by 0.55D and 0.83D towards more myopic refraction for +0.15 and +0.30 microns of SA. This trend was not accompanied by an increase in accommodation measured with the autorefractometer. Conversely, for -0.15 and -0.30 microns of SA the objective refraction became more myopic (max diff.: 0.75D, p<0.05) but the subjective focus did not change. Under tropicamide, the subjective focus shifted towards more myopic values with positive spherical aberration (max. diff.: 0.52D; p<0.05) and towards less myopic values with negative spherical aberration (max. diff.: 0.45D; p<0.05) under tropicamide. Results were not significantly different for reverse contrast chart.
Negative SA stimulated accommodation response to focus an extended object under controlled conditions of pupil size and luminance of the target, while positive SA shifted the subjective focus in the myopic direction even under cycloplegic conditions. The preferred subjective focus and the accommodative response behave differently under positive and negative SA.
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