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Sandeep Kaur Dhallu, James Stuart Wolffsohn, Amy L Sheppard, Thomas Edward Drew, Toshifumi Mihashi; Predictors of the subjective range of clear vision in pseudophakes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3775.
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© ARVO (1962-2015); The Authors (2016-present)
To identify the key determinants of the range of clear focus in pseudophakes and their relative contribution to the difference between the subjective and objective defocus curves.
Fifty subjects mean age 33.0±6.4 years (range 23-45 years) underwent simultaneous monocular subjective (electronic test chart at 4m with randomised letters between presentations) and objective (Aston open-field aberrometer) defocus curve testing for lenses between +2.00 to -10.00DS in -0.50DS steps, in a randomised order. Change in pupil size, ocular aberration at each level of blur and resulting objective accommodation range was measured by the aberrometer. Tolerance to blur was measured using a 4 alternative forced choice computer screen display, viewed through a pinhole to negate pupil and ocular aberrations effects and assessed using a stair-case procedure. Subjective amplitude of accommodation >10D was evaluated using the push-up test. The difference between objective and subjective range of clear focus was modelled using pupil size, tolerance to blur and ocular aberrations.
Subjective range of focus was principally accounted for by the change in spherical lens power (65.1% of the variance) with an additional 11.2% determined by the change in pupil size per dioptre within this range and 3.8% from higher order aberrations (≥3rd order), accounting for 80.1% of the variance in total (F=41.592,p<0.001). This was confirmed by analysis of the difference between objective accommodation and the subjective range of clear focus where 43.8% of the variance could be accounted for by the change in pupil size per dioptre and higher order aberrations. Age was correlated to objective accommodation and the subjective range of clear focus (p<0.001), but not pupil size, aberrations or tolerance to blur in the pre-presbyopes (p>0.05). Tolerance to blur was correlated with the difference between objective accommodation and the subjective range of clear focus (r=0.389,p=0.018) and spherical aberrations (r=0.343,p=0.044). Spherical aberrations were also related to pupil size (r=0.337,p=0.007).
Pre-presbyopes benefit from an increased range of clear vision beyond their objective accommodation due to the reduction in pupil size with accommodative effort and their higher order aberrations. Blur sensitivity and absolute pupil size are not independently contributing factors to the subjective range of clear focus in this age group.
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