Purchase this article with an account.
Karthikeyan Baskaran, Peter R. Lewis, Robert Rosen, Peter Unsbo, Jorgen Gustafsson; Effects of Optical Defocus on Resolution Acuity in Preferred Retinal Locus. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1900.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Resolution acuity in the peripheral visual field is primarily limited by retinal sampling. In healthy eyes, the correction of peripheral refractive errors does not produce significant visual benefits other than improved detection and low contrast acuity. However, studies (Lundstrom L et al, Optom Vis Sci, 2007;84:1046-52) have shown that peripheral refractive corrections improve resolution acuity in subjects with central visual field loss (CFL) who have an established preferred retinal locus (PRL). The aim of this study was to evaluate the effect of optical defocus on high contrast resolution acuity in the PRL.
Resolution acuity was evaluated under spherical defocus in the PRL of three low vision subjects (mean age 75 years) with long standing CFL (due to age-related macular degeneration). Off-axis refractive error at the PRL was measured by an open-field COAS-HD VR aberrometer and was corrected accordingly. The PRL for subject 1 was located at 10° in the temporal visual field (left eye), subject 2 at 20° in the nasal visual field (right eye) and subject 3 at 15° in the inferior visual field (left eye). Stimuli consisting of high-contrast Gabor patches with a visible diameter of 3º were presented on a CRT monitor situated 1.0 meter from the subject. Resolution thresholds for static visual acuity (SVA) and dynamic visual acuity (DVA) were obtained using an adaptive Bayesian algorithm. Fixation was aided using illuminated concentric rings covering ±25° in the visual field. Defocus was altered in 1D steps up to ±4D. When measuring DVA, the sine-wave gratings drifted within the Gaussian envelope at an angular velocity of 1°/sec.
Resolution thresholds for both SVA and DVA in the PRL varied significantly with the amount of optical defocus. The results show a 2 - 3 line decrease (logMAR) in SVA and DVA with 4 D positive and negative defocus. There was no significant difference between SVA and DVA with increasing defocus. In the absence of defocus, SVA was significantly better than DVA in the PRL.
Defocus as low as one dioptre has an impact on both static and dynamic high contrast resolution acuity for CFL subjects using a PRL. The results of this study suggest that, for CFL subjects using a PRL, resolution acuity is not only sampling limited but also influenced by the optics of the eye.
This PDF is available to Subscribers Only