Effect of induced blur on distance visual function

Abstract

Background: Tests of visual function assess the eye and visual system. Factors such as ageing, refractive error, strabismus, amblyopia and ocular diseases have a negative effect on different visual functions. Aim:To determine the effect of induced blur on three measures of distance visual function (visual acuity, stereopsis and contrast).Setting: University of KwaZulu-Natal eye clinic.Methods: A quasi-experimental research design was adopted and included 30 healthy young adults. Three convex test lenses (1 dioptre [D], 3 D and 5 D) were used to induce blur and a lens of no power (0 D) was a placebo. The binocular visual acuity (BVA), stereoacuity and binocular contrast were assessed with the LogMAR chart, Howard-Dolman apparatus and Lea low contrast test, respectively. Tests of visual function were measured with no test lens (habitual measurement), and also with each test lens. Data were analysed using descriptive and inferential statistics. Results:The mean habitual BVA and stereoacuity were 0.01 LogMAR ± 0.05 LogMAR and 29 arcsec ± 20 arcsec, respectively. The mean BVA and stereoacuity measurements with the convex test lenses were ≥ 0.24 LogMAR and ≥ 62 arcsec, respectively and significantly different from the habitual measurements (p < 0.001). Most participants were unable to achieve the habitual contrast level with the three convex test lenses. Conclusion:Induced blur reduced the three measures of distance visual function and the decrease was proportional to the power of the convex test lens. These findings should be considered when screening uncorrected ametropes for eligibility for a driver's licence.

The effect of induced blur monocularly and binocularly on stereoacuity

“…The findings of this study were found to be consistent with those of other studies that measured the effect of reduced vision monocularly (simulating anisometropia) on stereoacuity and concluded that the reduction of stereopsis increased proportionately to the increased power of plus lenses. 12,13,14,15,16,17 Even though the other studies measured stereoacuity using local targets (RST), the final findings are consistent with those of this study. However, in this study, the focus was not only on induced blur monocularly (simulating anisometropia) but also on comparing it with binocularly induced blur (simulating isometropia).…”

“…However, a VA of 6/9 or better in at least one eye is the requirement for drivers to qualify for vehicle licenses in South Africa. 16 The determination of the proportional decrease of induced stereoacuity monocularly and binocularly is likely to provide information related to its severity, which could contribute to the reduction of motor vehicle accidents. However, there are still ongoing debates related to reduced vision monocularly or binocularly and their severity on stereoacuity.…”