Effect of induced blur on distance visual function

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.