Low Amounts of Scattering Reduce Central as well as Peripheral Contrast Sensitivity

Abstract

 

Purpose

 

Irregularities and opacities in the ocular media cause light to scatter and thereby decrease the contrast of the retinal image and eventually reduce functional vision. Contrast reduction affects both foveal and peripheral vision. The purpose of this study is to investigate how the foveal and peripheral contrast sensitivity functions (CSF) are affected by scattering. The results are relevant in judging the importance of cataract surgery for eyes with central visual field loss and to determine the potential effects on vision of intraocular lenses (IOL) defects.

 

Methods

 

Different amounts of scattering were introduced by filters (¼, ½, 1, and 2 Black Pro-Mist^® filters from Tiffen) and by a plano lens for the right eye of two subjects. The straylight parameter, log(s), of the respective eye together with the different filters was measured using the C-Quant from OCULUS. The CSFs in the fovea and 25° in the temporal visual field were measured with fast psychophysical procedures. The monitor luminance was 35 cd/m² and the glare source gave 12 lx in the pupil plane. All measurements were performed monocularly under two conditions; glare source at 2.5° and at 7° from stimulus, with three repetitions. The CSFs were also assessed without glare source.

 

Results

 

The straylight parameter ranged from 1.1 to 1.6 for the glare source at 2.5° and from 0.9 to 1.4 at 7°. These log(s) values indicate that filter 2 corresponds to a preliminary stage of cataract and filters ¼-½ correspond to straylight values typical for varying levels of microvacuoles in IOLs. The figures show the area under the log CSF (AULCSF) as a function of log(s) for foveal and peripheral vision with the glare source at 2.5°. As can be seen, scattering reduced AULCSF for both cases. While the impact was larger in the fovea (1.4 area units/log(s)) than in the periphery (0.5), the AULCSF loss in the periphery was from a much lower level. The reductions were also present, but smaller, with the glare source at 7°.

 

Conclusions

 

Both foveal and peripheral CSFs were affected by low to moderate amounts of scattering. These results imply that patients with cataract will potentially benefit from surgery irrespective of whether they have central visual field loss or not.

 

 

 

The AULCSF as a function of the straylight parameter, log(s), for foveal (upper) and peripheral (lower) vision with the glare source at 2.5°.

 

Keywords: 478 contrast sensitivity • 445 cataract • 412 age-related macular degeneration