Subjective Straylight Index: A Visual Test for Retinal Contrast Assessment as a Function of Veiling Glare.

Spatial aspects of visual performance are usually evaluated through visual acuity charts and contrast sensitivity (CS) tests. CS tests are generated by vanishing the contrast level of the visual charts. However, the quality of retinal images can be affected by both ocular aberrations and scattering effects and none of those factors are incorporated as parameters in visual tests in clinical practice. We propose a new computational methodology to generate visual acuity charts affected by ocular scattering effects. The generation of glare effects on the visual tests is reached by combining an ocular straylight meter methodology with the Commission Internationale de l'Eclairage's (CIE) general disability glare formula. A new function for retinal contrast assessment is proposed, the subjective straylight function (SSF), which provides the maximum tolerance to the perception of straylight in an observed visual acuity test. Once the SSF is obtained, the subjective straylight index (SSI) is defined as the area under the SSF curve. Results report the normal values of the SSI in a population of 30 young healthy subjects (19 ± 1 years old), a peak centered at SSI = 0.46 of a normal distribution was found. SSI was also evaluated as a function of both spatial and temporal aspects of vision. Ocular wavefront measures revealed a statistical correlation of the SSI with defocus and trefoil terms. In addition, the time recovery (TR) after induced total disability glare and the SSI were related; in particular, the higher the RT, the greater the SSI value for high- and mid-contrast levels of the visual test. No relationships were found for low contrast visual targets. To conclude, a new computational method for retinal contrast assessment as a function of ocular straylight was proposed as a complementary subjective test for visual function performance.

A study on disability glare vision in young adult subjects.

The full assessment of the visual system must include the evaluation of the optical quality of the eye and neural visual functions. The objective evaluation of the retinal image quality is often carried out by computing the point spread function (PSF) of the eye. The central part of the PSF is associated with optical aberrations and the peripheral areas with scattering contributions. In that sense, visual acuity and contrast sensitivity function tests can be considered the perceptual neural response to those contributions characterizing the eye's PSF. However, in natural viewing conditions, visual acuity tests may provide good vision while contrast sensitivity tests can reveal visual impairment in glare vision conditions, such as exposure to bright light sources or night driving conditions. Here we present an optical instrument for the study of disability glare vision under extended Maxwellian illumination to assess the contrast sensitivity function under glare conditions. The limit of the Total Disability Glare threshold, tolerance, and glare adaptation will be investigated as a function of the angular size of the glare source (GA) and the contrast sensitivity function in young adult subjects.