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

Area of Science:

• Ophthalmology
• Computational Imaging
• Visual Psychophysics

Background:

• Current visual acuity and contrast sensitivity tests do not account for ocular aberrations or scattering effects.
• Ocular straylight significantly impacts retinal image quality and visual performance.
• There is a need for clinical visual tests that incorporate optical quality parameters.

Purpose of the Study:

• To develop a computational methodology for generating visual acuity charts affected by ocular scattering.
• To propose a new function for retinal contrast assessment, the subjective straylight function (SSF).
• To define and validate the subjective straylight index (SSI) as a measure of straylight tolerance.

Main Methods:

• Combined an ocular straylight meter methodology with the CIE general disability glare formula.
• Developed the subjective straylight function (SSF) and calculated the subjective straylight index (SSI).
• Evaluated SSI in 30 healthy young subjects and correlated it with ocular wavefront measures and time recovery from glare.

Main Results:

• Normal SSI values were established in healthy subjects, with a peak distribution around 0.46.
• SSI showed a statistical correlation with ocular wavefront aberrations (defocus, trefoil).
• Higher time recovery (TR) after glare correlated with greater SSI for high- and mid-contrast targets.

Conclusions:

• A novel computational method for retinal contrast assessment incorporating ocular straylight was proposed.
• The subjective straylight index (SSI) serves as a complementary subjective test for visual function.
• This approach enhances visual testing by considering optical quality factors like scattering.