Effect of visual blur on contrast sensitivity. Clinical implications.
Contrast sensitivity of normal subjects was measured under conditions of refractive blur that produced specific levels of visual acuity. Measurements were made at distance (with Vistech charts), at near (with Arden gratings), and with a pinhole to control pupil size. Under all conditions, when visual acuity was reduced by spherical lenses, there was a loss of contrast sensitivity over a broad range of spatial frequencies (i.e., not just at the higher frequencies that correlate with target letter size). By inference, it may be clinically hazardous to interpret contrast sensitivity results in patients with reduced acuity (from any cause) relative only to standard contrast sensitivity values based on subjects with normal visual acuity. If the potential effects of acuity are taken into account, contrast sensitivity testing can distinguish between deficits that are roughly equivalent to the loss of acuity and those which indicate more distinctive pathology of the media, retina, or optic nerve.
Marmor
M F
MF
Department of Ophthalmology, Stanford University Medical Center, CA 94305.
Gawande
A
A
D006801:Humans; D013028:Space Perception; D014787:Vision Tests / Q000379:methods*; D014792:Visual Acuity