Contrast sensitivity testing is a powerful tool for determining the capability of the visual system to process spatial and temporal information about the everyday objects we see. The current gold standard in the assessment of vision, visual acuity, provides only a limited amount of information, obtained under artificial conditions. Contrast sensitivity testing measures a range of visual performance under real-life conditions. It measures the least amount of contrast needed to detect a visual stimulus and gives us a more complete quantitization of patients' visual capabilities. Many instances in which losses in contrast sensitivity were detected when visual acuity (one point on the contrast sensitivity function) was normal have been reported. These include amblyopia, neuro-ophthalmology, retina, anterior segment disease, and glaucoma. Therefore, contrast sensitivity testing enables the clinician to diagnose selective deficits in visual processing at an earlier stage than is possible with conventional testing methods.