Contrast sensitivity (CS) is the ability to perceive sharp and clear outlines of very small objects. It is also defined as the ability to perceive minor illuminance changes between interspersed regions not separated by defined borders. Snellen’s test types help in only perceiving sharp and clear outlines of very small objects and not the changes in illuminance.
A patient can have 20/20 visual acuity in many ocular diseases with loss of CS. Sometimes the loss of CS can be more psychologically disturbing than the loss of visual acuity. Schade first measured CS by using the modulation transfer function. Contrast sensitivity using sinusoidal grating was first measured in 1968 by Campbell and Green, and they concluded that it is a complex and discrete function of the retina.
Contrast can be defined as the degree of blackness to the whiteness of a particular object or a target. The contrast threshold is the minimum contrast required to perceive an object clearly. CS is also the reciprocal of the contrast threshold. The various types of CS are spatial and temporal. CS can be measured by Arden grating, Cambridge low contrast grating, Pelli-Robson CS chart, Bailey Lovie chart, vision contrast test system (VCTS), Vistech chart, Regan chart, and FACT chart.
CS varies with the luminance, target, grating motion, and grating shape. Neural mechanism and channel theory have more profound insights into the mechanism of CS. The factors which affect CS are refractive error, age, cataract surgery, refractive surgery, glaucoma, diabetic retinopathy, optic neuropathy, pituitary adenoma, etc. This activity deals with the pathophysiology, indications, types, factors affecting, methods of measuring, and clinical implications of CS.
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