Browse the corpus

Contrast sensitivity (CS) is the ability to perceive sharp and clear outlines of very small objects. It is also defined as the ability to identify minute differences in the shadings and patterns. CS helps detect objects without a clear outline and distinguish them from their background contrast. The proposed mechanism for CS is the neuronal theory, the channel theory, and the M and P cellular pathways. There are various indications for CS examination, such as people applying for jobs, qualitative vision loss, glaucoma, ocular hypertension, cataract, retinal and optic nerve disease. CS can be measured by Michelson’s formula, weber, and various charts available, such as Pelli-Robson, Regan chart, Arden grating, etc. CS can be of two types temporal and spatial. CS is affected by age, cataracts, and diabetic retinopathy. Reduced CS also indicates optic nerve compromise, as seen in optic neuropathy patients. This activity deals with the pathophysiology, indications, types, factors affecting, methods of measuring, and clinical implications of CS. Objectives: Discuss the physiology of contrast sensitivity. Summarize the indications of contrast sensitivity. Review the methods of measuring contrast sensitivity. Outline and explain the clinical significance of contrast sensitivity. Access free multiple choice questions on this topic.

Contrast sensitivity (CS) is the ability to perceive sharp and clear outlines of very small objects.[1] 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.[2] 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.[3] 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.[4] 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.[5] 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.[6] 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.[7]

When patients present to the outpatient department with diminished or blurred vision, they should be examined in detail to pinpoint the pathology. A reduced CS should be suspected if the patient complains of reduced visual acuity despite 20/20 vision. The optometrist plays a crucial role in assessing the contrast sensitivity of the subject with the available charts. The examining ophthalmology should also keep a high suspicion of reduced CS in these cases. In case of reduced CS, the patient should be counseled well regarding the ocular condition and all symptoms the patient can have during nighttime. The patient should be explained the prognosis based on the ocular pathology.[38]