Ophthalmologists Discuss Methods to Help Physicians See What Patients Can’t See (part 3)

The results of his work so far, he says, lead him to believe that contrast sensitivity testing may prove to be a better, more precise way to measure visual function than the traditional Snellen chart. He also says it may be helpful in differential diagnosis, for instance, between macular and optic nerve diseases, though the exact connections between lesions and specific contrast sensitivity deficits are not yet clear.
To test contrast sensitivity, patients are shown a series of screens with grating patterns of alternate light and dark stripes. Keeping the stripe width the same, the patient is shown a series of screens with different contrasts until it is determined how much contrast is needed for the patient to perceive that there are stripes—as opposed to looking at a screen with just one solid shade. The minimum contrast needed to detect a grating pattern, called the contrast threshold, is noted.
The process is repeated for many different widths, ranging down to the finest grating pattern detectable at 100% contrast. The contrast threshold for each different size grating pattern can be plotted on a graph to form a contrast sensitivity curve. A complete test usually takes about 15 to 20 minutes per eye.
The test is providing information on both the function and dysfunction of the visual system. Bodis-Wollner says that testing shows there is a specific stripe width—equal to ten stripes in one degree of visual angle at the eye that is optimal for contrast detection. Cheapest drugs online – buy ampicillin at our place for you to spend less money every time.

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