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Given as the first number in a binocular description (e.g., 7×35, 10×50), magnification is the ratio of the focal length of the objective divided by the focal length of the eyepiece. This gives the magnifying power of binoculars (sometimes expressed as "diameters").
The Worth Four Light Test, also known as the Worth's four dot test or W4LT, is a clinical test mainly used for assessing a patient's degree of binocular vision and binocular single vision. Binocular vision involves an image being projected by each eye simultaneously into an area in space and being fused into a single image.
The "LEA Numbers Test" was the second of the LEA tests that was developed and can be used to test the visual acuity of older children and even adults. This test has a layout similar to a typical Snellen chart, with lines of numbers decreasing in size towards the bottom of the page. Like the optotypes of the LEA Symbols Test, these numbers are ...
An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [ 1 ] Eye charts are often used by health care professionals, such as optometrists , physicians and nurses , to screen persons for vision impairment .
The mechanism can be explained by some combination of probability summation, neural summation, and effects due to binocular-monocular differences in pupil size, accommodation, fixation, and rivalry. Probability summation comes from the principle that there is a greater chance of detecting a visual stimulus with two eyes than with one eye.
A good procedure is a chart, analogous to the familiar Snellen visual acuity chart, in which one letter in each row differs in depth (front or behind) sequentially increasing in difficulty. For children the fly test is ideal: the image of a fly is transilluminated by polarized light; wearing polarizing glasses the wing appears at a different ...
Binocular rivalry is a phenomenon of visual perception in which perception alternates between different images presented to each eye. [1] An image demonstrating binocular rivalry. If one views the image with red-cyan 3D glasses, the text will alternate between red and blue. 3D red cyan glasses are recommended to view this image correctly.
Here, lenses are switched in and out of a phoropter and the patient is asked "which looks better" while looking at a chart. This feedback refines the prescription to one which provides the patient with the best vision.