Eye chart, Snellen’s
Eye chart, Snellen’s: The familiar eye chart used to measure how well you see at various distances.
Snellen’s chart is imprinted with block letters that line-by-line decrease in size, corresponding to the distance at which that line of letters is normally visible.
The letters on Snellen’s chart are, not surprisingly, called Snellen’s test type. Each block letter is quite scientific in design (so that at the appropriate distance the letter subtends a visual angle of 5 degrees and each component part subtends an angle of 1 minute).
The chart and the letters are named for a 19th-century Dutch ophthalmologist Hermann Snellen (1834-1908) who came up with them as a test of visual acuity. Visual acuity refers to the clarity or clearness of the vision, a measure of how well a person sees. The word “acuity” comes from the Latin “acuitas” = sharpness.
Read Also:
- Eye color
Eye color: The color of the iris. The genetics of eye color are complicated. Eye color is polygenic. It is determined by multiple genes. The eye color genes include EYCL1 (a green/blue eye color gene located on chromosome 19), EYCL2 (a brown eye color gene) and EYCL3 (a brown/blue eye color gene located on chromosome […]
- Eye Institute, National
Eye Institute, National: One of the National Institutes of Health in the U.S., NEI’s mission is to “conduct and support research, training, health information dissemination, and other programs with respect to blinding eye diseases, visual disorders, mechanisms of visual function, preservation of sight, and the special health problems and requirements of the blind.”
- Eye Institute, National (NEI)
Eye Institute, National (NEI): One of the US National Institutes of Health, NEI’s mission is to “conduct and support research, training, health information dissemination, and other programs with respect to blinding eye diseases, visual disorders, mechanisms of visual function, preservation of sight, and the special health problems and requirements of the blind.” The National Eye […]
- Eye pressure test
Eye pressure test: A routine part of every routine eye exam that measures the fluid pressure inside the eye. The test is called tonometry. Increased pressure within the eye can be a sign of glaucoma, a common and potentially very serious eye problem, if it is not detected and treated promptly. The pressure inside the […]
- Eye, absent
Eye, absent: Also called anophthalmia, a congenital malformation (birth defect) of the globe. Anophthalmia refers, strictly speaking, to absence of the globe and ocular tissue from the orbit. However, in most cases of anophthalmia, CT scans show some remnants of the globe, indicating they represent severe microphthalmia (small eyes). Anophthalmia/microphthalmia may involve one or both […]