Snellenfractie

The Snellen fraction is a method used to measure visual acuity, which is the ability of the eye to distinguish fine detail. It is named after its inventor, Herman Snellen, a Dutch ophthalmologist. The Snellen fraction is expressed as a ratio of two numbers, such as 6/6, 6/9, or 6/12, where the first number represents the distance from which the test is conducted, and the second number indicates the size of the smallest line that can be discerned at that distance. For example, a Snellen fraction of 6/6 means that the smallest line that can be seen at a distance of 6 meters is 6 meters tall, while a Snellen fraction of 6/12 means that the smallest line that can be seen at a distance of 6 meters is 12 meters tall.

The Snellen chart is a standardized visual acuity test that uses the Snellen fraction to measure visual acuity. The chart consists of a series of letters of decreasing size, with the largest letter at the top and the smallest at the bottom. The patient is asked to read the letters from the top down, and the smallest line that can be read correctly is recorded as the Snellen fraction. The Snellen fraction is commonly used in clinical settings to assess visual acuity and monitor the progression of eye diseases such as glaucoma and macular degeneration.

In addition to the Snellen chart, there are other methods for measuring visual acuity, such as the LogMAR chart, which uses a logarithmic scale to express visual acuity. The Snellen fraction is still widely used, however, due to its simplicity and ease of interpretation. It is important to note that visual acuity is not the only factor in determining overall visual function, and other tests such as contrast sensitivity, visual fields, and color vision may also be necessary to fully assess visual function.