What is the Snellen Graph?

SNELLE Graph is a tool for measuring the sharpness of sight, the ability to solve fine details at a distance. The graph consists of rows of individual black characters printed on a white background. The first line is often the only capital letter, with the letters become more numerous and gradually smaller with each other row. The sharpness is determined by the fact that the entity has a standard distance from the graph and read the letters until they are able to accurately identify the letters in the line. These are standard accessories in the offices of most eye care experts. The graphs are cheap and available from most medical suppliers. The Snellian print charts can be found free online, but it is necessary to make sure that the graph is printed in the right size.

Correct lenses, such as glasses or contact lenses, should be removed before using the graph as part of the visual acuity test. The test is carried out by the patient with 20 feet (6 meters) from the Snelllen graph. They cover one eye, should start in the top row and read untilthey will not be able to continue. The Eye Care professional then records the smallest line that has been read. The guide, often printed in a small type on the graph itself, will indicate the sharpness score for each line. The test is then repeated for the other eye.

6 The test results are given in a fraction for each eye. The upper number indicates the distance the patient has been made to stand from the graph. The lower number is the distance assigned to the last row they could read. Normal growth is therefore described as 20/20 in the United States and 6/6 in countries using a metric system. A person with about half the normal amount of visual sharpness would have a result of 20/40. It is also possible to score better than 20/20; A person with about twice the normal amount of sharpness by a score of 20/10.

Snelllen decided that rather than using an existing script for his graph, he decided to design his own letters called optotypes to ensure that the test results are standardized. Its optotypeY are block letters in which the width of the space between the strokes equals the width of the strikes themselves. The large "E" commonly seen at the top of the graph was also part of the Skellen's original design. Eye charts often begin with a large "e" to provide a common reference point to determine the size of the graph, but there is no need to do so.

Because some letters are harder to recognize than others, eye charts almost always use the alphabetic subset, USUALLY letters C, D, E, F, L, N, O, P, T and Z. These letters are called Sloan Letters after Louis Sloan, which was specified in the 50th century. Sloan has also designed a new set of optotypes that replaced traditional patterns in many SELLEN eye charts. In addition to Sloan letters, the letters A, H, K, R, U and V.

are also commonly used

Snello chart has expanded to the Western world and required translations for readers who are not familiar with the Latin alphabet used in most European languages. Some are printed by Indian notBo Arabic numerals. Others use Greek, Cyrillic, Arabic or Hebrew characters. Another approach to internationalization was the use of graphs with the letter "E" or "C" was rotated at 90 ° intervals. Rather than reading the letter, the patient shows in which direction he is heading. These tests are known as tests Snello e and Landolt C , and can also be used for patients who are unable to read.

As a result of its immediate recognition, the graph regularly appears in popular culture. In illustrations and dramatic sets, it can be used as a visual abbreviation to immediately create an environment as an office of a doctor or ophthalmologist. This is also often referred to as a visual device in comics and posters. One such use is to edit the graph so that optotypes explain a phrase that is becoming increasingly difficult to read, either for a dramatic or comic book effect. The World Fund for the Wilderness released posters representing the silhouettes of rare animals arranged in the Snlenlen chart with the slogen “Saveendangered animals before you disappear before your eyes. ”