To nd an eye doctor near you, visit www. Snellen Eye Chart Home use of this Snellen eye chart will help you determine the clarity of your. A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the. Snellen designed his optotypes on a 55 grid, on which the line thickness is one unit and the letter width and height are five units. This system is followed for. Snellen Test www. Print the test page in A4 standard format. Place yourself 2. Far Cry 1 Utorrent. If the test page is in. Snellen chart Wikipedia. Typical Snellen chart to estimate visual acuity. A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist. Pin Serial Connector. Herman Snellen who developed the chart in 1. Snellen Chart' title='Snellen Chart' />Many ophthalmologists and vision scientists now use an improved chart known as the Log. MAR chart. Contents. Snellen developed charts using symbols based in a 55 unit grid. The experimental charts developed in 1. Snellens charts published in 1. The original chart shows A, C, E, G, L, N, P, R, T, 5, V, Z, B, D, 4, F, H, K, O, S, 3, U, Y, A, C, E, G, L, 2. Description. Edit. The normal Snellen chart is printed with eleven lines of block letters. The first line consists of one very large letter, which may be one of several letters, for example E, H, or N. Subsequent rows have increasing numbers of letters that decrease in size. A person taking the test covers one eye from 6 metres or 2. The smallest row that can be read accurately indicates the visual acuity in that specific eye. The symbols on an acuity chart are formally known as optotypes. In the case of the traditional Snellen chart, the optotypes have the appearance of block letters, and are intended to be seen and read as letters. They are not, however, letters from any ordinary typographers font. They have a particular, simple geometry in which the thickness of the lines equals the thickness of the white spaces between lines and the thickness of the gap in the letter Cthe height and width of the optotype letter is five times the thickness of the line. Only the ten Sloan letters C, D, E, F, L, N, O, P, T, Z are used in the common Snellen chart. The perception of five out of six letters or similar ratio is judged to be the Snellen fraction. Wall mounted Snellen charts are inexpensive and are sometimes used for approximate assessment of vision, e. Whenever acuity must be assessed carefully as in an eye doctors examination, or where there is a possibility that the examinee might attempt to deceive the examiner as in a motor vehicle license office, equipment is used that can present the letters in a variety of randomized patterns. BS 4. 27. 4 1 1. British Standards Institution Specification for test charts for determining distance visual acuity was replaced by BS 4. Test charts for clinical determination of distance visual acuity Specification. It states that the luminance of the presentation shall be uniform and not less than 1. Any variation across the test chart shall not exceed 2. According to BS 4. C, D, E, F, H, K, N, P, R, U, V, and Z should be used for the testing of vision based upon equal legibility of the letters. Snellen fraction. Edit. Visual acuity Distance at which test is made distance at which the smallest optotype identified subtends an angle of five arcminutes. Edit. Snellen defined standard vision as the ability to recognize one of his optotypes when it subtended 5 minutes of arc. Thus the optotype can only be recognized if the person viewing it can discriminate a spatial pattern separated by a visual angle of one minute of arc. Outside of the United States, the standard chart distance is 6 metres 2. Other acuities are expressed as ratios with a numerator of 6. Some clinics do not have 6 m eye lanes available, and either a half size chart subtending the same angles at 3 metres 9. In the most familiar acuity test, a Snellen chart is placed at a standard distance 6 metres. At this distance, the symbols on the line representing normal acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 66 or 2. Three lines above, the letters have twice the height of those letters on the 66 or 2. US line. If this is the smallest line a person can read, the persons acuity is 61. In an even more approximate manner, this person could be said to have half the normal acuity of 66. At exactly 6 meters distance from the patient, the letters on the 66 line shall subtend 5 minutes of arc such that the individual limbs of the letters subtend 1 minute of arc, which means that the chart should be sized such that these letters are 8. E should be 8. 8. Putting it another way, the eye should be at a distance 6. Another calculation for United States clinics using 2. Acuity charts are used during many kinds of vision examinations, such as refracting the eye to determine the best eyeglass prescription. During such examinations, acuity ratios are never mentioned. The largest letter on an eye chart often represents an acuity of 66. US. Some individuals with moderate myopia may not be able to read the large E without glasses, but have no problem reading the 66. By contrast, legally blind individuals have a visual acuity of 66. References. Edit. External links. Edit.