The symbols on the chart are formally known as "optotypes" Sniper Vision System (standard symbols for testing vision). In the chttps://freepdfreview.com/sniper-vision-system-review/ase of the traditional Snellen chart, the optotypes appear as block letters, and are intended to be seen and read as letters. They are not, however, letters from any ordinary typographer's font. They have a particular, simple geometry whereby the thickness of the lines equals the thickness of the white spaces between lines and the thickness of the gap in the letter "C." In addition, the height and width of the optotype is five times the thickness of the line. Only the letters C, D, E, F, L, N, O, P, T, and Z are used in the traditional Snellen chart.
The smaller letters on the chart are designed to give an accurate measure of how good your vision is. If you notice the big letter this is an excellent sign, because it implies that your overall eye vision is nice and healthy. But the smaller letters are what are used to give an even more accurate picture of how well your eyes are. If you wish to read well in addition to see signs from a far distance then you will need to be in a position to read small letters.
The largest letter on an eye chart often represents an acuity of 20/200 (6/60), the value that is considered "legally blind." Some individuals with moderate myopia may not be able to read the large E without glasses, but have no problem reading the 20/20 line (line which is supposed to represent a person's perfect visual ability without eyeglasses at a distance of 20 feet) with glasses. In contrast, people who are legally blind have a visual acuity of 20/200 (6/60) or less when using the best prescription eyeglasses.