(1) International standard visual acuity chart The international standard distance visual acuity chart and the near visual acuity chart designed by Xu's family in my country are widely used by the majority of medical workers. The international standard visual acuity chart is based on the word E as the visual standard. The stroke width and interval are both 1 visual angle. The edge width of visual standard E is 5 visual angles, and the gap width is 3 visual visual angles. The visual standard is arranged in a total of 12 lines. The target increment rate is the number of adjusted sets, and the visual acuity is an arithmetic progression (0.1-1.0), recorded in decimals.

(2) Lan's ring eye chart The Lan's ring eye chart uses a ring with a width of 1.5 mm in a 7.5 mm square, with a 1.5 mm wide gap on the ring, which is C-shaped. Standard visual acuity is recorded as 1.0 as a decimal. If the visual acuity is N, it means that the notch of the Lan's ring can be seen at 5 meters is a notch with a width of mm in a square of millimeters. The Lan's surround visual standard is calculated according to the arithmetic progression, and the increase rate is 0.1, 0.2...2.0, and the recording adopts the decimal method.

(3) Logarithmic visual acuity chart The logarithmic far and near visual acuity chart was designed by Miao Tianrong in my country in 1958, and it is also called the 5-point logarithmic visual acuity chart. The visual acuity is divided into 5 grades, visually marked as E or C, a total of 14 lines. The logarithmic distance visual acuity chart is tested at a distance of 5 meters, and the 11th line can be distinguished. It is the standard visual acuity, recorded as 5.0. The optotype increases in a geometric progression, and each time the optotype increases, the logarithm of the visual acuity decreases by 0.1. That is, the visual acuity record is increased or decreased according to the arithmetic level. The near vision chart is a chart used to check the visual acuity in the adjusted state and measure the near point distance. It can understand the degree of accommodation and assist in the diagnosis of refractive errors or eye diseases. In addition to the standard near vision chart, Lang's ring near vision chart, and logarithmic acuity chart introduced above, the near vision chart also includes Jager chart and turntable. The near vision chart with its own light source. It has the advantages of stable light, clear display, convenient use and wide application range.

(4) Visual inspection method When inspecting distance vision, the inspection distance is 5 meters, the height of the visual acuity chart should be 1.0 (or logarithmic visual acuity chart 5.0), and the visual standard should be parallel to the subject's eye, and the illumination should be appropriate. The visual acuity check is generally performed on the right and then the left, and the two eyes are performed separately. When checking one eye, the other eye can be covered with an eye-shading spoon. The subject's eyes must be wide open, not squinting, squinting, or tilting the head. When checking, point to the optotype from top to bottom. If the answer is correct, then point to the next line of optotype. The recognition speed averages 3 to 5 seconds per word. Record the visual acuity value of the last line of the correct answer next to the optotype. If you can’t see the 4.0 optotype clearly at 5 meters, you should approach the visual acuity chart gradually, write down the distance at which you can see the 4.0 optotype clearly, and press (D is the distance that a normal eye should see with 4.0 optotype, d is The distance between the examinee and the visual acuity chart) calculate the visual acuity under examination. You can’t see the 4.0 visual standard within 1 meter from the visual acuity chart. You can use the method of identifying the fingers in front of your eyes to measure your visual acuity. Record your visual acuity according to the distance you can see the index of your fingers from far to near. If you are close to 5 cm, you can’t see clearly. The index of the hand is changed to swing the whole hand in front of the eyes, and record the distance that the hand swing can be seen clearly from 30 cm to 5 cm. If you cannot distinguish manual operation, you can project light on your eyes in a dark room to check whether there is light perception and whether you can judge the direction of light projection. Such as loss of light perception is completely blind.

(5) The punctate visual acuity chart is suitable for the quantitative detection of near vision of infants and young children aged one to three years. Its characteristic is that it is not restricted by language barriers, and it is easy to accept by infants and young children. It is one of the simple and easy-to-operate infant and young children detection tools.