China's vision meter standards are as follows
The number of myopia corresponds to the numerical value of the vision meter: 4.0 corresponds to 650 diopters of myopia on the vision meter, 4.1 corresponds to 550 to 600 diopters of myopia on the vision meter, and so on. Myopia is proportional to visual acuity: the higher the degree of myopia, the lower the visual acuity of the naked eye. Visual acuity is affected by many factors: naked eye vision is also affected by other factors such as visual fatigue.
The visual acuity chart is designed according to the principle of angle of view. The so-called angle of view is the angle formed by the light emitted from two external points, through the nodes in the eye. Under normal circumstances, the human eye can distinguish the smallest distance between the two points formed by the angle of view for the smallest angle of view, that is, one point angle of view. Visual acuity charts are designed in units of one minute of visual angle.
Function
The visual acuity chart used is mainly to check the central visual acuity, that is, to check the sensitivity of the center of the macula of the retina, so as to easily and quickly understand the initial situation of visual function, which is of great significance to the clinical diagnosis and treatment of eye diseases.
Checking visual acuity is generally divided into two categories: distance vision and near vision. Distance vision is mostly measured by the International Standard Vision Scale (ISVS), which consists of 12 rows of different sizes and opening directions of the "E" character; the measurement is from 0.1-1.5 (or from 4.0-5.2); each row has a marking number, and the examined person's line of sight should be parallel to the row with a 1.0 mark. parallel to the line of 1.0, 5 meters from the optic table; the distance between the optic table and the examined person must be correctly fixed, and the patient is 5 meters from the table.
If the distance inside the room is not long enough for 5 meters, a plane mirror should be placed at 2.5 meters to reflect the vision table. The test is performed by covering one eye and identifying the direction of the "E" notch from top to bottom with one eye until it is not recognizable, and then recording it. Normal visual acuity should be at least 1.0.
If the test subjects can not see 0.1, to move forward until you can see 0.1, the visual acuity is "0.1 × distance / 5 = visual acuity"; if you still can not see 0.1 in half a meter, you can make the test subjects to identify the index, manual, light perception, and so on. Record visual acuity according to the examination.
Near vision with "J" near vision table, the same way to identify the "E" notch direction, until it can not be recognized, near distance can be adjusted on their own, the normal near vision in 30 centimeters to see a line of 1.0 can be near vision test helps to diagnose refractive error