How to convert an eye chart, the formula for calculating the eyesight

Old and new eye charts.

The conversion is as follows: Standard logarithmic eye chart - decimal record eye chart so the visual acuity of the right eye is converted to yes, and the conversion is yes, which is mild myopia.

The visual acuity of the right eye is yes, and the visual acuity of the left eye is left and right.

The eye chart conversion is as follows:

The standard logarithmic eye chart and decimal record eye chart are as follows.

Eye chart. It is designed according to the principle of perspective. The so-called angle of view is the angle formed by the light emitted by two points in the outside world through the nodes in the eye.

What is an eye chartThe eye chart is designed according to the principle of viewing angle. The so-called angle of view is the angle formed by the light emitted by two points in the outside world through the nodes in the eye. Under normal circumstances, the human eye can distinguish the minimum distance between two points to form a viewing angle as the smallest viewing angle, that is, a one-point viewing angle.

The eye chart is designed in units of one point of view.

International Standard Eye Chart ConversionThe conversion formula for the International Standard Eye Chart is: 5-point record = 5-log (1 decimal record method).

A comparison table between the old and new standard visual acuityThe conversion formula for the old and new eye chart power is: a=5-lg(1 b).

The old 1-point scale is b, and the new 5-point scale is a).

Old and New degrees.

Visual acuity is calculated as visual acuity, visual power, and distance from the eye for standard visual acuity markers.

1. The concept of vision.

Visual acuity refers to the degree of clarity with which the human eye sees objects. The human eye focuses light through an optical system composed of cornea, lens, vitreous humor, etc., so that the light can fall on the retina, and then converted into nerve signals and transmitted to the brain to form visual perception.

2. Calculation formula for visual acuity.

The visual acuity calculation formula is a method used to determine the visual performance of the human eye. The magnitude of visual power refers to the standard character size of human vision, for example, the visual acuity of ordinary eyes means that at a distance of 5 meters, you can see a character of the same size when you are 5 meters away from a normal person. The distance between the standard visual acuity marker and the eye of the person who is suffering from the source is generally 5 meters.

Third, different methods affect the accuracy of the formula.

It should be noted that different test methods and test conditions will affect the accuracy of the visual acuity calculation formula, so the application of the formula needs to be corrected and calculated in combination with specific test conditions. At the same time, in some cases, such as myopia, farsightedness, amblyopia and other eye diseases, the results of the formula also need to be corrected accordingly.

Near vision examination:

The common near eye charts in our country are the Jaeger near eye chart and the standard eye chart. The former table has 8 lines of words of different sizes, and each line has a number on the side, while the latter style is the same as the distance vision chart. During the examination, the light source shines on the watch, but the reflection should be avoided, and the person should hold the near vision chart in front of his or her eyes, and move it back and forth until he finds the smallest size he can see.

If you can read the number 1 character or time, let it gradually move closer until the handwriting begins to blur. The distance between the near point and the cornea is the distance between the near point and the cornea, and the record is in centimeters, such as J1 10 cm or centimeters, if you can't see the No. 1 character or, only record the smallest font size it sees, and no longer measure its distance.

Near vision chart. At a distance of 33 cm from the eye chart, those who can clearly see "the visual target is normal." It is also possible to allow the patient to change the examination distance, i.e. to hold the eye chart closer or farther away to make it clearly recognizable, so as to measure the best visual acuity and estimate the refractive properties and power of the patient.

Therefore, a near vision examination can understand the ability of the eye to accommodate.

The normal vision of the eyes is above and above, and this kind of vision should be protected daily. General protection requires attention:

1. Pay attention to the time you spend with your eyes.

Children's eye development is not perfect, the ability to work is low, every time you read or write for an hour, you should let the child go to outdoor activities, do games, look into the distance, or observe the flowers and trees, so that the tense eye muscles are relaxed, eliminate fatigue. In addition, it is necessary to make the child's life regular, have enough sleep, and let the eyes get enough rest.

2. Pay attention to the light of your eyes.

Do not let your child read or write in dark light or sunlight. If a 25-watt light bulb is used indoors at night, the distance between the book and the bulb should be within 1 meter. If you use a 60-watt bulb on a stool, the distance between the book and the bulb should be 1 2 meters.

Cloudy days, dusk, weak light in the moonlight, and strong light in the sun are not suitable for reading and writing. When watching TV, it is necessary to maintain a suitable distance, which should generally be 5 7 times the diagonal length of the phosphor screen. The time to watch TV should not exceed 2 hours at a time.

3. Pay attention to eye exercise.

Physical exercise can enhance blood circulation and metabolism, supply more nutrients to the eyes, and enhance the resistance of the eyes. The direct exercise is eye exercises, which is based on the Chinese medical type of massage, massage, acupuncture acupuncture points, combined with jujube Kuanhui medical sports, is a scientific method to protect eyesight. Parents should learn the basic knowledge of eye exercises, give specific guidance and often urge their children to do eye exercises, and persevere.

4. Pay attention to eye nutrition.

In order to protect children's eyes, children can eat more carrots, animal liver, lean meat, to supplement vitamin A, or regularly supplement the comprehensive nutrition of the eyes with Leyan vision nutrients, and at the same time, it is also necessary to appropriately consume millet, tofu, animal liver and other supplements of vitamin B2, so as to avoid night blindness, corneal malacia, red eyes, dry itching and other symptoms. Eating too much sugar will harm your child's eyesight, so your child's sugar intake should be controlled.

5. Pay attention to regular inspections.

Regular check-ups are due to the fact that children's eye structure, binocular visual function, and intelligence are still in the process of continuous development after birth, and the content of the examination is different at different ages. The usual age of ophthalmologic examination is generally 2-7 days after birth, 42 days after birth, 3 months, 6 months, and 1 year of age, and then once a year. In this way, the problem can be detected early and corrected early, instead of waiting until the vision has deteriorated and there is a vision problem before going for a check-up.

The visual acuity conversion table is as follows: Tease or.

<> Manifestations of myopia:

1. Reduced distance vision, normal near vision, and often squinting when seeing far;

2. Eye fatigue: eye swelling and pain, headache, nausea, etc.;

3. Exotropia: some people may have exotropia;

4. Fundus changes: myopia arc spots, leopard omentum, etc.;

5. Protrusion of the eyeball, opacity or liquefaction of the vitreous.

Ways to protect your eyes:

1. Do not read in an environment where the light is too strong or too dark;

2. Don't read books on a rocking car or boat;

3. Do not look directly at the luminous body with too strong light;

4. Keep the finger chain in a correct posture and keep a distance of one foot from the book;

5. Do not contact the video screen (computer, TV) for too long, so as to combine work and rest;

6. Myopia glasses should be worn scientifically, worn from afar, and no need to wear them for near-sightedness;

7. It is best to cooperate with effective means to improve one's eyesight and control the development of TV if you are already myopia.

8. Do more outdoor sports.

Since different people have different criteria for interpreting visual targets (as shown in the figure below), there is no constant one-to-one correspondence between the standard eye chart and the prescription.

The standard logarithmic eye chart" and the "decimal record visual acuity chart" can be converted to each other through a formula, and the formula for the conversion of the eye chart is as follows: five-point recording method = 5-lg (1 decimal recording method), note: the five-point recording method is the test value of the "standard logarithmic eye chart", and the decimal recording method is the test value of the "decimal recording eye chart".

The eye chart is designed according to the principle of viewing angle. The so-called angle of view is the angle formed by the light emitted by two points in the outside world through the nodes in the eye (that is, the angle of alliance caused by the intersection of two points of the external object into the eye).

Under normal circumstances, the angle of view formed by the minimum distance between two points can be distinguished by the eye of the human trouser cover is the minimum viewing angle, that is, the angle of view. The eye chart is designed to effectively measure visual acuity based on a one-point perspective.