How to calculate spherical refraction

1. These are generally set up by merchants to increase sales, and they are not photographed. They can be photographed by some cooperative platforms of businesses. For example, we can open WeChat, the official account: the goblin buys. The name is only three words right
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3. On behalf of the national youth myopia prevention and control research center of China health promotion foundation, I would like to answer this question:
let's first understand the concept of diopter. There is a close relationship between myopia and diopter. Diopter is defined as the focus of light passing through the lens one meter behind the lens. If D is used to represent the focal length and F is used to represent the focal length, there is a formula d = 1 / F. Distance if the focal length of the lens is 0.5 meters, then the diopter of the lens is 1 / 0.5 = 2. Traditionally, people like to call this 200 degrees
many friends want to know the relationship between visual acuity and diopter (myopia) on the visual chart. In fact, these two concepts are independent of each other, and there is no absolutely accurate conversion relationship between them
generally speaking, people with ametropia have poor vision. The higher the diopter, the lower the naked eye vision. But this is not absolute, some people diopter is not high, but the lack of vision is very low, because the influence of vision is not only diopter a factor. If the eye has other diseases or retinal imaging function, optic nerve function damage, etc., it will also make vision decline
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4. Examination is a technical skill to test eyesight and judgment. Due to the complicated process, it is impossible to explain the text clearly, but you can refer to it. The method of using spherical column lens is as follows:
1, select the strip light detector. Weak light is selected for the shadow detection light, because the strong light will make the pupil of the examinee shrink sharply, which increases the difficulty of shadow detection
2. Let the examinee take the test stand, look for the rupture, and turn the shadow detection light band to 45 °、 ninety °、 one hundred and thirty-five °、 one hundred and eighty ° If the light band reflected by the pupil is not in the same direction as the light band of the shadow detector, it will be broken
3, find the rupture, adjust the viewfinder light and pupil reflection light to the same direction, make the inside and outside light band overlap, and record the astigmatism axis
4 on the test frame at this time. In this way, we can scan the light band horizontally with the angle at the time, observe the forward and backward motion, plus the positive sphere mirror, reverse and negative ball mirror until the printing is not moving and full.
5. In the middle and back of the ball mirror, hit the light band on the axis perpendicular to the fracture axis, and scan the light band to observe the forward and reverse movement. The forward movement plus positive column mirror, and the reverse movement plus negative column mirror are neutral until the printing is not moving and full
6, record the degree of the spherical lens, and the spherical lens degree should be combined with -2.00d before the actual luminosity. If you add - 1.00d spherical mirror to achieve neutralization, record it as - 3.00d, which is the actual luminosity. The number of degrees added to the column mirror will be recorded, and the axis of astigmatism will be selected for the second time

if you can't understand the above, please look at my information.

5. The stronger the refractive power, the shorter the focal length. The focal length of the lens is 1 / 2m or 50cm. If you want to know the focal length of the lens, divide 100cm, that is, 1.00m, by the refractive power, and the result is the focal length. For example, the focal length of 5D diopter is 20cm 100cm divided by 5D = 20cm.) The refractive power of convex lens is indicated by "+", and that of concave lens is indicated by "-".

6. F=P*S=p*72*R

7. The transparent part of the anterior outer wall of the eyeball. It is round, accounting for one sixth of the outer area, about 1 mm thick, and mainly composed of vascular connective tissue. The front is slightly protruding, curved like a sphere, with refraction. Cornea is rich in sensory nerve endings, any small stimulation, injury or inflammation can cause pain and tears. If you touch the cornea with cotton, it will cause the protective reaction of eye fissure closure, which is called corneal reflex.

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9. For example, if you have high astigmatism, do you want to wear contact lens? If you want to use normal contact lens, you can wear it around - 5.75. You can go to the optician's shop and ask an optometrist to test it for you. Try to bring an optometry stand and insert the lens into the contact slot. You can see how it feels. If you need to be clear, you can add 25 degrees. Ordinary contact lenses don't have astigmatism, so astigmatism should be converted into spherical lenses, which are definitely not as clear as glasses. There is also a kind of astigmatism invisible, the price will be more expensive, tailored.