1. For the same material of a convex lens, the crown, the greater the diopter number is larger, the smaller and vice. In other words, for the same eye myopic degree is higher, the more prominent, the need to wear myopia glasses degree is higher.
2. Eye refractive system is adjustable “convex” and thus form variable, when placed in front concave lens, the eye still has the self-regulatory function, the eye can see at different distances goals and myopia or presbyopia patients wearing glasses can adapt itself illustrates this point.
3. As ordinary glasses and eye separation, visual image, easy to calculate. This section discusses the focus is on glasses for eye refraction influence on the discussion about the glasses are for ordinary glasses. Wearing contact lenses and glasses in general has the same refractive effect, its principles and techniques in the optical industry has matured. It is no longer discussed.
4. In dioptrics, only in certain special cases, refraction as the P1, P2 two refractive lens combinations produces the effect is P1 P2 diopter lens. Consisting of the lens in the eye in the optical path, or qualitative in effect in the calculation of P1 P2 can have such a situation, it is not the actual refractive lens combined effect, but a simplified and approximate, because the eye is self- the ability to change the refraction. Although difficult to verify by experiment, but the eye of the moderating effect of view, it should have a role in offsetting diopter lens, which has a simplified calculation formula has the role. For the eye and the lens systems composed of, at most two lenses of the refractive system, it can be calculated using the theory dioptrics. When put on the lens, because the eye of special regulation, the lens of the eye diopter adjustment and adaptation diopter addition and subtraction, an approximation can be obtained, although accurate measurement of the refractive power of the eye is still a distance, but in effect but close. In this argument, although theoretically deduced, but the experiment and measurements are very difficult, as the preparation of myopia needs tried, as in the glasses used to guide the process but also to experiment.
5. Look from eye refractive characteristics, someone measured the static refractive power of the eye 58.6D, although this is a special case, but it basically reflects the refractive power of the eye has a strong, its regulation is relatively small, the normal eye is 0 – 10D so, myopia is n – 10D (n refers to the number of eye myopia), while it also fixed in orbit, so a person who can be considered eye refraction system – “lens” of the center constant distance to the retina, in subsequent calculations, the image distance can be considered as a constant K, for refractive eye, if in a clear image on the retina, the refractive lens imaging system still satisfies the equation 1 / u 1 / k = P
Where K is a constant, P is the eye refractive power, is variable, meaning that people will look at different targets at different distances and different people of different refractive eye. U refers to the distance from the target to the eye.
This formula is valid when: a time, from the eyes of a target, and the target of the eye near and far points.
From the formula, face seeing infinity when 1 / u = 0, the above equation can be written as P = 1 / K, can make 1 / K = P0, ie, P0 is the static eye diopter. When looking from the target of the eyeball is L, “lens”, the imaging equation becomes 1 / L 1 / K = 1 / L P0, 1 / L increased the eye refraction, 1 / L P0 is the eye to see distance L The target diopter.
For wearing glasses, in general, the eye’s distance to the center of the glasses is about 1.2 – 2.4CM, the following denoted by h, but for a person at a time value is determined, the set diopter P ‘of the focal length of the lens is F, when looking at the target distance L, the imaging lens as follows:
1 / L 1 / V = P ‘==> 1 / V = P’-1 / L ①
At this time the imaging lens of the eyeball of the “lens” of the distance | V | h, the eye refractive state satisfies the equation: 1 / (| V | h) 1 / K = P ②
From the formula it, if | V | is much larger than h, according to the formula ①, ② simplified formula can be approximated as:
1 / | V | 1 / K = D = | D’-1 / L | 1 / K ③
As seen through the lens of the eye is a virtual image,V <0, then 1 / | V | 1 / K = 1 / L 1/K-D ‘= D1 D0-D’
From this formula to see, | V | L size depends on the object distance and the focal length of the lens, taking into account the actual situation, glasses diopter majority is greater than-6D, students’ reading, writing most of the distance is greater than 0.25M, and according to the imaging lens formula, concave refractive P ‘(Note D’ <0, the same below) is smaller, | V | is smaller; object distance is smaller, | V | is smaller, such as when D ‘= -5, U = 0.25 when , | V | = 0.111M, 0.02M still much larger than. So as the theoretical calculations, looking at the distance too close, objective lenses are not too high, it can be ignored H, this simplifies the calculations, is conducive to qualitative analysis.
In other words, for the thin lens, if ignored eyeball to lens distance, can be considered a result of wearing glasses cause eye adjustment to increase the degree of adjustment is equal to the lens refraction. The composition of the eye with glasses optical system, each part produced by addition and subtraction of refraction can be approximated, this analysis can simplify the calculation, the problem becomes easier.
6. Error analysis. If the formula is the standard, then the cause of the error is multifaceted, now this analysis.
(1) Since the regulation of the deformation of the eye the same time, there is deformation of the adjustment, there is a deformation of the eye around the diameter changes, but also the lens and cornea as a result of its deformation of the cornea, aqueous humor, lens composed of “convex” optical center changes. Although myopia or presbyopia itself does not explain the change in anteroposterior diameter (one that myopia is in front of the eye image on the retina, but in recent regulation can not relax too strong or ciliary muscle can accomplish this, you can not fully explain the eye around Path variable length), but more could not explain the invariance. The existence of these factors determines the equation, K is an approximation, and the larger the past adjustment, K value the greater the change, which is a cause of error. However, considering the regulation in the eye, the lens and the eye refractive diopter adjustment (about 60 diopters) is far away, and the amplitude of the eye is generally less than 10 diopters, is relatively small, smaller corneal refractive changes, therefore, can be considered “lens” optical center is almost unchanged from the retina.
(2) because each person’s eye anteroposterior diameter range of different people, K is not constant, it is difficult to accurately measure, but specific to an individual at a certain stage, the anteroposterior diameter of the eye unchanged, may that K is a constant.
(3) for different people, glasses to ‘lens’ optical center is difficult to measure the distance between the variables, which also affect the accuracy of the calculation. The calculation shows, h increases, the error increases, the smaller the contrary.
7. When placed in front of the lens, as compared with the normal eye, if the eye still see the target, the regulation from the eye effect, adjust the eye glasses to offset the lack of the first, so the subsequent calculations, as long as the eye within the normal range of adjustment , used to offset the effect of the lens can be set up in theory, we do not pay attention to the actual eye refraction changes. The Eye, no matter how many diopters wearing glasses to see the front of the goal, the role must be low consumption increases glass diopter adjustment.
8. Because glasses errors, to adapt other reasons, even if the various factors are taken into account, theory in practice only an approximation, adjust the eye by a big margin, this simplistic, idealized theoretical deformation due to their leaving error increases. Furthermore, the optical center of the lens to the eye distance with different people and different, which in turn cannot physically be expressed, in terms of preparation time to analyze specific issues.
9. For the eye and refractive lens composed of systems, lenses is determined, and the eye refraction is variable, so the eye as an adjustable lens means: eye can see through the glasses a target, eye refraction to determine, and thus can use dioptrics theory calculations, but the eye to see the target distance changes, its refraction also changes.
10. The composition of the eye and refractive optical systems, only the two “lenses”, and can be regarded as an equivalent lens group, the degree of the lens can be addition and subtraction, such as a lens 5D, can be regarded as a ( 2D) (3D) of the lens group, although in most cases is not established, but in theory we provide a convenient solution.