Difficulty seeing near

Introduction Patients with presbyopia will have near difficulty. With age, the ability of eye adjustment gradually declines, causing patients to be near-difficult, so that in close-range work, a convex lens must be added in addition to its static refractive correction to have clear near vision. This phenomenon is called old. Presbyopia. The essence of presbyopia is the decline of the adjustment ability of the eye. Age is one of the most important factors affecting the adjustment force. The adjustment, that is, the increase of the refractive power of the eye, is achieved by shaping and convexizing the crystal. The crystals continue to increase throughout life, as the epithelial cells in the equatorial region continue to form new fibers, adding new cortex to both sides of the crystal and squeezing the old fibers into the nuclear region. As the age increases, the crystal density increases gradually and the elasticity gradually decreases.

Cause

(1) Causes of the disease

1. Age and regulation: The essence of presbyopia is the decline of the adjustment ability of the eye. Age is one of the most important factors affecting the adjustment force. The adjustment is the increase of the refractive power of the eye, which is realized by the shaping and convexization of the crystal. of. The crystals continue to increase throughout life, as the epithelial cells in the equatorial region continue to form new fibers, adding new cortex to both sides of the crystal and squeezing the old fibers into the nuclear region. As the age increases, the crystal density increases gradually and the elasticity gradually decreases.

The shaping and convexization of the crystal are mediated by the lens capsule (mainly the anterior capsule), and the elasticity of the crystal capsule also gradually decreases with age. At the same time, with the increase of age, the ciliary body is enlarged due to the slow accumulation of fibrous tissue, and the crystal is gradually enlarged. Although it is not known how the age of the crystal cantilever is changed, the close proximity of the ciliary body and the crystal will inevitably affect the crystal suspension. The tension of the ligament.

In the early days of life, the adjustment of the human eye is very large, about 15.00D ~ 25.00D, gradually decreasing with the increase of age, reducing the adjustment amount of 0.25D ~ 0.40D every year, so that by the age of 40, the eye The adjustment power is not enough to complete the close work comfortably. The "presbyopia" began to appear among these people. By the age of 50, the adjustment power is lower, and most of them need to be corrected. Hofstetter proposed an empirical formula for the relationship between age and presbyopia as early as the 1950s:

Minimum adjustment range = 15-0.25 × age (the most frequently cited in clinical)

Average adjustment range = 18.5-0.30 × age

Maximum adjustment range = 25-0.40 × age

2. Other factors related to the appearance of presbyopia: the appearance of presbyopia is due to inadequate regulation, the time of occurrence of presbyopia can be early or late, depending on the person, and is related to the adjustment range owned by each of the above. When people use the adjustment force below half of their adjustment range, they feel comfortable and can watch for a long time. If the required adjustment force is more than half of the adjustment range, the symptoms of presbyopia are prone to occur.

Example: Someone adjusts the range to 3.50D. At this time, he needs to read a book with a distance of 40cm. Can he read it comfortably?

Analysis: Because when reading a 40cm book, the required adjustment power is 2.50D. To be comfortable to read, he must have twice the adjustment range of the required adjustment power, ie 5.00D, and his adjustment range is 3.50. D, in theory, if you want to read without fatigue, you can pay up to half of the adjustment range, which is 1.75D, so the other 0.75D required for reading (2.50D) can only give +0.75D reading additional mirror.

In addition to age, the occurrence and development of presbyopia is related to the following factors:

(1) Refractive error: The distance between presbyopia and presbyopia is earlier than that of myopia; after wearing the spectacles, myopia reduces the distance of 12mm~15mm from the apex of the cornea, which reduces the adjustment requirement of the same reading distance. Myopia with a contact lens, because the contact lens is worn on the corneal surface, the corrected optical system is close to the emmetropic eye. Therefore, the wearing contact lens is earlier than the presbyopic wearing the ordinary frame glasses.

(2) Eye method: Adjusting the demand is directly related to the working distance. Therefore, it is easy for the close-range fine workers to have the symptoms of presbyopia. Those who work in close-range work are older than those who work in the distance. .

(3) The patient's physical quality: the taller arm of the long arm has a longer working distance than the shorter short arm of the arm, and requires less adjustment, so the latter has presbyopia symptoms earlier.

(4) Location of the patient: Because of the effect of temperature on the crystal, people living near the equator have presbyopia symptoms earlier.

(5) The effect of drugs on patients: patients taking insulin, anti-anxiety drugs, antidepressants, antipsychotics, antihistamines, anticonvulsants and diuretics, due to the effect of drugs on the ciliary muscles, will compare Presbyopia appeared early.

(two) pathogenesis

As you age, your adjustments change. Figure 1 shows the results of Duane's adjustment of 4000 human eyes. It can be clearly seen from the figure that the adjustment force in adolescence is 14.0D, and the near point is at 7cm. Later, with the increase of age, the near point gradually and uninterruptedly retreats. At the age of 36, it has retreated to 14cm, and its adjustment power is 7.0D. By the age of 45, the point is retreated to 25cm, and the adjustment force is only 4.0D. By the age of 60, only about 1.0D adjustment is maintained. Table 1 shows the normal values of regulation at different ages (D).

Most of the near working distance is 28 to 30 cm. When the eye is 45 years old, only 3.5D ~ 4.0D adjustment. This degree of adjustment has reached the limit of seeing near objects. In this case, if you need to work closely at a close distance, use the full adjustment force to get the usual vision. In order to maintain close vision, the eyes must work nervously, and the constant tension will inevitably cause visual fatigue. In general, only 2/3 of the total adjustment force can be used when using the adjustment, and another 1/3 is used as the retention force to work comfortably. As mentioned above, for a 45-year-old emmetropia, if you perform a close-up work of 25 cm, you should use all the adjustment powers. Therefore, it is necessary to maintain the eye fatigue symptoms in the near homework. Therefore, it is about 45 years old. Began to become a presbyopia. In order to adhere to close work, presbyopia should be worn with a convex lens to help.

When the presbyopia is young, its near point is much farther than the emmetropia, and the symptoms of presbyopia appear earlier. A hyperopia 3.0D eye, with 7.0D adjustment can get 4.0D adjustment degree, about to show presbyopia symptoms at about 25 years old; on the other hand, a 4.0D myopia, because it is far away At 25cm, when you reach old age, you can use your far point as a near point to engage in close-up work. Therefore, although this eye is already presbyopia, it does not have symptoms of presbyopia.

Although the lens of the human eye is regularly hardened with age, the appearance of presbyopia symptoms depends not only on the age, but also on the refractive status, and also on the individual differences of each individual. Habits, working conditions and lighting conditions have changed. People who are used to reading books on their knees are more likely to appear than those who are used to working closely. For example, woodworkers, bookkeepers, and music workers are accustomed to working distances of 30 cm. Workers such as watch repairing, sewing, and engraving, although the age and refractive state are the same, due to the close working distance, the symptoms of presbyopia will appear in advance. Furthermore, if the ciliary body is in a weak or pathological state, physiological regulation may also be impaired. In summary, the age at which presbyopia symptoms appear cannot be determined as an absolute number, and the treatment should be considered comprehensively according to various conditions.

an examination

Related inspection

Eye and sacral area CT examination ophthalmologic examination

The discomfort of the presbyopic person varies from person to person because it is related to factors such as the individual's basic refractive status, eye habits, occupations and hobbies. For example, a subjective sensation of a close-up fine worker to presbyopia is much more intense than a traffic copist who is primarily tasked with watching distant vehicles and traffic lights.

1. Nearly difficult: The patient will gradually find that he is reading at the usual working distance, and can't see the small font. Contrary to myopia patients, the patient will unconsciously lean back or take the newspaper to a farther place. The words are clear and the required reading distance increases with age.

2. Reading requires more illumination: At the beginning, reading at night is somewhat uncomfortable because the night light is dark. Insufficient illumination not only raises the visual resolution threshold, but also makes the pupil dilated. Because the pupil dilation forms a large diffusion circle on the retina, the symptoms of presbyopia are more obvious. With age, even if you work close-up during the day, it is easy to fatigue, so people with presbyopia like to use brighter lights at night. Sometimes the light is placed in the middle of the book and the eye, which not only increases the contrast between the book and the text, but also reduces the pupil. However, the light will inevitably cause glare interference. The closer the interference source is to the visual axis, the greater the impact on vision. Some old people like to read in the sun, this is the truth.

3. The near vision can't last: The lack of adjustment is that the near point is getting farther and farther. After the effort, you can see the near objects. If this effort exceeds the limit, causing tension in the ciliary body, and when looking at distant objects, temporary crimine formation due to the tension of the ciliary body cannot be immediately relaxed. When you look at nearby objects, there is a short time of blurring, which is to adjust the slow response. When the action of the ciliary muscle is close to its functional limit and it does not work, fatigue occurs. Because the adjustment force is reduced, the patient has to work close to the eye in a state close to the adjustment limit of both eyes, so it cannot be sustained. At the same time, due to the linkage effect of the adjustment set, over-adjustment will cause excessive collection, which is also a factor that causes discomfort. Therefore, it is easy to serialize, the writing is double, and finally it is impossible to read. Some patients may experience eye fatigue such as eye swelling, tearing, headache, and itchy eyes.

According to the test results of presbyopia combined with the patient's age and clinical manifestations, it can be diagnosed.

Differential diagnosis

Hyperopia and presbyopia are two different refractive states, but because they are corrected with convex lenses, the distance vision is good, and the two are often confused. Hyperopia is a kind of refractive error. After wearing a convex lens, you can see both the distance and the near side. The presbyopia is only due to the weakening of the adjustment force, and it is not clear to the near target. Of course, it is a physiological obstacle. Although the near target (book, newspaper) can be seen after wearing the convex lens, it is not possible to use this mirror to see distant objects at the same time, which is different from the situation in which the far-sighted person wears a mirror.

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