Children's Science | What's wrong with grandparents' presbyopia?

Children, have you noticed that when grandparents read books or look at their phones, their eyes are getting farther and farther away. What is the reason?

1. The concept of presbyopia

As people age, their eyes' ability to adjust gradually decreases, resulting in symptoms such as difficulty seeing near objects. To the extent that when working at close range, they must add convex lenses on top of their refractive error correction to have clear near vision. This phenomenon is called presbyopia.

Presbyopia is a physiological phenomenon, not a pathological condition, nor a refractive error. It is a visual problem that inevitably occurs when people enter middle age or old age. It is usually called "presbyopia" or "presbyopia."

2. The occurrence and development of presbyopia

1. Age and Adjustment

The essence of presbyopia is the decline of eye accommodation ability, and age is the most important factor affecting accommodation ability.

Accommodation, the increase in the eye's refractive power when looking at close objects, is achieved through the contraction of the ciliary muscles, the relaxation of the suspensory ligaments, and the reshaping and convexity of the lens.

The lens continues to grow throughout life, as the equatorial epithelial cells continue to form new fibers, add new cortex to both sides of the lens, and squeeze old fibers toward the nucleus. As we age, the density of the lens gradually increases, its elasticity gradually decreases, and it becomes more and more rigid, causing its accommodation ability to show an absolute decline with age.

The lens loses its elasticity and the ciliary muscle weakens

In the early stages of life, the human eye's ability to accommodate is very strong, about 15.00-25.00D; as we age, the ability to accommodate gradually decreases, about 0.25-0.40D per year.

By the age of 40, the eye's ability to accommodate is no longer sufficient to comfortably perform close work, and "presbyopia" begins to appear in these people. By the age of 50, the ability to accommodate is even lower, and most people need presbyopia correction.

People feel comfortable and can maintain their vision for a long time when the accommodation required for near vision is less than half of the accommodation range. If the accommodation required is greater than half of the accommodation range, presbyopia symptoms are likely to occur.

Diagram of the decline in accommodation amplitude with age

2. Other factors related to the occurrence and development of presbyopia. For people of the same age, some people may develop presbyopia earlier, while others may develop presbyopia later. This shows that in addition to being closely related to the above-mentioned adjustment amplitude, the occurrence and development of presbyopia is also related to other factors:

(1) Existing refractive error.

(2) Eye habits. The need for accommodation is directly related to the working distance. The closer the working distance, the greater the need for accommodation. Therefore, people who do close-up fine work are more likely to develop presbyopia symptoms, and they develop presbyopia earlier than those who do long-distance work.

(3) Height. Taller people have longer arms, so they can place reading materials farther away to provide a greater working distance. This is a way to reduce the need for accommodation, so tall people tend to develop presbyopia symptoms later.

(4) Geographical location. Because temperature affects the lens, people living in areas with higher temperatures tend to develop presbyopia symptoms earlier.

(5) The influence of drugs. Patients who take insulin, anti-anxiety drugs, antidepressants, antipsychotics, antihistamines, anticonvulsants and diuretics will develop presbyopia earlier due to the effects of the drugs on the ciliary muscle.

3. Correction of presbyopia

Wearing frame glasses to compensate for the lack of accommodation is the most classic and effective method of correcting presbyopia. Depending on the design of the lenses, frame glasses are divided into three basic types: single-vision glasses, bifocal glasses and progressive multifocal glasses.

1. Frame glasses

(1) Single vision lenses: Suitable for close-range work. Generally used by presbyopes with low switching rates between near and far vision.

(2) Bifocals: Wearing bifocals saves presbyopic patients the inconvenience of frequently switching between distance and near vision glasses. At the same time, due to the abruptly different refractive powers in the two areas of the lens, bifocals inevitably have optical defects such as image jump and image shift.

(3) Progressive multifocal lenses: They can provide clear vision at near, medium and long distances, and the lenses are more beautiful in appearance.

2. Contact lenses

There are two types of contact lenses for presbyopia correction: simultaneous vision and monovision. The success rate of simultaneous vision contact lenses is higher for wearers with normal distance vision refraction; monovision is also called "one far and one near vision", which is a method of correcting the vision of one eye for distance vision and the vision of the other eye for near vision.

3. Surgical treatment

Surgical treatment for presbyopia can be divided into two categories: one is surgery performed for the purpose of correcting presbyopia, including corneal laser surgery, radiofrequency conductive thermal keratoplasty and scleral expansion; the other is the use of lens technology to achieve the purpose of improving presbyopia while performing senile cataract or other intraocular refractive surgery, including accommodative intraocular lens implantation technology and non-accommodative intraocular lens implantation technology.

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