The "sword" for myopia prevention and control - defocus lenses

Author: Zhang Wenjuan: The First Affiliated Hospital of Naval Medical University, Shanghai Changhai Hospital

Reviewer: Zhang Rui, deputy chief physician, Shanghai Changhai Hospital, the First Affiliated Hospital of Naval Medical University

Primary and secondary school students have already started their summer vacation. During the summer vacation, children have more opportunities to use mobile phones, televisions, computers, etc., and vision problems have become the focus of parents' attention. Myopia is currently the main cause of vision problems in children and adolescents. The prevention and control of myopia is imperative. Among the many myopia prevention and control methods, defocusing glasses that can delay the development of myopia are increasingly favored by parents.

1. What is myopia? What is peripheral defocus?

For normal eyes, parallel light from the outside world passes through the cornea and lens to form an image on the retina, and there is no defocus. Myopia means that when the eye is in a state of adjustment and relaxation, after parallel light from the outside world passes through the cornea and lens, its imaging focus is not on the retina, but in front of it, resulting in blurred vision. After the peripheral part of the light defocuses and enters the eye, it focuses behind the retina, forming peripheral defocus.

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2. What is the principle of defocus lens?

Ordinary frame glasses are ordinary single-vision lenses. The central light is refracted and focused on the retina, so that the central vision is corrected. However, the peripheral light comes in and focuses behind the retina, which does not solve the problem of peripheral defocus.

Peripheral defocus is an important factor leading to the progression of myopia. Correcting peripheral defocus may be beneficial to controlling myopia. How do defocus lenses work?

Defocus glasses are also called frame glasses that reduce peripheral defocus of the retina. The lenses are divided into two areas. The central optical area is a single-vision lens, and the peripheral functional area is distributed with concentrically arranged annular micro-cylindrical lenses. The image at the center of vision is projected onto the retina, and the periphery is projected onto the retina or in front of it. The defocused image is used to control the growth of the eye axis and delay the progression of myopia.

The position of the central corneal image on the retina does not affect the growth of the eye axis, but the position of the peripheral corneal field image on the retina is the important factor that truly affects the development of the eye axis.

3. What are the precautions when wearing defocus lenses?

1. Wear all day: The longer the peripheral defocus effect is maintained, the better the control of eye axis growth. Therefore, defocus glasses should be worn all day except when sleeping and bathing to achieve a more ideal control effect.

2. Putting on and taking off glasses with both hands: The key to wearing defocused glasses is to align the optical center of the lens with the center of the pupil. If the frame is deformed during wearing, causing the pupil position to shift, the best peripheral defocus effect will be lost. In daily life, putting on and taking off glasses with one hand is the action that is most likely to cause the frame to deform. Because when putting on and taking off glasses with one hand, the frame is always stressed in one direction, and over time it will tilt in one direction, so that the optical center of the lens cannot be aligned with the pupil position, affecting the effect.

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3. Avoid slipping: Putting on and taking off the glasses with both hands solves the problem of the frame being tilted to the left or right, while preventing the frame from slipping is to solve the problem of the frame being tilted downward. When using defocused lenses, you need to observe whether the temples can be stably hung on the ears. If it is easy to slip, you need to use ear hooks to keep the frame stable to achieve the ideal prevention and control effect.

4. Have reasonable expectations for the adaptation period: The periphery of the defocused glasses is a ring of micro-cylindrical lenses. The light entering the eye through this area is imaged in front of the retina, and the periphery of the visual field will feel a little blurry. If it is the first time for children to wear defocused glasses, they will feel tired or blurry when looking at close objects in a short period of time. This is normal, and you must not think that there is something wrong with the glasses and stop wearing them.

5. Avoid tilting your head when reading or writing, or lying sideways when reading: Wearing defocus glasses requires equal defocus stimulation for both eyes, but tilting your head when reading or writing, or lying sideways when reading, will cause the defocus glasses to be used unevenly for both eyes, which in turn causes unbalanced defocus stimulation for both eyes. As a result, the eye axes of both eyes may develop at different rates, leading to anisometropia. Anisometropia has a greater impact on vision than myopia. Therefore, you must avoid tilting your head when reading or writing, or lying sideways when reading, especially for children who wear defocus glasses.

6. Rinse with clean water: There are many protrusions on the annular micro-cylindrical lens around the defocus lens. If you use a dry cloth to wipe it repeatedly, it will wear out the micro-lens and cause the defocus stimulation formed in the eye to change. Therefore, if the glasses are dirty, you should rinse them with clean water. If they are particularly dirty, you can use a little glasses detergent to make foam and wash them gently. Then rinse with running water and dry with a soft paper towel. Do not rub them repeatedly.

Finally, defocus glasses are not a panacea. They can indeed control the rapid growth of the eye axis, but they cannot stop the growth of the eye axis. If the wrong eye use continues, and the factors that stimulate the growth of the eye axis are stronger than the control power of defocus glasses, myopia will still increase. Sufficient outdoor and visual function training can reduce the stimulating factors that form myopia and achieve ideal prevention and control effects.

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