Is eye axis length related to myopia? Parents must read!

What is axial length examination? Is it related to myopia?

Correct understanding of eye axis

Our eyeball is a nearly spherical shape. The distance from the outermost layer of the eyeball that receives light, that is, from the cornea-lens-vitreous body-retina, is called the "eye axis" length.

The eye axis of a newborn baby is short, about 16.5mm. When light enters the eye, it will focus behind the retina, so infants and young children are all hyperopic, also known as hyperopia reserve. As they grow and develop, the eye axis slowly grows, and when the focus falls exactly on the retina, it is emmetropia. When the eye axis continues to grow and the focus falls in front of the retina, myopia is formed.

Axial length reference for children

The axial length of the eye increases with age, just like our height. It will only grow and not shorten, and it is irreversible.
Usually, the development of the eyeball stops after the body's growth and development ends before the age of 18. The following figure shows the average axial development of children of different ages (for reference only)!

If you find that your child's eye axis is outside the reference range, you need to be alert!

As the eye axis continues to grow, the focal point falls in front of the retina, and myopia will form. The longer the eye axis, the deeper the myopia. On average, myopia deepens by about 250-300 degrees when the eye axis grows 1mm.

Monitoring the growth of the axial length is one of the important indicators for evaluating a child’s refractive development. The axial length of children of different ages is also different.

On the one hand, measuring the axial length of the eye is to evaluate the axial length and age to see if they match. On the other hand, it also depends on the growth rate of the axial length. The faster the axial length grows, the higher the degree of myopia. It is like blowing a balloon. When the balloon is small, the wall of the balloon is thick. When the balloon becomes larger, the wall of the balloon will become thinner.

The relationship between eye axis and refraction

The refractive power of the eye is mainly determined by the corneal curvature, axial length, and the refractive power and position of the lens.

Corneal curvature is the curvature of the cornea. The average corneal curvature is about 43D. If it is higher than 43D, the center of the cornea is steeper, and if it is lower than 43D, the center of the cornea is flatter. During eye development, the corneal curvature is relatively stable at the age of 3.

The lens changes slowly, so the axial length can be considered the only variable.

It can also be simply understood as: refractive power ≈ corneal curvature + lens refractive power + eye axis.

Regularly measure the eye axis

Generally, a 3-year-old child can cooperate with the measurement of the axial length of the eye. Axial length measurement is a non-invasive examination that does not require mydriasis. It is a more objective monitoring indicator than visual acuity or even myopia. For children in the growth and development period, the axial length of the eye can be measured every 3-6 months.

Prevent eye lengthening

1. Pay attention to children's eye use standards and maintain good eye habits;

2. Take your children outdoors more often to get in touch with nature and natural light;

3. Take your child to have their eyes checked regularly, and you can go to the optometry center to establish a child optometry file;

4. If you already have myopia, follow your doctor's advice and undergo optical correction.