How to wear contact lenses for myopia and astigmatism

Everyone wants to have a pair of bright eyes, but with the popularity of the Internet, people are looking at computers and mobile phones for longer and longer periods of time, so they all have varying degrees of myopia or even astigmatism. In the past, due to limited conditions, people could only wear thick glasses, but now with contact lenses, people can see things without affecting their appearance. So how do you wear contact lenses for myopia and astigmatism?

Adding the degree of astigmatism directly to the degree of myopia is actually a very simple and crude method, which is not healthy and scientific! Usually, astigmatism above 75 degrees needs to be corrected, otherwise it will cause blurry vision or double vision. Frequently wearing glasses with incompletely corrected astigmatism may cause worsening of myopia, eye fatigue, and even cause serious phenomena such as headaches. Therefore, it is recommended to wear contact lenses that can correct both myopia and astigmatism at the same time.

Astigmatism contact lenses are developed for people with astigmatism symptoms. The curvature radii of the two mutually perpendicular meridian directions of the hyperboloid surface (inner surface and outer surface) of the astigmatism contact lenses are different. The most important design principle of astigmatism contact lenses is the positioning of the lenses, because only by keeping the astigmatism axis stable can the astigmatism be corrected.

principle

Astigmatism contact lenses are divided into custom astigmatism and ordinary astigmatism contact lenses, so the principle is subdivided into two situations

Spherical glasses

Ordinary spherical contact lenses use the tear lens formed by the contact lens and the cornea to correct corneal astigmatism. The liquid lens composed of tears between the back surface of the contact lens and the front surface of the cornea is called a tear lens. However, only when corneal astigmatism is less than 0.75D can it be corrected with a tear lens formed by an ordinary spherical contact lens. The lower the water content and the better the formability of the contact lens, the better the effect of correcting low-degree astigmatism.

If the range exceeds this, custom astigmatism contact lenses are required.

Astigmatism glasses

When corneal astigmatism is greater than or equal to 0.75D, ordinary spherical contact lenses cannot be used to completely correct it. It can only be corrected by customized astigmatism contact lenses (customized astigmatism contact lenses). At the same time, non-corneal astigmatism (mainly caused by lens astigmatism) can also be corrected by customized astigmatism contact lenses.

Astigmatism contact lenses refer to contact lenses whose hyperboloid surfaces (inner and outer surfaces) have different radii of curvature in two mutually perpendicular meridian directions, and are also called complex curved contact lenses. The most important design of customized astigmatism contact lenses is the stability of the lens, because only by keeping the astigmatism axis stable can the astigmatism be corrected. Generally speaking, there are three principles for stabilizing custom astigmatism contact lenses:

A. Prism vertical weight method. A prism of 1Δ~1.5Δ is designed on the lens. Due to gravity, the thick side of the prism always moves downward to keep the lens stable. In addition, the prismatic base of the lens increases the thickness, and the oxygen conductivity of the thicker lens area decreases, which reduces comfort.

B. Double-sided thinning method. The upper and lower peripheral areas of the lens are thinned, and the thin areas interact with the eyelids (especially the upper eyelid) to position the lens and dynamically stabilize the axis. (This is the most common method.)

C. Edge cutting method. Cut off a portion of the lens at the bottom, about 0.5~1.5mm wide, and fix the missing portion to the lower eyelid margin to prevent rotation.