Contact lenses with astigmatism

Nowadays, more and more people are nearsighted, and people have no choice but to wear glasses. Some female comrades think that wearing glasses can easily collapse the bridge of the nose and make them look ugly, so they invented contact lenses. Contact lenses are soft lenses with prescription that are worn directly on the eyes without affecting the appearance. Now there are contact lenses with astigmatism, but contact lenses are more or less harmful to the eyes.

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.

Basic Information

1. Astigmatism exceeds a certain range: Before customized astigmatism lenses came out, astigmatism was generally converted into myopia degrees for fitting glasses, but medical experts recommend that only when the astigmatism degree is less than 0.75D, there is no need to customize astigmatism contact lenses. Otherwise, there will be discomfort. It is recommended to use customized astigmatism lenses, which can correct vision according to the degree of astigmatism and axis position;

2. Hyperopia and the need to wear contact lenses: Ordinary contact lenses only have myopia, not hyperopia, so those who are hyperopic and need to wear contact lenses can choose to have them custom-made;

3. Case of severe myopia: The degree of myopia of conventional contact lenses can generally only reach -1000 degrees, and some are even only -900 degrees. If you have severe myopia and need to wear contact lenses, you can choose to customize high-degree contact lenses.

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.