Selection of various parameters of contact lenses

- Jan 16, 2020-

There are many parameters for contact lenses. Different parameters make up different contact lenses, which will also affect our wearing experience. If you want to choose a pair of lenses that suits you, you still need to understand the meaning of each parameter and the correct choice to make Wear healthier, safer and more comfortable.

Selection of contact lens materials:

There are three types of soft contact lens materials, phema, hema, and non-hema. At present, more are hema and non-hema. Hema is a hydrophilic soft lens material based on hema and other auxiliary materials. Its water absorption and material are soft. The degree is good, the monomer added by each manufacturer is different, and the characteristics of different hema materials are different, such as water content and oxygen permeability. Non-hema materials are hydrophilic materials that do not contain hema components, such as crofilcom, atlafilcon, etc., which are more resistant to sedimentation and toughness.

Choice of contact lens power:

Because the distance between the frame glasses and the cornea is 10mm ~ 15mm, the distance between the Chinese eye and the eyeglasses is 12mm. After obtaining the prescription by using the conventional refractive examination method, a special refractive conversion method is required to determine the refractive power of the contact lens. prescription. The converted photometric formula for frame glasses and contact lenses is d '= d / 1-dd (d' is the contact lens power, d is the frame lens refraction power, and d is the eye distance 0.012m)

Astigmatism eye contact power conversion, when astigmatism <1.00d, lenticular power greater than or equal to 3: 1; astigmatism greater than 1.00d, lenticular power greater than or equal to 4: 1, you can consider using ordinary contact lenses for astigmatism correction. When choosing a lens, you can generally add half of the amount of astigmatism in the prescription to the spherical lens part, and then convert the invisibility. The purpose is to land the smallest diffuse spot of astigmatism on the retina to achieve relatively optimal vision. 4.00ds / -0.50dc * 180 can be worn with -4.00 for contact lenses.

The minimum photometric interval gradient of the actual contact lens piece is ± 0.25, and the photometric value converted by the formula is often an exact arbitrary decimal. Therefore, the mantissa must be rounded down, and the lower and closest power can be selected.

Selection of water content in contact lenses:

The moisture content of soft contact lenses is between 30% and 80%. The moisture content of lenses depends on the hydrophilic composition of the formula. The conventional moisture content of soft contact lenses is classified as low water content <50%, high water content> 50%, water It is the carrier of oxygen through soft lens material, ordinary hydrogel material, the permeability of oxygen is proportional to the water content.

High water content: more oxygen-permeable, lens soft and comfortable, but the lens is easy to break, astigmatism correction is not good, more used for frequent replacement lenses.

Low water content: better moldability, astigmatism correction and lens wearing, reducing dry eyes and deposits.

Selection of contact lens base arc (bc):

The curvature of the rear surface of the central optics is called the base arc. The curvature of the cornea determines the choice of the base curve of the lens. Because it cannot be observed visually, you can use a corneal curvature meter to measure the value of the wearing eye and choose the corresponding product according to your eyes.

Scientific selection of contact lenses suitable for you is very helpful for wearing experience and eye health.