How to choose contact lenses

Nowadays, almost everyone has a mobile phone. Except when sleeping, people spend most of their time playing with their mobile phones, which is very harmful to the eyes. Therefore, there are more and more people with myopia. However, many people do not like to wear glasses. Many people choose to wear contact lenses. The choice of contact lenses is also very important. So how should you choose the contact lenses that are suitable for you?

1. Contact lens replacement cycle selection:

Contact lenses that are used for more than 6 months are called traditional lenses; lenses that are used for 1 week to 6 months (not worn overnight) are called frequently replaced lenses; lenses that are discarded after one use are called disposable lenses.

2. Choice of contact lens materials:

There are three types of soft contact lens materials: phema, hema, and non-hema. Currently, hema and non-hema are more common. Hema is a hydrophilic soft lens material based on hema with other auxiliary materials added. It has good water absorption and material softness. Each manufacturer adds different monomers, and different hema materials exhibit different characteristics, 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 tougher.

3. Choice of contact lens degree:

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

Conversion of contact lens degree for astigmatism: when the astigmatism is less than 1.00d and the cylindrical power is greater than or equal to 3:1; when the astigmatism is greater than 1.00d and the cylindrical power is greater than or equal to 4:1, you can consider using ordinary contact lenses to correct the astigmatism. When choosing lenses, generally half of the astigmatism in the prescription can be added to the spherical part, and then the contact lens degree can be converted. The purpose is to place the minimum diffusion spot of astigmatism on the retina to achieve the relatively best vision. For example, if the prescription is -4.00ds/-0.50dc*180, then -4.00 contact lenses can be worn.

The minimum gradient of the actual contact lens brightness interval is ±0.25, but the brightness converted by the formula is often an accurate arbitrary decimal, so it is necessary to make a choice based on the decimal point, and you can choose the lower and closest degree.

4. Choice of contact lens diameter:

When wearing soft contact lenses, their edges can exceed the corneal edge by 1mm~1.5mm, so that they can adhere stably to the cornea. When choosing the diameter of contact lenses, you can choose according to your corneal diameter. Normally, add 2mm~3mm to the corneal diameter. The average corneal diameter of Chinese people is 11.5mm~12mm, so it is more appropriate to choose a lens diameter of about 14mm. You can choose according to your corneal diameter.

5. Choice of contact lens thickness:

The thickness of contact lenses has an important impact on wearing safety and comfort. It is usually measured based on the center thickness of a -3.00d lens. For soft contact lenses, the central thickness of ultra-thin lenses is below 0.06mm, the central thickness of thin lenses is between 0.06 and 0.10mm, and the central thickness of standard thickness lenses is between 0.10mm and 0.15mm. For wearers with drier eyes, thicker lenses should be selected. For first-time wearers, standard thickness can be selected. For those with higher diopters, thin lenses should be selected.

6 Choice of water content for contact lenses:

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

High water content: more oxygen permeable, soft and comfortable lenses, but easily damaged, poor astigmatism correction, more used for frequently replaced lenses.

Low water content: better molding degree, which is conducive to astigmatism correction and wearing glasses, and reduces dry eyes and attached sediment.

7. Choice of contact lens base curve (bc):

The curvature of the back surface of the central optic is called the base curve. The corneal curvature determines the choice of the lens base curve. Since it cannot be observed visually, a keratometer can be used to measure the value of the wearing eye and choose the corresponding product according to your own eyes.

8 As a medical optical device that corrects refractive errors, beautifies the eyes, and can also be used to treat certain corneal diseases, it is urgent to select contact lenses scientifically. When choosing contact lenses, you can refer to the various parameters and characteristics of contact lenses and choose the product that suits you best!