Conversion of contact lenses

Because wearing frame glasses for a long time will cause a person's eyeballs to bulge, eyes to deform, and make a person's eyes look dull, contact lenses have become a favorite of more and more myopic patients. When fitting contact lenses, doctors will also choose contact lenses of different degrees according to the patient's degree. If a patient has astigmatism symptoms, he or she should pay more attention to the conversion method for astigmatism contact lenses when wearing contact lenses.

Contact lens power conversion, contact lens and optometry power conversion. The degree of optometry is the degree of frame glasses. The degree of frame glasses is different from that of contact lenses. The distance between the back vertex of frame glasses and the cornea is about 12 mm for Asians. There is a conversion formula for the degree of contact lenses: contact lens diopter = frame glasses diopter ÷ (1-0.012×frame glasses diopter). 1 diopter is equivalent to 100 degrees as we usually say. The diopter of myopia is a negative number, and the diopter of hyperopia is a positive number. 0.012 is the distance between the frame glasses and the highest point of the eyeball, measured in meters.

Contact lens diopter = frame glasses diopter ÷ (1-0.012 × frame glasses diopter)

There is a conversion formula for the degree of frame glasses and contact lenses: Fo=Fs/(1-dFs)

Fo—contact lens degree Fs—frame mirror optometry degree d—distance between frame mirror and cornea (0.012m)

For example: if the power of frame glasses is -4.00D and the distance between the frame and the contact lens is 12mm, the power of the contact lens can be converted to Fo=-4.00D/[1-0.012(-4.00)]=-3.82D, and can be given as -3.75D.

(Below -4.00D, the difference is small and can be ignored)

If the power of frame glasses is between 4.00D and 5.00D, the power of contact lenses is: myopia minus 0.25D, hyperopia plus 0.25D;

If the frame plus lens power is between 5.00D and 7.00D, the contact lens power is: myopia minus 0.50D, hyperopia plus 0.50D;

If the frame plus lens power is between 7.00D and 9.00D, the contact lens power is: myopia minus 0.75D, hyperopia plus 0.75D;

If the power of frame glasses is between 9.00D and 11.00D, the power of contact lenses will be: myopia minus 1.00D, hyperopia plus 1.00D.

If a certain degree does not have a corresponding degree after conversion, you can choose the closest lower degree. For example, 800 degrees minus 75 degrees is 725 degrees. If there is no 725 degrees, you should choose 700 degrees, and so on.

Contact lenses can correct mild astigmatism. Generally speaking, the lower the water content, the better the effect of correcting astigmatism. For example, contact lenses with a water content of 38% can correct astigmatism within 200 degrees. In other words, if the astigmatism degree does not exceed 200 degrees, you can ignore the degree of astigmatism when choosing contact lenses with a low water content, and directly choose according to the degree of myopia. If the astigmatism degree is higher, you can go to a large optical shop to customize it, but the price will be very high. In principle, if the astigmatism degree is greater than 75 degrees, it is recommended to purchase special astigmatism contact lenses.