Stock lenses and RX lens

Stock lenses and RX lenses

Patients with high astigmatism have to pay extra for glasses. Why? Was he cheated by the dealer?

This is the reason for stock lenses and RX lenses. The maximum stock astigmatism for most lens models is only up to 2.00D. If the astigmatism exceeds this, you will have to pay more for RX lenses. RX lenses are produced in small quantities by professionals, making them more expensive than stock lenses, which are mass-produced in factories.

Why RX lenses ?

For example, if you are only stroe the 1.56 ASP lens. Spherical power from +4.00D to -10.00D , each diopter has a combination of cylinder power (for astigmatism) from 0.00D to -2.00D. Lens are going up by 0.25D interval, you will have 448 combinations for 1.56 ASP lens.

After 1.56 ASP , you will have 1.6 ASP , 1.67 ASP , 1.7 ASP , and 1.74 ASP. And then you start keeping lens with different coating.....

Just too costly to keep all the possible combination. Thus companies usually keep the cylinder power from 0.00D to -2.00D which is the most comment range of astigmatism.

Is astigmatism the only factor that affects RX lenses ?

No. For progressive lenses, they have more combinations than single vision lenses, so all progressive lenses are RX lenses.

Some low demand single vision lenses, companies will take the "zero inventory stretagy". Only RX version available.

For example: Hoya 1.74 ASP Full Control, Tokai 1.76 Bi-ASP Lutina, only RX version available.