ABSTRACT
The following are the main differences between a flexible ortho C lens and a conventional hard contact lens (or rigid gas permeable lens):
There is no prescription.
It is slightly flatter (or less curved) than the curvature of your cornea. (A generic rigid gas permeable lens is already designed to be slightly flatter than the flat meridian of the cornea for a better fit.)
It is slightly thinner and thus more flexible. (It is still within the thickness specifications proposed by Stein et al. (2002). It is classified as a thin design.)
There are two kinds of contact lens available on the market: soft and hard. If you are familiar with wearing a soft contact lens, it is easier to adapt to an ortho C lens. If your client is unfamiliar with wearing a contact lens, it will probably take a few applications before the eye can adapt to the lens I am recommending. Although an ortho C lens is still referred to as a “hard” or rigid gas permeable lens (RGP lens), it is more flexible. When you hold an ortho C lens by the edge between your thumb and forefinger and gently squeeze it, it will flex a bit. A typical hard contact lens is very stiff.
Although the lens has no prescription, it is not a generic design. It must specifically address the different ranges of myopia—whether it is mild, moderate, midrange, or severe myopia. In this publication, we are just dealing with the mild and moderate range.
The flatness of the lens is generally equal to the absolute value (ignoring the minus sign) of your client’s prescription as outlined in the chapter Specifications. An ortho C lens is slightly flatter than the curvature of the cornea, but it is not as flat as an orthokeratology (ortho K) lens. 86Wearing a flatter lens is not unusual. A conventional RGP lens is already designed to be flatter than the cornea in order to achieve a better fit.
