I’d like to share this information with people who wear glasses, especially those with high minus diopters (strong myopia) and significant astigmatism. This should help you avoid having to adapt every time you buy new glasses.
There are two really significant lens parameters that you should know. These parameters are not present in your prescription, unfortunately. Usually a prescription contains the following information:
| Sphere | Cylinder | Axis | |
| OD | -5.00 | -3.5 | 020 |
| OS | -5.00 | -3.5 | 130 |
PD 68
- OD — right eye
- OS — left eye
- Sphere — this is your myopia
- Cylinder — this is your astigmatism
- Axis — this the angle of astigmatism
- PD (Pupillary Distance) — this is the distance (in millimeters) between the centers of your pupils
I have strong myopia and astigmatism, so I need a specific base curve and type of lenses. By lens type, I mean spherical and aspherical lenses.
Base curve refers to the curvature of the front surface of a lens.
It describes how flat or how curved the lens is and is usually expressed as a number (for example, 2, 4, 6, or 8).
Spherical lenses have the same curvature across the entire surface. They are thicker, but in some strong prescriptions they can provide more predictable peripheral vision.
Aspherical lenses have a variable curvature designed to reduce thickness and magnification. However, for strong myopia combined with high astigmatism, they may cause more noticeable peripheral distortion and require longer adaptation.
All my life, I have used and still use base curve 4 spherical lenses.
In December, I ordered new glasses. I asked to make sure that the order contained information about the base curve and that it was 4. When I received my new glasses, I noticed that I saw as if I were in an aquarium, this is called the “barrel effect.” An assistant in the optical store measured the base curve, and it was 2, so he reordered the glasses for me. After two weeks, I received my glasses and found another issue: the bridge was defective, and the lenses were at different distances from my eyes. The assistant reordered the glasses again. After another two weeks, I received the new glasses, and… they had aspherical lenses. Therefore, the assistant reordered the glasses for the third time today. I hope I will receive my glasses with a base curve of 4 and spherical lenses, without any defects.
I cannot use aspherical lenses at all; my eyes become tired too fast, and the adaptation period is too long. Also, I have another pair of glasses with transitional spherical lenses, and switching between aspherical and spherical lenses when you have myopia and astigmatism is really painful. I mean strong discomfort and eye strain.
When you have strong myopia and astigmatism, aspherical lenses are not always a good choice. They are thinner and flatter, but they can make peripheral vision feel distorted. Images may look unnatural, especially when you move your eyes. Because of this, the adaptation period can be long, and your eyes may get tired quickly. For some people, spherical lenses feel more comfortable and predictable, even if they are thicker. Spherical lenses provide a visual field that my brain is already used to.
So, my advice to you: check your base curve and lens type before ordering your new glasses, and you won’t have any adaptation at all if your prescription is the same. Even with a new prescription, adaptation will be much easier. As I mentioned, this is especially noticeable with strong myopia and astigmatism when you change the base curve and lens type.
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