Glass prescription can be difficult to understand, especially when no one else in the family has worn glasses before. Most patients are puzzled by the ‘signs’ and ‘numbers’ on the glass prescription and would want to ask a lot of questions regarding it to the doctor, but are either too “shy” or they are gently “shoved out” of the consulting room for want of the doctor’s time.
This post will tell you most of the things that you need to know about your glass prescription.
But before that, let us review the common refractive error conditions.
Farsightedness, or hyperopia, as it is medically termed, is a vision condition in which distant objects are usually seen clearly, but close ones do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is not focused correctly.
Nearsightedness, or myopia, as it is medically termed, is a vision condition in which close objects are seen clearly, but objects farther away appear blurred. Nearsightedness occurs if the eyeball is too long or the cornea, the clear front cover of the eye, has too much curvature. As a result, the light entering the eye isn’t focused correctly and distant objects look blurred.
Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result, vision becomes blurred at any distance.
+ : farsighted, or longsighted prescription: hyperopia.
– : nearsighted, or shortsighted prescription: myopia.
How bad is the spherical prescription?
The number is in “diopters” but you don’t need to know too much about that, it’s a measure of how much the curvature of the eye is off from normal. Basically, the higher the number (ignoring the plus or minus), the worse the prescription.
Cylinder is the measure of astigmatism. Astigmatism is when there’s an irregular shape to the cornea, often described as a football shape. It causes blurriness at any distance. There are two measurements that go along with astigmatism, the first, cylinder, is a measure of how severe the astigmatism is.
How bad is the cylinder prescription?
Like the spherical error, the cylinder number is measured in diopters. The thing you want to pay attention to is the number. It may be written as a plus or a minus, but that doesn’t actually make any difference in how bad the prescription is. The higher the number after the plus or minus, the more severe the astigmatism.
If you think of astigmatism as a football shape, it makes sense that the football might be turned any direction. The axis number then, tells you the orientation of the astigmatism. The number is in degrees, it doesn’t have anything to do with how severe the astigmatism is, just how it is situated on your or your child’s eye.
If you or your child needs bifocals, you will likely see a number here. This tells you how the prescription should be changed for close up. Let’s say your child has a regular glasses prescription of +3.00, if the add number is +1.00, then the near distance prescription will be +3.00 + 1.00, which equals +4.00 (3+1=4). In the same vein, if your child is nearsighted, say -4.00, but has an add of +2.00, then the near distance part of the bifocals will have a prescription of -4.00 + 2.00, which equals -2.00.
Sometimes, you don’t have an “Add” part of the prescription, and instead you’ll just see a prescriptions for distance vision and a separate prescription for near vision.
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