Holding your glasses prescription, you must be wondering what the numbers mean. You are not the first person to be wondering about it. It is difficult to understand when you are getting your glasses for the first time. And when you are ordering your eyeglasses online, you will need to manually enter the prescription numbers as they are not legible enough for humans to understand. You barely can read it and can barely understand what CYL or SPH means.
To solve your problem, have a brief read of what these numbers mean and what they mean for your eyesight.
What does (+) or (-) means in an eye prescription?
Let’s start with the easiest one. Your prescription will have numbers either positive or negative. The positive numbers do not mean your eyes are good, and the negative does not mean they are too bad.
(+) denotes, you have farsightedness. During the eye test, you were given a handheld chart to read. This chart helps in determining how far or close you can read. You must have difficulty reading newspapers or minute texts on bills and documents. You might be squinting and stretching your arms to read the paper. You have (+) vision or hyperopia. You have difficulty seeing near objects.
(-) denotes, you have nearsightedness. During the test, you were tested with a vision chart on the wall or at a distance of 20 feet. You have trouble seeing anything at a far distance. You cannot drive well as you cannot see the road signs far away. This type of vision is called myopia. It is the most common eye defect.
How bad is your eyesight?
Suppose your numbers are closer to zero, between 0.75 to 0, whether negative or positive. In that case, you have almost good eyesight with no need for wearing glasses regularly. You don’t really need glasses to correct your vision. These slight changes almost go unnoticed.
If your eye prescription is between 0.75 to 3, both positive and negative, it means you have a mild eyesight defect. You will need to wear glasses for most of the tasks. You can survive without your glasses too. You won’t have too many survival issues like colliding in every nook and cranny.
Eye prescription more than 3 falls under high prescription power. You will be advised to use your glasses constantly. You get very blurry vision without your glasses.
What do OS and OD mean?
The full form of OS is oculus sinister, and OD is oculus dexterous. It might seem very much occult-related, but it simply means left and right, respectively. It is normal to have different numbers in both eyes. You can have -2.5 in the left eye and -3.0 in your right eye. You mostly see the vision through your dominant eye. So, this minute difference is rarely felt. You might even have perfect vision in your dominant eye and a slight vision issue in the other eye. You will not notice the difference until you go for an eye test.
What do CYL and SPH mean in eye prescription?
SPH stands for spherical power, and CYL stands for cylindrical vision power. The numbers under SPH means either myopia or hyperopia. You can either have myopia, the numbers with the (-) sign or hyperopia, the numbers with (+).
CYL or cylindrical vision denotes your astigmatism. Astigmatism is an eye condition where your eye is not completely round. You have slight vision because of it. If you have numbers marked under the CYL column, then you have astigmatism. During the test, you must have trouble reading some letters. Letters like L appeared as if it was I or difficult to differentiate between E and H.
You can have myopia and hyperopia along with astigmatism.
What does ADD mean?
There is a separate column of ADD, which might also have numbers with the (+) sign. If you have this column filled, then you have presbyopia. You have trouble seeing both far and near. You need glasses assistance for looking at a far distance and also for reading your favourite book. Your optician might have advised you to get varifocal glasses.
Varifocal glasses or progressive glasses are the glasses that aid your vision at all distances. You can see in every distance without having to adjust your position or changing your glasses.
More jargon - Axis, Base, Prism
If you have astigmatism in any or both of your eyes, your eyes will not be perfectly round. And this is denoted by axis. Axis measures the angle at which you have astigmatism. If your eye prescription has a -0.5 CYL X 180°, you have a -0.5 dioptre correction for astigmatism at the 180° axis. It is important to note this number when getting your glasses made as astigmatism correction will give you better vision. You will need to strain your eyes if you do not get your glasses made with your cylindrical power.
Prism is denoted for those who have eye alignment issues. This is marked generally with a triangle sign or p.d. (prism dioptre). This is a necessary correction for those suffering from strabismus or eye alignment conditions. Prism power gives correct vision with such eyesight.
Base is also used for eye alignment issues. You have the base down or base up in your eyes. It can be different for both your eyes. If your prescription says (+0.5 p.d. Up), then you need prism glasses with +0.5 prism dioptre correction in an upward direction.
What is PD?
PD (and not p.d.) is an abbreviation for pupillary distance. It is the distance between the centre of both eyes. Sometimes there are two PD denoted under OS and OD. You already know what OS and OD stand for. If your eye prescription has two PDs. The first one is for the distance between the centre of your left eye to the nose bridge. And the other is the distance of the centre of the right eye to the nose bridge. These numbers can be the same or vary in some cases. This number is important to get the right fit of glasses.
Is the prescription for eyeglasses and contact lenses the same?
No. If you are wondering about getting contact lenses with the same eye prescription as your glasses, you will have vision issues. Maybe slight issues but more if you have astigmatism too.
Glasses sit on your face at a nose distance while contact lenses are put right over your eyes. This difference means a lot for your eye prescription. Eyeglasses are made in a way that allows you correct vision when you see through them.
Contact lenses prescription is different. It has two additional parameters, BC and DIA, where BC stands for base curve and diameter of the lenses. In the case of astigmatism, the eyes are not perfectly round. This causes a problem when putting on contact lenses. You will not see clearly if the base curve is not taken into account when making your lenses. Toric lenses are widely used for astigmatism. These contacts are not round like the usual contact lenses.
Quite confusing, isn’t it? Leave the prescription for the experts. Always keep your prescription slip handy in case you need to get glasses made in an emergency. Tuck it inside your wallet and when required, take them out.