SPECTACLES PRESCRIPTION

How do I read a spectacles prescription? Why do I get different prescriptions from different optical shops? Why is my contact lens prescription different?



READING A SPECTACLES PRESCRIPTION

Practioners generally write a prescription using “diopter”, for instance “-5.00”. This is equivalent to the layman “500 degrees”. Locally we prefer to use “degree” to refer to the prescription or “power” of the eye.


A simple prescription looks something like this:




Or it can also be written as the following:

R -2.00 / -1.00 x 010
L -2.50 / -0.50 x 170
ADD +1.50


SPH
The first number, “Sph” refers to “Spherical Power”, which is either myopia (indicated by a minus sign) or hyperopia (indicated by a plus sign).

CYL
The second number, “Cyl” refers to the “Cylindrical Power”, which is the astigmatism. Locally, it is indicated by a minus sign.

AXIS
The third number, “Axis” is the ‘direction’ of the astigmatism. This can range from 1 to 180, and 180 is not higher than 1 or 180 times as large as 1! It is simply a direction, like a bearing on a map.

ADD
The last number, “ADD” is the addition for presbyopic wearers, i.e. those aged above 40 and have difficulties with near work when given a prescription for distant vision. This is generally similar for both eyes, except in circumstances such as if one eye had surgery done to remove the lens within the eye.


A full prescription (one that you can prescribe a pair of glasses from) will also generally include your personal details, the date of the prescription, distance between the pupils of your eyes (also known as PD or pupillary distance), and other useful information. As your frame and lens choice can also affect the vision and comfort, sometimes the optical store prescribing the glasses to you may adjust the prescription.


GETTING DIFFERENT PRESCRIPTIONS FROM OPTICAL STORES

Yes it’s normal.

You’d have noticed that the degree jumps in steps of 0.25, or “25 degrees”. In actual fact our eyes’ real degree can be something like “-2.135”, which would, depending on circumstances, result in a prescription of -2.00 or -2.25. In addition, other factors such as how tired we are when we did the eye test, as well as what we are doing prior to the eye test can also affect the results.

Sometimes, distance to the testing screen or types of wordings used for testing, or even the practitioner’s years of practice can affect the final prescription.

Rather than looking at what is right or wrong (and it will only give an endless international debate), we think it’s good to find the prescription that gives the best balance between vision and comfort, taking into account the specific use and purpose of the glasses where appropriate.



CONTACT LENS PRESCRIPTIONS

Your contact lens prescription may be different from your spectacles prescription. This is because the contacts are on the eye, whereas the lenses of your spectacles are positioned a distance away from the eye.

Generally, spectacles prescriptions above 400 degrees need to be altered when dispensing contact lenses.

Also, while we typically correct as per the prescription for glasses, disposable contact lenses may have a limited set of powers so the prescribed contacts are not the exact prescription; or the astigmatic contacts may rotate in your eye hence the practitioner may compensate by altering the prescription.

Combining the two above factors, this means that while you may have the same contact lens prescription as your friend, the spectacles prescription may be different due to difference in your nosebridges, frame choice, how the contact lenses fit in the eye, and the astigmatism.



PRESCRIPTION OVERSEAS

When going overseas to countries such as UK and Canada, doing a pair of glasses requires a verified prescription. This means that you can either get a refraction done there (approximately $50 - $90 without insurance coverage), or bring along your prescription from an optical store here.

We’d be happy to provide you with your prescription if you’ve done your glasses here!

Also, some countries use a different format of writing prescriptions, hence they need to be transposed into the appropriate local format, which your optical store can do for you. For instance, -2.00/-1.00x010 can also be written as -3.00/+1.00x100.



We hope you found the above useful. If you have any questions regarding your prescription, feel free to contact us; we’d be glad to be of help!