Ever wondered what are all those numbers on your glasses prescription (or "script")? Here's how to decipher it!
| SPH | CYL | AXIS |
Right | -1.25 | -0.50 | 180 |
Left | -1.50 | -0.75 | 005 |
ADD | R / L +1.00 | | |
PD | R 31 / L 31 | | |
Type of Lenses | Progressives | | |
This is what a typical simple prescription would look like.
We have a SPH, CYL, and AXIS value for both the Right and Left eyes.
SPH refers to the spherical component, it is either myopia (negative number) or hyperopia (positive number).
CYL refers to the cylindrical component, and it is your astigmatism; in Singapore this will be a negative number (e.g. -0.50), but in some parts of the world, it is given as a positive number (e.g. +0.50).
AXIS refers to the angle of the CYL, simply put, it is the direction of your astigmatism. It can range from 001 to 180, and a higher number does not mean it is worse - it is just like a bearing on a compass.
ADD refers to the addition, which is the power required to aid reading in people with presbyopia (usually those above 40 years old when reading starts getting difficult).
PD refers to the pupillary distance, which is the distance between the pupils of your eyes. This can be given as one number (e.g. 62mm) or as a right and left component (R31/L31).
Some prescriptions will state the type of lenses if they have been prescribed or are suggested to be prescribed. If you are over 40 years old and presbyopic (have presbyopia), single vision corrects for a single use - Far, Intermediate, or Near use. Office lenses correct for Intermediate and Near, while Progressives correct for Far, Intermediate, and Near vision, all-in-one. If you're under 40 years old, congratulations - it's almost always single vision lenses - we correct your vision for far, and your eyes do the work to focus for near tasks.
Detailed Prescription Information
You may also get a more detailed prescription or report, which includes your current glasses power, and other remarks or suggestions from your friendly optician or optometrist who did the eye check.
In the report above, you see three sections:
Current/Previous Spectacles, referring to the glasses you were wearing before doing a new pair of glasses;
Refraction, referring to the results of the 'eye power check', which also includes the VA or Visual Acuity;
Prescribed/Suggested, referring to the power that is done or suggested to be done for the new pair of glasses.
VA which is short for Visual Acuity, may be included in some prescriptions. 6/6 vision is the 'standard perfect vision', while a higher number below (like 6/12) shows a 'poorer' vision, and a lower number below (like 6/4.5) show a 'more perfect' vision. We like this detail because it can act as a benchmark in subsequent tests, to see if vision is getting worse (sometimes a sign of eye diseases or degeneration).
P.S. the number 6 is there because the vision chart is 6 meters away. Some places use feet, so it's 20/20 (or 20/40 or 20/15). If your vision is 6/12, it means what a 'perfect vision' friend can see while standing 12 meters away, you need to go closer to 6 meters in order to see, i.e. your vision is 'poorer' than your friend's. And vice versa.
Current Prescription VS Refracted VS Final Prescription
As seen in the prescription report above that is more detailed, you get your current glasses' power, the actual power tested (refraction is the process that we use to get your power), and the final glasses power that is prescribed or suggested to be prescribed.
"Whaaaaa...wait, how come test one power then give another power leh?"
We sometimes adjust the power (usually reduce) for easier adaptation. For example, if your current power is -1.00, tested is -1.50, we may give -1.25.
Of course things aren't that simple, as we may also consider factors like the astigmatism, current vision, symptoms that you may be having, and your visual needs. Sometimes even the frame choice can play a part in altering the final prescription!
There are no hard and fast rules here - what we want to achieve is a clear vision that is comfortable, tailored to the individual.
Some say it's an art as much as it is science. Experience helps!
Contact Lenses
So... do we order the contact lenses based on our spectacles prescription?
For certain prescriptions - the higher ones - the power has to be adjusted. This is because the spectacles sit at a distance from our eyes (usually 1cm to 1.5cm away), while contact lenses sit on the cornea itself!
In addition, the astigmatism may be 'compensated' into the spherical power, or it may be corrected using lenses that come with astigmatism, sometimes called toric lenses.
The final contact lens prescription can also differ based on the factors mentioned above - your visual needs, if you're happy with your current power, and so on.
This is why you should get contact lenses fitted for you - some places do allow for you to try on different powers, and even different lenses, in order to find one that best fits your needs as well as your eyes' needs! We call this a trial fitting. This is one of the ways to help keep your corneas healthy, as opposed to increasing your risk of an eye infection.
Always talk to your eye care practitioner and voice any concerns and clear up any doubts!
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