Understanding your eye test results can seem borderline foreign.
And it’s no wonder.
Those weird numbers have such importance but so little meaning when you see unfathomable terms like Sph, Cyl, Axis or Prism.
But on your prescription paper, it’s these digits that inform how your lenses are shaped, angled and cut.
In this article, I'll explain what this all means.
What do the numbers on eye test mean?
The numbers on your eyes test refer to three primary aspects. The dioptric correction for your vision and/or the dioptric correction and axis to correct any astigmatism. These three aspects are assigned with unique columns listed as SPH, CYL and AXIS. However, there are further aspects to your prescription such as ADD which denotes your requirement for multifocal (progressive) lenses.
How do I read my eye test results?
Your prescription details will be written (or printed) in an abbreviated form, relating to the various corrections required for your vision. Here's a quick breakdown of what each abbreviation means.
SPH = Sphere (dioptric power for near or farsightedness)
CYL = Cylinder (dioptric power for astigmatism)
AXIS = The orientation (in degrees) of your CYL power
ADD = Addition (Additional magnification required)
Prism = Dioptric correction for muscular imbalance in your eyes
Plano = Zero dioptric power required
OD = Right eye (Oculus Dexter)
OS = Left eye (Oculus Sinister)
OU = Both eyes (Oculus uterque)
Example of right eye Sphere prescription | Positive SPH | +2.50
What is SPH on eye prescription?
SPH is shorthand for sphere and refers to the required power of your lenses to correct either short or long sightedness. SPH is measured in dioptres and can be written as positive (+) or negative (-) values for each of your eyes.
Positive SPH means you're hyperopic (far-sighted) when you can see objects far away clearly, but close objects are blurry.
Negative SPH means you have myopic (near-sighted) when you can see objects near to you clearly, but objects far away are blurry.
Zero SPH (0.00) means you have no refractive error. (See plano below)
Regardless of the (+) or (-), the higher the number, the stronger the power of your lenses. If your SPH is stronger than +/-4.00, you should consider using high index lenses as they can be very thick and protrude from the rim of your glasses frame.
For aesthetics and for weight, here’s a guide on what thickness of lenses to choose based on your prescription.
- Thinned: SPH +/-4.00-6.75 CYL max +/- 2.00
- Super Thin: SPH +/-7.00-9.00 &/or CYL max +/- 2.00
- Ultra thin: SPH +/-7.00-9.00 &/or CYL +/-2.25-6.00
Example of right eye Cyl prescription | Minus Cyl | -0.25
What is CYL on eye prescription?
CYL is shorthand for Cylinder which denotes the dioptric power required to correct astigmatism in either of your eyes. Cylindrical power is written as a positive (+) or negative (-) value which refers to the dioptres requires to correct myopic or hyperopic astigmatism.
Astigmatism is a refractive error that occurs when the cornea (the outermost layer of the eye) has an uneven curvature, causing light rays to focus on multiple points instead of just one. This results in blurred or distorted vision at any distance.
If your CYL boxes are empty for either of your eyes, this means you have no astigmatism and therefore no requirement for any AXIS either. However, this condition is extremely common and it’s likely you’ll have slight astigmatism in at least one of your eyes.
- 0.00 to 1.00 = low astigmatism
- 1.00 to 2.00 = mild astigmatism
- 2.00 to 3.00 = high astigmatism
Example of right eye Axis prescription | 180 degrees from meridian
What is AXIS on eye prescription?
AXIS refers to the angle of orientation for your cylindrical (CYL) correction. This value is measured in degrees ranging from 1° to 180°. CYL and AXIS are inter-related, therefore if your prescription contains a CYL value, you'll have an AXIS value too.
AXIS has nothing to do with the severity of your prescription. This is simply an angle (in degrees) which will often be seen as 020°, 090°, 120° or 170° etc.
In some instances, your optometrist may have written your CYL and AXIS freehand which can be separated by an “X”.
For example: CYL 1.50 x 060.Back to top ↑
Example of right eye Addition on prescription | Positive (+) 2.75 dioptres in each eye
What is ADD on eye prescription?
ADD refers to any Additional magnification you may wish to have within your lenses. These digits are measured in dioptres and will always be written as a positive (+) value, identical in both your left and right eye.
In multifocal lenses such as bifocals or varifocals, Addition can be used for either for intermediate or close vision zones, depending on how you wish to use your glasses. Unlike single vision lenses, bifocals or varifocals use an additional magnification portion in the lower half of your lenses which you can look through to see things at a close or intermediate distance.
The inclusion of ADD indicates your required correction for presbyopia. A common condition which occurs during middle-age which inhibits your close reading capability. Anything within 30cm from your eyes is considered as close-vision and is catered for in the lowest region of your lenses.
If multifocal lenses such as bifocals or varifocals aren't your thing, you can opt to have a separate pair of single vision glasses which would be specifically for close reading (within 30cm) or intermediate vision (arms length).Back to top ↑
Example of right eye Prism prescription | 0.5 Sph, Base upwards
What is PRISM in eye prescription?
PRISM denotes the dioptric power required to correct any muscular imbalance in your eyes. Prism is measured in dioptres and caters for various conditions such as strabismus (lazy eye), diplopia (double vision) or amblyopia (squint.)
If PRISM is present on your eye test results there will be two boxes per eye. Together, these related figures communicate both the dioptric power and orientation of the prism required.
In the first box, the dioptric power of your PRISM will be noted using fractional or metric figures. Depending on the preference of the optometrist, this can be indicated as ½ or 0.5, ¾ or 0.75, 1 ½ or 1.5 etc.
If written freehand, you may see a small triangle (Δ) between your prismatic power and base orientation. This is the Greek symbol for Delta which, for example, can be used to write a base inwards prism as: 0.5 Δ BI
In the second box the orientation of your PRISM will be noted in full or shorthand terms as seen listed below.
BU = Base up
BD = Base down
BI = Base in (towards the middle of your frame)
BO = Base out (towards the outside of your frame)
Example of a plano prescription | No corrective power (0.00)
What does plano mean on eye prescription?
Plano refers to your lack of Spherical dioptric power. This means you're neither nearsighted or farsighted in that particular eye. Plano derives from the Latin word plānus for “flat” informing that your lens has no corrective power. Plano may be written in several ways such as 0.00, PL, or even an infinity symbol (∞).
It's worth noting that plano prescriptions can be used in conjunction with astigmatism correction. Whilst you may not require any spherical correction, you may still need a cylindrical power and associated axis orientation.
Plano lenses can be used for a number of reasons.
- No SPH power required
- Blindness in left or right eye
- For blue light protection/gaming glasses
- Fashion or acting purposes
*For more information about plano lenses, click here.Back to top ↑
Latin abbreviation for left eye | Oculus sinister (OS)
What does OD, OS and OU mean on prescription?
OD and OS are optical abbreviations referring to your left, right and both eyes. They derive from the Latin phrases and can be written on your prescription paper to precede optical information. Here are their translations.
- OD / Oculus dexter = Right eye
- OS / Oculus sinister = Left eye
- OU / Oculus uterque = Both eyes
Can I get a copy of my eye prescription?
By UK law, you are entitled to your eye prescription information.
Regardless of any changes or how frequently you have an eye examination, you should be provided with at least a physical copy of your results.
“Following an eye test, your ophthalmic practitioner is legally required to provide you with your optical prescription or a statement setting out that you have been referred for further tests."
However, it’s worth noting that certain optical measurements are not mandatory and may not be included on your eye test results. Most commonly? Your pupillary distance.
This is a basic measurement which can hinder you from buying glasses online, however is easily overcome by measuring it yourself using a ruler or PD ruler. Here’s one for free you can download and print. (It’s mighty accurate.)
Hopefully you found this article helpful. Please check out our other eyecare blogs. Thanks for stopping by.