A little lost?
Understanding your eye test results can seem borderline foreign.
And it’s no wonder.
All those digits and details have so much 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; they’re visually vital.
In this handy article, I wanted to explain what this all means.
To fast track, click a terminology in the link-box below.
On your prescription paper you’ll see various shorthand terminologies.
I’ve deciphered and explained each of them for you in the correct order, listed in the sections below.
Example of right eye Sphere prescription | Positive SPH | +2.50
What is SPH?
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 have hyperopia, an optical term for short-sightedness.
Negative SPH means you have myopia, an optical term for long-sightedness.
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.
To calculate the cost of your prescription lenses, click here.
For aesthetics and for weight, here’s a guide on what thickness of lenses to choose based on your prescription.
Example of right eye Cyl prescription | Minus Cyl | -0.25
What is CYL?
Following the SPH box on your prescription will be CYL.
This is shorthand for cylinder where numerical digits are only required if you have astigmatism in either or both of your eyes.
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.
Cylindrical power is written as a positive (+) or negative (-) value which refers to the dioptres requires to correct myopic or hyperopic astigmatism.
Example of right eye Axis prescription | 180 degrees from meridian
What is AXIS on prescription?
If your prescription CYL box contains a value, so will your AXIS box.
These digits are inter-related and are both used to correct your astigmatism in either or both of your eyes.
AXIS refers to the angle of the astigmatism in your eye and has nothing to do with the severity of your prescription. These digits can be anywhere between 0 and 180 degrees such 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 my eye prescription?
ADD refers to addition, also called near addition or reading addition.
These digits are measured in dioptres and will always be written as a positive (+) value, identical in both your left and right eye.
For multifocal glasses wearers such as bifocals, trifocals or varifocals, ADD indicates your required close-vision power which is used for correcting 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. Within bifocal lenses, your ADD is applied in the little reading segment in the bottom of your lenses.
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Example of right eye Prism prescription | Base Inwards with 0.5 Sph
What is PRISM?
Very few prescriptions contain PRISM.
This refers to the amount of prismatic power used to correct any muscular imbalance of your eyes. This can be for conditions such as strabismus (lazy eye) or amblyopia (squint.)
If PRISM is present on your eye test results there will be two boxes per lens. Together, these related figures communicate both the direction of the prism and the required dioptric power.
In the first box, the direction of your PRISM will be noted in full or shorthand terms as seen listed below.
In the second neighbouring 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 direction and base digits/fractions. This is the Greek symbol for Delta which, for example, can be used to write a base inwards prism as: BI Δ 1 ½.
If you require prism, we are currently unable to fulfil your prescription lenses and advise that you do this in conjunction with your local optician.
However your glasses frame can still be purchased via the links below.
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Example of a plano prescription | No corrective power (0.00)
What is Plano?
If you have a very weak prescription, it is common that one of your eyes may not require any refractive correction.
This is indicated in dioptres in your SPH section on your prescription as 0.00, PL or plano. Optically speaking, your lens has no power and can be described as “plano” deriving from the Latin word plānus for “flat.”
Plano lenses can be used for a number of reasons.
Latin abbreviation for right eye | Oculus sinister (OS)
What does OD, OS and OU mean?
These are occasionally printed or handwritten on prescription papers and 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.
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.
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.
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