Have you ever wondered what certain abbreviations and terms on your eyesight prescription mean? All glasses prescriptions are written in a standard format with common terms, including sphere (SPH), cylinder (CYL), axis, ADD and Prism. It’s important to know the meanings of these terms to understand your prescription properly, as they denote different aspects of your vision.
What is the Axis on an Glasses Prescription?
The axis on an eyesight prescription refers to the direction in which the cylindrical power is placed in the lens, which is required for individuals with astigmatism. It does not reflect the prescription strength. The axis number informs the optician about the eye’s angle or orientation, serving as a map. It is a positive number that ranges from 1 to 180 degrees. An axis value of 90 degrees indicates a vertical position and 180 degrees indicates a horizontal position.
Additional Terms on a Glasses Prescription
There are some other terms that you might notice on your eyesight prescription, such as:
- SPH: Measured in dioptres, SPH refers to Sphere, which is the lens power for correcting farsightedness (shown as a plus symbol) or nearsightedness (shown as a minus symbol).
- CYL: This term stands for cylindrical power and it refers to the lens power required for astigmatism correction.
- ADD: This term stands for Addition and is essential for a presbyopic prescription. It indicates the additional correction required to see nearby objects clearly. reading or using a computer.
- Prism: Measured in prism dioptres with a value going up to 10, prismatic correction is to treat diplopia, where the eyes don’t work well together. It helps prevent double vision.
- BVD: This term stands for Back Vertex Distance and denotes the distance between the cornea’s apex and the back of your glasses’ lens.
- PD: This term stands for Pupillary Distance, which represents the distance between the centres of both pupils.
- Near, Inter and Dist: These terms denote reading or close up, intermediate (computer or arm’s length) and distance. They refer to the eye prescription needed for different working distances.
- OS and OD: OS stands for Oculus Sinister, meaning the left eye and OD stands for Oculus Dexter, indicating the right eye.
A glasses prescription for astigmatism cannot have a cylindrical power without an axis value, as the two work together to improve astigmatic vision. Those who do not have astigmatism have a prescription showing only the SPH/PWR value. On the other hand, prescriptions for individuals with astigmatism mandatorily have CYL and Axis values mentioned on their prescription alongside SPH/PWR.
Frequently Asked Questions
What is a ‘normal’ axis value?
There is no ‘normal’ axis value because everyone’s eyes are different. People with ‘normal’ eyesight don’t have an axis number or any power value.
Does Axis Change with Time?
Yes, the axis, along with the cylinder and sphere, can change over time as your vision changes. Even if your vision changes slightly, it can significantly change your axis, which is completely normal. A person who wears prescription glasses can experience many changes in their eyesight throughout their life, which also shows in their prescription.
It’s important to protect your vision to ensure you can see clearly for a long time. Regular eye exams can help detect potential eye conditions. Moreover, an eye test can help identify conditions such as glaucoma and macular degeneration early, enabling timely treatment.
The NHS recommends having an eye exam at least every two years or more frequently if advised by your optician. Check here to see if you’re eligible for a free eye test and optical voucher.
Disclaimer: The advice in this article is for informational purposes only and does not replace medical care or an in-person check-up. Please check with an eye care professional before purchasing any products or remedies. For information on our article review process, please refer to our Editorial Policy.
Wut Win is a qualified Dispensing Optician at Feel Good Contacts and a member of the Association of British Dispensing Opticians (ABDO). She is registered with the General Optical Council (GOC) and adheres to its professional guidelines. Wut graduated from City & Islington College with a Diploma in Ophthalmic Dispensing in 2006 and has over 17 years of experience. She has worked with several leading high street opticians, dispensing eyewear, including prescription glasses and sunglasses. Wut has also assisted children with autism and special needs through the Special School Eyecare Service.
