Most of you must wondering on ‘how to read your contact lens prescription?’
Your contact lens prescription allows you to purchase contact lenses that match your requirements from optical shop or online suppliers.
You need to know your physical prescription with you in order to purchase contact lenses from physical or online shop and also you do need to have a good understanding of what it is. How to read your contact lens prescription? You can find your prescription on the piece of paper given to you by an optician during a check-up. However, contact lens prescriptions can vary in number depending on the brand of the product itself.
A written prescription usually includes the following specifications: base curve, diameter, power (or sphere), and then additional figures for Cylinder and Axis if you have astigmatism, and Addition and Dominant figures for presbyopia correction. The prescription for your left and right eye will be listed separately as they may vary.
What OD and OS mean
The first step to understanding your eyeglass prescription is knowing what “OD” and OS” mean. They are abbreviations for oculus dexter and oculus sinister, which are Latin terms for “right eye” and “left eye.”
Your eyeglass prescription also may have a column labeled “OU.” This is the abbreviation for the Latin term oculus uterque, which means “both eyes.”
Though use of these abbreviated Latin terms is common on prescriptions for glasses, contact lenses and eye medicines, some doctors and clinics have opted to modernize their eyeglass prescriptions and use RE (right eye) and LE (left eye) instead of OD and OS.
On your eyeglasses prescription, the information for your right eye (OD) comes before the information for your left eye (OS). Eye doctors write prescriptions this way because when they face you, they see your right eye on their left (first) and your left eye on their right (second).
What does each prescription figure mean?
- Base Curve (BC): The base curve determines what type of fit is required for the lens to meet the curve of your eye. This is usually written in millimeters or sometimes with the words: flat, median or steep.
- Diameter (DIA): The diameter of the contact lens is also written in millimetres and determines the width that best fits your eye.
- Power/Sphere (PWR/SPH): This figure shows whether you are long or short-sighted and how much correction your eyes require. If you are long-sighted your figure will begin with a + (plus sign) and if you are short-sighted it will begin with a – (minus sign). This will be followed by a number that goes up from 0 in measures of 0.25 dioptres, the higher the number the stronger the visual correction needed.
- Cylinder (CYL): The cylinder will always be a minus number that increases in measures of 0.25. Much like the power/sphere figure that is shown on all standard prescriptions, the cylinder denotes the extra visual requirements needed for astigmatism and how severe the astigmatism is.
- Axis (AX): Astigmatism is caused by the irregular curvature of the eye; the axis is a figure which determines the angle of the correction needed in order to see clearly. The Axis is always a number between 0 and 180 degrees.
- Addition (ADD): If you suffer from presbyopia it affects your near vision, the Addition figure determines what level of correction you need to be able to see clearly at a close distance. This is a number between 0.50 and 3.00, some contact lens brands refer to this as a high, medium or low.
- Dominant: If you wear multifocal contact lenses or bifocal contact lenses, the correction is determined by a dominant and non-dominant eye, this is the dominant figure usually marked with a “D” and “N” to express which eye is which.
An eyeglass prescription cannot be used to buy contact lenses
Eyeglass and contact lens prescriptions aren’t the same. An eyeglass prescription is for the purchase of eyeglasses only. It does not contain certain information that is crucial to a contact lens prescription and that can be obtained only during a contact lens consultation and fitting.
In addition to the information in an eyeglass prescription, a contact lens prescription must specify the base (central) curve of the back surface of the contact lens, the lens diameter, and the specific manufacturer and brand name of the lens.
Also, the power of an eyeglass prescription frequently is modified when determining the best contact lens power. This is because eyeglass lenses are worn some distance (usually about 12 millimeters) from the surface of the eye, whereas contact lenses rest directly on the cornea of the eye.
An accurate contact lens prescription can be written only after a contact lens fitting has been performed and the prescribing doctor has evaluated your eyes’ response to the lenses and to contact lens wear in general. Let’s make an appointment with us at Malaya Optical Optometrists, we are ready to teach you on how to read your contact lens prescription!