Understanding your Contact Lens Prescription

If a contact lens is not prescribed properly the bottom line is that you may not see well. Not only that but a poorly fitting contact lens or one made from material that is not suited to your eyes can cause extreme discomfort, inflammation, abrasion or other problems which may result in permanent eye damage. That coupled with the risk of infection is why it's so important to ensure you see a qualified optometrist for your contact lens prescription. That said, you've got your contact lens prescription but you may be wondering what it all means? What do all the abbreviations stand for? What's it got to do with my eyes?

Your contact lens script is made up of a number of components. The list below will show the abbreviations that may appear on your prescription, or your contact lens box, and what they mean.

• PWR - Stands for power and refers to the strength of your script. Preceded by a minus sign indicates you have Myopia (nearsightedness) and preceded by a plus sign indicates you have Hyperopia (farsightedness). The higher the number the greater the amount of correction you require.
• BC - Stands for base curve and refers to the curvature of the contact lens (in mm) and is relative to the curvature of your cornea (the clear covering over the front of your eye)
• DIA - Stands for diameter and refers to the diameters of your contact lens, which will dictate where on your eye the contact lens will sit.
• CYL - Stands for cylinder and is a number measured in dioptres to calculate how much of an astigmatism you may have (where your eye is more oval than round)
• AXIS - The axis is measured in degrees and indicates the orientation of the cylinder in the lens and will then compensate for your cornea being more oval than round
• ADD - Seen on bifocal contact lenses, indicates a further prescription for reading or other closer up activities
• OD - Is an abbreviation for Oculus Dexter, which is a Latin term for Right Eye
• OS - Is an abbreviation for Oculus Sinister, which is the Latin term for Left Eye

Your prescription will also include a brand name of a certain contact lens. It is just as important to order the correct brand name of the lens you have been prescribed as it is to get all of the other details correct as what is a measurement and standard in one company might not be the same in another – much like trying on a size eight shirt in one brand, then trying on another size eight in another brand and realising it doesn't fit as well as the first one. All brands also make their contact lenses from different materials and your optometrist has prescribed the contact lenses that best suit your personal requirements.