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Can you convert a glasses prescription to a contact lens prescription?Medically reviewed by Tina Patel, Contact Lens Optician at Feel Good Contacts.
Both contact lenses and glasses correct common refractive errors such as myopia (short-sightedness), hyperopia (long-sightedness), astigmatism which requires toric contact lenses and presbyopia which requires multifocal contact lenses. Although your contact lens and glasses prescription may look similar, it does not mean they will give you the same visual acuity if you try to convert one to the other.
Are glasses prescriptions and contact lens prescriptions the same?
A glasses prescription is not the same as a contact lens prescription. Glasses sit slightly away from your eyes and contact lenses sit directly over your eye, so two different tests and measurements are required. Depending on the refractive error, the strength of lens required to correct it and the type of contact lens you need, the parameters specified on your glasses prescription may be significantly different from those on your contact lenses prescription.
You may also find that there will be a cylinder and axis value on your glasses prescription, whilst it won’t always be prescribed for your contact lenses.
Glasses prescription vs contact lens prescription
Contact lens prescription
Note: The glasses prescription (left) and the contact lens prescription (right) above are just samples. Yours may differ but should contain the same information.
Note: not everything shown on the above table will necessarily be included on your prescription. The above is just an example of what could be found on your prescription and what will not be found on your prescription depending on whether you wear contact lenses or glasses.
Contact lenses prescriptions include certain specifications that are not part of a glasses prescription, these include:
Base curve: the base curve measures the curvature of the lens; it is determined by the actual shape of your eye and produces the right lens fitting.
Diameter: the lens diameter specifies the overall size of the lens. Along with the base curve, this determines how the lens fits on the eye.
Lens material: in days gone by, glasses were made from actual glass, nowadays, most glasses are made of a lightweight plastic. Contact lenses on the other hand, are made from a range of hydrogels. These are split into hydrogel or silicone hydrogel contacts. How each lens fits and feels depends on each individual wearer’s eyes. Those that require longer wearing times generally do better with silicone hydrogel contact lenses as they allow a greater level of oxygen and hydration into the eye.
Brand/manufacturer: A contact lens prescription may also include an axis and cylinder if it is a toric lens for astigmatism, or an add if it is a multifocal lens. These measurements can often be found on both contact lenses and glasses prescription.
A glasses prescription contains a sphere indicating the lens power, a cylinder indicating strength of any astigmatism (if there is one stated) and an axis showing the orientation of the cylinder. Multifocal lenses require an ‘add’ which indicates additional positive power that enable the eyes to focus for close work.
A contact lens prescription may also include an axis and cylinder if it is a toric lens for astigmatism, or an add if it is a multifocal lens.
You’ll find that the cylinder number on a contact lens prescription is usually written as a minus number. This indicates the extra power you need for astigmatism correction. A higher number denotes a more severe level of astigmatism. The cylinder value for a glasses prescription is most commonly written as a minus form but occasionally it can be written in plus form too. You won’t have any value’s in this column on your prescription if you don’t have astigmatism.
Can you convert glasses prescription to contact lenses?
No – you cannot directly convert a glasses prescription to a contact lens prescription. Equally, you cannot convert a contact lens prescription to a glasses prescription.
Can I use my glasses prescription for contact lenses?
The simple answer to this question is no – you cannot and should not use your glasses prescription to try to calculate your contact lens prescription. It should also be noted that not everyone who needs glasses can also wear contact lenses, it is important that you are examined separately. Some people have sensitive corneas or other eye related complications and will simply never be able to adapt to wearing lenses.
How can I order glasses and contact lenses online?
You can order contact lenses online, but you must have a valid prescription from an optician. Once you have your prescription, you may order you lenses anywhere you like and it is cheaper to order your contact lenses online.
You can order your glasses online from Feel Good Contacts simply by choosing your lens type and then entering your prescription. If you have already placed an order with us before, you will not need to enter your prescription again unless it has expired.
It is illegal for your optician to withhold your contact lens or glasses prescription from you.