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Eye Glass and Contact Lens Prescriptions: What’s the Difference?

Most people assume that there can only be one prescription […]

By Published On: 5 August 20123.1 min read

Most people assume that there can only be one prescription for the eye. If you have a vision problem, you would most probably wear eye glasses in the beginning. You go to your optometrist. He performs a number of tests and exams to determine the prescription of your eyes. Then he prescribes the glasses that you need to correct your eye condition.

Later on, you may want to try wearing contact lenses because they are more convenient to use. You go to another optometrist to buy contact lenses and the salesperson recommends that you undergo another eye exam. You refuse maybe because you are in a rush. You simply tell him that you know your prescription anyway so there is really no need to undergo another set of eye tests. You give him your prescription and you walk away with your contact lenses.

You excitedly wear your lenses and you hold judgment for a few days to give yourself time to adjust to your new gear.

Often no instructions are given about insertion, removal and disinfection.  Currently in Australia optical dispensing has been deregulated to the point that contact lenses can be purchased with virtually no regulations.  This might sound convenient but… contact lenses are medical devices that are placed on one of your most precious organs – your eyes!

Let’s assume you get the necessary instruction, after a few days or weeks, however, you sense that your contact lenses are not working as effectively as your eye glasses. You go back to your optometrist thinking that your vision problem worsened. Your doctor tells you that you still have the same prescription but you do have a problem – you were wrong in assuming that you can use the same prescription for eye glasses and contact lenses.

When you decide to shift to using lenses from wearing glasses, you have to know that each one has a different prescription and you may need separate eye exams to determine that. While using the prescription for one in the other will not necessarily improve or worsen your vision problem, it can affect its effectivity in correcting your vision issue.

The Difference

Eye glasses will always have a higher prescription than contact lenses. The reason is actually practical. Lenses are nearer to your eyes as they in fact sit directly on your eyes. On the other hand, eye glasses sit farther from your eyes. Normally, glasses are about 12mm away from your eyes.

The Test

As mentioned above, you may need a different eye exam to determine your contact lens prescription. The exam is more complicated than the one performed when you are getting eye glasses because your optometrist needs to measure your eye. The diameter and curvature of your cornea are measured. Your doctor will prescribe the right type of lens for you depending on the size of lens you need and the condition that you may be suffering.

For eye glasses, your optometrist will just measure your vision and the amount of refractive correction you need.

The Trial

Most of the time, your optometrist will ask you to wear a trial pair of contact lenses to check if you are comfortable with them and if they fit you perfectly. You will also need follow-up check-ups with your optometrist so he can assess if the lenses still have the same fit and if you are still comfortable wearing them.

Follow up visits are critical to ongoing success. Complications with contact lenses are common. A startling statistic is that 50% of people that start wearing contact lenses fail within the first year – most of the time this can be traced back to poor instruction and follow up visits.


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