One of the biggest misconceptions we deal with at Sight Care is that many members of the public believe that their lens prescription for eyeglasses can be used to get contact lenses. This is not the case.
The difference in prescriptions for eyeglasses and contact lenses arises because of how these vision-correcting devices are positioned relative to your eyes. Here is why they are different.
Distance from the Eye
- Eyeglasses sit about 12-14 millimeters away from the eye. This distance slightly changes how light is refracted as it enters your eye.
- Contact Lenses rest directly on the surface of your eye (the cornea), so there’s no gap between the lens and your eye.
Lens Power Adjustment
- Because contact lenses are closer to your eye, the power required to correct your vision can differ slightly from your eyeglass’s prescription.
- For people with higher prescriptions, this difference becomes more noticeable because even a small change in distance can significantly impact the correction needed.
Curvature and Fit
- Contact lenses must account for the curvature and shape of your cornea to ensure a proper fit, which is not a concern for glasses.
- Contact lens prescriptions include measurements like base curve and diameter, which are irrelevant for eyeglasses.
Astigmatism and Multifocal Lenses
- For people with astigmatism, contact lenses often require a specific orientation to correct the uneven curvature of the eye. This can result in different power specifications.
- Multifocal lenses for presbyopia might also have varying designs for glasses versus contacts.
In addition to the above, the way prescriptions are written differs slightly. A contact lens prescription includes additional parameters, such as lens brand and material, base curve, and diameter, which are tailored to the individual eye.
If you are interested in using contact lenses, our Optometrists can help. Visit us online at https://sightcareoptometry.com/ and select the “Contact Lens Evaluation” appointment.
Note: This posting is for informational purposes only and does not attempt to diagnose or
recommend treatment for any condition. Please refer to the Ontario Association Optometrists website (https://optom.on.ca/eye-health-library) for more information or consult an Optometrist if you are experiencing eyesight issues.
