Spectacle Power To Contact Lens Power Conversion Chart
If you're planning to switch from glasses to contact lenses, you may be wondering what your contact lens prescription would be. It's not as simple as just converting your spectacle power to contact lens power. There are a few factors that come into play, such as the curvature of the lens and the distance between the lens and your eye.
What is a spectacle prescription?
A spectacle prescription is a set of numbers that indicates the power of lenses needed to correct your vision. It's usually written in a specific format, with the sphere power, cylinder power, and axis listed separately.
The sphere power indicates the amount of nearsightedness or farsightedness you have, measured in diopters (D). A negative number indicates nearsightedness, while a positive number indicates farsightedness. The cylinder power indicates the amount of astigmatism you have, and the axis tells you the orientation of the cylinder power.
How is contact lens power determined?
Unlike glasses, contact lenses sit directly on your eye, so the power needed may be different from your spectacle prescription. The curvature of the lens and the distance between the lens and your eye can affect the power needed for the best vision correction.
Your optometrist will use a special instrument called a keratometer to measure the curvature of your cornea, which helps determine the base curve of the contact lens. They may also perform a trial and error process to find the right contact lens power for you.
Can I convert my spectacle power to contact lens power?
While there is no exact formula for converting your spectacle power to contact lens power, there are some general guidelines that can be used as a starting point. These are based on the average curvature of the cornea and the typical distance between the lens and the eye.
For nearsightedness, your contact lens power will generally be weaker than your spectacle power. For example, if your spectacle prescription is -2.00D, your contact lens power may be around -1.75D. This is because the contact lens sits closer to your eye than glasses, which magnify the image and require a weaker lens.
For farsightedness, your contact lens power will generally be stronger than your spectacle power. For example, if your spectacle prescription is +2.00D, your contact lens power may be around +2.25D. This is because the contact lens sits directly on your eye, which requires a stronger lens to correct the vision.
What are some other factors to consider?
Aside from the curvature of the lens and the distance between the lens and your eye, there are some other factors that can affect your contact lens prescription. These include the material of the lens, the size of the lens, and any specific features of the lens, such as toric lenses for astigmatism or multifocal lenses for presbyopia.
Your optometrist will take all of these factors into account when determining your contact lens prescription. It's important to follow their recommendations and not try to convert your spectacle power to contact lens power on your own.
Conclusion
Switching from glasses to contact lenses can be a great option for many people. However, it's important to remember that the power needed for contact lenses may be different from your spectacle prescription. Your optometrist can help you determine the right contact lens power for your eyes based on a variety of factors. By following their recommendations and taking good care of your contact lenses, you can enjoy clear vision and comfortable wear for years to come.