If you’re thinking about getting a professional eye exam, you might be wondering whether you should get prescription contact lenses or glasses with eyeglass frames. While both are designed to correct or improve your vision, the reasons behind prescribing contact lenses and eyeglasses are different. And if you think about whether it’s okay to interchange their prescriptions, you need to know that this isn’t possible. This is mainly because of the different types of refractive errors that can occur to your eyes.

Defining Refractive Errors

Contact lenses and eyeglasses are prescribed to correct common refractive errors that occur when the shape of your eye doesn’t bend light correctly. These include long-sightedness (hyperopia), short-sightedness (myopia), and the aging of the eye lenses (presbyopia). Prescription contact lenses or eyeglasses are also used to treat the curvature of the cornea when it’s asymmetrical, or better known as astigmatism.  

Keep in mind that a glasses prescription isn’t the same as a contact lens prescription. To understand more about prescriptive contact lenses and eyeglasses, you need to consult with a professional optometrist. As a reputable center for eyeglass frames, Excel Eyecare OD PA shares their insight:

Their Differences

In a typical contact lens prescription, you’ll find the strength of the lens required to correct your eyes and the type of contact lens you need. However, the parameters specified on your glasses prescription will differ significantly from those on your contact lenses prescription. This is partly because glasses sit slightly away from your eyes while contact lenses sit directly over them. As such, two different tests and measurements are required. 

Depending on the refractive error, you might also notice that there will be a cylinder and axis value on your glasses prescription, though it won’t be prescribed for your contact lenses. On the other hand, a contact lens prescription contains additional specifications that are not included in a glasses prescription. This is only determined through the comprehensive contact lens and eye health exams which include certain specifications that aren’t found in a glasses prescription.

What You’ll Find in a Contact Lens Prescription 

  • Diameter (DIA) – this is the specification of the overall size of the lens. It also determines how the lens fits on the eye, with the diameter of soft contact lenses typically ranging from 13.5 to 14.5 mm and the diameter of rigid gas permeable (GP) contacts ranging from 8.5 to 9.5 mm.
  • Base Curve (BC) – This measures the curvature of the lens, and is determined by the shape of your eyes. Along with the diameter, it also indicates how it fits in the eye and produces the right lens fitting. 
  • Lens Material – Contact lenses are made from a range of hydrogels depending on the prescription. They can be made from either hydrogel or silicone hydrogel contacts, so how each lens fits and feels will depend on the individual wearer’s eyes. If you have sensitive eyes, silicone hydrogel contact lenses may suit you better. However, if you’re also getting dry eyes from wearing contact lenses, consider getting a Lipiflow at our eye care center!
  • Expiry Date – A contact lens is typically valid for a year before it expires. Before it does, make sure to visit your trusted eye care provider for a replacement contact lens. But before you get your replacement, they’ll likely do an exam first to check your eye’s health.
  • Brand or Manufacturer – Contact lens prescriptions will typically include the brand name or manufacturer of the lenses. This is important in case you need to reorder them later on when it’s time to replace them.

What You’ll Find in a Contact Lens Prescription 

While you may also find some of these abbreviations in a contact lens prescription, you’ll typically find them on an eyeglasses prescription. These include:

  • ADD – This stands for addition, which is used in bifocals to add correction for farsightedness.
  • CYL – Also known as a cylinder. For those with astigmatism, this indicates how much power is needed to correct the eye condition.
  • SPH – Short for sphere, which is the amount of lens measured in diopters. A diopter is a unit used to measure your vision correction.
  • OD and OS – Short for the Latin terms oculus dexter and oculus sinister, it refers to the right and left eye respectively. Sometimes, you may also see OU, which means both eyes.
  • PD – This indicates the distances between the centers of your pupils (pupil distance).
  • Axis – This indicates the orientation for those with astigmatism.

In your eyeglass prescription, you’ll also notice a plus and minus sign. A plus means you’re farsighted while a minus means you’re nearsighted. And to know how strong your prescription is, just look how the further away from zero the number is on your prescription.

You can expect your eyeglasses to be about 12 millimeters from the eye, so the prescriptive power of a contact lens will be a bit less nearsighted. This is because the contact lenses are positioned directly on the tear film of the eye, with the difference becoming more significant with prescriptions of 4D or greater. To put it simply, the power of a contact lens prescription will be less than that of an eyeglass prescription.

Common Questions About Prescription Contact Lenses and Eyeglasses

  • “Why Can’t My Eyeglasses Prescription Be Used For Contact Lenses?” – This is because not everyone who needs eyeglasses can wear contact lenses successfully. Professionals recommend getting separate eye health exams at a trusted eye center for contact lenses. You may even have sensitive corneas or other pre-existing eye complications that may prevent you from wearing lenses, so make sure to have your eyes checked by a professional.
  • “Is It Better to Use Eyeglasses or Contact Lenses?” – Contact lenses and eyeglasses will have their specific advantages. Contact lenses conform to the curvature of your eye and provide a wider field of view. This causes fewer vision distortions compared to eyeglasses, but having dry or sensitive eyes can make it difficult to wear contact lenses. This is where eyeglasses can be better, as there’s less need for you to touch your eyes.

As a trusted center offering excellent Lipiflow services, you can count on Excel Eyecare OD PA for professional eye care! To schedule an appointment, call us today at (980) 399-6071 or fill out our online contact form