2

Aspheric lenses are used for treatment of astigmatism. I am curious what effects might happen if they were used by someone without an astigmatism.

  • What effects would it have on visual acuity?
  • Would there be any image distortion?
  • Could it cause harm to the eye?
3

A toric lens is the type that is used to treat astigmatism, not an aspheric lens. An aspheric lens is primarily designed to correct for the spherical aberration of the contact lens itself, the spherical aberration of the combination of the cornea and lens of the eye, or both.

A toric lens is shaped like a slice of the side of a torus. It has a different index of refraction along its horizontal axis than it does along its vertical axis, with a smooth gradient of the refractive power in the quadrants between those axes. Astigmatism is the condition where the corneal surface, the lens of the eye, or both have the same kind of difference in refractive power along the horizontal and vertical axes of the eye. The toric lens's corrective axes must line up correctly with the astigmatic axes of the eye. A common method of accomplishing this is by making the lens heavier near one part of the edge so that the heavy edge self-rotates to the bottom.

An aspheric lens, on the other hand, has a gradually changing refractive index moving radially from the edge of the lens to the center. It will either be "flatter" or "steeper" than a purely spherical lens, but the refractive index is constant moving along any circumferential path at a constant radius from the center of the lens. The magnitude of the lens's deviation from being purely spherical is known as its spherical aberration. An aspheric corrective lens is used to correct for the inherent spherical aberration that a spherically-surfaced contact lens introduces, which is directly proportional to its sphere power, and ideally also the spherical aberration of the eye itself.

Simply by the properties of optics, the effect of using either of these types of lenses if one does not have the corresponding visual defect the lens was designed to correct would be to introduce some degree of distortion into one's vision. This could only negatively affect visual acuity, though how severely would depend on the particular lens's strength. I could not find any references as to whether there are any long-term harmful effects of intentionally distorting a person's vision or visual acuity since the subject of all the references I checked was trying to achieve the opposite effect. The only mechanism I can postulate that could potentially cause damage to the eye would be by the long-term eye strain induced by the intentional distortion of a person's vision.

Here are two helpful references I found in further elaborating the above information: http://www.clspectrum.com/issues/2005/march-2005/aspheric-contact-lenses-fact-and-fiction https://coopervision.com/about-contacts/toric-contact-lenses

8
  • 3
    Have you got any references to support this?
    – Lucky
    Oct 2 '16 at 12:40
  • Downvoted until references can be provided. Note question has been edited for clarity of actual question and remove medical advice request
    – DoctorWhom
    Aug 8 '17 at 1:31
  • 2
    Are references required for all answers? I read the FAQ on providing answers and didn't see that mentioned. I'd think general medical knowledge and scientific reasoning should count for something. Also, what gives with the recent downvotes on an old answer to an old question with zero upvotes? It gets edited and suddenly my answer is worse than it was for so long before?
    – Fonebone
    Aug 11 '17 at 4:06
  • 2
    @Fonebone Yes, reconsidered. This Q either popped up on the main page by auto-bump the system does so we can continue to refine old questions / answers and improve the site (it's still in Beta), or in my queue to review and vote on closing/editing questions. This question needed an overhaul, and I saw the answer issue, so noted it. Thanks!
    – DoctorWhom
    Aug 11 '17 at 7:54
  • 2
    And yeah, even with 3 degrees and a decent helping of common sense I still try to provide references when there's something that the user might want to read more about OR check accuracy; something I had to get used to here. :)
    – DoctorWhom
    Aug 11 '17 at 7:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.