posted by .

How is it that contact lenses can be thinner than bifocales but just as effective at fixing someone's sight?

The power or 1/f of contact or framed glasses for the same person needs to be the same. Power is proportional to (N-1)[1/R1 - 1/R2]. N is the index of refraction of the material. N is not much different for contact or glass lenses. The difference in curvatures, [1/R1 - 1R2], is therefore also about the same

The reasons glass lenses are thinner are twofold:
(1) Glass lenses maintain an edge thickness of about 1/8" to make them less fragile and easier for the frames to hold.
(2) Contact lenses only have to cover the pupil of the eye, which means that their diameter can be as small as 1 cm. Glass lenses need to have at least 3 cm clear aperture because thay are located farther fcrom the eye and need to provide a wide field of view.
(3) The increase of thickness at the center, relative to the edge, is proportional to the square of the aperture size. If the glass lens has (typically) three times the diameter of the contact lens, its thickness change at the center must be nine times larger. Add the increased edge thickness to this and you get a much thicker glass lens.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions


  2. math

    I need help finding the answer In the US about 46% of the population wear glasses or contact lenses. A sample of 85 people is taken. About how many people would you ecpect to wear glasses or contact lenses?
  3. Physics

    A patient has a far point of 34.6 cm and a near point of 26.0 cm. What power (in diopters) should be prescribed to give the patient normal vision for: (a) contact lenses?
  4. physics

    A person sees clearly wearing eyeglasses that have a power of −2.92 diopters and sit 2.22 cm in front of the eyes. If the person wants to switch to contact lenses, which are placed directly on the eyes,what lens power should …
  5. Physics

    If you are wearing contact lenses with a dioptric power of 3.4 and your eye has a diameter of 2.6 cm, what is the effective focal length of your eye-contact lens combination, in centimeters?
  6. science

    Contact lenses improve lives. Contact lenses are an example of what?
  7. Science

    contact Lenses improve lives. Contact lenses are an example of an __________. my answer is indepentant variable. Someone help. it's for a science experiment.
  8. science

    fill in the blank. Contact lenses improve lives. Contact lenses are an example of a(n)__________ .
  9. College interview

    Hi! I was just wondering if one of the teachers could tell me whether or not it is unprofessional to wear colored contact lenses to a college interview?
  10. physics

    when two lenses of focal length +10cm and -5cm are placed in contact then find the net power ?

More Similar Questions