physics

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.

  1. 👍 0
  2. 👎 0
  3. 👁 59
asked by Tom

Respond to this Question

First Name

Your Response

Similar Questions

  1. 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.

    asked by rose on October 4, 2013
  2. Science

    PLEASE HELP ITS URGENT contact lenses improve your lives. contact lenses are example of an______? A.skeptical B.experiment C.invention D.evidence E.inference F.prototype G.biased H.technology I.hypothesis

    asked by Jojo on November 7, 2017
  3. 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?

    asked by Morgan on March 25, 2012
  4. science

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

    asked by victoria on October 24, 2013
  5. science

    Contact lenses improve lives. Contact lenses are an example of what? Is the answer physics?

    asked by Miai on September 16, 2013
  6. 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? The colors aren't drastic colors but they are contact lenses nonetheless.

    asked by Mary on January 30, 2015
  7. General chemistry

    Ammonia fumes can permanently fog soft contact lenses. Briefly explain why students wearing soft contact lenses should be particularly careful when doing this experiment.

    asked by Liv on February 12, 2018
  8. Physics

    Two lenses are in contact. One of the lenses has a focal length of +10.0cm when used alone. When the two are in combination, an object 20cm away from the lenses forms a real image 40cm away from the lenses. What is the focal

    asked by Jul on April 2, 2013
  9. 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? Do I multiply .46 to

    asked by Kyle on February 3, 2010
  10. UV

    the two lenses in contact are 45 cm away from the object and the distance of the object from the image is 110 cm. if one of the two lenses in contact has a focal length of 15cm, what is the focal length of the second lens? thanks

    asked by Melissa on March 8, 2014

More Similar Questions