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Course: MCAT > Unit 3

Lesson 1: Foundation 4: Physical and chemical principles

The physics of eyesight correction


While there are many factors that determine an individual’s ability to see, the most common and basic eyesight defects are those of myopia and hyperopia, or nearsightedness and farsightedness, respectively. These two terms describe the ability of the eye to focus an image. A nearsighted individual can clearly see things close to them, but their vision becomes increasingly blurred as distance to the object increases. A farsighted individual has the opposite issue: they are able to clearly see objects at a distance, but the object becomes blurrier the closer it is. Myopic vision generally results from the focal length of the eye being too short, while hyperopic vision is the result of the focal length being too long, as seen in figures 1 and 2.
As the eye can be conceived as a set of lenses through which light refracts and converges onto the retina, the complication of poor eyesight becomes a simple problem of optical physics to solve. A converging lens can be utilized to shorten the focal length in the case of hyperopia, and a diverging lens can be used to lengthen the focal length in myopic vision. A lens with a negative value of power will be a diverging lens, while a positive value is reserved for converging lenses. The degree of correction can additionally be adjusted by varying the magnitude of power of the lens.
Attribution: Gumenyuk I.S. CC-BY-SA 3.0/4.0
Severe myopia is defined as -6 diopters or worse. What would the minimum focal length of a lens have to be in order to correct for severe myopia?
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