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Optics - the human eye and coomon defects

Extracts from this document...

Introduction

Physics In Action               Eye Defects                        Gurmeet Sidhu

Eye Defects

Vision:-

The mammalian eye could be regarded as a miracle of evolution. In order to produce an image the eye has to act as an Optical refracting System (to focus a sharp image) and a Photo Detector (to analyse the image and send information to the brain). At the front of the eye is the optical system, made up of the transparent curved Cornea and the adjustable biconvex Lens. The photo detector is the layer of light-sensitive cells at the back of the eye, called the Retina. The amount of light entering the eye is controlled by the Iris. Sharp focusing is achieved by altering the shape of the lens.

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Middle

  1. Astigmatism

If the cornea is curved in an uneven manner, it will refract light that enters the eye in different planes to different extents. The eye will focus light in some planes better than others (i.e. verticals might be in focus, but horizontals not)

  1. Presbyopia

This is the natural reduction in the lens’s accommodation power with the age. (Accommodation is the process of changing the shape of the lens in order to focus the sharp image on the retina.)

Corrections:-

image02.png

  • Long Sight (Hypermetropia)

The situation can be corrected by placing a converging lens (convex lens) in front of the eye (by means of spectacles of contact lenses). In extreme cases laser surgery can be used to correct the shape of the cornea.

  • Short Sight (Myopia)

This situation can be corrected by placing a diverging lens (concave lens) in front of the eye. In extreme cases laser surgery can be used to correct the shape of the cornea.

  • Astigmatism

This situation can be corrected by using a cylindrical lens (i.e. one that only curves in one plane)

  • Presbyopia
...read more.

Conclusion

c11 c7">Eyes continue to deteriorate afterward with age anywayCorneal infectionFlap distortion – affects clear vision

Contact lenses

  • Infection – mustn’t sleep with them in
  • Should not be worn for extended periods

Eye Formulas:-image03.pngimage04.png

Focal length                                               Magnification m

image05.png

 Lens Power in Dioptres (D)

u = object distance                  v = image distance                  f = focal length

Normal eye power is +59D

References:-

  • The Eye, Page486-488, Advanced Physics by Steve Adams & Jonathan Allday 2000(Oxford University Press) ISBN: 978-0-19-914680-2
  • (http://hyperphysics.phy-astr.gsu.edu/Hbase/vision/eyedef.html#c4)
  • (http://www.riverdeep.net/current/2002/01/012002_images/eye.jpg)
  • (http://ezinearticles.com/?Laser-Eye-Surgery-Complication---6-Dangers-Of-Eye-Surgery&id=960156)
  • (http://en.wikipedia.org/wiki/Eye_surgery)

...read more.

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Here's what a star student thought of this essay

4 star(s)

Response to the question

Response to the question is done well. The candidate outlines a few common defects after explaining a bit about the biology of the eye and then explains how these can be corrected and some of the risks associated. The sections ...

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Response to the question

Response to the question is done well. The candidate outlines a few common defects after explaining a bit about the biology of the eye and then explains how these can be corrected and some of the risks associated. The sections are clearly set out. This piece is done to a high level.

Level of analysis

The biology is explained clearly, and the images outline the functions of the eye and possible defects. The different types of common defects are explained, but refraction should be defined before the candidate discusses problems with the eye to aid clarity. Pictures are used in a good way to explain the defects and how they can be corrected. The candidate should discuss how the lenses work exactly in the text but this is aided well by the images. I'm not sure why the eye formulas are included.

Quality of writing

Picture references are just placed anywhere in the main body of text and this looks untidy. Parts of the eye are given capital letters which they shouldn't have. Other punctuation, grammar and spelling looks okay. Some spaces occur in words due to the pdf file.


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Reviewed by skatealexia 03/07/2012

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