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THE HUMAN EYE

THE HUMAN EYE. Section - 13.6 PG. 572 - 577. PARTS OF THE HUMAN EYE. PARTS OF THE HUMAN EYE. Iris – coloured part of your eye, it opens and closes around a central hole to let in more or less light Pupil – hole in the iris, where light enters the eye

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THE HUMAN EYE

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  1. THE HUMAN EYE Section - 13.6 PG. 572 - 577

  2. PARTS OF THE HUMAN EYE

  3. PARTS OF THEHUMAN EYE • Iris – coloured part of your eye, it opens and closes around a central hole to let in more or less light • Pupil – hole in the iris, where light enters the eye • Lens – structure that causes light entering the eye to converge • Cornea- tissue structure that causes light to converge as well, it is the bulge on top of the pupil that focuses the light • Light is refracted more through the cornea than through the lens

  4. PARTS OF THE HUMAN EYE • Retina – converts the light signal into an electrical signal that is transmitted to the brain through the optic nerve • Optic Nerve – creates a blind spot at the back of each eye because there are no light sensitive cells in that small area. The blind spot goes unnoticed because each eye compensates for the blind spot of the other eye. • EX: Left eye can see what is in the blind spot of your right eye and vice versa

  5. THE LIGHT GATHERING INSTRUMENT

  6. THE LIGHT GATHERINGINSTRUMENT • The eye acts a light gathering instrument for the brain • The lens-cornea combination of the eye acts like a converging lens and produces a smaller, real, inverted image on the retina • Electrical impulses from the retina travel through the optic nerve to the brain • The brain takes the inverted image that came from the retina and flips it so the image we see is upright

  7. ACCOMMODATION & FOCUS • Accommodation – changing of shape of the eye lens by eye muscles to allow a sharply focus image to form on the retina • Shape of the eye lens changes in order to allow an inverted focused image to form on the retina • Ciliary muscles help focus the eye on distant and nearby objects by slightly changing the shape of the eye lens • Eye lens changes the focal lengths of the lens to allow focusing of the image on the retina • Not all people have properly functioning ciliary muscles which results in focusing problems

  8. FOCUSING PROBLEMS • Hyperopia (Far-sightedness) – the inability of the eye to focus light from near objects • No issues seeing distant objects, issues seeing nearby objects • The eye cannot refract light well enough to form an image on the retina • Occurs when the distance between the lens and retina is too small or when the lens-cornea combination is too weak • Light ends up focusing behind the retina resulting in a blurred image

  9. HYPEROPIA

  10. FOCUSING PROBLEMS • Presbyopia – a form of far-sightedness caused by a loss of accommodation as a person ages • Condition when the eye loses elasticity, usually an age related vision issue • Can be corrected by glasses or contacts with a converging lens shape • Myopia (Near-sightedness) – the inability of the eye to focus light from distant objects • The eye can focus light rays from nearby objects allowing them to see up close clearly, however issues with seeing distant objects • Occurs when the distance between the lens and retina is too large or because the cornea-lens combination is too strong • Light from distant objects is brought to a focus in front of the retina

  11. MYOPIA

  12. PRESBYOPIA

  13. CORRECTING VISIONPROBLEMS • Correcting Hyperopia • A converging lens will correct far-sightedness & a lens with a positive meniscus has the same effect • Positive meniscus lens is a modified form of the converging lens shape (middle part thicker than the edges) • Correcting Myopia • A diverging lens will correct near-sightedness & a lens with a negative meniscus has the same effect • Negative meniscus lens is a modified form of the diverging lens shape (edges are thicker than the middle part)

  14. CORRECTING VISIONPROBLEMS

  15. CORRECTING VISIONPROBLEMS • Contact Lenses • A lens that is placed directly on the cornea of the eye • Serve the same purposes as glasses, can be shaped to correct both far and near-sightedness • Can be used for cosmetic purposes; ex. Changing the colour of the eyes

  16. IN SUMMARY • The cornea-lens combination in the eye acts like a converging lens; the brain flips the inverted image that is receives from the eye so that what you see is upright • The eye focuses through accommodation; the shape of the eye lens is changed slightly by eye muscles • Hyperopia means that a person is far-sighted; near vision corrected with a converging lens • Presbyopia is an age-related condition of far-sightedness that is caused by a loss of accommodation • Myopia refers to a person who is near-sighted; distance vision is corrected with a diverging lens

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