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Maths
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The Structure of the EyeClick here for a diagram of the eye.Parts of the eye and their function: Conjunctiva This is a transparent membrane that covers and protects the front of the eye. Sclera This is the white part of the eye. It does not allow light to pass through. Its function is protection and shape. Cornea This is the transparent part of the sclera at the front of the eye. It can bend the light inward because of its convex shape. Choroid This layer is darkly pigmented to prevent light reflecting within the eye. It has blood vessels which nourish the eye. Retina It has the light receptors rods and cones.
This is the coloured part of the eye. It controls the size of the pupil, therefore controls the amount of light entering the eye. Pupil A hole in the iris. It allows light into the eye. Lens A biconvex transparent elastic structure. It focuses light onto the retina. Ciliary body Contains muscle that alters the shape of the lens. Suspensory ligaments Fibres that connect the ciliary body to the lens. Vitreous humour A clear jelly like substance. It supports the eye by exerting an outward pressure. Aqueous humour A clear liquid that helps maintain the shape of the front of the eye. Optic nerve Carries nerve impulses from the retina to the brain. Blind spot Part of the retina where the optic nerve leaves the eye. There are no rods or cones at this point. Fovea The area of the retina that has most accurate vision. AccomodationThis is the ability of the lens to change its curvature to focus near or distant objects.Distant object (a) Ciliary muscle relaxes (b) The suspensory ligaments are pulled tight (c) The lens is stretched into a flatter shape. Near object (a) Ciliary muscle contracts (b) The suspensory ligaments are no longer under tension (c) The lens become thicker and more convex. Click here for diagrams illustrating accomodation Light IntensityHow the eye adjusts to changing light intensity1. Dim light
Binocular VisionIn humans the two eyes are positioned so that an object can be viewed by both eyes at the same time. Each eye views the object from a slightly different angle, thus producing different images. The brain combines these images giving the perception that the object is three dimensional.Eye defectsShortsightedness or Myopia
Experiments
LC higher level exam questions1993 Q. 15 (b)In each of the following cases explain how the event indicated is brought about. (i) The control of light entering the eye. (ii) The focussing of light rays on to the retina when a person commences reading. (iii) The detection, by binocular vision, that an object is three dimensional. Solution 1997 Q.15 (d) (vii) Give a biological explanation for the following: Colour vision deteriorates as daylight declines in the evening. Answer: Colour is detected by the cones. The cones function only in brighter light. 1999 Q.12 (f) Give a concise biological explanation for the following: As the evening progresses and it gets darker, a time is reached when the human eye can no longer detect colour. Answer: Colour is detected by the cones. The cones function in bright light but cease to function in dim conditions. |