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1.6 SENSE OF SIGHT

1.6 SENSE OF SIGHT. The eye detects light . It is spherical in shape and set in a bony socket in the skull called the orbit which helps to protect it from injury. Structure of human eyes.

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1.6 SENSE OF SIGHT

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  1. 1.6 SENSE OF SIGHT The eye detects light. It is spherical in shape and set in a bony socket in the skull called the orbit which helps to protect it from injury.

  2. Structure of human eyes The eye has three-layered wall, consistingsclera(outer layer), choroid(middle layer) & retina(inner layer)

  3. Structure of human eyes Contains light-sensitive receptor cells known as photoreceptors : Rods (sensitive in dim light, black & white vision) Cones (sensitive in bright light, colour vision) Absorbs light, prevents internal reflection of light & supplies the eye with oxygen & nutrients Protects the eye and helps to maintain its shape.

  4. Structure of human eyes Colourless jelly-like substance that maintains the shape of eye, acts as a cushion for the lens & helps to focus light on retina Transparent watery fluid to maintain the shape of the eye & helps to focus light onto the retina

  5. Mechanism of sight 1. When you are looking at an object, light rays from the object enter the eye.2. Light rays are bent in towards one another as they pass through the cornea.3. Light rays continue to pass through the aqueous humour and reach the pupil.

  6. Mechanism of sight 4. The amount of light allowed to pass through the lens onto the retina is regulated by the size of the pupil which in turn controlled by the iris.(a) In bright light : size of pupil reduced(b) In dim light : size of pupil enlarged

  7. Mechanism of sight 5. Once the light rays pass through the pupil, they are focused by the lens onto the retina.6. To focus, the elastic lens changes its shape according to the distance of the object from the eye by the action of the ciliary muscles & suspensory ligaments.

  8. Mechanism of sight * When viewing a near object, the lens become thicker.* When viewing a distant object, the lens becomes thinner.

  9. Mechanism of sight 7. Light rays that are focused onto the retina form a clear image which is inverted & smaller than the object.8. The light of the image stimulates the photoreceptor cells of the retina and generates nerve impulses.9. The nerve impulses travel along the optic nerve to the brain10. The brain interprets these impulses to produce the sensation of sight.

  10. Mechanism of sight Light Light Light Cornea Aqueous humour Pupil Light Retina Vitreous humour Lens Image formed : clear, inverted, smaller than the object Light Light Interprets the nerve impulses to produce the sensation of sight Optic nerve BRAIN Nerve impulses

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