Biology

• Optic nerve


  Transmits impulses from receptor cells to the brain
• Circular muscles of the iris

  Relax to make the pupil larger in low light
• Iris


  Controls the size of the pupil, colored part of the eye
• Retina

  Made up of cone cells (color-sensitive) and rod cells (sensitive to light but see black and white), fovea is a spot full of cone cells for clear vision
• Iris reflex


  In bright light, pupils constrict to protect the retina from damage, in low light, pupils dilate to allow more light in for better vision
• In low light conditions


  Pupils dilate to allow more light in for better vision
• In bright light conditions

  Pupils constrict to protect the retina from damage
• Circular muscles of the iris

  Contract to make the pupil smaller in bright light
• Cornea


  First structure light meets in the eye, completely transparent, no blood vessels, causes light to refract
• Structure of the eye

  1. Cornea is the first structure that light meets, completely transparent and allows light to pass through, refracts light

  2. Iris controls the size of the pupil, pupil is a gap in the iris allowing light to pass through

  3. Lens refracts light and can change its shape to control refraction, focuses light onto the retina

  4. Retina made up of cone cells (color-sensitive) and rod cells (sensitive to light but only see black and white), fovea is a spot full of cone cells for clear vision

  5. Optic nerve transmits impulses from receptor cells to the brain
• Radial muscles of the iris


  Contract in low light conditions
• Radial muscles of the iris

  Relax in bright light conditions
• Pupil


  Gap in the iris allowing light to pass through
• Lens


  Refracts light, can change shape to control refraction, focuses light onto the retina
• Long-sightedness is hyperopia
• Changes in lens shape for nearby and distant objects

  Ciliary muscle contracts inwards for nearby objects, relaxes for distant objects
• Light focusing onto the retina

  Light needs to be refracted to focus onto the spot of the retina called the fovea
• Refraction for close objects

  Requires a powerful lens that is short and fat to refract the light enough
• Correction for short-sightedness

  Use glasses with concave lenses to counteract over-refraction of the lens
• Accommodation


  Reflex that changes the refractive power of the lens to see both near and distant objects
• Lens


  • Fine-tunes the refraction to converge light rays exactly on the fovea
• Short-sightedness is myopia
• Refraction for distant objects

  Lens needs to be stretched out to reduce its refractive power
• Role of the cornea and lens

  Cornea attracts light by the same amount, lens fine-tunes the refraction
• Correction for long-sightedness

  Use glasses with convex lenses to provide extra refracting power
• Ciliary muscles and suspensory ligaments

  • Control the shape of the lens
• Short-sightedness


  Unable to focus on distant objects, can see nearby objects fine
• Long-sightedness

  Unable to focus on nearby objects, can see long distances fine
• Cornea


  • Refracts or bends light
• Changes in lens shape for near objects

  Ciliary muscles contract, suspensory ligaments loosen, lens becomes fatter, light is refracted more
• Vitreous humour


  The jelly-like liquid filling the eyeball
• Choroid


  A pigmented layer of tissue lining the inside of the sclera that prevents the reflection of light rays inside the eyeball
• Accommodation


  The way the lens brings about fine focusing
• When an object is close up

  Ciliary muscles contract, suspensory ligaments slacken, lens becomes fatter, light is refracted more
• Sclera

  The strong outer wall of the eyeball that helps to keep the eye in shape and provides a place of attachment for the muscles that move the eye
• Ciliary muscle


  A ring of muscle that contracts and relaxes to change the shape of the lens
• Aqueous humour


  The watery liquid between the cornea and the lens
• Blind spot


  The point at which the optic nerve leaves the eye, where there are no receptor cells
• Suspensory ligaments


  Ligaments that connect the ciliary muscle to the lens
• Function of the Human Eye

  Focusing on near and distant objects