26 / 09 Tuesday Kuapapa: Dissect a cow’s eye to observe and describe the structure of eye
cornea iris sclera (white coat) lens retina pupil optic nerve
Eye Dissection
Sclera: the white, tough, outer covering Examine the outside of the eye. How many parts of the eye can you identify? Sclera: the white, tough, outer covering Cornea: the clear covering over the front of the eye Iris: the coloured part of the eye Pupil: the dark oval in the middle of the iris Source: adapted from www. http://www.exploratorium.edu
Cut away the fat and muscle Make an incision in the cornea Release all the clear liquid This liquid is the aqueous humor which is mostly made of water and helps keep the shape of the cornea
Make an incision in the sclera in the middle of the eye Cut around the middle of the eye You’ll end up with two halves Remove the cornea from the front half and place it on the cutting board Try cutting through the cornea – why is it so strong?
Pull out the iris – it should be between the cornea and the lens, but may have stayed with the back of the eye The hole in the centre of the iris is the pupil, which lets light into the eye Remove the lens It is a clear lump about the size and shape of a squashed marble
The lens feels soft on the outside and hard in the middle Hold the lens up and look through it – what do you see? Put the lens down on a newspaper and look through it at the words – what do you see?
The back of the eye is filled with a clear jelly, called vitreous humour, which helps the eyeball keep its shape – why is it clear? On the inside back of the eye, you can see some thin film with blood vessels – this is the retina Push the retina around and find where it is attached to the back of the eye This is the blind spot, which is the start of the optic nerve, which carries the electrical signals detected by the retina to the brain
Under the retina, the back of the eye is covered with shiny, blue- green tapentum It reflects light from the back of the eye Look at the other side of the back of the eye Squeeze the optic nerve to see the separate fibres Some white goo may ooze out – this is myelin which is a fatty layer that protects each fibre