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Eye Dissection Lesson

Eye Dissection Lesson

Welcome to our Eye Dissection Lesson aimed at GCSE students.

We have a eye dissection video demonstrating the methodology of the classroom dissection of a sheep & pig’s eye.  We have included a lesson plan and risk assessments that can be downloaded or simply reviewed here.

We hope to guide pupils through discovering as much as they can from the eye!

Aim: To explain how the structure of the eye is related to its function.

GCSE Biology

Methodology:

  • Place eye in dissection tray.
  • Examine the eye and identify the following parts:
    • The sclera – the whites of the eye, the tough, outer covering of the eyeball.
    • Fat and muscle surrounding the eye.
    • The cornea – the covering over the front of the eye.
    • The iris, the coloured part of the eye.
    • The pupil, the dark oval in the middle of the iris.
    • The optic nerve on the back.
    • To see the separate fibres that make up the optic nerve, pinch the nerve with fingers.
  • Cut away any excess fat and muscle from the eye.
  • Use a scalpel to make a cut in the cornea (its tough!).
  • Allow the clear liquid to run out.
  • Use the scalpel to make an incision through the sclera in the middle of the eye.
  • Use scissors to cut around the middle of the eye, cutting the eye in half so you end up with two halves, front with cornea and back with optic nerve.
  • Pull out the iris. The iris is between the cornea and the lens. It may be stuck to the cornea or it may have stayed with the back of the eye. Find the iris and pull it out. It should come out in one piece. You can see that there’s a hole in the centre of the iris. That’s the pupil,
  • Remove the lens. It’s a clear lump about the size and shape of a squashed marble.
  • Hold the lens up and look through it or Put the lens down on some text and look through it and magnify the words on the page.
  • On the inside of the back half of the eyeball, you can see some blood vessels that are part of a thin fleshy film called the retina.

Teaching Notes:

  • The eye is s a sense organ containing receptors sensitive to light intensity and colour.

Observations to point out:

  • In your sample eye, the cornea may be cloudy. It is translucent when alive.
  • The clear liquid is the aqueous humor. It’s made of mostly of water and keeps the shape of the cornea.
  • The clear jelly is the vitreous humor, a mixture of protein and water. It’s clear so light can pass through it. It also helps the eyeball maintain its shape.
  • The front half of the eye will be the cornea, that helps protect your eye. It also helps you see by bending the light that comes into your eye.
  • The pupil, the hole that lets light into the eye. The iris contracts or expands to change the size of the pupil. In dim light, the pupil opens wide to let light in. In bright light, the pupil shuts down to block light out.
  • The retina is made of cells that can detect light. The eye’s lens uses the light that comes into the eye to make an image, a picture made of light. That image lands on the retina. The cells of the retina react to the light that falls on them and send messages to the brain.
  • The nerves from all the cells in the retina come together. All these nerves go out the back of the eye, forming the optic nerve, the bundle of nerves that carries messages from the eye to the brain. The brain uses information from the retina to make a mental picture of the world.
  • Accommodation is the process of changing the shape of the lens to focus on near or distant objects.

To focus on a near object:

  • the ciliary muscles contract
  • the suspensory ligaments loosen
  • the lens is then thicker and refracts light rays strongly.

To focus on a distant object:

  • the ciliary muscles relax
  • the suspensory ligaments are pulled tight
  • the lens is then pulled thin and only slightly refracts light rays. 
Two common defects of the eyes are myopia (short sightedness) and hyperopia (long sightedness) in which rays of light do not focus on the retina.
  • Samples for Schools Eye (sheep or pig)
  • Dissection tray
  • Scalpel
  • Scissors
  • Mounting needle
  • Paper towel

AQA: Topic 4.5.2.3 (biology only)

Students should be able to relate the structures of the eye to their functions. This includes accommodation to focus on near or distant objects and adaptation to dim light.

Students should be able to identify the following structures on a diagram of the eye and explain how their structure is related to their function: retina, optic nerve, sclera, cornea, iris, ciliary muscles, suspensory ligaments.

Edexcel: Topic 2.15B, 2.16B and 2.17B

Explain the structure and function of the eye as a sensory receptor including the role of the the cornea and lens, the iris and rod and cone cells in the retina.

Describe defects of the eye including cataracts, long- sightedness, short-sightedness and colour blindness

Explain how cataracts, long-sightedness and short-sightedness can be corrected

Eduqas: Topic 4.1

Students should:

(f)  explain the functions of the following parts of the eye: sclera, cornea, pupil, iris, lens, choroid, retina, blind spot and optic nerve recognise and be able to label these parts on a diagram of a vertical section through the eye

(g)  describe common defects of the eye and explain how some of these problems may be overcome as exemplified by long-sightedness, short-sightedness and cataracts

OCR 21st Century: Topic B5.6

Students should explain how the main structures of the eye are related to their functions, including the cornea, iris, lens, ciliary muscle and retina and to include the use of ray diagrams.

OCR Gateway: Topic B3.1

Students should explain how the main structures of the eye are related to their function: cornea, iris, pupil, lens, retina, optic nerve, ciliary body, suspensory ligaments.