The Eye

Updated: 20/03/13
Note: According to an anonymous comment (see below), knowledge of the fovea and optic disc is now required so please beware of that. I did this blog according to the 2009 syllabus, which was what I did, so I am unaware of the differences in the new syllabus. And plus I've finished IGCSEs... so yeah. Thanks to the anonymous tipper!! :) 

This section focuses on the eye-its structure and function. I'll do things according to the syllabus, so it's WHAT YOU NEED TO KNOW. (for DOUBLE AWARD)

Specification 2.87 describe the structure and function of the eye as a receptor

Tip: Know about the cornea, iris, lens, pupil, retina and optic nerve mainly. You may be asked to label a diagram and possibly answer a few 1-2 mark questions on the functions of these parts. You should know the positions of the rest, but they aren't the main important bits you need to know.. 

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1. Sclera: the tough outer coat of the eye, which is the visible, white part of the eye. It protects the eyeball from mechanical damage. 

2. Cornea: at the front of the eye the sclera becomes a transparent 'window' which is the cornea-this lets light into the eye, refracting or bending the light rays into the eye. This plays a key part in the focusing of an image on the retina. 

3. Choroid: this is the middle layer of the eye (between the sclera and the retina), it is black, preventing reflection of light in the interior of the eyeball. (It also contains blood vessel that bring oxygen and nutrients to the eyeball and remove metabolic waste products.)

4. Ciliary body: this contains a circular ciliary muscle (just call it ciliary muscle) which is attached to the lens with the suspensory ligaments. These play a huge role in accomodation-which is basically changing the shape of the lens to focus light onto the retina so an image may be formed. 

5.Iris: this is in front of the lens, it is a circular diaphragm controlling the amount of light entering the eye.

6. Pupil: this is basically a hole/opening in the iris to let light through.

7. Retina: this is inside the choroid layer, it is a light-sensitive membrane with neurones and photoreceptor cells. There are 2 types of photoreceptor cells: rods and cones. Cones enables us to see colours in bright light while rods enable us to see in black and white in dim light. The photoreceptors are connected to the nerve-endings from the optic nerve. 

8. Macula: NOT NEEDED. Fyi, the fovea is in the centre of the macula. Basically, this is where visual perception is most acute.

9. Optic nerve: A nerve that transmits nerve impulses to the brain when the photoreceptors in the retina are stimulated. 

10. Optic disc: NOT NEEDED. Fyi, this connects the retina to the optic nerve. 

11. Vitreous humour: A transparent, jelly-like substance. This keeps the eyeball firm and helps to refract light onto the retina too. 

12. Aqueous humour: A transparent, watery fluid. This keeps the front of the eyeball firm and helps to refract light into the pupil. 

13. Canal of Schlemm: NOT NEEDED. Fyi, this is basically just a channel in the eye that collects aqueous humour and moves it into the bloodstream.

14. Lens: A transparent, circular, biconvex structure. It is elastic and changes it shape or thickness to refract light onto the retina. 

15. Conjunctiva: this is a thin transparent membrane covering the sclera in front. It is a mucous membrane, it secretes mucus, thus keeping the front of the eyeball moist.