Educational PowerPoint created by award winning Enfield optician 'Good Looking Optics' about the functioning of the eye, how refractive problems can arise and how these can be cured.

1. The Eye
Will Smith

2. Components of the eye
Cornea – a transparent protective layer which focuses light onto the
lens
Lens – refracts light, focusing it onto the retina
Iris – the coloured part of the eye which controls the amount of light
that enters
Pupil – the hole in the iris through which light enters
Retina – the surface inside the eye onto which all images are focused
on to
Ciliary muscles – contract to change the shape of the lens in order to
adjust focus for different distances
Suspensary ligaments – hold the lens in place and contribute to
changing lens shape

3. The Functioning of the eye
The lens of the eye is convex .
This means that the light rays converge after
passing through the lens and, in a healthy eye,
cross at (and focus onto) the retina.
Light receptors located on the retina process the
light into electrical signals and transmit these
signals to the brain along the optic nerve.
The image produced is actually upside-down but
this is corrected by the brain.
A healthy eye is 22mm long.

4. The functions of tears
Prevent the eyes from becoming too dry
Supplying oxygen and other nutrients to
the eyes (as there are no blood vessels)
Tears contain the enzyme lysozyme which
kills bacteria, preventing infection
Healing damage to the surface of the eye
Maintaining a smooth surface of the
cornea to ensure that light is correctly
refracted into the eye

5. The two types of lens
Convex:
This type of lens
converges light (i.e.
closes light in)
Concave:
This type of lens
diverges light (i.e.
Spreads light out)
These two types of lens are important as
they each treat different forms of sight
loss.

6. Myopia – i.e. Short sightedness
Myopia is caused by an eyeball being
longer than 22mm.
This means that the light rays cross before
they reach the retina, therefore focusing
in front of the retina.
This results in a distant objects being
blurred but close objects being clear.

7. Treating Myopia
A concave lens is used – diverges the light
rays slightly so that they focus onto the
retina as normal:

8. Hyperopia – Long sightedness
Hyperopia is caused by a person’s eyeballs
being shorter than 22mm.
This means that the refracted light rays
focus behind the retina, meaning that
nearby objects are blurred/out of focus
while distant objects can be seen clearly.

9. Treating hyperopia
A convex lens converges the light rays
slightly so that instead of focusing behind
the retina, they focus on the retina, so a
much clearer image is formed.

10. Summary of treatment of
refractive problems

11. Contact lenses
Like glasses, these are used to treat long
and short sightedness (as described in
previous slides).
Contact lenses are prescription lenses
which float on the tear film on the surface
of the cornea

12. Laser eye surgery
Laser eye surgery is used to treat
astigmatism – when the cornea is not
perfectly round, so light focuses on
multiple points on the retina, leading to
blurred images.
During laser eye surgery, a thin layer of
cornea cells are removed in order to
reshape the lens to make it perfectly
round:
Before laser eye
surgery:
After laser eye
surgery:

13. The Eye
Will Smith