Term |
Definition / Description |
|
| Aqueous
Humour |
The aqueous humour is a jelly-like
substance located in the anterior chamber
of the eye. |
|
| Choroid |
The choroid layer is located behind the
retina and absorbs unused radiation. |
|
| Ciliary
Muscle |
The ciliary muscle is a ring-shaped
muscle attached to the iris.
It is important because contraction and
relaxation of the ciliary muscle controls
the shape of the lens. |
|
| Cornea |
The cornea is a strong clear bulge located
at the front of the eye (where it replaces
the sclera - that forms the outside surface
of the rest of the eye).
The front surface of the adult cornea has
a radius of approximately 8mm.
The cornea contributes to the image-forming
process by refracting light entering the
eye. |
|
| Fovea |
The fovea is a small depression (approx.
1.5 mm in diameter) in the retina.
This is the part of the retina in which
high-resolution vision of fine detail is
possible. |
|
| Hyaloid |
The hyaloid diaphragm divides
the aqueous humour from the vitreous humour. |
|
| Iris |
The iris is a diaphragm of
variable size whose function is to adjust
the size of the pupil to regulate the amount
of light admitted into the eye.
The iris is the coloured part of the eye
(illustrated in blue above but in nature
may be any of many shades of blue, green,
brown, hazel, or grey). |
|
| Lens |
The lens of the eye is a
flexible unit that consists of layers of
tissue enclosed in a tough capsule. It is
suspended from the ciliary muscles by the
zonule fibers. |
|
| Optic
Nerve |
The optic nerve is the second cranial
nerve and is responsible for vision.
Each nerve contains approx. one million
fibres transmitting information from the
rod and cone cells of the retina. |
|
| Papilla |
The papilla is also known as the "blind
spot" and is located at the position
from which the optic nerve leaves the retina. |
|
| Pupil |
The pupil is the aperture through which
light - and hence the images we "see"
and "perceive" - enters the eye.
This is formed by the iris. As the size
of the iris increases (or decreases) the
size of the pupil decreases (or increases)
correspondingly. |
|
| Retina |
The retina may be described as the "screen"
on which an image is formed by light that
has passed into the eye via the cornea,
aqueous humour, pupil, lens, then the hyaloid
and finally the vitreous humour before reaching
the retina.
The retina contains photosensitive elements
(called rods
and cones)
that convert the light they detect into
nerve impulses that are then sent onto the
brain along the optic nerve. |
|
| Sclera |
The sclera is a tough white
sheath around the outside of the eye-ball.
This is the part of the eye that is referred
to by the colloquial terms "white of
the eye". |
|
| Visual
Axis |
A simple definition of the
"visual axis" is "a straight
line that passes through both the centre
of the pupil and the centre of the fovea".
However, there is also a stricter definition
(in terms of nodal points) which is important
for specialists in optics and related subjects. |
|
| Vitreous
Humour |
The vitreous humour (also known as the
"vitreous body") is a jelly-like
substance. |
|
| Zonules |
The zonules (or "zonule fibers")
attach the lens to the ciliary muscles. |
|
