Dissection: Jordon's Fish Eye

This Cow's Eye Dissection Guide is a useful starting point for dissecting an eye.
Fish face some special problems when it comes to seeing
under water - light rays bend or refract when passing through
water; as water gets deeper, more light is absorbed; light is
scattered by hitting particles of sand and silt in the water
which creates a veil-like blinding effect for the fish.
Fish eyes have adapted to see things in very low light levels.

Follow Jordan's study of light as she dissects

a fish eye in search of a lens....

Making an incision in the cornea- the transparent
covering over thefront of the eye.
The cornea is pretty tough. It bends light, like the lens
This cut allows the aqueous humour to drain out.
The aqueous humour is clear and watery at the front
of the eye and jelly-like at the back of the eye.
It's clear so that light can pass through it. It also helps
to keep the shape of the cornea. You can see some fat
and muscle around the eye.
Cutting through the sclera - the tough outer covering of
the eyeball.
The sclera with the iris, the vitreous humour, the fat and
the muscle removed. The retina is the dark colour at the
back of the eye.
Removing the lens. The lens feels soft on the outside
and hard in the middle. The fish eye lens is perfectly
round like a pearl bead, not convex in shape like ours.
The job of the lens is to bend light to magnify the image
of what the fish is looking at onto the retina at the back
of the eye. The lens rests against the cornea for close-up
vision and is pulled towards the back of the eye by special
muscles for seeing things far away.
Jordan wanted to see if shining a light through the lens
showed light rays bending in an way. Here, rays of
sunlight focused through the lens making a pinpoint of
light inside the lens. The edge of the lens looks fuzzy
because of the soft structure of the outer layer.
Jordon experimented with the slide projector light to try
to bend light rays through the lens. The light beam was
too wide. A narrow beam from a laser pointer may have
worked better.
Under the microscope.....
The clear structure of the lens inside is just visible below
the soft outer layer. The special structure of the lens
means that the fish eye can see things in very sharp focus.