Transcript DISSECTED SHEEP’S EYE

DISSECTED SHEEP’S EYE
PETER REONISTO, MD
MOORPARK COLLEGE
SHEEP EYE
The sheep eye has four externally
attached muscles (1-4), which
control eye movement. The human
eye has six (1-6). These additional
muscles allow humans the ability
to "roll" and move their eyes in all
directions.
DISSECTION
In the area near the top
of the eye where the
sclera and cornea
join (identified with
an X mark in the
photo), carefully
make a stab wound
incision using the
dissecting probe. At
the point of incision
you will notice a
small discharge of a
watery substance.
This important fluid
was internally
contained within the
aqueous humor.
Once the tough outer layer
of the sclera has been
pierced, remove the
dissecting probe and
carefully insert the
dissecting scissors at the
point of incision.
Following a circular pattern
around the sclera,
rotate the eye while
continuing to carefully
cut the eye in half.
Attempt to open and
separate the front from
the back of the eye
without damaging its
internal structures.
Cutting the sclera in a
circular pattern, as
followed in Step 5 of
this procedural
tutorial, resulted in
also cutting the thin
reflective middle
layer lining of the
sheep eye. This
colorful reflective
lining is called the
tapetum and is not
found in the human
eye.
Attached to the optic
nerve, observe a
wrinkled saclike
structure connected
to the back portion
of the eye. This is
the retina and is
considered the
inmost layer of the
eye. Just as the
tapetum surrounds
the inside of the
sclera, the living
tissue of the retina
would have been
smooth and would
have rested against
the reflective
tapetum. The point
at which the retinal
nerve tissue
connects to the optic
nerve is the eye’s
blind spot.
Separate the retina
from the back
portion of the eye
and again observe
the colorful
reflective layer of
the tapetum.
Removing the tapetum
from the tough
shell like outer
layer of the sclera
exposes the
choroid. With the
dissection of the
back portion of the
eye nearing
completion, return
your attention to
the frontal
structures and
tissues of the eye.
Rest the front section of
the eye with the cornea
facing downward.
Working back to front,
a clear jelly like body of
fluid should be evident.
This is the vitreous
humor. The vitreous
humor is attached to a
convex lens. In the
preserved eye, the lens
will have a slightly
discolored yellow
appearance but would
be perfectly
transparent as a living
structure.
Remove the lens and
vitreous humor by
turning the front
portion of the eye
inside out. A ring of
tiny ciliary muscles,
located along the inner
side of the iris,
connects the lens to
the middle layer of the
eye.
The black specks on the
outer edge of the lens
are small pieces of the
connecting ciliary
muscles.
Remove the lens from
the vitreous humor.
Use a paper towel
and dry the lens of
any excess fluid.
Although the yellowed
preserved lens is not
clear, it remains
transparent enough
to see through.
Having turned the front
portion of the eye
inside out and
removing the lens and
vitreous humor; allows
the ciliary muscles,
pupil, and cornea to
be more easily
observable. The pupil,
surrounded by the iris
on the front side of the
eye and by the ciliary
muscles within the
eye, is actually an
opening located in the
center of the iris. The
pupil is covered and
protected by the
transparent living
tissue of the cornea.
1. Cornea
2. Sclera
3. Optic Nerve
4. Iris
5. Pupil
6. Ora Serrata
7. Ciliary Body
8. Choroid
9. Tapetum Lucidum
10. Retina
11. Lens
12. Vitreous Humor
END