Download dissection of the eye

DISSECTION OF THE
EYE AND ITS ORBIT
IN THE CAT
©David B. Fankhauser, Ph.D.,
Professor of Biology and Chemistry
University of Cincinnati Clermont College,
Batavia OH 45103
the four rectus
muscles
File "CAT_EYE.htm" was last modified on 19 Feb
2009.
dissected cross section
Follow protocol Notebook Illustrations
The brain should have previously been removed from your cat (see Removal and Study of the Cat
Brain). You should identify the upper and lower eyelids, and the nictitating membrane which
comes up from below the eye. Note the conjunctival surfaces, and the inferior fornix.
REMOVAL OF THE EYE
Locate the optic nerves where they enter the cranium
through the optic foramina.
Draw lines from each optic nerve to the medial and lateral
limits of the orbits.
The accompanying image shows the location of the cut to
make.
Cut on these lines with the end of a hack saw. Be certain to
cut laterally enough to prevent part of the frontal from
overhanging, and all the way to the optic foramina.
Lift off the triangular section of the roof of the orbit, cutting
it free from any underlying tissue which may adhere to it,
preserving features attached to the eye.
Mark the superior-most muscle with an indelible "X" to
keep track of it later in the dissection.
(Can you find the superior oblique and its trochlea, on the
medial superior border of the orbit? This is a challenge.)
Cut the anterior portion of the eye loose from the socket by
cutting closely along the bone to free up the eye itself. Lift
up the entire structure, cutting any peripheral tissues which
may hold it down. After you have lifted it in the front, slide
the scalpel under the rear-most portion to free it from the
skull. Note that the nictitating membrane marks the
inferior portion of the dissected portion.
Note the membrane which surrounds the entire orbit
(periorbita). The lacrimal gland is under it on the lateral
superior side. Work the periorbita open with a blunt probe,
remove the adipose tissue which served as padding. The
most superficial superior muscle will be the levator
palpebrae superioris, which raises the eyelid. It does not
insert into the bulb.
DISSECTION OF THE EYE
The fat has been removed from the excised eye to
reveal the muscles (upper picture).
Find the four rectus muscles:
lateral, superior, medial and inferior rectus
Use a blunt probe to free them from the optic
nerve. The inferior obliquecrosses over the
inferior rectus. The superior oblique should be
present, but this dissection may not retain the
trochlear loop. Its tendon of insertion is
medial to the insertion of the superior
rectus. Here is a labeled version of the right
hand image.
(Do not confuse the deeper four retractor bulbi
muscles which are under the rectus muscles.)
Deep to the four rectus muscles (peeled back in
this image) are four portions of the retractor
bulbi. Note the optic nerve which exits the eye
at the center of these four parts.
The four retractor bulbi have been reflected to
show the rear of the eye ball. The sclera is
opalescent bluish white, the optic nerve at the
center.
With the fine scissors, make a small vertical snip
through the rear wall of the bulb just medial to
the optic nerve (do not squeeze the bulb during
this cut...).
Hold the eye over a petri dish lid, extend the cut
(keep it shallow) sagittally through the center of
the cornea. Note that aqueous humor drains out
as the cornea is being cut.
As you lift the cut anterior piece, note that the
lens is attached to it by suspensory ligaments.
Cut through the iris, and lift off the cut portion,
cutting its ligaments.
Note that the lens is opaque-white, an artifact of
preservation. The posterior cavity is filled with
clear jelly-like vitreous humor . Note the three
tunics of the wall of the eye:
fibrous tunic (sclera plus cornea)
vascular tunic (iris, ciliary body and
choroid)
nervous (retina)
Here is a labeled image of the components of the
eye (upper image in left frame).
The retina will appear pearly yellow. Note the
optic disk identifiable by the vessels may be seen
to emerge from it, and pass under the retina.
The fovea centralis will be towards the center
and seen as a yellowish depression. (Here is a
labeled image.)
The retina peels away easily from the underlying
choroid. This, a detached retina is a serious
condition requiring immediate attention in
patients to prevent death of the retina and
blindness in the patient.
In the anterior portion of the eye, note that the
lens is supported by suspensory ligaments.
Posterior to it is the ruffled surface of the black
pigmented ciliary processes which produce the
aqueous humor.
The ora serrata is the anterior boundary of the
retina. The iris is golden on the exterior surface,
black on the posterior. The cornea is tough and
relatively thick.
Make three illustrations:
1) Cuts made to remove eye
2) muscles teased out
3) cross section of the eye
Here is the collection of images of this disssection: