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
	This page has been accessed times since 11 February 2003.  17 February 1994, 31 Dec '94, 31 Dec. '96, 13 Feb. '97, 3 Jan 01

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.

Locate the optic nerve where it enters the cranium through the optic foramen. Draw imaginary lines from the medial and lateral limits of the orbit, and cut with the end of a hack saw towards either side of the optic nerve. Lift off the triangular section of the roof of the orbit, cutting loose 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.

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, removing the adipose tissue. The most obvious superior muscle will be the levator palpebrae superioris, which raises the eyelid. It does not insert into the bulb.

Find the four rectus muscles: lateral, superior, medial and inferior. The inferior oblique inserts just lateral to the inferior rectus. The superior oblique will be present, but this dissection may not retain the trochlear loop. Its tendon of insertion is near (or on?) the superior oblique. Deep to the four rectus muscles are four portions of the retractor bulbi. Note the optic nerve which exits the eye at the center of these four parts.

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...). Extend the cut sagittally through the center of the cornea. Note that aqueous humor drains out as the cornea is being cut. As you lift the cut 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, vascular and nervous. The retina will appear pearly yellow. Note the optic disk (vessels may be seen through the retina. emerge from it), and the fovea centralis. The retina peels away easily (detached retina). 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 ciliary processes. These are pigmented black. 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

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