Sheep Eye Dissection
1. Observe the external structures, noting the following:
a. cornea (oval and dark)
b. sclera (white and tough)
c. conjuctiva (thin, transparent, covering the sclera. Look from underneath eyelid to
the cornea)
d. adipose tissue (yellow or white)
e. external muscles (tan ribbon-like within the fat)
f. optic nerve (short thick bulge deep in the fat at the back of the eye. Are you
surprised at how big it is?)
2. Open the eye
a. I will make a small incision with a scalpel
b. Using sharp scissors, cut around the cornea approximately 1 cm (1/2 inch) away
from it.
c. Gently lift the front portion of the eye off the back portion. Observe the internal
parts as they separate. Note the following
1. vitreous humor (jelly-like and usually clear. Did you know you had a jelly like
structure in your eye?)
2. lens (hard ovoid structure, usually comes out stuck to the vitreous humor)
3. suspensory ligaments (fine lines radiating from the lens across the vitreous
humor. Sometimes they tend to hold the lens in place.)
4. aqueous humor (clear fluid behind the cornea)
d. Once the eye is opened, place both pieces onto a dissecting tray so the interior of
each part is visible. Find the following inside the anterior portion.
1. lens (if not stuck to vitreous humor)
2. ciliary body (thick black ridged circle surrounding the iris) If the lens is
attached to the ciliary body by the suspensory ligaments, remove it at this
point.
3. iris (thin oval flap. Look through its opening (pupil) to see the back of the
cornea)
e. Find the following inside the posterior portion.
1. gently remove vitreous humor if it is still in the posterior half of the eye. I
suggest pouring it out the way you would an egg yolk from its shell.
2. retina (thin, delicate layer behind the vitreous humor. It may detach when the
vitreous humor is removed. Are you surprised at how fragile it is?)
3. optic disc (“blind spot” where retina is attached to back of eye, and the optic
nerve leaves the eye)
4. choroid layer (thin black layer behind retina. It’s partially iridescent so the
sheep can see better in low light conditions.)
5. sclera (peel part of the choroid layer off and you will be able to see the sclera.
Are you surprised at how tough it is?)
Discard all parts of the eye and clean all instruments and trays.