KAAP309 Eye Dissection Laboratory Exercise
Equipment:
Gloves, eye protection (glasses, goggles, or face shield)
Dissection tray
Dissecting scissors
Hemostats
Bovine eye
Procedure:
A. Surface Anatomy of the Eyeball, Eyelids, and Lacrimal Apparatus
Inspect the living eye of your lab partner. Identify: [G 656, 657; L 353; N 81; R 135; C 593]
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Eyelashes (cilia)
Palpebral fissure (rima) – the opening between the eyelids
Medial and lateral palpebral commissures – where the upper and lower eyelids join
Medial and lateral angles (canthi) – the medial and lateral corners of the eye
Sclera – the whitish posterior five-sixths of the exterior coat of the eyeball
Cornea – the transparent anterior one-sixth of the exterior coat of the eyeball
Iris – the colored diaphragm seen through the cornea
Pupil – the aperture in the center of the iris
In the medial angle of the eye, observe:
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Lacrimal caruncle – a pink fleshy bump
Lacrimal lake – the area surrounding the lacrimal caruncle
Lacrimal papilla – a small bump on the medial end of each eyelid
Lacrimal puncta – a small opening at the apex of each lacrimal papilla
Evert the lower lid slightly and observe:
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Margin of the eyelid – flat and thick
Eyelashes (cilia) – arranged in two or three irregular rows
Use an illustration to study the following features and relate them to the living eye: [G 661; L
353; N 81; R 132; C 600]
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Bulbar conjunctiva – the membrane that lines the surface of the eyeball
Palpebral conjunctiva – the membrane that lines the inner surface of the eyelid
Superior and inferior conjunctival fornices (L. fornix, arch) – the regions where the
bulbar conjunctiva becomes continuous with the palpebral conjunctiva
Conjunctival sac – the potential space between the bulbar conjunctiva and the palpebral
conjunctiva
B. External structures of the bovine eyeball
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Check the eyeball for integrity, i.e. for lack of cuts or punctures.
Note bulbar conjunctiva and, if eyelids are present, palpebral conjunctiva. Explore the
conjunctival sac with a blunt probe or with closed hemostats.
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Carefully remove surrounding fat and skin from the eyeball and optic nerve. Preserve the
optic nerve and extraocular muscles as much as possible.
The extraocular muscles originate from a tendinous rung at the back of the orbit. Look for
it. It may or may not be present in your specimen.
The ciliary ganglion is a small bundle of parasympathetic nerve cells found in humans at
the back of the orbit, between the lateral rectus muscle (near its origin) and the optic
nerve. It may or may not be present.
Compare your “cleaned up” eyeball to those of other lab groups. Pay attention to
differences in the extent and condition of the optic nerve and extraocular muscles.
Use a probe to explore the conjunctival sac. Verify that the bulbar conjunctiva is
attached to the sclera.
Figure 7.55 How to transect the muscles of the left eye. Review the attachments of the
extraocular muscles on the eyeball. The four rectus muscles attach to the sclera near the
cornea (FIG. 7.55). The two oblique muscles attach to the sclera on the posterior half of
the eyeball.
Trace the four rectus muscles to their attachments on the common tendinous ring.
Identify the structures that pass through the common tendinous ring: the optic nerve (II)
and central artery of the retina, superior and inferior divisions of the oculomotor nerve
(III), abducent nerve (VI), and nasociliary nerve (FIG. 7.56).
Examine the cut surface of the optic nerve and try to identify the central artery of the
retina, which may be seen as a dark spot on the cut surface.
In most cases, the eyeball that is removed from the cadaver is poorly preserved.
However, if the eyeball is in dissectible condition, use a new scalpel blade to cut it in half
in the coronal plane. Remove the vitreous body.
Note the following features of the eyeball: [G 666; L 359; N 87; R 133; C 609]
a. Fibrous (outer) layer – sclera (posterior five-sixths) and cornea (anterior onesixth)
b. Vascular (middle) layer – choroid, ciliary body, and iris
c. Inner layer – retina, partially detached in the cadaver
d. Macula – only seen in well-preserved specimens
e. Optic disc – where the optic nerve and retinal vessels enter or leave
f. Lens – may be replaced by a prosthetic implant