Download Eye Lab Handout

Bio 1152L
Extrinsic Eye Muscles
Written by Dr. Diane Day
Name ________________________________________
Day & Lab time _______________________________________
Pre-Lab Exercise I – COMPLETE PRIOR TO LAB!
There are six extraocular (extrinsic) muscles that move the eyeball. Fill in Table 1 with the location, action, and cranial
nerve innervation for each of the extrinsic muscles.
Table 1: Extraocular (extrinsic) Muscles
Muscle
Location
Action
Cranial Nerve
Innervation
Superior rectus muscle
Inferior rectus muscle
Medial rectus muscle
Lateral rectus muscle
Superior oblique
muscle
Inferior oblique muscle
Pre-Lab Exercise II – COMPLETE PRIOR TO LAB!
You should be familiar with the following terms before coming to lab. Look up the functions of each of the following
structures.
Conjunctiva ________________________________________________________________________
Sclera ____________________________________________________________________________
Cornea ___________________________________________________________________________
Iris _______________________________________________________________________________
Pupil ______________________________________________________________________________
Lens ______________________________________________________________________________
Ciliary body ________________________________________________________________________
Choroid ___________________________________________________________________________
Retina ____________________________________________________________________________
In-Lab Exercise: Testing Extraocular Muscles
Determine which extracular muscles are responsible for moving the eyeballs in each direction. Also, list the cranial
nerve(s) involved.
1. Trace a line in the air about one foot in front of your partner’s eyes, moving from your partner’s left to right. Have
your partner follow your finger without moving his or her head. Which extraocular muscles produce the movements you
see for each eye? List which cranial nerve(s) are involved.
Right eye ____________________________________________________________________
CN(s) ______________________________________________________
Left eye ______________________________________________________________________
CN(s) ______________________________________________________
2. Trace a diagonal line, starting at the upper right corner and moving to the lower left corner. Have your partner follow
your finger again. Which extraocular muscles produce the movements for each eye?
Right eye ____________________________________________________________________
CN(s) ______________________________________________________
Left eye ______________________________________________________________________
CN(s) ______________________________________________________
3. Trace a horizontal line from left to right having your partner following your finger. Which extraocular muscles produce
the movements for each eye?
Right eye ____________________________________________________________________
CN(s) ______________________________________________________
Left eye ______________________________________________________________________
CN(s) ______________________________________________________
4. Trace another diagonal, this time from your partner’s lower right to the upper left, and have your partner follow
along. Which extraocular muscles produce the movements for each eye?
Right eye ____________________________________________________________________
CN(s) ______________________________________________________
Left eye ______________________________________________________________________
CN(s) ______________________________________________________
5. Test your partner’s vision by having her/him stand 20 feet from a Snelling chart, covering one eye, and reading the
largest line and progressing to the smallest line he/she is able to see clearly. Record the ratio (e.g., 20/30) next to the
smallest line your partner can read. Repeat for the other eye. Are the two eyes different?
Ratio (Left Eye): _______________________
Ratio (Right Eye): ______________________
CN(s) ___________________________________________________________
III. Lab Exercise
Identify the following structures of the eye and the eyeball on models. Use your textbook for reference. In Table 2,
record the name of the model and the structures you were able to identify. Name one function for all of the following
structures. Be able to identify them on the models, dissections, and PAL 3.0.
Be gentle with models. Do NOT leave marks on models with pens or pencils
You WILL LOSE points if caught marking the models
Eyeball
Sheep Eye – External Anatomy
1. Cornea
2. Sclera
3. Extrinsic muscles
4. Optic nerve
Sheep Eye – Dissected
1. Vitreous humor
2. Lens
3. Ciliary body
4. Iris
a. Pupillary dilator muscles
b. Pupillary constrictor muscles (not visible, but should know function)
5. Choroid
a. Tapetum lucidum
6. Retina
a. Optic disk
Eye Model
1. Sclera
2. Cornea
3. Optic nerve
4. Extrinisic (extraocular) eye muscles – on the models, you are required to be able to name the specific muscle
and give its specific motion (i.e., “moves eye” is not sufficient)
a. Superior rectus muscle
b. Medial rectus muscle
c. Lateral rectus muscle
d. Inferior rectus muscle
e. Superior oblique muscle
f. Inferior oblique muscle
5. Iris
a. Pupillary dilator muscles
6. Choroid
7. Lens
8. Ciliary body
9. Vitreous humor
10. Retina
a. Optic disk
Table 2: Model Inventory for the Eye
Model
Structures Identified
Eyeball Dissection:
1. Examine the external anatomy of the eyeball.
2. Identify the structures on your ID sheet.
3. Use scissors to remove the eye lashes and the adipose tissue surrounding the eyeball. Identify the optic nerve.
4. Hold the eyeball at its anterior and posterior poles (thumb on cornea, index finger on optic nerve), and use a
sharp scalpel or scissors to make an incision in the saggittal plane. Do NOT hold the eyeball in your hand. Hold it
on the dissection mat. Be CAREFUL, you may spray the fluid. The aqueous humor and vitreous humor will spill
out.
5. Complete the incision, and separate the anterior and posterior portions of the eyeball. Take care to preserve the
retina, the thin, delicate inner layer.
6. Vitreous humor (body) is gelatinous
7. Pull out circular lens (yellow)
The black ring is the ciliary body.
8. Pupil = hole
Next to pupil is the Pupillary dilator muscles – dilate pupil
Pupillary constrictor muscles hard to see, do not identify, but you may be asked function.
Back of eyeball
Thin light area – lift up  Retina
Pick up with probe, easily detaches from eyeball except at star shaped Optic disc
Layer behind Retina = Choroid, may be black or brown: has a rich blood supply
Blue/Green – Tapetum lucidum  not in humans