orbit

Question 1

Where are the Glands of Zeis?

What do they secrete?

Answer 1

located on the margin of the eyelid
secrete “sleep”, which prevents eyelids from sticking together
-inflammation = external stye or hodeolum

Question 2

Where are the Meibomian Glands? What do they secrete

Answer 2

They are inside the tarsal plate, responsible for the supply of meibum, an oily substance which prevents evaporation of the eye’s tear film.
-Inflammation = internal stye or chalazion

Question 3

Which nerves pass through the tendinous ring of zinn?

Answer 3

CNs II, III, V1 and VI

*CN IV passes above the ring

Question 4

Which eye muscles aren’t innervated by the occulomotor nerve (CNIII)

Answer 4

• the lateral rectus muscle (Abducts the eye: supplied by the Abducent [CN VI])
• The superior oblique (abducts, depresses, int. rotates) supplied by the trochlear nerve CN IV)

LR6SO4 (Chemical formula, to remember)

Question 5

What’s special about the levator palpebrae superioris?

Answer 5

• Its innervated by the oculomotor nerve (CN III), but it has smooth muscle mixed with it (the superior tarsal muscle or Mueller’s muscle)
• The superior tarsal muscle is innervated by sympathetic fibers
• This is why, under stress, the upper eyelid will reflexively open

Question 6

How do we clinically test the trochlear nerve?

Answer 6

• Have patient look in and then down
• By itself the superior oblique moves the eye Down and out
• BUT Inferior Rectus also depresses eye
• By medially rotating eye first (with medial rectus), the inferior rectus is no longer able to effectively depress eye: only the superior oblique can depress the eye in this position

Question 7

Explain the Corneal (or Blink) Reflex

Answer 7

Touching of the cornea will initiate a reflex arc in which the eye is closed by the orbicularis oculi muscle which is supplied by the Facial Nerve (VII)

• Afferent limb: CN V1 (long, short ciliary branches)
• Efferent limb: CN VII

Question 8

What nerves can be affected by an infection in the cavernous sinus?

Answer 8

CNs III, IV, V1, V2 and VI pass through the cavernous sinus and all can be affected by an infection there.

Question 9

Describe what functions autonomic innervation accomplishes in the eye

Answer 9

Dilation of the pupil (sympathetic)
Constriction of the pupil (parasympathetic-CN III)
Accomodation* (parasympathetic-CN III)
*Accomodation = rounding of the lens for near vision

Question 10

Pupillary Light Reflex

Answer 10

• Both pupils should contract if you shine light in only one eye
• Light from each eye travels to both sides of the brain, stimulating the Edinger-Westphal nuclei.
• This permits the bilateral pupillary light reflex.

Question 11

Horner’s Syndrome

Answer 11

Interruption of sympathetic innervation to the head resulting in:

1. Miosis: Constricted pupil due to unopposed PNS innervation
2. Ptosis: drooping eyelid due to weakness of smooth (Mueller’s) muscle in levator palpebrae superioris
3. Anhydrosis: lack of sweating on face
4. Vasodilation: due to dilated blood vessels on the face,

Question 12

What’s important about the ciliary artery?

Answer 12

• Its one of the terminal branches of the opthalmic artery (br of int carotid)
• Supplies the inner part of the retina, is an end-artery (No Anastomoses) –> occlusion results in blindness