Exam 3: Visual System Flashcards
What does CN 3 innervate? Where is the nucleus?
Dorsal, ventral, and medial recti, and ventral oblique
Midbrain
What does CN 4 innervate? Where is the nucleus?
Dorsal oblique
Midbrain
What does CN 6 innervate? Where is the nucleus?
Retractor bulbi and lateral rectus
Brainstem
How are conjugate eye movements coordinated?
By the medial longitudinal fasciculus
What is strabismus? What are some causes?
Abnormal position of eyes
Neurologic or mechanical issues
What are some causes of upper eyelid drooping (CN and muscles)?
CN 7: frontalis, levator anguli
CN 3: Levator palpebrae superioris
Sympathetic: Muller’s muscles
What is the grown up term for upper eyelid drooping?
Ptosis
What is the sensory innervation to the eyelid?
CN 5: opthalmic branch to the medial side
CN 5: maxillary branch to the lateral side
What is the motor innervation to close the eyelid? Through what muscle?
CN 7
Orbicularis oculi
What causes neuroparalytic keratoconjunctivitis sicca (KCS)?
CN 7 paralysis
What cause neurotrophic keratitis?
CN 5 issues
What does the corneal reflex test?
CN 5 and 6
What does the palpebral reflex test?
CN 5 and 7
What does the menace response test?
CN 2 and 7
What are the photoreceptors of the retina?
Rods and cones
Which photoreceptor of the retina works best in low light?
Rods (motion)
Which photoreceptor of the retina works best in light?
Cones (color)
Is the optic nerve a nerve or tract?
Tract
Axons from the right visual field hit the ______ retina of the right eye and the ______ retina of the left eye to course through the _______ nucleus and the left occipital lobe.
Medial
Lateral
Lateral geniculate
How much decussation occurs at the chiasm of people?
50%
How much decussation occurs at the chiasm of birds?
100%
How much decussation occurs at the chiasm of dogs?
75%
How much decussation occurs at the chiasm of cats?
65%
How much decussation occurs at the chiasm of farm animals?
75-80%
What percent of fibers branch off the optic tract to influence pupillary light reflexes? Where are they going?
20%
Pretectal nucleus
Will a disease of the retina cause vision deficits? PLR deficits?
Yes
Yes
Will a disease of CN 2 cause vision deficits? PLR deficits?
Yes
Yes
Will a disease of the optic chiasm cause vision deficits? PLR deficits?
Yes
Yes
Will a disease of the LGN cause vision deficits? PLR deficits?
Yes
No
Will a disease of PSANS nucleus of CN 3 cause vision deficits? PLR deficits?
No
Yes
Will a disease of the occipital lobe of the cerebrum cause vision deficits? PLR deficits?
Yes
No
Will a disease of CN 3 cause vision deficits? PLR deficits?
No
Yes
Will a disease of the ciliary ganglion cause vision deficits? PLR deficits?
No
Yes
Which ANS causes miosis? Mydriasis?
PSANS
SANS
If you have good PLRs, does it mean you are visual?
No
What is it called if you are blind with good PLR?
Cortical blindness
Which is stronger in vet patients, direct or consensual PLR?
Direct
When you shine a light in an eye and the eyelid blinks, what is that called? Can you say that the dog saw this light?
Dazzle reflex
No, but it lets you know that the optic nerve is intact
If a pupil only constricts when light is shown into the opposite eye and is otherwise dilated all the time, where is the lesion?
Optic nerve
Are TV shows correct when they freak out over “fixed and dilated” or “blown” pupils because this means a worse prognosis?
Yes
What ganglion does the PSANS and SANS synapse on when traveling to the eye?
Cranial cervical
What are the 4 clinical signs of lack of sympathetic tone to the eye?
Ptosis, enopthalmos, 3rd eyelid elevation, and miosis
What muscles are being affected when there is a lack of sympathetic tone to the eye?
Ptosis:
Enopthalmos
3rd eyelid elevation: Muller’s muscles
Miosis: ciliary muscles
What do horses do that is different from other species with Horner’s syndrome?
Sweating
If you dim the lights in a room with a patient with anisocoria and the anisocoria worsens, is it PSANS or SANS issues causing the problem?
PSANS
What is the most common thing that you might call Horner’s that has many of the same signs as Horner’s, but is not Horner’s? What area is affected with this disease?
Internal and external ophthalmoplegia (mydratic)
Cavernus sinus
What other nerves can be affected with a lesion in the cavernus sinus?
3, 4 , 5o, 6
What drug can you give to cause pupil dilation and pupil constriction in a denervated pupil showing hypersensitivity?
Phenylephrine- dilate- symphatomimetic
Pilocarpine- constrict- parasympathomimetic
Atropine dilates eye
