Iris and Pupil

Question 1

Which of the two iris muscles (sphincter or dilator) is the strongest?

Answer 1

sphincter (constrictor)

Question 2

In the rabbit eye, how are the adrenergic receptors distributed in the iris sphincter?

Answer 2

mainly beta, few alpha

Question 3

In the rabbit eye, how are the adrenergic receptors distributed in the iris dilator?

Answer 3

mainly alpha, few beta

Question 4

In the rabbit eye, how are the adrenergic receptors distributed in the ciliary muscles?

Answer 4

mainly alpha, few beta

Question 5

In the monkey eye, how are the adrenergic receptors distributed in the iris sphincter?

Answer 5

mainly alpha, perhaps beta

Question 6

In the monkey eye, how are the adrenergic receptors distributed in the iris dilator?

Answer 6

mainly alpha, few beta

Question 7

In the monkey eye, how are the adrenergic receptors distributed in the ciliary muscles?

Answer 7

beta only

Question 8

In the cat eye, how are the adrenergic receptors distributed in the iris sphincter?

Answer 8

mainly beta, some alpha

Question 9

In the cat eye, how are the adrenergic receptors distributed in the iris dilator?

Answer 9

mainly alpha, some beta

Question 10

In the cat eye, how are the adrenergic receptors distributed in the ciliary muscles?

Answer 10

mainly beta, some alpha

Question 11

In the dog eye, how are the adrenergic receptors distributed in the iris sphincter?

Answer 11

alpha and beta

Question 12

In the dog eye, how are the adrenergic receptors distributed in the iris dilator?

Answer 12

alpha and beta

Question 13

In the dog eye, how are the adrenergic receptors distributed in the ciliary muscles?

Answer 13

unknown

Question 14

Which nerve innervates the sphincter muscle?

Answer 14

cranial nerve 3 (oculomotor nerve)

Question 15

Which nerve innervates the dilator muscle?

Answer 15

sympathetic nerves

Question 16

Most synapses in the ciliary ganglion are involved in relaying impulses that result in what?

Answer 16

accommodation

Question 17

How does morphine ( and other pure mu agonists) influence pupillary function?

Answer 17

morphine leads to the release of catecholamines which act on subcortical cells in the oculomotor nuclear complex.

Question 18

How do the effects of morphine on pupillary function differ between dogs and cats?

Answer 18

dogs - constriction

cats - dilation

Question 19

What is the afferent pathway of the pupillary light reflex?

Answer 19

optic nerve/optic tract to pretectal area (ipsi and contralateral via posterior commissure)

Question 20

What is the efferent pathway of the pupillary light reflex?

Answer 20

pretectal area to anteriomedialn nuclei (ipsi and contralateral) which is rostral to the Edinger-Westphal nuclei, then parasympathetic fibers to the ciliary ganglion.

Question 21

What are some physiologic stimuli for pupillary dilation?

Answer 21

sudden body pain, asphyxia, anxiety

Question 22

What is the rostral extension of the Edenger-Westphal nucleus noted as?

Answer 22

aneteriomedian nucleus (pathway of efferent pupillary light reflex)

Question 23

What are the 4 pupillodilator pathways identified in the cat?

Answer 23

1 - descending excitatory pathway from the hypothalamus to the intermediolateral cell column (C8-T12)
2 - descending inhibitory pathway from the hypothalamus which projects to the Edinger-Westphal nucleus
3 - ascending inhibitory pathway from the reticular formation, which project the the Edinger-Westphal nucleus.
4 - ascending inhibitory pathway from the dorsal horn, which projects to the Edinger-Westphal nucleus.

Question 24

Aside from regulation of light into the posterior segment, what are two pupillary functions?

Answer 24

increasing depth of focus for near vision

minimization of optical aberrations by the lens

Question 25

Are the irides of young animals often different in color than those of the young?

Answer 25

yes

Question 26

What accounts for the vertical slit appearance in the feline pupil?

Answer 26

constrictor muscle fibers are vertically oriented, and the dilator muscle fibers are absent at the dorsal and ventral portions of the pupil

Question 27

What is the difference in pupil shape between young horses and adult horses?

Answer 27

pupil is more circular in young horses

Question 28

What is Scheiner’s disc phenomenon, and to what species does this apply?

Answer 28

Scheiner’s disc phenomenon is when a single in focus object becomes doubled when viewed through two apertures that are spaced apart at a distance less than the diameter of the pupil. This is seen in the horse due to the granule iridica. It happens in bright light when the pupil is constricted and two apertures are created.

Question 29

Which portions of the equine pupil do not constrict?

Answer 29

nasal and temporal portions

Question 30

Which drugs have been reported to be effective in dilating the avian pupil?

Answer 30

• 10% cocaine solution followed by epinephrine followed by gall amine triethoidide.
• D-tubocurarine
• vecuronium