34: Organs of Vision and CN II, III, IV, and VI

organs of vision

adnexa

eyeball (bulbus oculi)

Where are the bulbus oculi and adnexa located?

housed in the orbit

eyeball is embedded in fat

Adneza includes:

eyelids

ocular muscles

lacrimal apparatus

What are the differences between the body processes lateral to the orbit in cats and dogs?

cats: very close or fused

dogs: separated but joined together by the orbital ligament

optic axis

straight line passing through both poles

equator

line equidistant from the poles

tunics of the eye

external fibrous tunic

middle vascular tunic

internal nervous tunic

external fibrous tunic

exterior tunic of eyeball

gives form to and protects the eyeball

middle vascular tunic

middle tunic of the eyeball

blood vessels and smooth muscle, nutrition of the eyeball, and the regulation of the shape of the lens and size of the pupil

internal nervous tunic

internal tunic of the eyeball

translation of visual stimuli into nerve impulses

components of the external fibrous tunic

sclera

limbus

cornea

sclera

external fibrous tunic

white, fibrous tissue

covers outside of the eye

extends from the cornea to the optic nerve

cornea

forms ¼ of external fibrous tunic

outermost transparent layer of the eye

helps focus light and protect the eye

limbus

border between the cornea and sclera

innervation of the cornea

most densely innervated tissue

nerves are responsible for:

-sensation: touch, pain, temperature

-reflexes: blink reflex, tear production

-wound healing

components of the middle vascular tunic

AKA uvea

iris

ciliary body

choroid

pupil

anterior and posterior chamber

lens

iris

adjusts size of pupil

divides the space between the lens and cornea into anterior and posterior chambers

contains two layers of smooth muscles

-sphincter of the pupil

-dilator of the pupil

anterior and posterior chambers

communicate through the pupil

both filled with aqueous humor

miosis

constricted pupil

GVE parasympathetic (CN III)

sphincter of the pupil

horner’s syndrome

mydriasis

dilated pupils

GVE sympathetic (CN III)

dilator of the pupil

ciliary body

suspends the lens and regulates its curvature

raised ring with ridges converging towards lens

smooth ciliary muscle

accommodation (ability of the eye to focus on near or distant objects by changing the shape of the lens

ciliary body reaction to far objects

sympathetic CN III innervation 

smooth ciliary m. relaxes

zonular fibers tense

lens becomes more flat

ciliary body reaction to close objects

parasympathetic CN III innervation

smooth ciliary m. contracts

zonular fibers relax

lens becomes more spherical

choroid

dense network of blood vessels embedded in heavily pigmented connective tissue

tapetum lucidum

light reflecting area near optic nerve (black of eye, fundus)

internal nervous tunic components

retina

area centralis

optic disc

retina

light-sensitive receptor cells

area centralis

region of the retina with a higher concentration of photoreceptors

analogous to human macula, but does not have the concentration of cone receptors like humans

Why colors do dogs see?

limited to shades of blue and yellow

optic disc

“blind zone”

area where the axons of the 4th layer concentrate to leave the eye as optic nerve (CN II)

tapetum nigrum

dark, pigmented area of the fundus of the eye

eye chambers

anterior

posterior

vitreous

anterior chamber

between the cornea and iris, filed with aqueous humor

posterior chamber

between iris and ciliary body/lens, filled with aqueous humor

vitreous chamber

between ciliary body and retina, filled with vitreous humor

aqueous humor

role in the maintenance of intraocular pressure

produced by cells of the ciliary processes

glaucoma

disease of the eye in which the intraocular pressure is increased

intraocular pressure (IOP)

pressure within the eye

lens

soft, transparent tissue that sits posterior to the iris

helps focus incoming light to the retina

Name the structure(s) indicated by 1, 2, and 3.

zygomatic process of the frontal bone

orbital ligament

frontal process of zygomatic bone

Name the structure(s) indicated by a, b, and c.

monocular vision

binocular vision

blind area

Name the structure(s) indicated by a and b.

optic axis

equator

Name the structure(s) indicated by a, b, c, and d.

external fibrous tunic

sclera

cornea

limbus

Name the structure(s) indicated by a, b, and c.

limbus

cornea

sclera

Name the structure(s) indicated by a, b, and c.

iris

ciliary body

choroid

Name the structure(s) indicated by a, b, and c.

iris

pupil

anterior chamber

Name the structure(s) indicated by d and e.

posterior chamber

lens

Name the structure(s) indicated by a and b.

cat

dog

Name the structure(s) indicated by a, b, c, and d.

miosis

GVE sympathetic

mydriasis

GVE sympathetic

Name the structure(s) indicated by a, b, and c.

smooth ciliary m.

ciliary processes

zonular fibers

Name the structure(s) indicated by a, b, and c.

ciliary body

iris

cornea

Name the structure(s) indicated by a, b, and c.

choroid

tapetum lucidum

optic disc

Name the structure(s) indicated by a, b, and c.

retina

choroid

sclera

Name the structure(s) indicated by d and e.

area centralis

optic disc

Name the structure(s) indicated by a, b, c, and d.

optic nerve

optic disc

tapetum nigrum

tapetum lucidum

Name the nerves and/or muscle damaged in images a, b, and c.

CN III, medial rectus

CN IV, dorsal rectus

CN VI, lateral rectus

Name the structure(s) indicated by a, b, and c.

superior oblique m.

ventral rectus m.

inferior oblique m.

Name the structure(s) indicated by d, e, and f.

dorsal rectus m.

lateral rectus m.

dorsal rectus m.

Name the structure(s) indicated by g, h, I, and j.

lateral rectus m.

superior oblique m.

medial rectus m.

ventral rectus m.

accessory (adnexa) organs of the eye

eyelids

tunica conjunctiva

lacrimal apparatus

extrinsic mm. of the eye

cranial nerves III, IV, and VI

orbital fascia