4.8 Visual System

Question 1

What is the visual pathway?

Answer 1

the ganglion cell axons travel through the optic nerves, where some fibers cross at the optic chiasm
optic tracts travel to the thalamus, then to the Visual Cortex, hypothalamus, superior colliculus, or pineal gland

Question 2

What is the pretactal nucleus?

Answer 2

midbrain (behavioral response to light, pupillary reflex, circadian rhythm)

Question 3

What happens with partial retina damage?

Answer 3

leads to “black spots” in the visual field called scotomas

diabetic retinopathy, infarcts, degenerative diseases

Question 4

What happens with damage to an optic nerve?

Answer 4

loss of all vision from one eye
optic neuritis (early sign of MS), glaucoma, tumors, trauma

Question 5

What happens with damage at the optic chiasm?

Answer 5

loss of temporal visual field from both eyes “tunnel vision”.
pituitary tumor presses on optic nerve

Question 6

What happens with an occipital lobe lesion?

Answer 6

half of visual field from each eye (left occipital lobe = right visual field, right occipital lobe – left visual field)
vascular causes, tumor, infection, trauma

Question 7

What is the lacrimal apparatus? Path of a tear?

Answer 7

produces, collects and drains tears
lacrimal gland: produces watery lacrimal fluid (tears)
tears collect in the lacrimal sac as they leave the eye
drain into the nasolacrimal duct to the nasal cavity

Question 8

What are the tarsal glands of the eye?

Answer 8

thin oil through multiple ducts inside the eyelid
maintains protective layer over the eye, keeps eyelids from sticking together
** consider as cause of dry eye

Question 9

What are the ciliary glands of the eye?

Answer 9

gritty lipid on the margin of eyelid

especially active at night, prevents bacterial growth, pathogen entry

Question 10

What are the glands of Zeiss?

Answer 10

oil on eyelashes

lubricate eyelashes

Question 11

What is the conjunctiva? It’s two subtypes

Answer 11

mucous membrane lining the inner surface of the eyelids and the anterior surface of the eye
Palpebral conjunctiva – inside of eyelid
Bulbar (ocular) conjunctiva – on the eye

Question 12

What are the extra-ocular muscles? And which CN controls?

Answer 12

superior rectus: elevates, adducts eye
inferior rectus: depresses, abducts eye
medial rectus: adducts the eye (moves medially)
lateral rectus: abducts the eye (moves laterally) **CN VI abducens
superior oblique: (pulls back of the eye up) depresses, adducts eye **CN IV trochlear
inferior oblique: (pulls the back of the eye down) elevates, abducts eye
levator palpebrae superioris: lifts/elevates eyelid

Rest- CN III

Question 13

What are the tunics of the eye?

Answer 13

Fibrous tunic – tough outermost layer
Vascular tunic – middle layer, rich with blood vessels
Neural tunic – back of the eye, contains receptors and neurons

Question 14

What are the sclera and cornea? Which tunic do they form?

Answer 14

Sclera – white of the eye, dense connective tissue

Cornea – central anterior clear portion

Question 15

What is the choroid?

Answer 15

Pigmented layer of vascular tunic

Question 16

What is the ciliary body?

Answer 16

ring of smooth muscle attached to the lens by suspensory ligaments, controls the shape of the lens

Question 17

What is the iris?

Answer 17

smooth muscle which controls the diameter of the pupil; the colored part

Question 18

What are aqueous and vitreous humor? Where are they found?

Answer 18

Anterior cavity – in front of the lens, contains aqueous humor which provides nutrients to the lens and cornea
Anterior chamber – anterior to iris
Posterior chamber – posterior to iris, anterior to lens
Posterior cavity – posterior to the lens, filled with jelly like vitreous humor

Question 19

What is the lens?

Answer 19

bends to focus light on the retina – flattened for distance vision, bulged for near vision

Question 20

What is the canal of schlemm?

Answer 20

Regulates intra-ocular pressure – fluid accummulates when blocked

Question 21

What is the pupil?

Answer 21

the space in the middle of the iris, dilation allows more light to enter (distance vision), constriction to reduce light (near vision)

Question 22

What is mitosis? Causes?

Answer 22

constricted pupil
bright light
parasympathetic nervous system (Ach), CN III
opioids (morphine, heroine)

Question 23

What is mydriasis? Causes?

Answer 23

dilated pupil
low light
sympathetic nervous system (Epi/NE), CN V, stimulation
compression of CN III – rapidly rising intracranial pressure
anti-cholinergics
serotonin, SSRI’s
norepinephrine
stimulant drugs ( cocaine, amphetamines, MDMA, etc)
opioid withdrawal

Question 24

What are the macula and fovea?

Answer 24

Macula lutae – “yellow spot” lateral to the optic disc, contains mostly cones
Fovea centralis – small pit in the center of the macula which contains the greatest concentration of cones, sharpest vision

Question 25

What is myopia? How do you correct?

Answer 25

impaired distance vision
elongated eyeball, treated with concave lenses
= shortsighted

Question 26

What is hyperopia? How do you correct?

Answer 26

impaired near vision
short eyeball, treated with convex lenses
slackened ciliary muscle with age
=Farsighted

Question 27

What is macular degeneration?

Answer 27

loss of central vision (fovea)

primarily genetic, but some prevention possible

Question 28

What are cataracts?

Answer 28

thickened lens associated with age, smoking, diabetes, long-term steroid use and many other factors
surgical removal and replacement of lens

Question 29

What is glaucoma?

Answer 29

optic nerve damage due to IOP

preventable **aimed at reduction in intraocular pressure with medication, laser and incisional surgery