Vision - Fitz

Question 1

Blinking and tear production are for?

Answer 1

eye protection
conreal lubrication
visual info processing

Blinking can be spontaneous or reflexive

Question 2

What muscle is the sympathetic component of blinking?

What problems occur if this part of the blinking pathway is damaged?

Answer 2

The superior tarsal muscle is a smooth muscle innervated by sympathetic a1 receptors

Horner’s syndrome will occur
This will affect the ability to maintain the ocular opening all the way open

Question 3

3 layers of tear film of eye?

Answer 3

Lipid secreted by oil glands in eyelids

Aqueous solution from lacrimal glands

Mucus from conjunctiva

Question 4

What part of tear production is involved with “styes”

Answer 4

Staph infection of the oil glands in the eyelids will create “styes”

Question 5

What is epiphora?

What can it be caused by?

Answer 5

Crying!

1- increasing tear prodcution in lacrimal gland
2 - decreasing outflow by closing lacrimal duct passage

Stimulation of cornea (CN-5) make relfex tears
Strong Emotional Responses (mediated by limbic system) -AKA Watching Batboy on youtube…

Question 6

What is refraction and accomodation?

How does it relate to eye structures?

Answer 6

Refraction = Bending of light to focus it
(cornea does most of the work)
(lens can adjust focusing power)
Accomodation = adjustment of focusing to see clearly

Question 7

What is the lens doing in order to accommodate so you can see clearly?

Answer 7

Distant objects are easily focused through the eye appropriately on the fovea

With near objects, the image distance goes farther than the fovea and a clear picture in not seen.
So you have to change the shape of the lense to be fatter and shorter, this will increase the focusing power and allow the image to be on the right spot on the fovea. BAM!!!!

Question 8

Sympathetic vs Parasympathatics where vision is concerned?

Answer 8

Sympathetics - distance vision - relaxation of ciliary muscles through B2 receptors

Parasympathetics - Near vision - contract ciliary muscle through muscarnic receptors

Question 9

Hyperopia
vs
Myopia

Answer 9

Hyperopia - Farsightedness
(cause by too short eyeball or lens thats too weak)
correct with convex lens to increase refractive power

Myopia - NErshightedness
Correct with concave lense

Question 10

What is presbyopia?

Answer 10

Less felxible lens causes decreased accomodation

- happens in middle age - reading glasses needed

Question 11

Astigmatism is what?

Answer 11

Weakness in lens - part of visual field will be out fo focus

Question 12

What are cataracts?

Answer 12

Opaqueness in lens

Question 13

What is miosis and mydriasis?

Are they sympathetic or parasympathetic?

Answer 13

Miosis: Constriction of the pupil caused by: Parasympathetic stimulation of muscarinic receptors on sphincter pupillae muscles

Mydriasis: Dilation of pupil caused by:
Sympathetic stimulation of a1 receptors on dilator pupillae muscles

Question 14

Why is pupillary light reflex important clinically?

Answer 14

It’s a pretty complex circuit where shining light in one eye will cause constriction in both eyes. This can tell you a lot of info using one simple test

Question 15

What are the two things that will affect inflow into the aqueous humor?

Answer 15

Sympathetics

• b2 receptors increase flow
• a2 receptors decrease flow

Cl secretion

• H2O is driven by Cl
• Because Cl is regulated by Bicarbonate, carbonic anhydride is a pharmaological target!

Question 16

What two things will influence outflow from the aqueous humor in the eye?

Answer 16

Canal of Schlemm

• flow regulated by sphinctor pupilae
• contract sphinctor pupillae and this will increase flow

Uveoscleral System

• reabsorption through the ciliary muscle
• parasympathetics and ProstaG’s working on this side of the system

Question 17

Progression of eye damage in glaucoma

Answer 17

Increased IOP causes damage to:

1) Cornea - halos, blurring
2) Photoreceptor compression
3) optic nerve
4) arterial supply

Eventually have bad tunnel vision

Question 18

Give a brief overview of the circuitry of the retina:

Answer 18

Generate receptor potentials (transduction), then go to bipolar cells

Bipolar cells use graded potentials - and send to graded cells

Graded cells - produce action potential and send signals to optic nerve

Question 19

What is color and brightness is regards to the electromagnetic spectrum?

Answer 19

frequency = color

intensity - brightness

Question 20

Wat are the differences in responability between rods and cones?

Answer 20

Rods responsible for scotopic vision
(monochromatic vision occurring in low light)

Cones - responsible for photopic vision
better spatail and temporal resolution
3 types, blue-green-red

Question 21

Why does the military use red lights at night on naval ships

Answer 21

Red light allows people to conserve their night vision because there is no overlap between red light of a very long wavelength. Can use rods and red cones simultaneously

Question 22

Where are rods and cones lovated on the retina?

Answer 22

Cones in fovea, rods in periphery

Question 23

Compare physiology of rods and cones:

Answer 23

Rods:
extremely sensitive - respond to low levels of light - sacrifice speed and precision
best at night
scattered light

Cones:
Respond to higher levels of light, faster and more precise
have large dynamic range, better response in bright light
patterns

Question 24

3 tpyes of acuity in visual system:

Answer 24

Spatial acuity:
where is it?
Use snellen eye chart

Temporal Acuity:
Distinguish two events as separate
Flicks!

Spectral acuity:
Ability to distinguish color

Question 25

Activation of Rods

What happens on the moelcular level?

Answer 25

RODS
1st step - activate rhodopsin
Joins g-protein (tranducin)
Trasnducin converts GDP to GTP
This results in activation of Phosphodiesterase
This enzyme breaks down cGMP
When cGMP goes down it will close Na channel
This will hyperpolarize the cell
Will cause a decrease in release of NT
This will end up increasing current in the bipolar cell somehow. Kinda crazy right???

Question 26

Hallmark of Retinitis Pigmentosa?

Answer 26

Decrease in response of photreceptors
(they are dying or malfucntioning)

1st get nictalopia (loss of night vision) and tunnel vision because rods die first

2nd lose color and central vision when cones start dying

Question 27

What is retinopathy?

Answer 27

Non-inflammatory condition, usually a block in the blood supply

Can be caused by diabetes, sickle cell

Symptoms: lose night vision, flashes, decrease in acuity, can have total blindness

Question 28

What is the visual cycle?

Answer 28

A recycling system between photrecepotrs and retinal pigment epithelium (supportive of rods and cones)
4 steps:
1-light hits pigemnts and splits it into components
2-Pigment is split and loses function
3-Pumping of all-trans-retinol to RPE
4-11-cis-retinol is pumped back into rod to be made back into rhodopsin

In cones, it’s the same cycle, but is fast because it’s all in the cone

Question 29

What happens if you have Vit A deficiency?

Answer 29

Retinol is not produced which will give you night blindness

Question 30

The appearance of drusen is characteristic of what disease?

Answer 30

Age related macular degeneration

Question 31

Dry macular degeneration is cause by what?

Answer 31

Dry atrophy of RPE, you lose photorecptors

Question 32

Wet macular degeneration is caused by what?

Answer 32

Abnormal growth of blood vessels leading to photoreceptor damage
Lose central vision
-Treat with anti-angiogenesis drugs