Vision - Fitz Flashcards
Blinking and tear production are for?
eye protection
conreal lubrication
visual info processing
Blinking can be spontaneous or reflexive
What muscle is the sympathetic component of blinking?
What problems occur if this part of the blinking pathway is damaged?
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
3 layers of tear film of eye?
Lipid secreted by oil glands in eyelids
Aqueous solution from lacrimal glands
Mucus from conjunctiva
What part of tear production is involved with “styes”
Staph infection of the oil glands in the eyelids will create “styes”
What is epiphora?
What can it be caused by?
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…
What is refraction and accomodation?
How does it relate to eye structures?
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
What is the lens doing in order to accommodate so you can see clearly?
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!!!!
Sympathetic vs Parasympathatics where vision is concerned?
Sympathetics - distance vision - relaxation of ciliary muscles through B2 receptors
Parasympathetics - Near vision - contract ciliary muscle through muscarnic receptors
Hyperopia
vs
Myopia
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
What is presbyopia?
Less felxible lens causes decreased accomodation
- happens in middle age - reading glasses needed
Astigmatism is what?
Weakness in lens - part of visual field will be out fo focus
What are cataracts?
Opaqueness in lens
What is miosis and mydriasis?
Are they sympathetic or parasympathetic?
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
Why is pupillary light reflex important clinically?
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
What are the two things that will affect inflow into the aqueous humor?
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!
What two things will influence outflow from the aqueous humor in the eye?
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
Progression of eye damage in glaucoma
Increased IOP causes damage to:
1) Cornea - halos, blurring
2) Photoreceptor compression
3) optic nerve
4) arterial supply
Eventually have bad tunnel vision
Give a brief overview of the circuitry of the retina:
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
What is color and brightness is regards to the electromagnetic spectrum?
frequency = color
intensity - brightness
Wat are the differences in responability between rods and cones?
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
Why does the military use red lights at night on naval ships
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
Where are rods and cones lovated on the retina?
Cones in fovea, rods in periphery
Compare physiology of rods and cones:
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
3 tpyes of acuity in visual system:
Spatial acuity:
where is it?
Use snellen eye chart
Temporal Acuity:
Distinguish two events as separate
Flicks!
Spectral acuity:
Ability to distinguish color
Activation of Rods
What happens on the moelcular level?
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???
Hallmark of Retinitis Pigmentosa?
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
What is retinopathy?
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
What is the visual cycle?
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
What happens if you have Vit A deficiency?
Retinol is not produced which will give you night blindness
The appearance of drusen is characteristic of what disease?
Age related macular degeneration
Dry macular degeneration is cause by what?
Dry atrophy of RPE, you lose photorecptors
Wet macular degeneration is caused by what?
Abnormal growth of blood vessels leading to photoreceptor damage
Lose central vision
-Treat with anti-angiogenesis drugs
