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Medicine > Eye > Flashcards

Eye Flashcards

1
Q

what is the difference between the anterior and posterior segment

A

anterior:
cornea (light hits eye most refraction occurs here)
aqueous humour (water and nutrients)
lens (also refracts light, but less than cornea- water to lens has a smaller change)
FOCUSING

posterior:
retina
SENSING part

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2
Q

what is the refractive index

A

measure of bending of ray of light from one medium to another

index of air is lower than cornea index
change is greatest here, so more

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3
Q

describe the cornea
what it does
layout (layers)

A

major light focusing element of the eye
40D of fixed power

tear film
epithelium- constantly being replenished (damaged day to day)
stroma (90% thickness of cornea- gives structure and keeps it transparent)
endothelium (keep it transparent but DON’T REPLENISH) as you age the numbers reducde

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4
Q

discuss the refraction of the eye

A

CORNEA
-largest element (40D)
-interfaces with air (low RI0- big difference

LENS
-lesser element (20D)
-interfaces with aqueous- small difference
-vary in power

WHOLE EYE BALL
-about 60D

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5
Q

what is accommodation
what happens to ciliary muscles and lens during far and near accommodation

A

the act of focusing from distant to near and vice versa

DISTANCE
ciliary muscles are relaxed
zonular fibers under tension
lens flattens

CLOSE
ciliary muscles contract
zonular fibers relaxed
lens rounds

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6
Q

what does it mean to have dual innervation of the iris

A

sympathetic- dilation

parasympathetic- constriction

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7
Q

what is the near triad

A
  1. miosis
  2. convergence
  3. accommodation
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8
Q

what happens if you lose parasympathetic supply to the eye

A

3rd nerve palsy
-causes a big pupil

aneurysm in the posterior circulation of the brain
(eg. pca)

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9
Q

what is presbyopia

A

it is a refractive error
occurs in older people when they need glasses for reading
AGE RELATED

lose ability to focus on close
as lens gets thicker and less plasticity
muscles not working as well

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10
Q

what is myopia vs hypermetropia

A

MYOPIA
SHORT SIGHTED
eye too powerful (rays focused on front of retina)

HYPERMETROPIA
LONG SIGHTED
eyes not powerful enough (rays focused behind the retina)

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11
Q

what are some risks with myopia

A

-OPEN ANGLE GLAUCOMA
-RETINAL DETACHMENT

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12
Q

what are some risks with hypermetropia

A

-ANGLE CLOSURE GLAUCOMA
-ISCHAEMIC OPTIC NEUROPATHY

also associated with squint and lazy eye

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13
Q

what is the main cause of visual impairment world wide

A

UNCORRECTED REFRACTIVE ERROR (cataract is second type)
-errors that can be correct by glasses/spectacles but are not

PRESBYOPIA- main type

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14
Q

what is the commonest cause of blindness worldwide

A

CATARACT

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15
Q

what is the visual acuity assessment

A

standard way to measure someone’s vision
6/6
patient/normal

for example
20/80

patient sees it at 20 feet but a person with normal vision could see that at 80 metres

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16
Q

what is the standard distance for ‘big’ Snellen

A

6 metres/ 20 feet

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17
Q

what is the reduced visual acuity chart

A

use the chart at 3 metres
top line is still called the 60 line

18
Q

what are the steps to testing distance visual acuity

A
  1. measure out 3m
  2. cover left eye
  3. ask patient to read from top of chart
  4. chart perpendicular, good lighting, smoothed out and flat
  5. record number of smallest line
  6. if can’t read top line go to 1.5m
  7. if cant read go to 0.5m
  8. if cant read try counting fingers at 1m, hand movements then perception of light and classify with projection or with no projection of perception light then finally no perception of light

repeat for other eye
repeat with both eyes together
repeat with pinhole and with glasses

19
Q

what is driving vision (cars- not HVG)

A

6/12

20
Q

What is blindness 3

A

3/60

21
Q

what is blindness 4

A

1/60

22
Q

what is blindness 5

A

no light perception

23
Q

what is moderate visual impairment

A

6/18

24
Q

what is severe visual impairment

A

6/60

25
Q

what is TRACHOMA

A

infectious disorder caused by Chlamydia
transmitted by flies
causes lashes to go wrong way and abrasion of eye- blindness
cornea scarring

preventable ad treatment
eradicate fly
antibiotics
surgery

26
Q

describe the retinal structure

A

outer nuclear layer
(with rods and cones)- photoreceptors AT BACK produce signal to back of brain

plexiform layers

ganglion cell layers

outer nuclear layer

info from rods and cones is converged to ganglion cells, lateral cells and amacrine act to provide initial processing of visual signal

27
Q

describe difference between rods and coes

A

rods
far more - 120 million
HIGH CONVERGENCE to ganglion cells
VISION IN GREYSCALE- night vision
very light sensitive
widespread distribution in retina
broad spectral sensitivity

cones
6 million
LOW CONVERGENCE to ganglion cells
BLUE GREEN RED
1/30th sensitivity of rods
concentrated in macula
narrow spectral sensitivity

photoreceptors are depolarised in the dark
hyperpolarised in the light

28
Q

what is the most sensitive part of the eye in terms of visual acuity

A

FOVEA- high cones
sensitivity decreases as move away from centre

29
Q

what is found where the blind spot is

A

where optic nerve is

30
Q

discuss role of opsin

A

chromophore RETINAL (derived from vitamin A) is found in all rods and cones
changes shape when light hits it
bound to protein (opsin)
cascade

PHOTOTRANSDUCTION

there are different opsin types (each specific to a different type of cone)
- 3 colours with rod retinal binding an opsin– RHODOPSIN

when light hits retinal it changes conformation- appears bleached

31
Q

what does vitamin a deficiency cause

A

night blindness
then total corneal blindness
then death

32
Q

is retina/ photoreceptors active during sleep

A

metabolically more active when you are asleep in DARK

keep eye in hyperpolarised state which requires energy

therefore can exploit as therapy for retinal disease

33
Q

what adaptations do photoreceptors have

A

detect levels of light
-vision can be created in bright sunlight and star lit sky
adapt to different ambience light

dependent upon changes in Ca++ and cGMP levels within the cell altering the sensitivity of membrane channels

34
Q

what is cone fatigue

A

when you stare at a specific colour for too long, the cells that detect that frequency of light get fatigued

after image is a result of photoreceptors not bein gin balance
when they become less tired the balance is recovered and the after image disappears

35
Q

what happens due to age related macular degeneration

A

age related macular degeneration

  • eye does not readjust well to ambience light
    -retinal cell connectivity
36
Q

retinal cell connectivity to see objects and moving objects

A

how photoreceptors connect to ganglion cells by amacrine cells and bipolar cells

37
Q

what are bipolar cells

A

on cells- when light is shone they turn on
– NT release in the light- switch light on

off cells– opposite

allows when something is moving u can see shadow and edge (via on/off bipolar cells)

38
Q

what do horizontal and amacrine cells do

A

connect bipolar cells and allow for summation of info to allow detection of edges and contrast

RECEPTIVE FIELDS– convergence of info from FR into bipolar cells than a ganglion cell

39
Q

what conditions cause problems to the retina

A

age related macular degeneration
diabetes

40
Q

what is the optic nerve

A

collection of all the ganglion cells
exit back of the eye through a hole in the sclera
front focus light into retina, retina detects and changes it into electrical signal – brain

seen at the back of the eye (optic disc)

41
Q

does processing happen at the retina

A

yes
convergence- 100 million photoreceptors but only 1 million ganglion cells
ganglion cell transfers retinal info to the brain, optic nerve-chiasm-optic tract
first synapse is at the lateral geniculate nucleus
part of thalamus
major relay station for sensory info

Medicine (54 decks)

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