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PPO 1a > Lecture One > Flashcards

Lecture One Flashcards

1
Q

What does the tear film sit on?

A

Epithelium

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2
Q

Where does the first processing of light occur?

A

Retina, at photoceptors

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3
Q

What is the pathway of light from beginning of retina to end of retina?

A

Photoreceptors->bipolar cells->ganglion cells-> axons of ganglion cells out through optic nerve

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4
Q

What is the pathway of light from optic nerve?

A

Optic nerve->optic chiasm->optic tract->LGN->optic radiation->cortex

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5
Q

Are there rods located in the fovea? What is the fovea the center of?

A

NO. only cones. center of macula

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6
Q

Optic nerve head is located how far from fovea?

A

At a 15 degree angle.

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7
Q

Pathway of light from visual cortex?

A

visual cortex->V1->extrastriate Cortex->higher cortical areas

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8
Q

Visible light range?

A

390nm(violet) to 740nm (red)

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9
Q

Define visual acuity

A

The spatial resolving capacity of the visual system (NOT JUST THE EYE).

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10
Q

Define clinical VA

A

measure of ability of a patient to resolve fine detail. measures ability to see but not how well they see.

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11
Q

Normal VA is limited by what?

A

anatomy of eye and the visual system

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12
Q

Driving license requirements in MA?

A

for full: must be 20/40 BCVA in the better eye

day light: 20/50-20/70

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13
Q

Legal blindness?

A

VA is less than or equal to 20/200 in the better eye or they have a visual field of 20 degrees or less.

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14
Q

Define Amblyopia

A

“lazy eye” neurological development disorder with deficits in spatio- temporal vision processing. Diagnosed by a decrease in monocular or binocular VA of no organic cause and with known amblyogenic factors.

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15
Q

What are some reasons as to why VA is so important?

A
  1. Legal
  2. Evaluation of visual function
  3. Detect visual impairment
  4. Detect/monitor amblyopia
  5. Estimate RE
  6. Detect/diagnose disease
  7. Monitor disease and evaluate treatment
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16
Q

Early astronomers believed that two stars can be seen as separate if distance between them subtends a visual angle of what? what is the snellen equiv?

A

<1min arc (saying this is the limit of human eye)

20/20

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17
Q

1degree= how many min arc? therefore 1/60 of your thumb is how many min arc?

A

60

1

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18
Q

Define visual angle?

A

Important unit of relative size used in vision related sciences

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19
Q

Whether we can see two stars as separate depends on what distances?

A

distance between two stars, size of object and distance between object and observer.

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20
Q

What are the two types of Normal VA limits? what are examples of each?

A
  1. optical limits (eye=imperfect optical system)
    a) aberrations
    b) diffraction
  2. Neural limits
    a) Photoreceptor density/packing
    b) light/Dark adaptation
    c) other neuronal processes
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21
Q

Bigger pupil means what for diffraction and aberration? smaller?

A

Big: less diffraction, more aberration
small: more diffraction, less aberration

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22
Q

Cones at the fovea: theoretical limit to resolution of what? so new limit is?

A

30 sec arc

0.5min arc= 20/10 snellen equivalent.

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23
Q

What allows the new limit of 20/10?

A

photoreceptor packing/density. At the fovea, the cones are smaller and tightly packed which allows for max VA. VA decreases as cones becomes less packed and bigger (as you go toward periphery)

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24
Q

Where are the rods mostly present?

A

12 degrees in periphery

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25
Q

Define Photopic

A

Bright light condition, cones being used, best VA (resolution) and poor sensitibty

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26
Q

Define Scotopic

A

Dim light conditions, rods being used, best sensitivty poor VA.

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27
Q

Define Mesopic

A

Bright moon light, in between bright and dim.

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28
Q

Visual system is able to alter its sensitivity by a factor of? Do pupils have a large part in this?

A

10^8

no. only small fraction of this (x16)

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29
Q

Do cones or rods regenerate faster? what does this tell us?

A

Cones, rods slower. Therefore takes us longer to adapt to darkness. (TAKE VA BEFORE SHINING LIGHT INTO PATIENT EYES)

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30
Q

At macula, how many cones to bipolar/ganglion cells? at fovea? what does this tell us? What about rods?

A

Macula: few cones to 1 bipolar.ganglion cell
Fovea: one cone to one bipolar/ganglion cell. Therefore fovea has higher resolution.
Rods: many rods to one bipolar/ganglion cells poor resolution.

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31
Q

What are four types of acuity?

A
  1. Minimum detectable acuity (1 sec arc): whats the smallest object you can see?
  2. Resolution: (30 sec arc) can you resolve two objects as separate? i.e. landolt open C’s.
  3. Hyperacuity: (2-10 sec arc) we are the best at this, detecting misalignement (Vernier acuity)
  4. Recognition acuity: what is the smallest object you can see/identify? most complex, need higher processes.
32
Q

VA is what kind of test? therefore must consider what factors?

A

psychophysical, measures relationship between physical stimuli and perception. it is a detection threshold. therefore must consider effect of instructions, memorization and learning.

33
Q

Daca de Valdes discovered what? Donders stated what?

A

ability to resolve seeds (in Spain)

VA= ratio between a subjects performance and the standard performance.

34
Q

Snellen used what characteristics in his chart?

A

universal chart:

  • optotypes
  • letters with strong serifs
  • height= x5 detail
  • based on a detail (MAR) of 1 min arc
  • std distance 20 ft.
35
Q

Green proposed what?

A

geometric progression, proportional line spacing and non serif letters

36
Q

Sloan used what characteristics?

A
  • similar to green, different font
  • std distance 1m
  • proposed M-unit.
37
Q

Bailey and Louvie?

What is our current standard?

A 
Proportional spacing (logMAR)
Current:
- ETDRS
- bailey louvie layout
- logMAR spacing
- sloan optotypes
- standard dist. 4m
38
Q

Hand held printed charts good for what? if charts are projected onto a screen what must be done?
Back illuminated has what advantage?

A

children, screenings, NVA and low vision.
calibration for testing distances.
no change in contrast overtime, can change letters less memorization/learning.

39
Q

What six things need to be considered when making a VA chart?

A
  1. optotype
  2. Viewing distance
  3. Size
  4. Progression between lines
  5. Spacing between optotypes and lines
  6. Number of optotpes in each line
40
Q

MAR is a measure of what? How do we get the height of the letter using MAR?

A 
critical detail (tells you how much bigger it is than the 20/20 letter)
Critical detail x5
41
Q

Current snellen design has what disadvantages?

A

no geometrical progression, different spacing between letters for different sizes. low VA letters have fewer optotypes.

42
Q

When calibrating the snellen chart how many letters do you test? When do you stop for snellen?

A

test two different size letters choose a big and a small i.e. 20/100 and 20/60
When they get more than half wrong.

43
Q

What are your expected findings for VA? when do we use pinhole?

A

20/20-20/10

when patient has 20/30 or less.

44
Q

Decimal system advantage? disadvantage?

A

Advantage: higher number means better vision
Disadvantage: ex. 20/40 = 0.5, this does NOT mean 50% vision loss.

45
Q

Do we show one letter at a time with snellen?

A

NO. always use ENTIRE chart.

46
Q

logMAR advantage over snellen? 0.0 in logMAR corresponds to? positive numbers indicate what? negative?

A

uses geometric progression (0.1log units apart) and has the same number of letters in each line (14 lines, 5 letters in each)
20/20
+= VA worse than 20/20
-= VA better than 20/20

47
Q

standard distance for logMAR? is it the same as snellen? how does reading letters differ between logMAR and snellen?

A

4m
snellen= 20ft around 6m.
logMAR: read every line
Snellen: read smallest line you can

48
Q

When do we stop for logMAR?

A

when they miss 4/5 letters.

49
Q

What is the landolt chart? how many positions can gap be placed in? what type of acuity testing is this? another example?

A

Series of rings with 1min arc gap, gap can be in 1/8 positions. Resolution type acuity another example is tumbling E.

50
Q

VA scores are significantly better on which chart compared to which chart?

A

ETDRS compared to snellen.

51
Q

ICO near vision card has what on one side? other side? other examples of near vision cards?

A

one side= logMAR based design, sloan letters
other side: LEA symbols
Examples: lighthouse number and word recognition card, runge design (3 lines, limits only one letter of each size for each eye), near ETDRS, Jaeger and point size.

52
Q

When do you stop with near vision? standard distance?

A

they have to get all three letters/numbers to get that VA therefore stop at the last line they got all correct. standard distance - 40cm.

53
Q

near ETDRS chart uses what notation?

A

M units.

54
Q

Define accommodation

A

ability of the eye to adjust its optical power by changing the shape or position of the lens in order to maintain a clear image in the retina.

55
Q

Define Amplitude of Accommodation

A

the maximum amount a patient can accommodate

56
Q

LEA cards standard distance? what is the crtical line for less than 4 years old? 4 years and older? to get a pass how many must be correct?

A

10 ft.
20/40 (10/20)
20/32 (10/16)
4/5

57
Q

What is important to know about amblyopia in terms of VA testing? What is this due to?

A

single letter VA is much better than if you show entire line/chart. due to crowding effect.

58
Q

Define crowding

A

resolution impaired by neighbouring objects.

59
Q

What are six tests we perform in pediatric screenings?

A
  1. VA testing
  2. Cover test (both eyes working together)
  3. Eye movements
  4. Pupils (i.e. aniscoria)
  5. Retinoscopy (refractive error)
  6. Bruckners (fundus reflection)
60
Q

What are two tools that can be used to assess if VA is normal for patient?

A
  1. eggers (VAsc can give you an idea of the type/strength of the patients prescription, RE, amount of dioptic blur)
  2. pinhole
61
Q

Define Ametropia

A

images from distance objects are not formed at the retina i.e. myopia, hyperopia and astigmatism.

62
Q

Define Emmetropia

A

images from distance objects formed at the retina, RE=0.

63
Q

Myopia corrected with which lenses?

A

negative, divergent.

64
Q

Hyperopia corrected with which lenses?

A

positive, convergent

65
Q

Define astigmatism, corrected with?

A

different power between the main meridians in one eye, corrected with toric lenses.

66
Q

Eggers chart works well for what forms of Ametropia? exception and why?

A

Myopia and asitgmatism NOT hyperopia due to the fact that young hyperopes can accommodate.

67
Q

When using pinhole, if vision improves this is most likely due to? if it doesn’t improve?

A

most likely due to refractive error (lenses need improvement). if it doesn’t improve most likely something else going on i.e. disease, amblyopia.

68
Q

If there is poor vision but some still remains what test should you do?

A

measure VA with Low vision method

69
Q

What are two tests that can be used to measure distance VA low vision? their standard distances?

A

ETDRS (logMAR, M notation used) at 4, 2 or 1m.

Feinbloom at 10ft

70
Q

Snellen equivalent for 20/20 in M units?

A

4m/4M

71
Q

When do you stop with Feinbloom?

A

when you miss half or more letters in line.

72
Q

What are three possible reasons for differences in VA year to year in patients?

A
  1. Doctor: you! (knowledge, instructions, confidence)
  2. Test (i.e. equipment limitations, set up/room conditions, design of chart)
  3. Patient: visual and non visual factors
73
Q

Examples of non visual factors that could affect patients VA?

A

a) psychological (i.e. malignering, personality, cultural, experience)
b) systemic (drugs/medications)
c) ocular (drugs/medications)

74
Q

Examples of visual factors that could affect patients VA?

A

a) light/dark adaptations
b) nystagmus (rapid involuntary eye movements)
c) optical clarity of eye (opacities or distortions, i.e. dry eye)
d) pupil size
e) ptosis
f) retinal defocus (rx)
g) integrity of retina, choroid, sclera, optic nerve and pathways
h) amblyopia

75
Q

two examples of degenerative eye diseases?

A

cataract and AMD

76
Q

Two example of diseases in the optic nerve and pathway?

A

neuritis (inflammation of nerve) and MS.

PPO 1a (11 decks)

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