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Dark Adaptation Flashcards

1
Q

what do psychophysical Procedures?

A

procedures developed top measure threshold. aim to give accurate and reliable results

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2
Q

How do they get reliable results?

A
  • With the fewest number of stimulus presentation
  • Without requiring sophisticated judgments from observer
  • with minimal opportunities for psychophysical bias
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3
Q

what do psychophysical procedures involve?

A

presenting visual stimuli that vary along one of a number of possible dimensions but all parameters are kept the same

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4
Q

What example is a psychophysical procedure?

A

Visual Acuity

Amplitude of accommodation

Near point of convergence

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5
Q

What does visual acuity do?

A

Measured the threshold for resolution

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6
Q

How is VA a psychophysical procedure?

A

We only change the size of the letter everything else such as contrast, size of separation, stays the same

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7
Q

What does Amplitude of accommodation do?

A

Measures threshold for near resolution

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8
Q

What does near point of convergence do?

A

Measures threshold for BSV

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9
Q

what are the classics psychophysical methods?

A

Method of adjustment

method of limits

method of constant stimuli

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10
Q

What is method of adjustment?

A

Gradual smooth adjustment of intensity (usually by patient) until threshold is reached

can be ascending or descending

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11
Q

Give example of method of adjustment?

A

Bring reading chart until can see it

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12
Q

What is the advantage of method of adjustment?

A

Fastest technique
good for obtaining estimate
px more likely to pay attention

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13
Q

What is the disadvantage of method of adjustment?

A

psychological bias (differences in confidence)

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14
Q

What is method of Limits?

A

Adjustment of intensity in regular steps until threshold reached

can be ascending or descending

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15
Q

What is ascending method of limits?

A

Dark adaptometry- measurement of threshold during dark adaptation minimise light adaptation

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16
Q

What is descending method of limits?

A

Used in letter charts start with contrast and decrease until they cant detect it

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17
Q

What is descending method of limits?

A

Used in letter charts start with contrast and decrease until they cant detect it

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18
Q

Give example of method of limits?.

A

Peli robsopn

bailey lovie

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19
Q

What is the advantage of method of limits?

A

Quick and simple

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20
Q

What is the disadvantage of method of limits?

A

Errors of habituation
errors of anticipation
difference in confidence between subjects

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21
Q

How is method of limits modified?

A

Staircase

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22
Q

What do multiple simultaneous staircases do?

A

Increases accuracy

23
Q

Give example of staircase method?

A

Visual Field screeners

24
Q

What is method of constant stimuli?

A

Most accurate way of measuring threshold and most time consuming

Fixed intensity presented in random order

25
What is the advantage of method of constant stimuli ?
Most accurate technique as - px cannot anticipate the next stimuli - lots of presentation of each stimulus intensity - can include blank frames and frames well above threshold to check reliability false +ve and -ve
26
What is the disadvantage of method of constant stimuli?
Still problems with differences in confidence | time consuming
27
How do inaccuracies occur?.
Fatigue psychophysical bias Attention and motivation Habituation
28
What do we look for in dark adaptation?
``` How threshold drops over time in dark, bright light and then dark Cone recovery rod cone break rod recovery absolute threshold ```
29
How to we measure dark adaptation? procedure
1) Bleach substantial proportion of photopigments 2) Measuring thresholds at regular intervals in the dark 3) Shape of curve affected by how much photopigment bleached to begin with
30
What limits threshold during dark adaptation ?
Rhodopsin breaks down into other photoproducts when it absorbs light and is bleached
31
How does rhodopsin break?
Rhodopsoin-> transduction cascade initiating visual signal =opsin + retinal by metarhodopsin 11 intermediate step
32
What is Dowling Rushton Relationship?
Log sensitivity during dark adaptation is linearly related to concentration BLEACHED photopigment
33
What is Arden and weale (1954)
Post receptoral factors- changes in receptive field size, also involved in dark adaptation
34
What is possible causes for delayed dark adaptation/ Poor night vision ?
Choroidal Circulation abnormality Bruchs membrane abnormality RPE abnormality Photoreceptors abnormality Post receptoral abnormality
35
What effects rate of dark adaptation?
Age Retinal disease - retinitis pigmentosa systemic condition- vitamin A deficiency
36
How do we investigate and diagnose different causes of poor night vision?
psychophysical techniques Fundus and anterior eye examination Electrophysiology etc
37
How do you measure dark adaptation?
Goldmann adaptometer
38
How does Goldmann Adaptometer work ?
- --Adapting light in Ganzfeld Bowl - --All lights extinguished - --Threshold measured at intervals post bleach - --Take more than 30 mins for full dark adaption curve
39
What is photostress test?
Much quicker Bleach with ophthalmoscope time taken to return to within 1 line best VA >60 sec pathological
40
What are age related problems?
Miosis and lens opacities -> retinal illuminance reduced!
41
What are night myopia?
Eye focuses at about 1m in dark usually only when no visual stimulus, nut possible when stimulus is degraded may benefit from -0.50 over correction
42
How does age effect the retina?
Reduced rate of photopigment regeneration causes slowed dark adaptation
43
How does AMD effect the retina?
Worsening of normal ageing changes to retina Rod cell death raises absolute threshold Thickening of Bruchs membrane, RPE and photoreceptor damage and reduced choroidal circulation slow photopigment regeneration
44
How does glaucoma effect the retina?
Chronic open angle glaucoma causes ganglion cell loss which coincides with area of max rod density 15 degrees and reduced scotopic sensitivity
45
How does Vitamin A deficiency effect the retina?
- Vitamin A important part of rhodopsin - Deficiency reduces rhodopsin concentration and slows photopigment regeneration - Results in raised absolute threshold and prolonged dark adaptation
46
What is CSNB?
Congenital stationary night blindness
47
What is type 1 CSNB?
Normal Fundus - Most common type - Normal fundal appearance, VA normal - Rod branch of dark adaptation function absent - Cones less effected
48
What is type 11 CSNB?
Abnormal fundus - fundus albipunctatus - autosomal recessive - affects rod and cone photopigment kinetics - grossly extended adaptation times - eventually normal threshold
49
What is Oguchi's Disease?
``` Rare autosomal disease Fundus looks grey/yellow metalic regenration of pigment normal post receptoral abnormality Cone adaptation normal, rod adaptation grossly delayed( 2-24 hours) ```
50
What is type 111 CSNB?
- X linked recessive - Associated with myopia, nystagmus, and low vision - Cone dark adaptation is normal, rod phase of recovery is absent
51
What is retinitis Pigmentosa?
- -Autosomal recessive, autosomal dominant or X linked recessive - -Progressive photoreceptor degeneration - Caused by progressive shortening of rod and cone outer segment due to normal disc shedding - -First symptoms is night blindness(20 year old) - -Central vision initially good later effected
52
What does retinitis pigmentosa look like on fundus?
Pigment clumping in mid periphery (bone spicule appearance) and attenuated blood vessels
53
What is the threshold in retinitis pigmentosa?
Grossly elevated rod and cone threshold

psychopysics (10 decks)

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