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Flashcards in Dark Adaptation Deck (53):
1

what do psychophysical Procedures?

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

2

How do they get reliable results?

- With the fewest number of stimulus presentation
-Without requiring sophisticated judgments from observer
-with minimal opportunities for psychophysical bias

3

what do psychophysical procedures involve?

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

4

What example is a psychophysical procedure?

Visual Acuity

Amplitude of accommodation

Near point of convergence

5

What does visual acuity do?

Measured the threshold for resolution

6

How is VA a psychophysical procedure?

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

7

What does Amplitude of accommodation do?

Measures threshold for near resolution

8

What does near point of convergence do?

Measures threshold for BSV

9

what are the classics psychophysical methods?

Method of adjustment

method of limits

method of constant stimuli

10

What is method of adjustment?

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

can be ascending or descending

11

Give example of method of adjustment?

Bring reading chart until can see it

12

What is the advantage of method of adjustment?

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

13

What is the disadvantage of method of adjustment?

psychological bias (differences in confidence)

14

What is method of Limits?

Adjustment of intensity in regular steps until threshold reached

can be ascending or descending

15

What is ascending method of limits?

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

16

What is descending method of limits?

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

17

What is descending method of limits?

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

18

Give example of method of limits?.

Peli robsopn
bailey lovie

19

What is the advantage of method of limits?

Quick and simple

20

What is the disadvantage of method of limits?

Errors of habituation
errors of anticipation
difference in confidence between subjects

21

How is method of limits modified?

Staircase

22

What do multiple simultaneous staircases do?

Increases accuracy

23

Give example of staircase method?

Visual Field screeners

24

What is method of constant stimuli?

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