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PPMV > Dark adaptation > Flashcards

Dark adaptation Flashcards

1
Q

This is known as the process by which the visual system adjusts to the prevailing light level.

A

Visual adaption

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2
Q

What are the 4 mechanisms to visual adaptation?

A
  1. 2 different PRs
  2. Change in pupil size
  3. Conc. + level of bleached photopigment
  4. Change in neural responsiveness
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3
Q

What are the 3 characteristics of rods?

A
  1. High gain system
  2. High sensitivity
  3. Low resolution
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4
Q

What are the 3 characteristics of cones?

A
  1. Low gain system
  2. Low sensitivity
  3. High resolution
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5
Q

The pupil size can change from __ to ___ in less than 1 second

A

2 to 8 mm

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6
Q

The change in pupil size alters retinal illuminance by __ log units

A

1.2 log units

~16x

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7
Q

This is used to measure light reflected from the fundus of the eye

A

Retinal Densitometry (tells us the amount of photo pigment that has been bleached)

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8
Q

The time course for dark adaptation and rhodopsin regeneration are ____

A

the same/equal

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9
Q

bleaching rhodopsin by 1% decreases sensitivity by___

A

by 10 (or increases sensitivity threshold by 10)

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10
Q

Bleaching 50% of cones raises threshold only be __ log units.

A
  1. 5 log units

- bleaching of cones has a very small effect on threshold when compared to rods

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11
Q

T/F: Rod sensitivity is not based on changes at the receptor level alone.

A

True

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12
Q

This is known as the process that increases threshold luminance in response to an increased level of illumination

A

Light adaptation

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13
Q

This is known as the process that decreases threshold luminance as a function of time in the dark; happens slowly.

A

Dark adaptation

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14
Q

Cones recover in __ mins. Rods recover in __ mins.

A

1.5 mins

5 mins

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15
Q

This represents the rapid reduction in threshold up to about 10 mins where the curve plateaus; called the cone plateau

A

The cone or photopic threshold:

First section of dark adaptation curve

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16
Q

This represents the curve with a slow reduction in threshold to about 35 mins where the rod plateau occurs

A

Rod, scotopic threshold: Second section of dark adaptation curve

17
Q

What changes to the pupils occur at time zero?

A
  1. get larger
  2. allow in more light
  3. more retinal stimulation
18
Q

What % of cones become dark adapted within 5-10 mins ?

A

99.21%

19
Q

When do cones fully dark adapt?

A

10 mins

20
Q

This is known as the abupt change in shape (slope) of the curve

A

the rod-cone break

21
Q

This is known as the dividing point from where the cones were detecting the flash to where the rods are detecting the flash

A

Kohlrausch bend

22
Q

When do rods fully dark adapt?

A

35mins

23
Q

This is known as the difference in sensitivity between the cone plateau and the rod plateau

A

Phtochromatic interval - separation between the cone and rod plateau

24
Q

What 4 ways can the shape and time course of the DA curve be affected?

A
  1. If both rods and cones are present
  2. Changes in adapting light
  3. Changes in flash stimulus
  4. Task required of patient
25
Q

What are the 3 ways the adapting light can be changed?

A
  1. Luminance
  2. Duration
  3. Wavelength
26
Q

At a luminance that is too dark, which PRs will be affected?

A

rods only

27
Q

A short duration of the adapting light will cause what?

A

Only rods will be bleached

- need at least 5 mins for full bleaching

28
Q

A 400nm wavelength light will only cause __?

A

rapid cone adaptation (cones aren’t bleached)

29
Q

A 650nm wavelength will only cause what?

A

prolonged cone adaption (rods arent bleached

30
Q

Flashing testlight in the foveal area will only cause which PR response?

A

cone response

- theres no rods in fovea

31
Q

If we use a central test flash, what PR will be stimulated?

A

Cones

32
Q

If we use a very narrow grading..

A

we know the rods don’t have good detection ability (will see cone branch only)

33
Q

This is known as a rapid decrease in test flash detection threshold after the first offset of the adapting light (time 0)

A

Early adaptation

34
Q

This occurs within the first second after the adapting light is turned off

A

Early adaptation

35
Q

An adapting light of one minute will result in?

A

Rods only, no cone portion

36
Q

A wide flash stimulus during dark adaptation will result in?

A

Normal dark adaptation

PPMV (6 decks)

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