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Perception Block 9 > Duplex Retina 2 > Flashcards

Flashcards in Duplex Retina 2 Deck (56):
1

A patient whose retina contains only rods views the following four patches of monochromatic light: 440, 510, 555, and 565nm. Each patch emits 20 quantal absorptions. Which is brightest

510nm

2

Your patient, a rod monochromat, has asked for advice regarding tinted lenses. You should advise a darkly tinted lens of which color?

Red

PI=0 at 650nm. Want the smallest PI

3

A patient has degenerative disease that has destroyed her cones. The expected VA for this patient is closest to

20/200

4

Under daylight conditions, a red and green surface looks equally bright. Compared to the green surface, the red surface most likely emits

More energy

5

Which of the following classes of cones contributes least to the photopic spectral sensitivity curve

S cones

6

Assume that the absorption of 10 quanta of 510nm by an eye that contains only rods results in vision. If the wavelength were 450nm, how many quanta would need to be absorbed to produce vision

>10 quanta

7

Under scotopic conditions, a blue and yellow flower appear equally bright. Under photopic conditions, which flower will most likely appear brightest

Yellow flower

8

When foveal fixated by a person with trichromatic vision, a small target (o.5 degrees) of which of the following wavelengths will be least visible

430nm

No blue cones from 0.3-0.4 degrees, no rods

9

Photopic and scotopic thresholds are most similar to each other for which wavelength

650nm

10

Visual systems ability to adapt to the changes in the illumination levels

Light adaptation

11

Light adaptation may be studied with an ________procedure

Increment threshold

Stimulus only seen when brighter than background

12

How is threshold determined for light adaptation

Determined for a flash of light-an increment-that is presented on a background of a given intensity

13

After the threshold has been determined for the light adaptation

The background intensity is increased and the threshold measurement is repeated

14

Weber fraction for scotopic vision

0.14

15

M=0 on the scotopic light adaptation curve

Dark light, neural noise internal to retina

16

M=1/2 on the scotopic light adaptation curve

Square root law: this region is limited only quantal fluctuation of the background, and has a slope of 0.5

17

M=1 on the scotopic light adaptation curve

Weber law: the slope of the curve is equal to about 1. The ratio of increment intensity to background intentist remains constant, and covers ~4 log units range

18

M=infinity on the scoptopic light adaptation curve

Rod saturation: the slope increases rapidly becomes infinity. The rod system starts to beceom unable to detect the stimulus with the high background luminance

19

In terms of contrast, which is more sensitive, scotopic system or photopic system

Photopic system

20

Weber fraction for scotopic vision

0.14

21

Weber fraction for photopic vision

0.015

22

The smaller then Weber fraction

The more sensitive it is

23

Although the photopic systme is more sensitive (10x) to CONTRAST than the scoptopic system...

It's absolute sensitivity is less

24

Ability to resolve: photopic vision

Superior
1 log unit difference
20/20

25

Ability to resolve: scotopic vision

Inferior 20/200

26

Contrast sensitivity: photopic

10X better
Weber=0.015

27

Contrast sensitivity: scotopic

Poor
Weber=0.14

28

Ability to detect: photopic

Inferior

29

Ability to detect: scoptopic

Superior
3 log units photochromatic interval

30

Why the difference between visual resolution an visual sensitivity for photopic and scotopic vision

Scotopic is absolute more sensitive.

Photopic is more sensitive for contrast (threshold). Resolution

31

Difference between visual resolution and visual sensitivity

Due to the manner in which the rods and cones are connected to the post-receptoral elements of the retina

32

Rods are connected in such a manner as to _______ information over space. This produces great sensitivity, but poor resolution

Sum up

33

Cones manifest connections that _____________ at the expense of sensitivity

Maximize visual resolution

34

How many ganglion per rod

10-15

35

How many ganglion per cone

1:5, or 1:1 in the fovea

36

Many more rods communicate with a ganglion cell than is the case for cones. This illustrates that the scotopic system ______ information _______ to a greater extent than the photopic system, it manifests greater ___________

Sums up
Over space
Spatial summation

37

When two spots of light are shown on rods, it does not signal the presence of two lights, this information is lost because of

Spatial summation

38

This system has excellent sensitivity, yet poor spatial resolution

Scotopic system

39

Under ______ conditions, the two ganglion cells each reach threshold and signal the presence of a stimulus; sonsequntly, two stimuli are seen

Photopic

40

Excellent spatial summation

Scotopic system

41

Excellent spatial resolution

Photopic system

42

Scotopic and photopic vision also demonstrate significant difference in their

Temporal (time-related) properties

43

Scotopic conditions:two lights below threshold, separates by an interval greater than 100ms

No stimulus seen

44

Scotopic vision: 2 lights shown under threshold, but within 100ms

They will be summed up to reach threshold, stimulus seen, but only one flash of light

45

Scotopic vision: two lights shown that go beyond threshold and within the interval period

Still just one flash seen. The scotopic systems high degree of temporal summation limits its availability to resolve distinct temporal events

46

Scotopic vision: when two suprathreshold pulses are separated by greater than the interval period (greater than 100mn)

Two flashes seen

47

Which has a shorter period of temporal summation

Photopic, 10ms

48

Photopic: when a light shown at a longer interval than 10s and neither reach threshold

No flash seen

49

Photopic: two lights shown within the 10s, but do not reach threshold

One flash seen

50

Photopic: When two lights are shown that both reach above the threshold, but in two different time intervals

See two flashes

51

Threshold contrast, under photopic conditions, is closest to

0.010

52

To optimize the rod-cone break of the dark adaptation curve for clinical testing, the stimulus should be

5.0 degrees in diameter and green

53

Consider the region of the photopic light adaptation curve that follows Weber law. As the background intensity decreases, contrast

Remains constant

Ratio must remains close to one

54

The percentage of rhodopsin that is bleached at rod saturation is closest to

15%

55

The photochromatic interval is expected to be smalles for a

Centrally fixed 0.5 degree yellow target

56

An abnormal dark adaptation curve may be indicative of

ARMD and RP