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Optics Block 8 > Retinal Image Quality II > Flashcards

Retinal Image Quality II Flashcards

1
Q

In order to resolve fine details of the pattern imaged on the retina

A

The adjacent ‘receptor units’ must be sufficiently close together to correctly interpret the pattern

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2
Q

Pattern and the receptors are close enough to correctly interpret the pattern

A

Veridical

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3
Q

The visual system is just bale to resolve the pattern

A

Nyquist limit

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4
Q

The sampling rate of the receptor units are inadequate to correctly interpret the pattern. The visual system may perceive the under sampled pattern as much lower spatial frequency and different orientation

A

Aliasing

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5
Q

When the visual system correctly interprets the spatial frequency and orientation of pattern

A

Veridical system

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6
Q

The spatial frequency at which finest light pattern that can be correctly resolved by the retina

A

Nyquist limit

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7
Q

What is the nyquist limit in humans

A

60c/deg

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8
Q

The spatial frequency at whihc the visual system cannot distinguish between light patterns

A

Aliasing

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9
Q

Photoreceptor spacing limits resolution, true or false

A

False, loses resolution due to there being less ganglion cells for each photoreceptor

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10
Q

What is visual resolution limited by

A

The spacing of (beta) ganglion cells of the retina

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11
Q

Why is it the ganglion cells that limit the visual resolution

A

At fovea, there is a one to one correspondence between cones and ganglion cells.

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12
Q

Why is it that cone spacing is not a the limiting factor for visual resolution

A

Peripheral cones are spaced too closely to be a limiting factor for visual resolution

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13
Q

What is the correspondeance of ganglion to PR cells at 0 degrees (fovea)

A

1:3

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14
Q

Where is the correspondence 1:1

A

5-10 degrees outside the retina

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15
Q

Why does the resolution get poorer out in the periphery of the retina

A

Because fewer ganglion cells

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16
Q

Resolution/contrast cannot be better than 60cyl/degree, true or false

A

True-if optics + neural blur is taken into consideration

False-if only considering neural blur

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17
Q

What is the difference in contrast sensitivity between normal eye (optics + neural blur) and an eye that has no optics

A

10x difference

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18
Q

What could the nyquist limit be if we could bypass the optics

A

With laser interometry, the contrast sensitivity of the human eye could be increased from spatial frequency of 60cycl/deg to 120 c/deg

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19
Q

What limits the ability to resolve higher spatial frequency ?

A

Optics

20
Q

When frequency increases, what happens to grating spacing

A

Decreases

21
Q

What happens to MTF with increased frequency

A

Decreased

22
Q

What is the difference between monofocal and multifocal lenses in terms of MTF

A

Monofocal is close to ideal at 0.75 and multifocal is about 0.3, so multifocal have poorer image quality

23
Q

Resolves both SPATIAL FREQUCNY and ORIENTATION

A

Veridical

24
Q

How do we get to 120 nyquist limit

A

Get rid of optics

25
Q

What are the two major spatial tasks performed by human system

A

Resolution and detection

26
Q

What do cones limit

A

Detection

27
Q

Ability of the patient to detect that a spot of light is present. Details not impiotant

A

Detection

28
Q

Half period of the finest detectable grating

A

Minimum angle of detection (MAD)

29
Q

The detection in the central and peripheral vision is limited by the size of the

A

Cone photoreceptors

30
Q

What is resolution limited by

A

Ganglion cells

31
Q

Resolution and detection at the fovea

A

Patterns may be reliable resolved anad detected

32
Q

Resolution and detection in the periphery

A

Can detect, cannot resolve

33
Q

Difference between ability to detect and resolve in the periphery

A

Aliasing

34
Q

Where is detection and resolution pretty much matched

A

Fovea

35
Q

What are the 3 components of the recognition pyramid

A
  1. Detection
  2. Resolve elements
  3. Identification
36
Q

Discriminating optical and neural blur

A

May help in distinguishing between diseases and in establishing a course of treatment

37
Q

Central vision retinal image

A

Considerable variation

38
Q

When is there an over estimation of retinal image quality

A

When scattering effect being ignored

39
Q

The most important optical defect affecting retinal image quality is

A

Defocus

40
Q

What are the main things that affect optic blur

A

Diffraction
Aberration
Scatter
Defocus

41
Q

Why is it important to correct even the smallest refractive error

A

To prevent incorrect attribution of losses to retinal/neural pathological causes

42
Q

TCA causes _____ much loss of resolution for 3mm displacement of small aperture

A

3 times

43
Q

What is the anchoring role

A

Stiles crawford effect

44
Q

What si the stiles crawford effect

A

Max intensity of light in the center of the pupil compared to the periphery, this helps reduce aberrations entering the eye

45
Q

Pupil decentration on retinal IQ

A

Decentration of the eyes pupil induces additional optical aberrations such as transverse chromatic aberration and coma, which decrease spatial visual performance

This is either temporally or nasally.

46
Q

What is peripheral vision important for

A

Detection, not resolution

47
Q

Improving peripheral vision

A

Has little improvement in resolution but marked improvement in detection occurs

Optics Block 8 (9 decks)

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