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Vision science > Spatial vision > Flashcards

Spatial vision Flashcards

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1
Q

Spatial vision

A

The study of visual mechaisms used for the detection and discrimination of objects

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2
Q

Visual acuity

A

Visual-based measure of the threshold to detect or discriminate the details comprising a specific target

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3
Q

Recognition acuity

A

Infers resolution by requiring the identification of targets

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4
Q

Resolution acuity

A

Resolve the minimum separation

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5
Q

Localization acuity

A

Detect the minimum change in location or relative position of two or more targets

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6
Q

Detection acuity

A

Minimum luminance or contrast required to see a stimulus

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7
Q

Absolute measure

A

The resolving capactiy of the eye

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8
Q

Relative measure

A

Whether or not the threshold is normal

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9
Q

Resolving capacity

A

Inferred from the size of the smallest letter than cen be recognized orrectly

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10
Q

Optotypes

A

Specially designed letters

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11
Q

What can a normal observer see?

A

Correctly identify an optotype that subtends 5 arc minutes

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12
Q

What is the gold standard of visual acuity?

A

Landolt C

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13
Q

How to tell is two letters are equally legible?

A

Share similar probabilities of confusion

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14
Q

What are the two standardized groups of optotypes?

A

Sloan letters and British standard

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15
Q

Critical distance

A

Distance at which the optotype will habe a total angular subtence of 5’ min

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16
Q

How to get equivalent snellen from actual snellen?

A

20 x Cirtical distance/actual test distance

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17
Q

Minimu angle of resolution

A

Stroke width of the optotype or the reciprocal of the snellen fraction

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18
Q

When is LogMAR negative?

A

When the MAR is less than 1 or when visual acuities are greater than 20/20

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19
Q

Visual acuity rating

A

100-50*LogMAR

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20
Q

At what rating of VAR is there considered profound vision loss?

A

0

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21
Q

M-notation

A

Used for near visual acuity, distance in meteres at which a near optotype will subtend 5 arc minutes

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22
Q

What are the 4 design flaws of the snellen chart?

A

Number of optoypes per acuity line is notequal
Legibility of optotypes is not equal
Spacing between optotypes
Progression of acuity sizes

23
Q

ETDRS

A

Early treatment of diabetic retinopathy study

24
Q

What are the 5 advantages of the Bailey-Lovie chart?

A

Equal number of optotypes in each row
Letter spacing scales with letter size
Letter size follows a logarithmic progression
Letter legibility
Adatable for use at non-standard distances

25
Q

Point spread function

A

The area the retinal image is spread over resulting from a point source target

26
Q

5 factors that affect two point threshold

A 
Magnitude of defocus 
Magnitude of aberrations 
Magnitude of diffraction 
Contrast sensitivity 
Subjective criterion
27
Q

What creates the contrast signal to the eye?

A

A dip between the two PSF functions

28
Q

What is the peak contrast threshold for the eye?

A

1%

29
Q

What is the diameter of a foveal cone?

A

30arc seconds

30
Q

How does the PSF change with increasing magnitudes of defocus, aberrations and diffraction?

A

It becomes wider and shorter

31
Q

Why is the two point resultion acuity not normally used?

A

Criterion of doubleness
Worsens with increasing luminance
Astigmatism creates differential meridional blur

32
Q

What is the airy disc?

A

Pattern of light distribution characterized by peak intensity followed by a minimum and smaller peaks

33
Q

Rayleigh’s criterion

A

Resolution of two point targets within a diffraction limited eye occurs when the peak of the airy disc of one target coincides with the first minimum of the airy disc of the other target

34
Q

What is the MAR of a perfect optical system?

A

31.45 arcseconds

35
Q

Rayleigh’s criterion formula

A

theta= (1.22 x wavelength)/area

36
Q

Grating acuity

A

The highest spatial frequency that can be reliably detected by an observer

37
Q

What are the three things affecting grating acuity?

A

Optical factors
Receptor sampling
Contrast sensitivity

38
Q

How do you go from spatial frequency to snellen denominaotr?

A

30/SF * 20

39
Q

What does spurious resolution enable?

A

Higher spatial frequencies to be visible in defocused image with contrast reversal

40
Q

Types of localization acuity

A

Dot vernier
Line vernier
Spatial interval acuity
Bisection acuity

41
Q

Hyperacuity

A

Acuity thresholds that are several factors smaller than the receptive field limit of 30 arcseconds

42
Q

Factors limiting use of localization acuity

A

Time
Electronics
Lateral judgements
Stimulus design

43
Q

What does detection acuity measure?

A

The sensitivity to detect the contrast of the line or dot target

44
Q

What factors affect VA?

A 
Refractive error 
Retinal eccentricity
luminance 
contrast 
contour interaction
45
Q

What happens to VA with increased refractive error

A

Progressive decrease in letter based acuity

46
Q

Retinal eccentricity

A

distance relative to the fovea expressed in angular units

47
Q

What happens to VA with increased retinal eccentricity

A

Acuity decreases progressively

48
Q

What happens to VA with increased luminance

A

Better VA, until plateau at 100-300cd/m2

49
Q

Where is the peak VA for scotopic luminance levels

A

5 degrees

50
Q

What happens to VA with an increase in contrast

A

Increases until plateaus at 80%

51
Q

What is the Pelli-Robson chart for?

A

Attempts to robe contrast detection sensitivity using acuity charts in order to detect any abnormalities

52
Q

What is contour interaction?

A

How closely the letters are spaced

53
Q

What happens with a decrease in contour interaction?

A

Declines past 5*MAR

Vision science (13 decks)

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