Spatial vision

Question 1

Spatial vision

Answer 1

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

Question 2

Visual acuity

Answer 2

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

Question 3

Recognition acuity

Answer 3

Infers resolution by requiring the identification of targets

Question 4

Resolution acuity

Answer 4

Resolve the minimum separation

Question 5

Localization acuity

Answer 5

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

Question 6

Detection acuity

Answer 6

Minimum luminance or contrast required to see a stimulus

Question 7

Absolute measure

Answer 7

The resolving capactiy of the eye

Question 8

Relative measure

Answer 8

Whether or not the threshold is normal

Question 9

Resolving capacity

Answer 9

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

Question 10

Optotypes

Answer 10

Specially designed letters

Question 11

What can a normal observer see?

Answer 11

Correctly identify an optotype that subtends 5 arc minutes

Question 12

What is the gold standard of visual acuity?

Answer 12

Landolt C

Question 13

How to tell is two letters are equally legible?

Answer 13

Share similar probabilities of confusion

Question 14

What are the two standardized groups of optotypes?

Answer 14

Sloan letters and British standard

Question 15

Critical distance

Answer 15

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

Question 16

How to get equivalent snellen from actual snellen?

Answer 16

20 x Cirtical distance/actual test distance

Question 17

Minimu angle of resolution

Answer 17

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

Question 18

When is LogMAR negative?

Answer 18

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

Question 19

Visual acuity rating

Answer 19

100-50*LogMAR

Question 20

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

Answer 20

0

Question 21

M-notation

Answer 21

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

Question 22

What are the 4 design flaws of the snellen chart?

Answer 22

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

Question 23

ETDRS

Answer 23

Early treatment of diabetic retinopathy study

Question 24

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

Answer 24

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

Question 25

Point spread function

Answer 25

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

Question 26

5 factors that affect two point threshold

Answer 26

``` Magnitude of defocus Magnitude of aberrations Magnitude of diffraction Contrast sensitivity Subjective criterion ```

Question 27

What creates the contrast signal to the eye?

Answer 27

A dip between the two PSF functions

Question 28

What is the peak contrast threshold for the eye?

Answer 28

1%

Question 29

What is the diameter of a foveal cone?

Answer 29

30arc seconds

Question 30

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

Answer 30

It becomes wider and shorter

Question 31

Why is the two point resultion acuity not normally used?

Answer 31

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

Question 32

What is the airy disc?

Answer 32

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

Question 33

Rayleigh's criterion

Answer 33

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

Question 34

What is the MAR of a perfect optical system?

Answer 34

31.45 arcseconds

Question 35

Rayleigh's criterion formula

Answer 35

theta= (1.22 x wavelength)/area

Question 36

Grating acuity

Answer 36

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

Question 37

What are the three things affecting grating acuity?

Answer 37

Optical factors Receptor sampling Contrast sensitivity

Question 38

How do you go from spatial frequency to snellen denominaotr?

Answer 38

30/SF * 20

Question 39

What does spurious resolution enable?

Answer 39

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

Question 40

Types of localization acuity

Answer 40

Dot vernier Line vernier Spatial interval acuity Bisection acuity

Question 41

Hyperacuity

Answer 41

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

Question 42

Factors limiting use of localization acuity

Answer 42

Time Electronics Lateral judgements Stimulus design

Question 43

What does detection acuity measure?

Answer 43

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

Question 44

What factors affect VA?

Answer 44

``` Refractive error Retinal eccentricity luminance contrast contour interaction ```

Question 45

What happens to VA with increased refractive error

Answer 45

Progressive decrease in letter based acuity

Question 46

Retinal eccentricity

Answer 46

distance relative to the fovea expressed in angular units

Question 47

What happens to VA with increased retinal eccentricity

Answer 47

Acuity decreases progressively

Question 48

What happens to VA with increased luminance

Answer 48

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

Question 49

Where is the peak VA for scotopic luminance levels

Answer 49

5 degrees

Question 50

What happens to VA with an increase in contrast

Answer 50

Increases until plateaus at 80%

Question 51

What is the Pelli-Robson chart for?

Answer 51

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

Question 52

What is contour interaction?

Answer 52

How closely the letters are spaced

Question 53

What happens with a decrease in contour interaction?

Answer 53

Declines past 5*MAR