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Ocular Physiology 2 > Visual Acuity > Flashcards

Visual Acuity Flashcards

1
Q

What does VA refer to

A

The spatial limit of visual discrimination

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2
Q

Image of the iris formed by the cornea refers to

A

Entrance pupil

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3
Q

Where is the entrance pupil situated

A

about 3 mm behind the corneal vertex

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4
Q

What are some contributing factors to light spreading and interference

A
  1. Diffraction
  2. Abberations
  3. Scatter
  4. Absorption
  5. focus factors
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5
Q

What does diffraction cause

A

limitation of the aperture causes a spread of light

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6
Q

Small pupil diameter

A

actual image spread = the diffraction image

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7
Q

What does aberration refer to

A

Rays entering the periphery of the pupil may not converge on the geometric image point. This is more prominent as the pupil widen

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8
Q

What happens with pupil diameters larger than 5 mm

A

the spread is usually increased because the peripheral regions of the cornea and lens are often afflicted with optical aberrations

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9
Q

Why does scatter happen

A

Ocular media has some microscopic structure so light is scattered in passing from the cornea to the retina.

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10
Q

What does absorption refer to

A

Media is not uniformly transparent to incoming light

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11
Q

The ______the wavelength of the entering light the _____the proportion that reaches the retinal receptors

A

shorter, the smaller

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12
Q

Defocus refers to

A

a person having active accomodation

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13
Q

One example of focus not being correct

A

Night myopia…No target to look at, dont know where to focus. Your accomodation system focuses more than needed

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14
Q

Fogging refers to

A

Getting more minus refraction than needed

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15
Q

In the fovea, how are cones packed

A

Two to the linear minute of arc

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16
Q

In the retinal periphery, where do rods converge

A

on a ganglion cell

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17
Q

How would you detect that a double star is composed of two separate stimuli

A

The trough between the two light peaks must be deep enough that an intensity discrimination can be made . delta i/i

18
Q

T/F As resolution is detiorating, peaks have to be brought closer together

A

false! As resolution deteriorates, peaks have to be separated further to create a trough large enough to be detected

19
Q

What is minimum visible VA

A

The criterion of the presence of a single feature

20
Q

What is the threshold value of minimum visible VA

A

1 second of arc

21
Q

What is minimum resolvable/ordinary VA

A

The criterion of the presence or internal arrangement, of identifying features in a visible target. You’re dealing with a resolution task

22
Q

What is the MAR for ordinary va

A

between 30 seconds to 1 minute of arc

23
Q

What is minimum discriminable/hyperacuity

A

The criterion of the relative location of visible features. Threshold is much lower than ordinary VA

24
Q

What is the best known acuity for hyperacuity

A

Alignment or vernier acuity

25
Q

What is the threshold value for hyperacuity

A

a few seconds of arc

26
Q

What does refractive error mean

A

optics of the eye are defocused

27
Q

What does the width of the defocused point spread function depend upon

A

Directly on the amount of defocus

Inversely on the pupil size

28
Q

What does retinal eccentricity refer too

A

How far off the fovea the VA is taken

29
Q

In regards to luminescence, what does shlaer’s study define:

A

evidence points to a sep rod and cone branch of the curve

30
Q

What happens with reduced contrast

A

Reduced resolution

Worsened stereoscopic acuity, but vernier acuity not affected much

31
Q

What happens with short exposure

A

Dont see very well

32
Q

What is vernier acuity immune to

A

Decreased exposure duration

33
Q

Things that are horizontal and vertical are easier to detect

A

true

34
Q

What is crowding

A

Targets that are too close together. Not purely optical

35
Q

which light is scattered the most in eye

A

blue

36
Q

The color blue is absorbed by

A

cataracts and caratenoids

37
Q

What can cause amblyopia

A

Presence of anisoometropia
strabismus
stimulus deprivation (someone that has droopy eyelid and doesnt get help for it)

38
Q

what is critical period

A

Time span during which visual functional integrity is needed for subsequent development of normal adult vison

39
Q

Can amplyobia be treated at any time

A

YES

40
Q

What happened when monkeys were raised with one eye optically blurred

A

LGN cells were smaller on the affected side. Retina looked normal but visual cortex had changes in structures associated with processing of small detail in the blurred eye. Resolution and contrast sensitivity were reduced

41
Q

What is present in all types of amblyopia

A

Contrast discrimination is reduced. Hyperacutites are poorer

Those with anisometropic amblyopia have reduced letter acuity

Ocular Physiology 2 (8 decks)

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