Visual Acuity Flashcards Preview

Ocular Physiology 2 > Visual Acuity > Flashcards

Flashcards in Visual Acuity Deck (41)
Loading flashcards...
1

What does VA refer to

The spatial limit of visual discrimination

2

Image of the iris formed by the cornea refers to

Entrance pupil

3

Where is the entrance pupil situated

about 3 mm behind the corneal vertex

4

What are some contributing factors to light spreading and interference

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

5

What does diffraction cause

limitation of the aperture causes a spread of light

6

Small pupil diameter

actual image spread = the diffraction image

7

What does aberration refer to

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

8

What happens with pupil diameters larger than 5 mm

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

9

Why does scatter happen

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

10

What does absorption refer to

Media is not uniformly transparent to incoming light

11

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

shorter, the smaller

12

Defocus refers to

a person having active accomodation

13

One example of focus not being correct

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

14

Fogging refers to

Getting more minus refraction than needed

15

In the fovea, how are cones packed

Two to the linear minute of arc

16

In the retinal periphery, where do rods converge

on a ganglion cell

17

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

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

18

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

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

19

What is minimum visible VA

The criterion of the presence of a single feature

20

What is the threshold value of minimum visible VA

1 second of arc

21

What is minimum resolvable/ordinary VA

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

22

What is the MAR for ordinary va

between 30 seconds to 1 minute of arc

23

What is minimum discriminable/hyperacuity

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

24

What is the best known acuity for hyperacuity

Alignment or vernier acuity

25

What is the threshold value for hyperacuity

a few seconds of arc

26

What does refractive error mean

optics of the eye are defocused

27

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

Directly on the amount of defocus
Inversely on the pupil size

28

What does retinal eccentricity refer too

How far off the fovea the VA is taken

29

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

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

30

What happens with reduced contrast

Reduced resolution
Worsened stereoscopic acuity, but vernier acuity not affected much