Clinical 1: VA

Question 1

4 types of acuity
in order of increasing resolution

Answer 1

1. Minimum visible/detectable
2. Minimum alignment
3. Minimum separable/resolvable
4. Recognition

Question 2

Difference between the 4 types of VA

Answer 2

1. Minimum Visible — detect presence (I can see something is there)
2. Minimum Alignment — detect distance in position (I can see that is not aligned)
3. Minimum Separable — detect smallest resolvable separation (I can see the space/gap between those two things)
4. Recognition — identify (I know what that is)

Question 3

What is the ideal ambient light (relative to VA luminance)?

Answer 3

No more than 1/2 of luminance
any more will decrease contrast

Question 4

1 degree = how many seconds of arc?

Answer 4

3600 sec of arc

Question 5

1 min of arc = what size in mm?

Answer 5

1.746 mm

Question 6

The ideal contrast for a VA chart

Answer 6

≥ 85%

Question 7

Disadvantages of Snellen VA chart (4)

Answer 7

1. Varying optotypes per row
2. Different manufacturers = difference in luminance
3. Different spacing
4. Different optotypes

Question 8

How do you convert snellen fraction to MAR?

Answer 8

MAR = 1/ snellen

Eg. If snellen = 20/40, MAR = 1/(40/20) = 40/20 = 2

Question 9

Describe the Bailey-Lovie chart,
In comparison to Snellen

Answer 9

Equal number of optotypes per row
Equal spacing per letter (space = optotype size)
Constant change in increments

Question 10

When should Feinbloom be used

Answer 10

If pt is unable to read 20/400

Question 11

What does the Lighthouse Continuous Text test?

Answer 11

Functional/reading acuity
(As opposed to single letter acuity)

Question 12

How do you denot M-notation and how does it differ from snellen?

Answer 12

Test distance (usually 40 cm) / Letter size in M-units
(E.g. if pt reads 1.0 M letter at 40 cm, acuity: 0.40/1 M)

Snellen uses ft; M-notation uses meters

Question 13

Most commonly used near acuity chart

Answer 13

Reduced/equivalent snellen

Question 14

Difference between luminance and illuminance

Answer 14

Luminance is the the light from the chart

Illuminance is light on the chart

Question 15

What is the ideal pupil size to test VA?

Answer 15

2.5 mm

Question 16

What is the Stiles Crawford effect?

Answer 16

Cones within the fovea result in less acuity if light rays enter at an angle

Question 17

If you are testing the VA of a hyperope in a lane shorter than 20 ft (that is not properly calibrated), what effect will it have on the refraction?

Answer 17

Over-plus

Question 18

What is the most effective diameter for a pinhole? How much power does it neutralize?

Answer 18

1.32 mm

Neutralizes 3 D

Question 19

How does testing distance affect luminance?

Answer 19

It doesnt

Question 20

What constitutes legal blindness?

Answer 20

Best corrected VA in better eye is 20/200 or worse

Max diameter of their VF in eye with larger field does not exceed 20 degrees