Visual Resolution

Question 1

What is the Snellen Fraction?

Answer 1

Test Distance/ Distance at which the letter subtends 5 minutes (5/60*) of arc

Question 2

What does VA 20/40 mean?

Answer 2

The smallest letter the pt could read subtended 5 minutes of an arc at 40 feet

Question 3

What is recognition acuity?

Answer 3

Snellen Chart
Must be able to see and name the letters

Question 4

What is detection acuity?

Answer 4

The direction the child moves it eyes to the area with more stimulus

Question 5

What is resolution acuity?

Answer 5

The direction the letter points

Question 6

What is localization acuity?

Answer 6

What is the smallest gap between the lines that a patient can resolve

Question 7

What is vernier acuity?

Answer 7

The smallest angle between lines that a pt can resolve

Question 8

How do you find the height of a 20/200 letter?

Answer 8

20/200 letter subtends 5 mins of arc at 200ft thus half the letter subtends 2.5 mins at 200 ft

Question 9

How much does a 20/100 letter subtend at 20ft?

Answer 9

20/100 subtends 5’ at 100ft thus at 20ft it would subtend 5 x5= 25’

Question 10

How much does a 20/15 letter subtend at 20ft?

Answer 10

20/15 subtends 5’ at 15ft thus at 20ft it would subtend 5 x(15/20)= 3.75’

Question 11

What happens when you halve or double the viewing distance?

Answer 11

When you halve the viewing distance the angular subtense doubles.

When you double the viewing distance the angular subtense halves

Question 12

What does vernier acuity give you?

Answer 12

Vernier acuity displays the smallest angle between the lines that the patient can resolve thus you must solve for the angle theta= Tan(x)

Question 13

Can you average snellen VA?

Answer 13

NO you can only average MAR

Question 14

What is MAR?

Answer 14

The minimum angle of resolution which is the angle that must be resolved for the patient to be able to identify the letter correctly

Question 15

What does each limb of a letter subtend?

Answer 15

Snellen letters are made on 5x5 thus each limb subtends 1’

Question 16

What does a 5x4 non serif subtend?

Answer 16

Each limb is still only 1’ because it is on 5x5

Question 17

How do you calculate MAR?

Answer 17

Denominator/ Numerator ie: 20/100= 100/20= MAR=5
logMAR= 1.0

Question 17

What does each limb of a 20/40 letter subtend at 20ft?

Answer 17

Each limb would subtend 2’ each thus at 20ft it is 5x2= 10 minutes

Question 18

What is the space between each letter on a logMAR chart equal to?

Answer 18

The width of a letter

Question 19

How much is each letter on a logMAR chart worth?

Answer 19

0.02

Question 20

Is logMAR 20/20= 0.0 good?

Answer 20

No, 75yo can see this.

Question 21

What is the decimal equivalent of 20/100 letter?

Answer 21

0.2 (Numerator/ Denominator)

Question 22

If the patient can’t read the letters what is the order of tests your perform?

Answer 22

1. Hand motion
2. Light Projection
3. Light perception
4. No light perception

Question 23

What is near VA performed at?

Answer 23

16in or 40cm

Question 24

What is near Jaeger?

Answer 24

Letter ranging from J1- J20 but they are not standardized size

Question 25

What is M notation?

Answer 25

M denotes the distance in meters which the letter subtend 5'. M= denominator of a Snellen fraction (in meters)

Question 26

If the smallest print a pt can read is 0.5M what is their VA at 40 cm?

Answer 26

0.4/0.5

Question 27

What is N notion?

Answer 27

Used for near VA. One point= 1/72 of an inch. The smallest size is N5 or 5/72.

Question 28

What does point size refer to?

Answer 28

It refers to the size of the block the letter is on. Ie: 10 point means the block was 10/72 in high.

Question 29

How big are lower case letters with or without ascenders considered to be?

Answer 29

5/72in. high

Question 30

Which factors affect VA?

Answer 30

Blur Contrast Retinal Eccentricity

Question 31

What happens if blur circles are overlapping?

Answer 31

The patient will be unable to resolve a letter

Question 32

What does a pinhole od?

Answer 32

It reduces the diameter of the blur circle. It does not change where the light focuses thus the eye still has the same refractive power

Question 33

What is the contrast equation?

Answer 33

Lmax-Lmin/ Lmax + Lmin

Question 34

At which point in contrast does VA change?

Answer 34

Less about 40% contrast do we see a drop off in VA

Question 35

What is retinal eccentricity?

Answer 35

Retinal eccentricity describes how far a point on the retina lies away from the fovea (center of macula)

Question 36

How is retinal eccentricity expressed?

Answer 36

It is expressed as an angle. In this picture point X lives alpha degrees away from the fovea.

Question 37

What is the VA for retinal eccentricity on the fovea?

Answer 37

20/20

Question 38

What is the VA for retinal eccentricity on 1 degree off the fovea?

Answer 38

20/30

Question 39

What is the VA for retinal eccentricity 1.5-2 degrees off the fovea?

Answer 39

20/40

Question 40

What is the VA for retinal eccentricity 3-5 degrees off the fovea?

Answer 40

20/60