Chapter 2- Measurement of visual acuity I (1)

Question 1

What are the definitions for vision?

Answer 1

1- The eye’s ability to discriminate or resolve spatially organised detail.

2- What we see without our spectacles or contact lenses (unaided vision)

Question 2

Why do we measure vision?

Answer 2

1- For early detection and diagnosis of disease.

2- Allows us to quantify what people can and cannot see.

Question 3

What are some of the reasons for reduced vision/ visual acuity?

Answer 3

1- Eye disease, e.g, cataract, AMD

2- Uncorrected refractive error

3- Amblyopia (lazy eye)

Question 4

What is Amblyopia?

Answer 4

The failure of visual acuity to develop normally.

Question 5

What is visual acuity?

Answer 5

What we see with spectacles or contact lenses.

Question 6

How is each eye recorded?

Answer 6

You record them separately

Question 7

How far is the standard letter chart from the patient?

Answer 7

6 metres

Question 8

What are the commonly used charts?

Answer 8

Snellen chart and logMAR chart.

Question 9

What would a standard observer’s vision be like?

Answer 9

A person with a 6/6 or 20/20 vision

Question 10

What is the vision with snellen chart formula?

Answer 10

Test distance (normally 6m) / Number of smallest lines of letters read (small number on the left)

Question 11

How would you determine the VA/vision of someone?

Answer 11

Ask what is the smallest line you can read?

Always ask if they can read more

Question 12

How can the Snellen fraction be recorded?

Answer 12

Can be recorded as a decimal, “v =” or as MAR- minimum angle resolution

Question 13

How do you calculate MAR?

Answer 13

1/ Decimal V

Question 14

When you do log 10 MAR, what does this allow?

Answer 14

Allows for more accurate testing over a large scale.

Question 15

How would you record vision using the snellen chart?

Answer 15

You would write down the vision score and add a minus score to however many letters they got wrong.

Question 16

How would you record vision using the logMAR chart

Answer 16

Look at their vision score on the smallest line that they can read.

For each error that is made, add 0.02 to the vision score.

Question 17

What are the advantages of the snellen chart?

Answer 17

1- Cheap and readily available

2- Can be used to obtain baseline visual acuity measurements.

Question 18

What are the disadvantages of a Snellen chart?

Answer 18

1- Inability to control the crowding phenomenon- letters being closely together.

2- Insufficient acuity levels for accurately testing a low vision patient

Question 19

What are the advantages of a log MAR chart?

Answer 19

1- Equal number of letters on every line

2- Letter by letter acuity can also be measured- more accurate when it comes to measuring acuity levels.

Question 20

What are the disadvantages of a LogMAR chart?

Answer 20

1- Large size
2- Expensive