Information for clinicians and researchers

Choosing an assessment aid

Several types of assessment aids are available. You should instruct participants on which type to download.

There are several key choices which must be made:

1. Letter vs symbol optotypes

If the person using the measurement aid cannot reliably identify letters, you should use the symbol-based measurement aid. If you’re using the symbol-based aid, the person using the chart should practice the symbols beforehand using this document.

2. Standardised vs randomized

1. a standardised aid - a simple download which will be the same every time. This approach will be useful in participants using the aid only once or twice.
2. and; a randomized aid is useful in participants who are regularly monitoring vision. This randomization means the participant cannot memorize the assessment aid. If you are using the randomized aid, you must also decide whether to use the telephone, or postal, assessment aids.

How to decide which type of randomized aid to use

If you are working with a participant multiple times AND checking their answers using telephone/video call: you should use the telephone assessment aid. Using this assessment, the participant can give you a 6 character code over the phone, which you can enter into this web page to view the correct answers. This allows you to have the correct answers in front of you when the participant is reading the chart over the phone.

If you are working with a participant multiple times AND asking them to self-check their answers, or post their answers in: you should use the self-assessment aid. Each aid is identified by a 16 character code, which means more random combinations are possible than with the 6 character telephone code. The code allows you to identify the correct answers. To view the correct answers from a code, you should enter the code into this web page.

Using an assessment aid

You should typically administer the chart from 150cm, providing the participant with a pre-measured string to use for measuring this distance.

At 150cm, the lines equate to 3/60, 6/60, 6/30, 6/15, 6/7.5.

At 190cm, the lines equate to 6/96, 6/48, 6/24, 6/12, 6/6.

If different parts of your clinic use different distances for the charts, it is recommended that you colour code the string given to participants, using one colour per distance. This should be checked before each trial.

Viewing the correct answers

Scoring an assessment aid

The charts are scored based on how many symbols the participant was able to correctly identify.