Instructions

Calibration

The app must be calibrated to ensure that the letters (optotypes) displayed are the correct size. This is critical for accurate measurement, hence the "Near" and "Far" buttons will not work until this is done.

For calibration you will require a ruler which measures millimetres, regardless of whether you will be using the app in feet or metres.

Tap "Calibrate" on the home screen of the app, and follow the instructions.

This only needs to be done once, unless the app is reinstalled.

After calibration is done, go to the home screen of the app and click on the "Far" button. At least one letter of size 6/60 should display. The height and width of the letter should be 87.3mm. If it is more than 1mm different, repeat the calibration, taking care to measure the calibration line accurately.

Distance Acuity Assessment

Ensure even and comfortable ambient light. A bright light in the subject's field of few will constrict the pupils and this may cause a falsely better measurement due to an increase in depth of field if they have a refractive error.

The subject should be seated or standing 6 metres from the iPad screen. If you are using a mirror, the subject is seated or stands next to the iPad, 3 metres from the mirror. Ensure that the total light path is 6 metres. For measurement in feet, these distances are 20 and 10 feet.

Ensure that the iPad brightness is set to maximum.

Test each eye separately then both eyes together. Start with the worst eye, if known. Have the subject cover the other eye with an occluder, which may be a commercial occluder, or a card, or even their hand, however instruct them not to press on the eye.

Click the Far button on the start screen of the Near and Far app. The 6/60 or 20/200 optotype should be displayed. To change from 6/60 to 20/200 or back, tap on the blue "6/60" or "20/200" text. If a mirror is being used, swipe from right to left to reverse the optotype letters. Note that the app will display as many letters as will fit on the screen, up to a maximum of five. The actual number will depend on what model of iPad you are using.

If you have tested the subject with this app previously, it is recommended to randomise the letters by tapping on them.

Ask the subject to read the letters.

Progressively make the text smaller by tapping "Smaller" until the subject has successfully read the smallest letters (6/4 or 20/15).

Record the smallest size correctly read for each eye, stating whether it is corrected or uncorrected (with or without lenses).

If the subject cannot read the largest (top) letter at 6 metres, move him/her closer, one metre at a time, until the largest letter can be seen and record the acuity as, for example, 5/60.

If the top letter cannot be read at 1 metre (1/60), hold up your fingers at varying distances of less than 1 metre and check whether the subject can count them. This is recorded as counting fingers (CF).

If the subject cannot see hand movements, shine a light toward his/her eye from four directions of a quadrant. Record this LD (light and dark) or X (nil vision).

Near Acuity Assessment

Ambient lighting and iPad brightness setting should be as for distance acuity assessment.

Ask the subject to remove any corrective lenses.

Tap Near on the home screen of the Near and Far app.

Hold the screen 400mm from the subjects eyes, or as required by the requester of the test. For example, some statutory licencing authorities require measurements at 300-500mm and at 1000mm.

A set of texts will display.

Record the "N" number of the smallest text read, for example, N6.

Repeat this for each eye separately and both together, and with correction if necessary.

Some authorities require Times New Roman Font for near vision testing. To select between Helvetica Neue (default) and Times New Roman, open the Settings app, scroll to "Near and Far", and select the desired font family.