What is the shortest viewing distance I can use?
The software can be scaled for any viewing distance. However, a viewing distance of less than 3 metres is not recommended because a) distance visual acuity measurements will be less accurate, b) some adjustment to the distance refractive correction may be required and c) the endpoint to a refraction becomes less precise. A study carried out by Professor Thomson suggested that measurements of VA and refractive error are more accurate for viewing distances of greater than 4m. If a consulting room is less than 4m long, the display may be viewed via a mirror. Simply mount the monitor above the patient’s head (as shown above) with a mirror at the other end of the room. Ensure the mirror is correctly positioned so that the display is seen in the centre of the mirror. Measure the distance from the patient’s eyes to the mirror and from the mirror to the chart and enter the total viewing distance into the program. Remember to select “Mirror Optotypes” from the program setup.
