OM t of c.iii - Vision Research Coordinating Center - Washington ...

2/22/96 Chapter 6 Vision Assessment page 6-3
less light is needed. This range applies to the whole useful area of the chart (the bottom
corners are unimportant). Calibrating using the high contrast charts and testing in the
four areas shown in Figure 6-2 is recommended.
Figure 6-2. Areas for visual acuity chart lighting calibration.
THE
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EV numbers should be logged weekly and at each new set-up.
Important: The numbers 100 and 125 should always appear on the right of the
display when in EV mode. If not, then the settings have been disturbed, most likely
from interference with the vertical arrows on the right. These should never be pressed,
and doing so will render your readings worthless. In this event, take the battery out of
the meter., and wait 15 seconds and re-insert the battery. Then, the horizontal arrows
should be set to move the square cursor to the EV setting.
The light meter turns itself off after use.
6.1.3 Visual Acuity Technique
For each of the testing conditions listed above in Table 6-1, the following protocol
is completed. Start with high contrast visual acuity measurement in the right eye,
followed by high contrast visual acuity measurement in the left eye. After high contrast
visual acuity is completed, this same protocol is employed using the low contrast
Bailey-Lovie charts.
Visual acuity testing begins at 4 meters for both the high and low contrast charts.
The distance from the patient’s eye to the visual acuity chart must be exactly 4 meters.
The patient may stand or sit for the testing. The Clinician or Technician should ensure
that the patient’s head does not move forward or backward during the test so that the
patient's eyes remain at the set test distance.