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[Effect of exposure time using single landolt-rings on visual acuity in normal individuals and patients with
1Augenklinik der Ruprecht-Karls-Universität Heidelberg.
Background:
The recommendations of the German Society of Ophthalmology (DOG) concerning the examination of candidates or holders of a driving licence allow a maximum time interval of 1 s for identifying a single Landolt-C for normal individuals as well as for patients with nystagmus. The aim of this study was to determine whether visual acuity decreases with shortening of the exposure time.
Patients And Methods:
We measured the visual acuity of 18 patients with manifest nystagmus and 26 normal individuals with single Landolt-C at exposure times of 10 s, 1 s, 0.25 s and 0.1 s.
Results:
Visual acuity dropped significantly at exposure times of 1 s in the group of patients with nystagmus (P = 0.01). In normal individuals, visual acuity decreased significantly only at exposure times below 1 s.
Conclusion:
Determining visual acuity according to the recommendations of the DOG shows a significant drop of visual acuity in nystagmus patients, but not in normal individuals. Applying the maximum time limit of 1 s exposure time to these patients will ensure that they will be able to identify traffic signs quickly and orient themselves safely.