Evaluation of mid-term stability of night vision tests

Background: Dark adaptation rate, scotopic retinal sensitivity and contrast sensitivity under mesopic conditions, but not visuaL acuity, have been shown to be directly related to the ability to identify military targets at night. These parameters can be used to select personnel for specific military tasks demanding excellent night vision, as well as to assess pharmacological effects on night vision. Purpose: To evaluate the midterm (2 to 6-week period) stability of flight vision tests based on assessment of the above parameters. Methods: Dark adaptation rate, scotopic retinal sensitivity and contrast sensitivity under mesopic conditions were studied in 16 young volunteers during a 6-week period. Results: Tests of scotopic retinal sensitivity (after 30 min of dark adaptation) exhibited high reproducibility and a low fluctuation rate, with a high correlation between values at week 0 and at 2-week intervals during the following 6 weeks of the study (r(s) (week 0 to week 6) = 0.81, p = 0.0001). The reproducibility of mesopic contrast sensitivity tests (average of 1, 5, 3, 6 and 12 cycles per degree (cpd)) was fair (r(s) (week 0 to week 2) = 0.67, p = 0.0045), whereas that of dark adaptation rate tests was poor. Conclusions: In view of the reproducibility characteristics of these night vision tests, assessment of night vision ability in pilots and military personnel, as well as assessment of pharmacological effects on night vision, may be based on scotopic retinal sensitivity (after 30 min of dark adaptation) and contrast sensitivity under mesopic conditions (average of 1.5, 3, 6 and 12 cpd).