The goal of this study was to test the hypothesis that adding a collimating lens to a stereo display will alleviate stereo fatigue caused by extended viewing. The idea was that presenting stereo images close to infinity (with the aid of the collimating lens) would decreas the conflict between the two oculomotor mechanisms. This was tested in two separate sessions on 11 participants who performed a visual search task on a stereo display for 45 minutes. In one session, the stereo display was viewed through the collimating lens, and in the second the same task was carried out without the lens. Fatigue was then assessed using three objective measures: 1. Critical Fusion Frequency (CFF), 2. The resting points of both the vergence and accommodative mechanisms, and 3. The near points of both the vergence and accommodative mechanisms. In addition, the participnats answered a subjective questionnaire about their personal sense of fatigue. These objective and subjective measures were assessed before and after the visual search task in each session. The results indicated that the collimating lens attenuated visual fatigue. Without the lens, the objective measures exhibited an increase in fatigue. A decrease of 5% in the CFF is considered a sign of visual fatigue. A 7% decrease was shown without the lens, while the lens reduced the CFF to only 3.7%. The other measures also showed greater fatigue when the lens were not used, but these results were not statistically significant (possibly due to the small sample size). The resting point of accommodation was shown to become closer when the lens was not used. The near point of vergence became more distant without the lens than when the lens was included. The subjective questionnaire consisted of 16 fatigue characteristics that the observers were asked to rate. Overall, the fatigue reports did not yield significant differences between the two condotopns (with and without the lens). Several specific questions did indicate greater fatigue when the lens were not used.
