Stationary Haptic Stimuli Do not Produce Ocular Accommodation in Most Individuals.

This study aimed to determine the extent to which haptic stimuli can influence ocular accommodation, either alone or in combination with vision. Accommodation was measured objectively in 15 young adults as they read stationary targets containing Braille letters. These cards were presented at four distances in the range 20-50 cm. In the Touch condition, the participant read by touch with their dominant hand in a dark room. Afterward, they estimated card distance with their non-dominant hand. In the Vision condition, they read by sight binocularly without touch in a lighted room. In the Touch with Vision condition, they read by sight binocularly and with touch in a lighted room. Sensory modality had a significant overall effect on the slope of the accommodative stimulus-response function. The slope in the Touch condition was not significantly different from zero, even though depth perception from touch was accurate. Nevertheless, one atypical participant had a moderate accommodative slope in the Touch condition. The accommodative slope in the Touch condition was significantly poorer than in the Vision condition. The accommodative slopes in the Vision condition and Touch with Vision condition were not significantly different. For most individuals, haptic stimuli for stationary objects do not influence the accommodation response, alone or in combination with vision. These haptic stimuli provide accurate distance perception, thus questioning the general validity of Heath's model of proximal accommodation as driven by perceived distance. Instead, proximally induced accommodation relies on visual rather than touch stimuli.