Influence of Vision on Ocular Comfort Ratings

To evaluate the influence of blur on ocular comfort while systematically manipulating vision using habitual refractive correction, induced spatial blur, dioptric defocus, and under the absence of visual structure.

Twenty emmetropic subjects rated vision, ocular comfort, and other sensations (burning, itching, and warmth) under clear viewing condition, spatial blur, and dioptric defocus, each lasting for 5 min. During each condition, subjects viewed digital targets projected from a distance of 3 m, and vision and ocular sensations were rated using magnitude estimation. Dioptric defocus was induced using +6.00DS contact lens, and equivalent spatial blur was produced by spatially filtering the targets. In a separate study, 15 participants rated vision and comfort while viewing a ganzfeld and behind an occluding patch (each of which provided an absence of visual structure) in addition to the above experimental conditions. Repeated-measures analysis of variance was used to compare the ratings of vision and comfort under the different experimental conditions.

Vision under blurred conditions (both spatial blur and dioptric defocus) was rated significantly different (p < 0.001) from clear viewing condition. Vision was significantly different when targets were dioptrically defocused than when they were spatially blurred (p < 0.001). Ratings of comfort showed significant differences between clear and blurred conditions (p < 0.001). However, there was no significant difference in comfort ratings between dioptric defocus and spatial blur (p value at least 0.28). There were also no differences in comfort (p value at least 0.99) between clear vision, ganzfeld viewing, and occlusion despite the lack of visual structure in the latter two conditions.

There does seem to be an association between clarity of vision and ocular comfort. Although the pathways for ocular surface pain and vision are perhaps exclusive, complex psychological influences such as nocebo or Hawthorne effects can subtly influence the participants to anticipate a change in comfort when vision is blurred.