Superior short‐wavelength contrast sensitivity in asthenopics during reflexive readjustments of ocular accommodation

Abstract

The purpose of this work was to characterize contrast sensitivity (CS) under short-wavelength illumination in 20 symptom-free subjects and eight asthenopics: all had normal unaided or corrected visual acuity and no sign of oculomotor disease. Threshold CS was assessed using the von Békésy tracking method from a viewing distance of 2.4 m (0.40 D). Three counterbalanced tasks required central fixation of black-and-white square-wave gratings (1, 5, 10, 14 and 17 c/deg) presented through a low-pass filter blue lens and (1) a +1.50 D lens; (2) a -1.50 D lens and (3) a 0 D lens, while attempting accommodation to minimize blur. Baseline increases in eye strain, which approached high levels at the end of the experiment, did not differentiate between the two groups of volunteers. All the subjects made evident appropriate accommodation during the low blur condition (0 D); the CS curve exhibited the expected characteristics. When the minus lens was placed before the eyes of the observers the distant square-wave gratings were still seen clearly, the eyes presumably had accommodated by an amount equal to the power of the negative lens. Compared with symptom-free subjects, asthenopics exhibited greater CS at the intermediate spatial frequencies both during the low blur and the minus blur conditions. Asthenopics may exhibit an individualized sensory tendency to react more strongly to shorter wavelengths of light and may therefore reflexively 'drive' their accommodative system harder than symptom-free subjects. This would explain the presence of their asthenopia in the first place. Blue light may, in addition, induce more arousal and higher alertness in this category of participants. This would boost the oculomotor aspects of their performance. These findings add to the current understanding of individual variability in the level of oculomotor loads following strenuous near work.

Accommodation response and visual discomfort

“…This hypothesis is consistent with previous work that has shown longerwavelength light (red) interferes with reading performance and that relative L-cone sensitivity is negatively correlated with childrenÕs reading skills (Chase et al, 2003. However, Richter and Knez (2007) proposed that asthenopes may drive their accommodative systems harder with shorter wavelengths of light, thus inducing fatigue. Future studies are needed to investigate these conflicting hypotheses.…”

“…, 2003, 2007). However, Richter and Knez (2007) proposed that asthenopes may drive their accommodative systems harder with shorter wavelengths of light, thus inducing fatigue. Future studies are needed to investigate these conflicting hypotheses.…”

Neck pain brought into focus

“…), causes not only eye symptoms, but also gives rise to a parallel increase in musculoskeletal load and symptoms in the neck/scapular area [11]. These complaints may either be physiologically interrelated [12], or be a result of a change in posture e.g. triggered by eye-fatigue [13] or non-optimal spectacle correction [7].…”

Optimizing the operating theatre environment

“…Eye accommodation focuses on wavelengths in the middle of the spectrum, with longer (towards red) wavelengths in virtual focus behind the retina and shorter (towards blue) wavelengths in front of the retina. Less eye accommodation is required to focus short wavelengths on the retina 11 . In a study of 94 office workers, blue‐enriched white light (compared with white light) improved subjective alertness, mood, performance, evening fatigue, concentration and eye discomfort 12 .…”

“…Less eye accommodation is required to focus short wavelengths on the retina. 11 In a study of 94 office workers, blue-enriched white light (compared with white light) improved subjective alertness, mood, performance, evening fatigue, concentration and eye discomfort. 12 Other studies have also shown an association between increased psychomotor vigilance and reduced sleepiness with exposure to short wavelength light compared with polychromatic light.…”