Time Course and Decay of Effects of Near Work on Tonic Accommodation and Tonic Vergence

Abstract

Changes in tonic accommodation and tonic vergence were monitored before, during and immediately after a 45 min period of reading adult level text displayed on either a computer monitor or hard copy at 20 cm under binocular viewing conditions. Both tonic accommodation and tonic vergence gradually increased during the reading period, with changes in tonic accommodation occurring more rapidly. The average increases in tonic accommodation and tonic vergence following reading were 0.35 dioptres and 0.38 metre angles, respectively. Decay of both tonic components to the baseline in either light or total darkness occurred within the first 3 min. These results suggest that a moderate period of interrupted reading at a close distance can produce a transient increase in the tonic oculomotor levels.

Binocular Adaptation to +2 D Lenses in Myopic and Emmetropic Children

“…The magnitude of esophoric shift in emmetropes (1.01 Ϯ 0.74 ⌬), although small, is similar to previous studies. 58,61 Ehrlich 61 reported an esophoric shift of only 1.62 ⌬ after sustained near fixation despite using a longer task duration (45 min) and closer fixation distance (20 cm) compared with this study. The difference in the magnitude of adaptation between the Binocular Adaptation in Myopic Children- Sreenivasan et al 737 no add (1.01 Ϯ 0.34 ⌬) and the add condition (4.41 Ϯ 0.08 ⌬) could be attributed to the variable demand (low/high) on fusional vergence system in either (no add/add) condition.…”

“…Prior to the start of the study sessions, all participants were dark adapted for 3 min to avoid effects of previous near work. 58 The lighting in the examination room was then reduced to ϳ10 lux to obtain sufficiently large pupil sizes (Ͼ4 mm as recommended by the manufacturer of PowerRefractor) for the measurement of accommodation. Each session involved measurement of pretask tonic accommodation (open loop accommodation immediately after dark adaptation), followed by baseline measurement of phoria (vergence open loop) and binocular and monocular plane of focus (closed loop accommodation).…”

Quantifying interactions between accommodation and vergence in a binocularly normal population

“…However, no evidence of a reciprocal relationship between the response AC/A and CA/C ratios was demonstrated, similar to the findings of Rosenfield (Rosenfield, Ciuffreda, & Chen, 1995). This inverse relationship adds to the body of evidence which suggests two separate neural mechanisms control the accommodative vergence cross-link and the vergence accommodation cross-link Owens, 1980;Rosenfield, Ciuffreda, & Chen, 1995;Semmlow & Hung, 1981;Wolf, Ciuffreda, & Jacobs, 1987). The lack of a reciprocal relationship between the AC/A and CA/C ratios means that measuring only the AC/A ratio, which is common in current clinical practice, does not give a true representation of both cross-link interactions.…”

Effect of Vergence Adaptation and Positive Fusional Vergence Training on Oculomotor Parameters

“…6 emmetropes took part in the testing. During each session, subjects sat in the dark for 5 minutes to avoid the previous near task's influence (Wolf et al, 1987). All participants were seated comfortably with their head reduced by removing 1 data point before and 1 after the blink.…”