The effect of artificially reduced bilateral visual acuity on vergence adaptation

• Main Authors: Pooja S. Bhatt, Alison Y. Firth
• Format: Article
• Language: English
• Published: White Rose University Press 2009-08-01
• Series: British and Irish Orthoptic Journal
• Subjects: Vergence adaptation; Visual acuity
• Online Access: https://www.bioj-online.com/articles/9

Aim: To investigate the effect of bilateral artificially reduced vision on vergence adaptation, in participants with normal binocular single vision. Methods: Seventeen participants were recruited from a student population. The inclusion criteria included the ability to adapt to a 6Δ base-out prism to within ±1Δ of the baseline heterophoria  measurement in 10 minutes. The size of the prism-induced heterophoria was measured at the start and end of the adaptation period using a Maddox rod and tangent scale. Eleven participants fitted the inclusion criteria and proceeded to a second visit; involving adaptation to a 6 Δ base-out prism within 10 minutes, whilst vision was bilaterally reduced with Bangerter foils (0.3). Participants who did not demonstrate adaptation to within  ±1Δ of the baseline measure in 10 minutes were given a further 10 minutes to adapt, with the size of the residual deviation being measured at 5-minute intervals. Results: Eight of 11 participants demonstrated vergence adaptation to within ±1 Δ of the baseline measure in 10 minutes when vision was bilaterally reduced. Three participants required an additional 5 minutes before they achieved this level of adaptation. Statistical analysis revealed the rate of vergence adaptation was affected in some participants when vision was bilaterally reduced (p = 0.0260, t = 2.6116, d.f. =10). Conclusion: Individuals who demonstrate vergence adaptation in normal viewing conditions appear capable of doing this with an artificial bilateral reduction in vision. In some participants, a longer period of time is required to vergence-adapt.