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Optom Vis Sci. 2010 Jul;87(7):487-93. doi: 10.1097/OPX.0b013e3181e19ec2.

Effect of vergence adaptation and positive fusional vergence training on oculomotor parameters.

Author information

1
School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. pthiagarajan@sunyopt.edu

Abstract

PURPOSE:

Clinical studies have shown that positive fusional vergence (PFV) can be trained through a program of orthoptic exercises. Models of accommodation and vergence predict that training PFV would require a reduction in the convergence accommodation (CA) cross-link. Recent investigations have found that the CA/C ratio is not changed in a clinical population after orthoptics. We hypothesized that such orthoptic programs may instead act to reduce CA through changes in the relationship between fast and slow vergence components. METHODS.: Eleven visually normal subjects were tested. Phoria adaptation to a 12-Delta base-out (BO) wedge prism and the resulting CA responses were monitored every 3 min for 15 min to a DoG target at 0.4 m. These measures were repeated after 2 weeks of orthoptics. Phorias, stimulus accommodative convergence (AC)/A and CA/C ratios, and PFV amplitudes at near were also determined. Before the orthoptics program, these measures were repeated under "adapted" conditions.

RESULTS:

Phoria adaptation following prolonged viewing through the 12-Delta BO wedge prism was associated with a concomitant reduction in the CA. These changes were asymptotic over time with 95% of the change occurring within the first 3 to 6 min. After 2 week of orthoptics, the rates and magnitudes of both phoria adaptation and CA reduction increased significantly (p < 0.01). PFV at 40-cm limits showed increases with orthoptics and under vergence adaptation. CA/C and AC/A ratios were unchanged after orthoptics, but the former was reduced, and the latter increased under the vergence adapted condition.

CONCLUSIONS:

Orthoptics acts to change the time constant and magnitude of vergence adaptation to BO prisms, which leads to a concomitant reduction of CA over a similar time course. This process appears to underlie the increase in positive fusion limits. Although reductions in CA/C ratio occur under the vergence adapted state, this ratio is not directly changed with orthoptics.

PMID:
20473234
DOI:
10.1097/OPX.0b013e3181e19ec2
[Indexed for MEDLINE]

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