Vergence adaptation and the order of clinical vergence range testing.
When measuring horizontal relative vergence ranges, the conventional clinical procedure is to assess the base-in (or divergence) range before the base-out (or convergence) determination. The rationale for this order of testing is that the convergence responses stimulated during the base-out measurements may produce vergence adaptation (i.e., a fusional aftereffect), which may temporarily bias the subsequent base-in values in the base-out direction. However, the effect of reversing this order of testing (i.e, base-out before base-in) has not been directly evaluated. Accordingly, the present study compared distance base-in vergence ranges measured both before and after base-out testing at separate test sessions. Additionally, tonic vergence (TV) was assessed before and after each vergence range measurement. The results indicated that base-out vergence range testing stimulated vergence adaptation, and furthermore produced a statistically significant reduction in the subsequently measured base-in recovery value. However, the magnitude of this shift was less than the estimated degree of repeatability of the vergence range measurement. Therefore, a more appropriate order of testing would be to assess the heterophoria compensating range first in order to obtain accurate results during this more critical measurement.
Rosenfield
M
M
Department of Vision Sciences, State College of Optometry, State University of New York, New York, USA.
Ciuffreda
K J
KJ
Ong
E
E
Super
S
S
D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D004215:Distance Perception / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D014787:Vision Tests / Q000379:methods; D014792:Visual Acuity