Static vergence and accommodation: population norms and orthoptics effects.
The steady-state characteristics of the accommodation and vergence systems can be described by a model with six major oculomotor parameters. These include the system biases (tonic vergence and accommodation) and forward-loop gains (vergence and accommodative gains), as well as the interactive system gains (AC/A and CA/C ratios). We investigated these parameters in two populations: (1) 22 visually-normal asymptomatic individuals, and (2) 21 visually-abnormal symptomatic individuals before and after conventional orthoptic therapy. Two parameters related to system gain differentiated between the symptomatic and asymptomatic individuals: the slope of the fixation disparity curve with accommodation open-looped and the slope of the accommodative response/stimulus curve. Following orthoptic therapy, 4 static model parameters and 1 dynamic clinical parameter showed changes toward the normal mean; this included tonic accommodation, slope of the fixation disparity curve with accommodation closed-loop (2.5D), slope of the accommodative response/stimulus curve, the CA/C ratio, and the +/- 2D monocular accommodative flipper rate.
D000065:Accommodation, Ocular; D000293:Adolescent; D000328:Adult; D003290:Convergence, Ocular; D005069:Evaluation Studies as Topic; D005133:Eye Movements; D006801:Humans; D009988:Orthoptics / Q000379:methods*; D012016:Reference Values; D014786:Vision Disorders / Q000503:physiopathology / Q000628:therapy; D014787:Vision Tests / Q000295:instrumentation