Convergence accommodation to convergence (CA/C) ratio in patients with intermittent exotropia and decompensated exophoria.
OBJECTIVE
To evaluate the convergence accommodation to convergence (CA/C) ratio in strabismic patients and to clarify its clinical implications.


METHODS
Seventy-eight consecutive patients (mean age: 12.9 +/- 6.0 years) with intermittent exotropia and decompensated exophoria who showed binocular fusion at least at near viewing were recruited. The CA/C ratio was estimated by measuring accommodative responses induced by horizontal prisms with different magnitudes under accommodation feedback open-loop conditions. The CA/C ratios were compared with accommodative convergence to accommodation (AC/A) ratios and other clinical parameters.


RESULTS
A linear regression analysis indicated that the mean (+/-SD) CA/C ratio was 0.080 +/- 0.043 D/prism diopter or 0.48 +/- 0.26 D/meter angle. There was no inverse or reciprocal relationship between CA/C and AC/A ratios. The patients with lower CA/C ratios tended to have smaller tonic accommodation under binocular viewing conditions and larger exodeviation at near viewing.


CONCLUSIONS
The CA/C ratio, like the AC/A ratio, is an independent parameter that characterizes clinical features. A lower CA/C may be beneficial for the vergence control system to compensate for ocular misalignment with minimum degradation of accommodation accuracy.
Nonaka
Fumitaka
F
Department of Ophthalmology, Okayama University, Graduate School of Medicine and Dentistry, Okayama, Japan.
Hasebe
Satoshi
S
Ohtsuki
Hiroshi
H
D000065:Accommodation, Ocular; D002648:Child; D003290:Convergence, Ocular; D005099:Exotropia / Q000503:physiopathology*; D006801:Humans; D012044:Regression Analysis; D015348:Vision, Binocular