New methods for the assessment
of accommodative convergence.
(Nouvelles méthodes d'évaluation de la convergence accommodative)
Asakawa K, Ishikawa H, Shoji
N.
Department of Ophthalmology and Visual Science, Kitasato University Graduate
School, Doctors Program of Medical Science, Kanagawa, Japan.
PURPOSE: The
authors introduced a new objective method for measuring horizontal eye movements
based on the first Purkinje image with the use of infrared charge-coupled device
(CCD) cameras and compared stimulus accommodative convergence to accommodation
(AC/A) ratios as determined by a standard gradient method.
METHODS: The study included 20 patients, 5 to 9 years old, who had
intermittent exotropia (10 eyes) and accommodative esotropia (10 eyes).
Measurement of horizontal eye movements in millimeters (mm), based on the first
Purkinje image, was obtained with a TriIRIS C9000 instrument (Hamamatsu
Photonics K.K., Hamamatsu, Japan). The stimulus AC/A ratio was determined with
the far gradient method. The average values of horizontal eye movements (mm) and
eye deviation (Delta) (a) before and (b) after an accommodative stimulus of 3.00
diopters (D) were calculated with the following formula: horizontal eye
movements (mm/D) and stimulus AC/A ratio (Delta/D) = (b - a)/3.
RESULTS: The
average values of the horizontal eye movements and the stimulus AC/A ratio were
0.5 mm/D and 3.8 Delta/D, respectively. Correlation analysis showed a strong
positive correlation between these two parameters (r = 0.92). Moreover,
horizontal eye movements are directly proportional to the AC/A ratio measured
with the gradient method.
CONCLUSIONS: The methods used in this study allow objective recordings of
accommodative convergence to be obtained in many clinical situations.
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