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Dissociated Near Reflex and Accommodative Convergence Excess
Gräf M., Kloss S.,
Justus-Liebig-Universität Gießen, Zentrum für Augenheilkunde, Abt. Schielbehandlung und Neuroophthalmologie (Gießen)
Introduction: We report on an eight-year-old boy with an unusual, dissociated near reflex which became apparent by a monolateral convergence excess esotropia.
Methods: Determination of visual acuity (Landolt-C) at 5 m and 0.3 m distance. Titmus- and Lang-stereotests. Refractometry in cycloplegia. Measurement of squint angles using the simultaneous and alternating prism and cover tests at 5 m and 0.3 m distance both while the right eye (RF) and while the left eye was fixing (LF). Testing of the pupillary light reflexes and near reaction during both RF and LF. Subjective und objective (retinoscopy during both RF and LF) measurement of accommodative amplitude. Biomicroscopy of the anterior and posterior segments.
Results: Biomicroscopy showed normal findings. Refraction was RE +1.25/-1.25/169°, LE +1.0/-0.75/24°. The corrected visual acuity was 1.0 OU at 5 m distance and RE 0.5, LE 1.0 at 0.3 m distance, improving to 1.0 OU with a near addition of 3.0 dpt. Stereopsis: 100 (Titmus-test). At 5 m distance there was an esophoria of 4° (RF/LF), at 0.3 m there was an esotropia of 6° (RF) and 28° (LF). With the near addition of 3.0 dpt there was only an esophoria of 3° (RF/LF). Accommodation was hardly elicitable on both eyes during RF, while during LF both eyes showed accommodation of 8 dpt (streak retinoscopy). The pupils constricted normally to light. The near reaction was lacking during RF but normal during LF.
Discussion: The near reflex - with an exaggerated convergence could be evoked, when the patient was viewing with his LE. It was lacking when the RE was fixing. Therefore, at short distances the boy used his LE and an accommodative esotropia became apparent. Correction by bifocal glasses yielded orthotropia with random-dot stereopsis at near. The pathomechanism of the dissociated near reflex remains unclear. Obviously, the efferent pathways and the mesencephal neurons involved in accommodation, miosis and convergence are intact. They are activated by both retinal disparity (fusional vergence) and defocus (accommodative vergence), but the latter mainly by neurons representing the afference of the LE. The primary neuronal defect is presumed either to affect monocular cortical neurons representing the RE or the projection of these neurons to the pretectal nuclei.