Abstract

P 021

Effect of diagnostic occlusion in acquired trochlear nerve palsy

Gräf M., Weihs J.
Department of Ophthalmology, University of Gießen

Objective: Monocular occlusion interrupts binocular vision and eliminates the need of fusional vergence. Thus, diagnostic occlusion may be useful to isolate the genuine profile of the fundamental disorder as an important finding regarding both the diagnosis of the palsy and the dosage of surgery. In this study, the effect of diagnostic occlusion on the motility pattern of unilateral acquired trochlear nerve palsy was investigated.
Methods: 47 patients (age, 6-78 years, median 49 years) with unilateral acquired trochlear nerve palsy were examined before and after diagnostic occlusion of 3 days. The onset of the palsy was 1-35 years ago (median 2 years). The squint angles localized with a dark red glass in front of the non-paretic eye were measured at a distance of 2.5 m at the Harms tangent scale. The vertical and torsional angles at primary position (PP), at 25° abduction of the non paretic eye (adduction of the paretic eye), and at 25° down gaze were compared.
Results: The relation between the hyperdeviation of the paretic eye and the excyclodeviation (medians of the angles in degrees, ranges in brackets) before and after diagnostic occlusion was at PP 5/5 and 4/6 (0;14/-1;10 and 0;19/2/13), in adduction 8/5 and 8/6 (0;21/0;10 and 1;24/1;15), and at down gaze, 10/7 and 8/8 (0;21/1;14 and 0;23/3;18). The individual ratio between the vertical and the excyclodeviation at PP decreased under diagnostic occlusion from 1.15 (-1;5) to 0.8 (0;3.3) (p=0.0008). The increase of the excyclodeviation was statistically significant (p=0.0002) but rather small, with the median at 1° and large variability (-7;6). At down gaze, there was a significant decrease of the hyperdeviation (p=0,007).
Conclusions: In acquired trochlear nerve palsy, the diagnostic occlusion does not regularly cause a decrease of the vertical and an increase of the excyclodeviation. The diagnostic occlusion can eliminate adaptive side effects modulating the motility pattern and may thereby help to isolate the original motility pattern, but the occlusion can also generate artificial squint angles into the opposite direction.

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