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S. E. Loudon, C. A. Rook, D. S. Nassif, N. V. Piskun, D. G. Hunter; The Pediatric Vision Screener: Detection of Strabismic and Anisometropic Amblyopia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2830.
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The Pediatric Vision Screener (PVS), a polarized binocular retinal birefringence scanner that generates a binocularity score (BIN; 0-100%), detects strabismus with high accuracy. This study was undertaken to further assess the performance of the PVS as a screening device, particularly for patients with anisometropic amblyopia and no measurable strabismus.
Children visiting the Department of Ophthalmology at Children’s Hospital Boston with anisometropia, constant or intermittent strabismus were included, along with healthy controls. All children received a gold-standard orthoptic examination, and patients were classified as amblyopic or at risk for amblyopia. Under monocular viewing conditions, fixation accuracy and the sensitivity of the BIN to defocus were quantified using a PVS-generated fixation score (0-1.00).
Two hundred two children were studied. Mean age was 7.4 years. In the range of -3D to +7D defocus, the PVS was able to provide a BIN. The BIN (±SD) was significantly higher in the control group (92%±11%; n=48) than in the group at risk (28%±39%; n=90) and in the group with amblyopia (12%±23%; n=64; P<0.001). Mean BIN was lower in anisometropic amblyopia (20%±26% (n=22)) than in anisometropia without amblyopia (90%±29% (n=12)). The fixation score was highest in control eyes (1.00) and lowest in amblyopic eyes (0.35; P<0.001). The sound eye of amblyopic patients had an intermediate fixation score (0.75; P=0.047 when compared with controls). With the pass/refer threshold set at BIN 60%, sensitivity was 97.2% and specificity was 100% for the detection of amblyopia or constant strabismus. Assuming a prevalence of amblyopia in the general population of 5%, this translates to a PPV of 100% and a NPV of 99.8%.
The PVS identified patients with anisometropic amblyopia or strabismus with high sensitivity and specificity. The sound eye of amblyopic patients had poorer fixation scores than control eyes. Considering the poor fixation of amblyopic eyes and that the PVS detected extremely small angles of strabismus, the pathogenesis of anisometropic amblyopia thus appears to involve a previously unrecognized microstrabismus.
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