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LM Ayres, RC Caruso, WA Gahl, MI Kaiser-Kupfer; Diagnosis of Optic Chiasm Decussation Anomalies in the Hermansky-Pudlak Syndrome Using Steady-state Flash Visual Evoked Potentials . Invest. Ophthalmol. Vis. Sci. 2002;43(13):237.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism (OCA), absence of dense bodies in platelets, which causes a hemorrhagic diathesis, and ceroid lipofuscin accumulation in lysosomes, leading to pulmonary fibrosis. The objective of this project was to determine whether patients with HPS showed the abnormal pattern of optic chiasm decussation seen in persons with non-syndromic OCA, i.e., an increase in the proportion of decussating fibers. Methods: To date, 59 patients with HPS (34 women and 25 men) and 30 normally pigmented control subjects have been studied. Steady-state flash visual evoked potentials (SS VEPs) were elicited by monocular stimulation with standard 2.9 cd.s/m2 Ganzfeld flash stimuli at a 9.3 Hz rate, and recorded at 5 electrode sites (O3, O1, Oz, O2, O4). The area under the waveforms was computed by integration of the digitized waveforms and used to measure asymmetries in VEP amplitude. Cross-correlation between waveforms was used to assess asymmetries in VEP timing. Results: The ratio between SS VEP amplitude recorded at the electrode site contralateral to the stimulated eye and amplitude recorded at the ipsilateral electrode site (contra/ipsi ratio) was the main outcome variable. In patients with HPS, the contra/ipsi ratio was high (1.84 ± 0.87) (mean ± sd). In the control group, this ratio was considerably lower (1.15 ± 0.23). This indicated that monocular projections to the contralateral hemisphere were greater in HPS patients than in the control group. In control subjects, the cross-correlation between waveforms recorded at electrode sites ipsilateral and contralateral to the stimulated eye was higher (0.79 ± 0.20) than in HPS patients (0.00 ± 0.46). This implied that waveforms recorded in opposite hemispheres were more in phase in the control group than in the HPS group. All differences between the two groups were highly significant (P less than 0.001), using both parametric and non-parametric methods (Student's t-test and the Mann-Whitney test). Conclusion: Our results indicate that a majority of patients with HPS show VEP evidence of the abnormal chiasmal decussation pattern seen in patients with albinism. Phenotypic heterogeneity may be related to the genetic heterogeneity of this patient population. The SS flash VEP was more useful to explore the optic chiasm decussation anomaly than the transient flash VEP.
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