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S.A. Tedesco, N. Ungaro, E. Delfini, S.A. Gandolfi, C. Macaluso; Patterns of Optic Nerve Damage in Different Optic Neuropathies Assessed by Combined HRT and GDx Imaging . Invest. Ophthalmol. Vis. Sci. 2003;44(13):629.
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Purpose: To investigate whether different patterns of optic nerve damage in optic neuropathies can be assessed by combining the quantitative analysis of the neuroretinal rim and of the retinal nerve fiber layer (NFL), obtained with the Heidelberg Retinal Tomograph (HRT) and the scanning laser polarimeter (GDx) equipment. Methods: Examinations were performed with the HRT-II and the GDx VCC (compensating for corneal birefringence variability). We took the HRT global rim area and the GDx total average thickness, as global indexes of optic nerve damage. 40 eyes of 30 patients were examined, evenly distributed among the following categories of optic nerve diseases: glaucomatous optic neuropathy, anterior ischemic optic neuropathy (AION), and retrobulbar optic neuropathy. All examinations were performed distant from the stage of acute neuropathy, when present. Results: The loss of nerve fiber layer as reflected by the GDx total average thickness was evident in all types of optic neuropathy, and it was related to the severity of the disease. Differently, HRT global rim area measurements were clearly affected in glaucomatous optic neuropathy, while they were normal in both AION and retrobulbar neuropathy (Moorfields regression analysis). By plotting HRT vs. GDx indexes, the different pattern of ganglion cell loss could be readily identified: eyes with glaucomatous damage showed a close relationship between NFL and neuroretinal rim losses, while in AION and retrobulbar neuropathy points tended to lie parallel to the GDx axis, i.e. with reduction in the NFL not associated to corresponding modifications of the neuroretinal rim. Conclusions: Ganglion cell loss in different optic neuropathies leads to different patterns of clinical appearance of the optic disc, reflecting different pathophysiological processes. While reduction of the NFL is a generalized finding across all types of optic neuropathy, reduction of the volume of the neuroretinal rim in the optic disc varies depending on the underlying disease. The present work, by exploiting the ability of the HRT and GDx equipments to measure different morphometric aspects related to the optic nerve, suggests that combining the data provided by both tests could represent an objective aid in the clinical classification of optic nerve diseases, as well as in the quantification of their severity. Moreover, researches on the mechanisms underlying different optic neuropathies might benefit from the quantitative and complementary information offered by HRT and GDx.
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