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E. D. Weber, M. M. Marzban, S. A. Newman; Retinal Nerve Fiber Layer (RNFL) Thickness and Thyroid Orbitopathy. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5253.
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Currently, the status of the optic nerves in thyroid orbitopathy is evaluated by visual acuity, visual fields, afferent visual function, color vision, and optic disc appearance. In this study we examine the usefulness of optical coherence tomography (OCT) as an additional measurement tool, and to determine if there is any abnormality of the retinal nerve fiber layer (RNFL) thickness which is not observed by conventional exam techniques.
This is a retrospective chart review of 65 patients. Inclusion criteria included all patients seen by the neuro-ophthalmology service who were coded as having thyroid orbitopathy and who received Humphrey® visual fields and Zeiss Stratus OCTTM RNFL measurements between January 1, 2004 and October 1, 2007. Visual acuity, sex, age, clinical symptoms, and surgical interventions were also recorded. RNFL average thickness, visual field mean deviation (MD), visual acuity, and the presence of an afferent papillary defect were all compared to determine if there was an association between RNFL thickness and other signs of optic neuropathy.
Most patients with thyroid orbitopathy have an RNFL thickness that is average (92.47±16.44 µm) compared with other OCT studies. RNFL thickness varied from 48.59 µm to 133.92 µm. There was no significant difference in RNFL if an APD was present or absent (p=0.48). In patients presenting with signs of acute orbitopathy who had one or more signs of mild optic nerve dysfunction, the presence of an APD was weakly significant for thickening of their RNFL (p=0.06) despite a normal fundoscopic exam without evidence of nerve head swelling.
While our study included all patients with signs of orbitopathy and therefore included both patients with acute swelling and chronic atrophy of the RNFL, OCT appears to be an additional tool that can be used to determine the severity of orbital congestion and optic nerve compression seen in thyroid orbitopathy. While many patients have completely normal RNFL thickness measurements despite signs of optic nerve dysfunction, some patients demonstrate occult thickening on OCT that is not seen by conventional exam techniques.
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