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M. J. Kupersmith, G. Mandel, S. Anderson, R. Kardon; Acute Optic Imaging of the Peripapillary RNFL in Optic Neuritis - Alterations in Birefringence and Retardance Properties. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5389.
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Retinal nerve fiber layer (RNFL) loss frequently occurs with chronic MS or after optic neuritis. Previously, in a small case series of acute optic neuritis we found OCT evidence of optic nerve swelling not obvious on fundus exam. We hypothesize that in acute optic neuritis thickening of the RNFL is common, RNFL thinning can occur early and alterations in birefringence and retardance may differentially reflect these changes.
First episode unilateral optic neuritis of 40 subjects had prospective clinical evaluation, OCT 3 and laser polarimetry (GDx) with extended corneal compensation (ECC) within 3 weeks (mean 6 days) of vision loss and 1 month later. MRI of the optic nerve was performed in 21. We compared the RNFL thickness of 12 clock-hour OCT sectors and GDx plot data combined into 12 similar sectors to 30 fellow unaffected eyes and 81 controls. We defined swelling, using a ratio comparison to the fellow unaffected eye (30), as having 3 sectors with a ratio ≥ 1.1 (10% thicker; found in only 1% of controls). RNFL loss was judged if 2 sectors were ≥ 10µ thinner than corresponding sectors of fellow eyes.
At presentation, swelling occurred in 85% by OCT (mean 7/12 sectors) and in 83% by GDx (mean 5/12 sectors) of affected eyes. The number of swollen sectors or average RNFL did not correlate with location or extent of the MRI optic nerve lesion or baseline visual loss. At 1 month, RNFL loss occurred in 53% by OCT (mean 16µ) and in 71% by GDx (mean 18µ). RNFL loss occurred in 50% of eyes that still had some swollen sectors at 1 month.
RNFL thickening in occurs in the majority of eyes with acute optic neuritis with both GDx and OCT, using sector analysis and with comparison to unaffected fellow eyes. When lesions are distal to the globe, axoplasmic blockade at the site of the lesion, and not inflammation of the optic disc region, could be the cause. Both methods show that RNFL loss can start to be observed within 1 month.
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