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Axonal loss is thought to be a likely cause of persistent disability after a multiple sclerosis relapse; therefore, noninvasive in vivo markers specific for axonal loss are needed. We used optic neuritis as a model of multiple sclerosis relapse to quantify axonal loss of the retinal nerve fiber layer (RNFL) and secondary retinal ganglion cell loss in the macula with optical coherence tomography. We studied 25 patients who had a previous single episode of optic neuritis with a recruitment bias to those with incomplete recovery and 15 control subjects. Optical coherence tomography measurement of RNFL thickness and macular volume, quantitative visual testing, and electrophysiological examination were performed. There were highly significant reductions (p < 0.001) of RNFL thickness and macular volume in affected patient eyes compared with control eyes and clinically unaffected fellow eyes. There were significant relationships among RNFL thickness and visual acuity, visual field, color vision, and visual-evoked potential amplitude. This study has demonstrated functionally relevant changes indicative of axonal loss and retinal ganglion cell loss in the RNFL and macula, respectively, after optic neuritis. This noninvasive RNFL imaging technique could be used in trials of experimental treatments that aim to protect optic nerves from axonal loss.

Axonal loss is thought to be the predominant cause of disability in progressive multiple sclerosis (MS). The retinal nerve fibre layer (RNFL) is composed largely of unmyelinated axons of retinal ganglion cells, and is accessible to study with optical coherence tomography (OCT), giving a measure of axonal loss. OCT measures of the RNFL thickness (RNFLT) and macular volume were studied in 23 patients with primary progressive multiple sclerosis (primary progressive MS) (13 male; 10 female; mean age 52 years; median EDSS 6.0; mean disease duration 11 years), and 27 patients with secondary progressive multiple sclerosis (secondary progressive MS) (8 male; 19 female; mean age 50 years; median EDSS 6; mean disease duration 22 years). Of the patients with secondary progressive MS, 14 had clinical history of optic neuritis (ON) in a single eye; the remaining patients had not had ON. Twenty healthy controls (11 male; 9 female; mean age 46 years) had RNFLT and macular volume studied. Of the patients' eyes not previously affected by ON, both the mean RNFL thickness and macular volume were reduced when compared with control values. The mean RNFL thickness and macular volume were significantly reduced in secondary progressive MS, but not in primary progressive MS when compared with control RNFL thickness and macular volume. RNFL loss was most evident in the temporal quadrant, where significant reduction was seen in primary progressive MS versus controls and in secondary versus primary progressive MS. There were significant correlations of decreased RNFLT and macular volume with measures of visual acuity, low contrast visual acuity and visual field mean deviation in the MS patients. There are significant global reductions in RNFLT and macular volume in the eyes of secondary progressive MS patients not previously affected by ON, but not in primary progressive MS patients, compared with controls. This may indicate a difference in the extent of the pathological processes that cause axonal loss in the retina, and by inference the optic nerve, in secondary progressive MS and primary progressive MS.

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Exfoliation syndrome (XFS) is the commonest known risk factor for secondary glaucoma and a significant cause of blindness worldwide. Variants in two genes, LOXL1 and CACNA1A have been previously associated with XFS. To further elucidate the genetic basis of XFS, we collected a global sample of XFS cases to refine the association at LOXL1, which previously showed inconsistent results between populations, and to identify new variants associated with XFS. We identified a rare, protective allele at LOXL1 (p.407Phe, OR = 25, P =2.9 × 10−14) through deep resequencing of XFS cases and controls from 9 countries. This variant results in increased cellular adhesion strength compared to the wild-type (p.407Tyr) allele. A genome-wide association study (GWAS) of XFS cases and controls from 24 countries followed by replication in 18 countries identified seven genome-wide significant loci (P < 5 × 10−8). Index variants at the new loci map to chromosomes 13q12 (POMP), 11q23.3 (TMEM136), 6p21 (AGPAT1), 3p24 (RBMS3) and 5q23 (near SEMA6A). These findings provide biological insights into the pathology of XFS, and highlight a potential role for naturally occurring rare LOXL1 variants in disease biology.

Following an episode of optic neuritis, thinning of the retinal nerve fibre layer, which indicates axonal loss, is observed using optical coherence tomography. The longitudinal course of the retinal changes has not been well characterized. We performed a serial optical coherence tomography study in patients presenting with optic neuritis in order to define the temporal evolution of retinal nerve fibre layer changes and to estimate sample sizes for proof-of-concept trials of neuroprotection using retinal nerve fibre layer loss as the outcome measure. Twenty-three patients (7 male, 16 female, mean age 31 years) with acute clinically isolated unilateral optic neuritis were recruited to undergo optical coherence tomography, visual assessments and visual evoked potentials at presentation (median 16 days from onset of visual loss) and after 3, 6, 12 and 18 months. Compared with the clinically unaffected fellow eye, the retinal nerve fibre layer thickness of the affected eye was significantly increased at presentation and significantly reduced at all later time points. The evolution of retinal nerve fibre layer changes in the affected eye fitted well with an exponential model, with thinning appearing a mean of 1.6 months from symptom onset and the rate of ongoing retinal nerve fibre layer loss decreasing thereafter. At presentation, increased retinal nerve fibre layer thickness was associated with impaired visual acuity and prolonged visual evoked potential latency. Visual function after 12 months was not related to the extent of acute retinal nerve fibre layer swelling but was significantly associated with the extent of concurrent retinal nerve fibre layer loss. Sample size calculations for placebo-controlled trials of acute neuroprotection indicated that the numbers needed after 6 months of follow up are smaller than those after 3 months and similar to those after 12 months of follow-up. Study power was greater when investigating differences between clinically unaffected and affected eyes rather than retinal nerve fibre layer thickness of the affected eye alone. Inflammation in the optic nerve and impaired axonal transport (implied by retinal nerve fibre layer swelling) are associated with visual dysfunction and demyelination (long visual evoked potential latency) during acute optic neuritis. Retinal nerve fibre layer thinning is usually evident within 3 months. Optical coherence tomography-measured retinal nerve fibre layer loss after 6 months is a suitable outcome measure for proof-of-concept trials of acute neuroprotection in optic neuritis.

The strength of the structure/function relationships compare well with previous reports in the literature. The relationships were curvilinear with the dB scale and linear with the 1/L scale, and were much stronger with VCC than with FCC RNFL thickness measurements.

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