Abstract
AimTo examine the relationship between retinal ganglion cell loss and changes in the inner nuclear layer (INL) in optic neuritis (ON).Methods36 multiple sclerosis (MS) patients with a history of ON and 36 age and sex-matched controls underwent Optical Coherence Tomography. The paramacular retinal nerve fiber layer (RNFL), combined ganglion cell and inner plexiform layers (GCL/IPL) and inner nuclear layer (INL) thickness were measured at 36 points around the fovea. To remove inter-subject variability, the difference in thickness of each layer between the ON and fellow eye of each patient was calculated. A topographic analysis was conducted.ResultsThe INL of the ON patients was thicker than the controls (42.9µm versus 39.6µm, p=0.002). ON patients also had a thinner RNFL (27.8µm versus 32.2µm, p<0.001) and GCL/IPL (69.3µm versus 98.1µm, p<0.001). Among the controls, there was no correlation between RNFL and GCL/IPL as well as RNFL and INL, but a positive correlation was seen between GCL/IPL and INL (r=0.65, p<0.001). In the ON group, there was a positive correlation between RNFL and GCL/IPL (r=0.80, p<0.001) but a negative correlation between RNFL and INL (r=-0.61, p<0.001) as well as GCL/IPL and INL (r=-0.44, p=0.007). The negative correlation between GCL/IPL and INL strengthened in the ON group when inter-subject variability was removed (r=-0.75, p<0.001). Microcysts within the INL were present in 5 ON patients, mainly in the superior and infero-nasal paramacular regions. While patients with microcysts lay at the far end of the correlation curve between GCL/IPL and INL (i.e. larger INL and smaller GCL/IPL compared to other patients), their exclusion did not affect the correlation (r= -0.76, p<0.001).ConclusionsINL enlargement in MS-related ON is associated with the severity of GCL loss. This is a continuous relationship and patients with INL microcysts may represent the extreme end of the scale.
Highlights
Multiple sclerosis (MS) is recognized as a chronic inflammatory demyelinating disease with concomitant neurodegeneration
All the patients with a history of optic neuritis (ON) were diagnosed with relapsing remitting MS (RRMS)
All MS patients had a history of unilateral ON except for one who had binocular disease
Summary
Multiple sclerosis (MS) is recognized as a chronic inflammatory demyelinating disease with concomitant neurodegeneration. In ON significant axonal loss occurs following the acute inflammatory process, which eventually results in retinal ganglion cell (RGC) neuronal loss through retrograde degeneration. This mechanism is well established by numerous studies [2,3,4,5,6]. Post-mortem studies, supported by electrophysiological investigations, have demonstrated significant pathological changes in retinal cells deeper to the retinal ganglion cell layer (GCL), including bipolar cells and photoreceptors [7,8,9]
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