Retinal nerve fiber layer thickness measured by optical coherence tomography in Optic Neuritis and the comparison with neuroophthalmologic examination, VEPs and Cranial-Orbital MRI

Objective and Hypothesis: Optic neuritis (ON) is an acute inflammatory disorder of the optic nerve and its relationship with multiple sclerosis (MS) is well defined. ON, often occurs as the initial manifestation of multiple sclerosis ( 20 %) or develops during the course of this disease ( 55-60 %) . Axonal loss is the main cause of neurological disability in this disease. Since the retinal nerve fiber layer (RNFL) is composed only of unmyelinated axons, measuring RNFL thickness , represents a viable method of monitoring axonal loss in these patients. In this study, we aimed that RNFL thickness, measuring with optical coherence tomography (OCT), could be a biomarker for axonal degeneration. We also aimed to investigate the relation RNFL thickness changes between neuroophthalmologic findings,P 100 latency and amplitude of visual-evoked potentials (VEPS) and magnetic resonance imaging (MRI) features especially brain volume measurements.Material and Methods: Seventeen patients with multiple sclerosis ( n=34 eyes) and 6 patients with clinically isolated syndromes ( CIS) (n=12 eyes) after an acute ON episode were studied. All tests (Neuroophthalmologic examination, VEPs, MRI and OCT) were performed 2 times; at baseline and one year later . Fifteen age-matched control subjects (n=30 eyes) were also examined. Only neuroophthalmologic examination, RNFL thickness and brain volume measurements were performed in control subjects once. All assessments were performed through the eyes; also affected, unaffected and control eyes. Brain total volume measurements were studied in patients (MS and CIS) and control groups according to a MRI protocol ?3 dimensional gradient eko T1? by programme Slicer.Results: RNFL thickness in eyes affected by ON was in MS 83±20.7 µm and in CIS85±14.2 µm. In unaffected eyes RNFL thickness was 95±9.8 µm in MS and 103±6.1 µm in CIS patients. In control eyes that value was 104±10.4µm. All studies found a significant reduction in RNFL in eyes affected by ON compared with unaffected eyes (p=0.009) and eyes of controls (p< 0.001). Differences in one year, after ON attack were clear that RNFL thinning was certain in each eye particularly in affected eyes. But there was statistical significance only in affected MS and CIS eyes (p=0.001;p=0.046). Temporal quadrant thinning was often seen in each group; affected MS eyes (p=0.001), affected CIS eyes (p=0.028 ) and unaffected CIS eyes (p=0.043). Although improvement was seen in visual acuity and EDSS scores for each group after one year, there was no correlation between the two parameters (p=0.176,r = - 0. 324 ). If RNFL thickness changes were compared with visual acuity, VEPs and optic nerve atrophy measured by MRI, there was not correlation between all tests. Only P100 amplitüd change in unaffected MS eyes was statistically difference correlated with RNFL thinning (p=0.003; r = -0.854). When brain volume changes were examined, there was significant difference between MS patients with control subjects and CIS patients at first evaluation. One year later after ON attack, the brain volume reductions were clear in patients when compared with control subjects (p< 0.001). The relationship between RNFL thinning and brain volume changes was statistically significant (p< 0.001).Conclusion: Within one year, variation of RNFL thickness measured by OCT, was correlated with brain MRI volume changes . This mean that, RNFL thickness could be a biomarker for neurodegeneration in multiple sclerosis.Key Words: Optic neuritis, Optical coherence tomography, retinal nerve fiber layer, axonal degeneration