MORPHOFUNCTIONAL METHODS OF ASSESSING OPTIC NEURITIS DYNAMICS

PURPOSE: To define morphofunctional criteria for evaluating the state of the optic nerve, depending on the stage of optic neuritis (ON).

METHODS: The study included 42 patients (84 eyes) with different stages of bilateral ON, who were divided into 2 groups according to the stage of the pathological process. The first group consisted of 22 patients (44 eyes) with optic nerve head (ONH) hyperemia and edema; the second group consisted of 20 patients (40 eyes) with ONH ischemia and atrophy. The control group consisted of 5 healthy people (10 eyes) of the same age and sex.

RESULTS: According to the visual evoked potentials (VEP) assessment, mean N75 latency in Group I was significantly increased compared to the control group (p<0.05). In the second group of patients, this index was higher than in Group I (p<0.01). Further VEP analysis showed a significant increase of N75-100 component amplitude in Group I and a significant decrease of the same index in Group II compared to the control group (p <0.05). A significant (p <0.0001) decrease in fractional anisotropy (FA 252.5Ѓ}11.89) was revealed during the analysis of the optic nerve by means of MR-tractography in Group I, compared to the control group (369.2Ѓ}5.6). Statistically significant changes in FA of the optic radiation (OR) have not been identified. In Group II patients showed a significant reduction in FA (148.6Ѓ}7.15) of the optic nerve. There was also an increase of apparent diffusion coefficient — ADC (2184.3Ѓ}63.16) compared to the control group (1438.4Ѓ}58.5). A significant FA decrease and ADC increase was revealed in the optic radiation area. In Group I the tractography 3D map did not find significant changes in the amount and direction of the white matter tracts. Meanwhile, in Group II it showed a marked thinning of OR fiber and features of partial breaks of occipital forceps fibers at the point of their attachment to the OR beam.

CONCLUSION: Significant (p<0.05) differential diagnostic criteria of ON stages include OCT and VEP data. OCT can reveal an increase in RNFL thickness and rim changes during the stage of ONH swelling and ischemia, and a decrease of these parameters in patients with optic atrophy. VEP evaluation of these patients shows an increase in N75 and P100 latency as well as a change in N75-P100 amplitude in all stages of the disease. Changes in FA and ADC in optic nerve and OR areas demonstrate the neurodegenerative process spread to the fourth order neuron in the course of disease progression.

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