Structure-function relationship between magnetic resonance imaging lesion areas and visual field defects in initial optic neuritis with altitudinal hemianopsia.

PURPOSE: To study the spatial association of magnetic resonance imaging (MRI) contrast enhancement (CE) areas with visual field defect (VFD) asymmetry in initial cases of optic neuritis (ON) with altitudinal hemianopsia (AH) with reference to nonarteritic anterior ischemic optic neuropathy (NAION) with AH. STUDY DESIGN: Multicenter, cross-sectional study. METHODS: The present study comprised 19 ON patients and 20 NAION patients with AH who underwent orbital contrast fat-suppressed MRI. The signal-to-intensity ratio (SIR) was calculated by dividing the maximum CE of the optic nerve by the mean CE of the cerebral white matter in 11 coronal sections at 3-mm intervals from immediately posterior to the eyeball to the optic chiasm. Sections in ON patients with an SIR exceeding the mean plus 2 standard deviations of the SIR at the corresponding section in the NAION group were considered abnormal. The correlation between upper-to-lower CE asymmetry in the maximum SIR section and VFD counterpart was determined. RESULTS: The ON group had significantly higher maximum SIR than that of the NAION group (1.77 ± 0.88 vs. 1.25 ± 0.32; P < .01). Seven of the 19 patients had sections with abnormally high CE extending posteriorly beyond the orbital apex. Significant spatial correspondence was observed between CE and VFD asymmetry (rs = 0.563; P = .015) in the ON group but not in the NAION group (rs = - 0. 048; P = .850). CONCLUSIONS: ON patients with AH frequently show CE even in the intracerebral optic nerve, maintaining a moderate structure-function correspondence.

Effects of steroid administration and transcorneal electrical stimulation on the anatomic and electrophysiologic deterioration of nonarteritic ischemic optic neuropathy in a rodent model.

PURPOSE: To elucidate the effectiveness of steroid administration and transcorneal electrical stimulation (TES) on anatomic changes and visual function in a rodent model of nonarteritic ischemic optic neuropathy (rNAION). METHODS: Methylprednisolone (20 mg/kg) was injected through a central venous catheter twice a day for 3 days. TES was delivered with biphasic square pulses of 1 ms/phase, 100 µA of current, and 20 Hz of frequency for 60 min 3 h after induction on the 1st, 4th, 7th, 14th, and 28th days. RESULTS: Intravenous infusion of methylprednisolone significantly decreased the degree of acute disc edema but did not preserve the inner retinal thinning, decreasing the amplitude of scotopic threshold responses (STR) and decreasing retinal ganglion cell (RGC) numbers in rNAION. TES preserved the decreasing STR amplitude and the decreasing RGC numbers in rNAION. CONCLUSION: Steroids are effective for reducing disc edema in the acute stage in rNAION. TES is effective for preserving decreasing RGC numbers and function in the chronic stage of rNAION.

Laser speckle flowgraphy for differentiating between nonarteritic ischemic optic neuropathy and anterior optic neuritis.

PURPOSE: The aim of this study was to investigate the usefulness of laser speckle flowgraphy (LSFG) for the differentiation of acute nonarteritic ischemic optic neuropathy (NAION) from anterior optic neuritis (ON). METHODS: To investigate blood flow in the optic disc under normal conditions, NAION, and anterior ON, we compared the tissue blood flow of the right eye with that of the left eye in the control group, and that of the affected eye with that of the unaffected eye in the NAION and anterior ON groups. RESULTS: In the normal control group, the tissue blood flow did not significantly differ between the right and left eyes. In the NAION group, all 6 patients had decreased optic disc blood flow in the NAION eye when compared with the unaffected eye. By contrast, in the anterior ON group, all 6 patients had increased optic disc blood flow in the anterior ON eye when compared with the unaffected eye. In the NAION group, the mean blur rate (MBR) of the affected eyes was 29.5 % lower than that of the unaffected eyes. In the anterior ON group, the MBR of the affected eyes was 15.9 % higher than that of the unaffected eyes. CONCLUSIONS: LSFG could be useful in differentiating between NAION and anterior ON. In addition, this imaging technique saves time and is noninvasive.

Effects of L-arginine on anatomical and electrophysiological deterioration of the eye in a rodent model of nonarteritic ischemic optic neuropathy.

PURPOSE: The aims of this study were to clarify the effectiveness of L-arginine (1) for reducing the severity of anatomical changes in the eye and improving visual function in the acute stage of a rodent model of nonarteritic ischemic optic neuropathy (rNAION) and (2) in preventing those changes in anatomy and visual function. METHODS: For the first aim, L-arginine was intravenously injected into rats 3 h after rNAION induction; for the second aim, rNAION was induced after the oral administration of L-arginine for 7 days. The inner retinal thickness was determined over time by optical coherence tomography, and the amplitude of the scotopic threshold response (STR) and the number of surviving retinal ganglion cells (RGCs) were measured. These data were compared with the baseline data from the control group. RESULTS: Both intravenous infusion of L-arginine after rNAION induction and oral pretreatment with L-arginine significantly decreased optic disc edema in the acute stage and thinning of the inner retina, reduced the decrease in STR amplitude, and reduced the decrease in the number of RGCs during rNAION. CONCLUSION: Based on these results, we conclude that L-arginine treatment is effective for reducing anatomical changes in the eye and improving visual function in the acute stage of rNAION and that pretreatment with L-arginine is an effective therapy to reduce the severity of the condition during recurrence in the other eye.

Evaluation of inner retinal thickness around the optic disc using optical coherence tomography of a rodent model of nonarteritic ischemic optic neuropathy.

PURPOSE: To clarify the usefulness of optical coherence tomography (OCT) for the objective and quantitative evaluation of retinal nerve fiber layer (RNFL) thickness around the optic disc in a rodent model of nonarteritic ischemic optic neuropathy (rNAION). METHODS: Inner retinal thickness was measured using OCT before and after rNAION induction. The thicknesses of the RNFL and the inner plexiform layer (IPL) were measured using a histologic preparation before and 56 days after induction. We compared the inner retinal thickness measured by OCT with that measured by the histologic preparation. RESULTS: The mean inner retinal thickness around the optic disc of normal rats measured using OCT was similar to that measured using a histologic preparation (73.50 ± 4.94 vs. 75.94 ± 5.90 µm). The mean inner retinal thickness of rNAION significantly increased until the 7th day, returned to baseline on the 14th day, and decreased until the 90th day after induction. On the 56th day after rNAION induction, histologic measurements indicated that the mean RNFL thickness had decreased but that the IPL thickness was similar to that at baseline. CONCLUSION: The mean inner retinal thickness measured by OCT correlated with the RNFL thickness of rNAION. OCT is useful for the objective and quantitative evaluation of RNFL thickness around the optic disc in a model of rNAION.

Rodent model of nonarteritic ischemic optic neuropathy and its electrophysiological evaluation.

PURPOSE: Our aim was to establish a rodent model of nonarteritic ischemic optic neuropathy (rNAION). METHODS: To induce rNAION, after administration of Rose Bengal (RB) (2.5 mM), the small vessels of the left optic nerve were photoactivated using a 514-nm argon green laser with about 500-µm spot size for 12 s (RB-laser induction). To evaluate the induction, funduscopic examination, fluorescein angiography (FA), visualization of capillaries within the optic disc, histologic evaluation, and electrophysiological testing were performed. RESULTS: In the RB-laser-induction eyes, the optic disc became swollen on day 3 followed by atrophy on week 8. FA showed filling defects in the choroid and optic disc at an early stage, followed by hyperfluorescence at a late stage. The capillaries within the optic disc were reduced markedly. Histopathologic examination showed acellular nerve fiber layer (NFL) swelling anterior to the optic disc. The morphologic retinal changes were apparent only in the retinal ganglion cell (RGC) layer, with a reduction in the number of cells. Visually evoked potential (VEP) amplitude decreased significantly, but electroretinography (ERG) showed no significant difference. The positive scotopic threshold response (pSTR) was not reduced on the 1st day but was significantly reduced 3 days after induction. CONCLUSIONS: The findings are similar to human NAION. Therefore, RB-laser induction is well suited to establish the presence of rNAION.