Retinal nerve fiber structure versus visual field function in patients with ischemic optic neuropathy. A test of a linear model.

PURPOSE: To test a linear model relating the regional loss in retinal nerve fiber (RNFL) thickness to the corresponding regional loss in sensitivity with data from patients with previous anterior ischemic optic neuropathy (AION). DESIGN: Case-control study. PARTICIPANTS: Twenty-four individuals with AION and 20 with normal vision were tested. The time since the AION attack ranged from 5.2 months to more than 20.3 years (median, 2.95 years). METHODS: Eyes were tested with standard automated perimetry (SAP) and with optical coherence tomography (OCT), both RNFL thickness scans. The average RNFL thickness of the inferior and superior disc sectors was plotted against the average total deviations (linear units) of the corresponding superior and inferior arcuate field regions, and a linear model was fitted. According to the model, the RNFL thickness R=s(o)T+b, (1), where T is the relative SAP sensitivity loss (on a linear scale; e.g., for -3 dB, T = 0.5), s(o) is the RNFL thickness attributable to axons in the healthy or normal state (T = 1.0), and b is the residual RNFL measured when all sensitivity and axons are lost. MAIN OUTCOME MEASURES: Optical coherence tomography RNFL thickness and SAP sensitivity. RESULTS: The data from the AION patients resembled the data from glaucoma patients previously tested and were described by the linear model. For patients with SAP losses of more than -10 dB in the arcuate region, the RNFL thickness provided an estimate of residual RNFL thickness, b. The median value of b (45.5 microm) was similar to the value for patients with glaucoma. It varied among individuals (range, 30.4-63.3 microm), showing a very weak correlation with patient's age (r = 0.30) and the time since the AION episode (r = 0.26), but an excellent correlation (r(2) = 0.94; P<0.01) with the value of s(o), estimated from the unaffected eyes. CONCLUSIONS: The relationship between a structure (OCT RNFL thickness) and function (SAP sensitivity loss) is the same for patients with AION and glaucoma and can be approximated by a simple linear model. The model may provide a framework for identifying those patients with ganglion cell axons that are malfunctioning but are alive.

Improvement in conduction velocity after optic neuritis measured with the multifocal VEP.

PURPOSE: To test the efficacy of the multifocal visual evoked potential (mfVEP) technique after long-term latency changes in optic neuritis (ON)/multiple sclerosis (MS), mfVEPs were recorded in 12 patients with ON/MS. METHODS: Sixty local VEP responses were recorded simultaneously. mfVEP was recorded from both eyes of 12 patients with ON/MS. Patients were tested twice after recovery from acute ON episodes, which occurred in 14 of the 24 eyes. After recovery, all eyes had 20/20 or better visual acuity and normal visual fields as measured with static automated perimetry (SAP). The time between the two postrecovery tests varied from 6 to 56 months. Between test days, the visual fields obtained with SAP remained normal. RESULTS: Ten of the 14 affected eyes showed improvement in median latency on the mfVEP. Six of these eyes fell at or below (improved latency) the 96% confidence interval for the control eyes. None of the 10 initially unaffected eyes fell below the 96% lower limit. Although the improvement was widespread across the field, it did not include all regions. For the six eyes showing clear improvement, on average, 78% of the points had latencies that were shorter on test 2 than on test 1. CONCLUSIONS: A substantial percentage of ON/MS patients show a long-term improvement in conduction velocity. Because this improvement can be local, the mfVEP should allow these improvements to be monitored in patients with ON/MS.

The effects of retinal abnormalities on the multifocal visual evoked potential.

PURPOSE: To examine the effects on the amplitude and latency of the multifocal visual evoked potential (mfVEP) in retinal diseases associated with depressed multifocal electroretinograms (mfERG). METHODS: Static automated perimetry (SAP), mfERGs, and mfVEPs were obtained from 15 individuals seen by neuro-ophthalmologists and diagnosed with retinal disease based on funduscopic examination, visual field, and mfERG. Optic neuropathy was ruled out in all cases. Diagnoses included autoimmune retinopathy (n = 3), branch retinal arterial occlusion (n = 3), branch retinal vein occlusion (n = 1), vitamin A deficiency (n = 1), digoxin/age-related macular degeneration (n = 1), multiple evanescent white dot syndrome (n = 1), and nonspecific retinal disease (n = 5). Patients were selected from a larger group based on abnormal mfERG amplitudes covering a diameter of 20 degrees or greater. RESULTS: Fourteen (93%) of 15 patients showed significant mfVEP delays, as determined by either mean latency or the probability of a cluster of delayed local responses. Thirteen of 15 patients had normal mfVEP amplitudes in regions corresponding to markedly reduced or nonrecordable mfERG responses. These findings can be mimicked in normal individuals by viewing the display through a neutral-density filter. CONCLUSIONS: Retinal diseases can result in mfVEPs of relatively normal amplitudes, often with delays, in regions showing decreased mfERG responses and visual field sensitivity loss. Consequently, a retinal problem can be missed, or dismissed as functional, if a diagnosis is based on an mfVEP of normal or near-normal amplitude. Further, in patients with marked mfVEP delays, a retinal problem could be confused with optic neuritis, especially in a patient with a normal appearing fundus.

A comparison of multifocal and conventional visual evoked potential techniques in patients with optic neuritis/multiple sclerosis.

PURPOSE: To compare conventional visual evoked potential (cVEP) and multifocal visual evoked potential (mfVEP) methods in patients with optic neuritis/multiple sclerosis (ON/MS). METHODS: mfVEPs and cVEPs were obtained from eyes of the 19 patients with multiple sclerosis confirmed on MRI scans, and from eyes of 40 normal controls. For the mfVEP, the display was a pattern-reversal dartboard array, 48 degrees in diameter, which contained 60 sectors. Monocular cVEPs were obtained using a checkerboard stimulus with check sizes of 15' and 60'. For the cVEP, the latency of P100 for both check sizes were measured, while for the mfVEP, the mean latency, percent of locations with abnormal latency, and clusters of contiguous abnormal locations were obtained. RESULTS: For a specificity of 95%, the mfVEP(interocular cluster criterion) showed the highest sensitivity (89.5%) of the 5 monocular or interocular tests. Similarly, when a combined monocular/interocular criterion was employed, the mfVEP(cluster criterion) had the highest sensitivity (94.7%)/specificity (90%), missing only one patient. The combined monocular/interocular cVEP(60') test had a sensitivity (84.2%)/specificity (90%), missing 3 patients, 2 more than did the monocular/interocular mfVEP(cluster) test. CONCLUSION: As the cVEP is more readily available and currently a shorter test, it should be used to screen patients for ON/MS with mfVEP testing added when the cVEP test is negative and the damage is local.