Multifocal Visual Evoked Potential in Normal Subjects

PURPOSE: To introduce the clinical utility of multifocal visual evoked potential (mfVEP) and to assess the waveform from normal Korean subjects. METHODS: mfVEP with 4 channel recording was performed using the RETIscan(R) system (Roland Consult, Wiesbaden, Germany) for 25 eyes of 25 normal subjects. Amplitudes and implicit times were obtained from ring-shaped 6 areas and 4 sectors. To investigate the false-positive ratio of the examination, stimuli were given with one-half of the CRT monitor completely covered and the results were compared. RESULTS: Amplitudes of P1, N2 were larger in the central 10degrees area than other areas (p<0.001). Amplitudes were reduced and implicit times were prolonged on peripheral areas. P1 amplitudes were larger in the inferior field. Waves with large amplitudes by noise were recorded in 13.7% of covered areas. CONCLUSIONS: mfVEP is useful tool to detect local optic nerve damage and rule out the non-organic cause of visual field defect. However, mfVEP results are difficult to interpret due to noise and poor patient cooperation. Standardization of mfVEP is necessary for its application.

Electroretinograms in Cataract Patients: Changes in Electroretinographic Responses According to the Cataract Type and Severity

PURPOSE: To evaluate the changes of electroretinographic responses according to the lens opacity type and severity in cataract patients with normal retina. METHODS: Retrospective study was performed on 79 eyes of 79 patients who had undergone electroretinograms (ERG) before cataract surgery. The patients with high myopia, diabetes mellitus, hypertension or glaucoma were excluded. Cataracts were classified using Lens Opacities Classification System III (LOCS III). Whether the ERG results are different according to the location and severity of lens opacity was analyzed. RESULTS: Marked reduction in amplitude and delay in implicit time were observed in mature cataracts. Amplitudes of a- and b-wave were reduced significantly, especially a-wave in maximal combined response and b-wave in rod response (P<0.01). Among the 4 groups, excluding the mature opacity, amplitude was reduced in posterior subcapsular opacity. Implicit times were also delayed, but not significant. CONCLUSIONS: Lens opacity, especially posterior subcapsular opacity affects the ERG results significantly. These findings should be considered in evaluating the retinal abnormalities in patients with cataract.

Normal values of Positive wave in the Multifocal Electroretinography in Korean

PURPOSE: To obtain normal values of positive wave (b-wave) in the multifocal ERG in terms of age and sex of Koreans. METHODS: The multifocal ERGs by using RETIscan visual evoked response imaging system were tested for 80 eyes. 61 retinal locations were stimulated concurrently. We analyzed the average responses of 5 concentric rings. RESULTS: In the amplitudes of b-wave, ring 1, 84.1 5.4 nV/deg, was the largest of all the other rings and ring 5, 23.1+/-1.5 nV/deg, was the smallest of all the other rings (P<0.05). No statistically significant difference was observed in amplitude between sexs. The implicit time of b-wave was the longest in the ring 1, 40.8 1.6 ms, and shortest in the ring 4, 36.7+/-0.9 ms (P<0.05). CONCLUSIONS: The amplitude of b-wave was the largest in the fovea, and became smaller with eccentricity. The largest amplitude of b-wave was observed in the age of twenties. The amplitude of b-wave was decreased with age in the ring 3, 4, and 5. The interindividual variation of the amplitude of b-wave was greatest in the fovea. The implicit time of b-wave in the fovea was the longest, and that in the ring 4 was the shortest. It became longer from the ring 5, again.

The electroretinogram sensitivity in patients with diabetes

Electroretinograms (ERGs) were measured in 65 patients with diabetes and 10 control subjects. The single flash ERGs were recorded as a function of the stimulus intensity. A Naka-Rushton-type function was fit to b-wave amplitudes, measured as a function of stimulus intensity, to evaluate changes in ERG amplitude and sensitivity. We also measured the temporal aspects of the ERG b-waves. The ERG sensitivity tended to decrease as the retinopathy progressed. An average sensitivity loss in eyes with diabetic retinopathy was statistically significant. However, the eyes of diabetic patients without visible retinopathy did not show significant ERG sensitivity loss. There was less variability in temporal compared with amplitude measurements of ERG components, and significantly prolonged b-wave implicit times were found in all stages of retinopathy and in eyes of diabetic patients without retinopathy.

Focal ERG Changes During Experimental Retinal Detachment and Spontaneous Reattachment in the Rabbit

The present study evaluated alterations in the focal electroretinogram (FERG) in cases of retinal detachment and spontaneous reattachment in 11 ablino rabbits. FERGs were obtained under direct visualization of the fundus by an infrared television fundus camera with a light stimulator. The pre-operative b-wave amplitude al1c. implicit time were 0.52 +/- 0.07 micro V and 59.7 +/- 4.1msec (mean +/- S.D.), respectively. Thirty minutes after making the retinal detachment, the amplitude decreased significantly to 0.08 +/- 0.09 micro V (p

Evaluation of clinically applied visual evoked potential (VEP) in ophthalmological and neurological diseases

VEPs weie recorded in 222 cases of different disease groups and in 42cases of the control group using a Nicolet CA 1000 system. The latency time of N1, P1, N2, and P2 from the prominent surface peak and the P1-N2 amplitude at full field pattern reversal VEP. The score of each disease group was compared with those of the control group. The results are as follows; 1. Functional amblyopia, optic neuritis, and optic nerve atrophy patients presented a significant derrease in amplitude in comparison to normal subiects. 2. In the P1 implicit time, optic neuritis, and optic nerve atrophy patients presented a marked delay. Functional amblyopia patients presented a moderate delay while other disease group patients presented normal to mild delays. 3. More than half of the optic neuritis and optic nerve atrophy patients presented a detraction of the P1 wave form.