Study of visual evoked potentials in asymptomatic HIV-positive persons

Background: Visual Evoked Potentials (VEPs) was studied in asymptomatic Human Immunodeficiency Virus (HIV) positive persons and corresponding controls to detect subclinical visual system involvement in the early stage of HIV. Aim and Objectives: To study VEPs in asymptomatic HIV-positive persons and corresponding controls. Materials and Methods: In this study,100 participants in the age group 25–45 years were recruited, fifty were HIV positive and asymptomatic (CD4 count >350 cells/mm3) and were not on Anti-Retroviral Treatment, and 50 were healthy age-matched individuals who were HIV negative. Results: P 100 latency was significantly prolonged in the study group than in the control group. No significant difference was observed between the control group and study group for the amplitude of VEP. Conclusion: Study of VEPs in asymptomatic HIV positive persons suggests subclinical visual nervous system involvement in early stages of HIV, as evidenced by prolonged P 100 latency. Hence, VEPs is important to detect subclinical nervous system involvement in the early stages of HIV.

Association of pattern reversal VEP parameters with the Meandefect of Humphrey visual field in patients of primary open Angleglaucoma.

Glaucoma is a chronic, progressive bilateral optic neuropathy which disturbs the structural or functional integrity of the optic nerve that causes characteristic atrophic changes in it, which leads to specific visual field defects over time with loss of visual function. Primary open angle glaucoma (POAG) is the most common form of glaucoma in India and is fast emerging as a major cause of bilateral blindness. This rural hospital based study was conducted to evaluate whether glaucomatous visual field defects particularly the mean defect of Humphrey visual field could be related to VEP parameters of patients having POAG. Visual field by Humphrey perimeter and simultaneous recordings of pattern reversal visual evoked potential (PRVEP) were assessed in 100 patients with POAG. There was a significant (P<0.05) negative correlation of P100 latency, N155 latency and P100 duration and a highly significant (P<0.001) positive correlation of P100 amplitude with mean deviation (index of global visual field damage, MD) of Humphrey visual field in the subjects of POAG in various age groups. N70 latency showed a non-significant positive correlation with MD. The VEP changes observed by us in POAG patients were consistent with the progressing mean defect quantitatively. Therefore, it can be concluded that the VEP parameters can be useful quantitative indices in the evaluation of glaucomatous visual function damage.

Pattern Visual Evoked Potential as a Predictor of Occlusion Therapy for Amblyopia

PURPOSE: This study was conducted to investigate the role of the pattern visual evoked potential (pVEP) as a predictor of occlusion therapy for patients with strabismic, anisometropic, and isometropic amblyopia. The secondary aim was to compare the characteristics of pVEP between strabismic and anisometropic amblyopia. METHODS: This retrospective comparative case series included 120 patients who had received occlusion therapy or a glasses prescription for correction of strabismic, anisometropic, and isometropic amblyopia (20 patients had strabismic amblyopia, 41 patients had anisometropic amblyopia, and 59 patients had isometropic amblyopia). For each patient, the value of the P100 latency on pVEP at the time of the initial diagnosis of amblyopia was collected. Subsequently, the P100 latency was compared according to types of amblyopia. Fifty of 120 patients (7 patients with strabismic amblyopia, 21 patients with anisometropic amblyopia, and 22 patients with isometropic amblyopia) who were followed-up for longer than 6 months were divided into two groups based on the value of their P100 latency (Group 1, P100 latency 120 msec or less; Group 2, P100 latency longer than 120 msec.) The amount of visual improvement after occlusion therapy or glasses was compared between two study groups. RESULTS: The mean P100 latency was 119.7+/-25.2 msec in eyes with strabismic amblyopia and 111.9+/-17.8 msec in eyes with non-strabismic (anisometropic or isometropic) amblyopia (p=0.213). In Group 1, the mean visual improvement after occlusion therapy or glasses was 3.69+/-2.14 lines on Dr. Hahn's standard test chart; in Group 2, the mean improvement was 2.27+/-2.21 lines (p=0.023). CONCLUSIONS: The P100 latency on pVEP at the time of initial diagnosis was significantly related to the visual improvement after occlusion therapy or glasses in patients with strabismic, anisometropic, and isometropic amblyopia. Therefore, it was presumed that patients with a delayed P100 latency might have less visual improvement after occlusion therapy or glasses. In addition, there was no apparent difference in P100 latency between patients with strabismic and non-strabismic (anisometropic or isometropic) amblyopia.

The Change of Visual Evoked Potential in Patients with Myopia in Correction of Refraction

OBJECTIVE: Multiple factors including age, sex, habituation, refraction, cooperation and technical variables are associated with P100 latency of Visual evoked potential (VEP). So we tried to evaluate the P100 latency of visual evoked potential according to refraction. METHOD: We studied 28 patients (12 males, 16 females) with myopia. Subjects were divided into 3 groups (mild, moderate, severe myopia) according to refraction and we evaluated the results of VEP studies. RESULTS: Mean values of refraction and latency (P100) of naked eyes were -4.27 D, 103.95 msec. and those of corrected eyes (in glasses) were -0.25 D, 100.59 msec. Respectively, in mild, moderate and severe myopia, the each P100 latency of naked eyes were 101.27 msec, 102.59 msec, 107.99 msec and those of corrected eyes were 98.33 msec, 100.58 msec, 102.19 msec respectively (p<0.05). There was significant negative correlation between refraction and P100 latency in myopia. CONCLUSION: Our results suggested that there were significant changes in VEP (P100 latency) according to refraction. In performing the VEP study, we should consider the refraction and visual acuity.

Effect of Refractive Error on the P100 Latency of Visual Evoked Response

OBJECTIVE: Absolute or relative increase in the latency of the major surface positive component is almost invariably found in patients with demyelination optic neuropathy. Using the pattern- reversal method, our study illustrates the significant changes in the latency of the P100 component when refractive errors are introduced to defocus in normal person. METHOD: Four women and ten men aged 20 to 27 years were selected after a thorough ophthalmological assessment. Visual acuity (VA) was 6/6 or better in all subject and none had dyschromatopsia or significant astigmatism. Refractive errors were created by the combined standard lenses. RESULTS: The mean value of P100 latency were as follows: 93.74 +/- 3.30 msec, naked eyes; 98.14 +/- 7.37 msec, the +2/+x 90 lens; 96.50 +/- 3.76 msec, the +1/ +1 x90 lens; 94.55 +/- 4.20 msec, the -1/ -1x90; 96.29 +/- 2.88 msec, the -2/ -2 x90 lens. The P100 latencies showed singnificant standard lens except with -1/ -1 x90 lens. The P100 latency was prolonged according to the progression of refractive error. CONCLUSION: Because a relative or absolute prolongation of P100 latency is often found in cases of suspected multiple sclerosis, and because of their similarity to the findings of our study, we would emphasize that refractive errors should be reduced or eliminated to minimize the false-positive results.

P100 Latency in Normal Persons by Pattern Reversal VEP and Flash VEP

The Flash Light Emitted Diode Flash Visual Evoked Potential(Flash VEP) is useful when patients are unable to cooperate sufficiently for a Pattern Reversal Visual Evoked Potential(RP-VEP). In order to evaluate the clinical utility of Flash VEP, we performed the PR-VEP and Flash VEP in 208 eyes of 104 normal persons. The average P100 latency(LaP100) was analyzed according to check size, age, sex, and the laterality of the eye. The LaP100 of PR-VEP stimulated with 8 X 8(120' X 96'), 16 X 16(60' X 48'), 32 X 32 (30' X 24') and 64 X 64(15' X 12') check size were 98.88 +/- 7.57msec(mean S.D msec) , 97.68 +/- 7.44msec, 96.31 +/- 7.21msec, 101.20 +/- 7.81msec, respectively. The LaP100 of PR-VEP stimulated with 32 X 32 check size at 3rd, 4th, 5th, 6th and 7th decades were 93.95 +/- 5.61msec, 94.70 +/- 7.71msec, 92.92 +/- 6.28msec, 97.78 +/- 6.24 msec, 102.79 +/- 5.27msec, respectively. The LaP100 of PR-VEP remained relatively stable until over 6th decade when it increased significantly (p0.05), and between male and female(p>0.05) in the LaP100 of both VEP. These results showed that LaP100 of PR-VEP changes according to the check size and patient's age. We should interprete the LaP100 of PR-VEP or Flash VEP after the processing of averaging its P100 according to the patient's.