Effect of attention on the VEP in binocular and monocular conditions

To study the effect of voluntary concentration on the visual evoked potential (VEP) with monocular and binocular rivalry stimulation, pattern reversal VEPs were recorded using 5.5 min arc and 50 min arc check sizes. Subjects viewed the VEP stimulus with the left eye and a light emitting diode (LED) with the right eye. They were asked to concentrate on either the VEP stimulus or the LED. The two targets were arranged so that the left eye remained accurately focused on, and directed to, the centre of the VEP stimulus throughout the recordings. The binocular VEP wave became attenuated when the subject concentrated on the LED. The wave was reduced to around two-thirds of the amplitude present when concentrating on the VEP stimulus. This reduction in the VEP amplitude is considered to be due to a binocular interaction because there was a lack of amplitude attenuation when the experiment was repeated with monocular conditions. The results also suggest that the wave is smaller when the non-dominant eye receives the VEP stimulus compared with that when the dominant eye is stimulated by the VEP target.     

Visual evoked potentials to red-green stimulation in schoolchildren

The aim is to study chromatic visual evoked potentials (VEP) to isoluminant red-green (R-G) stimulus in schoolchildren. Sixty children (7-19 years) with normal color vision were examined, 30 binocularly and 30 monocularly. The isoluminant point was determined for each child subjectively by using heterochromatic flicker photometry, and objectively from recordings. The stimulus was a 7 degrees circle composed of horizontal sinusoidal gratings, with spatial frequency 2 cycles/degrees and 90% contrast, presented in onset-offset mode. VEP were recorded from Oz (mid-occipital) position. Age-dependent waveform changes and changes of the positive and negative wave were studied to both binocular and monocular R-G stimulation. Age-dependent waveform changes were observed to binocular and monocular R-G stimulation. In younger children the positive wave was prominent, whereas in older children also the negative wave became more evident. The latency of the positive wave decreased linearly with age to R-G binocular stimulation. To monocular stimulation no significant changes of the latency were observed. The amplitude of the positive wave dropped exponentially with age to binocular and monocular stimulation. The latency of the negative wave increased linearly with age to binocular and monocular stimulation, whereas the amplitude did not show age-dependent changes. These findings suggest that the chromatic VEP response undergoes evident age-dependent changes during the school-age period.     

Effects of Duane's retraction syndrome on sensory visual development

PURPOSE: To study the effects of Duane's retraction syndrome on sensory visual development. METHODS: Monocular and binocular visual function and ocular motility have been studied and pattern reversal visual evoked potentials recorded from 22 patients with Duane's syndrome aged from 4 to 55 years. RESULTS: Sixteen of the patients maintained binocular single vision using an abnormal head posture. All had normal visual acuities in both eyes. The 12 adults in this group had a mean stereoacuity of 78 seconds of arc with the mus stereotest and 101 seconds of arc with the TNO test. Both these values were significantly worse than for normal adults with a similar age range. The binocular VEPs from these patients showed enhancement of the binocular P100 VEP amplitude compared to the mean monocular P100 amplitude when they used their head posture but, unlike in normal subjects, this binocular enhancement was not reduced significantly after the age of 5. Six patients had lost binocular function and had a manifest convergent squint. Of these, 4 were anisometropic. VEPs in this group showed mildly delayed P100 latencies in the affected eye with asymmetric amplitudes even though their amblyopia had been successfully treated by patching and only one patient had a substantially reduced acuity. In neither group was there any relationship between the degree of restriction of ocular motility and the sensory changes. CONCLUSION: Patients with Duane's syndrome who retain binocular single vision show abnormal binocular visual maturation after the age of 5 years. This results in reduced stereoacuity in the absence of amblyopia.     

VEP maturation and visual acuity in infants and preschool children

Purpose Visual processes continue to mature well into childhood, due to the development of the retina, optic nerve, visual pathway and visual cortex. Normal development of visual acuity and maturation of visual evoked potentials (VEPs) have been well studied, although rarely for their correlation. The purpose of this study was to investigate the same population of infants and preschool children for their VEP maturation to flash, pattern-reversal (reversal) and pattern-onset (onset) stimulation, which are normally used in our everyday clinical protocol, and to determine the relationships between the VEP parameters obtained and the development of visual acuity. Methods Forty-one healthy children from 1.5 months to 7.5 years old were included. Their visual acuity for distance was tested with Teller Acuity Cards (<2 years of age) and Cambridge Visual Acuity Crowding Cards (>2 years of age). VEP latencies and amplitudes were evaluated to flash (P2 wave), reversal (P100 wave) and onset (C1 wave) binocular stimulation. For reversal and onset stimulation, checkerboard pattern (check) sizes of 25', 50' and 100' were used. Results Age-dependent exponential decreases in latencies to flash, reversal and onset stimulation were seen. For amplitudes, there was an age-dependent increase only to onset stimulation. There was a significant correlation between VEPs and visual acuity (P < 0.05) for latencies to flash, reversal and onset stimulation and amplitudes to onset stimulation. Conclusion These findings indicate the expected maturation of flash, reversal and onset VEPs, and demonstrate their correlation to normal development of visual acuity. Maturation of VEP latencies is associated with development of visual acuity.     

外斜视儿童多导视觉诱发电位的研究

目的探讨不伴有弱视的恒定性外斜视儿童的多导视觉诱发电位（ｖｉｓｕａｌｅｖｏｋｅｄｐｏｔｅｎ－ｔｉａｌｓ,ＶＥＰｓ）的临床意义及外斜视的发病机理。方法采用１４个盘状作用电极行全视野及半视野棋盘格翻转刺激,记录正常对照组与不伴有弱视的恒定性外斜组儿童的视觉诱发电位。结果斜视组全视野刺激所记录的双眼与单眼ＶＥＰｓ潜伏期（ＬＰ１）、振幅（ＡＮ１Ｐ１）比较,差异无显著性（Ｐ＞０．０５）,此结果与正常对照组不同;斜视组主眼和非主眼ＬＰ１较正常对照组延长（Ｐ＜０．０１）,斜视组非主眼ＡＮ１Ｐ１较正常对照组下降（Ｐ＜０．０１）;斜视组鼻、颞侧视网膜ＬＰ１、ＡＮ１Ｐ１比较,差异无显著性（Ｐ＞０．０５）。结论ＶＥＰｓ检测可为恒定性外斜视者的双眼视功能异常提供客观依据;恒定性外斜视者视力虽正常但ＶＥＰｓ并非正常,提示有初级视皮层功能障碍存在;不伴有弱视的恒定性外斜视者在单眼半视野刺激条件下,无颞侧视网膜抑制现象。     

Incremental binocular amplitude of the pattern visual evoked potential during the first five months of life: electrophysiological evidence of the development of binocularity

The amplitude of the pattern visual evoked potential (VEP) of a binocular stimulus has been shown to be generally larger than the VEP obtained monocularly. There is evidence that this effect can be considered an electrophysiological index of fusion.To study how binocular vision develops in infancy we evaluated the incremental binocular amplitude (IBA) in three infants in a longitudinal investigation during the first five months of life. The stimuli were phase-alternating square-wave gratings with spatial and temporal parameters chosen to be appropriate for neonates. IBA was defined as the percentage increment of the largest binocular response compared with the monocular response. In the first two months of life IBA values were near zero, that is, no summation occurred. Between the second and third month IBA values rose markedly and after the third month its value was greater than 100%, demonstrating binocular facilitation. Thus in the first two months of life the eyes do not seem to cooperate as in adults. By the second and third month the binocular pattern VEP reflects an increasing binocular interaction. Other studies of the development of stereopsis have also found evidence of binocularity at similar ages.     

Acuity estimated by visually evoked potentials is affected by scaling

Seven subjects whose corrected Snellen acuities were normal had their monocular acuities (14 eyes) tested by visually evoked potentials (VEPs) elicited by eight checkerboard patterns which reversed 15 times per second. Check size ranged from 20 to 3.4 min arc. Monocular VEP acuities were determined by least squares regression with linear or logarithmic scales of amplitude and pattern size. Pattern size was measured as arc minutes (horizontal size) or fundamental spatial frequency of the checkerboard. The extrapolated VEP acuities were obtained by analyses of variance and post hoc tests. The presence of statistically significant differences in VEP acuity which result from varying combinations of stimulus and response scales indicates a need for caution in selecting scales for VEP estimates of visual acuity.     

Binocular interaction in the VEP to grating stimulation. II. Spatial frequency effects

The size specificity of the binocular interaction in the VEP was investigated. VEPs elicited by sine wave gratings were recorded on 3 subjects, with the exception of one experiment where 6 subjects were tested. The recording technique made it possible to obtain responses from each eye, even during binocular stimulation. The VEP amplitude for each eye during monocular stimulation was compared with the response of the same eye during binocular stimulation. A low binocular/monocular ratio indicated a high binocular interaction. When each eye was stimulated by the same spatial frequency, the binocular interaction was highest in the spatial frequency band of 2-4 c/d. When each eye was stimulated by a different spatial frequency, the binocular interaction decreased as the frequencies were made progressively more unequal. The bandwidth at half amplitude was about 1 octave around the center frequency.     

Binocular interaction and steady-state visual evoked potentials

A correlate of binocular-neuron activity was found in some properties of visual evoked potentials (VEPs), such as facilitation (defined as a binocular response greater than the sum of the monocular responses) and changes in latency (shortening of binocular VEP latency as compared to that of monocular VEPs). Monocular and binocular steady-state VEPs in response to phase-alternating gratings of different contrast and both spatial and temporal frequency were recorded in three normal subjects. Fourier analysis of the responses was performed to isolate the component at the reversal frequency. Binocular VEPs showed facilitation in the low-contrast range (3%–10%). Facilitation was highest for gratings that had spatial frequency of 0.6–2 cycles/degree (c/d), alternating at 16 reversals per second. Phase shortening was found across a parameter range larger than that at which amplitude facilitation occurred. These results suggest that both amplitude facilitation and phase shortening in binocular VEPs may provide an objective measure of binocular visual function in clinical ophthalmology.Dedicated to Dr. G.K. von Norden on the occasion of his 60th birthday     

单眼弱视与双眼弱视病儿视觉诱发电位的分析

分别对单眼弱视和双眼弱视两组病儿进行了图形反转视觉诱发电位及白光、红光、蓝光闪光视诱发电位P100波的观察,结果表明单眼弱视与双眼弱视的发病机制不同。     

单眼视设计的人工晶状体眼视功能临床研究

目的 探讨应用单眼视原理设计双眼白内障超声乳化联合植入单焦点人工晶状体术后的视功能情况.方法 对双眼年龄相关性白内障患者42例(84只眼),分为常规组21例(42只眼)及单眼视组21例(42只眼).常规行白内障超声乳化联合折叠式人工晶状体植入术.分别记录术前最佳矫正视力及术后1周单眼裸眼远、近视力及双眼裸眼远、近视力.采用SAS8.2统计软件对结果进行统计学分析.结果 (1)术前平均最佳矫正视力常规组4.44,单眼视组4.47(P ＞0.05),患者平均年龄常规组71岁,单眼视组69.5岁(P ＞0.05),差异无统计学意义.(2)术后1周单眼裸眼远视力常规组4.90,单眼视组:优势眼4.94(P ＞0.05),与常规组比较差异无统计学意义;非优势眼4.71(P < 0.05),与常规组比较差异有统计学意义.术后1周单眼近视力常规组4.36,单眼视组:优势眼4.37(P＞0.05),与常规组比较差异无统计学意义;非优势眼4.78(P < 0.05),与常规组比较差异有统计学意义.(3)术后1周双眼裸眼远视力常规组4.91,单眼视组4.91(P ＞0.05),与常规组比较差异无统计学意义;术后1周双眼近视力常规组4.42,单眼视组4.78(P < 0.05),与常规组比较差异有统计学意义.结论 单眼视设计的人工晶状体眼术后双眼远视力与常规设计人工晶状体眼相同,但近视力明显好于常规设计.按照单眼视原理设计人工晶状体可以较好的临床应用.     

弱视儿童双眼总和视觉诱发电位变化的研究

目的探讨弱视儿童双眼视功能及总和图形视觉诱发电位（P-VEP）反应的特点,评估总和P-VEP反应对双眼视觉功能检测的意义。方法选取80名正常儿童和在南昌大学附属第二医院儿童眼科确诊的远视性弱视儿童151例,进行双眼总和P-VEP检查,分析总和P-VEP反应的特点。正常儿童与弱视儿童的人口基线学特征经统计学分析差异无统计学意义。P-VEP检查方法和刺激条件的选择参照吴乐正等的方法,记录电极的放置按照视觉电生理国际标准化的要求。视力检查采用国际标准视力表,双眼视觉功能检查采用Titmus立体图、同视机三级画片。P-VEP检测结果以双眼反应/单眼反应（B/M）比值作为评价指标。结果弱视组儿童总和P-VEP反应低于正常对照组（t=10.75,P〈0.01）;不同程度弱视组的B/M值随弱视的严重程度明显减低（F=10.93,P〈0.01）;无同时视者总和P-VEP与有同时视者比较,差异有统计学意义（t=7.835,P〈0.01）。结论总和P-VEP反应作为一种客观指标,可以反映弱视儿童的双眼视功能状况,对其双眼视功能的评价具有一定的价值。     

The visual evoked potential in glaucoma and ocular hypertension: effects of check size, field size, and stimulation rate

In order to determine the optimum stimulus conditions for the detection of optic nerve damage due to glaucoma and ocular hypertension, checkerboard pattern reversal visual evoked potentials (VEPs) were recorded from 20 glaucoma patients, 20 ocular hypertensive patients, and 20 age-matched normals. Two check sizes (12' and 48'), two field sizes (14 degrees and 28 degrees), and two alternation rates (1.9 and 7.5 alt/sec) were used. All subjects had visual acuities of 20/40 or better in each eye and equal pupils of 2 to 5 mm diameter. The largest number of VEP abnormalities were found with large checks (48') reversing at a fast rate (7.5 alt/sec). After correcting for the effects of age, visual acuity, and pupil size, 16 of 30 eyes with glaucomatous visual field defects had abnormally long VEP latencies under this condition (beyond the 99% confidence limit of the normal subjects). Nine of 40 ocular hypertensive eyes also had abnormally long latencies. Increased pattern VEP latency was significantly correlated with both the severity and location of visual field defects and the degree of cupping and pallor of the optic disc. VEP latency was not significantly related to intraocular pressure.     

Reduced binocular beat visual evoked responses and stereoacuity in patients with Duane syndrome.

PURPOSE: To study the effects that the abnormal eye movements of patients with Duane retraction syndrome have on the development of binocular function. METHODS: Pattern reversal visual evoked responses (VEPs) to 15-minutes-of-arc and 60-minutes-of-arc checks and binocular beat VEPs to diffuse sinusoidally modulated 18- and 20-Hz stimuli were recorded in 10 patients with Duane retraction syndrome who maintain binocular function by using an abnormal head posture. Visual acuity, stereoacuity, and eye movements were measured. The results have been compared to those from 10 normal subjects. RESULTS: The patients with Duane retraction syndrome had reduced stereoacuity compared to the normal control group (TNO mean, 82.5 seconds of arc compared to 37.5 seconds of arc; Titmus mean, 143 seconds of arc compared to 44 seconds of arc). The binocular beat VEPs showed a significantly reduced difference beat response at 2 Hz in the patients with Duane syndrome compared to normal subjects (mean signal-to-noise ratio 2.40 +/- 1.05 compared to 4.30 +/- 2.66; t = 2.21, df = 18, P < 0.05). Binocular enhancement of the P100 pattern reversal amplitude to 15-minute checks was increased in these patients, because of a reduction of the monocular P100 amplitudes compared to the normal group. CONCLUSIONS: Patients with Duane syndrome who maintain binocular function using an abnormal head posture have reduced stereoacuity and show electrophysiological evidence of reduced cortical binocular interaction.     

Neural and Vascular Responses to Fused Binocular Stimuli: * A VEP and fNIRS Study

Purpose. The aim of our study was to investigate the correlation between neural and hemodynamic responses to stereoscopic stimuli recorded over visual cortex. Methods. Test stimuli consisted of a static checkerboard (checks) and dichoptic static random dot (RD) presentations with no binocular disparity (ZD) or with horizontal disparity (HD). Hemodynamic responses were recorded from right and left occipital sites using functional near-infrared spectroscopy (fNIRS). Visual evoked potentials (VEPs) were recorded over three occipital sites to the onset of the same stimuli. Results. Early components, N1 and P2, were sensitive to HD, suggesting that an enhanced N1-reduced P2 complex could be an indicator of binocular disparity and stereopsis. VEPs to checks and ZD stimulation were similar. fNIRS recordings showed changes in hemodynamic activation from baseline levels in response to all stimuli. In general, HD elicited a larger vascular response than ZD. Oxyhemoglobin concentration (HbO) was correlated with the VEP amplitude during the checks and HD presentations. Conclusions. We report an association between neural and hemodynamic activation in response to checks and HD. In addition, the results suggested that N1-P2 complex in the VEP could be a neural marker for stereopsis and fNIRS demonstrated differences in HbO. Specifically, checks and HD elicited larger hemodynamic responses than random dot patterns without binocular disparity.     

Attentional shifts have little effect on the waveform of the chromatic onset VEP

Attention is important for sufficient performance on many visual tasks. This has been shown using achromatic steady‐state and pattern‐reversal VEPs. Waveform characteristics typically attenuate when attending to distractor stimuli and ignoring VEP stimuli. Chromatic pattern‐onset responses have not been tested under conditions of selective attention: as they can be used in clinical settings to test color vision, it is important to know what effects attentional shifts would have on this response. In the present study chromatic pattern‐onset VEPs were recorded using spatially divided and spatially contiguous VEP and distractor stimuli. VEP stimuli were 1 cycle.deg^?1 horizontal sine wave patterns (onset mode 100 ms on/400 ms off) used to selectively modulate the L?M and S‐(L+M) visual pathways. Distracter stimuli were letters. Subjects attended to either the letters or the gratings and pressed a button when a predetermined stimulus appeared. In Experiment one, VEP and distractor stimuli were superimposed and spatially contiguous. In Experiment two, stimuli were presented to different hemifields. No significant changes in waveform amplitude and latency were found between VEP and distractor attention conditions for either visual pathway. For the chromatic pattern‐onset response, modulation of attention does not change responses either with spatially contiguous or spatially separate selective attention manipulations. Consequently, it may not be necessary to monitor attention during recording of this response.     

眼外伤后视力的视觉诱发电位评估

目的:研究眼外伤后189眼的视觉诱发电位资料,探讨将诱发电位技术应用于视力评估的可行性及方法。方法:全部受检对象为志愿合作者,使用国际标准视力表对其视力随机筛查、盲测并分组,以刺激模式空间频率、P100波幅和潜伏期作为检测指标,探索最小空间频率,研究其与视力的对应关系,分析最小空间频率条件下P100波幅和潜伏期与视力的关系,确定应用视觉诱发电位技术评估视力的方法,比较受检眼的视力表筛查与视觉诱发电位评估结果。结果:最小空间频率22’,11’,5’及3’所对应的视力分别为0.1~0.2,0.3~0.5,0.6~1.0及1.2~1.5,不同视力P100波幅存在显著性差异,而P100潜伏期却未表现出明显差异,结合最小空间频率及P100波幅对全部受检眼视力的视觉诱发电位随机评估,其结果与国际标准视力表筛查结果比较无显著性差异。结论:应用视觉诱发电位技术可对志愿合作者的视力水平进行客观评估。     

Visual evoked potentials in patients with Graves' ophthalmopathy complicated by ocular hypertension and suspect glaucoma or dysthyroid optic neuropathy

The study compared visual evoked potentials of patients with uncomplicated Graves' ophthalmopathy, patients with ophthalmopathy and elevated intraocular pressure or suspect glaucoma, and patients with dysthyroid optic neuropathy (DON). The aim of the study was to investigate the clinical potential for the visual evoked potentials (VEP) in the differential diagnosis among the groups. The VEPs were obtained from 43 subjects with endocrine ophthalmopathy. Group I included patients with uncomplicated ophthalmopathy (30 eyes); group II included patients with ophthalmopathy, intraocular pressure 23 mmHg with and without early visual field defects, and no evidence of apical crowding on coronal computed tomography scan (28 eyes); group III included patients with DON (28 eyes). Amplitude and latency of major component of pattern VEP were obtained at three visual angles (60', 30', 15'). Data from each group was compared with data from age-matched normal subjects. Disturbances of VEP were found mainly in patients of Group II and Group III. Control Group had normal VEP. About the differential diagnosis between Group II and Group III the most important parameter was the N75-P100 amplitude for 15' of pattern stimulation. Only for this visual angle, Group II and Group III had not overlapped N75-P100 amplitude. This study shows that VEP detect visual function abnormalities noninvasively in patients with complicated Graves' ophthalmopathy. Results also indicate the clinical potential for VEP in the differential diagnosis between patients suffering from ophthalmopathy complicated by ocular hypertension or suspect glaucoma and patients with dysthyroid optic neuropathy.     

A VEP measure of the binocular fusion of horizontal and vertical disparities

PURPOSE: Because of the lateral separation of the orbits, the retinal images differ in the two eyes. These differences are reconciled into a single image through sensory and motor fusional mechanisms. This study demonstrates electrophysiologically the effects that normal horizontal and vertical fusional processes have on the processing of monocular position signals. METHODS: VEPs were recorded in 16 healthy adults in response to a vernier onset-offset target presented to one eye. The vernier offsets appeared and disappeared at 2 Hz and were introduced into bar targets that were oriented either vertically (horizontal offsets) or horizontally (vertical offsets). The magnitude of the offsets was varied over the range of 0.5 to 10 arc min. VEP amplitude was measured as a function of the size of the dynamic offset under monocular viewing conditions and in the presence of two different static targets presented to the other eye. One of the static targets matched the dynamic test, except that it had no vernier offsets. The other static target, the static pedestal, matched the dynamic test, but contained a set of static vernier offsets in locations corresponding to the locations of the dynamic offsets presented to the other eye. RESULTS: VEP amplitude was a monotonically increasing function of vernier offset size under monocular viewing conditions. The addition of the static target without offsets in the other eye resulted in an increased amplitude VEP response. The addition of the static target with vernier offsets resulted in a decrease in VEP amplitude for both horizontal and vertical disparities. CONCLUSIONS: The normal process of fusion results in a single visual direction. To obtain a single visual direction, the visual system must synthesize a binocular visual direction that differs from the monocular components. One of the conditions (the static pedestal with offsets) produces binocular visual direction shifts that degrade the appearance of vernier onset-offset, and reduce VEP amplitude for both horizontal and vertical disparities. This characteristic evoked response marker is a promising tool for measuring binocular fusion objectively in patients with strabismus.