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.     

用视诱发电位和富里叶变换作视力客观估计

目的:研究用图形视觉诱发电位(PVEP)和离散富里叶变换(DFT)作视力客观估计的方法。方法:检测对象为33只正常眼。用翻转频率为10次/秒,条纹张角分别为30、20、18、12、10、6、4和2弧分的垂直方波光栅图形刺激,记录相应的稳态图形视诱发电位。用离散富里叶交换提取WEP频谱中10Hz成分的幅值。以光栅条纹张角为横坐标、相应的VEP频谱幅值为纵坐标作关系曲线,取阈值附近的近似线性部分的数据点作直线回归,用外推法求得阈值和视力。结果:比较VEP所测之视力与用国际标准视力表所测之视力,可见在本研究中70％的受检眼VEP视力估计较准确。结论:用本研究中的VEP技术客观地测量视力可靠性较高。眼科学报1997;13:59～61。     

Miniature fiber-optic pattern-reversal stimulator for determination of the visual evoked potential threshold; comparison with Snellen acuity

In this report we recommend the estimation of visual acuity by detection of the visual evoked potential (VEP) threshold, defined by the smallest visual angle of a constant check size that evokes potentials. This approach was implemented using a fiber-optic pattern-reversal stimulator placed at measured, increasing distances from the examined eye. Snellen visual acuity as determined in 113 subjects was correlated with the VEP detection threshold. A highly significant correlation was found between visual acuity and the threshold visual angle of check size in subjects whose vision was impaired due to opacity in ocular media. For any given visual acuity a somewhat wide range of threshold check sizes, typically 5– 10 min of arc was observed. Technical difficulties that need to be overcome to improve these results are discussed.     

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。     

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.     

Effect of defocusing and of distracted attention upon recordings of the visual evoked potential

Pattern reversal visual stimuli are used to evoke potentials (VEPs) for assessment of visual acuity and for localizing defects along the visual pathways. Our goal was to assess the importance of attention and defocusing to the recordings of pattern VEP. Forty-one volunteers with normal (6/6) corrected visual acuity participated in this study. Twenty-one were asked to defocus intentionally the visual stimulus (located 200cm away) by fixating at a target 25 or 50cm from the eye. Twenty other subjects performed auditory tasks to distract their attention from the visual stimulus. Pattern VEPs were elicited by different check sizes. The amplitude and time-to-peak of the P₁₀₀ wave were measured. Intentional defocusing caused amplitude reduction and prolongation of the time-to-peak in young subjects (20–34years old). With the smallest checks used (7.5) we could not record a reliable response from 43 of the young subjects (6 out of 14). In older patients (35–61years old), intentional defocusing induced negligible effects on pattern VEPs regardless of check size. There were no effects of auditory distraction upon the pattern VEPs. Our data suggest that intentional defocusing can produce false positive results (reduced VEP with prolonged time-to-peak) only when small checks are used in young subjects. Divided attention has negligible effect on the recordings of pattern VEPs. With proper controls, the pattern VEP test can be used for objective assessment of visual function.     

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.     

Pattern visual evoked potentials in the assessment of objective visual acuity in amblyopic children

The aim of this study was to determine the value of pattern visual evoked potentials (PVEP) to five consecutive check size patterns in the assessment of visual acuity (VA) in children. One hundred unilateral amblyopic (study group) and 90 healthy children with best-corrected visual acuity (BCVA) of 1.0 (control group) were planned to be included. PVEP responses to five consecutive check sizes (2°, 1°, 30′, 15′, and 7′) which are assumed to correspond to VAs of 0.1, 0.2, 0.4, 0.7 and 1.0 Snellen lines were recorded in both groups. Eighty-five children in the study group (85.0%) and 74 children in the control group (82.2%) who cooperated well with PVEP testing were included. Normal values for latency, amplitude, and normalized interocular amplitude/latency difference in each check size were defined in the control group. PVEP-estimated VA (PVEP-VA) in the amblyopic eye was defined by the normal PVEP responses to the smallest check size associated with normal interocular difference from the non-amblyopic eye, and was considered predictive if it is within ±1 Snellen line (1 decimal) discrepancy with BCVA in that eye. Mean age was 9.7 ± 1.9 and 9.9 ± 2.2 years in the study and the control groups, respectively. LogMAR (logarithm of minimum angle of resolution) Snellen acuity was well correlated with the logMAR PVEP-VA (r = 0.525, P < 0.001) in the study group. The Snellen line discrepancy between BCVA and PVEP-VA was within ±1 Snellen line in 57.6% of the eyes. PVEP to five consecutive check sizes may predict objective VA in amblyopic children.     

Visual evoked potentials in macular hole

Pattern reversal visual evoked potentials (VEPs) with checks of 50 and 12 were recorded in 15 patients with idiopathic unilateral macular hole. VEPs from the affected eyes were reduced in amplitude compared with those from the fellow eyes, especially with checks of 12 (percentage of the amplitude in the affected eye to that in the fellow eye was 86% ± 19% with checks of 50 and 61% ± 35% with checks of 12). The latencies showed no statistically significant difference between the affected and the fellow eyes, although a marked interocular delay was found in a few patients. The degree of amplitude reduction and interocular delay had no relation to the size of the macular hole or visual acuity. The effects of experimental scotomata of various sizes on the VEPs, which were evaluated in nine normal subjects, were also variable among the subjects. We conclude that although the macula predominantly participates in the pattern VEP, an estimation of the extent of macular pathology from the VEP changes may be difficult because the VEP changes induced by a macular hole have wide individual variation and have no relation to the size of the hole.     

Is the motion system relatively spared in amblyopia? Evidence from cortical evoked responses

Visual evoked potentials (VEPs) produced by pattern reversal were compared with those elicited by onset of motion in 37 amblyopic children (20 with anisometropic amblyopia, seven with strabismic amblyopia and 10 with both anisometropia and strabismus). The amplitudes and peak latencies of the main P₁ peak in the pattern-reversal VEP and of the motion-specific N₂ peak in the motion-onset VEP through the amblyopic eye were compared with those through the normal fellow eye. Regardless of the type of amblyopia, the amplitude of the pattern-reversal VEP for full-field stimulation was significantly smaller and its latency significantly longer through the amblyopic eye (P < 0.001). In contrast, neither the amplitudes nor the latencies of the N₂ motion-onset VEPs differed significantly between amblyopic and non-amblyopic eyes. For pattern-reversal VEPs through the amblyopic eyes, the extent to which amplitude was reduced and latency prolonged correlated well with the reduction of visual acuity, whereas the amplitudes and latencies of motion-onset VEPs did not vary with visual acuity. Even for stimuli restricted to the central visual field (5 or 2 deg diameter) or to the peripheral field (excluding the central 5 deg), motion-onset responses were indistinguishable through the two eyes, while pattern-reversal responses always differed significantly in amplitude. These results suggest that the source of motion-onset VEPs (probably an extrastriate motion-sensitive area) is less affected in amblyopia than that of pattern-reversal VEPs (probably the striate cortex). The motion pathway, presumably deriving mainly from the magnocellular layers of the lateral geniculate nucleus, may be relatively spared in amblyopia.     

Acuity predictions from visually evoked potential to checkerboard pattern reversal stimuli: the effect of reversal rate

Introduction : A pattern reversal stimulus (check size 5.5 minutes of arc) was used to elicit the visually evoked potential (VEP). Methods : The peak to trough amplitude of the VEP wave was measured and compared to subjective visual acuity (Landolt C). The recordings were made at three, six and 12 pattern reversals per second. Results : The correlation between VEP amplitude and visual acuity was found to decrease at higher temporal frequencies. The decrease is not confined to the use of a television system reversing checkerboard pattern stimulus as suggested by previous workers. Discussion : It may well be concerned with a change in processing of the visual information as could be expected at these higher frequencies.     

眼挫伤30例视力的恢复与视觉诱发电位变化相关性的分析

目的探讨将诱发电位技术应用于眼外伤后视力评估的可行性。方法眼挫伤致视力受损者30例（48眼）进行视觉诱发电位检查,每例受检对象均记录3次,检测时间分别为伤后1月、3月及1年,以刺激模式空间频率、P100波幅和潜伏期作为检测指标,检测与记载各受检眼P100波幅和潜伏期的变化,以盲测的视力表视力为参照,分析不同时期视觉诱发电位结果与视力恢复状况的相关性。结果一定的视觉刺激模式空间频率大小与视力表现出一致性,P100波幅与视力水平呈正相关,P100波潜伏期长短与视力状况未见必然联系,视觉诱发电位变化与眼挫伤后视力的恢复状况有关,视力表筛查与VEP检测结果比较无差异。结论应用视觉诱发电位技术可对眼挫伤后视力的恢复状况进行客观评估。     

Mechanism of binocular interaction in refraction errors: study using pattern-reversal visual evoked potentials

In this study we sought to determine whether a natural condition involving fine discrimination, for example moderately severe myopia, might yield interesting information regarding the binocular interaction expressed by visual evoked potentials (VEPs). We studied ten normal subjects with a mild refraction deficits. Transient VEPs were elicited by monocular and binocular stimulation under conditions of natural and lens-corrected vision. The visual stimulus was a pattern-reversal checkerboard consisting of 15' and 40' checks. VEPs in response to binocular stimulation were compared with monocular VEPs. We plotted the monocular `better-VEP' and `worse-VEP' response, since significant differences between individual eye stimulations were present. We found no significant difference between the mean N75 and P100 latencies of the binocular VEP and the better monocular VEP, regardless of the check size used and of natural or corrected vision. Under all stimulus conditions, the mean amplitude of the N75-P100 of the binocular VEPs was also larger than the better monocular VEP response. The difference proved more significant when we stimulated our subjects with smaller squares and left vision uncorrected. The mean P100-N145 amplitude obtained with binocular stimulation was larger than the better monocular VEP response only when using small checks (15') and uncorrected vision. Overlapping latencies are consistent with an earlier hypothesis that monocular and binocular VEPs originate postsynaptically from the binocular neurons in the primary visual cortex. The gain in amplitude achieved by binocular stimulation may depend upon the removal of `tonic interocular inhibition' and/or on a cortical modulatory mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Predicting potential acuities in amblyopes

PURPOSE: Amblyopic patients, or their parents, often want to know the potential for success before committing to treatment. Recent reports have indicated that the pattern visual evoked potential (pVEP) can be used as a predictor of the success of amblyopia therapy. Unfortunately, these studies did not determine if acuity estimates from pVEPs could accurately predict the acuity post-treatment. Furthermore, pVEPs are not always practical to obtain because of the time necessary to acquire the data. Sweep VEPs (sVEP) offer the advantage of rapidly estimating visual acuity in amblyopic patients. In this retrospective study, the relationship between sVEP acuities measured pre-amblyopic therapy and Snellen acuities measured post-amblyopic therapy was determined. METHODS: Seventeen patients with amblyopia were studied. Monocular sVEP and Snellen acuities were determined pre-amblyopic therapy and Snellen acuities were determined post-amblyopic therapy. An Enfant 4010 computer system was used to produce the stimuli, record the VEPs, and extrapolate the acuity. The stimuli were horizontally oriented, sine wave gratings (11 spatial frequencies from 2 to 24 cpd) with a contrast of 80%, counterphased at 7.5 Hz. Standard VEP recording techniques were employed. Therapy consisted of the full refractive correction and occlusion combined with active vision therapy. RESULTS: The patients demonstrated a significant improvement in pre- to post-amblyopic therapy Snellen acuities (P < 0.00001). The intraclass correlation coefficient (r (i)) between the pre-therapy sVEP acuities and the post-therapy Snellen acuities was 0.73. A paired t-test did not find a significant difference between the two sets of data (P = 0.94). For the amblyopes in this study, the average difference (+/-SD) in the sVEP acuity estimate and the final Snellen visual acuity was +0.002 +/- 0.123 logMAR acuity lines. CONCLUSION: The results indicate that pre-amblyopic therapy sVEP acuity can be a good predictor of post-amblyopic therapy Snellen acuity.     

正视眼波前像差与低对比度视力相关性研究

目的 分析正视眼波前像差与低对比度视力的相关性.方法 对95例(95眼)健康正视眼用WASCA(wavefront supported corneal ablation)波阵面像差仪测眼波前像差,对瞳孔6 mm时第2,3,4阶像差的各项Zernike函数(C3-C14)进行分析.用多功能电子视力测量仪检测亮、暗环境中对比度为10﹪和5﹪时的裸眼视力和最佳矫正视力.用多元线性回归分析眼波前像差与各低对比度视力间的相关关系.结果 离焦像差(C4)与亮、暗环境中对比度为10﹪和5﹪时的裸眼视力间的直线相关关系有统计学意义(P＜0.01);水平彗差(C8)与亮、暗环境中对比度为10﹪和5﹪时的最佳矫正视力间的直线相关关系有统计学意义(P＜0.01).其余Zernike 函数与各低对比度视力间的直线相关关系均无统计学意义(P＞0.05).结论 正视眼的波前像差与低对比度视力有关,其中离焦像差与裸眼视力有关,水平彗差与最佳矫正视力有关.     

The pattern electroretinogram in optic nerve disease

Pattern evoked electroretinograms (PERG), diffuse flash electroretinograms (ERG) and visual evoked potentials were studied in patients with unilateral optic nerve disease. Patients with Snellen acuities of less than 6/30 did not have recordable PERGs in their affected eye, whereas their diffuse flash ERGs were normal. The VEPs were correspondingly reduced or absent when recorded from the poorer seeing eyes. A second group of patients with Snellen acuity between 6/6 and 6/30 in the involved eye showed reductions in the mean PERG amplitude of the affected as compared with the normal eyes. All affected eyes showed an abnormal contrast threshold measured with the PERG amplitude. Such results underscore the diagnostic value of the PERG in detecting even mildly affected cases of optic nerve disease.     

Visual evoked potential importance in the complex mechanism of amblyopia

To compare the visual evoked potential (VEP) responses of amblyopic eyes with VEP responses of sound eyes in amblyopic children. A study of 65 amblyopic children with pattern-reversal VEPs elicited by checkerboard stimuli with large, medium and small checks. The children were classified into three groups: Group A, 22 children with anisometropic amblyopia; Group B, 16 children with exotropic strabismic amblyopia; and Group C, 27 children with esotropic strabismic amblyopia. Visual acuity (VA) was significantly worse in the amblyopic eye as compared to the sound eye. However, no statistically significant difference was found between the amblyopic and sound eye of amblyopic children in the three groups for VEP P1 amplitude and latencies for any check sizes. VEP is a very important tool in understanding the complex amblyopic mechanism. Although the sound eye has superior VA, the absence of differences in VEP P1 amplitudes and latencies demonstrate the functional abnormality of the eye considered ‘good’. More studies are necessary to explain why the sound eye in amblyopic children cannot be considered completely normal. Special attention should therefore be paid to amblyopic treatment, as patching can have a negative effect on the sound eye.     

Assessment of patients with suspected non-organic visual loss using pattern appearance visual evoked potentials

Background The aim of the study was to validate the use of the short duration pattern onset visual evoked potential (PappVEP) in the objective assessment of visual acuity (VA) in patients referred with presumed non-organic visual loss. Methods The combination of minimum check size and minimum contrast required to elicit a consistently discernible PappVEP (amplitude ≥5 μV) were measured in ten normal subjects under conditions of induced optical blur (0 to +3 dioptres) and the relationship to Snellen VA established. The data from 100 consecutive patients (167 eyes) referred for possible non-organic visual loss (NOVL) and 20 patients with confirmed visual pathway dysfunction were reviewed in relation to the results in normal subjects. Results Snellen VA, under conditions of blur, could be predicted in normal subjects from the check size and contrast required to elicit a criterion PappVEP. These data were tabulated and a quantitative guideline established for the estimation of VA in the patients referred with suspected NOVL. Most (88%) patients referred with suspected NOVL had normal electrophysiology and PappVEPs consistent with normal Snellen VA. In others, they suggested a degree of non-organic overlay. In 20 cases of organic visual loss, PappVEPs were in close agreement with subjective VA. Conclusions The short duration pattern onset visual-evoked potential is confirmed as a clinically useful tool in the objective assessment of patients with suspected non-organic visual loss.     

Usefulness of visual evoked potentials in visual acuity examination

Determination of visual acuity by means of VEP is carried out usually by the calculation of the amplitude function response from the value of pattern single element. That purpose is achieved by carrying out several tests of transient VEP performed each time with stimulation, using the pattern of different size of individual elements or changing sweep the following sizes of the pattern single element. Concentration of a patient is necessary during any examination and therefore in clinical practise the second of the listed methods is preferred because of its short duration. Correlation factor of visual acuity, determined by means of VEP and Snellen tests, differs depending on the examined group from about 0.4 to 0.9 and it is the lowest in case of ophthalmological disorders connected with optic nerve. Fixing of VEP optimal parameters when evaluating the visual acuity remains an open matter.     

Visual evoked potentials elicited by pseudorandom stimulation in macular degeneration]

PURPOSE: To investigate the effect of a central scotoma on the amplitude, latency, and temporal frequency characteristics(TFCs) of the visual evoked potentials(VEPs) elicited by a pseudorandom binary stimulus(PRBS). METHOD: Patients with age-related macular degeneration(AMD) were selected, and VEPs were recorded from 26 eyes with AMD(17 eyes with visual acuity of less than 0.2, and 9 eyes with visual acuity between 0.3 and 0.9). Nine eyes of age-matched normal volunteers served as controls. To acquire the PRBS-VEPs, one eye was stimulated with a PRBS stimulus. The first order kernel was calculated from a cross correlation between PRBS and VEPs. The Fourier transformed first-order kernel was used as the TFC of the VEPs. RESULTS: The P2 latency of the first order kernels was delayed(p < 0.05), and the P2-N2 amplitude was reduced(p < 0.01) in AMD. A depression of the TFC values in the 6-18 Hz band was prominent in the patients with AMD(p < 0.01). CONCLUSION: The TFC, were strongly correlated with the visual acuity of patients with macular degeneration.