Decreased activation of the lateral geniculate nucleus in a patient with anisometropic amblyopia demonstrated by functional magnetic resonance imaging

Although postmortem morphological changes in the lateral geniculate nucleus (LGN) have been reported in human amblyopia, LGN function during monocular viewing by amblyopic eyes has not been documented in humans. We used functional magnetic resonance imaging (fMRI) to study monocular visual activation of the LGN in a patient with anisometropic amblyopia. Four normal subjects, a patient with optic neuritis and a patient with anisometropic amblyopia were studied with fMRI at 1.5 T during monocular checkerboard stimulation. Activated areas in the LGN and visual cortex were identified after data processing (motion correction and spatial normalization) with SPM99. In the 4 normal subjects, comparable activation of the LGN and visual cortex was obtained by stimulation of either the right or left eye. In the patient with unilateral optic neuritis, activation of the LGN and visual cortex was markedly decreased when the affected eye was stimulated. Similarly, decreased activation of the LGN as well as the visual cortex by the affected eye was demonstrated in the patient with anisometropic amblyopia. Our preliminary results suggest that activation of the LGN is diminished during monocular viewing by affected eyes in anisometropic amblyopia. fMRI appears to be a feasible method to study LGN activity in human amblyopia.     

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。     

Binocular summation in visual evoked cortical potential in patients who have significantly different P100 peak latencies in their two eyes

Purpose To determine whether binocular summation in visual evoked cortical potential (VEP) is present in patients who have significantly different P100 peak latencies in their two eyes.Methods Twelve patients with unilateral optic neuritis (ON) and 11 normal controls were studied. All of them had visual acuity of 20/20 in both two eyes and good stereoacuity. Transient and steady-state VEPs were recorded with monocular and binocular pattern-reversal stimulation.Results In normal controls, the binocular summation ratio was 1.05 with transient stimulation and 1.21 with steady-state stimulation, and in ON patients it was 1.19 and 1.30, respectively. In ON patients, the peak latency of P100 components was delayed significantly when the affected eye was stimulated, but with binocular stimulation the waveform was very similar to that when the fellow eye was stimulated.Conclusion Binocular summation of VECP is not present in ON cases with large differences in the peak latency between the two eyes even if they have good stereoacuity. Binocular summation may not be correlated with stereopsis in adults whose binocular function has already matured.     

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.     

Electroretinogram findings in unilateral optic neuritis

To report the electrophysiological findings in patients with unilateral optic neuritis (ON), with particular reference to the electroretinogram (ERG). A retrospective analysis of full-field ERG, pattern ERG (PERG) and pattern visual evoked potential findings from 46 patients with clinical and electrophysiological findings in keeping with unilateral ON. ISCEV standard ERGs did not significantly differ between the optic neuritis and fellow eyes, nor between patients with and without MS. Differences were present in the N95 component of the PERG, which was significantly lower in the affected eye, and the pattern reversal visual evoked potential, which showed significantly longer peak time (latency) in the affected eye. In addition, there was a significant difference between patients with and without multiple sclerosis (MS). No significant inter-ocular asymmetry in ISCEV standard ERGs was present in these cases of unilateral optic neuritis, either as a clinically isolated syndrome or as part of multiple sclerosis. All ERGs recorded were normal.     

急性视神经炎的功能磁共振成像研究

目的应用功能磁共振成像技术探讨急性视神经炎的皮层功能变化。方法以1.5T磁共振成像系统采集14例单眼急性视神经炎、12例正常人视皮层BOLD-fMRI数据,比较正常组与视神经炎组两眼分别刺激时的视皮层激活像素数与激活信号平均强度,分析BOLD-fMRI数据与PVEPP100波潜时的相关性。结果正常组与视神经炎组枕叶视皮层、颞下回、后顶叶都有不同程度的兴奋,主要兴奋区位于枕叶距状裂周围。与对侧眼相比,视神经炎患眼刺激的皮层激活像素减少、激活信号平均强度降低。治疗4周后,患眼视力提高,皮层激活像素明显增多,屏状核、额前叶、丘脑亦有不同程度的兴奋。P100波潜时与皮层激活像素数呈负相关。结论功能磁共振成像技术可以反映视神经炎的皮层功能改变,为视神经炎的临床诊断和预后评估提供新的依据。     

Impact of alternative eye photostimulation technique on visually evoked potentials in children with amblyopia

Before and after alternative eye photostimulation (AEPS), the pattern of visually evoked potentials (VEP) was studied in children with amblyopia. It can be said that there is a persistent abnormality in the binocular visual system as asymmetry of the latency and amplitude of peak P100 of VEP to the 7'-sized structured pattern. Pathogenetically oriented AEPS rearranged the functional state of the binocular system, by differently affecting monocular canals. Along with the increased visual acuity of the amblyopic eye, there is recovery of interocular symmetry of the parameters of the latency and amplitude of peak P100 to the 7'-sized pattern, with the delayed binocular latency to this pattern and the binocular system becomes more equilibrium.     

Binocular enhancement of the visual evoked potential in patients with Duane's syndrome

Monocular and binocular visual evoked potentials were recorded in eight patients with Duane's syndrome who used an abnormal head posture to maintain binocular single vision. With their abnormal head posture, all patients had stereoscopic vision, although with mildly reduced stereoacuity, and the visual evoked potential showed binocular enhancement (mean binocular to monocular ratio, 1.44). Without their head posture, the patients experienced diplopia or suppressed vision in one eye. Binocular visual evoked potentials recorded under these conditions were of lower amplitude (mean binocular to monocular ratio, 1.05). However, without the abnormal head posture, a manifest strabismus was present and the deviating eye was not fixating the stimulus screen. Monocular visual evoked potentials recorded with the eye fixating just to one side of the screen gave little or no response, and this lack of fixation may account for the loss of binocular enhancement of the visual evoked potential in strabismus.Abbreviation AHP abnormal head posture     

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。     

Bee sting optic neuritis. A case report with visual evoked potentials.

Simultaneous recordings of the pattern visual evoked potential and the pattern electroretinogram were recorded in a case of unilateral optic neuritis following a bee sting on the eye. The patient presented with severe eye pain, apoplectic visual loss, acute optic disc swelling and minimal signs of ocular inflammation and eyelid edema. The vision failed to recover. The electrophysiological recordings initially showed a delay in the P100 wave of the pattern visual evoked potential. On follow-up, a normal latency and amplitude of the P50 wave of the pattern electroretinogram was recorded with the flattening of the N95 component, but the pattern visual evoked potential was absent. The data suggests that the optic nerve was demyelinated acutely, and that subsequently axonal loss and degeneration of retinal ganglion cells occurred.     

An interocular comparison of the multifocal VEP: a possible technique for detecting local damage to the optic nerve

PURPOSE: To develop a quantitative measure of local damage to the ganglion cells/optic nerve based on an interocular comparison of multifocal visual evoked potentials (mVEP). METHODS: Multifocal VEPs were recorded from both eyes of six normal subjects and four patients; each eye was stimulated separately. Two of the patients had glaucoma, one had ischemic optic neuropathy, and one had unilateral optic neuritis. All four patients had considerably more damage in one eye than in the other, as indicated by their Humphrey visual fields. The multi-input procedure of Sutter was used to obtain 60 VEP responses to a scaled checkerboard pattern. The amplitude in each response was obtained using a root mean square measure of response magnitude. For each of the 60 pairs of responses, a ratio between the amplitude of the responses from the two eyes was obtained as a measure of the relative health of one eye compared with the other. The mean and SD of this ratio measure for the control group were used to specify confidence intervals for each of the 60 locations. All patients had Humphrey 24-2 visual fields performed. To allow a comparison of the mVEPs to the visual fields, a procedure was developed for displaying the results of both tests on a common set of coordinates. RESULTS: Except for a small interocular difference in timing attributable to nasotemporal retinal differences, the pairs of mVEP responses from the two eyes of the control subjects were essentially identical. Many of the pairs of responses from the patients were significantly different. In general, there was reasonably good agreement with the Humphrey 24-2 visual field data. Although some regions with visual field defects were not detected in the mVEP due to small responses from the better eye, other abnormalities were detected that were hard to discern in the visual fields. CONCLUSIONS: Local monocular damage to the ganglion cell/optic nerve can be quantitatively measured by an interocular comparison of the mVEP.     

Contrast sensitivity in multiple sclerosis. A study in 35 patients with and without optic neuritis

Binocular and monocular contrast sensitivity (CS) functions were determined for 35 patients with multiple sclerosis (MS) of whom only 21 had a history of optic neuritis. CS was abnormal in all 21 of these patients; alterations of CS affected all spatial frequencies, not only for the eye with optic neuritis, but also for the clinically unaffected eye (p less than 0.01). Approximately one third of the 14 patients with MS but without any history of past visual disturbances showed an optic nerve involvement. Our results show that (1) clinically visual impairment is bilateral, even if optic neuritis seems unilateral, and (2) CS can detect silent lesions of the visual pathways in MS and may prove to be more sensitive than visual evoked potentials.     

Differential diagnosis of amblyopia and retrobulbar neuritis with electroophthalmologic methods]

The electroretinogram (ERG), the brightness visual evoked cortical potential (H-EP) and the pattern reversal visual evoked cortical potential (M-EP) were recorded from 7 patients with amblyopia and 5 patients with neuritis retrobulbaris. The ERGs and the H-EPs of the amblyopic eyes were normal whereas the amplitude of the M-EP was significant diminished. The parameters of the ERG recorded from the patients with neuritis retrobulbaris showed normal values, however the H-EPs were significantly decreased and the peaktimes were delayed. Also a decrease in the amplitudes of the M-EPs was noticed. This method is a usefull clinical contribution in the differential diagnosis between amblyopia and neuritis retrobulbaris.     

Normal pattern electroretinograms in amblyopia

Checkerboard reversal stimuli were used to evoke transient pattern electroretinograms (P-ERGs) from the eyes of 14 patients with amblyopia and 14 normal subjects. In the control group, and in normal eyes of patients, pattern electroretinograms were obtained with monocular central fixation. Amblyopic eyes were examined by monocular and binocular fixation, and the fixation point was shifted horizontally and/or vertically until the P-ERG reached its maximal amplitude. After adjusting visual fixation, there were no significant differences in amplitude between the normal and the amblyopic eyes. In addition, the differences between both eyes were compared with the right-left eye variability of the 14 normal subjects. In the amblyopic eyes, no P-ERG abnormality was observed. These results do not support previous reports of reduced P-ERG amplitudes and are in agreement with recent findings obtained under steady-state conditions.     

Saccadic latency as a measure of afferent visual conduction

Latency to initiate a saccadic eye movement to a visual target, and visual evoked potential, were measured in seven patients with resolved unilateral optic neuritis. Saccades were delayed when the target was presented to the clinically involved eye, but were normal when the contralateral eye was tested. With binocular target presentation, saccades were symmetric between eyes and normal in latency. In two patients with pituitary adenoma and low-grade bitemporal field defects, saccades were delayed when targets were presented in the temporal field, but were within normal limits when presented in the nasal field. These results cannot be attributed to lesions in the motor pathways. It is concluded that saccadic latency to visual targets is a valid measure of afferent conduction. If the robust delays found in this study prove to have test-retest reliability, saccadic latency may provide a measure of afferent function which is sensitive to the demyelination that preceeds neuronal degeneration and sensitivity loss in patients suspected of having optic neuropathy.     

Clinical application of motion-onset visual evoked potentials

The results of motion-onset visual evoked potentials and pattern-reversal visual evoked potentials were compared in 5 adults with amblyopia, in 13 patients with unilateral retrobulbar neuritis and in 62 patients with multiple sclerosis. While the pattern-reversal visual evoked potentials had reduced amplitudes and prolonged latencies in all amblyopic eyes, the motion-onset visual evoked potentials were normal. Thus, motion-onset visual evoked potentials cannot be used for diagnosis of amblyopia. In patients with retrobulbar neuritis, both types of visual evoked potentials were delayed on stimulation of the affected eye. The latency increase was, however, greater for pattern-reversal visual evoked potentials than for motion-onset visual evoked potentials. Examination of the patients with multiple sclerosis showed that the additional use of motion-onset visual evoked potentials increased the sensitivity of the investigation. In some patients, only the motion-onset visual evoked potentials had pathologic latency increases, whereas the pattern-reversal visual evoked potentials stayed within normal limits.     

Near-infrared spectroscopy of the visual cortex in unilateral optic neuritis

PURPOSE: To examine the occipital-lobe activation of patients with optic neuritis using near-infrared spectroscopy. DESIGN: Experimental study. METHODS: NIRS was performed on five patients with acute unilateral optic neuritis during monocular visual stimulation. As controls, six normal subjects were also tested in the same manner. RESULTS: In the patients with optic neuritis, the changes in the hemoglobin concentrations (oxyhemoglobin, deoxyhemoglobin, and total hemoglobin) in the occipital lobe were found to be markedly reduced when the clinically affected eyes were stimulated compared with the fellow eyes. The response induced by the stimulation of the affected eye was decreased, even when the patient's visual acuity improved to 20/20 in the recovery phase. There was no difference in the concentration changes between the two eyes in the control subjects. CONCLUSIONS: NIRS may be useful in detecting visual dysfunction objectively and noninvasively in patients with visual disturbance, especially when used at the bedside.     

Stereoacuity degradation by experimental and real monocular and binocular amblyopia

Fourteen normal adult volunteers with normal binocular single vision and normal stereoacuity submitted to monocular and binocular degradation of their stereoacuity by cycloplegia and fogging with spherical lenses. Stereoacuity (SA) was reduced as soon as visual acuity (VA), both monocular and binocular, was reduced. There was a marked similarity in the degree of SA reduction produced by monocular and binocular amblyopia. The degree of SA reduction was slightly more marked with monocular decrements than with binocular at VAs between 20/25 and 20/50. Significant intersubject variation was noted. The majority of subjects maintained gross SA at 20/200 monocular or binocular. One subject was reduced to gross stereopsis at 20/30 monocular and 20/50 binocular VAs. Two subjects were able to retain 40 sec of SA until vision was degraded to 20/50. Conversely, 40 sec of SA was not achieved by any subject at monocular or binocular vision less than 20/40 (test for malingering). Thirteen patients with real monocular and binocular organic or functional amblyopia were then compared with the experimental group. On the whole, patients scored somewhat better than normals but their scores fell within the range of responses found in the normal group.     

双眼相位整合平衡点检测在单眼弱视患者眼间抑制定量评估中的应用

目的采用双眼相位整合的测量范式定量评估单眼弱视患者的眼间抑制情况,并探讨患者眼间抑制度与其他视功能的相关性。方法前瞻性临床对照研究。收集在安徽医科大学第一附属医院眼科门诊就诊的未治疗过的单眼弱视患者51例,正常对照者25例,采用计算机程序呈现的双眼整合的测量范式进行双眼相位整合平衡点检测,比较单眼弱视患者和正常对照者双眼平衡点的差异,并将弱视患者检测结果与弱视眼视力、立体视锐度及屈光参差程度进行相关性分析。结果弱视组双眼平衡点（BP）值为0.227±0.016,正常对照组BP值为0.984±0.020,两组间差异有统计学意义（t=27.316,P<0.01）;弱视眼视力（r=-0.339,P<0.05）、立体视功能（Titmus：r=-0.421,P<0.01;RDS：r=-0.548,P<0.01;Fishy：r=-0.553,P<0.01）与BP值之间均存在显著的相关关系,屈光参差程度与BP值之间无明显相关性（r=-0.086,P>0.05）。结论双眼相位整合平衡点检测可定量评估弱视患者弱视眼的受抑制程度,有一定的临床应用前景。     

Binocular interactions in normal and anomalous binocular vision

Binocular interactions for grating patterns were investigated in humans with normal binocular vision and in humans with abnormal binocular visual experience due to strabismus and/or amblyopia via 1) comparison of monocular and binocular contrast thresholds; 2) interocular transfer of the threshold elevation aftereffect; and 3) dichoptic masking. Whereas the normal observers showed improved binocular over monocular contrast sensitivity (i.e., binocular summation) and substantial interocular transfer of the threshold elevation aftereffect, the abnormal observers showed an absence of binocular summation and no significant interocular transfer. The dichoptic masking experiments showed that a suprathreshold masking grating presented to one eye elevated the contrast threshold for gratings presented to the fellow eye, within a narrow range of spatial frequencies (about 1 octave wide at half height) and orientations, centered about the spatial frequency and orientation of the mask. The magnitude and bandwidth of this masking effect was similar in subjects with normal and abnormal binocular vision, occurring even when the masking grating was presented to the amblyopic eye. These effects depend upon the contrast of the masking grating. In individuals with normal binocular vision, a grating with subthreshold contrast presented to one eye reduces the contrast threshold for detection of gratings of similar spatial frequency and orientation presented to the fellow eye. No such subthreshold summation is evident in the amblyopic observers. We conclude that while strabismus and/or amblyopia disrupted the normal excitatory interactions between the two eyes, cortical inhibitory binocular connections were not disrupted.