A comparison of the suitability of cathode ray tube (CRT) and liquid crystal display (LCD) monitors as visual stimulators in mfERG diagnostics

The aim of this study was to determine up to which extent the specific characteristics of cathode ray tube (CRT) and liquid crystal display (LCD) monitors influence the retinal biosignal when used as stimulators in ocular electrophysiology. In a conventional CRT monitor, each pixel lights up only for a duration of a few milliseconds during each frame. In contrast, liquid crystal displays are quasi-static, i.e. each pixel has a constant luminance during the whole length of the frame, but lights up only with a certain delay after the trigger. These different display characteristics may affect the mfERG signal. The temporal and spatial luminance distributions of a CRT and an LCD monitor were measured in white flashes. The total amount of emitted light was calculated by integration of the intensity versus time curves. By means of an mfERG recording system (RETIsystem, Roland Consult, Brandenburg, Germany) first-order kernel (FOK) mfERG signals were computed and then analysed using customized MATLAB (TheMathWorks, Natick, MA, USA) software. With the two stimulator monitors, differences in the mfERG signal were observed. The latencies of mfERG responses recorded with the LCD monitor were significantly increased by 7.1 ms for N1 and 9.5 ms for P1 compared to the CRT. Due to a higher luminance, the N1 amplitude was significantly higher by approx. 2 dB in measurements with the LCD monitor while no significant difference could be detected with regard to the more contrast sensitive P1 amplitude. When using LCD monitors as stimulators the increase in latencies and differences in the luminance versus time profile must be taken into account. Prior to clinical application, the establishment of guidelines for the use of LCD monitors is recommended.     

Effect of biological factors on latency of pattern-reversal visual evoked potentials associated with cathode ray tubes and liquid crystal display monitors in normal young subjects

Documenta Ophthalmologica - Owing to several factors, peak latencies of pattern-reversal visual evoked potentials (p-VEP) are delayed when viewing liquid crystal display (LCD) monitors compared to...     

Comparison of pattern VEP results acquired using CRT and TFT stimulators in the clinical practice

There are several electrophysiological systems available commercially. Usually, control groups are required to compare their results, due to the differences between display types. Our aim was to examine the differences between CRT and LCD/TFT stimulators used in pattern VEP responses performed according to the ISCEV standards. We also aimed to check different contrast values toward thresholds. In order to obtain more precise results, we intended to measure the intensity and temporal response characteristics of the monitors with photometric methods. To record VEP signals, a Roland RetiPort electrophysiological system was used. The pattern VEP tests were carried out according to ISCEV protocols on a CRT and a TFT monitor consecutively. Achromatic checkerboard pattern was used at three different contrast levels (maximal, 75, 25%) using 1° and 15′ check sizes. Both CRT and TFT displays were luminance and contrast matched, according to the gamma functions based on measurements at several DAC values. Monitor-specific luminance parameters were measured by means of spectroradiometric instruments. Temporal differences between the displays’ electronic and radiometric signals were measured with a device specifically built for the purpose. We tested six healthy control subjects with visual acuity of at least 20/20. The tests were performed on each subject three times on different days. We found significant temporal differences between the CRT and the LCD monitors at all contrast levels and spatial frequencies. In average, the latency times were 9.0 ms (±3.3 ms) longer with the TFT stimulator. This value is in accordance with the average of the measured TFT input–output temporal difference values (10.1 ± 2.2 ms). According to our findings, measuring the temporal parameters of the TFT monitor with an adequately calibrated measurement setup and correcting the VEP data with the resulting values, the VEP signals obtained with different display types can be transformed to be comparable.     

屈光参差性弱视多焦图形视觉诱发电位与传统图形视觉诱发电位的比较

目的了解多焦图形视觉诱发电位(visualevokedpotential,VEP)的特征及其检测方法在弱视临床中的应用价值。方法我们对20例屈光参差性弱视患者用德国罗兰公司生产的电生理仪检测了多焦图形VEP,并同时检测传统图形VEP,以其对侧正常眼为对照组,分析图形VEPP1波的振幅和潜时,分析多焦图形VEP1～5环及四个象限P1波的振幅密度值、振幅均值、潜时。将各数值用SPSS10.0统计软件进行统计学处理。结果弱视眼传统图形VEP与正常组比较,其P1波潜时延长(P<0.01),振幅下降,幅度近50%(P<0.01)。弱视眼多焦图形VEP检查结果与正常对照组比较,1环的振幅密度值、振幅均值均明显下降,下降幅度近50%(P<0.01),潜时延长(P<0.01)。2环的振幅密度值下降(P<0.05),振幅均值及潜时两组间差异无显著性(P>0.05)。3、4、5环及鼻上、鼻下、颞上、颞下四个象限的各数值两组间差异无显著性(P>0.05)。结论多焦图形VEP虽然可以详细分析弱视眼在视野各部位的特征,但其波形不够稳定,必须取得患者很好的配合,保持良好固视,否则很难得到与视网膜相对应的点对点的检测结果。这都有待于我们对检测方法、刺激参数等进行进一步研究探讨。传统图形VEP检查时间短,波形稳定,重复性好,患者易于配合,特别是对于儿童患者,目前其仍是一种不可替代的检测方法。     

Normative ranges and specificity of the multifocal VEP

Purpose: To describe a normative database for the multifocal VEP (mfVEP) and to evaluate specificity for a range of cluster criteria. Methods: One hundred persons (62 females and 38 males) with normal visual fields and ranging in age from 21.6 to 92.4 years participated in this study. Self-reported race in 80 of these 100 persons was `White or Caucasian,' eight were `Black or African-American,' eight were `Asian,' and four were `Hispanic or Latino.' Pattern-reversal mfVEPs were obtained using a dartboard stimulus pattern in VERIS^TM and two 8-min runs per eye were averaged. A bootstrap technique was used to estimate the normal range of mfVEP response signal-to-noise ratio (SNR) and inter-ocular amplitude ratio at each location. Specificity (1 – false alarm rate) was evaluated for a range of cluster criteria, whereby the number and probability level of the points defining a cluster were varied. Results: There was no overall effect of age on SNR (r ²=0.16, p=0.22) nor was the interaction between age and location significant (F=0.83, p=0.82, ANOVA). The location with the largest age effect had an r ² of only 0.13. There was a small but significant effect of sex (t=2.1, p=0.04) such that SNR was slightly (11) larger in females than males, but there was no significant interaction between sex and age (t=0.82, p=0.41). There was a slight trend toward higher SNR in the Asian group and lower SNR in the African-American group, but the overall effect of race was not significant (F=1.99, p=0.12). Specificity depended on the number and probability level of the points defining a cluster. Specificity did not vary by age group in a simple monotonic manner. False positive rates were slightly higher in females than males, and slightly higher in the African-American group as compared with the Asian group. Conclusions: Excellent specificity can be achieved for the mfVEP by using particular cluster criteria for monocular and inter-ocular tests. The effects of age, sex, and race were all very small and only the effect of sex was statistically significant. This normative database can be used for analyses of mfVEP results from individual patients with little risk that demographic factors such as age and sex will confound diagnostic accuracy.     

Repeatability of normal multifocal VEP: implications for detecting progression

PURPOSE: To assess the repeatability of the multifocal visual evoked potential (mfVEP) and to compare it with the repeatability of standard automated perimetry (SAP) in the same group of 50 normal controls retested after 1 year. Our second aim was to assess the repeatability of false alarm rates determined previously for the mfVEP using various cluster criteria. METHODS: Fifty individuals with normal vision participated in this study (33 females and 17 males). The age range was 26.7 to 77.9 years and the group average age (+/- SD) was 51.4 (+/- 12.1) years. Pattern-reversal mfVEPs were obtained using a dartboard stimulus pattern in VERIS and two 8-minute runs per eye were averaged. The average number of days between the first and second mfVEP tests was 378 (+/- 58). SAP visual fields were obtained within 17.4 (+/- 20.3) days of the mfVEP using the SITA-standard threshold algorithm. Repeatability of mfVEPs and SAP total deviation values were evaluated by calculating point-wise limits of agreement (LOA). Specificity (1-false alarm rate) was evaluated for a range of cluster criteria, whereby the number and probability level of the points defining a cluster were varied. RESULTS: Point-wise LOA for the mfVEP signal-to-noise ratio (SNR) ranged from 2.0 to 4.3 dB, with an average of 2.9 dB across all 60 locations. For SAP, LOA ranged from 2.4 to 8.9 dB, with an average of 4.0 dB (excluding the points immediately above and below the blind spot). Clusters of abnormal points were not likely to repeat on either mfVEP or SAP. When an mfVEP abnormality was defined as the repeat presence (confirmation) of a 3-point (P < 0.05) cluster anywhere within a single hemifield, only 1 (of 200) monocular hemifield was deemed abnormal. Although the LOA of the mfVEP were similar throughout the field, the limited dynamic range of SNR at superior field locations will limit the ability to follow progression in "depth" at those locations. CONCLUSIONS: Repeatability of the mfVEP was slightly better than SAP visual fields in this group of controls with a 1-year retest interval. This suggests that progression in early stages should be more easily detectable by mfVEP. However, in certain field locations (eg, superior periphery), the relatively more narrow dynamic range of the SNR of the mfVEP may limit detection of progression to just 1 event. Confirmation of a 3-point cluster abnormality is highly suggestive of a true defect on the mfVEP.     

斜视性弱视多焦VEP与多焦ERG的对比研究

目的对比研究斜视性弱视患者多焦视觉诱发电位(multifoeal VEP)及多焦视网膜电图(mERG)的特征性变化，探讨弱视发病的可能机制。方法采用VERIS Science^TM4．2多焦电生理系统记录并比较正常组30例、斜视性弱视患者20例各眼mVEP及mERG。结果弱视眼不同视网膜区域mVEP、mERG的特征峰反应振幅密度都较对侧眼和正常眼明显降低，mVEP的特征峰潜时延长。弱视眼mVEP、mERG波形异常程度随离心度增加而减小，mVEP波形异常程度大于mERG，且与弱视眼的视力异常程度有相关性。结论斜视性弱视患者的mVEP和mERG具有明显的特征性改变，表明弱视患者的视网膜、视皮层都存在明显损害。     

屈光参差性弱视mfVEP的临床分析

目的分析屈光参差性弱视患者多焦视觉诱发电位(mfVEP)的特征性变化,以探讨弱视发病的可能机制。方法采用VERISScienceTM4.2多焦电生理系统对23例屈光参差性弱视患者、30例正常人进行双眼图形mfVEP检查,以潜伏期与振幅为分析指标,进行了屈光参差性弱视眼、对侧眼和正常对照三组mfVEP的对比研究。结果在六个离心度上弱视眼反应振幅密度较其对侧眼和正常眼均显著降低,潜伏期延长。弱视眼波形异常程度随离心度增加而减小,在六个离心度上弱视眼mfVEP的波形异常程度都与弱视眼的视力异常程度有相关性。结论屈光参差性弱视患者的mfVEP具有明显的特征性改变,表明弱视患者的视觉传导通路存在明显损害,在中心区损害重于周边区,弱视眼波形异常程度与视力异常程度有明显的相关性,mfVEP检查对于弱视的诊断、治疗和预后判断具有一定的指导意义。     

应用眼动仪评价观看线偏光液晶电视与圆偏光液晶电视诱导的视疲劳研究

目的 探讨应用眼动仪评价观看两种偏振光液晶电视对人眼视觉舒适度影响的差异。设计 实验研究。研究对象 屈光状态为正视眼的健康受试者60例。方法 受试者随机分两组,分别观看线偏振光液晶电视显示的视频内容（线偏组,30例）和圆偏振光液晶电视显示的视频内容（圆偏组,30例）。记录受试者在观看两种偏振光液晶电视视频时的眨眼频率、眨眼持续时间的变化。主要指标 眼动仪记录观看视频中的眨眼频率和眨眼持续时间。结果 两组受试者随观看时间延长,眨眼频率均呈现先下降再上升的趋势。在观看视频的初期时段,线偏组眨眼频率从初始时15.83次/分降至13.95次/分,圆偏组从初始时13.93次/分降至11.46次/分。随观看时间延长,两组眨眼频率均增加,观看末期时段,线偏组眨眼频率22.63次/分,圆偏组16.33次/分。线偏组与圆偏组眨眼持续时间初始阶段为2272毫秒/分、2001毫秒/分,结束时段为4084毫秒/分、2596毫秒/分。线偏组与圆偏组的眨眼频率、眨眼持续时间在观看视频前后的差值比较（P=0.030、0.031）,线偏组的眨眼频率、眨眼持续时间变化较圆偏组显著。 结论 观看两种偏振光电视视频内容后受试者的眨眼频率和眨眼持续时间均较观看前有所增加,观看圆偏光液晶电视时诱导的视疲劳较观看线偏光液晶电视的视疲劳程度略轻。（眼科,2016,25： 63-67）     

Liquid crystal display screens as stimulators for visually evoked potentials: flash effect due to delay in luminance changes

Purpose

The cathode-ray tube (CRT) screen has recently been replaced by liquid crystal display (LCD) screens as visual stimulators for pattern-reversal visually evoked potentials (p-VEPs). The aim of the study was to evaluate the usefulness of LCD screen to elicit p-VEPs.

Methods

The waveforms of the p-VEPs elicited by a LCD panel were compared with those elicited by a conventional CRT screen. The changes in the luminance of each screen were measured with a photodiode, and the mean luminance change was measured with a luminance meter. VEPs and electroretinograms (ERGs) were also recorded when the monitor was covered by a diffuser.

Results

The p-VEPs elicited by the LCD consisted of the N75 and P100 components of the conventional VEPs and had good reproducibility. The average latency of these components was significantly delayed by 9.8 ms for N75 and 10.2 ms for P100, and the N75-P100 amplitude was significantly larger than the conventional p-VEP elicited by the CRT screen. During the reversal phase, especially from black-to-white, the luminance of the LCD screen was transiently reduced, and it elicited a flash VEP and ERG. A reduction in the contrast of the checks minimized the transient change in the luminance, and the VEP waveform was more similar to that elicited by the CRT screen.

Conclusions

The results suggest that when an LCD monitor is used as an alternative visual stimulator to elicit p-VEPs, the delay in the luminance change and the flash effect needs to be taken into account.     

中国人单通道多焦视诱发电位的可重复性研究

目的：探讨单通道多焦视诱发电位（mVEP)在中国人应用的可重复性。方法：应用VERIS多焦电生理系统对7例受试者在非同一日记录单通道图形mVEP，刺激图案为60个扇面组成与大脑皮质成比例的飞镖盘样图形。用PhotoShop软件将mVEP曲线叠合分析mVEP波形的一致性，并用VERIS软件定量测量mVEP曲线主要波形的潜伏期，峰－谷振幅，数据采用Excel软件进行统计学分析，结果：受试者自身不同时间的2－7次检查得出的mVEP波形的叠合程度高，潜伏期变异系数（CV）小于10％，但振幅有一定程度的变异，60个位点曲线振幅的平均CV左、右眼分别为36％、37％、象限平均反应曲线的振幅CV分别为19％、21％、26％、27％，上、下半野平均反应曲线的振幅CV分别为13％和11％，结论：单通道mVEP多位点反应波形的可重复性良好，但振幅存在一定程度的变异，当刺激与记录条件一致时，mVEP尤其是象限与半野平均反应可用于视神经损害的随访研究。     

Optimizing electrode positions and analysis strategies for multifocal VEP recordings by ROC analysis

The multifocal visual evoked potential (mfVEP) is an important tool to test visual pathway function. The aim of this study was to optimize electrode positions in mfVEP recordings. For analysis we applied a receiver operating characteristic (ROC), a method that inherently corrects for multiple testing. We found that a combination of two perpendicular derivations-both straddling the inion-was the most effective recording setup. Adding more than two derivations did not significantly increase the sensitivity. Thus optimal mfVEP detection can be achieved with a fairly simple recording setup which may facilitate mfVEP recordings in basic research and clinical routine.     

Simultaneous recording of multifocal VEP responses to short-wavelength and achromatic stimuli

A paradigm is introduced that allows for simultaneous recording of the pattern-onset multifocal visual evoked potentials (mfVEP) to both short-wavelength (SW) and achromatic (A) stimuli. There were 5 sets of stimulus conditions, each of which is defined by two semi-concurrently presented stimuli, A64/SW (a 64% contrast achromatic stimulus and a short-wavelength stimulus), A64/A8 (64% achromatic/8% achromatic), A0/A8 (0% (gray) achromatic/8% achromatic), A64/A0 and A0/SW. When paired with A64 as part of A64/SW, the SW stimulus yielded mfVEP responses (SWmfVEP) with diminished amplitude in the fovea, consistent with the known sensitivity of the S-cone system. In addition, when A8, which is approximately equal to the L and M cone contribution of the SW stimulus, was recorded alone, the response to A8 was small, but significantly larger than noise. However, when A8 was paired with A64, the response to A8 was reduced to close to noise level, suggesting that the LM cone contribution of the SWmfVEP can be suppressed by A64. When A64 was recorded alone, the response to A64 was about 32% larger than the mfVEP for A64 when paired with the SW. Likewise, the presence of A64 stimulus also reduces the response of SWmfVEP by 35%. Finally, an intense narrow-band yellow background prolonged the latency of SW response for the A0/SW stimulus but not the latency of SW response for the A64/SW stimulus. These results indicate that it is possible to simultaneously record an SWmfVEP with little LM cone contribution along with an achromatic mfVEP.     

Full-field ERG, multifocal ERG and multifocal VEP in patients with retinitis pigmentosa and residual central visual fields

PURPOSE: To evaluate (with three different electrophysiological methods) the residual retinal function in a selected group of patients with retinitis pigmentosa and remaining small central visual fields. METHODS: Fourteen patients from several different genetic subgroups, who had been followed with visual acuity and visual field testing for periods up to 32 years, were examined. Ophthalmological examination included full-field electroretinography (ERG), multifocal electroretinography (mfERG) and multifocal visual evoked potential (mfVEP). RESULTS: The ERGs were severely reduced in all patients. The mfERGs demonstrated the residual central retinal function in five of the patients. The mfVEPs showed measurable amplitudes centrally in most of the patients. The follow-up examinations demonstrated the slowly progressive course of the disease with preservation or only slight further loss of visual fields over a period of 7-32 years. CONCLUSION: Patients with retinitis pigmentosa may not always follow the typical natural course with progressive loss of visual fields, which may in some patients remain unaffected over several decades. Multifocal ERG and mfVEP may be clinically useful for evaluating remaining visual function in these patients.     

Diagnostic value of multifocal VEP using cross-validation and noise reduction in glaucoma research

Background The diagnostic value of multifocal visual evoked potentials (mf VEP) in glaucoma research is still under debate. Several previous studies proclaim it to be a useful tool for clinical applications, but according to other studies, different problems (low specificity, poor records, and interindividual variation) still retard its clinical use. The aim of the present study was to examine whether the mf VEP data obtained with the RETIscan system are appropriate for formulating a classification rule for glaucoma.Method We examined and evaluated 65 eyes in 38 advanced glaucoma patients and 27 normal subjects, using four occipital gold cup electrodes (cross layout) for bipolar recording and a CRT monitor (display diameter 60 °, chequerboard pattern reversal, 60 segments in dartboard layout) for stimulation. In each case, eight cumulative measurements (77 s each) were made. The data of the 60 segments were cross-correlated with a RETIscan-internal VEP norm (VEP finder), combined in 16 sectors, and evaluated via the classification technique double-bagging and the Wilcoxon U-test.Results In three out of the 16 sectors, the VEP amplitudes of the patients were significantly reduced (Wilcoxon U-test). Applying double-bagging on the cross-correlated data (with VEP finder) resulted in a sensitivity of 75% and a specificity of 71%, and the estimated misclassification rate was 27%. For uncorrelated data (without VEP finder), the same analysis achieved a sensitivity of about 60% and a specificity of 40%.Conclusions Estimated sensitivity and specificity suggest that by using the RETIscan system for recording, a classification of the VEP data—i.e. a separation between normal and glaucoma subjects—is possible.     

A signal-to-noise analysis of multifocal VEP responses: an objective definition for poor records

Sixty local VEP records, called the multifocal VEP (mfVEP), can be obtained over a wide retinal area. From subject-to-subject, from day-to-day, and from location-to-location, these records can vary in quality presenting a challenge to quantitative analyses. Here three procedures are described for specifying the quality of mfVEP recordings in terms of signal-to-noise ratios. Monocular mfVEPs were recorded in two, 7-min runs. A 2-run signal-to-noise ratio (2rSNR) was obtained as {[RMS(RunA+RunB)]/[RMS(RunA–RunB)]}–1, where RMS is the root-mean-square amplitude of the response over the period from 45 to 150 ms (signal window). Two noise-window signal-to-noise ratios were obtained with the same numerator as the 2rSNR but with the denominators based upon the RMS of a signal-free window from 325 to 430 ms. In one case, inSNR, the denominator was the RMS of the record's noise window and in the other case, mnSNR, the denominator was the mean of the RMS amplitudes of all the signal-free noise windows for the subject. The SNRs were related to false-positive rates (i.e., detecting a signal when none was present) by recording mfVEPs with some of the sectors of the display occluded. In particular, the outer three rings (36 sectors) of the display were occluded so that only noise was recorded; false-positive rates for different values of SNR were calculated. The 2rSNR had the highest false-positive rate largely due to alpha in the records of some subjects. The mnSNR had a lower false-positive rate than did the inSNR because there was little correlation between the RMS of the noise in the signal-free window and the RMS of the noise within the signal window. Use of the mnSNR is recommended over the 2rSNR, especially where alpha contamination can not be eliminated. Ways to improve the SNR of the records are discussed.     

Comparing multifocal VEP and standard automated perimetry in high-risk ocular hypertension and early glaucoma

PURPOSE: To compare the diagnostic performance of multifocal visual evoked potential (mfVEP) and standard automated perimetry (SAP), in eyes with high-risk ocular hypertension or early glaucoma. METHODS: Both eyes of 185 individuals with high-risk ocular hypertension or early glaucoma were evaluated. Subjects ranged in age from 37 to 87 (mean +/- SD: 61 +/- 11 years). Pattern-reversal mfVEPs were obtained by using VERIS (Electro-Diagnostic Imaging, San Mateo, CA) with a four-electrode array and were analyzed with custom software. SAP visual fields (SITA-standard; Carl Zeiss Meditec, Inc., Dublin, CA) were obtained within 22.3 +/- 27.0 days of the mfVEP. Stereo disc photographs and Heidelberg Retina Tomograph (HRT) images were obtained during one visit, which was within 24.8 +/- 50.4 days of the mfVEP and 33.1 +/- 62.9 days of the SAP visual field. Abnormalities on the mfVEP were defined by using a variety of cluster criteria: SAP with pattern standard deviation (PSD) P 相似文献   

VEP临床应用的经验

用VEP检查了9种病26例患者,报告了其中白内障、视神经疾患、角膜移植术后及心理性弱视等5例。介绍了在屈光间质混浊时的光栅效应、视神经疾患治疗前后的VEP表现、心理性弱视的客观检查与主观检查结果显然不一致等VEP的特点。说明VEP检查法在日常临床工作中确实非常有用。     

Effects of fixation instability on multifocal VEP (mfVEP) responses in amblyopes

The cortical activity of subjects with compromised central vision (e.g., amblyopes) is thought to be much weaker for stimulation of the affected eye than in the fellow eye. Because these subjects are known to exhibit considerable difficulties in keeping steady fixation, we investigated the effects of anomalous fixation on their multifocal visual-evoked potential (mfVEP) responses using a dual Purkinje image (dPi) eye tracker. Our results show that mfVEP responses to stimulation of the central 5 degrees were depressed in the affected eye compared to those in the normal eye and the magnitude of response reductions was proportional to the degree of visual acuity loss in amblyopic subjects. Fixation was far less stable while viewing with the affected eye than with the fellow eye, some exhibiting jerk nystagmus and/or saccadic oscillations. Normal subjects with artificially imposed nystagmus showed similar reductions of VEP responses. The relative magnitudes of the deficits in mfVEP responses were tightly correlated with the degree of fixation instability. These results suggest that the interpretation of anomalous neural or perceptual processing in amblyopic subjects must take the effects of unsteady fixation during measurements into consideration in order to reveal the true nature and extent of sensory neural deficits.     

用瞬目频率评价液晶电视机的偏振光特性对视疲劳的影响

目的 比较液晶电视射出的线偏振光和圆偏振光对视疲劳的影响程度.方法 64例正常人随机分为两组,每组32例,分别观看出射光为线偏振光或圆偏振光的液晶电视机播放的故事片125min.用眼电图(EOG)记录观看故事片前后及观看故事片过程中的瞬目频率,分析比较瞬目频率的变化特性.结果 线偏振光组观看故事片后的瞬目频率比观看前高,差异有统计学意义(P<0.01);圆偏振光组观看故事片前后的瞬目频率差异无统计学意义(P>0.05).结论 长时间观看出射光为线偏振光的液晶电视机较出射光为圆偏振光时易引起视疲劳.