动态随机点立体图视差诱发电位的研究

目的从电生理学角度探讨立体视的机制,为客观检测立体视提供参数。方法由微机产生动态随机点立体图刺激,记录30名近距离立体视健康成年人4′-150′不同大小交叉和非交叉引起的视差诱发电位（disparity evoked potential,DEP）。结果（1）不同视差的DEP均为宽大负正波;（2）45′交叉视差DEP的N波潜伏时最长,150′的N波潜伏时最短;4′和30′非交叉视差DEP的N波潜伏时最长,124′的N波潜伏时最短;（3）交叉视差DEP的P波振幅高峰出现在23′、60′及150′,非交叉视差DEP出现在15′、45′及72′;（4）各视差DEP的N波潜伏时、P波振幅的非交叉视差变化曲线较交叉视差整体性左移;小视差的交差视差与非交差视差DEP的N波潜伏时演变规律不同。结论DEP的N波潜伏时、P波振幅能够为客观检测立体视提供参数;立体视宜分为精细交叉与精细非交叉、粗略交叉与粗略非交叉立体视。（中华眼科杂志,2006,42：878-882）     

间歇性外斜视患者交叉视差和非交叉视差的临床观察

目的　了解间歇性外斜视患者交叉视差和非交叉视差的临床变化。方法　对 5 5例间歇性外斜视患者 ,术前应用颜少明的《立体视觉检查图》检测其近零视差、交叉视差及非交叉视差 ,并根据检测情况分为 3组进行分析。结果　第 1组 2 5例 ,近零视差立体视锐度正常者占 4 8 0 % ,其交叉视差和非交叉视差立体感知度检测值均不在正常范围 ,交叉视差者的立体感知度检测值比非交叉视差者大 ,差异有显著意义 (t =84 3 5 ,P <0 0 0 0 1)。第 2组 2 6例 ,近零视差立体视锐度正常者占30 8% ,其交叉视差立体感知度检测值不在正常范围 ,未见有非交叉视差者。第 3组 4例 ,为仅查到不正常的近零视差立体视锐度者。 5 5例中 ,无近零视差仅和非交叉视差共存者 ,也无交叉视差和非交叉视差各自独立存在者 ,亦无交叉视差和非交叉视差两者共存者。结论　 (1)本组间歇性外斜视患者近零视差立体视锐度及交叉视差和非交叉视差立体感知度不健全 ;(2 )间歇性外斜视患者视差的损害顺序依次为非交叉视差、交叉视差、近零视差。 (3)双眼黄斑颞侧视网膜对应的是交叉视差 ,双眼黄斑鼻侧视网膜对应的是非交叉视差     

间歇性外斜视手术前后交叉视差和非交叉视差立体视觉的临床研究

目的探讨间歇性外斜视患者手术前后近零视差、交叉视差及非交叉视差的临床变化规律。方法将100例间歇性外斜视患者分为4组,使用立体视觉检查图检测手术前后的近零视差、交叉视差及非交叉视差,使用同视机测定远融合范围和远立体视,分析、比较检查结果。结果在全部患者中,手术前后均无近零视差仅与非交叉视差共存者和交叉视差仅与非交叉视差共存者,也无交叉视差、非交叉视差独立存在者。4组患者术后近零视差、交叉视差、非交叉视差、远融合范围及远立体视均较术前明显改善,差异有统计学意义（P〈0．01）。手术前后远融合范围4组患者比较,差异均无统计学意义（P〉0．05）。术后远立体视4组患者比较,差异有统计学意义（P〈0．01）,1组和2组患者远立体视的重建均优于3组和4组。结论（1）间歇性外斜视患者近零视差立体视锐度、交叉视差和非交叉视差立体感知度不健全,损伤次序依次为非交叉视差、交叉视差、近零视差,重建顺序与之相反。（2）非交叉视差立体感知度严重受损或消失,也应视为间歇性外斜视的手术指征,此时应立即进行手术治疗,以利双眼视功能的重建。     

Detection threshold differences to crossed and uncrossed disparities

Using a sample of 85 subjects measurements were made of minimum stimulus durations necessary for detection of crossed and uncrossed disparity stimuli which were presented in five positions in the visual field: centre, lower, upper, right, and left field. The results indicated large detection duration differences between the two disparity conditions, with a marked superiority for crossed disparity detection at all positions. A left-right visual field anisotropy was demonstrated for crossed disparity stimuli.     

Effect of recipient-donor trephine size disparity on refractive error in keratoconus

A retrospective study was performed to evaluate the effect of recipient-donor trephine disparity on refractive error and corneal curvature post-suture removal in keratoconus. A double running suture technique was used and donor corneas were trephined from the endothelial side. When keratoconus patients with 0.25-mm larger donor than recipient trephines were compared with keratoconus patients with the same size recipient and donor trephines, a statistically significant increase in the mean keratometer value (45.4 and 43.8 diopters [D], respectively; P = 0.03) and increase in myopic spherical equivalent (-3.5 and -1.8 D, respectively; P = 0.03) was found. When keratoconus patients were compared with phakic Fuchs' dystrophy patients (both groups had 0.25-mm oversize donor trephines), the keratoconus group had a statistically significantly higher myopic spherical equivalent (-3.5 and -1.4 D, respectively; P = 0.03) despite only a 0.7-D difference in mean keratometer value which was not statistically significant (45.4 and 44.7 D, respectively). This study supports the hypothesis that the degree of post-penetrating keratoplasty myopia in patients with keratoconus can be decreased by reducing recipient-donor trephine disparity.     

Occlusion contributes to temporal processing differences between crossed and uncrossed stereopsis in random-dot displays.

Stereoscopic depth discrimination was investigated in crossed and uncrossed directions using stimuli defined by binocular disparity differences embedded in dynamic random-dot stereograms. Across three experiments, fixation was directed to a point on the display screen (which placed crossed stimuli in front of and uncrossed stimuli behind, the background dots of the stereogram), to a point in front of the display screen (which placed both crossed and uncrossed stimuli in front of the background dots), and to a point behind the display screen (which placed both crossed and uncrossed stimuli behind the background dots). Results showed that depth discrimination was always good when the stimuli appeared in front of the background dots of the stereogram, whereas discrimination was always poor when the stimuli appeared behind the background dots. These results suggest that differences between crossed and uncrossed stereopsis as reported in past research arose, in part, from effects related to occlusion.     

Stereoacuity development for crossed and uncrossed disparities in human infants

The development of stereoacuity for crossed and uncrossed disparities was assessed by means of a preferential looking procedure in a cross-sectional sample of infants aged 2-12 months and by following a longitudinal sample over the first 8 months of life. Crossed stereoacuity was found to develop earlier but at approximately the same rate as uncrossed stereoacuity. These data are consistent with the hypothesis that there exist two binocular mechanisms, one subserving disparity detection and one for uncrossed disparity detection.     

Binocular disparity in visual evoked responses. Clinical evidence in normal and stereoblind subjects

The authors have utilized a binocular flat or stereoscopic pattern (grating) to record visual evoked responses (VER) in normal and strabismic subjects. The aim was to find an electrophysiological correlate with the degree of binocular interaction in these subjects. The perception of the grating as tridimensional or flat derived from the disparity obtained with Polaroid filters placed in front of the eyes. In normal subjects, the results demonstrated a significant increase of VER amplitude during tridimensional perception of the pattern. In strabismic subjects the electrophysiological response was not correlated with the binocular conditions.     

Absolute stereoscopic thresholds as measured by crossed and uncrossed disparities

Stereoscopic tests of 30 subjects by means of diastereo instruments showed a lower threshold for crossed disparities than for uncrossed disparities. These findings support Richards' conclusion that crossed and uncrossed disparity limits are the result of two different mechanisms.     

Visual evoked cortical potential can be used to differentiate between uncorrected refractive error and macular disorders

The visual evoked cortical potential (VECP) is widely used to verify complaints of reduced visual performance and to identify the site of the disorder. In this study, we investigated the correlation between reduced visual acuity and VECP in volunteers with normal corrected visual acuity and in patients suffering from inherited macular degeneration or from age related macular degeneration (ARMD). Flash evoked VECP was not affected by the visual acuity in the cases of refractive error and in ARMD patients but was reduced in amplitude and delayed in implicit time in the patients suffering from inherited macular degeneration. The VECP elicited by pattern reversal checkerboard (PVECP) was not affected by the quality of the visual image in volunteers with uncorrected refractive error when checks of 60 or larger were used but were considerably reduced in size and prolonged in implicit time for checks smaller than 15. In both groups of patients suffering from macular dysfunction, pattern reversal VECP was very subnormal and was characterized by prolonged implicit time compared to values expected from their visual acuity. These findings indicate that the PVECP does not directly correlate with visual acuity but rather with foveal function. Therefore, we suggest that recordings of PVECP can be used to differentiate between refractive error and macular disorders as causing reduction in visual acuity when other clinical signs are missing or not available.     

Monocular deprivation in kittens differently affects crossed and uncrossed visual pathways

The effects of monocular deprivation (MD) on the crossed and uncrossed visual projections were studied using both electrophysiological and behavioural criteria. Our results show that Visual Evoked Potentials (VEPs) from the deprived eye (DE) in response to contrast reversing gratings are more reduced in the ipsilateral than in the contralateral cortex. This suggests a different sensitivity of the crossed and uncrossed visual pathways to MD. In the behavioural experiments comparable findings were obtained.     

Myopia and refractive error in dogs.

The refractive error of 240 phakic dogs of various breeds was measured using streak retinoscopy and averaged (-0.27 +/- 1.41 D relative to infinity). Analysis by breed showed that the German Shepherd, Rottweiler, and Miniature Schnauzer breeds had an increased prevalence of myopia with an average refractive error of -0.86 +/- 1.31 D, -1.77 +/- 1.84 D, and -0.66 +/- 1.05 D, respectively. Myopia also was found in older dogs with marked nuclear sclerosis of the crystalline lens. Fifty-three percent of all German Shepherd dogs in a veterinary clinic population (n = 58 eyes) had a myopic refraction of greater than or equal to -0.50 D; 64% of all Rottweiler dogs (n = 28 eyes) were myopic. An in-depth investigation of German Shepherd dogs, using A-scan ultrasonography, photokeratoscopy, and streak retinoscopy, was done at Guide Dogs for the Blind (San Rafael, CA). By contrast with the results obtained in the veterinary clinic population, the overall average refractive error of guide dog German Shepherd dogs (n = 106 eyes) was +0.19 +/- 0.81 D, and only 15% of these dogs were myopic. The axial length and corneal curvature of myopic eyes did not differ significantly from nonmyopic eyes.     

Optic nerve crescents and refractive error.

In this paper we discuss whether the presence of an optic nerve crescent might affect the way in which axial length and corneal curvature interact to determine refractive error. Subjective refraction, keratometry, measurement of body height, axial length of the eye, and stereophotography of the optic nerves were performed on 224 subjects, 8- to 25-years-old. Photographs were examined under magnification; optic nerve crescents, if present, were measured in the horizontal dimension. Those measurements were then corrected for magnification due to the eye and the camera. Logistic regression analysis suggested that male gender and myopic refractive error were most directly associated with the presence of a large crescent, whereas axial length, age, and horizontal keratometry reading were less directly associated with the presence of a crescent. The relation between axial length and refractive error differed among those with large crescents compared to those with small or no crescents. Simple regression showed that, for those with a crescent at least 0.2-mm wide, a 1-mm greater axial length was associated with, on the average, 1.26 D of myopia. For those with smaller or no crescents, a 1-mm greater axial length was associated with only 0.66 D of myopia. This difference was statistically significant at the 0.02 level of confidence.     

Model of human refractive error development.

PURPOSE: To construct a model of refractive error development that can account for the different interactive mechanisms and time courses of refractive error in the hyperope (HYP), emmetrope (EMM), early-onset myope (EOM), and late-onset myope (LOM) over the first 30 years of life. METHODS: First, a baseline short-term (1 mo.) simulation of a previously developed nearwork-induced transient myopia (NITM) model was performed under both far- and near-viewing paradigms to obtain the critical relationships between AErms and refractive error for the four refractive groups. Then, two control pathways were added to the NITM model. The genetically-controlled pathway was associated with the long-term growth of the cornea, lens, and the eyeball. The environmentally-controlled pathway was associated with retinal-defocus during nearwork, wherein the root mean square (rms) of the accommodative error (AE) above a threshold level resulted in an increase in axial length of the eyeball. The thresholds for defocus-induced axial length change were empirically determined to correspond to the differential susceptibility in the four refractive groups. The combination of effects from the two pathways produced the overall refractive error. The relationship between AErms and refractive error was combined with the two control pathways for the long-term simulations (30 yrs: the initial 15 yrs using a far-viewing paradigm followed by an additional 15 yrs using a near-viewing paradigm) to quantify refractive error development as related to daily nearwork activity in the four refractive groups. RESULTS: All refractive groups began early in life with a genetically-determined hyperopic refractive error. The HYP had the lowest susceptibility or highest threshold to retinal defocus effects, and remained at a hyperopic level. The EMM exhibited a relative myopic shift in the first 2 years to become and remain at emmetropia. In the myopic groups, the EOM exhibited both a genetically-controlled component (starting 2 years of age) and a defocus-induced component (starting at 15 years of age), whereas the LOM manifested only a defocus-induced factor (starting at 15 years of age) in the development of myopia. In addition, simulations indicated that emmetropization occurred only for "induced" refractive error that was less than 0.5 D, which was consistent with the non-monotonic relationship between AErms and refractive error, wherein the minimum AErms occurred at 0.5 D. CONCLUSIONS: The model showed that both genetic and defocus-induced environmental factors play important roles in the development of refractive error in the different refractive groups. The model also provides a framework for further detailed quantitative analysis of the processes of refractive error development and emmetropization.     

屈光不正者的视差诱发电位检测

目的 应用视差诱发电位检查探讨屈光不正对立体视功能的影响及其机制。方法 用新型静态随机点立体图深度翻转作视刺激，对21名屈光不正者（屈光度>±0.75D，≤±8.00D）和40名正常人进行视差诱发电位检测。 结果 在不同视差刺激时屈光不正者与正常人一样均可记录到与立体刺激相关的宽大正波（即P₂₅₀波）；随视差的增大P₂₅₀波形和振幅发生相应的变化，变化的特征与正常人相类似；近视与远视者的视差诱发电位P₂₅₀波振幅和潜伏时无明显差别。 结论 在一定屈光范围内的屈光不正经完全矫正后对立体视功能没有明显的影响。 (中华眼底病杂志,1998,14:225-227)     

Corneal asphericity and refractive error

The relationship between corneal curvature measured by classical keratometry and refractive error raises the question of a possible systematic relationship between refractive error and the degree of corneal asphericity. A recomputation and analysis of previously published data leads to the conclusion that the different refractive groups have similar values of the parameter 'p' and differ only in the apical radius of the cornea.     

Near retinoscopy and refractive error

Tonic accommodation (TA) was measured in 100 optometry students using near retinoscopy. Subjects were divided into three refractive groups comprising 42 myopes, 48 emmetropes and 10 hyperopes. The myopic group was found to have the lowest values of TA (mean = 0.47 D; s.d. = 0.38 D), the hyperopes the highest (mean = 0.89 D; s.d. = 0.50 D) and the emmetropes intermediate values (mean = 0.65 D; s.d. = 0.42 D). No significant difference was found between subjects exhibiting myopia which was early in onset (prior to the age of 15 years) and those exhibiting late-onset myopia (after the age of 15 years). The results are discussed with respect to theories of refractive error development.