Risk of strabismus and ambylopia in children with hydrocephalus

Objectives The present study was undertaken to determine the risk of strabismus and ambylopia in children who underwent operation for hydrocephalus and to compare our results with those in previous studies. Methods Full orthoptic and ophthalmological examinations, including cycloplegic refraction, were performed in all subjects. Results Ten of 25 patients (40%) were found to have manifest squint. Four of these had esotropia and six had exotropia. No paretic squint or alphabetic pattern strabismus was determined. Refraction measurements revealed amblyogenic refractive errors (significant refractive errors that cause amblyopia) in five of the 25 (20%) patients in this study. Strabismus and the risk of amblyopia were found to be significantly higher in patients who experienced shunt revision than those who had not (P<0.05). Conclusion Amblyopia, strabismus, and other acquired defects in the visual system related to hydrocephalus should be closely monitored and treated when indicated. Regular ophthalmic supervision will provide and help to maintain the best possible standard of vision in children with hydrocephalus.     

Stimulus specificity in spatially-extended interocular suppression

In typical binocular rivalry demonstrations, disparate images presented in corresponding locations to the two eyes are found to alternate perceptually over time. Alternation in perception can occur even if the images presented to the two eyes do not overlap, if they are sufficiently close in space. This implies a spatial spread in the interocular interaction. The current set of experiments explores how the luminance pattern of a target, in relation to a rivalrous suppressor, affects its susceptibility to suppression. It was found that the susceptibility to suppression of a target pattern was nonlinearly related to the amount of luminance variation along the target in the direction perpendicular to the suppressing stimulus. For instance, there was a strong effect of the orientation of the grating pattern within the target on the total time of suppression, with much more suppression for horizontal gratings than vertical gratings when suppressor bars were oriented vertically, regardless of the luminance pattern within the suppressors. Furthermore, it was shown that the inclusion of a spatial gap between the vertical suppressors and the central portion of the target does more than simply change the spatial relationships, it adds new figural information, such as vertically orientated edges in the targets, that modify the susceptibility to suppression of the target, thereby interfering with measurements of spatial interaction functions. All of the results are consistent with selectively suppressing stimulus information that would interfere with stereoscopic matching to aid the binocular fusion of disparate retinal images.     

Factors influencing interocular blur suppression

An Important feauture of monovision correction is the ability of the binocular system to suppress blur from the defocused eye (interocular blur suppression). We conducted a study with three subjects and found that interocular blur suppression improved with higher levels of monocular defocus (addition powers in monovision) but was not affected by the eye defocused (sighting dominant or non-domninant) or by pupil size. The selection and management of monovision patients may be assisted by an understading of the understanding of the underlying suppression preocesses.     

Eye gaze adaptation under interocular suppression

The perception of eye gaze is central to social interaction in that it provides information about another person's goals, intentions, and focus of attention. Direction of gaze has been found to reflexively shift the observer's attention in the corresponding direction, and prolonged exposure to averted eye gaze adapts the visual system, biasing perception of subsequent gaze in the direction opposite to the adapting face. Here, we tested the role of conscious awareness in coding eye gaze directions. To this end, we measured aftereffects induced by adapting faces with different eye gaze directions that were presented during continuous flash suppression, a potent interocular suppression technique. In some trials the adapting face was rendered fully invisible, whereas in others it became partially visible. In Experiment 1, the adapting and test faces were presented in identical sizes and to the same eye. Even fully invisible faces were capable of inducing significant eye gaze aftereffects, although these were smaller than aftereffects from partially visible faces. When the adapting and test faces were shown to different eyes in Experiment 2, significant eye gaze aftereffects were still observed for the fully invisible faces, thus showing interocular transfer. Experiment 3 disrupted the spatial correspondence between adapting and test faces by introducing a size change. Under these conditions, aftereffects were restricted to partially visible adapting faces. These results were replicated in Experiment 4 using a blocked adaptation design. Together, these findings indicate that size-dependent low-level components of eye gaze can be represented without awareness, whereas object-centered higher-level representations of eye gaze directions depend on visual awareness.     

Role of visual cortex in interocular alignment.

The role which the visual cortex plays in the development of interocular alignment in the cat was examined by removing this structure bilaterally in 4 groups of subjects. These included (1) kittens 10 to 14 days of age, (2) 10- to 14-day-old kittens in which one eyelid was sutured shut at the same time, (3) normally reared adult cats, and (4) cats dark-reared until 4 months of age. If the cortex is removed in young kittens, interocular alignment appears to develop normally until the kittens are 60 to 80 days of age. At this time, an abrupt change in alignment resulting in incyclotorsion of the optic axes is observed. If binocular vision is prevented in kittens with neonatal visual cortex lesions by suturing one eyelid shut, convergent strabismus and/or incyclotorsion are frequently observed. This characteristic incyclotorsion does not develop if similar lesions are made in adult cats; no significant alterations of eye alignment occur in these animals even after postoperative survival times of more than 6 months. Incyclotorsion characterizes dark-reared cats when they are first brought into the light, but this diminishes with time and may even be replaced by excyclotorsion after the animals spend a few weeks in the light. If dark-reared cats are decorticated on being brought into the light, these changes are largely prevented. Such animals remain permanently incyclotorted relative to normal cats. The results indicate that the visual cortex plays an important role in the development of torsional alignment of the eyes.     

屈光参差眼屈光度差值与脉络膜厚度和眼轴的相关性研究

目的:研究青少年屈光参差眼屈光度差值与脉络膜厚度差值、眼轴差值的相关性.方法:采用回顾性系列病例研究设计,收集2015-09/2016-05在仙桃市第一人民医院眼科就诊,完成脉络膜厚度测量、眼轴测量及常规屈光检查的屈光参差患者66例.按双眼等效球镜差进行分组:第一组:双眼等效球镜差＜1D,共22例,其中男13例,女9例,年龄7～14岁;第二组:双眼等效球镜差为1 ～2.5D,共22例,其中男12例,女10例,年龄7～ 16岁;第三组:双眼等效球镜差为＜2.5～5.0D,共22例,其中男12例,女10例,年龄7～18岁.结果:三组患者间双眼屈光度差值、眼轴差值、脉络膜厚度差值的差异均具有统计学意义(P＜0.05).三组患者间两两比较,屈光度差值、眼轴差值、脉络膜厚度差值的差异均具有统计学意义(P＜0.05).第一组患者中双眼屈光度差值与眼轴和脉络膜厚度差值,无显著相关关系(r=0.192,P=0.396;r=0.182,P=0.418).第二组患者中双眼屈光度差值与眼轴差值呈正相关关系(r=0.582,P＜0.01);与脉络膜厚度差值呈正相关关系(r=0.658,P＜0.01);第三组患者中双眼屈光度差值与眼轴差值呈正相关关系(r=0.912,P＜0.01);与脉络膜厚度差值呈正相关关系(r=0.967,P＜0.01).三组患者合并分析双眼屈光度差值与眼轴差值呈正相关关系(r=0.965,P＜0.01),与脉络膜厚度差值呈正相关关系(r=0.968,P＜O.01).结论:不同程度屈光参差患者双眼脉络膜厚度都存在明显差异.屈光参差程度越大,脉络膜厚度差异与屈光度差值的相关性更强.     

Infant interocular acuity differences and binocular vision

Monocular acuity, binocular acuity, and stereopsis were assessed with preferential-looking techniques in a sample of 114 normal infants aged 0-11 months in order to examine developmental trends in: (1) interocular differences in acuity, (2) test-retest reliability, (3) the relationship between monocular and binocular measures of acuity, and (4) the relationship between interocular differences in acuity and stereopsis. Mean interocular acuity difference was largest during months 0-5 (approximately 1 octave) and decreased to approximately 0.5 octaves by months 9-11. Test-retest reliability was constant throughout months 0-11 (0.5 octaves). The superiority of binocular acuity over monocular acuity was evident after the 6th month. The presence or absence of stereopsis during months 3-5 was directly related to the magnitude of interocular acuity differences. These age trends suggest that the third to fifth months of life may represent a period of binocular competition in the human visual system which, during normal development, culminates in small interocular acuity differences and the onset of binocular function, including stereopsis.     

Intraocular and interocular symmetry in normal retinal capillary perfusion

PURPOSE: To investigate retinal capillary perfusion in different areas of the posterior pole (intraocular symmetry) and to compare capillary perfusion between the right and left eyes (interocular symmetry). METHODS: The study consisted of 52 clinically healthy patients between the ages of 45 and 74 years. Good quality images were obtained in 30 patients. By using scanning laser Doppler flowmetry with the Heidelberg Retina Flowmeter, three 10 degree scans were obtained from the fovea and superior and inferior retina of the study eye (for intraocular symmetry) and from the fovea of the fellow eye (for interocular comparison). Values of volume, flow, and velocity were recorded from each of these areas. Repeated measures analysis of variance, with Bonferroni correction, was used for groupwise comparison between areas in the study eye. Paired t tests, with Bonferroni correction, were used to compare nonfoveolar perfusion between the right and left eyes for each patient. RESULTS: Capillary volume in the foveola was significantly less than that in areas superior and inferior and 3 degrees nasal and temporal, and it was found to increase with eccentricity in the macular region. Only 2 of 30 patients had significant interocular differences between the extrafoveolar areas. CONCLUSION: Significant differences in retinal capillary perfusion were found across the macular region and corresponded with the increase in capillary beds. The Heidelberg Retina Flowmeter also measured the expected decrease in volume at the foveolar avascular zone. There were no significant interocular differences in perfusion. Eye movements, media opacities, and poor tear film quality had a deleterious effect on image quality.     

Quantitative measurement of interocular suppression in children with amblyopia

In this study we explored the possibility of using a dichoptic global motion technique to measure interocular suppression in children with amblyopia. We compared children (5–16 years old) with unilateral anisometropic and/or strabismic amblyopia to age-matched control children. Under dichoptic viewing conditions, contrast interference thresholds were determined with a global motion direction–discrimination task. Using virtual reality goggles, high contrast signal dots were presented to the amblyopic eye, while low contrast noise dots were presented to the non-amblyopic fellow eye. The contrast of the noise dots was increased until discrimination of the motion direction of the signal dots reached chance performance. Contrast interference thresholds were significantly lower in the strabismic group than in the anisometropic and control group. Our results suggest that interocular suppression is stronger in strabismic than in anisometropic amblyopia.     

Importance of phase alignment for interocular suppression

We measured contrast thresholds for Gabor targets in the presence of maskers which had higher or lower spatial frequencies than the targets. A high-pass fractal masker elevated target contrast thresholds at low and intermediate pedestal contrasts in both monocular and dichoptic modes of presentation, suggesting that the masking occurs after a monocular processing stage. Moreover we found that a high-pass checkerboard masker elevated thresholds at the low and intermediate pedestal contrasts and that most of this threshold elevation disappeared when the phase of the masker’s spatial components were scrambled. This masking was effective only in the dichoptic presentation, not in the monocular presentation. These results indicate that phase alignment of the high spatial frequency components plays a crucial role for interocular suppression. We speculate that phase alignments signal the existence of a luminance contour in the monocular image and that this signal suppresses processing of information in the other eye when there is no corresponding signal in that eye.     

The spatial frequency dependence of interocular transfer in amplyopes

Contrast sensitivity functions were measured for anisometropic and strabismic amblyopes. Interocular transfer was investigated at two spatial frequencies for each subject and was found to be dependent upon the sensitivity ratio of the non-amblyopic to the amblyopic eye. Where contrast sensitivity in the two eyes is similar, transfer exists and is independent of the presence of stereopsis. Predicting power for binocularity from measurements of contrast sensitivity functions is reasoned.     

Lines and gratings: Different interocular after-effects

The contrast threshold for a line or for a grating is elevated following prolonged inspection of a line or a grating of high contrast and suitable orientation and spatial frequency. This after-effect (that shows a significant interocular transfer when the test pattern is a grating) does not transfer from one eye to the other when the test pattern is a single line or a pattern consisting of a small number of bars. The critical width of the pattern for the interocular transfer of the after-effect is about 0.5°. These findings suggest that the detection of a line and the detection of a grating represent either two successive stages in the processing of visual signals or two parallel processes at least partially independent from each other.