Suppression of sympathetic nervous system during fasting

We describe 3 patients within whom ocular torsion could be induced by application of positive air pressure to one external ear canal. In all cases, the superior pole of the eye rotated away from the stimulated ear when positive pressure was applied. The amplitude of torsion ranged from 3 degrees to 16 degrees. Exploratory tympanotomy was performed in all 3 patients. In 2 patients, round-window fistulas were found and repaired. In the third patient, no fistula was noted but the oval- and round-window areas were patched. There was no resolution of symptoms after surgery in any patient. Based on these cases, patients presenting with pressure-induced ocular torsion are unlikely to have resolution of their symptoms, even when a perilymphatic fistula is confirmed and repaired. We hypothesize that pressure-induced ocular torsion is caused by an irreversible juxtaposition of the utricle and stapes footplate.     

Saccular impact on ocular torsion

When someone is tilted laterally, the shear force on the maculae of the utriculus and the sacculus is described by the sine and the cosine of the angle of tilt, respectively. So both the sacculus and the utriculus are stimulated, but in the literature, ocular torsion is normally attributed to utricular function alone (and, thus, seen as a response to y-axis linear acceleration). However, on the base of a series of experiments on a tilt chair, a linear track, human centrifuges, and during parabolic flights, we conclude that the sacculus contributes to ocular torsion as well (there is a response to z-axis linear acceleration). The data suggest that the ratio of the utricular and saccular impact on ocular torsion is 3:1. The utriculus generates conjugate and the sacculus disjunctive torsional eye movements.     

Optimizing gaze control in three dimensions

Horizontal and vertical movements of the human eye bring new objects to the center of the visual field, but torsional movements rotate the visual world about its center. Ocular torsion stays near zero during head-fixed gaze shifts, and eye movements to visual targets are thought to be driven by purely horizontal and vertical commands. Here, analysis of eye-head gaze shifts revealed that gaze commands were three-dimensional, with a separate neural control system for torsion. Active torsion optimized gaze control as no two-dimensional system could have, stabilizing the retinal image as quickly as possible when it would otherwise have spun around the fixation point.     

Average optical performance of the human eye as a function of age in a normal population

PURPOSE: To determine the average optical performance of the human eye, in terms of the modulation transfer function (MTF), as a function of age. METHODS: An apparatus was constructed to measure the ocular MTF, based on the recording of images of a green, 543-nm laser-point source after reflection in the retina and double pass through the ocular media. MTFs were computed from the average of three 4-second-exposure double-pass images recorded by a slow-scan, cooled charge-coupled device camera. The ocular MTF was measured for three artificial pupil diameters (3 mm, 4 mm, and 6 mm) with paralyzed accommodation under the best refractive correction in 20 subjects for each of three age categories: young subjects aged 20 to 30 years, middle-aged subjects aged 40 to 50 years, and older subjects aged 60 to 70 years. The selected subjects passed an ophthalmologic examination, excluding subjects with any form of ocular or retinal disease, spherical or cylindrical refractive errors exceeding 2 D, and corrected visual acuity lower than 1 (0.8 in the older age group). RESULTS: The average MTF was determined for each age group and pupil diameter. A two-parameter analytical expression was proposed to represent the average MTF in each age group for every pupil diameter. The ocular MTFs declined as age increased from young to older groups. The SD of the MTF results within age groups was lower than the differences between the mean for each group. CONCLUSIONS: The average optical performance of the human eye progressively declines with age. These MTF results can serve as a reference for determining mean ocular optics according to age.     

Drug effects on intraocular pressure and vascular flow in the bovine perfused eye using radiolabelled microspheres

A novel technique is described in which the effect of the beta-adrenoceptor antagonists timolol and carteolol, and the vasodilators sodium nitroprusside (SNP) and verapamil on intraocular pressure (IOP) and the distribution of ocular flow in the bovine arterially perfused eye is investigated using radiolabelled microspheres. At maximum IOP-reducing dose timolol was found to significantly reduce perfusion in the choroid and, at higher dose, it was found to significantly reduce perfusion in the iris. By contrast, a maximal IOP-reducing dose of carteolol markedly reduced perfusion in the iris, ciliary body and choroid. Vasoconstriction induced by carteolol was not inhibited by the alpha-antagonist phentolamine. Against a background of vascular tone induced by noradrenaline, SNP and verapamil were found to significantly increase perfusion in the iris, ciliary body and choroid. The effects of these drugs upon the vasculature of the bovine perfused eye are varied and complex and may not bear a direct relationship to their ocular hypotensive effect.     

Neonatal lensectomy and intraocular lens implantation: effects in rhesus monkeys

PURPOSE: To compare the effects of a lensectomy with and without intraocular lens (IOL) implantation on a neonatal rhesus monkey eye. METHODS: A lensectomy and anterior vitrectomy was performed on 75 monkeys during the first 16 days of life; 21 of these monkeys also had an IOL implanted into the posterior chamber. The eyes were examined at regular intervals using biomicroscopy, applanation tonometry, and ophthalmoscopy. RESULTS: The pseudophakic monkeys were studied until they were 92.5 +/- 5.8 weeks of age and the aphakic monkeys until they were 80.4 +/- 5.7 weeks of age. Pupillary membranes (100% versus 55.5%; P < 0.01) and lens regeneration into the pupillary aperture (28.6% versus 5.6%; P = 0.02) occurred more often in the pseudophakic than the aphakic eyes. As a result, the pseudophakic eyes required more reoperations than the aphakic eyes to keep the visual axis clear (P < 0.01). There was not a significant difference in the incidence of ocular hypertension between the pseudophakic and aphakic eyes (9.5% versus 12.7%; P = 0.34). Pupillary capture of the IOL optic occurred in 52% and haptic breakage in 33% of the pseudophakic eyes. All of the eyes with broken haptics had a prominent Soemmerring's ring varying in maximum thickness from 0.6 to 2 mm. Nine of the haptics from the seven eyes with broken IOLs had eroded into the iris, two into the ciliary body, and one into the anterior chamber. CONCLUSIONS: Implanting an IOL into a neonatal monkey eye after a lensectomy and anterior vitrectomy increases the likelihood of a reoperation being necessary. Haptics frequently erode into the iris and ciliary body and may break because of stress placed on the optic-haptic junction by forward movement of the IOL.     

Comparison of ciliary sulcus fixation techniques for posterior chamber intraocular lenses

OBJECTIVE: To anatomically and histologically evaluate suturing techniques for sulcus fixation of posterior chamber intraocular lenses. SETTING: Kitano Hospital, Osaka, Japan. METHODS: The reproducibility of three suturing techniques (perpendicular to the eye wall; parallel to the iris; midway between perpendicular to the eye wall and parallel to the iris) were evaluated in a postmortem eye. Histologic sections of another eye and ultrasound biomicroscopy (UBM) images of 21 normal eyes were evaluated to determine the safety zone for the needle to avoid damaging adjacent structures. RESULTS: The ciliary sulcus was completely penetrated in the three techniques in 100, 40, and 70% of cases, respectively. The histologic sections and the UBM images showed that when sutures were placed perpendicular to the eye wall, there was the possibility of postoperative angle closure and suturing parallel to the iris might damage adjacent structures because of a narrow safety zone. CONCLUSIONS: The needle should penetrate obliquely, as in the technique in which the suturing is midway between perpendicular to the eye wall and parallel to the iris. This technique provides better reproducibility and causes less damage to adjacent tissue.     

Evaluation of the torsional VOR in weightlessness

The experimental concept and findings from a recent manned orbital spaceflight are described. Together with ongoing terrestrial and parabolic studies, the present experiment is intended to further our knowledge of the sensory integrative processing of information from the semicircular canals and the otolithic receptors, and to quantify the presumed otolithic adaptation to altered gravito-inertial force environments in a more reliable manner than to date. The experiment included measurement of the basic vestibulo-oculomotor response during active head rotation about each of the three orthogonal axes. Priority was given to the recording of ocular torsion, as elicited by head oscillation about the roll axis, and thus due to the concomitant stimulation of the semicircular canals and otolith receptors. Videooculography was employed for the measurement of eye movements; head movement was measured by three orthogonally arranged angular rate sensors and a triaxial linear accelerometer device. All signals were recorded synchronously on a video/data recorder. Preliminary results indicate alterations in the torsional VOR under zero-g conditions, suggesting an adaptive modification of the torsional VOR gain over the course of the 6-day orbital flight. In addition, the inflight test findings yielded discrepancies between intended and performed head movement, indicating impairment in sensorimotor coordination under prolonged microgravity conditions.     

Partial ocular tilt reaction due to unilateral cerebellar lesion

We report on two patients each with tonic, contraversive partial ocular tilt reactions due to unilateral cerebellar lesions: one patient had had a caudal cerebellar hemorrhage, the other a posterior inferior cerebellar artery territory infarct. Both patients had tonic contraversive conjugate ocular torsion; one had skew deviation; neither had a head tilt. One patient had no specific neurologic deficit apart from the conjugate ocular torsion, which was first suspected because of a deviation of the subjective visual horizontal. These observations imply that the ocular tilt reaction (OTR), a brainstem otolith-ocular reflex of probable utricular origin, is under the inhibitory control of the ipsilateral caudal cerebellum, possibly the nodulus, and that a patient with a cerebellar infarct can present with imbalance as the only neurologic symptom and with conjugate ocular torsion as the only specific neurologic sign.     

Seesaw nystagmus associated with involuntary torsional head oscillations

OBJECTIVE: To assess the diagnostic value of eye-head coupling in seesaw nystagmus (SSN). BACKGROUND: SSN is a rare binocular disorder characterized by alternating skew deviation and conjugate ocular torsion. METHODS: We examined a patient with a congenital nystagmus that switched to a pendular SSN on near viewing and was associated with involuntary torsional head oscillations. RESULTS: The binocular torsional eye movements were in phase with the clinically visible head oscillations (i.e., head movements were not compensatory for the torsional eye movements). CONCLUSION: This finding suggests that torsional eye-head coupling in pendular SSN has a common pathologic origin. We suggest that alternating vertical disparity of both eyes in pendular SSN is compatible with an oscillating signal acting on an intact vestibular system. The absence of brainstem lesions on high-resolution MRI supports this assumption.     

New approach for elucidating the oxygen sensitivity and calibration of the antimony electrode

BACKGROUND: Phototoxic maculopathy most likely results from longer exposure to light from sources such as the sun, welding arcs, tungsten halogen lamp filaments or operation microscopes. The value of the multifocal ERG for the evaluation of functional defects in this rare entity has not been described to date. CASES: We describe the case of a 38-year-old male patient who presented to his local ophthalmologist with bilateral loss of vision and acute ocular pain after having worked for two hours at an electric welding arc. A foveal lesion was found in both eyes, resulting in a bilateral reduction of visual acuity. Nine months later, the patient underwent examination and further investigations at the university eye clinic in Tübingen. Visual field defects on both sides could be detected with automatic threshold perimetry. Using the multifocal ERG with a central element of 2 degrees diameter, a central defect was detected only for the right eye. CONCLUSIONS: In rare cases, a photic maculopathy can result from exposure to light during arc welding. It can be masked in the first days by a phototoxic keratitis. Multifocal ERG and automatic perimetry are useful tools for the detection and quantification of the functional defects.     

Effect of binocular cortical misalignment on ocular dominance and orientation selectivity

We model a two-eye visual environment composed of natural images and study its effect on single cell synaptic modification. In particular, we study the effect of binocular cortical misalignment on receptive field formation after eye opening. We show that binocular misalignment affects principal component analysis (PCA) and Bienenstock, Cooper, and Munro (BCM) learning in different ways. For the BCM learning rule this misalignment is sufficient to produce varying degrees of ocular dominance, whereas for PCA learning binocular neurons emerge in every case.     

Structure, development and function of cytoskeletal elements in non-neuronal cells of the human eye

The cytoskeleton, of which the main components in the human eye are actin microfilaments, intermediate filaments and microtubules with their associated proteins, is essential for the normal growth, maturation, differentiation, integrity and function of its cells. These components interact with intra- and extracellular environment and each other, and their profile frequently changes during development, according to physiologic demands, and in various diseases. The ocular cytoskeleton is unique in many ways. A special pair of cytokeratins, CK 3 and 12, has apparently evolved only for the purposes of the corneal epithelium. However, other cytokeratins such as CK 4, 5, 14, and 19 are also important for the normal ocular surface epithelia, and other types may be acquired in keratinizing diseases. The intraocular tissues, which have a relatively simple cytoskeleton consisting mainly of vimentin and simple epithelial CK 8 and 18, differ in many details from extraocular ones. The iris and lens epithelium characteristically lack cytokeratins in adults, and the intraocular muscles all have a cytoskeletal profile of their own. The dilator of the iris contains vimentin, desmin and cytokeratins, being an example of triple intermediate filament expression, but the ciliary muscle lacks cytokeratin and the sphincter of the iris is devoid even of vimentin. Conversion from extraocular-type cytoskeletal profile occurs during fetal life. It seems that posttranslational modification of cytokeratins in the eye may also differ from that of extraocular tissues. So far, it has not been possible to reconcile the cytoskeletal profile of intraocular tissues with their specific functional demands, but many theories have been put forward. Systematic search for cytoskeletal elements has also revealed novel cell populations in the human eye. These include transitional cells of the cornea that may represent stem cells on migration, myofibroblasts of the scleral spur and juxtacanalicular tissue that may modulate aqueous outflow, and subepithelial matrix cells of the ciliary body and myofibroblasts of the choroid that may both participate in accommodation. In contrast to the structure and development of the ocular cytoskeleton, changes that take place in ocular disease have not been analysed systematically. Nevertheless, potentially meaningful changes have already been observed in corneal dystrophies (Meesmann's dystrophy, posterior polymorphous dystrophy and iridocorneal endothelial syndrome), degenerations (pterygium) and inflammatory diseases (Pseudomonas keratitis), in opacification of the lens (anterior subcapsular and secondary cataract), in diseases characterized by proliferation of the retinal pigment epithelium (macular degeneration and proliferative vitreoretinopathy), and in intraocular tumours (uveal melanoma). In particular, upregulation of alpha-smooth muscle actin seems to be a relatively general response typical of spreading and migrating corneal stromal and lens epithelial cells, trabecular cells and retinal pigment epithelial cells.     

Transneuronal WGA-HRP: can it demonstrate development of ocular dominance patches and effects of monocular deprivation?

We have attempted to use intraocular injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to label ocular dominance patches in developing layer 4 of cat visual cortex. The cortices of animals killed at 49 days or later showed normal ocular dominance patches similar to those seen in [3H]proline material. Animals killed at 42 days showed some patches, but also showed unsegregated regions. Animals killed younger were difficult to stain and did not have patches. We also examined the ability of the WGA-HRP technique to demonstrate the effects of monocular deprivation (MD). MD for the first 3 months of life produced expansion of the afferents from the nondeprived eye and retraction of the patches from the deprived eye. One week of MD at about 5 weeks of age produced an expansion of the patches innervated by the nondeprived eye, but did not obviously affect the patches innervated by the deprived eye. We conclude that WGA-HRP is useful for examining the effects of long-term MD on ocular dominance patches but not for following the development of segregation. Its advantages over the [3H]proline technique are that it does not require a delay of many weeks before the sections can be examined and is much less expensive.     

Three-dimensional modeling of static vestibulo-ocular brain stem syndromes

Static vestibulo-ocular brain stem syndromes characterized by skew deviation, a vertical disconjugacy of the eyes, and ocular torsion are the result of a vestibular tone imbalance in the frontal (roll) plane. Similar physiological changes in static eye position, ocular counter-roll and conjugated deviations of vertical eye position, are caused by the influence of gravity mediated by the utricles. These observations prompted our approach with the model described here: based on the known deviations of static eye position, we devised a three-dimensional mathematical model of otolith-ocular function including detailed brain stem anatomy. This model is able to explain and predict the differential effects of unilateral and bilateral peripheral or central vestibular lesions on static eye position in roll, pitch, and yaw planes.     

Nitric oxide-mediated renal epithelial cell injury during hypoxia and reoxygenation

If two targets are both on the visual axis of one eye or the other, and binocular fixation is shifted from the farther one to the nearer, the aligned eye consistently makes an initial, seemingly pointless saccade in a temporal direction. The size of those saccades typically differs markedly, depending on whether the targets are aligned with the observer's dominant or non-dominant eye. Pickwell [(1972) Vision Research, 12, 1499-1507] proposed that this binocular asymmetry in oculomotor performance reflects a subject-specific lateral displacement of the egocenter (the "binoculus" of Hering, which has traditionally been assumed to be on the midline). An empirical test of Pickwell's widely endorsed hypothesis has now been conducted and the proposal has been found wanting. In an otherwise darkened room, subjects were required repeatedly to set a small light to a perceived straight-ahead location in the horizontal plane, first for a target at 300 cm distance and then for one at 30 cm. Extrapolation of a line that connects the two averages of those settings to the inter-ocular axis provides an estimate of the subjective egocenter to which visual directions are referred. Contrary to Pickwell's proposal, those locations of the inferred egocenter were usually quite near the midline, and were completely uncorrelated with same-subject data on the extent of saccadic asymmetry at the onset of asymmetrical convergence. The data on perceived straight-ahead underlying this result indicate the availability of extraretinal information about eye orientation that is quite precise at a given moment (median standard deviation of 47 min arc) but conspicuously non-stationary over several-minute intervals (monotonic drifts in sequential settings being very common).     

基于灰度信息和支持向量机的人眼检测方法

提出一种基于灰度信息和支持向量机的人眼检测方法.首先,利用人眼区域灰度变化比人脸其他部位灰度变化明显的特征,采用图像灰度二阶矩(方差)建立人眼方差滤波器,在固定人眼搜索区域内,应用人眼方差滤波器搜索候选人眼图像;然后,使用训练的支持向量机分类器精确检测人眼区域位置;最后,采用图像灰度信息率定位人眼中心(虹膜中心).该方法在BioID、FERET和IMM人脸数据库中的测试结果显示:没有佩戴眼镜人脸图像正确率分别为98.2%、97.8%和98.9%,406幅佩戴眼镜人脸图像正确率为94.9%;人眼中心定位正确率分别为90.5%、88.3%和96.1%.通过与目前方法比较,该方法获得较好的检测效果.      

Ocular neovascularization: an epidemiologic review

Neovascularization occurs in many eye diseases, and its epidemiologic impact is significant. However, data on the prevalence and incidence of ocular neovascularization have never been compiled to demonstrate its pervasiveness. This overview of ocular angiogenesis provides a review of the epidemiologic literature for neovascularization in various parts of the eye, including the cornea, iris, retina, and choroid. Relevant disease states are reviewed, as are their risk factors, so that their pathogenesis can be better understood. Data on the prevalence and incidence of the major diseases involving angiogenesis are synthesized to provide statistical evidence of the span and magnitude of ocular neovascularization. These prevalence and incidence data on ocular neovascularization are extrapolated to USA population data where possible, and "worst-case" estimates are calculated as well. Information was gathered with a search of the MEDLINE database, published monographs and volumes, and consultation with a number of primary authors. This study attempts to unify much of past and present epidemiologic research, and the information is presented in sections divided according to the anatomy of the eye.     

Human oculomotor system accounts for 3-D eye orientation in the visual-motor transformation for saccades

A recent theoretical investigation has demonstrated that three-dimensional (3-D) eye position dependencies in the geometry of retinal stimulation must be accounted for neurally (i.e., in a visuomotor reference frame transformation) if saccades are to be both accurate and obey Listing's law from all initial eye positions. Our goal was to determine whether the human saccade generator correctly implements this eye-to-head reference frame transformation (RFT), or if it approximates this function with a visuomotor look-up table (LT). Six head-fixed subjects participated in three experiments in complete darkness. We recorded 60 degrees horizontal saccades between five parallel pairs of lights, over a vertical range of +/-40 degrees (experiment 1), and 30 degrees radial saccades from a central target, with the head upright or tilted 45 degrees clockwise/counterclockwise to induce torsional ocular counterroll, under both binocular and monocular viewing conditions (experiments 2 and 3). 3-D eye orientation and oculocentric target direction (i.e., retinal error) were computed from search coil signals in the right eye. Experiment 1: as predicted, retinal error was a nontrivial function of both target displacement in space and 3-D eye orientation (e.g., horizontally displaced targets could induce horizontal or oblique retinal errors, depending on eye position). These data were input to a 3-D visuomotor LT model, which implemented Listing's law, but predicted position-dependent errors in final gaze direction of up to 19.8 degrees. Actual saccades obeyed Listing's law but did not show the predicted pattern of inaccuracies in final gaze direction, i.e., the slope of actual error, as a function of predicted error, was only -0. 01 +/- 0.14 (compared with 0 for RFT model and 1.0 for LT model), suggesting near-perfect compensation for eye position. Experiments 2 and 3: actual directional errors from initial torsional eye positions were only a fraction of those predicted by the LT model (e. g., 32% for clockwise and 33% for counterclockwise counterroll during binocular viewing). Furthermore, any residual errors were immediately reduced when visual feedback was provided during saccades. Thus, other than sporadic miscalibrations for torsion, saccades were accurate from all 3-D eye positions. We conclude that 1) the hypothesis of a visuomotor look-up table for saccades fails to account even for saccades made directly toward visual targets, but rather, 2) the oculomotor system takes 3-D eye orientation into account in a visuomotor reference frame transformation. This transformation is probably implemented physiologically between retinotopically organized saccade centers (in cortex and superior colliculus) and the brain stem burst generator.