Eye In Turn Research Articles

Induced Vertical Disparity Effects on Local and Global Stereopsis

Purpose: Although significant amounts of vertical misalignment could have a noticeable effect on visual performance, there is no conclusive evidence about the effect of very small amount of vertical disparity on stereopsis and binocular vision. Hence, the aim of this study was to investigate the effects of induced vertical disparity on local and global stereopsis at near.Materials and Methods: Ninety participants wearing best-corrected refraction had local and global stereopsis tested with 0.5 and 1.0 prism diopter (Δ) vertical prism in front of their dominant and non-dominant eye in turn. This was compared to local and global stereopsis in the same subjects without vertical prism. Data were analyzed in SPSS.17 software using the independent samples T and the repeated measures ANOVA tests.Results: Induced vertical disparity decreases local and global stereopsis. This reduction is greater when vertical disparity is induced in front of the non-dominant eye and affects global more than local stereopsis. Repeated measures ANOVA showed differences in the mean stereopsis between the different measured states for local and global values. Local stereopsis thresholds were reduced by 10 s of arc or less on average with 1.0Δ of induced vertical prism in front of either eye. However, global stereopsis thresholds were reduced by over 100 s of arc by the same 1.0Δ of induced vertical prism.Conclusion: Induced vertical disparity affects global stereopsis thresholds by an order of magnitude (or a factor of 10) more than local stereopsis. Hence, using a test that measures global stereopsis such as the TNO is more sensitive to vertical misalignment than a test such as the Stereofly that measures local stereopsis.

Temporal visual field defects are associated with monocular inattention in chiasmal pathology

Chiasmal lesions have been shown to give rise occasionally to uni-ocular temporal inattention, which cannot be compensated for by volitional eye movement. This article describes the assessments of 46 such patients with chiasmal pathology. It aims to determine the clinical spectrum of this disorder, including interference with reading. Retrospective consecutive observational clinical case study over a 7-year period comprising 46 patients with chiasmal field loss of varying degrees. Observation of reading behaviour during monocular visual acuity testing ascertained from consecutive patients who appeared unable to read optotypes on the temporal side of the chart. Visual fields were evaluated by kinetic (Goldmann) and static (Octopus) techniques. Five patients who clearly manifested this condition are presented in more detail. The results of visual field testing were related to absence or presence of uni-ocular visual inattentive behaviour for distance visual acuity testing and/or reading printed text. Despite normal eye movements, the 46 patients making up the clinical series perceived only optotypes in the nasal part of the chart, in one eye or in both, when tested for each eye in turn. The temporal optotypes were ignored, and this behaviour persisted despite instruction to search for any additional letters temporal to those, which had been seen. This phenomenon of unilateral visual inattention held for both eyes in 18 and was unilateral in the remaining 28 patients. Partial or full reversibility after treatment was recorded in 21 of the 39 for whom reliable follow-up data were available. Reading a text was affected in 24 individuals, and permanently so in six. A neglect-like spatial unawareness and a lack of cognitive compensation for varying degrees of temporal visual field loss were present in all the patients observed. Not only is visual field loss a feature of chiasmal pathology, but the higher visual function of affording attention within the temporal visual field by means of using conscious thought to invoke appropriate compensatory eye movement was also absent. This suggests the possibility of 'trans-synaptic dysfunction' caused by loss of visual input to higher visual centres. When inattention to the temporal side is manifest on monocular visual testing it should raise the suspicion of chiasmal pathology.

The Mydriatic Effect of Multiple Doses of Tropicamide

We investigated whether two drops of 0.5% tropicamide produced a wider pupillary dilation when compared with a single drop and saline control in subjects with dark-colored irides. Twelve young adult subjects with dark irides and who were free from ocular disease participated in the study. One eye of each subject, selected at random, was designated as experimental and the fellow eye as control. A single drop of 0.5% tropicamide was instilled in the lower cul-de-sac of each eye in turn. Immediately after, a second drop of 0.5% tropicamide was instilled in the experimental eye and a single drop of unpreserved saline into the control eye. A double-masked experimental protocol was followed. Digital images of both pupils of each subject were taken at baseline (predrug instillation) and then every 5 minutes up to 30 minutes postdrug instillation and at 40, 50, and 60 minutes. The images were subsequently viewed on a PC monitor, and pupil size was measured using a calibrated millimeter scale. Pupil diameter increased as a function of time for both conditions reaching a maximum between 20 and 30 minutes after drop instillation. Pupil diameter was greater under the experimental condition compared with the control (analysis of variance p < 0.001). Pupil diameter reached at least 6 mm under both the experimental and control conditions. In young healthy subjects, compared with a single drop of tropicamide, two drops were associated with a greater degree of pupillary dilation on average over the 60-minute study period. However, the magnitude of the difference was small and not clinically significant. A single drop of tropicamide produced a pupillary diameter of at least 6 mm, which should be sufficient for the conduct of a thorough dilated fundus examination.

Recurrent Migraine Aura Triggered by Coronary Angiography

Fifteen minutes after having a coronary angiogram, as a preoperative test before replacement of my ascending aorta in 1998, at 41 years of age (Hankey 1999), I was lying on...

Ophthalmic manifestations of acute leukaemias: the ophthalmologist's role.

With evolving diagnostic and therapeutic advances, the survival of patients with acute leukaemia has considerably improved. This has led to an increase in the variability of ocular presentations in the form of side effects of the treatment and the ways leukaemic relapses are being first identified as an ocular presentation. Leukaemia may involve many ocular tissues either by direct infiltration, haemorrhage, ischaemia, or toxicity due to various chemotherapeutic agents. Ocular involvement may also be seen in graft-versus-host reaction in patients undergoing allogeneic bone marrow transplantation, or simply as increased susceptibility to infections as a result of immunosuppression that these patients undergo. This can range from simple bacterial conjunctivitis to an endophthalmitis. Leukaemia can present as pathology in the adnexae, conjunctiva, sclera, cornea, anterior chamber, iris, lens, vitreous, retina, choroid, and optic nerve. Recognition of the varied ocular presentations is also important in assessing the course and prognosis of leukaemia. We have presented a systematic approach taking each part of the eye in turn and outlining how leukaemia has been shown to affect it.

Cajou’s Reason: Michèle Lacrosil and Post-war Intellectual Liberalism

Les choses que l'on tait sont-elles moins pernicieuses? Michele Lacrosil, Cajou Cajou, the eponymous heroine of Michele Lacrosil's second novel, to represent the very embodiment of racism. In her eyes the world is strictly divided along color lines, between a superior white race and an inferior black one. The child of an interracial marriage, Cajou inevitably turns this vision of the world upon herself, convinced she is doomed to failure because of her black ancestry. Lacrosil published Cajou in 1961, thus introducing the self-hating heroine to her public against the backdrop of an ever more visible rise to power in the former French colonies of Africa. It is not surprising that the work was subject to a considerable amount of criticism in this context, and indeed the extent of Cajou's self-degradation is such that it may be tempting to join contemporary readers, as well as subsequent critics, in characterizing the novel as the portrait of a madwoman. But to do so would be to risk being simplistic or even dismissive, and would obscure an important component of Lacrosil's narrative: that its formal composition as a series of first-person journal entries articulates not only a tortured investigation of the self, but a penetrating look outward at the society that surrounds Cajou. Closer examination of this critical undercurrent suggests that Cajou's acquaintances and colleagues label her discourse as neurotic not only because it is racist but more importantly because it exposes fundamental problems in their own discourse of social equality. Through this tragic heroine Lacrosil mounts a subtle and unexpected critique of the paradoxes that underlie certain strains of self-proclaimed liberalism in post-war Paris, and suggests further that Cajou's condition may in fact be symptomatic of her contemporary experience of negritude. Michele Lacrosil published only three novels before effectively disappearing from public view at the end of the 1960s, but her brief oeuvre reveals a writer intent on exposing the painful realities of race relations in her native Guadeloupe and in metropolitan France. Her unwavering gaze on the damaging effects of colonialism is most distinctive in its portrayal of the individual subject, alienated and eventually destroyed by contemporary social conditions. In her first novel, Sapotille et le serin d'argile (1960), the young heroine recalls a series of traumatic encounters with the French colonial system during her school days and early adulthood in Guadeloupe. Most striking of these are repeated efforts to exclude and belittle her as one of only a few black students in an elite boarding school run by nuns. Sapotille chronicles these experiences while on board a ship bound for the metropole, thus laying the groundwork for the incisive look at Parisian society engaged in Cajou. In Demain Jab-Herma (1967), Lacrosil shifts from the introspective journal format of her first two novels to a third-person narrative. Here the focus is no longer the female self but a complex network of political and economic struggles amongst a group of men at a sugar factory in Guadeloupe. Threaded through this panoramic narrative, however, is the secondary but no less devastating portrait of the self-hating mulatto Cragget, whose sense of inferiority ultimately destroys him. Like Cajou's, his story plays out thematically the consequences of the formative experiences traced in Lacrosil's first novel, and points to the same tragic conclusion. Training her eye in turn on the educational system in Guadeloupe, metropolitan intellectual circles, and the complexities of an island economy, Lacrosil thus reiterates her call to attention to the destructive internalization of racism as one of the most lasting and urgent legacies of French colonialism. Calou is certainly the most dramatic and sustained of these portraits, and as such has also received the most stringent criticism. Cajou is read primarily as a post-war Mayotte Capecia, as someone who fits a little too closely Fanon's by now infamous profile of the self-hating black woman attempting to erase her race through a relationship with a white man. …

Short latency visual evoked potentials in occupational exposure to organic solvents

Objectives. Short latency visual evoked potentials (SVEP), in response to high-intensity flashes from light emitting diodes (LED), were used to detect subclinical effects along the visual pathway in four groups of subjects with different levels of exposure to gasoline, all within legally acceptable limits. Methods. Potentials and exposure levels were obtained from 31 subjects with different occupational exposure levels to gasoline fumes, as well as from 17 non-exposed control subjects. SVEP were recorded from four electrode sites (infra-orbital, C z, P z, O z), in response to flashes presented to each eye in turn from goggle-mounted LEDs. SVEP components were defined after digital filtering, which eliminated the high-frequency oscillatory potentials and accentuated five major components: a periocular P 30, attributed to the retina; a fronto-central N 50, attributed to the optic nerve; centro-parietal P 65 and N 85, attributed to the optic tracts and radiation; and an occipital, cortical P 105. Results. The latencies of successive SVEP components of the exposed subjects showed a significant latency prolongation compared to controls, beginning with activity attributed to the optic nerve and increasing cumulatively with the later components. Retinal components were not affected by the exposure to organic solvents. Among the exposed groups, differences in latency prolongation corresponded to occupational exposure. Conclusion. The low-frequency components of SVEP were reliably measured and proved to be sensitive to subclinical effects of organic solvents on conduction along the visual pathway. These components are likely to be sensitive to other subcortical visual pathway lesions, but their clinical promise needs further verification.

Role of suppression in shaping orientation and direction selectivity of complex neurons in cat striate cortex.

1. Single binocularly driven complex neurons in cat striate cortex were recorded extracellularly under nitrous oxide-oxygen-halothane anesthesia and muscle relaxant. Orientational/directional tuning was initially derived for each eye in turn, with sine wave gratings of optimal spatial frequency and velocity, while the other eye viewed a uniform field. 2. For the dominant eye, previously concealed suppression was revealed against elevated levels of firing induced with a conditioning grating, drifting continuously in the preferred direction, simultaneously presented to the nondominant eye. During steady-state binocular conditioning, orientational/directional tuning was reestablished for the dominant eye. In a subset of cells, tuning curves during conditioning were also derived for the reverse configuration, i.e., nondominant eye tuning, dominant eye conditioning: results were qualitatively identical to those for conditioning through the nondominant eye. 3. Neurons were initially segregated into five groups, according to the observed suppression profiles induced at nonoptimal orientations/directions during conditioning: Type 1, suppression centered on orthogonal directions; Type 2, suppression around null directions; Type 3, null suppression combined with orthogonal suppression; Type 4, lateral suppression, maximal for directions immediately flanking those inducing excitation; and Type 5, the residue of cells, totally lacking suppression or showing complex or variable suppression. 4. Sharpness of (excitatory) tuning was correlated with directionality and with class of suppression revealed during binocular conditioning. Direction-biased neurons were more sharply orientation tuned than direction-selective neurons; similarly, neurons exhibiting lateral or orthogonal suppression during conditioning were more sharply tuned than neurons with null suppression. 5. Application of suboptimal directions of conditioning weakened the induced suppression but altered none of its main characteristics. 6. The relationship between excitation, suppression, and spatial frequency was investigated by comparing tuning curves for the dominant eye at several spatial frequencies, without and during conditioning. End-stopped neurons preferred lower spatial frequencies and higher velocities of motion than non-end-stopped neurons. Confirming previous reports, suppression in some neurons was still present for spatial frequencies above the cutoff frequency for excitation, demonstrating the tendency for suppression to be more broadly spatial frequency tuned than excitation. 7. Scatterplots of strength of suppression, in directions orthogonal and opposite maximal excitation, partially segregated neurons of Types 1-3. Clearer segregation of Types 1-4 was obtained by curve-fitting to profiles of suppression, and correlating half-width of tuning for suppression with the angle between the directions of optimal suppression and optimal excitation in each neuron. 8. Two interpretations are advanced-the first, based on three discrete classes of inhibition, orthogonal, null and lateral; the second, based on only two classes, orthogonal and null/lateral--in which null and lateral suppression are manifestations of the same inhibitory mechanism operating, respectively, on broadly tuned direction-selective or on sharply tuned direction-biased neurons. Orthogonal suppression may be untuned for direction, whereas lateral and null suppression are broadly direction tuned. Within each class, suppression is more broadly spatial frequency tuned than excitation. 9. It is concluded that orientational/directional selectivity of complex cells at different spatial frequencies is determined by the balance between tuned excitation and varying combinations of relatively broadly distributed or untuned inhibition.

Short latency visual evoked potentials to flashes from light-emitting diodes

Short latency visual evoked potentials (SVEPs) have been described in response to high-intensity, strobe flashes. High-intensity flashes can now be generated from goggle-mounted light emitting diodes (LEDs) and the SVEPs to such flashes have been shown to be reproducible across subjects, avoiding photic spread to the examination room and acoustical artifacts from the strobe stimulator. In this study, SVEPs from multichannel records are described in terms of normative latencies and amplitudes, as well as scalp distributions, to explore their generators. Potentials were recorded from 10 young male subjects, from 16 scalp locations, in response to flashes from goggle-mounted LEDs. Flashes were presented to each eye in turn, as well as binocularly. The latencies, scalp distributions and intersubject variabilities of the LED evoked SVEPs were similar to those obtained with strobe flashes. SVEP components were divided into 3 groups, according to their latency and the electrodes at which they were recorded with the largest amplitudes: periocular (under 40 msec latency), fronto-central (40–55 msec) and parieto-occipital (55–80 msec latency). The scalp distributions observed in this study suggest subcortical generators along the visual pathway, beginning at the retina. The use of goggle-mounted LEDs should promote routine evaluation of the integrity of the visual pathway between retina and cortex using SVEPs.

Visual disturbance of the uncovered eye in patients wearing an eye patch.

We questioned 104 consecutive eye casualty patients about any visual disturbance experienced while wearing an eye patch as part of their treatment. Many (31%) reported momentary loss of vision in the uncovered eye. Some experienced this while driving. It was more common (p < 0.0008) if the 'dominant eye' had been patched (47%) rather than the 'non-dominant eye' (16%). In a separate experiment, a number of co-operative subjects were provided with a translucent-coloured occluder to be worn over each eye in turn. They reported a recurring coloured interference in the uncovered eye sparing the monocular crescent. We propose that the loss of vision in the unpatched eye is due to binocular rivalry suppression by the patched eye. This visual disturbance may be a cause of anxiety or risk for the patient. Patched patients should be warned this may occur, and advised to avoid driving or operating machinery.

After effect of seen movement: evidence for peripheral and central components.

Three experiments showed that the movement after-effect (MAE) contains both peripheral and central components. In Experiment I, the left eye viewed a sectored disc rotating to the left, and the right eye viewed a disc rotating to the right, on corresponding retinal areas. Result: when each eye in turn then viewed a stationary disc, the left eye saw a MAE to the right, and the right eye a MAE to the left. These MAEs must be peripheral. In Experiment II, it was arranged that the movement information was shared out between the eyes, using a ring of lights which were switched on and off to give rotating phi movement. It was arranged that each eye on its own saw a random flashing oscillation but the two eyes together saw rotation anticlockwise. Result: a clockwise MAE was seen, which must be central. In Experiment III, the switching programme was modified to arrange that now each eye on its own saw rotation clockwise, but the two eyes together saw rotation anticlockwise. Result: a clockwise MAE was seen, which must be central. (Peripheral MAEs from each eye on its own would have been anticlockwise.)

Further Studies of the Positive Visual After-image

The binocular matching technique, in which the sensation of brightness of an after-image formed in one eye only is balanced by a comparison light stimulus in the other eye, has been used for further studies of the positive after-image. By dark-adapting each eye in turn, it is shown that the cone receptors in the retina are mainly responsible for the after-image, whereas the matching stimulus acts mainly on the rods. The decay curves of the after-image in white light for two observers are given, with a discussion of the region in which after-image effects follow a reciprocity law. The after-images formed by monochromatic stimuli give exponential decay curves, compared with power-law decay curves for white light stimuli. It is suggested that the origin of positive after-images may be the electrotonic polarisation of the axons of the ganglion cells. La technique de fusionnement binoculaire dans laquelle la sensation de brillance d'une « image consecutive » formee dans un œil est compensee par un stimulus lum...

Lehrbuch der vergleichenden Mikroskopischen Anatomie der Wirbeltiere

WE have on former occasions expressed a high opinion of the “Comparative Microscopic Anatomy of Vertebrate Animals”, now appearing under the editorship of Prof. Oppel. The parts here noticed (Nos. 7 and 8) deal with the eye and pituitary body, and maintain the high standard set by the earlier parts. In systematising our present knowledge of the various forms assumed by the eye in vertebrates, Dr. Franz has utilised more than 6o papers published in recent scientific journals, and in the light of his own researches grouped a multitude of facts together, so that his text and numerous illustrations form a consecutive treatise as well as a most valuable encyclopaedia for reference. He describes the minute structure of each part of the eye in turn—the retina, vitreous body, pecten, choroid, ciliary body, etc., tracing the variations undergone by each throughout the ramifications of the kingdom of vertebrate animals. The opening chapter deals with the visual cells of amphioxus; the closing one with the structure of the eye of species in which the sense of sight has been impaired or lost from disuse.