Long-term cellular and regional specificity of the photoreceptor toxin, iodoacetic acid (IAA), in the rabbit retina

This study investigated the anatomical consequences of a photoreceptor toxin, iodoacetic acid (IAA), in the rabbit retina. Retinae were examined 2 weeks, 1, 3, and 6 months after systemic IAA injection. The retinae were processed using standard histological methods to assess the gross morphology and topographical distribution of damage, and by immunohistochemistry to examine specific cell populations in the retina. Degeneration was restricted to the photoreceptors and was most common in the ventral retina and visual streak. In damaged regions, the outer nuclear layer was reduced in thickness or eliminated entirely, with a concomitant loss of immunoreactivity for rhodopsin. However, the magnitude of the effect varied between animals with the same IAA dose and survival time, suggesting individual differences in the bioavailability of the toxin. In all eyes, the inner retina remained intact, as judged by the thickness of the inner nuclear layer, and by the pattern of immunoreactivity for protein kinase C-alpha (rod bipolar cells) and calbindin D-28 (horizontal cells). Müller cell stalks became immunoreactive for glial fibrillary acidic protein (GFAP) even in IAA-treated retinae that had no signs of cell loss, indicating a response of the retina to the toxin. However, no marked hypertrophy or proliferation of Müller cells was observed with either GFAP or vimentin immunohistochemistry. Thus the selective, long lasting damage to the photoreceptors produced by this toxin did not lead to a reorganization of the surviving cells, at least with survival as long as 6 months, in contrast to the remodeling of the inner retina that is observed in inherited retinal degenerations such as retinitis pigmentosa and retinal injuries such as retinal detachment.

Distance doubling visual acuity test: a reliable test for nonorganic visual loss

BACKGROUND: To determine the value of the distance doubling visual acuity test in the diagnosis of nonorganic visual loss in a comparative observational case series. METHODS: Twenty-one consecutive patients with nonorganic visual acuity loss and 21 subjects with organic visual loss as controls were included. Best corrected visual acuity was tested at the normal distance of 5 meters using Landolt Cs. The patient was then repositioned and best corrected visual acuity was tested with the previous optotypes at double the distance via a mirror. RESULTS: Nonorganic visual acuity loss was identified in 21 of 21 patients. Sensitivity and specificity of distance-doubling visual acuity test in functional visual loss were found to be 100% (CI; 83%-100%) and 100% (CI; 82%-100%), respectively. CONCLUSION: Distance doubling visual acuity test is widely used to detect nonorganic visual loss. Our results show that this test has a high specificity and sensitivity to detect nonorganic visual impairment.

Neglect-like visual exploration behaviour after theta burst transcranial magnetic stimulation of the right posterior parietal cortex

The right posterior parietal cortex (PPC) is critically involved in visual exploration behaviour, and damage to this area may lead to neglect of the left hemispace. We investigated whether neglect-like visual exploration behaviour could be induced in healthy subjects using theta burst repetitive transcranial magnetic stimulation (rTMS). To this end, one continuous train of theta burst rTMS was applied over the right PPC in 12 healthy subjects prior to a visual exploration task where colour photographs of real-life scenes were presented on a computer screen. In a control experiment, stimulation was also applied over the vertex. Eye movements were measured, and the distribution of visual fixations in the left and right halves of the screen was analysed. In comparison to the performance of 28 control subjects without stimulation, theta burst rTMS over the right PPC, but not the vertex, significantly decreased cumulative fixation duration in the left screen-half and significantly increased cumulative fixation duration in the right screen-half for a time period of 30 min. These results suggest that theta burst rTMS is a reliable method of inducing transient neglect-like visual exploration behaviour.

Hypervigilance-avoidance pattern in spider phobia

Cognitive-motivational theories of phobias propose that patients' behavior is characterized by a hypervigilance-avoidance pattern. This implies that phobics initially direct their attention towards fear-relevant stimuli, followed by avoidance that is thought to prevent objective evaluation and habituation. However, previous experiments with highly anxious individuals confirmed initial hypervigilance and yet failed to show subsequent avoidance. In the present study, we administered a visual task in spider phobics and controls, requiring participants to search for spiders. Analyzing eye movements during visual exploration allowed the examination of spatial as well as temporal aspects of phobic behavior. Confirming the hypervigilance-avoidance hypothesis as a whole, our results showed that, relative to controls, phobics detected spiders faster, fixated closer to spiders during the initial search phase and fixated further from spiders subsequently.

The retina in Parkinson's disease

As a more complete picture of the clinical phenotype of Parkinson's disease emerges, non-motor symptoms have become increasingly studied. Prominent among these non-motor phenomena are mood disturbance, cognitive decline and dementia, sleep disorders, hyposmia and autonomic failure. In addition, visual symptoms are common, ranging from complaints of dry eyes and reading difficulties, through to perceptual disturbances (feelings of presence and passage) and complex visual hallucinations. Such visual symptoms are a considerable cause of morbidity in Parkinson's disease and, with respect to visual hallucinations, are an important predictor of cognitive decline as well as institutional care and mortality. Evidence exists of visual dysfunction at several levels of the visual pathway in Parkinson's disease. This includes psychophysical, electrophysiological and morphological evidence of disruption of retinal structure and function, in addition to disorders of ‘higher’ (cortical) visual processing. In this review, we will draw together work from animal and human studies in an attempt to provide an insight into how Parkinson's disease affects the retina and how these changes might contribute to the visual symptoms experienced by patients.

Effect of chlorzoxazone in patients with downbeat nystagmus: A pilot trial

Objective: Downbeat nystagmus (DBN) is the most frequent form of acquired persisting fixation nystagmus with different symptoms such as unsteadiness of gait, postural instability, and blurred vision with reduced visual acuity (VA) and oscillopsia. However, different symptomatic therapeutic principles are required, such as 3,4-diaminopyridine and 4-aminopyridine, that effectively suppress DBN. Chlorzoxazone (CHZ) is a nonselective activator of small conductance calcium-activated potassium (SK) channels that modifies the activity of cerebellar Purkinje cells. We evaluated the effects of this agent on DBN in an observational proof-of-concept pilot study. Methods: Ten patients received CHZ 500 mg 3 times a day for 1 or 2 weeks. Slow-phase velocity of DBN, VA, postural sway, and the drug's side effects were evaluated. Recordings were conducted at baseline, 90 minutes after first administration, and after 1 or 2 weeks. Results: Mean slow-phase velocity significantly decreased from a baseline of 2.74°/s ± 2.00 to 2.29°/s ± 2.12 (mean ± SD) 90 minutes after first administration and to 2.04°/s ± 2.24 (p < 0.001; post hoc both p = 0.024) after long-term treatment. VA significantly increased and postural sway in posturography showed a tendency to decrease on medication. Fifty percent of patients did not report any side effects. The most common reported side effect was abdominal discomfort and dizziness. Conclusions: The treatment with the SK-channel activator CHZ is a potentially new therapeutic agent for the symptomatic treatment of DBN. Classification of evidence: This study provides Class IV evidence that CHZ 500 mg 3 times a day may improve eye movements and visual fixation in patients with DBN.

The impact of loupes and microscopes on vision in endodontics.

AIM To report on an intraradicular visual test in a simulated clinical setting under different optical conditions. METHODOLOGY Miniaturized visual tests with E-optotypes (bar distance from 0.01 to 0.05 mm) were fixed inside the root canal system of an extracted maxillary molar at different locations: at the orifice, a depth of 5 mm and the apex. The tooth was mounted in a phantom head for a simulated clinical setting. Unaided vision was compared with Galilean loupes (2.5× magnification) with integrated light source and an operating microscope (6× magnification). The influence of the dentists' age within two groups was evaluated: <40 years (n = 9) and ≥40 years (n = 15). RESULTS Some younger dentists were able to identify the E-optotypes at the orifice, but otherwise, natural vision did not reveal any measurable result. With Galilean loupes, the younger dentists <40 years could see a 0.05 mm structure at the root canal orifice, in contrast to the older group ≥40 years. Only the microscope allowed the observation of structures inside the root canal, independent of age. CONCLUSION Unaided vision and Galilean loupes with an integrated light source could not provide any measurable vision inside the root canal, but younger dentists <40 years could detect with Galilean loupes a canal orifice corresponding to the tip of the smallest endodontic instruments. Dentists over 40 years of age were dependent on the microscope to inspect the root canal system.

The Neuroscience of Visual Hallucinations

Each year, some two million people in the United Kingdom experience visual hallucinations. Infrequent, fleeting visual hallucinations, often around sleep, are a usual feature of life. In contrast, consistent, frequent, persistent hallucinations during waking are strongly associated with clinical disorders; in particular delirium, eye disease, psychosis, and dementia. Research interest in these disorders has driven a rapid expansion in investigatory techniques, new evidence, and explanatory models. In parallel, a move to generative models of normal visual function has resolved the theoretical tension between veridical and hallucinatory perceptions. From initial fragmented areas of investigation, the field has become increasingly coherent over the last decade. Controversies and gaps remain, but for the first time the shapes of possible unifying models are becoming clear, along with the techniques for testing these. This book provides a comprehensive survey of the neuroscience of visual hallucinations and the clinical techniques for testing these. It brings together the very latest evidence from cognitive neuropsychology, neuroimaging, neuropathology, and neuropharmacology, placing this within current models of visual perception. Leading researchers from a range of clinical and basic science areas describe visual hallucinations in their historical and scientific context, combining introductory information with up-to-date discoveries. They discuss results from the main investigatory techniques applied in a range of clinical disorders. The final section outlines future research directions investigating the potential for new understandings of veridical and hallucinatory perceptions, and for treatments of problematic hallucinations. Fully comprehensive, this is an essential reference for clinicians in the fields of the psychology and psychiatry of hallucinations, as well as for researchers in departments, research institutes and libraries. It has strong foundations in neuroscience, cognitive science, optometry, psychiatry, psychology, clinical medicine, and philosophy. With its lucid explanation and many illustrations, it is a clear resource for educators and advanced undergraduate and graduate students.

Post-Empire Imaginaries? Anglophone Literature, History, and the Demise of Empires

Empires as political entities may be a thing of the past, but as a concept, empire is alive and kicking. From heritage tourism and costume dramas to theories of the imperial idea(l): empire sells. Post-Empire Imaginaries? Anglophone Literature, History, and the Demise of Empires presents innovative scholarship on the lives and legacies of empires in diverse media such as literature, film, advertising, and the visual arts. Though rooted in real space and history, the post-empire and its twin, the post-imperial, emerge as ungraspable ideational constructs. The volume convincingly establishes empire as welcoming resistance and affirmation, introducing post-empire imaginaries as figurations that connect the archives and repertoires of colonial nostalgia, postcolonial critique, post-imperial dreaming.

Visual Perception and Acuity of Hand Surgeons Using Loupes.

PURPOSE To assess the visual performance of Swiss hand surgeons in an environment similar to their workplace. The influence of Galilean (lenses only) and Keplerian loupes (lenses and prisms), the surgeon's age, and the credibility of a self-assessment of his or her own optical performance were evaluated. METHODS Sixty-three hand surgeons between 29 and 68 years of age with 70 loupes were included in the study (Galilean n = 35, Keplerian n = 35). The visual performance as surgeons was self-assessed on a modified visual analog scale and objectively measured with miniaturized visual tests in a simulated clinical setting. We evaluated the influence of the optical device by comparing Galilean and Keplerian loupes and the influence of the surgeon's age by comparing 2 subgroups: < 40 years and ≥ 40 years. RESULTS The correlation between self-assessment and objective visual performance was weak, with a Spearman rank correlation coefficient of 0.25. The near visual acuity with habitual optical aids showed considerable variability, with a range of 300% in the dimension of the smallest detected structure. The near visual acuity was significantly lower in the older group ≥ 40 years than in the younger group < 40 years with both Galilean and Keplerian loupes. Keplerian loupes allowed a significantly higher visual performance than Galilean loupes. Surgeons 40 years or older using Keplerian loupes had a similar visual acuity to surgeons younger than 40 years with Galilean loupes. CONCLUSIONS The magnified near vision of hand surgeons showed an important individual variability. Self-assessment was not a valuable instrument for surgeons to estimate their own near vision. Hand surgeons older than 40 years should use higher magnification loupes. TYPE OF STUDY/LEVEL OF EVIDENCE Diagnostic III.

Birth date predicts alternative life-history pathways in a fish with sequential reproductive tactics

1.In species with plastic expression of alternative reproductive tactics (ARTs), individuals of the same sex, usually males, can adopt different reproductive tactics depending on factors such as body size. 2.The ‘birth date hypothesis’ proposes that condition-dependent expression of ARTs may ultimately depend on birth date, because individuals born at different times of the year may achieve different sizes and express different reproductive tactics accordingly. However, this has rarely been tested. 3.Here, we tested this hypothesis in a fish with ARTs, the peacock blenny (Salaria pavo). A long-term (6 years) mark–recapture study demonstrated that ARTs in the peacock blenny were sequential and that males may follow at least two alternative life-history pathways: a nest-holder pathway, in which males express the nest-holder tactic from their first breeding season onwards, and a parasitic pathway, where males reproduce on their first breeding season as sneaker males and subsequently as nest-holders. 4.We have found evidence of a birth date effect on the expression of ARTs in the peacock blenny. Males following the nest-holder pathway are born earlier and are larger at the first breeding season than males following the parasitic pathway, but they have similar growth curves. 5.The mechanisms underlying a birth date effect are far from clear and might be diverse. We have not found support for a mechanism of body size threshold triggering sexual maturation and subsequent ARTs. A mechanism of tactic determination that is strictly based on timing of first maturation is also unlikely. 6.A proxy of lifetime reproductive success shows crossing (body size associated) fitness curves for the two main life-history pathways.