Vesicular glutamate transport at a central synapse limits the acuity of visual perception in zebrafish

The neural circuitry that constrains visual acuity in the CNS has not been experimentally identified. We show here that zebrafish blumenkohl (blu) mutants are impaired in resolving rapid movements and fine spatial detail. The blu gene encodes a vesicular glutamate transporter expressed by retinal ganglion cells. Mutant retinotectal synapses release less glutamate, per vesicle and per terminal, and fatigue more quickly than wild-type in response to high-frequency stimulation. In addition, mutant axons arborize more extensively, thus increasing the number of synaptic terminals and effectively normalizing the combined input to postsynaptic cells in the tectum. This presumably homeostatic response results in larger receptive fields of tectal cells and a degradation of the retinotopic map. As predicted, mutants have a selective deficit in the capture of small prey objects, a behavior dependent on the tectum. Our studies successfully link the disruption of a synaptic protein to complex changes in neural circuitry and behavior.

Visual impairment and circadian rhythm disorders

Many aspects of human physiology and behavior are dominated by 24-hour circadian rhythms that have a major impact on our health and well-being, including the sleep-wake cycle, alertness and performance patterns, and many daily hormone profiles. These rhythms are spontaneously generated by an internal "pacemaker" in the hypothalamus, and daily light exposure to the eyes is required to keep these circadian rhythms synchronized both internally and with the external environment. Sighted individuals take this daily synchronization process for granted, although they experience some of the consequences of circadian desynchrony when "jetlagged" or working night shifts. Most blind people with no perception of light, however, experience continual circadian desynchrony through a failure of light information to reach the hypothalamic circadian clock, resulting in cyclical episodes of poor sleep and daytime dysfunction. Daily melatonin administration, which provides a replacement synchronizing daily "time cue, " is a promising therapeutic strategy, although optimal treatment dose and timing remain to be determined.

Cortical Gene Expression in the Vitamin E-Deficient Rat: Possible Mechanisms for the Electrophysiological Abnormalities of Visual and Neural Function

In mammals, severe and chronic deficiency of vitamin E (alpha-tocopherol) is associated with a characteristic neurological syndrome. Previously, we have shown that this syndrome is accompanied by electrophysiological abnormalities of neural and visual function. To investigate the molecular basis of the observed abnormalities, we used microarrays to monitor the expression of approximately 14,000 genes in the cerebral cortex from rats which had received diets containing 0, 1.25 and 5.0 mg/kg diet of all-rac-alpha-tocopheryl acetate for 14 months. Compared to the groups receiving 1.25 and 5.0 mg/kg alpha-tocopheryl acetate, a total of 11 genes were statistically significantly upregulated (> or =1.3-fold) and 34 downregulated (< or =1.3-fold) in the vitamin E-deficient group. Increased expression was observed for the genes encoding the antioxidant enzyme catalase and the axon guidance molecule tenascin-R, while decreased expression was detected for genes encoding protein components of myelin and determinants of neuronal signal propagation. Thus our observations suggest that vitamin E deficiency results in transcriptional alterations in the cerebral cortex of the rat which are consistent with the observed neurological and electrophysiological alterations.

Distribution of calbindin-28kD and parvalbumin in V1 in normal adult Cebus apella monkeys and in monkeys with retinal lesions

Several proteins have their normal patterns of distributions altered by monocular visual deprivation. We studied the distribution of the calcium-binding proteins calbindin-28kD (Cb) and parvalbumin (Pv) in V1 in normal adult Cebus apella monkeys and in monkeys with monocular retinal lesions. In normal monkeys, the interblobs regions in layers 2/3 and the layer 4B are intensely labeled for Cb, while Pv reaction showed a complementary labeling pattern with a stronger staining in layers 4A, 4C and in the blob regions in layers 2/3. In monkeys with monocular retinal lesion, the laminar distribution of these proteins was differentially affected, although both reactions resulted in stronger labeling in non-deprived ocular dominance columns. While Cb reaction resulted in stronger labeling in layers 1 through 5, Pv labeling was heavier in layers 2/3, 4A and 4C. There was a clear reduction in the intensity of neuropil staining for both Pv and Cb in deprived ocular dominance columns with little or no reduction in number of labeled cells. This reduction could thus be attributed to activity-dependent changes at synapses level.

Semaphorins and their receptors in lamprey CNS: Cloning, phylogenetic analysis, and developmental changes during metamorphosis

The large, conserved semaphorin gene family encodes axon guidance molecules in both invertebrates and vertebrates. The primitive vertebrate lamprey diverged near the time of vertebrate origins and is useful for understanding the gene duplication events that led to the increased complexity of the vertebrate genome. We characterized the sequence and expression pattern of semaphorins and their receptors genes in the sea lamprey, Petromyzon marinus. We uncovered two members of the semaphorin family in sea lamprey. The first encodes a diffusible class 3 type semaphorin protein that is most similar to the human and mouse Sema3F (71% amino acid identity). The second encodes a transmembrane class 4 type semaphorin that is most similar to mouse Sema4D and human Sema4G, with 38% amino acid identity within the Sema domain. We also identified in lamprey two members of the semaphorin receptor family, lamprey Plexin A1 and Plexin A2. Phylogenetic analysis indicates that lamprey Sema3 and Sema4 represent precursor genes existing prior to the origin of the vertebrate Sema3A-G and Sema4A-G subfamilies. Therefore, the gene duplication event that gave rise to those subfamilies must have occurred after the divergence of jawed vertebrates from jawless fish. These semaphorins and plexins are expressed in unique and dynamic patterns in lamprey spinal cord and brain during development.

Pilot study of efficacy of tongue and body acupuncture in children with visual impairment

We studied the efficacy of tongue and body acupuncture in affecting visual recovery in children with central and peripheral visual disorders. Twelve children (five boys, seven girls) (age range 18 months to 14.5 years) with visual disorder with static functional visual ability for at least 12 months were recruited for the study. The causes of cortical visual impairment (10) included severe perinatal asphyxia (4), postencephalitis (1), traumatic brain injury (1), hydrocephalus (1), and increased intracranial pressure (3). Peripheral causes (2) were due to congenital optic atrophy. We used the following assessment tools: clinical visual improvement, defined as improvement of vision by one grade in one or both eyes with measurement of visual acuity; the functional visual outcome scale of 0 to 5, with positive outcome defined as improvement in one level on a functional scale; visual evoked potential, with positive improvement defined as 10% improvement in P100 latency of one or both eyes; [18F]-fluorodeoxyglucose (FDG) positron emission tomography (PET) of the brain, with positive improvement defined as a 10% increase in glucose metabolism in one or both occipital lobes; and the Clinical Global Impression Scale (parental report). Tongue and body acupuncture consisted of 60 sessions, with 5 sessions per week. Four children showed clinical or functional improvement (33%). Of nine children with abnormal visual evoked potentials, five had improvement (56%). Of seven children who underwent PET, six had improvement in glucose metabolism in the visual cortex (86%). Seven parents (58%) reported improvement (three children had 75% improvement; four children had 25% improvement). There was a significant correlation between the interval of onset of visual impairment and starting treatment with clinical or functional outcome, with a longer interval resulting in a better outcome (P = .0282). However, there was no correlation between cause, severity, or clinical or functional visual outcome with improvement in the visual evoked potential or PET. We demonstrated that tongue and body acupuncture can improve the visual status of children with visual disorders, both peripheral and central in origin. As children with chronic visual impairment also showed some visual recovery, more studies should be done to assess the full potential of acupuncture as an adjunct to Western medicine in neuroplasticity.

The prognosis of hearing impairment complicating HIV-negative cryptococcal meningitis

Eight patients who had sensorineural hearing loss (SNHL) associated with cryptococcal meningitis were studied. After a minimum 3-year follow-up, one had died. Among the seven survivors, three had improved, two stabilized, and two progressed. Predictive factors included visual disturbance, meningeal enhancements on MRI, and a CSF cryptococcal antigen titer of >1:1,024. SNHL accounted for 30.8% (8/26) of cryptococcal meningitis patients in our study.

Near-infrared spectroscopy of the visual cortex in unilateral optic neuritis

PURPOSE

To examine the occipital-lobe activation of patients with optic neuritis using near-infrared spectroscopy.

DESIGN

Experimental study.

METHODS

NIRS was performed on five patients with acute unilateral optic neuritis during monocular visual stimulation. As controls, six normal subjects were also tested in the same manner.

RESULTS

In the patients with optic neuritis, the changes in the hemoglobin concentrations (oxyhemoglobin, deoxyhemoglobin, and total hemoglobin) in the occipital lobe were found to be markedly reduced when the clinically affected eyes were stimulated compared with the fellow eyes. The response induced by the stimulation of the affected eye was decreased, even when the patient's visual acuity improved to 20/20 in the recovery phase. There was no difference in the concentration changes between the two eyes in the control subjects.

CONCLUSIONS

NIRS may be useful in detecting visual dysfunction objectively and noninvasively in patients with visual disturbance, especially when used at the bedside.

An explanation of transient visual loss associated with leaking filtering bleb

PURPOSE

To report a presumed cause for the transient visual loss noted by a patient with a leaking bleb following trabeculectomy.

DESIGN

Case report.

METHODS

Description of an otherwise healthy woman who developed delayed-onset transient visual loss associated with a leaking filtering bleb.

RESULTS

A 62-year-old woman who underwent trabeculectomy with mitomycin C in her right eye 5 years earlier (Feb 23, 1999) presented with a 3-month history of transient decreased vision. The apparent cause was a periodic gush of aqueous flowing across the surface of the cornea.

CONCLUSIONS

One cause of bleb-associated transient visual loss can be aqueous leaking from the bleb on to the anterior surface of the cornea, disturbing vision as it flows past the visual axis. This is temporarily relieved by blinking.

Ophthalmic drug discovery

Millions of people suffer from a wide variety of ocular diseases, many of which lead to irreversible blindness. The leading causes of irreversible blindness in the elderly--age-related macular degeneration and glaucoma--will continue to effect more individuals as the worldwide population continues to age. Although there are therapies for treating glaucoma, as well as ongoing clinical trials of treatments for age-related macular degeneration, there still is a great need for more efficacious treatments that halt or even reverse ocular diseases. The eye has special attributes that allow local drug delivery and non-invasive clinical assessment of disease, but it is also a highly complex and unique organ, which makes understanding disease pathogenesis and ocular drug discovery challenging. As we learn more about the cellular mechanisms involved in age-related macular degeneration and glaucoma, potentially, new drug targets will emerge. This review provides insight into some of the new approaches to therapy.

Ocular surface, ocular adnexal, and lacrimal complications associated with the use of systemic 5-fluorouracil

PURPOSE

To determine the prevalence rates and associated characteristics of patients who have ocular surface, ocular adnexal, and lacrimal complications associated with the systemic use of the cancer chemotherapeutic agent 5-Fluorouracil (5-FU).

METHODS

An exposure-based cohort study was designed. Adult patients who had completed at least 3 months of systemic 5-FU therapy within the past 5 years were eligible for enrollment. Study subjects had a detailed medical history taken with emphasis on preexisting conditions known to be associated with the development of ocular surface, ocular adnexal, and lacrimal complications. An ocular examination was then performed. A complete nasolacrimal system evaluation was performed if symptoms or findings were identified. The prevalence was then determined for each ocular symptom and each ocular finding identified that was not present pretreatment. An exploratory analysis was then performed to identify patient characteristics that might influence the likelihood of developing any of the above complications.

RESULTS

Fifty-two patients were enrolled in the study. The prevalence rates of the following ocular abnormalities were calculated: ocular irritation, 5.8%; blepharitis, 3.8%; conjunctivitis, 3.8%; keratitis, 3.8%; eyelid dermatitis, 5.8%; cicatricial ectropion, 1.9%; tearing, 26.9%; punctal-canalicular stenosis, 5.8%; and blurred vision, 11.5%. Blacks had tearing at a significantly higher rate when compared with whites (P = 0.022, 2-sided Fisher exact test). Three patients had permanent complications that will require surgery for correction. Of the 7 patients who had a single abnormality, 6 had tearing and one had eyelid dermatitis. All of the 8 patients who had multiple findings had tearing as one of their abnormalities.

CONCLUSIONS

Ninety-three percent of the patients who had an ocular abnormality had tearing as one of the complications. Patients who are receiving systemic 5-FU and begin to tear should have an ocular examination, looking for ocular surface, ocular adnexal, and lacrimal complications.

Retinol-binding protein-deficient mice: biochemical basis for impaired vision

We reported previously that mice lacking plasma retinol-binding protein (RBP) are phenotypically normal except that they display impaired vision at the time of weaning. This visual defect is associated with greatly diminished eyecup levels of retinaldehyde and is reversible if the mutants are maintained for several months on a vitamin A-sufficient diet. Here we provide a biochemical basis for the visual phenotype of RBP-deficient mice. This phenotype does not result from inadequate milk total retinol levels since these are not different for RBP-deficient and wild-type mice. The eye, unlike all other tissues that have been examined, takes up dietary retinol very poorly. Moreover, compared to other tissues, the eye displays a strong preference for retinol uptake when retinol is delivered bound to RBP. The poor uptake of dietary retinol by the eye coupled with its marked ability to take up retinol from RBP, we propose, provides a basis for the impaired vision observed in weanling RBP-deficient mice. Further study of the mutants suggests that the impaired vision is reversible because the eyes of mutant mice slowly acquire sufficient retinol from the low levels of retinol present in their circulation either bound to albumin or present in lipoprotein fractions. Thus, the eye is unlike other tissues in the body in that it shows a very marked preference for acquiring retinol needed to support vision from the retinol-RBP complex and is unable to meet adequately its retinol need through uptake of recently absorbed dietary retinol. This provides an explanation for the impaired vision phenotype of RBP-deficient mice.

Neurotrophin-3 is required for appropriate establishment of thalamocortical connections

In the vertebrate brain, the thalamus serves as a relay and integration station for diverse neuronal information en route from the periphery to the cortex. Formation of the thalamocortical tract occurs during pre- and postnatal development, with distinct thalamic nuclei projecting to specific cortical regions. The molecular forces that underlie the invasion by axons into specific cortical layers followed by activity-dependent maturation of synapses are poorly understood. We show that genetic ablation of neurotrophin-3 (NT-3) in the mouse neocortex results in reduction of a set of anatomically distinct axonal bundles projecting from thalamus through cortical white matter. These bundles include thalamocortical axons that normally establish connections with retrosplenial and visual cortex, sites of early postnatal NT-3 expression. These results implicate neurotrophins in the critical stage of precise thalamocortical connections.

Diffuse metabolic abnormalities in reversible posterior leukoencephalopathy syndrome

Two cases of reversible posterior leukoencephalopathy syndrome were examined with proton MR spectroscopic imaging. Widespread metabolic abnormalities, consisting of increased choline and creatine levels and mildly decreased N-acetylaspartate, occurred in regions with both normal and abnormal MR imaging appearances. In one case for which proton MR spectroscopic imaging follow-up was available, all metabolite levels had returned to normal by 2 months. Proton MR spectroscopic imaging may be helpful for the diagnosis and investigation of the underlying pathophysiology of reversible posterior leukoencephalopathy syndrome.

[Clinical investigation of hyaluronidase and nerve growth factor (NGF) at the ocular level: detailed review of the international literature]

In this paper the authors analyse the international bibliography about clinic tests on hyaluronic acid and Nerve Growth Factor at ocular level. This study was performed on request of a private oculistic clinic in the centre of Rome about the clinic test of the drugs mentioned above. Therefore, this paper is a joint work of Public Health physicians and oculists.

[Postoperative opacification of 12 hydrogel foldable lenses (Hydroview(R))]

BACKGROUND

To evaluate postoperative lens opacifications in foldable hydrophilic intraocular lenses.

PATIENTS AND METHODS

12 patients (9 female; 3 male; mean age 77.5 +/- 3 years) were referred from one ophthalmologic surgeon because of opacification of IOLs and markedly decreased visual acuity. Time between implantation and explantation varied from 8 month to 3 years. IOL explantation was performed in all 12 patients and IOL were examined by light-, transmission- and scanning electron microscopy.

RESULTS

IOL-explantation was uneventful in all 12 patients. The explanted IOLs showed crystalline deposits 0.5 to 2 microm in diameter immediately beneath the surface of the lens. Eight of 12 patients had elevated serum levels for glucose (6 patients with manifest diabetes mellitus, 2 patients with pathological elevated levels for glucose).

CONCLUSIONS

Postoperative opacification of hydrogel foldable lenses (Hydroview(R)) are apperantly caused by formation of crystalline deposits beneath the lens surface. These deposits may be associated with metabolic disorders, e.g. diabetes mellitus.

Changes of contrast gain in cat dorsal lateral geniculate nucleus by dopamine receptor agonists

The modulatory effects of dopamine (DA) on the contrast gain of retino-geniculate transmission were tested with local micro-iontophoretical application of DA and the DA receptor agonists SKF38393 (SKF, D1/D5) and quinpirole (QUIN, D2/D3/D4) while recording visually induced spike activity of relay cells of the dorsal aspect of cat lateral geniculate nucleus (dLGN) in the anesthetised and paralyzed preparation. DA and QUIN could either facilitate or inhibit visual activity in a dose-dependent fashion: small amounts caused a facilitation while larger quantities resulted in a more (DA) or less (QUIN) strong inhibition. The effect of SKF was almost always suppressive and increased with the amount of drug applied. The absolute change in activity was depending on stimulus contrast and the strength of the elicited response: facilitation and inhibition of activity was proportional to stimulus contrast and response strength and thus resulted in a changed contrast gain. The results indicate that the visual deficits found in Parkinson's disease patients my be not solely related to retinal dysfunctions.

Rate of visual field loss and long-term visual outcome in primary open-angle glaucoma

PURPOSE

To evaluate long-term visual field outcome in primary open-angle glaucoma.

METHODS

In this retrospective cohort study, 40 eyes of 40 patients with primary open-angle glaucoma with elevated intraocular pressure and a minimum of 8-year longitudinal series of visual fields were plotted with Goldmann perimeter. Eyes with any other ocular disease except cataract were excluded. Manual grid templates were used to quantify the visual fields. Linear regression was performed to estimate the rate of visual field decline. Pertinent clinical factors were evaluated for statistical association with the rate of decline. Long-term clinical outcome including visual acuity, rate of legal blindness, and rate of medical and surgical interventions was also measured.

RESULTS

In the 40 eyes studied, with a mean follow-up of 14 years, the visual field score decreased at the rate of -1.5% per year. Overall, 68% showed significant decrease, and the rate of decrease among these eyes was -2.1% per year. Five eyes became legally blind from glaucoma; the cumulative rate of blindness from glaucoma was 19% at 22 years. Higher intraocular pressure and greater number of antiglaucoma medications on initial presentation were associated with faster and slower deterioration of visual field (compared with the average), respectively.

CONCLUSIONS

With standard glaucoma therapy, the rate of visual field loss in primary open-angle glaucoma is slow. Lower intraocular pressure and more antiglaucoma medications are associated with slower visual field decline. Legal blindness from glaucoma is 19% over a follow-up of 22 years.

Optical and visual impact of tear break-up in human eyes

PURPOSE

The purpose of this study was to examine the optical and visual impact of tear break-up.

METHODS

Optical quality of the eye was assessed during periods of nonblinking by quantifying vessel contrast in the fundus image and by monitoring the psychophysical contrast sensitivity and the spatial distribution of tear thickness changes by retroillumination. All measures were obtained from three eyes either with or without a soft contact lens.

RESULTS

A noticeable decrease in retinal vessel contrast and contrast sensitivity were observed soon after a blink. Both of these measures of optical quality of the eye showed a similar pattern of image degradation both with and without a soft contact lens. Although trial-to-trial variability was considerable, sample means show that image contrast in the low spatial frequency range can drop to between 20% and 40% of initial values after 60 seconds of nonblinking. Retroillumination of the tear film showed local intensity fluctuations that progressively spread across the pupil with increasing time after the blink.

CONCLUSIONS

Optical aberrations created by tear break-up contribute to the decline in image quality observed objectively and psychophysically. The decline in image quality that accompanies tear break-up may be a direct cause of the blurry vision complaints commonly encountered in dry-eye patients.

Disturbances of spatial vision and object vision correlate differently with regional cerebral glucose metabolism in Alzheimer's disease

There is evidence of two neuronal systems for visual cognition which are referred to as spatial vision and object vision. We subjected 49 patients with mild-to-moderate probable Alzheimer's disease (AD) to tasks associated with these two types of visual cognition. Visual counting was employed as a task to assess visuospatial recognition. Identification of overlapping figures and discrimination of visual forms were used as visuoperceptual tasks that require an ability to recognize objects. Regional cerebral glucose metabolism (rCMRglc) of the subjects was also determined by positron emission tomography. Multivariate statistics controlling for the confounding factors assessed the correlation between the task performances and the rCMRglc. The visual counting score significantly correlated with the metabolic rate of the bilateral inferior parietal lobules. On the other hand, the scores of the visuoperceptual tasks significantly correlated with the metabolic rate of the right middle temporal gyrus and the right inferior parietal lobule. The present study showed that visuospatial disturbance was related to bilateral parietal metabolism, and that visuoperceptual disturbance was related to right temporo-parietal metabolism in patients with mild-to-moderate AD.

Visually significant calcification of hydrogel intraocular lenses necessitating explantation

PURPOSE

To report two cases of HydroviewR (Storz H60M) hydrogel intraocular lens (IOL) opacification necessitating explantation. To analyse the explanted lenses and compare them with a new lens in order to determine the cause of opacification.

METHODS

Two cases are presented. Both patients complained of subjective decreases in vision approximately 1 year following uneventful cataract extraction and implantation of hydrogel lenses by the same experienced surgeon in the same institution. The reduced contrast sensitivity was thought to be due to failure of the hydrogel lenses which appeared opacified at the slit-lamp. They were then exchanged for acrylic lenses. Pre- and postoperative contrast sensitivity testing was performed using the VectorvisionR CSV-1000E instrument. A detailed comparative analysis of the opacified explanted lenses and a new lens was undertaken. This included surface microscopy, infrared spectral analysis, X-ray elemental analysis, scanning electron microscopy, and electron microscopy of lens slices.

RESULTS

Lens exchange resulted in an improvement in subjective visual acuity (VA) and in objective contrast sensitivity testing. Analysis revealed deposits of calcium phosphate (hydroxyapatite) on the explanted lens' surfaces.

CONCLUSIONS

The surface of the HydroviewR H60M intraocular lens is subject to opacification as a result of calcium phosphate (hydroxyapatite) deposition, thereby limiting the patient's visual outcome, and in some cases necessitating explantation. The reason for surface calcification requires further study.

NMDAR-1 staining in the lateral geniculate nucleus of normal and visually deprived cats

In normal adult cats, a monoclonal antibody directed toward the NR-1 subunit of the N-methyl-D-aspartate (NMDA) receptor (Pharmingen, clone 54.1) produced dense cellular and neuropil labeling throughout all layers of the lateral geniculate nucleus (LGN) and adjacent thalamic nuclei, including the thalamic reticular, perigeniculate, medial intralaminar, and ventral lateral geniculate nuclei. Cellular staining revealed well-defined somata, and in some cases proximal dendrites. NMDAR-1 cell labeling was also evident in the LGN of early postnatal kittens, suggesting that developing LGN cells possess this receptor subunit at or before eye opening. Within the A-layers of the adult LGN, staining encompassed a wide range of soma sizes. Soma size comparisons of NMDAR-1 stained cells with those stained with an antibody directed toward a nonphosphorylated neurofilament protein (SMI-32), which selectively stains Y-relay cells (Bickford et al., 1998), or an antibody to glutamic acid decarboxylase (GAD), which stains for GABAergic interneurons, suggested that NMDA receptors are utilized by relay cells and interneurons. NMDAR-1 staining was also observed in the LGN of cats with early monocular lid suture. Although labeling was apparent in both deprived and nondeprived A-layers of LGN, the distribution of soma sizes was significantly different. In the deprived A-layers of LGN, staining was limited to small- and medium-sized cells. Cells with relatively large soma were lacking. However, cell density measurements as well as soma size comparisons with cells stained for Nissl substance suggested these differences were due to deprivation-induced cell shrinkage and not to a loss of NMDAR-1 staining in Y-cells. Taken together, these results suggest that NMDA receptors are utilized by both relay cells and interneurons in LGN and that alterations in early visual experience do not necessarily affect the expression of NMDA receptors in the LGN.