SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A transient episode of bilateral amaurosis fugax, or transient visual loss, occurred in a patient with ophthalmic migraine associated with mitral valve prolapse while computerized visual field testing was performed. This fortunate finding illustrated characteristic defects which are compared with the patient's visual field tested 24 hours later. Statistical analysis of both examinations is stressed here.
We present results from 64 glaucoma patients and glaucoma suspects followed up for a median period of 7.4 yr who had a median of seven examinations using Program 31 on the Octopus perimeter. The patients also had manual visual fields recorded on either the Tübinger or Goldmann perimeter during the same period. By examining all manual fields over the follow-up, we classified 37 patients as deteriorating and 27 as nondeteriorating by using predetermined field criteria which we believed to be clinically significant. In a masked fashion, the indices mean defect (MD) and corrected loss variance (CLV), in addition to the three cluster analysis indices SIZ, CLUS, and PCLUS were computed for each patient and regressed on time. When a significant positive index/time slope (P less than 0.05) was defined as indication of deterioration, all indices had remarkably poor sensitivities because their slopes did not reach statistical significance in the great majority of patients. When, regardless of statistical significance, positive slopes were defined as indication of deterioration and negative slopes as nondeterioration, the most sensitive index, PCLUS, still had a sensitivity of less than 65%. The indices were better in detecting the presence or absence of visual field deterioration in fields that were initially normal than in those that were initially abnormal. Since the testing modalities of manual and automated perimetry are different, our study was not designed to compare the sensitivity of one technique over the other. Our study does, however, demonstrate that the indices used currently may not be clinically reliable in the assessment of changes in the visual field.
Examination of visual induced potentials on reversible chess-pattern in 46 children with bilateral congenital zonular cataracts before and after surgical intervention has revealed correlation between these potentials and degree of lens opacification. After cataract extraction, positive dynamics of the potentials was observed in case of slightly opacified lenses and was absent in intensive lens opacification. The authors consider it reasonable to use visual induced potentials for prognosticating visual results after surgical treatment of bilateral congenital zonular cataracts, this being of particular importance for early surgical interventions.
The postnatal development of the Na-independent 3H-glutamate binding sites has been studied in the retina, lateral geniculate nucleus, superior colliculus, frontal and visual cortex of the rat. In the visual cortex, lateral geniculate nucleus and superior colliculus the highest binding was found at postnatal day 15. Until day 25 glutamate binding decreases drastically reaching the adult values. In contrast, in the retina and in the frontal cortex binding exhibits a maximum already at postnatal day 10 and then decreases to reach the adult value at day 25. Comparing glutamate binding within the visual areas and frontal cortex, highest binding was found in the lateral geniculate nucleus at all stages of age studied. Unilateral eyelid closure from day 11 postnatally resulted in a decreased binding level in the lateral geniculate nucleus ipsilateral to the sutured eye of both 25- and 90-day-old monocularly deprived rats in comparison to controls. A decreased glutamate binding was also observed in the retina of both eyes of 90-day-old monocularly deprived animals, which was not detectable in rats monocularly deprived only until the age of 25 days. The other regions studied were not affected by monocular deprivation. In contrast to that, monocular deprivation until postnatal day 90 failed to affect glutamate high-affinity uptake in both retinas. Binocular deprivation had no effect on glutamate binding in the retina of adult rats. Since monocularly deprived rats use their open eyes for longer periods of time than animals with both eyes open [1], the decreased glutamate binding in the lateral geniculate nucleus might be the consequence of a down-regulation of the increased functional activity of the cortico-geniculate pathway of the non-deprived (open) eye. The decreased glutamate binding in the retina of both eyes of monocularly deprived animals suggests a physiological coupling between both retinas and/or central nervous control of retinal glutamatergic mechanism.
Cataract patients suspected of having disease that might interfere with good postoperative visual function were evaluated by eliciting monocular steady-state luminance visual evoked potentials (VEPs) with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have visual acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The predicted and observed postoperative acuities were quantitatively compared for the 59 patients who met these criteria, using a 2 X 2 contingency table. The chi-square was significant (p less than .001). The overall accuracy of prediction was 80%. Accuracy of the predictions for patients with preoperative acuities of 6/60 (20/200) or better was compared with the accuracy of the predictions for those with preoperative acuities of 60/120 (20/400) or worse. There was no significant difference (p greater than 0.10).
It has been shown by two-wavelength cytospectrophotometry of gallocyanin-chrome alum-stained sections that visual deprivation in adult rats kept in a complete darkness for 30 days resulted in an accumulation of cytoplasmic RNA by layer V neurons of the visual cerebral cortex and by the cells of the perineuronal neuroglia of this layer. The nuclear RNA content remained unchanged. Stimulation of intact rats with a flickering or constant light induced an increase in the cytoplasmic RNA in these neurons rather than in the nuclear RNA as well as in RNA in their glial satellite cells. Similar light stimulation of the deprived animals gave rise to a complete return of the neuronal RNA to normal with only a slight decrease in the deprivation-induced RNA accumulation by the neuroglial cells. Neither visual deprivation nor light stimulation affected the RNA content in the neurons and neuroglia of layer V of the motor cerebral cortex. Compartmentation of RNA metabolism within the neuronal-neuroglial unit is discussed.
Visual-evoked potentials (VEPs) were recorded using a laser speckle pattern. Stimulation with a speckle pattern was elicited either by pattern appearance-disappearance or by pattern shift. The VEPs obtained by this method were similar in properties to the previous pattern VEPs that were obtained either by pattern appearance-disappearance or by pattern reversal. Patients in whom dense and diffuse ocular media opacity defied measurement by the interferometric visual acuity method were studied to test if the speckle pattern generated by diffusion from lens opacity itself could act as a stimulus for obtaining VEPs. It is concluded that the present method enables one to obtain a reliable VEP and to assess the visual function of the retino-cortical system, even in patients with mature cataracts.
The objective measurement of visual acuity in infants is reviewed. Recent techniques have shown that visual acuity levels as early as four to six months after birth. This and other evidence indicates that the most sensitive period in the development of the visual system may be during the first six months of life. With this as a rationale, it is suggested that eye care practitioners consider eye examinations and correction of refractive errors during infancy as a means of prevention of future strabismus and amblyopia.
We have examined the responses of 141 layer VI cells in the feline visual cortex. Within this group we compared the responses of a subpopulation of cells checked for connectivity by electrical stimulation in the dLGN and the visual claustrum. The antidromically identified corticogeniculate projecting cells had relatively short receptive fields, as judged from length response curves, measured quantitatively, and were located at the "short" end of the receptive field length spectrum seen in the general population. Of the 17 corticogeniculate projecting cells, 71% were S type cells, which were typically monocular and directionally selective, with relatively long latencies following electrical stimulation. The remaining 29% were C type cells, also directionally selective, but with a wider spread of ocular dominance preferences and shorter latencies following electrical stimulation. S and C type subpopulations did not differ in their receptive field lengths. The mean receptive field length for this subpopulation was 2.2 degrees +/- 0.27, the shortest field being 1 degrees and the longest 5 degrees. The five layer VI cells activated by electrical stimulation from electrodes within the dorsocaudal (visual) claustrum all had much longer receptive field lengths than the corticogeniculate population, often 10 degrees or longer and were monocular and directionally selective S type cells. These data indicate that the information carried in the corticogeniculate stream (and that from layer VI directly to layer IV carried by axon collaterals) is relatively tightly focused in spatial terms whilst the less spatially focused, long receptive field output from layer VI projects to the claustrum.
The authors analyse 200 visual fields (examine with automatic perimetry) of patients with the chiasmal syndrome. On the basis of their own results they recommend the use of quantitative perimetry for early diagnosis of visual field changes in the range of central visual field (0-30 degrees).
Subunit proteins that make up functional GABAA receptors were localized immunocytochemistry in the primary visual cortex (area 17) of adult monkeys and humans. Immunoreactivity for the alpha 1, beta 2/3, and gamma 2 subunits is greatest in layers (II-III, IVA and IVC) of monkey area 17 that contain the highest density of GABA neurons and terminals. Immunostaining for each subunit is unevenly distributed in layers II and III, where patches of immunoreactivity correspond to regions of intense cytochrome oxidase (CO) staining, and in layer IVA, where intense immunoreactivity forms a honeycomb pattern identical to the CO staining pattern. Immunoreactivity for the subunits is localized principally within the neuropil, which, by simultaneous comparison with the distribution of microtubule-associated protein immunostaining, was found to include bundles of thin dendrites and zones of numerous dendritic segments. In addition, gamma 2 immunostaining surrounds the somata of a subpopulation of GABAergic neurons, immunoreactive for the calcium-binding protein parvalbumin. All three subunits are present in the somata and processes of neurons that occupy the white matter subjacent to monkey area 17. In human visual cortex, the alpha 1, beta 2/3, and gamma 2 subunits are distributed in a manner similar to that found in monkeys, with relatively intense immunostaining in layers IVC and IVA. In layer IVC, vertical stripes of intense receptor immunostaining (20-30 microns wide) alternate with wider stripes of pale immunostaining (30-60 microns wide). In the upper and lower halves of IVC beta, these stripes form lattices similar to those in layers IVC and IVA of monkeys. Following monocular deprivation by intravitreal injections of TTX in adult monkeys, immunoreactivity for each subunit in layer IVC consists of alternating intensely and lightly stained stripes. Comparison with the pattern of CO staining indicates that intense immunostaining for alpha 1, beta 2/3, and gamma 2 occurs in normal-eye stripes while abnormally light immunostaining is present in deprived-eye stripes. For all three subunits, immunoreactivity in deprived-eye stripes is reduced within 5 d of monocular deprivation and remains abnormally low for deprivations that extend to at least 30 d. These findings indicate that each of several GABAA receptor subunits adopt similar laminar and compartmental distributions in monkey and human area 17 and are likely to be expressed by the same neurons. The deprivation-dependent reduction in immunoreactivity for alpha 1, beta 2/3, and gamma 2 subunits suggests that all are regulated by visually driven activity.(ABSTRACT TRUNCATED AT 400 WORDS)
Relative micropsia was measured by a matching technique in patients with unilateral, benign, macular edema. Quantitative assessment of foveolar micropsia to be a sensitive indicator of receptor displacement in this disorder, and may be a useful tool both for diagnosing and for monitoring macular edema. Parallel measurements of grating acuity showed a close proportionality between acuity and micropsia parameters. This result validates a new quantitative theory for the neuro-retinal basis of visual acuity. The theory allows prediction of the proportion of working visual neurons in patients with impaired acuity due to diseases that produce a diffuse loss, or disconnection, of macular cones. Our results indicate that so-called normal visual acuity (1.0 or 20/20) requires no more than 44% of the normal quantity of fovelar, neuro-retinal channels.
Computational models of periodic- and aperiodic-pattern selective cells, also called grating and bar cells, respectively, are proposed. Grating cells are found in areas V1 and V2 of the visual cortex of monkeys and respond strongly to bar gratings of a given orientation and periodicity but very weakly or not at all to single bars. This non-linear behaviour, which is quite different from the spatial frequency filtering behaviour exhibited by the other types of orientation-selective neurons such as the simple cells, is incorporated in the proposed computational model by using an AND-type non-linearity to combine the responses of simple cells with symmetric receptive field profiles and opposite polarities. The functional behaviour of bar cells, which are found in the same areas of the visual cortex as grating cells, is less well explored and documented in the literature. In general, these cells respond to single bars and their responses decrease when further bars are added to form a periodic pattern. These properties of bar cells are implemented in a computational model in which the responses of bar cells are computed as thresholded differences of the responses of corresponding complex (or simple) cells and grating cells. Bar and grating cells seem to play complementary roles in resolving the ambiguity with which the responses of simple and complex cells represent oriented visual stimuli, in that bar cells are selective only for form information as present in contours and grating cells only respond to oriented texture information. The proposed model is capable of explaining the results of neurophysiological experiments as well as the psychophysical observation that the perception of texture and the perception of form are complementary processes.
A computer test for visual field deficits and visual neglect was developed and evaluated by testing 63 patients with brain damage. This computer test controls the sequence of unilateral or bilateral lights series, and stores the responses. Test results are compared to clinical and ophthalmological tests and neuropsychological assessment. Visual field deficits were present in 17 patients on the computerized test, in 16 patients on ophthalmological test, and in 13 patients on clinical examination. Neglect was present in 12 patients on the computerized test, and in 10 patients on the neuropsychological assessment. Eighteen patients had mixed disorder (hemianopia and neglect). Results of the chi 2 statistic confirm the greatest correlation between the computerized test and the ophthalmological (phi = 0.93; p < 0.001) and neuropsychological (phi = 0.90; p < 0.001) tests. Correlation between the computerized test and the clinical examination was poorer (phi = 0.85; p < 0.001). The computerized test makes it possible to detect mixed disorder with the same tool, during the same examination.
The ability to generate visual mental images, to maintain them, and to rotate them was studied in deaf signers of American Sign Language (ASL), hearing signers who have deaf parents, and hearing non-signers. These abilities are hypothesized to be integral to the production and comprehension of ASL. Results indicate that both deaf and hearing ASL signers have an enhanced ability to generate relatively complex images and to detect mirror image reversals. In contrast, there were no group differences in ability to maintain information in images for brief periods or to imagine objects rotating. Signers' enhanced visual imagery abilities may be tied to specific linguistic requirements of ASL (referent visualization, topological classifiers, perspective shift, and reversals during sign perception).
Report that concurrent speaking reduces right hand sequential finger tapping performance selectively only if the movements are guided non-visually. In these replication experiments, concurrent speaking of both rhyme and prose passages reduced performance both of the right and left hand under visual and non-visual guidance. In the replication experiments the performance of the right hand was slightly more reduced by concurrent speaking than was the case for the left hand. The interference effects are interpreted in terms of the temporal constraints imposed by given motor tasks.
The effects of melatonin given systemically at night-time were investigated in the visual system of cats by means of electrophysiological recordings from single cells in the striate cortex (area 17). Following intravenous injection of melatonin, the spontaneous discharge rate (SDR) was found to decrease in the majority of units when compared to control situations. In addition, the amplitude of responses to photic stimulation (moved light bars on a dark background) was augmented. These results reveal that, following application of melatonin, an improved signal-to-noise ratio is found in response to visual stimuli. The physiological source and putative action sites of melatonin are discussed with regard to its physiological role as a neuromodulating substance. The present data, in addition to previous work, suggest that melatonin is involved in visual information processing such as object detection and dark adaptation.
The postnatal development of laminar pattern of the m2 muscarinic acetylcholine receptor subtype mRNA in the visual cortex of both normally raised and monocularly deprived rats (one eyelid sutured at the age of 11 days) was studied using in situ hybridization histochemistry and computer-assisted image analysis. In normally raised rats, on birth, the m2 transcript was found to be more concentrated in the superficial zones of the cortex. This laminar pattern alters to a more homogeneous distribution of the label throughout the cortex already detectable on day 7. From day 10 onwards a bimodal laminar pattern gradually develops with increased mRNA levels in layer IV and upper layer VI. From postnatal day 21 onwards the hybridization peak in layer VI decreases as compared to the peak level in layer IV resulting in an adult distribution with highest labeling in layer IV, low labeling in layer I to III and moderate labeling in layers V and VI. Monocular deprivation results in decreased m2 mRNA levels in visual cortical layers IV-VI in both deprived and non-deprived cortices already detectable at the age of 18 days and persisting up to the age of 21 days; but this effect disappears following further deprivation until adulthood. The data suggest that the changes in m2 receptor level from a more homogeneous distribution to a bimodal pattern during postnatal development seem to be related to synaptogenesis and final tuning of connectional pattern within the rat visual cortex.