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At least 1,207 records · Page 67Linked to original sources
PubMed2005

Intraoperative awakening for vision examination during ophthalmic artery aneurysm clipping: technical case report.

OBJECTIVE AND IMPORTANCE: We present a case of a patient with an ophthalmic artery aneurysm in which the ophthalmic artery originated from the body of the aneurysm, requiring sacrifice of the ophthalmic artery to achieve complete aneurysm obliteration. We awakened the patient intraoperatively to assess optic nerve function after clipping and were able to confirm optic nerve function. Controlled intraoperative awakening proved a valuable adjunct to intraoperative angiography in determining the immediate consequences of sacrifice of the ophthalmic artery. CLINICAL PRESENTATION: The patient was a 55-year-old right-handed woman with a 3-month history of episodic blurriness in her left eye; imaging demonstrated an unruptured 5-mm left ophthalmic artery aneurysm in which the ophthalmic artery originated from the body of the aneurysm. INTERVENTION: Complete obliteration of the aneurysm required clip placement across the neck of the aneurysm, incorporating not only the aneurysm but also the ophthalmic artery. Aware that sacrifice of the ophthalmic artery was likely, we awakened the patient after clipping and before dural closure to evaluate her optic nerve function. Once fully awake, the patient was able to execute simple commands and conclusively confirm light perception in both of her eyes. She was then reanesthetized, and intraoperative angiography showed successful aneurysm obliteration and parent artery patency. CONCLUSION: The ophthalmic artery can be sacrificed during aneurysm clipping without loss of vision in many cases, most likely because of adequate collateral filling from the external carotid artery. Certainty about the visual consequences of sacrifice of the ophthalmic artery, however, is difficult to obtain preoperatively or intraoperatively. Intraoperative awakening for evaluation of optic nerve function served as a useful technique to assess the acute results of interruption of ophthalmic artery flow in this case.

Aneurysm↗
PubMed1989

Usher syndrome: an otoneurologic study.

Usher syndrome is an autosomal recessive disorder characterized by severe hearing loss or deafness and retinitis pigmentosa. Eleven families with 25 affected members were studied. The test battery included genetic studies, clinical examination, audiological, ophthalmologic, and otoneurological tests, and magnetic resonance imaging. Sixteen affected persons had profound hearing loss or were considered anacusic, with absent bilateral vestibular responses. These patients had varying degrees of retinitis pigmentosa. These 16 patients were considered to have type I Usher syndrome. Nine persons were diagnosed as Usher type II with a moderate to profound hearing loss, normal vestibular function, and retinitis pigmentosa of varying degree. Magnetic resonance imaging was normal in all cases. Otoneurological tests indicated no central nervous system disturbances. The conclusion is that hearing loss and balance problems in Usher syndrome are due to inner ear damage with no evidence of central nervous system disturbances. Furthermore, the ataxia seen in Usher type I is due to a combination of retinitis pigmentosa and bilateral peripheral vestibular deficiency.

Adolescent↗
PubMed1999

Bayesian analysis of square ordinal-ordinal tables.

We analyse square contingency tables with ordered categories. Assuming that the observed ordinal categorical variables are manifestations of underlying continuous variables, we formulate a model which allows the comparisons of locations and dispersions between variables. We identify the model by imposing stochastic constraints on the thresholds that define the relationship between the observed and the underlying variables. As a result, the underlying continuous variables' location and dispersion parameters which were not estimable before can be estimated by the Bayesian approach. Illustrative examples are given based on several reported data sets.

Bayes Theorem↗
PubMed1977

Transient visually evoked potential.

A light delivered to the human eye will instigate changes in electrical potentials recorded over the visual cortex that last for some finite time, at least several hundred milliseconds. If the rate of stimulation is sufficiently low, the response is completed before the next visual stimulus arrives; the cortical potential is then called a transient evoked response. This review of the transient evoked potential describes the techniques by which the response is obtained, the problems inherent in its use, and procedures by which these difficulties can be overcome or minimized. A summary of the research results from the field enumerates those findings which have been well established and replicated by many investigators, those that are more controversial or as yet inconclusive, and the many practical applications of the technique for science and medicine. Finally, the needs for an underlying physiological theory and for future research are discussed.

Color Vision Defects↗
PubMed1981

Effect of stimulus size on fusion and vergence.

Objective measurements were carried out to determine the effect of stimulus size on fusional and vergence amplitudes. It was shown that increasing the stimulus size to include peripheral retinal regions results in significant increases in horizontal and vertical fusional amplitudes. This increase is realized by proportionate increases in both motor (vergence) and nonmotor components.

Eye Movements↗
PubMed1982

Eliminating transient artifacts in stabilized-image contrast thresholds.

In the measurements of contrast thresholds for stationary, stabilized images, the choice of the psychophysical procedure may profoundly affect the results by constraining the time course of the stimulus presentation. With some procedures, the subject is unable to ignore transients; as a result, he necessarily responds to onset and offset transients rather than to the intended stimulus. Here we report significant effects of (a) the rapidly of onset and (b) the duration of the stimulus on thresholds for stabilized sinusoidal-grating patterns; these effects occur with both forced-choice and standard yes/no procedures. No value of either parameter (a) or (b) can eliminate such presentation effects when these procedures are used. However, we have devised a new, continuous-presentation procedure that yields results that do not depend on these parameters. Contrast thresholds for stabilized and for unstabilized stimuli measured by this procedure differ by 1 log unit or more, in good agreement with the results obtained by careful use of the method of adjustment.

Differential Threshold↗
PubMed1982

Simultaneous visual detection and identification: theory and data.

A signal-detection model is presented for the two-alternative forced-choice procedure that gathers simultaneous detection and identification judgments. By using vector representation, a measure of independent processing within the visual system is derived. The independence measure is applied to data on the detection and identification of stimuli that differ along the dimensions of orientation, spatial frequency, and size. Data are presented that favor the signal-detection model over a high-threshold model.

Humans↗
PubMed1984

Figure-ground segregation by motion contrast and by luminance contrast.

Some naturally camouflaged objects are invisible unless they move; their boundaries are then defined by motion contrast between object and background. We compared the visual detection of such camouflaged objects with the detection of objects whose boundaries were defined by luminance contrast. The summation field area is 0.16 deg2 , and the summation time constant is 750 msec for parafoveally viewed objects whose boundaries are defined by motion contrast; these values are, respectively, about 5 and 12 times larger than the corresponding values for objects defined by luminance contrast. The log detection threshold is proportional to the eccentricity for a camouflaged object of constant area. The effect of eccentricity on threshold is less for large objects than for small objects. The log summation field diameter for detecting camouflaged objects is roughly proportional to the eccentricity, increasing to about 20 deg at 32-deg eccentricity. In contrast to the 100:1 increase of summation area for detecting camouflaged objects, the temporal summation time constant changes by only 40% between eccentricities of 0 and 16 deg.

Humans↗
PubMed1995

Enhancement of text for the visually impaired.

Previous research has established the benefits of image enhancement by spatial filtering for face perception and motion video appreciation among elderly low-vision observers [Invest. Ophthalmol. Vis. Sci. 32, 2337 (1991); J. Opt. Soc. Am. A 11, 1929 (1994)]. It has also been reported that similar enhancement could increase reading speeds by a factor of 2-4 in the same population [cf. Ophthalmology 96, 115 (1989)]. In our experiments we sought to determine what benefit, if any, was derived from spatial filtering of text for low-vision readers. Results from this series of studies indicate that 66% of patients do increase their reading rate with enhancement, but this increase is small. Change in reading rate with spatial filtering ranged from a 100% decrement to a 125% improvement, with an average 13% improvement. Only 10 of 67 subjects increased their reading rates by 50% or more. The clinical information that we gathered does not allow us to predict accurately which patients will benefit from spatial filtering. On the basis of these findings we conclude that enhancement of text by spatial filtering does not substantially increase reading rates for most low-vision patients.

Adult↗
PubMed1995

Scrolled and rapid serial visual presentation texts are read at similar rates by the visually impaired.

Visually impaired observers read dynamically displayed text faster than text displayed in a normal page view. The goal of this study was to compare reading rates from two dynamic-presentation methods that have been proposed to facilitate reading from computer-based displays. Prior research has shown that both normally sighted and low-vision observers read text displayed to the same location, one word at a time [known as rapid serial visual presentation (RSVP)], faster than a page of text. A similar comparison with text scrolled continuously across the screen also shows faster reading for low-vision patients, but the relative change from a standard page view is substantially less (15% faster for the scroll display versus 80% faster for RSVP). In this study we directly compared these techniques. For those with normal vision, reading from the RSVP display was 1.3 times faster than reading from the scroll display [t(9) = 3.32, P = 0.009]. Although the difference in reading rates for the visually impaired group did not reach statistical significance, as a group they read 13% slower from the RSVP than from the scroll display.

Adult↗
PubMed2005

Foveal contour interaction: detection and discrimination.

Contour interaction, the detrimental effect of flanking features on the discrimination of optotypes, has been studied mainly close to the visual acuity limit. We were interested to know how these results compare with those for the detection of targets. According to the simplest model of contour interaction, comparable detection effects would be expected. The case for low-level masking would be further strengthened if the form and nature of the dependence on flank separation and flank polarity followed that typically found in studies of lateral spatial masking [Vision Res. 33, 993 (1993)]. Landolt Cs subtending a visual angle of 0.25 degrees, 0.5 degrees, and 1.0 degrees were presented and contrast thresholds for detecting the presence of the Landolt C and discriminating its orientation were measured in five normal subjects as a function of flank separation and flank polarity. The results obtained for the relationship between detection and discrimination depend on the size of the target used. For small letters, discrimination but not detection was significantly affected by flanking bars. For large letters, detection and discrimination were affected to the same extent. However, in this case the effectiveness of opposite-polarity flanks and the finding that facilitation occurred at close, not far, flank separations suggests that the simplest explanation in terms of masking may not be applicable.

Differential Threshold↗
PubMed1986

Spectral luminous efficiency functions in the mesopic range.

Spectral luminous efficiency functions for mesopic vision were measured extensively to establish a basic data set for the mesopic photometry system. These functions were obtained by the direct brightness matching for a 10 degrees field at nine retinal illuminance levels from 100 to 0.01 Td in 0.5-log-unit steps. Data for 12 subjects were collected. In the mesopic range, the spectral luminous efficiency function, averaged over 12 subjects, gradually changes form with retinal illuminance. This suggests that the mesopic function should be established for all the levels in that range. An attempt was made to find an empirical formula that expresses the mesopic function as a simple combination of the photopic and the scotopic brightness functions.

Humans↗
PubMed1987

Determination of the point-spread function of human eyes using a hybrid optical-digital method.

A method for the determination of the bidimensional optical transfer function (OTF) and the point-spread function of human eyes is presented. Aerial short-term images of a point source are directly recorded with a TV camera and fed into a digital image-processing system that allows one to determine and display such functions. The method has been implemented in such a way that recording and computation can be carried out on a routine basis with minimum discomfort for the observer. A detailed description of the method and typical aerial and retinal images of a point source as well as the OTF's results are presented in this paper.

Humans↗