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Biomedical subjects

A B Safran

Publications and source records attributed to A B Safran.

At least 37 records · Page 2Linked to original sources
PubMed2000

Monocular central dazzle after thalamic infarcts.

The authors observed a patient after he had ischemic strokes in both paramedian thalamic regions, which were more marked on the left side. Symptoms included dysphasia, vertical binocular diplopia, right-sided hemianopia, and a right-sided sensory and motor deficit, sparing the face. However, the most disturbing phenomenon was a painless, left monocular dazzle, which was the presenting symptom and also the only persisting symptom. This report shows that a thalamic lesion may be at the origin of central dazzle, and to the authors' knowledge, it is the first clinical observation of its monocular occurrence. It is conceivable that this dazzle was due to optic-trigeminal summation.

Brain Infarction↗
PubMed1999

Combined use of several preferred retinal loci in patients with macular disorders when reading single words.

To investigate the use of several preferred retinal loci (PRL) when attempting to read, two patients with bilateral central scotomas were asked to decipher single words, successively projected onto the retina using a scanning laser ophthalmoscope (SLO). Video-recordings of the fundus image, on which the projected targets were superimposed, were analyzed frame by frame. One patient used two PRL in association and the other used three, each PRL having a specific function. Single word reading made it easier than with full texts to correlate the images parts scrutinized and the retinal areas involved. Then, as patients were unable to describe their reading behavior, the examiner monitored refixation movements using the SLO and asked questions to help them to become aware of their reading behavior. Eventually, they could localize their PRL, describe their specific functions, and switch at will between them.

Adaptation, Physiological↗
PubMed1999

Does visual sensitivity improve between 5 and 8 years? A study of automated visual field examination.

In 74 normal subjects (62 children aged 5-8 years and 12 adults), we tested the widely-held belief that visual sensitivity improves substantially during childhood. Maturation of the retino-striate pathways is generally invoked to account for age-related changes in visual sensitivity. We evaluated the extent to which attentional factors unduly emphasized the effect of age on the purely physiological mechanisms. After a specially-designed familiarization procedure, sensitivity was fully evaluated at two locations in the superior temporal field using a bracketing technique (Octopus 2000R). False-positive (FP) and false-negative (FN) catch-trials were interspersed with the sequence of stimuli. Analyses demonstrated that: (1) age affected sensitivity; and (2) the general level of attentiveness varied not only with age, but also among subjects in the same age group. We then estimated the extent to which improved visual sensitivity may reflect a concomitant evolution of vigilance. Firstly, controlled variance analyses indicated that factors for evaluating attentiveness (rate of FN responses, slope of the psychometric function at the median, and goodness of fit) were indeed much better predictors than age of the sensitivity measured. Secondly and more significantly, the grouping of subjects into homogeneous subgroups, on the basis of their attentional performance, showed that children as young as 5 years may have a visual sensitivity that is only marginally lower than that of adults.

Adult↗
PubMed1999

Full text reading with a central scotoma: pseudo regressions and pseudo line losses.

AIMS: To investigate the reading strategy of a patient with central scotoma, using several preferred retinal loci (PRL). METHODS: A 47 year old man with Stargardt's disease was asked to decipher texts projected onto his retina using a scanning laser ophthalmoscope. A recording of the fundus image, on which the projected texts were superimposed, was analysed frame by frame. RESULTS: The subject used a combination of three PRL, located above the scotoma and laterally to the left and right of it. He first used his left PRL to search for the beginning of a line, then switched to his right PRL, thus performing an apparent regression which was called "pseudo regression", to read the line with successive rightward saccades. To decipher a particularly difficult word, he switched to his upper PRL, showing an apparent line loss which was called ("pseudo line loss"), and then used his three PRL in combination. CONCLUSION: The patient used a complex, well structured reading strategy. These data showed that backward saccades and unexpected line losses, hitherto thought to be inappropriate and uneconomical, may in fact represent purposeful changes of PRL. It is thought that this is the first structured reading behaviour ever identified in such a condition. Such adaptive oculomotor behaviour should be taken into account when considering rehabilitation procedures.

Eye Movements↗
PubMed1999

The "thin man" phenomenon: a sign of cortical plasticity following inferior homonymous paracentral scotomas.

AIM: To investigate an image distortion, experienced by patients with homonymous paracentral scotomas. METHODS: Two consecutive patients with right inferior homonymous paracentral scotomas resulting from ischaemic brain insults were examined. Neuro-ophthalmological examination included tangent screen and Amsler grid evaluation. In addition, the patients were asked to describe a figure showing two vertical lines, identical in length and symmetrically located on either side of a fixation point. This figure was presented in such a way that when the subject looked at the fixation point the right line crossed the scotoma. Finally, the patients were asked whether, when looking at the face of an interlocutor, both sides of the body looked the same. RESULTS: In both patients field defects were markedly smaller when delineated with Amsler grids than using a tangent screen. With the parallel line test, the right line appeared uninterrupted in patient 1, whereas in patient 2 it looked slightly blurred in a two degree long segment corresponding to the middle of the scotoma. To both subjects the right line appeared shorter than the left line. Finally both subjects indicated that, after steadily fixating their interlocutor's face or neck for 5-10 seconds, the left shoulder appeared narrower than the right one, which made him look surprisingly thin. This perceptual alteration was called the "thin man" phenomenon. CONCLUSIONS: Paracentral homonymous scotomas can be associated with perceptual completion and shape distortion, owing to apparent displacement of images adjacent to the scotoma towards the field defect. Occurrence of such a perceptual change should alert one to the possibility of paracentral homonymous scotomas, which often go undetected when using routine visual field testing procedures.

Brain Ischemia↗
PubMed1999

Subjective visual vertical in peripheral unilateral vestibular diseases.

In humans, the perception of vertical is provided by input from various sensorineural organs and pathways: vision, eye-movements, and proprioceptive and vestibular cues, particularly from the otolithic organs and graviceptive pathways. Well known in several types of brainstem lesions, subjective visual vertical (SVV) abnormalities may also be observed after peripheral vestibular lesions, such as surgical deafferentation, with a deviation directed toward the operated ear. Subjective visual vertical abnormalities are presumably related to a lesion of the otolithic organs and/or to changes in the afferent graviceptive pathways. The goal of this prospective study was to measure the SVV and to define the influence of the otolithic organs in patients suffering from various types of peripheral vestibular diseases: unilateral sudden cochleo-vestibular loss, so-called "viral labyrinthitis" (VL), sudden idiopathic unilateral peripheral vestibular loss, so-called "vestibular neuritis" (Ne). Data were compared with findings after unilateral surgical deafferentations such as vestibular neurectomy (VN) and labyrinthectomy (Lab). Subjective visual vertical was measured with a binocular test (vertical frame) and a monocular test (Maddox rod). In all patients, after VN and Lab, the SVV showed a 10-30 degrees tilt with the vertical frame (N: 0 +/- 2 degrees), 5-15 degrees with the Maddox rod (N: 0 +/- 4 degrees). With the vertical frame, SVV was tilted > 2 degrees in VL (47%) and in Ne (37%); the Maddox rod showed a > 4 degrees tilt in VL (41%) and in Ne (42%). The tilt was directed toward the affected ear. Our results demonstrate that SVV is frequently tilted in acute peripheral vestibulopathies such as VL and Ne. These findings suggest that otolithic function is implicated in the deficit depending on the extent and/or the localisation of the peripheral vestibular lesion.

Adult↗
PubMed1999

From cortical plasticity to unawareness of visual field defects.

It was long held that, following alterations in sensory input, structural changes in the primary visual cortex take place only in early life, during so-called "critical periods." Recently, however, it has been established that, in adults, cortical maps in the brain are not fixed, and the cortex does not perform stereotyped operations. Instead, neuronal receptive fields in the cortex can reorganize following deactivation or an altered pattern of activation. Plasticity is essential for the normal adjustment of the brain to modifications in the sensory environment, and for improving perceptual skills and sensorimotor performances. It also plays a crucial role in recovery from damage to the visual system. Cortical remapping generates a filling-in of visual field defects. Consequently, it alters the image perceived. Cortical rearrangement following lesions in the visual pathways does not restore function to the destroyed tissue, but it helps to compensate for gaps in perception. In this review article, we focus on effects of plasticity in the adult visual cortex which are of major importance in the daily practice of neuroophthalmology. Cortical reorganization, together with resulting filling-in, affects the early recognition and evaluation of visual field defects. The importance of brain remapping in these matters is still largely underestimated by clinicians.

Adult↗
PubMed1998

Automated visual field examination in children aged 5-8 years. Part I: Experimental validation of a testing procedure.

In 106 children aged 5-8 years, we determined how much training was needed to stabilize the response strategy prior to actual visual field assessment and we evaluated the reliability and acceptable duration of automated static perimetry (Octopus 2000R). A specially designed familiarization procedure was used to train the children to: (1) gaze at the center of the visual field while paying attention to light stimuli projected onto the periphery and (2) press the buzzer only when light stimuli were perceived. The subsequent examination phase consisted of 15 successive identical blocks of 27 trials (12 stimulus trials, 12 false-positive catch-trials, and three false-negative catch-trials), and was stopped before the end if signs of fatigue appeared. Age had a marked influence both on endurance (the number of blocks performed increased significantly) and on response reliability (false-positive responses decreased between 5- and 6-year-olds). The increase in false-negative responses toward the end indicates that examination is no longer reliable, and should be stopped. We concluded that most children as young as five can undergo examination by automated static perimetry. Changes regarding learning, stimulus intensity and testing procedure are suggested in order to adapt the examination to age, level of vigilance and health condition of the children.

Age Factors↗
PubMed1998

Automated visual field examination in children aged 5-8 years. Part II: Normative values.

We determined normative values for the visual sensitivity threshold in 118 children aged 5-8 years, using automated static perimetry (Octopus 2000R, program 32). In addition, 17 normal adults were tested. The children first underwent a familiarization procedure. One week later, quantitative examination was performed according to a specially designed schedule divided into three phases. For each of the 76 points tested, mean thresholds and standard deviations were calculated as a function of age. In contrast to previous studies, sensitivity difference between adults and children over the central 30 degrees of the visual field emerged only for the youngest age groups (5- and 6-year olds). Both the response rate in false-negative trials, and values of a within-subject threshold variability index, suggested that 5- and 6-year-olds' higher thresholds were inflated by non physiological factors, such as vigilance and cognitive processes. For these ages, the data reported here should therefore be considered as an approximation of the upper level of the thresholds. In contrast, our results for 7- and 8 year-old children provided reliable normative values for light sensitivity across the visual field.

Adult↗
PubMed1998

[Visual perception of movement. A normative study].

BACKGROUND: A battery of tests has been developed to better define the variety of defects which can occur in the process of visual perception of motion. METHODS: The tests assessed the perception of 1) coherent motion, in each of the four cardinal directions; (2) form from motion; (3) flow in depth; and (4) motion of a target moving in depth, within or without an optic flow surround. A normative study was conducted with 34 subjects, 21 to 69 years of age. RESULTS: Recognition of form from motion was better with upwards than with downwards motion. Perception of motion in depth was better with backward than forwards motion. The presence of an optic flow altered the perception of a motion in depth. CONCLUSION: The recognition of form from motion demonstrated an asymmetry in threshold between the upward and downward movements. This asymmetry did not occur with global coherent motion, thus reflecting the variety of mechanisms involved in the visual process of motion. Moreover, alteration of perception of motion in depth within an optic flow reflected background effect.

Adult↗
PubMed1998

Periodic downbeat nystagmus.

The authors observed a periodic downbeat nystagmus with a cycle of 3 minutes 30 seconds, beating downward for a period of 90 seconds every 2 minutes. It lasted 86 hours in a patient with severe hypomagnesemia associated with complications from scleroderma. There was no lesion on brain imaging, and an EEG performed during the nystagmus was normal, indicating that the most likely explanation for this periodic nystagmus is metabolic. This form of nystagmus may have resulted from severe hypomagnesemia, possibly associated with thiamine deficiency.

Activity Cycles↗
PubMed1998

Terminating attacks of ocular neuromyotonia.

We examined a 30-year-old woman who, for 6 months, had suffered from ocular neuromyotonia, which consisted of episodic ocular depression. Apart from the ocular complaint, her medical history and the clinical findings were unremarkable. The patient discovered that she could terminate each episode of tonic ocular depression instantly by forcefully directing her gaze upward. Stretching the affected muscle might also prove to be an effective way of ending attacks of neuromyotonia in other patients suffering from this condition.

Adult↗
PubMed1997

[Scotomas: assessment by the patient and by the physician. There's nothing to see].

Contrary to long-held beliefs, plasticity occurs in the adult cerebral cortex, and allows the brain to adapt to background modifications or to damage of the nervous system. Cortical changes occurring following focal visual deafferentation modify visual perception, by filling in visual field defects with information from the area surrounding the scotoma. This causes affected subjects to ignore or underestimate their defects. With visual field defects, cortical plasticity also causes distortion in spatial perception. In ophthalmological daily practice, the effects of cortical plasticity are prominent, but are usually unrecognized. They result in unawareness of field defects following retinal photocoagulation, and cause delay in recognizing visual field defects, they e.g., in early stages of simple chronic glaucoma. In addition affect the results of some procedures for testing the visual field, and increase patients' difficulty in coping with activities in everyday life. It is important to introduce into clinical practice the concept of dissociation between actual and perceived defects in the visual field, resulting from the filling-in process. It can be demonstrated using a "double Amsler grid test".

Adult↗
PubMed1996

Multiple evanescent white dot syndrome after hepatitis B vaccine.

PURPOSE: Hepatitis B vaccine has become an effective means of preventing complications of hepatitis B. However, it occasionally induces serious side effects. We report a case of multiple evanescent white dot syndrome (MEWDS) that occurred following hepatitis B vaccination. METHODS: A 23-year-old woman with a one-week history of progressive loss of vision in the left eye and bilateral photopsia was referred for examination. Her symptoms appeared 24 hours after a booster intramuscular injection of hepatitis B vaccine. RESULTS: Clinical examination, fluorescein angiography, and the course of events were typical of MEWDS. CONCLUSIONS: This case demonstrates the occasional occurrence of MEWDS after hepatitis B vaccine and suggests that hepatitis B virus immunization may be a risk factor for this retinal condition.

Adult↗