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PubMed2005

Endoscopic decompression of the optic nerve in pseudotumor cerebri.

Pseudotumor cerebri is a neurological condition in which patients develop headaches and visual loss that may not be successfully treated with medication. In these cases surgery is indicated, and decompression of the optic nerve is the preferred surgical procedure. We report a case of decompression of the optic nerve performed through an endonasal endoscopic approach in a patient with pseudotumor cerebri where enhancement of visual acuity was successful. To our knowledge, no previous investigators have reported this approach to treat pseudotumor cerebri.

Adolescent↗
PubMed2004

Exploring structure-function relationships in neocortical networks by means of neuromodelling techniques.

Determining the neuronal architecture underlying certain visual functions is of fundamental importance for understanding how sensory processing is implemented in the brain. The wealth of anatomical, physiological and biophysical data that is being currently acquired on the neocortex could be used to constrain its functional architecture. However, given the intrinsic complexity and diversity of the data, it is difficult to provide a comprehensive framework to use these data in order to characterize structure-function relationships. Here, we discuss the use of biophysically plausible models of dynamics of neuronal networks, constructed to reflect the known properties of neocortical connectivity and modularity, as a tool to bring together anatomy and physiology. We illustrate the utility and rationale of the neuro-dynamics modelling approach by considering recent studies on the relationship between functional structure of the visual cortex and its response timing, and on the cellular and network origin of neuronal oscillations in the gamma frequency range. We also critically discuss how an interaction between theory and experiments could help this approach to become directly relevant for clinical applications.

Animals↗
PubMed2006

Ozzy, a Jag1 vestibular mouse mutant, displays characteristics of Alagille syndrome.

The mouse mutant Ozzy, originating from an ENU-mutagenesis programme, displays a head bobbing phenotype. We report here that Ozzy mice show a clear deficit in vestibulo-ocular reflex (VOR). Micro-CT scanning of the inner ears showed narrowing and truncations of at least one of the semicircular canals and loss of the ampullae. Frequency-specific auditory-evoked brainstem response (ABR) tests revealed a slight threshold increase in the middle frequency range compared to wild-type littermates. Linkage analysis localised the gene in a 5.5-cM region on chromosome 2. Subsequently, a 499 T-->A missense mutation was identified in Jag1, leading to a substitution of an evolutionary conserved tryptophane (W167R). Mutations in the human homologue of Jag1 cause Alagille syndrome (AGS), an autosomal dominant disorder associated with liver, heart, eye and skeletal abnormalities, accompanied by a characteristic facies. In human patients, it occasionally affects other organ systems like the kidney or the inner ear. Liver disease is the main diagnostic factor for AGS. Ozzy mice showed significantly less intrahepatic bile ducts than wild-type littermates. Thirty-seven percent of Ozzy mice showed heart defects. No eye or vertebral abnormalities could be detected. In conclusion, Ozzy mice show two of the major and one minor characteristic of AGS.

Alagille Syndrome↗
PubMedDate not supplied

Separate neural definitions of visual consciousness and visual attention; a case for phenomenal awareness.

What is the relation between visual attention and visual awareness? It is difficult to imagine being aware of something without attending to it, and by some, visual consciousness is simply equated to what is in the focus of attention. However, findings from psychological as well as from neurophysiological experiments argue strongly against equating attention and visual consciousness. From these experiments clearly separate neural definitions of visual attention and visual consciousness emerge. In the model proposed here, visual attention is defined as a convolution of sensori-motor processing with memory. Consciousness, however, is generated by recurrent activity between cortical areas. The extent to which these recurrent interactions involve areas in executive or mnemonic space depends on attention and determines whether a conscious report is possible about the sensory experience, not whether the sensory experience is there. This way, a strong case can be made for a pure non-cognitive form of seeing, independent of attentional selection, called phenomenal awareness. This can be dissociated from the reportable form, depending on attention, called access awareness. The hypothesis explains why attention and consciousness seem so intricately related, even though they are fully separate phenomena.

Attention↗
PubMed2005

Oriented multiscale spatial filtering and contrast normalization: a parsimonious model of brightness induction in a continuum of stimuli including White, Howe and simultaneous brightness contrast.

The White effect [Perception 8 (1979) 413] cannot be simply explained as due to either brightness contrast or brightness assimilation because the direction of the induced brightness change does not correlate with the amount of black or white border in contact with the gray test patch. This has led some investigators to abandon spatial filtering explanations not only for the White effect but for brightness perception in general. Offered instead are explanations based on a variety of junction analyses and/or perceptual organization schemes which in the case of the White effect are usually based on T-junctions. Recently, Howe [Perception 30 (2001) 1023] challenged T-junction based explanations with a novel variation of White's effect in which the T-junctions were constant while the brightness effect was eliminated or reversed, and proposed an alternative explanation in terms of illusory contours. The present study argues that an analysis at the level of illusory contours is not necessary and that a much simpler spatial filtering based explanation is sufficient. Brightness induction was measured in a set of stimuli chosen to illustrate the relationship between the Howe stimulus [Perception 30 (2001) 1023], the White stimulus [Perception 8 (1979) 413] and the classical simultaneous brightness contrast (SBC) stimulus. The White stimulus and the SBC stimulus occupy opposite ends of a continuum of stimuli in which the Howe stimulus is the mid-point. The psychophysical measurements were compared with the predictions of the oriented difference-of-Gaussians (ODOG) computational model of Blakeslee and McCourt [Vision Research 39 (1999) 4361]. The ODOG model parsimoniously accounted for both the direction and relative magnitude of the brightness effects suggesting that more complex mechanisms are not required to explain them.

Contrast Sensitivity↗
PubMed1996

Visual loss as the manifesting symptom of ventriculoperitoneal shunt malfunction.

PURPOSE: To treat a 30-year-old man with a ventriculoperitoneal shunt who had progressive visual loss. METHODS: The patient underwent computed tomographic and magnetic resonance imaging scans and ocular examination. RESULTS: He was diagnosed with ventriculoperitoneal shunt failure despite the lack of ventriculomegaly on computed tomographic scan of the head and the lack of papilledema. The patient eventually underwent ventriculoperitoneal shunt revision, but visual function did not improve. CONCLUSIONS: Loss of visual acuity or visual field, or both, may be the initial and only symptom of ventriculoperitoneal shunt malfunction. Shunt failure may occur without other features of increased intracranial pressure or ventriculomegaly on neuroimaging studies.

Adult↗
PubMed1987

Transient cortical blindness in a child.

A previously healthy 3-year-old girl with minor head injury developed a transient cortical blindness lasting approximately two hours. There were no objective findings on examination, but the child complained of loss of vision. She was evaluated with a computed tomography scan of the head, which was normal, and then was admitted for observation. The child regained her eyesight and had no further neurological problems. Various theories include either vasospasm or localized cerebral edema as being responsible for the transient nature of the cortical blindness. CT scans have not been diagnostic, while EEGs have shown absence of alpha waves in the occipital lobes. Prognosis in the pediatric age group is excellent with no reports of persistent visual loss.

Blindness↗
PubMed2003

Refractory headache due to spontaneous intracranial hypotension from a CSF leak at C1-2.

A case of spontaneous intracranial hypotension presenting with refractory headaches is reported. After exhaustive investigation, the cause of the patient's symptoms was found to be spontaneous leak of CSF at the C1-2 level. The patient underwent surgical repair of the CSF leak and made a good recovery. This case represents a typical presentation of a rare condition. The investigation and treatment of this condition is discussed.

Cerebrospinal Fluid↗
PubMed2003

Tension pneumocephalus following transsphenoid surgery for pituitary adenoma - report of two cases.

Occurrence of symptomatic pneumocephalus following transsphenoid surgery is a rare event. Two cases of symptomatic pneumocephalus were observed in our series of 480 transsphenoidal surgeries. The first case reported presented with a head injury 4 years earlier and had a left frontotemporal haematoma evacuation. He underwent surgery for sellar mass extending into suprasellar region. He developed postoperative CSF rhinorrhea and in spite of conservative therapy, developed progressive visual deterioration necessitating a re-exploration and repair leading to resolution of the neurological deficits. The second case presented with delayed CSF rhinorrhea leading to rapid alteration in sensorium, requiring external ventricular drainage. The leak subsided without any further surgical intervention.

Accidents, Traffic↗
PubMedDate not supplied

An adaptation of the Cambridge Colour Test for use with animals.

Recently, molecular biological techniques have presented new opportunities for addressing questions concerning the neural mechanisms involved in color coding, thereby rousing renewed interest in animal color vision testing. We have modified a computer-based assessment tool, the Cambridge Colour Test, to make it suitable for use with animals. Here, the validity and reliability of the testing method were evaluated using squirrel monkeys. Because the chromatic stimuli and the achromatic backgrounds of the test consist of dots that vary in lightness, the stimulus parameters can be adjusted so that animals are not able to use luminance differences to make correct discriminations. Thus, in contrast to methods used previously, this test does not require that time be spent equating the luminance of each chromatic stimulus examined. Furthermore, the computer video-display based design of the testing apparatus can be easily replicated and adapted for use with many species in a variety of settings. In the present experiments, the squirrel monkeys' behavioral results agreed with the predictions for their color vision based on genetic analysis and electroretinography (ERG) spectral sensitivity data. Repeated measurements were highly consistent. Thus, an adaptation of the Cambridge Colour Test provides a valid and reliable method for testing color vision in animals.

Animals↗
PubMed2000

Measuring contrast sensitivity in patients with Graves' ophthalmopathy complicated by ocular hypertension and suspect glaucoma or dysthyroid optic neuropathy.

The present study compares contrast sensitivity functions of patients with uncomplicated Graves' ophthalmopathy, patients with ophthalmopathy and elevated intraocular pressure or suspect glaucoma, and patients with dysthyroid optic neuropathy (DON). Aim of the study was to investigate the clinical potential for the contrast sensitivity functions (CSF) in distinguish between the groups. Contrast sensitivity measurements were obtained from twenty-seven subjects with endocrine ophthalmopathy. Group I included patients with uncomplicated ophthalmopathy (n=20 eyes); group II included patients with ophthalmopathy, intraocular pressure > or = 24 mmHg with and without early visual field defects, and no evidence of apical crowding on coronal computed tomography scan (n=14 eyes); group III included patients with DON (n=12 eyes). Contrast thresholds were determined for stationary and 6.87 Hz phase-alternating gratings at eight spatial frequencies from 0.18 to 15.7 c/deg. Data from each group was compared with data from age-matched normal subjects. Observers with uncomplicated ophthalmopathy had normal CSFs. Eyes affected with DON showed contrast sensitivity disruption at overall intermediate-high spatial frequencies. Eyes with elevated intraocular pressure or suspect glaucoma had pronounced sensitivity loss in the low frequency range (0.18-0.70 c/deg) as compared to eyes with DON. This study shows that CSF detects visual function abnormalities noninvasively in patients with complicated Graves' ophthalmopathy. Results also indicate that the clinical potential for CSF in distinguish between patients suffering from ophthalmopathy complicated by ocular hypertension or suspect glaucoma and patients with DON improves when a temporal modulation of 6.87 Hz and gratings of low spatial frequency (< 1 c/deg) are used.

Adult↗
PubMed2002

Blurred vision.

Explore the source record for details and available documents.

Biotechnology↗
PubMed2000

Fred Hollows lecture: digital screening for eye disease.

The purpose of this study was to explore progress, in the adaptation to community screening for blinding eye disease, of digital imaging devices and technology for storage and transmission. Available imaging systems were compared to gold standard clinical photography in terms of sensitivity and specificity for diagnosis of common blinding eye conditions. Since the use of expensive non-portable imaging devices is likely to be limited for widespread community screening purposes, a portable fundus camera (Nidek, Chiyoda-ku, Japan) and a prototype monocular digital indirect ophthalmoscope constructed at the Lions Eye Institute (LEI) were selected for comparative trials for the screening of optic disc cupping, glaucoma and clinical signs of diabetic retinopathy. Fifty-one eyes of 27 consecutive patients being assessed at the LEI clinic for glaucoma were dilated and photographed with a Zeiss retinal camera, and digital images were taken with the portable Nidek NM100 fundus camera (Carl Zeiss, Oberkochen, Germany) or with a prototype digital monocular indirect ophthalmoscope. Vertical cup: disc ratios (VCDR) were measured on the disc photographs by one ophthalmologist while three other clinicians were presented with compressed digital images in random order to estimate VCDR. Field trials were also carried out to demonstrate the practicality of compression, local storage and then transmission by mobile telephone ISDN lines and satellite, of optic discs and fundus images of patients with diabetes in either rural Western Australia or Surabaya, Indonesia. Kappa values of correlations of measurement of agreement between measured and estimated VCDR were 0.87, 0.45 and 0.84, respectively, for the three observers, corresponding to a specificity of 79-97% and a sensitivity of 70-95%. The portable Nidek fundus camera was also assessed for specificity and sensitivity in the diagnosis of diabetic retinopathy in comparison to standard Zeiss fundus camera photographs. Of 49 eyes in 25 consecutive patients attending the LEI clinic for assessment of diabetic retinopathy, three ophthalmologists assessed photographs and images in random order. When used for screening diabetic retinopathy, the digital images of the Nidek camera were graded as adequate quality in only 56% of eyes compared to 93% of the photographs. The kappa value of agreement in analysis of diabetic retinopathy was only 0.30. The prototype digital monocular indirect ophthalmoscope compared favourably with the Nidek camera. At 1:5 compression, images of size 36 kB transmitted from Surabaya to Perth took 29 s on the mobile telephone, while uncompressed images took 170 s. Images compressed 1:5 were transmitted in 60 s using the satellite telephone, while the uncompressed images took 240 s. Satellite transmission was more expensive but the lines were more stable than telephone connections from Indonesia. Digital imaging is becoming a powerful tool for ophthalmology in clinical records, teaching and research, and interoffice diagnostic opinions. It also has enormous potential for community screening for blinding eye diseases, such as glaucoma and diabetic retinopathy. Inexpensive portable imaging devices that are easy to use, and on which local health workers might be trained, must be developed and validated in terms of sensitivity and specificity of performance. The technology of image capture, image compression, transmission, data base storage and analysis is rapidly evolving and becoming less expensive.

Diabetic Retinopathy↗
PubMed1998

[Objective assessment of minimum visual acuity by suppression of optokinetic nystagmus].

PURPOSE: To develop and to validate an objective method which allows an estimation of the visual acuity (VA) of adults. METHODS: A horizontal optokinetic nystagmus (OKN) was elicited by a vertical rectangular grating presented on a PC-screen and was recorded by an infrared reflection method. Superimposition of three stationary black detection stimuli was used to suppress the OKN. The size of these stimuli was increased every two seconds, in ten steps. Suppression of the OKN was taken as an indication that the stimuli were detected. The relation between the smallest effective stimulus and logVA was evaluated in 65 healthy volunteers (130 eyes) with artificially reduced VA and 425 cooperative patients (842 eyes) whose VA was reduced due to different etiologies. The tolerance intervals of logVA related to the discrete detection stimuli were calculated. RESULTS: The method allows an estimation of the least expectable VA in steps of 0.8, 0.32, 0.25, 0.12, 0.1, 0.06, 0.03 und 0.025 due to the smallest value of three trials. The least VA of strabismic amblyopic eyes can only be estimated in steps of 0.16, 0.06, and 0.02. A VA > 0.02 can be proven with high reliability. CONCLUSION: The method allows a clinically useful, objective estimation of the least VA without observer bias in non-amblyopic eyes.

Adolescent↗
PubMed1995

[Sensitivity of refraction measurement with the infrared videorefractometer VRB 200].

AIM OF THE STUDY: This study investigates the sensitivity of a computerised videorefractor (VRB 200) for refractive errors, especially amblyopiogenic, in babies and infants. PATIENTS AND METHODS: Videopictures from 312 eyes of 156 babies and infants were taken, evaluated and compared with the current measurements (skiaskopy or refractometry) of the university eye hospital Erlangen-Nürnberg. RESULTS: 255 (81.7%) of 312 eyes were evaluable. The VRB 200 achieves a sensitivity of 96.1% in hyperopic eyes (219 of 228 eyes) and 94.7% in myopic eyes respectively (18 of 19 eyes). Of 8 emmetropic eyes 6 were recognized correctly negative. Astigmatism could be estimated coarsely quantitatively in power and qualitativ in the axis with a sensitivity of 80% (92 of 115 eyes) and a specificity of 86% (121 of 140). Anisometropia over 2 dpt was recognized in 5 of 6 patients. A general statement concerning the specificity is not possible with this study, because it is not a mass screening procedure. CONCLUSION: This videorefractor is able to recognize semi-quantitatively ambylopiogenic refractive errors with high sensitivity.

Amblyopia↗
PubMed1989

[Graphic and numerical presentation of visual field findings].

This article reviews the various ways in which visual field defects can be represented and the advantages and disadvantages of the most commonly used methods. In addition, the G1 analysis program, which will soon be available, is briefly described.

Computer Graphics↗
PubMed1985

Hydrocephalus following toxoplasmosis.

Between 1966-1983 ten children with hydrocephalus following toxoplasmosis were shunted. Hydrocephalus was diagnosed at ages ranging from birth to one year. Except for one with stenosis of the foramen of Monro all had aqueductal obstruction. A high ventricular fluid pressure and distinct cerebral mantle reduction were always present. Intracerebral calcifications were common. Only 1 had normal eyes. All 9 survivors remained shunt dependent during a mean follow-up period of 9.6 years. One fifth of revisions were related to problems specific for toxoplasma-associated hydrocephalus. A temporary external ventricular drainage or a multiple shunt system were found useful in some cases. Two thirds of the children had a reasonable outcome. Neonatal hydrocephalus, extensive intracerebral calcification and severe ocular involvement were poor prognostic indicators.

Brain Diseases↗