B. Skarf - Academia.edu (original) (raw)

Papers by B. Skarf

BMC Ophthalmology, 2006

Background: The objective of this report is to describe the methods used to develop and validate ... more Background: The objective of this report is to describe the methods used to develop and validate a computerized system to analyze Humphrey visual fields obtained from patients with non-arteritic anterior ischemic optic neuropathy (NAION) and enrolled in the Ischemic Optic Neuropathy Decompression Trial (IONDT). The IONDT was a multicenter study that included randomized and non-randomized patients with newly diagnosed NAION in the study eye. At baseline, randomized eyes had visual acuity of 20/64 or worse and non-randomized eyes had visual acuity of better than 20/64 or were associated with patients refusing randomization. Visual fields were measured before treatment using the Humphrey Field Analyzer with the 24-2 program, foveal threshold, and size III stimulus. Methods: We used visual fields from 189 non-IONDT eyes with NAION to develop the computerized classification system. Six neuroophthalmologists ("expert panel") described definitions for visual field patterns defects using 19 visual fields representing a range of pattern defect types. The expert panel then used 120 visual fields, classified using these definitions, to refine the rules, generating revised definitions for 13 visual field pattern defects and 3 levels of severity. These definitions were incorporated into a rule-based computerized classification system run on Excel ® software. The computerized classification system was used to categorize visual field defects for an additional 95 NAION visual fields, and the expert panel was asked to independently classify the new fields and subsequently whether they agreed with the computer classification. To account for test variability over time, we derived an adjustment factor from the pooled short term fluctuation. We examined change in defects with and without adjustment in visual fields of study participants who demonstrated a visual acuity decrease within 30 days of NAION onset (progressive NAION). Results: Despite an agreed upon set of rules, there was not good agreement among the expert panel when their independent visual classifications were compared. A majority did concur with the computer classification for 91 of 95 visual fields. Remaining classification discrepancies could not be resolved without modifying existing definitions. Without using the adjustment factor, visual fields of 63.6% (14/22) patients with progressive NAION and no central defect, and all (7/7) patients with a paracentral defect, worsened within 30 days of NAION onset. After applying the adjustment factor, the visual fields of the same patients with no initial central defect and 5/7 of the patients with a paracentral defect were seen to worsen. Conclusion: The IONDT developed a rule-based computerized system that consistently defines pattern and severity of visual fields of NAION patients for use in a research setting.

Vision Research, 1999

Visual evoked potentials to pattern reversal (PR-VEPs) are used to assess the integrity and matur... more Visual evoked potentials to pattern reversal (PR-VEPs) are used to assess the integrity and maturation of the visual pathways in infants and young children. To establish normal ranges and to facilitate interpolation, we consider the maturation rate of PR-VEPs using published normative data. Curves based on the logistic function (a sigmoid model) are introduced and compared with three other models: (1) the power law function; (2) the sum of two decaying exponentials; and (3) a two-stage linear model. Although methods vary somewhat, remarkable consistency among laboratories is found for the maturation of the major positivity (P 1) of PR-VEP. The P 1 occurs at approximately 260 ms in neonates and is quite variable. It matures rapidly before 12-14 weeks of age and becomes much less variable. The logistic model provides a parsimonious description of P 1 maturation with most rapid maturation at around 6 weeks of age for large patterns and around 9 weeks for small patterns. As inter-laboratory agreement is generally good, the normal ranges based on this model could be used in centres, which do not have their own normative databases for infant VEPs.

New England Journal of Medicine, 1986

Archives of Ophthalmology, 1982

It has been suggested that the pupillary response to hydroxyamphetamine hydrobromide eyedrops wil... more It has been suggested that the pupillary response to hydroxyamphetamine hydrobromide eyedrops will separate distal from proximal lesions of the sympathetic pathway from the brain to the eye (the pupil fails to dilate in postganglionic lesions). We studied the pupillary response to hydroxyamphetamine in two groups of rabbits with surgically produced Horner's syndrome. Rabbits in one group had postganglionic lesions. In all animals, a miotic pupil developed ipsilateral to the surgical lesion, and oculosympathetic paresis was confirmed in each by testing pupillary response to topically applied cocaine. In rabbits with postganglionic lesions, hydroxyamphetamine failed to dilate the miotic (Horner's) pupils as well as it dilated the normal pupils, while in rabbits with preganglionic lesions both miotic and normal pupils dilated equally. Hydroxyamphetamine appears to be a diagnostically useful drug in Horner's syndrome.

Archives of Ophthalmology, 1985

Contrast sensitivity measurements were obtained from 64 patients with insulin-dependent (IDDM) an... more Contrast sensitivity measurements were obtained from 64 patients with insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetes mellitus who had normal Snellen acuity and minimal or no visible diabetic retinopathy. Contrast thresholds were determined for stationary gratings at six spatial frequencies, ranging from 0.5 to 22.8 cycles/degree (c/deg), and for 1.0-c/deg gratings phase-alternated at 15 Hz. Data from each group of diabetic patients were compared with data from age-matched normal subjects. We found that (1) patients with IDDM and no retinopathy had normal contrast sensitivity, (2) patients with NIDDM and no retinopathy had abnormal contrast sensitivity at only one spatial frequency (22.8 c/deg), and (3) patients with NIDDM and background retinopathy had abnormal contrast sensitivity at all spatial frequencies tested. We also found a dissociation of Snellen acuity and contrast sensitivity, indicating that contrast sensitivity can be used as an early index of changes in the retina not demonstrated by measurements of visual acuity.

Archives of Neurology, 1984

A 60-year-old man fell; a subdural hematoma developed and he lost consciousness. Visual evoked po... more A 60-year-old man fell; a subdural hematoma developed and he lost consciousness. Visual evoked potentials demonstrated a total conduction block in the left optic nerve and slowed conduction on stimulation of the right eye. He died four weeks later, and necropsy showed focal infarcts in the intracranial portion of both optic nerves.

British Journal of Ophthalmology, 2002

Investigative Ophthalmology and Visual Science, 1998

To determine the feasibility of adapting confocal scanning laser (CSL) tomography of the optic di... more To determine the feasibility of adapting confocal scanning laser (CSL) tomography of the optic disc for quantitative evaluation of papilledema in pseudotumor cerebri (PTC). Confocal scanning laser tomography of the optic disc was performed in 11 patients with diagnosed PTC and 12 visually normal control subjects of similar age. In five patients with active papilledema, CSL tomography was performed serially over several months. To quantify optic disc characteristics, surface topography was measured in 0.1-mm steps along the horizontal and vertical meridians and four oblique meridians. Best fit polynomial functions, describing surface topography along each meridian, were derived using linear regression analysis. Third-order polynomials provided excellent fits (significantly better than the second-order functions) to the surface topography for all meridians in the control subjects and patients with PTC. In control subjects and PTC patients an asymmetry in the slope of the optic disc co...

New England Journal of Medicine, Jun 29, 1989

Investigative Ophthalmology and Visual Science, 1999

To investigate sensory fusion responses in infants and children with early-onset esotropia to gai... more To investigate sensory fusion responses in infants and children with early-onset esotropia to gain insights into the sequence of events that leads to strabismus. Sensory fusion was tested by measuring visual evoked potential (VEP) responses to dynamic random dot correlograms (DRDCs) in a group of children (n = 23) with early-onset esotropia. Thirteen children were tested before surgical alignment, and 13 children were tested after surgical alignment (three children were tested before and after surgery). If the angle of strabismus was larger than 5 prism diopters, it was corrected with Fresnel prisms (Fresnel Prism and Lens, Scottsdale, AZ). Five (38%) of the 13 children who were tested before surgery showed detectable VEP responses to correlogram stimuli compared with 11 (85%) of the 13 children who were tested after surgical alignment. There were no significant statistical differences between VEP responses to DRDCs from the postsurgery group and VEP responses from an age-matched co...

New England Journal of Medicine, Oct 15, 1981

Journal of neuro-ophthalmology, 1994

Journal of pediatric ophthalmology and strabismus

Visual evoked potentials (VEPs), that provide unequivocal objective evidence of cortical binocula... more Visual evoked potentials (VEPs), that provide unequivocal objective evidence of cortical binocularity have been recorded from adults and young infants using a new VEP system developed for this purpose. The system uses alternating field stereoscopy (AFS) to present separate visual stimuli to each eye. With this system, the binocular image pairs to the right and left eyes alternate at a high rate on a single video monitor. The subject wears spectacles incorporating light-scattering liquid crystal lenses which alternate electronically between opaque and clear modes in synchrony with the video monitor. To detect cortical binocularity, the system analyzes VEP activity mathematically and identifies significant responses at test frequencies reflecting binocular cortical interactions exclusively. Three types of binocular stimuli were presented: (1) dynamic random dot correlograms (correlograms); (2) dynamic random dot stereograms (stereograms); and (3) dichoptic checkerboard stimuli. The co...

Pattern visual evoked potentials (P-VEPs) were recorded in 161 human infants who were between 3 w... more Pattern visual evoked potentials (P-VEPs) were recorded in 161 human infants who were between 3 weeks and 2 yr of age. The latency of the first reproducible positive peak in the P-VEP was measured monocularly and binocularly for five sizes of phase alterations checkerboard stimuli (range: 120' to 7.5' check widths). Rapid visual maturation in the first 6 months of life was shown by the development of reproducible P-VEPs to smaller check sizes and by a rapid decrease in the latency of the first reproducible positive peak. Monocular P-VEPs have slightly longer latencies than the binocular P-VEPs. This latency difference is invariant with age, but is significantly greater with larger check stimuli. Normal ranges for this large population are provided as a reference for clinical studies.

Toxicology, 1988

We have documented visual and auditory neurotoxicity in 42 of 89 patients with transfusion-depend... more We have documented visual and auditory neurotoxicity in 42 of 89 patients with transfusion-dependent anemia who were receiving iron chelation therapy with subcutaneous deferoxamine (DFO). Of the affected groups, 13 presented with visual loss or deafness or both, and ophthalmologic, audiologic, and visual evoked potential studies (VEPs) uncovered abnormalities in 29 more. Four patients with visual loss had optic neuropathy with a marked decrease in acuity and loss of color vision. These 4, and 16 other asymptomatic patients, had abnormal VEPs. When DFO was stopped, 3 of 4 with visual problems regained normal visual function but VEPs remained abnormal. Of the other 16 with abnormal VEPs, 9 became normal or improved and 7 did not change; on restarting DFO, the 9 became abnormal again. There were 22 abnormal audiograms that showed a high-frequency sensorineural deficit; 13 patients were symptomatic and 4 needed hearing aids. On stopping DFO, 9 became asymptomatic but 15 audiograms remained abnormal and 2 deteriorated further on restarting the drug. An analysis of the clinical data showed that members of the affected group were younger, had lower serum ferritin values, and were self-administering higher doses of DFO/kg body weight. Significantly lower doses of DFO were being taken by patients without abnormalities than by those with visual symptoms, abnormal audiograms, or prolonged VEPs (P less than 0.001, less than 0.006, and less than 0.04, respectively). The data implicate high-dose DFO as a central factor in the pathogenesis of the neurotoxicity. Our serial studies provide the basis for effective yet safe DFO administration for patients who require the agent.

Experimental Neurology, 1974

Binocular vision requires that neurons in the visual centers of the brain receive input from both... more Binocular vision requires that neurons in the visual centers of the brain receive input from both eyes. In the frog, Rana pipiens, the convergence of 'these inputs to binocularly driven neurons in the optic tectum develops during metamorphosis. Experiments were designed to test whether the formation of functional connections onto these binocularly driven cells may be regulated by the pattern or the quantity of activity conveyed by the nerve fibers converging onto them. Frogs were raised from various premetamorphic stages either with one eye rotated 180" or with one eye covered with a graft of pigmented back skin. Animals with these asymmetries in the visual stimulation of the two eyes were raised for up to 3 months after metamorphosis before being used for electrophysiological recording. Rigorous criteria were adopted for identification of binocularly driven neurons, whose activity in response to visual stimulation was recorded by extracellular microelectrodes in the tectum. Binocularly driven units were recorded in animals raised with visual asymmetries as well as in normal frogs. In normal animals and those raised with skin grafts until the time of recording, such units could be activated through either eye from a single position in visual space. However, after eye rotation, binocularly driven neurons were activated by a stimulus in one position viewed by the normal eye and a different position viewed by the rotated eye. The results demonstrate that the formation of functional connections onto binocularly driven neurons in the tectum does not depend qualitatively or quantitatively on symmetrical patterns of impulse activity in the afferent fibers converging onto the individual neurons from the two eyes.

New England Journal of Medicine, 1989

American Journal of Ophthalmology, 1979