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Biomedical subjects

A Jampolsky

Publications and source records attributed to A Jampolsky.

At least 19 recordsLinked to original sources
PubMed1995

Plasticity of human motion processing mechanisms following surgery for infantile esotropia.

Monocular oscillatory-motion visual evoked potentials (VEPs) were measured in prospective and retrospective groups of infantile esotropia patients who had been aligned surgically at different ages. A nasalward-temporal response bias that is present prior to surgery was reduced below pre-surgery levels in the prospective group. Patients in the retrospective group who had been aligned before 2 yr of age showed lower levels of response asymmetry than those who were aligned after age 2. The data imply that binocular motion processing mechanisms in infantile esotropia patients are capable of some degree of recovery, and that this plasticity is restricted to a critical period of visual development.

Adolescent↗
PubMed1994

The measurement of the lateralization of narrow bands of noise using an acoustic pointing paradigm: the effect of sound-pressure level.

The effects of varying interaural time delay (ITD) and interaural intensity difference (IID) were measured in normal-hearing subjects as a function of eleven frequencies and at sound-pressure levels (SPL) from 60 to 90 dB SPL and at 25-dB sensation level. Using an "acoustic" pointing paradigm, the IID of a 500-Hz narrow-band (100 Hz) noise (the "pointer") was varied by the subject to coincide with that of a "target" ITD stimulus. ITDs of 0, +/- 200, and +/- 400 microseconds were obtained through total waveform delays of narrow-band noise (NBN), including envelope and fine structure. The results of this experiment confirm the traditional view of binaural hearing for like stimuli: There is little perceived displacement away from 0 IID at frequencies of 1250 Hz and above. In the low frequencies, subjects required IIDs greater than the expected 10 dB to perceive a fully lateralized image, and they varied in the maximum value of IID that they required, regardless of frequency. Our subjects did not always perceive the intracranial locations of ITD targets symmetrically: When the signal was delayed to one ear, the resultant matching IID was often different in magnitude than for the same ITD target delayed to the opposite ear for the identical frequency. The results of two subjects suggested that people with asymmetric normal hearing have adapted to their asymmetry for lateralization tasks: The subjects were found to lateralize toward the ear with the greater SPL stimulus, regardless of the ear to which the signal was delayed, when signals of equal SL were presented, and toward the leading ear when signals of equal SPL were presented (unequal SL). Increasing the presentation levels above 60 dB SPL had an effect on the perception of high-frequency ITD targets: As the intensity level increased, the slopes of the IID versus ITD functions increased indicating better discrimination of ITD. This study is in agreement with other studies in providing strong evidence of individual differences in lateralization experiments. These individual differences might be attributable to differential sensitivity to ambiguous time stimulus cues, differential task sensitivity, age effects, threshold asymmetries, or criterion variability.

Adult↗
PubMed1994

Consequences of retinal image clarity versus occlusion (absent) versus diffusion.

A series of clinical questions and stated hypotheses suggested in the pre-1960s regarding the differences between stimuli of occlusion and diffusion are presented (Part I) and are answered and confirmed by a series of experiments and data in animals and humans. A diffusion stimulus is extremely destructive to development of the acuity system in an eye per se (as well as producing myopia), and a unilateral diffusion stimulus is also destructive to development of the binocular system. Real occlusion is a no-stimulus condition that can be used to preserve normal acuity and binocular development, and as a delay tactic to successfully counteract the detrimental effect of diffusion. Binocular input differences (especially if one is a diffusion stimulus) are a major cause of strabismus in both the immature and mature binocular systems. The hypothesis was proposed that preoperative full-time alternate occlusion in infantile esotropia enhanced the binocularity outcome (for which supportive experimental data in animals and humans from our laboratories are discussed in Part III). Animal experiments during the 1960s and 1970s are reviewed relative to the confusion and conflict generated (Part II), since many of these experiments were based on the false assumptions that the unilateral eyelid closure model was a no-stimulus condition (because of the small amount of light transmitted). In fact, it was a worst-case severe stimulus with both monocular and binocular detrimental consequences. And the unilateral eyelid closure model usually produced either undetected or ignored strabismus in the animal experiments, with such strabismus severely compounding the detrimental effects of the eyelid closure model. Further confusion was added by the amblyopia therapeutic model in animals of "reverse eyelid occlusion" (which was really reverse diffusion) and which the author maintains was a gross distortion of the clinician's real occlusive patch over the better eye in the therapy of amblyopia of the poorer eye. These confusions and conflicts were at variance with long-standing clinical percepts. Part III provides data from the series of animal and human experiments from our laboratories at Smith-Kettlewell Eye Research Institute, which clarify the confusion and conflicts of some of the animal experiments described. Our data support the original hypotheses (Part I) enabling the clinician to use occlusion measures in selected patients to expand the therapeutic timing options and to improve visual outcomes. Binocular system outcomes are shown to be improved by our recent data in animal and human experiments, thus supporting the beneficial sensory effects of preoperative full-time alternate occlusion regimes in infantile esotropia.

Adult↗
PubMed1994

Foveal vision function before and after fluorescein angiography.

PURPOSE: Fluorescein angiography is routinely used in ophthalmologic practice with minimal changes in vision reported by the patient after the procedure. Recent animal work has suggested that fluorescein may be cytotoxic in the presence of light and may cause retinal damage. The authors examined whether any changes occur in foveal vision function after fluorescein angiography. METHODS: A battery of tests of vision function--including visual acuity, contrast sensitivity, color vision, and two-color increment thresholds designed to isolate individual cone pathways--was administered before and 48 hours after fluorescein angiography to a group of 10 patients with good visual acuity. RESULTS: Most of the patients showed significant abnormalities with the nonstandard tests; however, no significant changes in central vision function were found 48 hours after fluorescein angiography. CONCLUSION: Even sensitive vision tests show no measurable effect of fluorescein angiography on foveal vision function in eyes with significant disease.

Adult↗
PubMed1991

Cortical recovery from effects of monocular deprivation caused by diffusion and occlusion.

Two forms of visual deficit were induced in 12 pairs of kittens (4-6 weeks of age) by monocular lid suture combined with either an opaque soft contact lens ('occlusion' amblyopia) or a clear lens ('diffusion' amblyopia) which had been kept behind the sutured eyelids for 5-9 weeks. The kittens were then reverse-sutured at the age of 9-15 weeks, and the previously open eye was occluded with an opaque lens for the next 5-7 weeks. We compared across the two groups the proportion of binocularly driven cells (group 2-6) and cells predominantly activated by stimulation of the initially deprived eye (groups 1-3). Both values were significantly higher in the 'occlusion' kitten, though the difference was small, compared to the 'diffusion' kitten. In addition, we measured visual acuity and peak contrast sensitivity for the two eyes in 4 of the 12 pairs, using the sweep VEP method applied under anesthesia and paralysis. The 'occlusion' kitten showed consistently better acuity and higher peak contrast sensitivity than the 'diffusion' kitten, when the initially deprived eye was tested. Taken together, the present results suggest that there is a difference in the depth of amblyopia caused by monocular 'occlusion' and monocular 'diffusion'. The cortical effects of the latter are more difficult to reverse than those of the former.

Amblyopia↗
PubMed1991

Length-tension recording system for strabismus surgery.

To meet the need for both scientific information and a clinical means for measurement of the mechanical parameters of the most difficult individual strabismus cases we present a technique for directly measuring and plotting the length-tension characteristics of the tissues supporting the eye. Semiconductor strain gauges mounted on the shanks of a custom machined eye forceps and an ultrasonic method of making continuous duction measurements of the eye have proved feasible. When the forceps are interfaced with a dedicated microcomputer, the system provides a permanent, quantitative, length-tension record displayed in real-time. The instrumented length-tension forceps system has provided a noninvasive means for quickly and simply assessing the mechanical underlying determinants of strabismus pathology in the office, the laboratory or in the operating room, and can aid in the planning and immediate intraoperative alteration of strabismus surgery. Under operator coordination, measurements can be made which precisely define the mechanical load which the eye muscles must move. The resulting objectively determined tissue stiffness asymmetries and muscle restrictions limiting ocular motion indicate the purely mechanical contributions to a patient's strabismus. Measurements of active force indicate the magnitudes and patterns of innervation over the entire range of gaze. By comparison of these active force and passive stiffness records, nerve signal imbalances may be quantitatively distinguished from mechanical imbalances in strabismus. It is the detailed interaction of these nonlinear muscle forces and mechanical elements which determines the position of each eye in strabismus and therefore the proper surgical treatment. A brief description of actual use and a few examples of clinical results are included from over 200 human records.

Calibration↗
PubMed1987

Effects of atropine and 2-PAM chloride on vision and performance in humans.

These experiments assessed the time course and severity of effects of atropine and 2-PAM chloride on selected visual functions, physiological measures, and a tracking performance task. Atropine up to 4 mg X 70 kg-1 body weight and 2-PAM Cl in doses up to 1200 mg X 70 kg-1 body weight were administered intramuscularly in a double-blind Latin square design. A long lasting and dose-related increase in pupillary diameter and decrease in accommodative amplitude with accompanying loss of near visual acuity was found following atropine administration. These functions returned to baseline 2 d after injection. Distance acuity, contrast sensitivity, color vision, and intraocular pressure showed no changes after atropine. Tracking performance was significantly decreased by 4 mg of atropine. The changes in vision function cannot readily explain the tracking performance loss, since the tracking involved a distant visual target while the atropine produced degradation of near vision. Most of the physiological tests, tracking performance and all visual functions were unaffected by 2-PAM Cl.

Accommodation, Ocular↗
PubMed1984

Predicting visual resolution from detection thresholds.

Visual acuity is one of the most frequent health measures and is central to vision assessment in schools, industry, aviation, drivers' licensing, and ocular health examinations. There is a need for a rapid, simple, and interpretation-free measure of visual acuity which is amenable to automated and objective assessment. This study shows that a rapid (15 s) and simple contrast threshold measure for a 5 min arc spot correlates highly (r = 0.75) with letter acuity in 360 clinic patients. Assessments by optometrist and technician correlated highly (r = 0.88) as did repeated measures by the same examiner (r = 0.85). The instrumentation appears to be well suited for rapid, automated, and interpretation-free assessment of visual acuity and for visual acuity screening.

Humans↗
PubMed1983

Overcorrecting minus lens therapy for treatment of intermittent exotropia.

The purpose of this paper is to determine the value of overcorrecting minus lenses in treating children with intermittent exotropia. The aim with this therapy is to secure an increase in the quality of fusion and to induce a quantitative decrease in the angle of strabismus. Thirty-five children were treated with 2.00 to 4.00 diopters of overcorrecting minus lenses for a median of 18 months duration. Of these, 46% had an improved quality of fusion during therapy; 26% had an improved quality of fusion and also had a quantitative decrease in their angle of deviation; and 28% had an inadequate improvement in their quality of fusion and decrease in the angle of their deviation with this therapy. Two children went from intermittent exotropia to esotropia while wearing their minus lenses--both had high accommodative-convergence/accommodation ratios (11.5 delta/1D and 10.7 delta/1D). Seventy percent of good responders who were followed for at least 1 year after discontinuing the therapy maintained a qualitative or quantitative improvement in their intermittent exotropia.

Child↗