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Biomedical subjects

R V Kenyon

Publications and source records attributed to R V Kenyon.

31 records · Page 2Linked to original sources
PubMed1980

Dynamic vergence eye movements in strabismus and amblyopia: symmetric vergence.

Dynamic vergence eye movements in response to step target displacements along the midline were measured by an infrared reflection technique in 11 patients having either intermittent strabismus, constants-strabismus amblyopia, or amblyopia without strabismus. We found the absence of normal disparity (fusional) vergence in all patients having strabismus and in some patients having amblyopia without strabismus. A characteristic response consisting of a binocular accommodative vergence component and an early binocular saccadic component was used to foveate the target of interest with the dominant eye. Vergence responses in our control subjects and patients with the nondominant eye occluded were similar to those recorded in our patients during binocular viewing. These results suggest that disparity information is not utilized by patients, probably as a result of long-term, ongoing suppression in the deviated or amblyopic eye. Accommodative vergence with the aid of an early foveating saccade was the primary mechanism for tracking targets in three-dimensional space.

Accommodation, Ocular↗
PubMed1980

Disparity vergence: a proposed name for a dominant component of binocular vergence eye movements.

A proposal to name the dominant aspect of vergence "disparity vergence" is put forward. Support for this proposal is gathered by briefly reviewing the components of vergence: (1) disparity vergence, the visual feedback control system for removing binocular disparity with an appropriate binocular convergence or divergence, (2) accommodative vergence, a synkinesis with accommodative motor control, (3) proximal vergence, and (4) tonic vergence. Sensory fusion is a higher level perceptual process aided by disparity vergence, and historically the term fusional vergence called attention to this relationship. However, it now appears to obscure the fact that disparity is the only direct stimulus to vergence.

Accommodation, Ocular↗
PubMed1979

Saccadic intrusions in strabismus.

Fixational eye movements were studied to determine the presence of and to quantify saccadic intrusions under monocular and binocular viewing conditions in subjects with intermittent strabismus, amblyopia without stabismus, or constant strabismus amblyopia. Saccadic intrusions were present under most test conditions in intermittent strabismus, were rarely observed in amblyopia without strabismus, and were prominent during monocular fixation with the amblyopic eye in constant strabismus anblyopia. This suggests that the presence of saccadic intrusions was related to strabismus and not amblyopia. There was no relationship between saccadic intrusion amplitude and visual acuity. Two possible mechanisms for producing intrusions are abnormally rapid regional visual adaptation and strabismus-induced fixation degradation.

Adolescent↗
PubMed1979

Abnormal saccadic substitution during small-amplitude pursuit tracking in amblyopic eyes.

Small-amplitude, low-velocity, predictable triangular tracking was tested in patients having amblyopia without strabismus, intermittent strabismus, or constant strabismus amblyopia by means of a photoelectric eye-movement recording technique. In the majority of amblyopic patients, abnormal saccadic substitution was found; that is, abnormally large saccades rather than small-amplitude smooth movements were used by the amblyopic eye to follow a spot stimulus that moved horizontally with low to high frequencies. Pursuit for the same range of stimuli was normal for binocular tracking and for monocular tracking with the dominant eye, pointing to a sensory rather than motor basis for the defect. This abnormal saccadic substitution response appeared to be related to the presence of amblyopia rather than strabismus. Several possible mechanisms responsible for causing this unusual response are discussed, including impairment of direction sense over small central regions of the amblyopic eye.

Adolescent↗
PubMed1979

Fixational eye movements in amblyopia and strabismus.

Horizontal eye position was monitored using a photoelectric method during monocular and binocular fixation in four patients having amblyopia without strabismus, thirteen patients having constant strabismus with amblyopia, and five patients having intermittent strabismus. Four abnormalities of fixation were found: increased drift, saccadic intrusions, manifest nystagmus, and latent nystagmus. Increased drift was related to the presence of amblyopia, while saccadic intrusions and nystagmus were related to the presence of strabismus. Understanding dynamic aspects of oculomotor control can provide insight into clinical assessment of fixation in amblyopia and strabismus.

Adolescent↗
PubMed1979

Different rates of functional recovery of eye movements during orthoptics treatment in an adult amblyope.

Although it is common clinical knowledge that oculomotor control appears to normalize during the course of successful orthoptics therapy for amblyopia, reports providing a quantitative analysis of eye movements during extended periods of treatment are lacking. We provide for the first time such a report in an adult amblyope. Aspects of eye movement control that tended to normalize with therapy include drift amplitude and velocity, duration and frequency of steady fixation, and pursuit gain. These results suggest that smooth pursuit control can be modified, even in an adult amblyope. Aspects of eye movement control that remained abnormal throughout therapy, in spite of normalization of visual acuity and centralization of fixation, include increased saccadic latencies, use of large saccades during small-amplitude pursuit tracking, and static overshooting. These results suggest that certain aspects of saccadic and pursuit control could either no longer be modified or would require longer periods for this to occur.

Adolescent↗
PubMed1978

Processing delays in amblyopic eyes: evidence from saccadic latencies.

Saccadic latencies were measured in amblyopes with constant strabismus, amblyopes without strabismus, and intermittent strabismics with or without amblyopia. Subjects tracked a small spot of light, either monocularly or binocularly, which moved with random horizontal step displacements of 0.25--8.5 deg over the central field. Increased saccadic latencies were observed in the amblyopic eyes of 6 of 11 subjects, with or without strabismus; saccadic latencies were similar in each eye of 2 subjects having intermittent strabismus without amblyopia. Amblyopia was a necessary condition for increased saccadic latencies and not strabismus. Evidence for normal motor control of eye movements in amblyopic subjects is as follows: normal saccadic durations in the amblyopic eyes, normal saccadic-latency distribution curves for binocular tracking and monocular tracking with the nonamblyopic eyes, and synchronous movements of the 2 eyes. Our results are interpreted in terms of a processing delay in the sensory pathways leading from the central region of the amblyopic eye to the centers involved in saccadic initiation.

Amblyopia↗
PubMed1978

Increased saccadic latencies in amblyopic eyes.

Increased saccadic latencies were measured in the amblyopic eyes of subjects having amblyopia without strabismus, constant strabismus amblyopia, and intermittent strabismus. The subjects tracked a small, bright spot of light moving with random, horizontal step displacements of 0.25 to 8.5 degrees over the central retina. Normal saccadic latencies were generally found during monocular tracking with the nonamblyopic eye as well as during binocular tracking. Studies of eye-hand reaction time in amblyopic eyes have shown delays to occur over the central retina; our new finding establishes this for saccadic initiation. Normal trajectories found for all tracking saccades, normal saccadic latencies measured when the nonamblyopic eye was utilized for tracking, and synchronous movement of the eyes under all test conditions point to a sensory rather than motor basis underlying these delays. Our results are interpreted in terms of a processing delay in the sensory pathways leading from the central region of the amblyopic eye to those centers involved in saccadic initiation.

Adolescent↗
PubMed1977

Neuro-optometry: an evolving specialty clinic.

Neuro-optometry is evolving as an optometric clinical specialty focusing on neurological dysfunctions of the visual system. Initially, we focused upon abnormalities of ocular movements, and our investigations have now broadened to include static and dynamic measurements of eye movements, accommodation, and the pupil. We feel the clinic serves three fundamental purposes: (1) to provide service to the patient, (2) to perform clinical research, and (3) to broaden the scope of the students' clinical experience. Operation of the clinic, technical methods of measurement, the testing protocol, and examples of interesting clinical recordings are described.

Accommodation, Ocular↗
PubMed1976

Eye movements during reading: case reports.

Since the time of Javal, it has been well established that normal reading eye movement patterns have 3 principal components: (1) small saccades that move the eyes from word to word, (2) large saccades that return the eyes to the beginning of the next line, and (3) fixation pauses between each saccade for information processing. We discuss the vision analysis results and show the quantitative reading eye movement records, measured with the infrared photoelectric method, of 5 patients examined in the Neuro-optometry Clinic. The reading records showed a wide variety of behavior: 1 patient performed normal reading movements, 1 "slow reader" manifested an excessive number of fixations as well as extended fixational durations, another "slow" reader only exhibited an excessive number of fixations, a patient with dyslexia performed backward reading movements, and 1 patient exhibited nystagmus superimposed upon the reading pattern.

Adult↗
PubMedDate not supplied

Training in virtual and real environments.

Transfer of training between real and virtual environments was examined using a pick-and place task with two different difficulty levels. The task was to minimize the time to move cans from one color coded location in the first row to the same color coded location in the back row and then to reverse the process. In the first task, the front and back disk colors were aligned, and in the second disk order, the front and back disk colors were randomly placed on the table. Subjects trained in one environment were then tested in the other and their performance compared with that of subjects being trained in that environment. Some virtual world-trained subjects showed small but significant improvement in performance compared with the untrained subjects for the real world task for both disk arrangements. The differences in performance between the two groups decreased with trial number until no difference was seen at the end of the sessions. None of the real world-trained subjects showed any significant improvement when performing the task in the virtual world compared with the untrained subjects. These results suggest that transfer-of-training from virtual to real world tasks can take place under certain conditions.

Adult↗
PubMedDate not supplied

Normal vestibular function in chicks after partial exposure to microgravity during development.

Sixty-four fertilized chicken eggs, half at developmental Day 2 and half at Day 9, were exposed to micro-gravity for 5 days aboard the shuttle. Postflight examination showed that none of the Day 2 flight embryos had survived, whereas the Day 9 flight group and both groups of synchronous ground control embryos appeared viable. One-half of the Day 9 flight and ground control embryos were dissected and the temporal bones preserved in acetone for morphological examination. The other half was allowed to hatch to examine vestibularly related behavioral changes. Morphology of the lagenar otoconia was evaluated by scanning electron microscopy. Behavioral changes were accessed by a battery of reflex tests and recordings of spontaneous and vestibularly driven head movements. The results from both the morphological and behavioral studies showed no consistent difference between the flight and the control animals. Several hypotheses may account for this negative result. Because all the Day 2 embryos failed to survive, the remaining Day 9 chicks may have passed the critical developmental period of the chick's vestibular system. Also, the reexposure of the developing chick embryo to earth's 1-g environment may have masked any adverse behavioral effects that exposure to Microgravity may have caused.

Animals↗