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Biomedical subjects

J L Demer

Publications and source records attributed to J L Demer.

At least 91 records · Page 5Linked to original sources
PubMed1987

Vestibulo-ocular reflex during magnified vision: adaptation to reduce visual-vestibular conflict.

This report describes the short-term effect of 2.2X telescopic spectacles on the vestibulo-ocular reflex (VOR) in seven volunteers. VOR gain was initially measured in darkness and light during passive sinusoidal rotations. Subjects were then rotated in light for 15 min while wearing telescopic spectacles. Dynamic visual acuity (DVA), vision during head rotation, was measured with telescopic spectacles. Initial VOR gain in darkness was 0.74 +/- 0.10 (mean +/- S.D.); VOR gain with unmagnified vision was 1.07 +/- 0.04. Initial VOR gain with magnified vision was 1.37 +/- 0.53. DVA was poorer than static acuity in three of four subjects. After adaptation, VOR gain in darkness increased to 0.83 +/- 0.12, with six of seven subjects exhibiting a gain increase of 7-23% (p less than 0.05 for 5). Adapted VOR gain with magnified vision was 1.54 +/- 0.25. Adapted performance was more consistent and oscillopsia was reduced. Adapted DVA improved 30-100% in four subjects. These changes indicate VOR adaptation to telescopic spectacles decreases visual-vestibular conflict.

Adaptation, Physiological↗
PubMed1986

Persistent elevation in intraocular pressure after Nd:YAG laser treatment.

A bilaterally pseudophakic patient, who had no previous evidence of glaucoma, underwent Nd:YAG laser posterior capsulotomy and dispersal of vitreous syneresis opacities of his left eye. The eye developed persistent intraocular pressure elevation and visual field loss, requiring medical therapy and argon laser trabeculoplasty. His fellow eye remained normotensive after Nd:YAG laser posterior capsulotomy. Nd:YAG laser treatment can result in chronic intraocular pressure elevation and glaucomatous visual field loss.

Cataract Extraction↗
PubMed1985

Effects of electrical stimulation and reversible lesions of the olivocerebellar pathway on Purkinje cell activity in the flocculus of the cat.

The activity of Purkinje cells (P-cells) in the flocculus of 8 lightly anesthetized cats and one alert cat was recorded for periods of up to several hours each. The resting simple spike (SS) rate in the anesthetized cats was 37 +/- 21 Hz (mean +/- standard deviation), similar to that observed in the alert cat. Complex spikes (CSs) were evoked by an electrode placed in the climbing fiber (CF) decussation or inferior olive (IO). For each P-cell, SS activity was suppressed completely at or above a cut-off frequency of evoked CSs; median cut-off rate was 5 Hz (range 1-10 Hz, 15 cells). Reversible lesions of the CF pathway were made by microinjection of 1-10 microliter of saturated lidocaine into the IO or CF decussation. This abolished spontaneous CS activity and produced two reversible effects on SS discharge: (1) an increase in mean SS rate of 98%, from 23 +/- 13 to 40 +/- 18 Hz (11 cells); and (2) a decrease of 50% in the variability of SS firing rate. Similar effects were observed in two P-cells whose CF axons were lesioned mechanically. These results show that electrical stimulation and reversible lesions in areas previously shown to alter the gain of the vestibulo-ocular reflex (VOR) also alter CF input to the flocculus, suggesting that the gain changes were caused by changes in CS rate. This study confirms and extends the observation that a reciprocal relationship exists between CS rate and SS background rate, and therefore further suggests that the changes in the gain of the VOR might be due to changes in SS background rate.

Animals↗
PubMed1984

Vestibulo-ocular and optokinetic deficits in albinos with congenital nystagmus.

Vestibular and optokinetic responses were recorded in three albino subjects with congenital nystagmus. Although an ice-water caloric stimulus did not elicit nystagmus, all patients showed a response to rotational stimuli containing high frequency components. Vestibular responses to a constant velocity rotation decremented with abnormally short time constants of 1-2 sec (normal 15-20 sec). For sinusoidal oscillation, in one subject, the cut-off frequency (where the amplitude of the response was 70% of maximum) was increased to 0.8 Hz (normal about 0.01 Hz). Full-field optokinetic stimulation generated no nystagmus response. These abnormalities may be due to defects in networks that act as mathematical integrators : either the final common neural gaze-holding network that converts velocity into position information for the ocular motor neurons or the "velocity-storage" mechanism that normally combines sensory inputs from both the labyrinths and visual system to generate appropriate (per-rotatory) nystagmus during rotation and to suppress inappropriate (post-rotatory) nystagmus after rotation.

Adult↗
PubMed1983

Different time constants for optokinetic and vestibular nystagmus with a single velocity-storage element.

Models have been proposed for the combined optokinetic system and vestibulo-ocular reflex that share a single, common, velocity-storage element that generates both optokinetic after-nystagmus and prolongs post-rotatory nystagmus. It has been thought by many that such a model requires the time course of these two types of nystagmus to be similar. The demonstration that vestibular or optokinetic habituation can selectively and significantly reduce the duration of each type of nystagmus without affecting that of the other has been taken to imply that the concept of shared velocity storage is incorrect. This need not be the case because post-rotatory nystagmus is described by two time constants, not one. Changes in the model's parameters can create time courses of this nystagmus that, when fit by single exponentials, have apparent time constants quite different from that of optokinetic after-nystagmus. Consequently, a common velocity-storage mechanism is still a tenable hypothesis for optokinetic and vestibular eye movements.

Animals↗
PubMed1981

The variable gain element of the vestibulo-ocular reflex is common to the optokinetic system of the cat.

The gain (slow-phase eye velocity/head velocity) of the vestibulo-ocular reflex (VOR) of 6 alert cats was sequentially adapted to values between 0.2 and 1.66 by the chronic wearing of visual reversing or 2 X magnifying spectacles, combined with forced rotation in the light. Gain was measured during sinusoidal oscillation in darkness at 0.05 Hz at a peak velocity of about 30 degrees/s. In each state of VOR gain adaptation, optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN) were measured in a full-field optokinetic drum at velocities of 20-80 degrees/s. Steady-state, slow-phase, optokinetic eye velocity nearly equaled low drum velocities, but saturated at higher velocities and declined when drum velocity further increased. The saturation velocity varied in relation to VOR gain, ranging from 10-20 degrees/s at a VOR gain of 0.2-0.4, to 65 degrees/s at a VOR gain of 1.66. The means that the variable gain element of the VOR is shared by the optokinetic system (OKS). OKAN, measured in darkness, had a roughly exponential decay. The time constant of OKAN (Tokan) also varied with VOR gain, ranging form about 2 s at a VOR gain of 0.2, to 10 s at a VOR gain of 1.66. This is a novel finding which suggests that the velocity-storage mechanism was also affected by gain changes. A model is proposed in which a neural, variable-gain element is located in a positive-feedback, velocity-storage loop common to both the VOR and the OKS. Computer simulation showed that this hypothesis could account for most of the observed changes in OKN saturation and Tokan with changes in VOR gain. The model also predicts that low frequency VOR phase lead in darkness should increase with decreasing VOR gain. Experimental VOR phase lead at 0.05 Hz varied from about 10 degrees for VOR gains above 1.1 to about 50 degrees for VOR gains below 0.3. Such phase-lead data agree with the trend predicted by the model.

Animals↗
PubMed1980

The effect of lesions of the dorsal cap of the inferior olive on the vestibulo-ocular and optokinetic systems of the cat.

The gain (eye velocity/head velocity) of the vestibulo-ocular reflex (VOR) of cats was measured in the dark and light for sinusoidal head oscillations at 0.05 and 1.2 Hz with peak velocity of about 30 deg/sec. Animals wore visual reversing prisms chronically and were also subjected to forced oscillation in the light at 0.05 Hz for 2 h per day. Such experience produced adaptive reduction in VOR gain in the dark from 0.85 to 0.10 within about 4 days; qualitatively similar effects were observed at 1.2 Hz. In 4 cats, the dorsal cap of the inferior olive was located electrophysiologically by its responses to visual motion, and bilateral electrolytic lesions were made in or near this structure. The location of lesions was subsequently identified by histology. After lesions, 3 cats were unable to make adaptive changes in VOR gain when confronted with the same reversing prism paradigm; the fourth exhibited appreciable retardation of adaptation. These results imply that the dorsal cap is essential for plastic adaptation of the VOR. However, all cats retained the ability to use reversed vision to reduce VOR gain in the light after lesions. Optokinetic nystagmus (OKN) and optokinetic after nystagmus (OKAN) were measured in a striped optokinetic drum, before and after dorsal cap lesions, at drum velocities of 20 and 40 deg/sec. Lesions of the dorsal cap in 4 cats did not impair either OKN or OKAN. This result indicates that the climbing fiber system reaching the flocculus from the inferior olive is not essential for such optokinetic movements.

Animals↗
PubMedDate not supplied

High myopia as an unusual cause of restrictive motility disturbance.

Endocrine ophthalmopathy is a common cause of restrictive ocular motility disorder associated with abnormal forced duction testing. We report ultrasonographic and computed tomographic findings in a highly myopic patient without thyroid abnormality in whom the restrictive findings of endocrine ophthalmopathy were simulated by contact between elongated globes and the bones of the orbital apices.

Endocrine System Diseases↗
PubMedDate not supplied

Computed tomography and magnetic resonance imaging in the diagnosis of inflammatory disease of the optic nerve.

Enlargement of the optic nerve and chiasm as demonstrated by high-resolution CT scanning or magnetic resonance imaging is often assumed to indicate tumor. However, this is not always true. The mode of clinical presentation of the disease process must be correctly applied to the interpretation of the radiographic studies. In the case illustrated here, neuro-ophthalmologic evaluation prevented an unnecessary biopsy in a patient whose presentation was atypical for anterior visual pathway glioma and whose clinical course was otherwise compatible with optic neuritis.

Child↗
PubMedDate not supplied

Congenital double elevator palsy: vertical saccadic velocity utilizing the scleral search coil technique.

Four patients with congenital double elevator palsy were studied who had clinically brisk elevation of the affected eye from downgaze to the midline position of rest, but severely limited or absent elevation above primary position. Forced duction tests were negative and Bell's phenomenon was present preoperatively in all patients. To clarify why upgaze saccades clinically seemed intact below but not above midline, vertical saccadic velocities were measured using the scleral search coil technique. The tracings of three cases suggest sufficient superior rectus function to generate a normal upward saccadic trajectory. A supranuclear lesion is the most likely etiology of the inability to elevate the eye well above primary position in these three patients. In a fourth patient, the reduced ability to elevate the affected eye above primary position is caused by a superior rectus paresis with decreased upward saccadic velocities. We suggest at least three distinct groups of patients present clinically as double elevator palsy: primary inferior rectus restriction, primary superior rectus paresis or palsy, and congenital supranuclear elevation deficiency.

Adolescent↗
PubMedDate not supplied

Quantitative magnetic resonance morphometry of extraocular muscles: a new diagnostic tool in paralytic strabismus.

Paralytic strabismus is often diagnostically ambiguous due to the similarity of patterns of misalignment produced by different mechanisms. To address this problem, we have developed a new technique employing high-resolution, surface coil magnetic resonance imaging to quantify extraocular muscle size and contractility. Adjacent coronal images are obtained spanning the anteroposterior extent of each orbit, and repeated in multiple directions of gaze. Contractility is evaluated from analysis of muscle cross-sectional areas. The quantitative size and contractile characteristics of normal rectus and superior oblique muscles are reviewed, along with the effects of superior oblique palsy. The morphometric features of lateral rectus palsy are illustrated by three clinical cases exhibiting deficient contractility and atrophy of the lateral rectus muscle. A case of superior oblique palsy is presented illustrating atrophy and lack of contractility of the involved superior oblique muscle. This imaging technique can be employed in any clinical center and permits insight into extraocular muscle function in complex strabismus cases.

Adult↗
PubMedDate not supplied

Magnetic resonance imaging of the superior oblique muscle in superior oblique myokymia.

High resolution, magnetic resonance imaging was used to quantitatively study the morphometry of the superior oblique muscles of two patients with superior oblique myokymia, as well as 18 superior oblique muscles of 14 patients with normal superior oblique function. The cross sectional area of each superior oblique muscle was measured at 3-millimeter intervals along the entire muscle length. In both cases of myokymia, the affected superior oblique muscles were significantly smaller than normal (P < .05). These anatomical changes in the superior oblique muscle of patients with myokymia suggest that an antecedent injury to the trochlear nerve has occurred. This injury, even if clinically unapparent, may be the initial event which leads to subsequent development of superior oblique myokymia.

Adult↗
PubMedDate not supplied

Saccadic velocity analysis in patients with divergence paralysis.

Twelve patients with clinical findings of divergence paralysis underwent horizontal saccadic velocity testing. Peak velocities were measured using digitally sampled electro-oculography during 10 degrees, 20 degrees, and 30 degrees saccades. Results were compared with those of 12 age-matched controls. The peak saccadic velocities of each eye in adduction and 10 degrees abduction did not differ from those of age-matched controls (P > .05). The 20 degrees and 30 degrees abducting saccades showed mildly reduced saccadic velocities when compared with controls (P < .05). The finding of only mildly reduced abduction saccadic velocities bilaterally is not consistent with bilateral lateral rectus palsy. The data support the hypothesis that divergence paralysis represents a distinct clinical entity unrelated to abducens nerve paresis and argues for the existence of an active divergence center. We further report the surgical results of five patients who were treated with strabismus surgery. A 4.0 to 6.0 mm bilateral lateral rectus muscle resection corrected 16 to 30 delta of esotropia at distance without resulting in an overcorrection at near. Bilateral lateral rectus muscle resection is an effective therapy for divergence paralysis.

Abducens Nerve↗
PubMedDate not supplied

Surgical implications of the rectus extraocular muscle pulleys.

PURPOSE: Magnetic resonance imaging (MRI) shows that the paths of rectus extraocular muscle bellies remain fixed in the orbit during large ocular rotations, and across large surgical transpositions of their insertions. This stability of muscle paths is due to their passage through pulleys which are coupled to the orbit and located in a coronal plane anterior to the muscle bellies near the equator of the globe. Autopsy studies have shown the pulleys to be fibroelastic sleeves consisting of dense bands of collagen and elastin, suspended from the orbit and adjacent extraocular muscle sleeves by bands of similar composition. Immunohistochemical studies have revealed substantial smooth muscle in the pulley suspensions and in posterior Tenon's fascia. The pulleys function as mechanical origins of the rectus extraocular muscles in the sense of determining extraocular muscle pulling directusons. This study was conducted to determine the theoretical effects of the pulleys on the outcome of rectus transposition surgery. METHODS: The functional and anatomical evidence for the existence of the rectus extraocular muscle pulleys was reviewed. In two patients, binocular alignment data were collected using the Hess screen test before and after vertical rectus transposition surgeries for lateral rectus paralysis. Paths of the rectus extraocular muscles were determined using high resolution MRI. The OrbitTM 1.5 extraocular biosimulation program was employed to compute theoretical binocular alignment and muscle paths, under alternative conditions including or omitting the pulleys. RESULTS: Pulleys are required to account for observed paths of rectus extraocular muscles following transposition surgery. In the absence of pulleys, transposition of the superior and inferior rectus muscles to the lateral rectus insertion for abducens paralysis would result in bizarre ocular misalignments not observed clinically. CONCLUSIONS: The human orbit contains specialized musculofibroelastic tissues in and just posterior to Tenon's fascia, which serve as pulleys, determining actions of rectus extraocular muscles. These pulleys are located in a roughly coronal plane just posterior to the equator of the globe. Unimpaired pulley function is essential to effective muscle transposition surgery.

Adult↗
PubMedDate not supplied

High resolution, dynamic, magnetic resonance imaging in complicated strabismus.

Strabismus cases, especially after previous surgery or trauma to extraocular muscles, often present diagnostic challenges. Conventional clinical tests are helpful in some cases but may be inconclusive. High resolution, dynamic, orbital magnetic resonance imaging (MRI) may yield additional critical information about orbital and extraocular muscle anatomy and function. We report four complicated strabismus cases for which dynamic surface coil MRI helped formulate a precise diagnosis and the most appropriate surgical plan.

Adult↗
PubMedDate not supplied

Effect of telescopic spectacles on head stability in normal and low vision.

Telescopic spectacles, highly magnifying visual aids mounted in spectacle frames, markedly alter the visual consequences of head movements. To evaluate the effect of this altered visual feedback on head stability, angular head velocity of normally sighted and low vision subjects was measured in the roll, pitch, and yaw axes. Measurements were made under two postural conditions: (1) quiet standing; and (2) walking in place, as well as three visual conditions: (1) eyes closed; (2) unmagnified vision; and (3) vision with 4 x binocular telescopic spectacles. For normal subjects during quiet standing, both unmagnified vision and vision with telescopic spectacles tended to reduce spontaneous head velocity in all axes as compared to the eyes-closed condition. However, in low vision subjects neither unmagnified vision nor vision with telescopic spectacles produced significant changes in values of head velocity relative to those measured with eyes closed. Spontaneous head velocities for standing low vision subjects tended to be higher than in normal subjects, although not all differences were statistically significant. During walking in place, Fourier analysis demonstrated prominent frequency components related to harmonics of the walking frequency under all viewing conditions. In normal subjects, vision with telescopic spectacles, to a greater degree than unmagnified vision, reduced head velocity during walking in the roll and yaw, but not the pitch, axes. For low vision subjects, significant reductions in head velocity during walking were observed only during vision with telescopic spectacles. These findings indicate that vision reduces angular instability of the head during standing and walking. Magnification produced by telescopic spectacles further improves head stability under some conditions, although the effect of vision is least evident in the pitch axis. The stabilizing effect of vision is reduced in low vision subjects.

Adult↗