1,721,013 research outputs found
Isometric force measured in human horizontal eye muscles attached to or detached from the globe.
No full textBACKGROUND: Human eye muscle tension has been measured directly only in detached condition. The purpose of this study is to compare force development in single, horizontal human eye muscle during saccadic eye movements, first when the muscle was still attached and later when it was detached from the globe. METHODS: Eleven horizontal muscles of eight patients were examined during surgery under topical anesthesia for concomitant strabismus. None of the muscles examined had been operated before. Isometric muscle tension was recorded with a strain gauge system, to which the muscle tendon was attached by a silk suture. The subjects made saccadic eye movements with the non-recorded eye by fixating light-emitting diodes in the center and at 10, 20, and 30 degrees horizontally to each side. Continuous and stepwise saccades were produced. In the tension signals, peak tension (Fp), steady tension (Fs), and the ratio Fp/Fs were measured. Statistical analysis was done with multivariate analysis of variance. RESULTS: The values of Fp, Fs, and Fp/Fs at different amplitudes of the saccadic eye movements were compared in the attached and the detached muscle. There were no consistent statistical differences between the values obtained in the two conditions. CONCLUSIONS: The muscle force development, measured at the tendon, was the same in muscles attached to the globe and in muscles free from the globe. Thus isometric muscle tension can be adequately recorded in muscles still attached to the globe, which increases the possibilities for studying contractile properties of various eye muscles during ophthalmic surgery procedures performed under topical anesthesia
Eye muscles force development in thyroid-associated ophthalmophaty in different stages of disease.
No full textPURPOSE: Ocular motility disturbances are common in patients with thyroid-associated ophthalmopathy (TAO). A quantitative evaluation of the isometric force of the eye muscles in TAO might be useful in the detection of early stages of this disease. METHODS: A total of 32 patients with TAO were divided into three groups according to whether they had mild active, pronounced, active, or longstanding, inactive disease. A group of six patients with Graves' disease without clinical signs of TAO and a group of 10 control subjects were also studied. The development of isometric force during saccadic eye movements of 5-, 10- and 20-degree amplitude in horizontal and vertical directions of gaze were recorded in the more affected eye in patients and the non-dominant eye in normal subjects, using a suction contact lens/strain gauge technique. RESULTS: Peak tension (Fp) in vertical and horizontal saccadic movements was not significantly different between groups. Steady-state tension (Fs) was significantly higher in the groups with pronounced, active and longstanding, inactive disease than in the other groups for vertical (p < 0.01) and horizontal movements (p < 0.05). Abnormal force development in any of the gaze directions was seen in all patients with pronounced, active and longstanding, inactive TAO, and in some of the patients with mild, active TAO and Graves' disease without TAO. CONCLUSIONS: Increased eye muscle tension was recorded in different gaze directions, confirming multiple extraocular muscle involvement in TAO. It is suggested that the increased force development reflected contractile compensations for restrictions of ocular motility due to higher muscle stiffness in thyroid-associated eye muscle disease. Tension measurements can be used to identify muscle involvement in TAO
Isometric force of extraocular muscles measured in a case of dysthyroid restrictive esotropia. Effects of chemodenervation and surgery to correct esotropia on eye muscle tension.
No full text
Isometric force development in human horizontal eye muscles and pulleys during saccadic eye movements
Full text linkPurpose: The connective tissue elements forming the check ligaments and portals of the human eye muscles have recently been ascribed with a pulley function. Active positioning of the pulleys over orbital layer contraction during eye movements has been suggested. Other studies have instead demonstrated fibrous tissue connections between all parts of the muscle and the pulleys. We aimed to compare the isometric force developed at the muscle tendon and at the pulleys of the horizontal eye muscles, and to investigate which eye muscle structures might exert force on the pulleys.
Methods: Isometric force development was recorded from the lateral and medial rectus muscles in six patients operated for strabismus under topical anaesthesia. Two strain gauge probes were used, each attached with 5–0 silk sutures either to the muscle tendon or to the pulley. The eye muscles were activated by horizontal saccadic eye movements in steps from 30 degrees in the off-direction to 30 degrees in the on-direction of the muscles.
Results: The forces developed at the tendon and pulley were almost identical with respect to amplitude and other parameters. No differences were found in forces developed at the pulleys of the medial and lateral rectus muscles.
Conclusions: The results support the presence of fibrous tissue connections between all eye muscle fibres and pulley structures, rather than orbital fibre control of the pulley
Changes of saccadic eye movements in thyroid-associated ophthalmopathy.
No full textPurpose: To establish whether or not the dynamics of saccadic eye movements are significantly changed in patients with different stages of thyroid-associated ophthalmopathy (TAO) and, subsequently, if analysis of saccades could serve as an additional
diagnostic tool for early detection of inflammatory activity in TAO.
Methods: Thirty-seven patients with TAO and 10 age- and gender-matched control subjects were investigated. The patients were divided into four groups according to the stage of the disease: (i) early mild disease (n = 10), (ii) early severe disease (n = 11),
(iii) long-standing restrictive disease (n = 10) and (iv) proven auto-immune hyperthyroidism without any signs of TAO (n = 6). Horizontal and vertical saccades with amplitudes of 10, 20, 30 and 40 were recorded binocularly using the induction scleral search coil technique. The two main sequence constants Vmax and C were calculated for each eye. Repeated measurement analysis of variance was carried out to test for differences between different gaze directions, eyes and groups.
Results: In horizontal saccades, significant differences were found between groups but not between abduction and adduction. In vertical saccades, differences between groups and the interaction between groups and up- and down-gaze saccades were significant.
Compared with the control group, analysis of the main sequence curves revealed larger differences in patients of group 3 and 4 than in those of group 1 and 2. Whereas in the control group down-gaze saccades were faster than up-gaze saccades, the opposite
behaviour was found in all patient groups. The largest differences were detected among those patients who had no signs of TAO (group 4).
Conclusions: In this study, significant saccade differences were detected in all patients with TAO. In contrast to our earlier studies where evaluation of multiple individual saccade parameters did not reveal significant differences, analysis of the main sequence
constants and mathematical reconstruction of the main sequence curves turned out to be a sensitive technique for reliable detection of subtle ocular motility changes. Significant differences were detected even in patients with auto-immune thyroiditis where no
clinical signs of TAO were apparent
Magnetic resonance imaging and ultrasound measurements of extraocular muscles in thyroid-associated ophthalmopathy at different stages of the disease.
No full textPURPOSE: To assess extraocular muscle (EOM) involvement in thyroid-associated orbitopathy (TAO) of different stages with magnetic resonance imaging (MRI) and ultrasound techniques. METHODS: A total of 32 patients with TAO were divided into three groups according to whether they had mild active, pronounced active or longstanding inactive disease. Six patients with Graves' disease but no clinical signs of TAO and 10 healthy control subjects were also studied. Muscle volume and cross-sectional area were measured with MRI. A-scan ultrasound was used to measure muscle thickness. RESULTS: The average MRI volume and maximal cross-sectional area of the EOM were significantly larger in patients with pronounced active and longstanding inactive TAO than in control subjects. Increased average muscle thickness measured by ultrasound was found mainly in patients with longstanding disea
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Succinylcholine activation of human horizontal eye muscles.
No full textAbstract:
Purpose: Succinylcholine (Sch) can induce contracture in slow, multiply innervated muscle fibres of the extraocular muscles in animals of different species. Slow muscle fibres also exist in human eye muscle but their physiological properties have not been studied.
Methods: Isometric tension development was recorded in the lateral and medial rectus muscles in 12 patients operated under general anaesthesia. A strain gauge probe was attached with 5-0 silk sutures to the muscle tendon. Recordings were made in 12 eye muscles with the tendon attached to the globe and in four muscles detached from the globe.
Muscle activation was produced by i.v. injection of Sch at a dose of 0.2-0.3 mg/kg bodyweight. Results: A single injection of Sch induced slow contractures lasting for several minutes. In the muscles attached to the globe, mean maximal isometric tension was 12.2 g in the lateral rectus and 12.8 g in the medial rectus. Similar tension was shown in the muscles detached from the globe.
Conclusions: The contracture of eye muscles in response to Sch showed characteristics typical of slow muscle fibre activation in amphibian and avian muscle and confirmed the participation of slow fibre systems in ocular motor control
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