Extraocular muscle changes after cryotherapy for retinopathy of prematurity and the development of strabismus in premature infants.
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To find out whether the cryotherapy for the treatment of the retinopathy of prematurity (ROP) causes structural changes of the extraocular muscle (EOM), and also whether the changes are related with the occurrence of strabismus. To examine the acute stage change, we conducted a transconjunctival cryotherapy around the superior rectus muscle of a rabbit and resected it 0, 3, 7, 14, and 28 days after the cryotherapy. In observing chronic changes, we first categorized patients who had an esotropia surgery into groups, one of which combined prematurity and cryotherapy and one group affected by prematurity but without having had cryotherapy. Then we compared the change of EOM with that of a fullterm infant group. In a rabbit, edema, acute inflammatory cells and a large amount of degenerated muscle fibers were observed immediately after the cryotherapy and on the 3rd day. On the 7th day, regenerated muscle fibers were observed and on the 14th day, the inflammatory cells decreased and the amount of regenerated muscle fiber increased. On the 28th day, abnormal findings were not observed any more and the muscle was found to be normal. When chronic changes of EOM in human on 1 1/2 to 8 1/2 years after cryotherapy, there were no abnormal findings observed in three groups. From the study, we can infer that cryotherapy can cause acute inflammation and necrosis of muscle fiber but such an acute change will improve and does not result in structural change in the long term. Therefore, the occurrence of strabismus in patients with ROP is considered to be attributable to reasons other than injury of EOM. (+info)
A quantitative analysis of extraocular muscle cooperation and squint.
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The mechanical properties of human extraocular muscles have recently been described. This allows one to use the force-balance equation of mechanics to solve for the complete mechanical state of all six extraocular muscles and the passive orbital tissues in any eye position. This includes each muscle's force, length, innervation, and unit action vector, which describes how its force is distributed to act horizontally, vertically, and in torsion. Most important, this calculation method allows one to predict the tropias that occur in an eye subject to any imaginable form of peripheral pathology. It also permitts, by calculation, an estimation of the correction that might be expected from any sort of muscle surgery. The tight lateral rectus syndrome is used to illustrate the application of the method in diagnosis and surgery. It also offers, for the first time, a quantitative estimate of the multitude of ways in which muscles can interact and interfere with each other when they hold the globe. Two of the results are interesting: because muscles have different lengths and sizes, their innervational participation in a movement can appear to be quite different than their mechanical participation. From an innervational standpoint, the vertical recti and obliques participate equally in vertical gaze. Muscles interfere with each other a good deal and necessitate changes of innervation to counteract these cross-couplings. This causes unexpected dependencies of innervation on eye position and leads, for example, to the fact that the superior rectus innervation in up gaze is just as large in adduction as in abduction. (+info)
Genetic analysis of indices of corneal power and corneal astigmatism in human populations with varying incidences of strabismus.
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Heritability estimates for corneal power were found to be high and similar for two populations which differed in their incidence of esotropia. This similarity suggest (1) that genetic differences for corneal power do not contribute to the difference in heritability for spherical refractive error reported for these populations and (2) that this character is not a critical variable contributing to the pathophysiology of esotropia. Heritability estimates for corneal astigmatism were, in most cases, rather low. The pattern of population and sex differences among heritability estimates was consistent with those previously reported for cylindrical refractive error. These population differences in heritability suggest that they contribute to population differences found for cylindrical refractive error. (+info)
Changes in Listing's plane after sustained vertical fusion.
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PURPOSE: To determine whether prolonged fusion of an imposed vertical disparity leads to a change in the orientation of Listing's plane, even when measured during monocular viewing. METHODS: Four normal subjects (age range, 24-37 years) wore Fresnel prisms of increasing power for 72 hours to produce a final left-over-right disparity (range, 7-11 prism diopters [approximately 3.9 - 6.2 degrees]) that was still fusible. Eye movements were measured binocularly, using three-axis search coils, as subjects fixed on an array of light-emitting diodes (LEDs) arranged on a flat screen, 124 cm away. A regression was used to fit the data points to a plane (Listing's plane) during monocular and binocular viewing. From each planar fit, the horizontal and vertical components of primary position (the direction of gaze that is perpendicular to Listing's plane) were calculated. Baseline data were collected in the unadapted state, either just before or at least 4 days after wearing the prisms. RESULTS: After the period of viewing through the prisms, there was a change in vertical phoria (prism adaptation) ranging from 1.6 to 3.3. There was a significant (P < 0.01) shift of the relative orientation of the vertical component of primary position between the two eyes of 6.3 +/- 1.7 degrees (right eye value minus left eye, up being positive, each measured during monocular viewing). There was no consistent pattern of change in the horizontal component of primary position. CONCLUSIONS: Prolonged fusion of a vertical disparity is associated with a change in the orientation of Listing's plane that persists under monocular viewing. Possible mechanisms include phoria adaptation, the prolonged fusional effort itself, and the residual disparity that must be overcome by sensory mechanisms. (+info)
Impaired vertical phoria adaptation in patients with cerebellar dysfunction.
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PURPOSE: To determine whether phoria adaptation to a vertical prism disparity is altered in patients with cerebellar dysfunction. METHODS: With a computer-aided haploscope, adaptive responses of fusion-free eye position to a 10- or 30-minute period was measured in subjects wearing a 3-prism diopter vertical prism over one eye. Thirteen patients with well-documented cerebellar diseases who did not have manifest ocular misalignment or limited versional eye movement and age-matched healthy subjects participated. RESULTS: The mean +/- SD percentage of vertical phoria adaptation was 13% +/- 22% and 20% +/- 16% for the 10- and 30-minute adaptations, respectively. These levels were significantly smaller than the respective ones in the age-matched control group (P < 0.001, repeated measures MANOVA). Seven (54%) of 13 patients, including two with genetically confirmed pure cerebellar lesions (spinocerebellar ataxia type 6), showed markedly reduced responses to both the 10- and 30-minute adaptations. In all three patients with acute cerebellar ataxia, the adaptive response was improved at the same time as remission of cerebellum-associated neurologic deficits. CONCLUSIONS: Phoria adaptation to vertical binocular disparity is frequently impaired in patients with cerebellar dysfunction. These results bolster the hypothesis that phoria adaptation is a cerebellar-dependent response. (+info)
Long-term effects of ricin-mAb 35 on extraocular muscles of rabbits: potential treatment for strabismus.
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PURPOSE: The immunotoxin, ricin-mAb 35, composed of ricin conjugated to a monoclonal antibody against the nicotinic acetylcholine receptor of skeletal muscle, has been proposed as a potential new agent for treatment of focal muscle dystonias. It has been demonstrated that direct injection of ricin-mAb 35 into rabbit extraocular muscle (EOM) results in significant muscle loss within 1 week. In this study, the long-term myopathic effects of ricin-mAb 35 on extraocular muscle were investigated. METHODS: Rabbit superior rectus muscles were injected with ricin-mAb 35 at a dose of 0.2 microg/kg, with the contralateral superior rectus muscle serving as the control. After 56 days, 105 days, and 1 year, the superior rectus muscles were removed and prepared for light or electron microscopy. Postinjection changes in muscle fiber morphometry and ultrastructure were examined. Immunohistochemical markers were used to identify inflammatory cellular infiltrate and myosin heavy chain (MHC) isoform expression. RESULTS: Despite evidence of ongoing regeneration, treated muscles continued to show a decrease in both myofiber number and in total cross-sectional area 56 and 105 days after injection. Individual myofiber cross-sectional areas were markedly heterogeneous at 56 days. Myofiber number and muscle cross-sectional area returned to normal 1 year after injection, but pronounced heterogeneity of myofiber size remained. The most significant changes in myosin heavy chain (MHC) isoform expression occurred in the orbital layer, where, at 56 and 105 days, there were increased numbers of fast and neonatal myofibers and decreased numbers of slow myofibers. In the global layer, after both 105 days and 1 year, there was a decrease in myofibers that were positive for slow, neonatal, and developmental MHC expression. CONCLUSIONS: EOM injection with ricin-mAb 35 results in a sustained decrease in muscle mass at 105 days after injection, with subtler morphometric changes persisting even to 1 year. Changes in muscle force development as a result of ricin-mAb 35 injection are currently under investigation. This novel immunotoxin may be useful in the treatment of strabismus if these studies show sustained weakness in treated muscles. (+info)
Deep topical fornix nerve block versus peribulbar block in one-step adjustable-suture horizontal strabismus surgery.
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BACKGROUND: We compared the efficacy of deep topical fornix nerve block anaesthesia (DTFNBA), which does not paralyse the extraocular muscles, with peribulbar block in patients undergoing one-step adjustable-suture horizontal strabismus surgery. Patients with a vertical, oblique squint were excluded from the study. METHODS: We studied 100 patients, allocated randomly to two groups. Group 1 (n=50) received peribulbar block with 5 ml of 1:1 mixture of 0.5% plain bupivacaine and 2% lignocaine supplemented with hyaluronidase 300 i.u. ml(-1). Group 2 (n=50) received DTFNBA with placement of a sponge soaked in 0.5% bupivacaine deep into the conjunctival fornices for 15 min. No sedation was given to either group. Analgesia was assessed by direct questioning of patients during the procedure. A three-point scoring system was used (no pain = 0, discomfort = 1, pain =2). If the pain score was 1, the patient was asked to look in the opposite direction to decrease the tension on the periosteal attachment of the muscle to relieve discomfort. If the pain score was 2 at any stage of the operation, general anaesthesia was given. RESULTS: In Group 2, significantly more patients (15) experienced discomfort than in Group 1 (no patients) (P<0.05), but general anaesthesia was not needed. CONCLUSIONS: DTFNBA is a useful technique for intraoperative adjustable-suture strabismus surgery. It does not alter muscle tone, thus allowing the surgeon to adjust the muscle sutures intraoperatively, and reducing the incidence of under- or over-correction of the squint in the immediate postoperative period. (+info)
Use of random-dot sterograms in the clinical assessment of strabismic patients.
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Random-dot stereograms were shown to a sample of strabismic patients for whom there was clinical evidence of stereopsis. Two kinds of sterograms were used, one of the usual sort and the other having a contour surrounding the disparate area in each field of view. The patients tested could be clearly classified as belonging to one of three response groups. The first group could fuse both kinds of stereogram, the second could fuse only he contoured kind, and the third could not fuse either kind. This grouping was found to relate to the degree to which bifoveal binocular single vision had been absent in the clinical histories of these patients. The result is discussed in terms of the consequences for vergence and stereopsis of period of absence of normal binocular function. (+info)