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At least 217 records · Page 12Linked to original sources
PubMed2003

Eye muscle force development and saccadic velocity in thyroid-associated ophthalmopathy.

BACKGROUND: Ocular motility disturbances are very common in patients with thyroid-associated ophthalmopathy (TAO). The force duction test has demonstrated that limitations of eye movements may be caused by mechanical restrictions in the muscles. A quantitative evaluation of isometric force production and ocular motility in all directions of gaze could further elucidate the mechanism of the movement disorder. METHODS: In eight patients with TAO and eight controls of the same age range, horizontal and vertical saccadic movements of both eyes were recorded by means of electro-oculography (EOG). The corresponding force development in muscles of the more affected eye in patients and the non-dominant eye in normals was measured, using a suction contact lens/strain gauge technique. RESULTS: Steady-state tension in the patients was increased in all directions of gaze both horizontally and vertically, most markedly for vertical fixations in the upper field of gaze. However, peak tension was increased only for the downward movements in the upper field of gaze and for the horizontal movements in the abduction field of gaze. Vertical saccadic velocity was slower than normal in downward movements, and horizontal saccadic velocity was reduced in the abduction field of gaze. CONCLUSION: The increased active eye muscle tension in different directions of gaze could represent an adaptational mechanism of the ocular motor system to overcome the eye movement restriction in TAO.

Aged↗
PubMed2002

The influence of eye muscle surgery on shape and relative orientation of displacement planes: Indirect evidence for neural control of 3D eye movements.

Is Listing's law a consequence of 2D control of eye positioning, where eye torsion is determined by the biomechanical properties of the orbit, or is it a reflection of full 3D neuronal control? This was investigated by observing the influence of a change in mechanical properties of the eye socket on 3D eye movements. The shape and relative orientation of displacement planes were measured using scleral search coils before and after operation of five patients with strabismus. The operation influenced the shape of displacement planes in both eyes of all patients. After the operation, most patients obeyed Listing's law more accurately: a monocular, surgically induced, orbital change caused binocular improvements of torsional control. The relative orientation of planes also changed, but no clear relationship was found between the type of operation and the direction of rotation. The results suggest that Listing's law is not just a result of the biomechanical properties of the eye socket, but has a neural basis.

Adult↗
PubMed1988

Stage I intraoperative adjustment of eye muscle surgery under general anesthesia: consideration of graduated adjustment.

The eyes diverge under general anesthesia. The amount of divergence is predictable; there is a linear relationship between the preoperative and the anesthetized eye position. We have confirmed Apt and Isenberg's regression formula for this relationship (A = 0.8 P + 30). We have previously also reported that adjusting the amount of surgery to be done (stage I adjustment) in cases deviating from this correlation by one standard deviation or more (anomalous) significantly improved our surgical success rate to 85%. Since a fixed arbitrary adjustment of 1 mm more or less surgery had improved our surgical success rate significantly, but still left room for higher success rates, we reviewed our anomalous cases to determine whether a graduated adjustment might be expected to produce even higher success rates. A review of cases including additional ones since our last report failed to support this hypothesis. Satisfactory results in these most recent cases have, however, almost doubled the surgical success rate (in anomalous cases) for our stage I fixed arbitrary 1 mm intraoperative adjustment, from 47% to 90%.

Adolescent↗
PubMedDate not supplied

Evidence suggesting individual ocular motor control of each eye (muscle).

Current models of the ocular motor system are usually presented in their most reduced form, are unilateral in architecture, and precise yoking is presumed. Although this simplifies the models, it does not accurately simulate the actual neuroanatomy and limits the models to simple, stereotyped responses. Studies of normal humans and monkeys have demonstrated striking disconjugacies in normal responses. Normal saccades may be disconjugate, or 1 eye may exhibit a dynamic overshoot. Asymmetric vergence can result in disconjugate saccades, unequal magnification spectacles cause differential saccadic gain adjustment, and saccades to unequal disparities also cause unequal saccades in the 2 eyes. In strabismus, deviated eyes typically do not mimic the movements of the fixating eye nor do their latent or congenital nystagmus waveforms duplicate those of the fixating eye. In spasmus nutans, each eye oscillates independently of the other. In achiasmatic dogs, uni-ocular saccades and uni-ocular nystagmus waveforms are seen; the same may be true in human achiasma. These data from both normals and those with abnormalities suggest that current models for ocular motor control are inadequate representations of the actual system. The inability of unilateral, yoked control (or even bilateral, yoked control) system models to duplicate the ocular motor responses of binocular mammals suggests that their ocular motor systems evolved from the bilateral, independent control systems seen in chameleons. One need only postulate a yoking overlay superimposed on two independent control systems to achieve conjugacy (bilateral, yoked, independent control) of the eyes. Abnormalities producing grossly disconjugate eye movements may then be simulated using the independent control of each eye released by a deficiency in the yoking overlay. Independent control of each eye coupled with the essential bilateral brain stem architecture implies that each individual muscle is driven by independent populations of neurons (burst cells, neural integrator cells, etc.). The agonist muscles of each eye are usually coordinated (yoked) but may function independently if the task dictates or if binocularity did not develop. Models based on the above architecture would be robust and could duplicate the many responses (both normal and abnormal) possible from the neurophysiological system.

Animals↗