Increased muscle tension and reduced elasticity of affected muscles in recent-onset Graves' disease caused primarily by active muscle contraction

In 3 patients with Graves' disease of recent onset, length-tension diagrams were made during surgery for squint under eyedrop anesthesia. The affected muscles were found to be very stiff when the other eye looked straight ahead. It was expected that these stiff muscles would be able to shorten to some extent but would be unable to lengthen, due to fibrosis of the muscle. We found that the affected muscles did not shorten very much when the other eye looked into the field of action of the muscle. Unexpectedly however, they lengthenend considerably when the other eye looked out of the field of action of the muscle. This finding implies that the raised muscle tension and reduced elasticity of affected muscles in these cases of Graves' disease of recent onset were primarily caused by active muscle contraction, not by fibrosis

Robinson's Computerized Strabismus Model Comes of Age

In this article we review our further development of D.A. Robinson's computerized strabismus model. First, an extensive literature study has been carried out to get more accurate data on the anatomy of the average eye and the eye muscles, and about how these vary with age and with refraction. Secondly, the force-length relations that represent the mechanical characteristics of the eye muscles in the model have been determined more accurately in vivo recently, and the model was changed accordingly. Thirdly, many parameters that were free in the original model and not derived from in vivo measurements were replaced by derivatives from in vivo measurements or made redundant. Fourthly, the ease of operation was improved greatly and the algorithms were made so much faster that a calculation for nine positions of gaze now takes ten seconds on a handheld HP 200LX Palmtop. The predictions of the model compared well with clinical results in horizontal muscle surgery, oblique muscle surgery, forced duction tests and abducens, oculomotor or trochlear palsies. Consequently, complex strabismus surgery in our clinic is now guided by the predictions of the computerized model

Sixty strabismus cases operated with the Computerized Strabismus Model 1.0: When does it benefit, when not?

While, in routine strabismus surgery, empirical guidelines and experience are the best in judging which eye muscles to operate, a complex case may need a unique surgical approach, the consequences of which cannot always be envisioned in detail. We sought to improve the results of surgery in these cases by preoperative simulation of each case with the Computerized Strabismus Model 1.0 (CSM). The basis of this model was laid by David A. Robinson. It has been improved by us over the past years to the point that it can be used clinically. Improvements concerned, for example, the mechanics of the eye muscles and the anatomy of insertions and origins. The ease of operation has been improved and the algorithms have been made so much faster that a full calculation for 9 positions of gaze now takes 10 seconds on a hand-held Hewlett Packard 200LX Palmtop. From 1994 onwards, all cases to be operated in our department which were more complex than straightforward horizontal rectus muscle surgery were simulated in the model preoperatively. The predictions of the model compared well with the actual result of surgery in most cases. The model was particularly good in handling complex and unique disorders of motility. However, the model could not reliably predict the effect of strabismus surgery in cases with mechanical restrictions of motilit

Force-length recording of eye muscles during local-anesthesia surgery in 32 strabismus patients

Abstract. Force-length recordings were made from isolated human eye muscles during strabismus surgery in local, eye-drop anesthesia in 32 adult patients. From each muscle three recordings were made: (1) while the patient looked with the other eye into the field of action of the recorded muscle, (2) looked ahead, and (3) looked out of the field of action of the recorded muscle. Non-innervated eye muscles (state 3) had an approximately exponential relation between force and length. During contraction evoked by letting the patient look ahead or into the field of action of the muscle (states I or 2), the relation between force and length was grossly linear. The approximate spring constants of horizontal rectus muscles that had not been operated on before ranged from 2 to 4 g/mm. In palsies, the degree of muscle paresis could be quantified accurately using this method and, accordingly, cases of true superior oblique palsy could be well differentiated from strabismus sursoadductorius (= upshoot in adduction) that may mimic a superior oblique palsy. In seven patients with Graves' disease of recent onset, affected muscles were found to be very stiff when the other eye looked ahead. It was expected that these stiff muscles would be able to shorten to some extent but would not be able to lengthen, due to fibrosis of the muscle. We found, however, that the affected muscles lengthened considerably when the other eye looked out of the field of action of the muscle. This implies that, in these cases of Graves' disease of recent onset, the raised muscle tension and reduced elasticity of the affected muscles and, hence, the strabismus were primarily caused by active muscle contraction, not by fibrosis

The fourth monitoring report of the Early vs. Late Infantile Strabismus Surgery Study

The Early vs. Late Infantile Strabismus Surgery Study Group is a group of strabismologists and orthoptists from 58 clinics in 11 European countries. They investigate whether early or late surgery is preferable in infantile strabismus, in a non-randomized, prospective, multi-center trial. Infants between 6 and 18 months of age receive a standardized entry examination and are then operated either before their second anniversary in clinics A, or between their 32nd and 60th month of age in clinics B. The children are evaluated at age six. After completion of the study, the two groups can then be compared regarding degree of binocular vision, angle of strabismus and visual acuity of the worse eye relative to the better. The current status of the study is reported here. Up to December 13, 1996, 58 clinics have entered a total of 532 patients. Currently, 232 children have been entered in the early surgery group and 300 in the late surgery group. Completeness of data and forms are excellent. Thirty-eight patients have definitively dropped out. There is no evidence for inhomogeneities between the two therapy groups concerning the distribution of the four most important prognostic factors: spherical equivalents, horizontal angle of squint, degree of amblyopia and limitation of abduction

A reexamination of end-point and rebound nystagmus in normals.

In order to detail the characteristics of end-point (EPN) and rebound nystagmus (RN), two series of experiments were performed with infrared oculography for measurement of horizontal eye movements. Experiment 1 consisted of EPN recordings during sustained lateral gaze (40° and 50°) in 20 normal subjects. Experiment 2 consisted of recordings of RN in 5 normal subjects. Nine of 20 subjects demonstrated a jerk EPN. EPN almost always appeared immediately and was sustained for 15-25 sec. In Experiment 2, RN occurred in 5 of the 5 subjects who demonstrated EPN. The mean amplitude of RN was always less than that of EPN, and decayed over a 5-10-sec time period. The experiment demonstrated that RN can be evoked in normals even when a fixation target, in a fully lit room, is present

Phakomatosis Pigmentovascularis

We report a patient with phakomatosis pigmentovascularis IIb and numerous iris hamartomas. Phakomatosis pigmentovascularis IIb is characterized by the simultaneous occurrence of a nevus flammeus, a mongolian spot, and sometimes a nevus anemicus in the same individual, with systemic involvement. To our knowledge, the association with multiple iris hamartomas has been reported only once. This second patient suggests that the association might be more common. Additional reports will indicate if such an association is more frequent than is now assumed

Length-tension curves of human eye muscles during succinylcholine-induced contraction

We have made intraoperative, continuous-registration, length-tension diagrams of detached eye muscles in 80 strabismus patients under general anaesthesia. In 47 of these we repeated the measurements after contraction evoked by succinylcholine chloride. In contracting horizontal and vertical rectus muscles, we found a linear relation between length and tension. In contracting oblique muscles, however, the relation between length and tension was frequently nonlinear. In superior oblique palsies, the superior oblique was found to be stiff after elongation and before injection of succinylcholine, and it did not contract after injection of succinylcholine. The ipsilateral inferior oblique did contract after injection of succinylcholine, but with a higher spring constant than usual (ie, contracture of the ipsilateral antagonist). In three cases the superior oblique contracted vividly after administration of succinylcholine despite the presence of excyclotropia, stereopsis, torticollis (two cases) and a hypertropia that increased in adduction, in down-gaze, in adduction and down-gaze and on ipsilateral head-tilt. In a case of general fibrosis syndrom we found almost normally contracting vertical recti, which is compatible only with a supranuclear or misdirectional cause. These cases demonstrate the usefulness of the assessment of the length-tension diagram of an eye muscle during surgery, before and during contraction evoked by succinylcholine chloride