|Year : 1983 | Volume
| Issue : 5 | Page : 470-472
Contracture of extraocular muscle
Prem Prakash, Taenla Yanger, V Menon, V Singhal
Dr. R.P. Centre for Ophthalmic Sciences, A.I.I.M.S., New Delhi, India
Dr. R.P. Centre for Ophthalmic Sciences, A.I.I.M.S., New Delhi-29
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Prakash P, Yanger T, Menon V, Singhal V. Contracture of extraocular muscle. Indian J Ophthalmol 1983;31:470-2
|How to cite this URL:|
Prakash P, Yanger T, Menon V, Singhal V. Contracture of extraocular muscle. Indian J Ophthalmol [serial online] 1983 [cited 2020 Jan 21];31:470-2. Available from: http://www.ijo.in/text.asp?1983/31/5/470/29524
| Introduction|| |
Contracture is clinically characterized by fixed resistance to a passive stretch of muscle. In the case of extraocular muscles, fixed resistance is evident by forced duction test in an attempt to move the eye ball passively in a direction opposite to the direction of action of the muscle.
There are no studies for experimental contracture available. This study was therefore undertaken to study the early histological and histochemical changes occurring in an experimentally attempted contracture.
| Material and Methods|| |
Twenty Indian Rhesus monkeys were studied, each weighing about 2-1/2 Kg. The experiments were done under general anaesthesia using I.V. Nembutal (30 mg/ Kg body wt.) One lateral rectus was extirpated in each animal to result in an esodeviation of the eye. Forced duction test was done every week after extirpation to note any passive resistance to movement of eyeball under general anaesthesia, After specified periods in different groups the ipsilateral medial rectus which was likely to undergo contracture was used as experimental and the contralateral medial rectus as the control muscle. The animals were divided into five groups with four animals in each group and experiments done after 2, 4, 8, 12 and 24 weeks of lateral rectus extirpation.
Muscles removed were stained for the following histochemical studies:-Nitroblue tetrazolium stain for SDH activity and Modified trichrome for fibre typing,
For histological studies H & E, Masson trichrome and Verhoeff van Gieson were used for morphological,, collagen tissue and elastic tissue respectively.
| Results|| |
Following lateral rectus extirpation an esodeviation of upto 10° was evident as judged by the corneal reflex. Only sixteen out of twenty animals showed the deviation. [Figure - 1]. Forced duction test revealed mild passive; resistance in three out of four animals in the twenty four weeks' group,
No obvious changes were observed in any group by H & E and Verhoeff van Gieson stain. The Masson trichrome stain revealed mild increase in collagen tissue in experimental specimens in the twenty four weeks' group [Figure - 2].
A statistically significant decrease in the lightly staining fibres (type II) were observed in the twenty four weeks' group by the Nitroblue tetrazolium stain for SDH activity, (P 0.05) [Figure - 3][Figure - 4]. Fibre typing by the Modified trichrome stain also revealed a statistically significant decrease in type II fibres in the twenty four weeks' group, (P, 0.01) [Figure - 5][Figure - 6],
The ipsilateral antagonist and the contralateral synergist have shown similar changes by histochemical and histological examinations.
| Discussion|| |
Contracture which is a very common sequel to strabismus is unfortunately not a very well understood phenomenon structurally. The attempt to produce experimental squint and subsequent contracture has resulted in the following conclusions.
Clinical observations by corneal reflex method after extirpation of lateral rectus revealed a small esodeviation of upto 10° in majority of animals. Considering that a large amount of lateral rectus was extirpated, the deviation was rather small. This may be due to the fact that the musculofascial apparatus of the monkey is not conducive to the production of large degree of esodeviation in spite of quite a large extirpation of lateral rectus.
Mild passive resistance observed only in twenty four weeks' group could be because of insignificant contractural changes that had taken place during the period of this study. It is possible that greater duration of observation might reveal more significant changes.
The histopathological findings of a slight increase in collagen tissue by the presence of areas of fibrosis by the Masson trichrome stain in the twenty four weeks' group could indicate a replacement of muscle tissue by the fibrous tissue. Since decrease in type II fibres was observed, it is possible that these have been replaced by collagen tissue.
These changes cannot however, be labeled as very early changes since clinical contracture was also evident by twenty four weeks' time. It is likely that some other enzyme studies may be able to reveal some early changes even before the slightest evidence of clinical contracture.
No change was seen in elastic tissue content in any group. Possibly a change may take place only in the advanced stages of contracture which could not be demonstrated in these experiments even upto twenty four weeks' duration.
The similarity of changes seen in both medial recti are likely to be due to either (i) overacting contralateral synergist i.e. medial rectus of the other eye during fixation with affected eye (ii) due to the possible usage of a convergent position of the eyes in order to maintain binocularity because of the relatively small degree of esodeviation produced after the extirpation of lateral rectus.
| Conclusion|| |
No significant clinical contracture took place within twenty four weeks'. However, histochemically twenty four weeks specimens showed a statistically significant decrease in type II fibres by the Modified trichrome stain and a decrease in the lightly staining fibres (type II) by the Nitroblue tetrazolium stain for succinic dehydrogenase activity.
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6]