Sir William Read's Treatise of the Eyes.

Operative Akinesia. -The enormous influence of the extra-ocular muscles on the intra-ocular pressure demonstrates the necessity for adequate akinesia in all intra-ocular operations. When it is remembered that a relatively mild contraction of the orbicularis raises the intra-ocular pressure from 27 to 53 mm. Hg, the danger of loss of vitreous in a cataract extraction is obvious unless this muscle is thrown out of action. It follows that in all such operations the orbicularis should be paralysed, either by injection of the facial nerve as it crosses the ramus of the mandible or by a local injection around the orbit: the former method is the prettier, the latter the easier and more certain. Further, the action of looking down raises the pressure of the eye by the contraction of the recti, a rise which becomes quite marked if the action is forced. If every precaution is to be taken, a retro-bulbar injection of novocaine should be employed. This should be employed as a very dilute (0 25 or 05 per cent.) solution injected immediately before commencing the operation so that the muscles are not wholly paralysed but merely weakened, allowing the patient to look down but not to do so forcibly; or alternatively, a stitch should be inserted into the superior rectus so that the eye can be adequately controlled. Such a procedure incidentally infiltrates the ciliary ganglion thus rendering the inner eye completely anaesthetic, and results in a degree of immobility and control which has to be seen to be believed.