The anesthetic eye: an investigation of changes in the anterior ocular segment of the monkey caused by interrupting the trigeminal nerve at various levels along its course.

Abstract

Operations were performed at four different levels on the fifth nerve of the monkey to determine which procedure offers the best chance of avoiding ocular complications after surgical treatment of trigeminal neuralgia (Figure 18). (1) Section of the ophthalmic branch of N V results in immediate corneal anesthesia. After one week, chromatolysis of the unipolar gasserian ganglion cells subserving the first division occurs and Wallerian degeneration of the corneal nerves of the ipsilateral eye is seen. This is associated with perilimbal round cell invasion of the superficial cornea and subconjunctival area. In addition, iritis develops de novo or becomes worse if it pre-exists. Miosis occurs, but the chemodiagnostic tests of cocaine and adrenalin indicate an intact sympathetic system. The cause for this inflammatory reaction and pupillary change is unexplained by this study. The intraocular pressure is slightly lower on the side of the section than in the normal fellow control eye after surgery, but the difference is not statistically significant. (2) Section of the posterior sensory root of N V in the middle cranial fossa at a point between the gasserian glanglion and the tentorium results in similar ocular changes as is seen after interrupting the ophthalmic division alone. Wallerian degeneration of the corneal nerves, however, is not seen after seven, twelve or twenty-one days. (3) Transtentorial section of the trigeminal posterior sensory root performed in the middle cranial fossa, results in immediate corneal anesthesia. The gasserian ganglion cells, however, remain healthy and there is no perilimbal round cell invasion of the superficial cornea or subconjunctival tissue. Miosis occurs but the chemodiagnostic tests of cocaine and adrenalin indicate an intact sympathetic system. The intraocular pressure is only slightly lower on the side of section than in the control eye, but the difference is not statistically significant. (4) Suboccipital rhizotomy of the posterior sensory root of NV at the pons results in immediate corneal anesthesia. The gasserian ganglion cells remain healthy and there is no perilimbal round cell invasion of the superficial cornea or subconjunctival tissue. Miosis occurs in most animals (2 of 3) and is associated with an intact sympathetic system as indicated by the chemodiagnostic tests of cocaine and adrenalin. Intraocular pressure is very slightly lower on the side of section than in the control eye, but the difference is not statistically significant. (5) Thinning of the corneal epithelium occurs in an anesthetic eye regardless of the location of the section of N V and is not adversely affected by tarsorrhaphy. The corneal stroma, however, remains unchanged. (6) The experimental data demonstrate that to decrease ocular complications, operations on the trigeminal nerve should be performed on the caudal end of the sensory root as far from the gasserian ganglion as is techanically feasible.

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