INTRASCLERAL NERVE LOOPS ALGERNON B. REESE, M.D. New York The long ciliary nerves accompany the long posterior ciliary arteries through their emissaries in the posterior part of the sclera, each nerve dividing into two branches before emerging into the suprachoroidal space. These four nerves course forward in a meridional direction between the sclera and the choroid. In some instances the ciliary nerve enters the sclera near the junction of the orbiculus ciliaris and the corona ciliaris, or 2.5 to 3 mm. from the angle of the an- terior chamber, then turns abruptly back again, to resume its forward course into the ciliary body. Occasionally the nerve loop thus formed extends through the entire thickness of the sclera, with its cupola projecting above the external surface, covered only by conjunctiva. This nerve loop may enter into the sclera perpendicular to or at an angle with the surface, or it may be retroverted or be anteflexed. Its apex is sometimes mushroom-shaped, due to a neuroma-like en- largement. At times chromatophores from the supracho- roidea appear, extending up into the interspace of the loop, and occasionally similar pigment cells, as well as smooth muscle from the ciliary body, are seen along the wall of the scleral foramen through which the loop passes. On rare oc- casions a cyst is seen accompanying a loop. The anterior ciliary artery, in its inward course, may share the emissary with the nerve loop, or the blood-vessel accompanying the loop may be an anastomotic branch between the episcleral and the ciliary vessels. Either the cupola or the stem of the loop may send off nerve branches which extend forward into the cornea. 148 .zz An intrascleral nerve loop as it appears clinically. REESE: Intrascleral Nerve Loops 149 Of the seven cases examined clinically by the writer, six .loops were in the horizontal plane on the nasal side of the globe, and one was in the vertical plane inferiorly. One pa- tient showed a loop in each eye nasally. However, these loops may appear temporally or superiorly, and Fritz claims that a common site is superiorly under the insertion of the superior rectus muscle. Reports on the frequency with which these loops appear in these various sites have been, for the most part, based on microscopic specimens, and, since practically all globes are sectioned in the horizontal plane, are misleading. E. Fuchs reported on 13 eyes ex- eamined microscopically in which the finding of the loops was incidental. In 11 of these eyes the loop extended entirely through the sclera and projected above the external scleral surface, therefore it could unquestionably have been seen clinically. Nine eyes showed neuroma-like enlargement of the cupola; 5 were accompanied by anterior ciliary arteries; 3 eyes showed loops in the posterior part of the sclera, near the entrance of the nerve through the emissary, and in 1 eye there were two loops. Fischer records 40 loops seen in mi- croscopic preparations. In 13 of these there was complete perforation of the sclera to a point beyond the external scleral surface, and 27 showed only partial perforation. Seven loops were accompanied by the anterior ciliary artery, and 1 was in the posterior part of the sclera, near the emissary of the nerve. One eye had 3 loops. Kyrieleis reported the growth of a tumor, superiorly at the site of a loop, in a patient, aged fourteen years. On microscopic examination the growth proved to be a neuroma, which Kyrieleis believed had originated in a nerve loop. This view is strengthened by the fact that fully one-half of the loops show neuroma- like enlargements at their apices. Axenfeld, who first de- scribed these loops from microscopic preparations, was later the first to report a case observed clinically. The patient complained of intermittent pain on movement of the lower 150 10REESE: Intrascleral Nerve Loops lid over the eyeball. Examination revealed a sharply cir- cumscribed and demarcated, grayish-white flat prominence, below in the vertical meridian, 3 mm. from the limbus, measuring 2.5 mm. in diameter. It was free of any signs of irritation or inflammation, and the conjunctiva moved freely over its surface. The temporal half of this mass joined the sclera, while the nasal end could be moved freely, and. lying under it was a dark emissary, through which the ad- herent temporal portion seemed to emerge. The mass was sensitive to the touch, and extreme pain was elicited by pulling the free nasal end. Excision showed it to be com- posed of nerve tissue, and resulted in hypesthesia of the cornea almost to the horizontal meridian. Kyrieleis also pro- duced hypesthesia by the excision of a loop. The embryology of the intrascleral nerve loop is in dispute. Axenfeld believed that it probably served as an anchorage in the sclera at the point where the nerve changes its meridional direction for a circular one. Groenouwwas of the opinion that the artery which often accompanies the loop coursed from within outward, and that this artery pulled the already formed nerve with it to a greater or lesser degree. The ob- jections to this theory are that the loop is usually not ac- companied by an artery, and that when it is, the artery is, in a majority of cases, unmistakably an anterior ciliary artery with a course from without inward. Fritz assumes the artery to be an anterior ciliary one, and claims that, as it courses inward through the sclera, it is growing in a direction opposite to the ciliary nerve, thereby serving to hinder the forward course of the nerve, and that, therefore, the nerve reacts by growing in loop formation around the obstacle. The objections to this explanation are that the nerve loop and anterior ciliary artery do not always share the same emis- sary, and that if the nerve looped to avoid an obstacle, it would probably do so along the course of less resistance, which would be in the more rarefied subchoroidal space a. .6 b /: ": ........ A nerve loop extending to the external scleral surface. a, The cupola of a retroverted nerve loop lying on the external scleral surface and covered only by conjunctiva. The scleral emissarv through which it ex- tended is somewhat dilated and ectatic, due to the fact that this was a glau- comatous eye. Some of the ciliary muscle is pushed into the foramen. b Cornea. c, Ciliary body. d, Iris with peripheral anterior synechiae. a, A nerve loop extending through the sclera just to the external surface. b, Cornea. c, Ciliary body. d, Iris. t 6 -:;,- :-S. T ---8 .1 ,.A h - - - ..---.-.M.--7- - - A nerve loop extending through the sclera to the external surface (Fischer). K, The cupola of the loop with a neuroma- like enlargement. S', Ascending stem of nerve. S, Descending stem of nerve. P Space between ciliary body and sclera. .. *: :: .: .: :: Section showing the long ciliary nerve throughout its entire course. a, The long ciliary nerve before entering the sclera posteriorly. ai, Coursing through its emissary in the sclera. aii, aiii, In the subehoroidal space. ai, Looping obtusely in the sclera before entering the ciliary body. b, Short ciliary nerves cut in cross-section.....S..-............... c,(-Optic.:.-:-.b:/..nerve.....:.c. REESE: Intrascleral Nerve Loops 151 or choroidal tissue instead of in the denser scleral tissue. Fischer studied human embryos in all stages of development, and concluded that the ciliary nerve reaches the region of the ciliary body before the sclera and uveal layer have be- come differentiated. This greater capacity for growth, and therefore greater length of the nerve, is compensated for by a loop or a fold brought about by a shifting of the sclera and the ciliary body in the act of development and differ- entiation. This explanation has much to recommend it. E. Fuchs reports that, from a study of human embryos, he does not believe that the correct explanation of these loops rests on a mechanical basis, but rather on an abnormal ten- dency to growth. The ciliary nerves grow more rapidly than the sclera, and their greater length is compensated for by their duplication or by folds in the sclera. He cites a similar abnormal growth of the optic nerve whereby aberrant bundles of the nerve grow blindly into the sheaths and are lost there. Also, similar abnormal growths of the optic chiasm are seen, in which a conical process composed of loops of aberrant nerve bundles extends outward from the anterior wall. Thus, opinion is divided between the theory that these intrascleral nerve loops are a normal anatomic variation and the belief that they represent an abnormal tendency to growth. There are several factors in favor of the latter theory: 1. About 65 per cent. show a neuroma-like enlargement of the cupola. 2. A neuroma has been reported as arising in all prob- ability from one of these loops. 3. A loop in an eye with a congenital coloboma of the iris has been reported. 4. Similar abnormal growths are occasionally seen in the optic nerve and chiasm. The clinical characteristics of an intrascleral nerve loop which serve to make the diagnosis are as follows: 152 REESE: Intrascleral Nerve Loops A grayish-white nodule from one to several millimeters in diameter. The cupola of the loop may just peep through the external surface of the sclera, in which case it will be visible practically flush with the scleral surface. All degrees, from this slight manifestation to several millimeters in ele- vation, may be seen. The loop may be flexed on itself, or it may show a mushroom-like shape due to enlargement of its cupola.