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Correlation of Naturally Occurring Detachments with Long-Term Retinal Detachment in the Owl Monkey
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AMERICAN JOURNAL OF OPHTHALMOLOGY
distinct cell boundaries. The nuclei, always single, were round or slightly oval, showed only very slight variation in size and shape. One or two mitotic figures could be detected in a medium power field. The cells tended to arrange in an incompletely formed alveo lar pattern (Fig. 3). Histologie diagnosis was malignant pheochromocytoma originating in the organ of Zukerkandel, with involvement of bones, lymph glands, lungs, and liver. SUMMARY
A unique case of métastases to the orbit from malignant pheochromocytoma is pre sented. In this case, exophthalmus was the
APRIL, 1970
first presenting symptom of the orbital me tastasis, appearing 10 years after diagnosis of the disease. During the initial examina tion of the exophthalmus in this patient, it was noted that after massage of the eye there was a significant rise in blood pressure and pulse, a typical finding in pheochromo cytoma. REFERENCES
1. Albert, D. M., Rubinstein, R. A., and Scheie, H. G. : Metastasis to the eye. Am. J. Ophth. 63:723, 1967. 2. Duke-Elder, S.: Ophthalmology. London, Kimpton, 1966, vol. 9, p. 917. 3. Duke-Elder, S.: Textbook of Ophthalmology. London, Kimpton, 1952, vol. 5, p. 5617.
CORRELATION O F NATURALLY OCCURRING DETACHMENTS W I T H LONG-TERM R E T I N A L DETACHMENT I N T H E O W L MONKEY THOMAS M. AABERG, M.D.,
AND ROBERT MACHEMER,
M.D.
Miami, Florida
The clinical and histologie findings of short-term (up to 14 weeks) experimental retinal detachments in the owl monkey have been previously reported by Machemer and Norton,1 and Machemer.2 Long-term experi mental detachments, with the advantage of known duration, should further clarify the evolution of histologie change in eyes with retinal detachment. In addition, naturally oc curring retinal detachments in the owl mon key should be studied to evaluate the validity of the experimental model. Better compari sons can then be made with pathologic speci mens of human retinal detachments, the maFrom the Bascom Palmer Eye Institute, Depart ment of Ophthalmology, University of Miami School of Medicine, 1638 N.W. 10th Avenue Miami, Florida. This study was supported by USPHS Special Fellowship No. 2 F i l NB1972 VSN (Dr. Aaberg), and USPHS Research Grant No. 1 Ro 1 NB0840S-01 (Dr. Machemer), and in part by Fight for Sight, Inc., Grant-in-Aid No. G387, and the Florida Lions Eye Bank. Reprint requests to Thomas M. Aaberg, M.D., Marquette University Medical School, Department of Ophthalmology, 8700 West Wisconsin Avenue, Milwaukee, Wisconsin 53226.
jority of which are of long duration. This paper presents both a naturally occurring and experimentally produced long-term reti nal detachment in the owl monkey. A com parison of the clinical and histologie findings is presented with correlation to long-term human retinal detachments. METHODS
An adult owl monkey, noted upon arrival to have right leukocoria, was examined by slit lamp biomicroscopy (including Goldmann lens examination of the fundus) and indirect ophthalmoscopy. The eye was then enucleated and was fixed in a modified Kolmer fixative, as previously described by Machemer.2 Vertical serial sections of 5micron thickness were made and stained with hematoxylin-eosin and PAS. Represen tative sections, and a control specimen, were stained with a modified Mallory iron stain. Experimental retinal detachments were produced as previously described by Mach emer and Norton. 1 One unit of hyaluronidase was injected into the vitreous and
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under direct visual control the vitreous was repeatedly aspirated and finally reinjected against the temporal equatorial retina, pro ducing a retinal hole with surrounding de tachment. Two eyes were enucleated at 10 and 13 months, respectively, following cre ation of the retinal detachment. During the period prior to enucleation, the animals were periodically examined by indirect uphthalmoscopy. The eyes were fixed and sectioned as stated above. The sections were stained with hematoxylin-eosin and PAS. RESULTS IN NATURALLY OCCURRING RETINAL DETACHMENT
Clinical picture—Slit lamp examination of the anterior segment, with the exception of the lens, was unremarkable. There was no indication of a perforating wound. The lens consisted of a thin, avascular, veil-like mem brane, translucent except for a central, white opaque area protruding anteriorly. Study of the vitreous structure was precluded by the lens membrane, although no definite vitreous strands were present. Indirect ophthalmoscopy revealed a 360° dialysis, with a total ret inal detachment. The retina was draped over the disk and folded upon itself with the pe ripheral torn edges rolled inwardly. Except for a few areas of residual torn retinal tags, the retina had been disinserted at the ora and was freely movable in the vitreous with its only attachment at the disk. The retina ap peared very thin and it was impossible to un fold it with positioning the animal. A cyst like portion of tissue, which looked like ret ina, floated freely in the vitreous indepen dent of the main retinal tissue. Large, heavily pigmented, sharply demar cated areas were present inferiorly in the pigment epithelial layer. Superiorly, the pig mentary changes were finer and fewer in number. No direct pupillary light response was present. Applanation tension was 8 mm Hg. Histology—Intensive inspection of the gross specimen revealed no site of ocular
641
perforation. Microscopically, the cornea was normal. Proteinacious material filled the an terior chamber. The angle was open. The lens was a flat membrane consisting of intact anterior and posterior lens capsule surround ing proliferative metaplastic epithelial cells and remaining lens material. A connective tissue membrane with clusters of heavily pigmented cells extended across the diame ter of the eye behind the lens. The only fibrillar vitreous present was over the pars plana and in the immediate retrolental area. The retina was totally detached and heavily folded in a funnel-shaped configuration (Fig. 1). In general, the retina tore at the ora (Fig. 2 ) . The ganglion cell layer was generally intact (Fig. 3), although it had areas of discontinuity and an increased num ber of glial cells. Cystoid spaces were located in the outer plexiform layer (Fig. 4) with extension into the outer and inner nuclear layers. The outer nuclear layers showed the greatest degree of abnormality. Considerable variability existed in the width of this layer (Fig. 3). Pyknotic nuclei were present in most microscopic fields. The receptor outer segments were gone and only a few areas of intact inner segments remained. Macro phages were present in both segment layers (Fig. 3). In the periphery, at the retinal tear, the outer retinal layers were inverted by a nonvascular, flat cellular membrane (Fig. 5). This membrane was in connection with the edge of the tear and extended over the inter nal limiting membrane, frequently causing areas of puckering (Figs. 5 and 6). A proliferative mass starting from the pigmented epithelium of the pars plana at the ora had formed where the nonpigmented epithelium had detached from the underlying pigmented epithelium. A membrane extended inward from the edge of the detached pars plana nonpigmented epithelium (Fig. 2). This avascular membrane contained both pigmented and nonpigmented cells in conti nuity with the proliferating cells at the ora. Iron stain preparations of the pigmented
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'4\\ Fig. 1 (Aaberg and Machemer). Naturally occurring detachment: free-floating detached retina. Note convolutions and fixed folds (PAS, Xl6). cells, utilizing a modified Mallory iron stain, were negative. The free-floating cyst was comprised of viable retinal tissue. Some layers were easily recognizable and exhibited most of the above-mentioned histologie changes of longterm detachment (Fig. 7-A). Cystoid change was slightly more pronounced, extending even into the gliotic ganglion cell layer. In some areas, inner and outer nuclear layers were recognizable. Cellular membranes, present on both the inner and outer surfaces, joined the ends of the avulsed retina, thus creating the cyst. Nonadherence of the two membranes gave the appearance of a pseudocyst within the wall of the actual cyst (Fig. 7-B). The pigment epithelium was primarily a layer of flattened cells, occasionally unpigmented, with scattered areas of highly protu berant, densely pigmented cells. All the pig ment epithelial cells were negative by iron
stain. Adjacent to these cells were broad, flat, densely pigmented cells with many nu clei (Fig. 8 ) . All types of these cells, with the exception of the extremely flat ones, had an internal more homogenous part, which consisted of apical processes. LONG-TERM EXPERIMENTAL DETACHMENTS
Clinical picture—Slit lamp examination of the two eyes with experimental retinal de tachments created 10 and 13 months pre viously, revealed normal anterior segments. Minimal vitreous condensation was present. The only vitreous fibrillar structure was in the immediate retrolental space. Both eyes were noted to have 360° tears with the retinas folded inferiorly over the disks. The retinal surface in one case was smooth with the peripheral edge rolled inwardly. In the other eye, the entire retina was irregularly folded with the peripheral edge drawn sharply inward.
RETINAL DETACHMENT
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Fig. 2 (Aaberg and Machemer). Naturally occurring detachment: Retina disinserted at the ora. Reactive proliferation starting from the pigmented epithelium of the pars plana with strand formation (PAS, X64). Histology—The majority of significant histologie findings were similar to those de scribed above in the naturally occurring de tachment. The ganglion cell layer was dis continuous, although long intervals of normal appearing nuclei were present. An increased amount of glial tissue was present in this layer. The inner nuclear layer looked rela tively well preserved. Large cystoid spaces were present in the outer plexiform and nu clear layers. In areas, small cystoid spaces were confined entirely to the outer nuclear layer. The receptor layer was atrophie. The outer segments, shortened and of varying width, were greatly reduced in number with interspersed macrophages. Scattered areas of remaining inner segments appeared short and thickened (Fig. 9). An interrupted nonvascular membrane was present on the inner retinal surface. This was primarily a single-layered mem
brane, consisting partly of flattened cells and occasionally of cells similar in appearance to pigment epithelium with a homogeneous inner part (Fig. 10). Proliferation of cells of the pigmented layer of the pars plana was present on both sides of the globe when the unpigmented cells were detached. The only remaining vit reous structure consisted of a single fibrillar layer, corresponding to the anterior hyaloid membrane, which extended into the vitreous cavity from the ora serrata. The pigment epithelium showed both pro tuberant cells and larger flattened cells. A homogenous inner part was always present regardless of morphologic changes of the cellular components. DISCUSSION
The technique for producing retinal de tachment in the owl monkey, as described by
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Fig. 3 (Aaberg and Machemer). Naturally occurring detachment: Relatively intact retinal structure. Reduction of cell number in photoreceptor layer (PAS, χ!60). Machemer and Norton, 1 has provided an ex perimental model which is thought to be sim ilar in appearance and behaviour to that of human retinal detachments. The histologie correlation of experimental with naturally
occurring detachments in the owl monkey and human detachments previously undemonstrated, is therefore necessary to increase the validity of inferences made to clinical situations.
Fig. 4 (Aaberg and Machemer). Naturally occurring detachment: Cystoid spaces affecting outer plexiform and outer nuclear layer (PAS, X160).
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Fig. S (Aaberg and Machemer). Naturally ocurring detachment: Retinal tear folded over by preretinal proliferation in connection with the edge of the tear (arrow), causing puckering of internal retinal surface (PAS, X64).
Retinal detachment has been documented by Roberts 3 to occur naturally in dogs, cats, horses, swine, cattle and other mammals, and birds. Recently heredo-familial rhegmatogenous retinal detachments have been reported in the collie by Freeman and associates.4 No report, however, of naturally occurring ret inal detachment in lower primates was found in the literature. The owl monkey observed with a natur ally occurring detachment had not been sub jected to any artifactual techniques, presum ably sustaining a traumatic detachment with out apparent ocular perforation. The retinal detachment was of long duration, as evi denced by the lens changes, the great varia bility in pigment epithelial structure and the retinal changes. The histologie findings are similar to those described by Machemer2 in retinal detachments of 12 to 14 weeks' dura tion and with the long-term experimental de tachments described in this paper. Both types of long-term owl monkey reti
nal detachments, the naturally occurring and the experimental, show a continuation in the spectrum of histologie change occurring in the detached retina. Following resolution of early transient generalized edema, the inner layers continue to be rather well preserved. The location of cystoid formation moves in creasingly toward the outer layers as the age of the detachment increases. A new state of equilibrium is attained, maintaining the in tegrity of the inner layer. The posterior lay ers, void of a capillary network and sepa rated from nourishment through the pigment epithelium, do not reach such an equilibrium. Generalized atrophy of the detached retina is greatest in the retinal layers where cystoid formation is pronounced, i.e., the outer lay ers. As the duration of detachment increases, the cystoid change shifts toward the outer layers. Concomitantly, a change in the size of the cystoid spaces occurs, enlarging often to form huge cavities before eventually de creasing in size as glial tissue begins to accu-
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Fig. 6 (Aaberg and Machemer). Naturally occurring detachment: Another area of preretinal pro liferation with puckering of internal retinal layers (PAS, X400).
mulate. As mentioned previously by Mache mer,2 the atrophy and cystoid formation are most likely expressions of metabolic abnor malities. Mechanical destruction of sur rounding structures by the increasing cyst size may be a contributing factor to retinal atrophy. The retinal atrophy is a slow con tinuous process, beginning with scattered
pyknotic nuclei in the outer nuclear layer. Generalized atrophy is barely recognizable until the detachment is of considerable dura tion. The free-floating retinal cyst, present in the naturally occurring detachment, is some what in discord with this formulation. De void of all vascular supply, there is an aston-
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647
O
Fig. 7 (Aaberg and Machemer). Naturally occurring detachment: Intravitreal floating cyst. (A) Cyst wall consists of fairly well preserved retina; ganglion cells gone; cystoid space formation present with remnants of inner (i) nuclear and outer (o) nuclear layers best preserved (PAS, Xl60). (B) Another section with more extensive degeneration and membrane formation (PAS, X64).
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Fig. 8 (Aaberg and Machemer). Naturally occurring detachment: Pigment epithelium with broad flat multinucleated cells and highly protuberant cells. Typical for pigment epithelium in retinal detachment is the homogeneous part of the cell (arrow) consisting of apical processes (PAS, X400). ishing preservation of structure. Although the ganglion cell layer is absent, as would be expected after complete severance of the nerve fiber layer, the inner nuclear layer is preserved well enough to be a recognizable structure. In many areas the outer nuclear layer is also well preserved. It would there fore appear that retinal tissue can survive for a considerable period of time without
blood supply. A discrepancy does exist with the recent histologie description by Kroll5 of experimental central retinal artery occlusion. In the latter study, necrosis of all inner reti nal layers occurred after 16 hours with eventual destruction of even the Müller cells. An explanation for the variance of these findings is not possible at this time. The duration of retinal detachment seems
Fig. 9 (Aaberg and Machemer). Experimental detachment, 13 months: Cystoid spaces of the outer plexiform layer affecting the inner and outer nuclear layers. Compare with Figure 4 (PAS, X400).
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Fig. 10 (Aaberg and Machemer). Experimental detachment, 13 months: Preretinal cells simulating pigment epithelial cells. Note homogeneous part of cells (arrow) and compare with Figure 8 (PAS X400).
to be poorly correlated with the presence, or extent, of preretinal membranes. This is ap parent from the differing extent of mem brane formation in the two long-term exper imental detachments. Furthermore, the cellu lar morphology has great variation. In some areas the cells resemble fibrocytes, while in others they resemble even pigment epithe lium (Fig. 10). The origin of these prereti nal cells is uncertain at present. Prolifera tion originating at the retina wound suggests retinal origin, whereas pigment epithelium like cells raise the possibility of an origin in the pigment epithelium. It is impressive that the pigment epithe lium, although separated from its contiguous neuroepithelial structures, does not signifi cantly atrophy for a long time. On the con trary, the layers show morphologic evidence of activity. Some individual protuberant cells become binucleated. Adjacent cells appear to hypertrophy in the plane of the original layer, not inward toward the detached retina, and become multinucleated. Even the apical processes persist as identifiable structures. The histologie appearance of the naturally occurring and long-term experimental owl monkey detachments bear a strong resem blance to that seen in the long-term human
retinal detachment. In the past, when only short-term experimental detachments were present, it was unclear as to whether a difference in cystoid space location existed between the human and experimental detach ments. In long-term human detachment, the cystoid spaces are seen in the outer plexiform layer, whereas in the short-term exper imental detachments they were found in the inner nuclear layer. The present long-term experimental detachments show there is no difference—it is merely a question of dura tion as to where the cystoid spaces are lo cated. As the human detachment increases in age, the cystoid spaces tend to decrease to gether with a clinical appearance of a thinned retina. A corresponding histologie appearance of an atrophie inner and outer nuclear layer develops. Preretinal membrane formation is almost universally present, al though quite variable. Pigment epithelium shows changes very similar to that described in the owl monkey. There are areas of indi vidual protuberant cells together with mul tinucleated, flattened cells. It therefore appears that the histologie and clinical appearance of experimental reti nal detachment in the owl monkey does not differ from detachments occurring naturally
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in the same species. It can furthermore be stated that both the naturally occuring and the long-term experimentally produced reti nal detachment in the owl monkey have his tologie appearances which are not signifi cantly different from long-term human reti nal detachment.
tachments, is presented as evidence for the validity of the experimental model.
SUMMARY
1. Machemer, R., and Norton, E. W. D. : Experi mental retinal detachment in the owl monkey. I. Methods of production and clinical picture. Am. J. Ophth. 66:388, 1968. 2. Machemer, R.: Experimental retinal detach ment in the owl monkey. II. Histology of retina and pigment epithelium. Am. J. Ophth. 66:396, 1968. 3. Roberts, S. R. : Detachment of the retina in animals. J. Am. Vet. Med. Ass. 135:423, 1959. 4. Freeman, H. M., Donovan, R. H., and Schepens, C. L. : Retinal Detachment, chorioretinal changes, and staphyloma in the collie. Arch. Ophth. 76 :412, 1966. 5. Kroll, A. J. : Experimental central retinal ar tery occlusion. Arch. Ophth. 79 :453, 1968.
The retina of a long-term naturally oc curring retinal detachment in an owl monkey shows cystoid degeneration of the outer plexiform layer with accompanying degeneration of the outer and inner nuclear layers. Pig ment epithelial cells often appear flat and multinucleated. Preretinal and intravitreal cellular proliferation is common. The excel lent agreement between the naturally occur ring and experimental states, in addition to close correlation with long-term human de
ACKNOWLEDGMENTS
We thank Mrs. M. Halley for her assistance during the operative procedures and in the prepara tion of histologie sections. REFERENCES
EFFECT O F COMPLEXED SYNTHETIC RNA ANALOGUES ON H E R P E S SIMPLEX VIRUS INFECTION IN RABBIT CORNEA RALPH POLLIKOFF, P H . D . , PATRICIA CANNAVALE, B . S C , PAUL DIXON, B . S C , AND ANTHONY D I P U P P O , B . S C .
Philadelphia, Pennsylvania
in 1967, Field, Tytell, Lampson, and Hilleman1 demonstrated in mice that the an tiviral efficacy of complexed polyribonucleotides—notably that derived from polycytidylic (PC) and polyinosinic ( P I ) acids— was based on induction of inter feron ( I T F ) . These results provided a promising approach to therapy of virus infection. Since our own studies on rabbit corneas concerning the effect of induction of I T F by endotoxin on herpetic keratitis 2 and a similar effect by From the Wills Eye Hospital and Research Insti tute, Philadelphia, Pennsylvania. This investigation was supported in part by USPHS Research Grant NB-AI 07013, from the National Institute of Neu rological Diseases and Blindness. The study was also aided by a grant from the National Society for the Prevention of Blindness, Inc. Reprint requests to Ralph Pollikoff, Ph.D., Wills Eye Hospital, 1601 Spring Garden Street, Philadelphia, Pennsylvania 19130.
statolon on vesicular stomatitis virus (VSV) keratitis were also promising,3'4 it was thought that treatment with the complexed polyribonucleotide ( P C : P I ) , another inducer of I T F formation, would also be a most likely method of therapy of virus ker atitis in the rabbit eye. An initial study by Pollikoff, DiPuppo, and Cannavale4 showed that the complexed copolymer was highly effective in topical treatment of rabbit cor nea infected with VSV. In addition, the re sults of Park and Baron 5 have also indi cated that there was great promise in ther apy of herpetic keratitis by this method. In the present report, data are presented which extend preliminary reported observa tions and records in full the efficacy of the copolymer alone and in combined therapy with dexamethasone or idoxuridine in rabbit eyes infected with herpes simplex virus.3·6
AMERICAN JOURNAL OF OPHTHALMOLOGY
distinct cell boundaries. The nuclei, always single, were round or slightly oval, showed only very slight variation in size and shape. One or two mitotic figures could be detected in a medium power field. The cells tended to arrange in an incompletely formed alveo lar pattern (Fig. 3). Histologie diagnosis was malignant pheochromocytoma originating in the organ of Zukerkandel, with involvement of bones, lymph glands, lungs, and liver. SUMMARY
A unique case of métastases to the orbit from malignant pheochromocytoma is pre sented. In this case, exophthalmus was the
APRIL, 1970
first presenting symptom of the orbital me tastasis, appearing 10 years after diagnosis of the disease. During the initial examina tion of the exophthalmus in this patient, it was noted that after massage of the eye there was a significant rise in blood pressure and pulse, a typical finding in pheochromo cytoma. REFERENCES
1. Albert, D. M., Rubinstein, R. A., and Scheie, H. G. : Metastasis to the eye. Am. J. Ophth. 63:723, 1967. 2. Duke-Elder, S.: Ophthalmology. London, Kimpton, 1966, vol. 9, p. 917. 3. Duke-Elder, S.: Textbook of Ophthalmology. London, Kimpton, 1952, vol. 5, p. 5617.
CORRELATION O F NATURALLY OCCURRING DETACHMENTS W I T H LONG-TERM R E T I N A L DETACHMENT I N T H E O W L MONKEY THOMAS M. AABERG, M.D.,
AND ROBERT MACHEMER,
M.D.
Miami, Florida
The clinical and histologie findings of short-term (up to 14 weeks) experimental retinal detachments in the owl monkey have been previously reported by Machemer and Norton,1 and Machemer.2 Long-term experi mental detachments, with the advantage of known duration, should further clarify the evolution of histologie change in eyes with retinal detachment. In addition, naturally oc curring retinal detachments in the owl mon key should be studied to evaluate the validity of the experimental model. Better compari sons can then be made with pathologic speci mens of human retinal detachments, the maFrom the Bascom Palmer Eye Institute, Depart ment of Ophthalmology, University of Miami School of Medicine, 1638 N.W. 10th Avenue Miami, Florida. This study was supported by USPHS Special Fellowship No. 2 F i l NB1972 VSN (Dr. Aaberg), and USPHS Research Grant No. 1 Ro 1 NB0840S-01 (Dr. Machemer), and in part by Fight for Sight, Inc., Grant-in-Aid No. G387, and the Florida Lions Eye Bank. Reprint requests to Thomas M. Aaberg, M.D., Marquette University Medical School, Department of Ophthalmology, 8700 West Wisconsin Avenue, Milwaukee, Wisconsin 53226.
jority of which are of long duration. This paper presents both a naturally occurring and experimentally produced long-term reti nal detachment in the owl monkey. A com parison of the clinical and histologie findings is presented with correlation to long-term human retinal detachments. METHODS
An adult owl monkey, noted upon arrival to have right leukocoria, was examined by slit lamp biomicroscopy (including Goldmann lens examination of the fundus) and indirect ophthalmoscopy. The eye was then enucleated and was fixed in a modified Kolmer fixative, as previously described by Machemer.2 Vertical serial sections of 5micron thickness were made and stained with hematoxylin-eosin and PAS. Represen tative sections, and a control specimen, were stained with a modified Mallory iron stain. Experimental retinal detachments were produced as previously described by Mach emer and Norton. 1 One unit of hyaluronidase was injected into the vitreous and
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under direct visual control the vitreous was repeatedly aspirated and finally reinjected against the temporal equatorial retina, pro ducing a retinal hole with surrounding de tachment. Two eyes were enucleated at 10 and 13 months, respectively, following cre ation of the retinal detachment. During the period prior to enucleation, the animals were periodically examined by indirect uphthalmoscopy. The eyes were fixed and sectioned as stated above. The sections were stained with hematoxylin-eosin and PAS. RESULTS IN NATURALLY OCCURRING RETINAL DETACHMENT
Clinical picture—Slit lamp examination of the anterior segment, with the exception of the lens, was unremarkable. There was no indication of a perforating wound. The lens consisted of a thin, avascular, veil-like mem brane, translucent except for a central, white opaque area protruding anteriorly. Study of the vitreous structure was precluded by the lens membrane, although no definite vitreous strands were present. Indirect ophthalmoscopy revealed a 360° dialysis, with a total ret inal detachment. The retina was draped over the disk and folded upon itself with the pe ripheral torn edges rolled inwardly. Except for a few areas of residual torn retinal tags, the retina had been disinserted at the ora and was freely movable in the vitreous with its only attachment at the disk. The retina ap peared very thin and it was impossible to un fold it with positioning the animal. A cyst like portion of tissue, which looked like ret ina, floated freely in the vitreous indepen dent of the main retinal tissue. Large, heavily pigmented, sharply demar cated areas were present inferiorly in the pigment epithelial layer. Superiorly, the pig mentary changes were finer and fewer in number. No direct pupillary light response was present. Applanation tension was 8 mm Hg. Histology—Intensive inspection of the gross specimen revealed no site of ocular
641
perforation. Microscopically, the cornea was normal. Proteinacious material filled the an terior chamber. The angle was open. The lens was a flat membrane consisting of intact anterior and posterior lens capsule surround ing proliferative metaplastic epithelial cells and remaining lens material. A connective tissue membrane with clusters of heavily pigmented cells extended across the diame ter of the eye behind the lens. The only fibrillar vitreous present was over the pars plana and in the immediate retrolental area. The retina was totally detached and heavily folded in a funnel-shaped configuration (Fig. 1). In general, the retina tore at the ora (Fig. 2 ) . The ganglion cell layer was generally intact (Fig. 3), although it had areas of discontinuity and an increased num ber of glial cells. Cystoid spaces were located in the outer plexiform layer (Fig. 4) with extension into the outer and inner nuclear layers. The outer nuclear layers showed the greatest degree of abnormality. Considerable variability existed in the width of this layer (Fig. 3). Pyknotic nuclei were present in most microscopic fields. The receptor outer segments were gone and only a few areas of intact inner segments remained. Macro phages were present in both segment layers (Fig. 3). In the periphery, at the retinal tear, the outer retinal layers were inverted by a nonvascular, flat cellular membrane (Fig. 5). This membrane was in connection with the edge of the tear and extended over the inter nal limiting membrane, frequently causing areas of puckering (Figs. 5 and 6). A proliferative mass starting from the pigmented epithelium of the pars plana at the ora had formed where the nonpigmented epithelium had detached from the underlying pigmented epithelium. A membrane extended inward from the edge of the detached pars plana nonpigmented epithelium (Fig. 2). This avascular membrane contained both pigmented and nonpigmented cells in conti nuity with the proliferating cells at the ora. Iron stain preparations of the pigmented
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'4\\ Fig. 1 (Aaberg and Machemer). Naturally occurring detachment: free-floating detached retina. Note convolutions and fixed folds (PAS, Xl6). cells, utilizing a modified Mallory iron stain, were negative. The free-floating cyst was comprised of viable retinal tissue. Some layers were easily recognizable and exhibited most of the above-mentioned histologie changes of longterm detachment (Fig. 7-A). Cystoid change was slightly more pronounced, extending even into the gliotic ganglion cell layer. In some areas, inner and outer nuclear layers were recognizable. Cellular membranes, present on both the inner and outer surfaces, joined the ends of the avulsed retina, thus creating the cyst. Nonadherence of the two membranes gave the appearance of a pseudocyst within the wall of the actual cyst (Fig. 7-B). The pigment epithelium was primarily a layer of flattened cells, occasionally unpigmented, with scattered areas of highly protu berant, densely pigmented cells. All the pig ment epithelial cells were negative by iron
stain. Adjacent to these cells were broad, flat, densely pigmented cells with many nu clei (Fig. 8 ) . All types of these cells, with the exception of the extremely flat ones, had an internal more homogenous part, which consisted of apical processes. LONG-TERM EXPERIMENTAL DETACHMENTS
Clinical picture—Slit lamp examination of the two eyes with experimental retinal de tachments created 10 and 13 months pre viously, revealed normal anterior segments. Minimal vitreous condensation was present. The only vitreous fibrillar structure was in the immediate retrolental space. Both eyes were noted to have 360° tears with the retinas folded inferiorly over the disks. The retinal surface in one case was smooth with the peripheral edge rolled inwardly. In the other eye, the entire retina was irregularly folded with the peripheral edge drawn sharply inward.
RETINAL DETACHMENT
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Fig. 2 (Aaberg and Machemer). Naturally occurring detachment: Retina disinserted at the ora. Reactive proliferation starting from the pigmented epithelium of the pars plana with strand formation (PAS, X64). Histology—The majority of significant histologie findings were similar to those de scribed above in the naturally occurring de tachment. The ganglion cell layer was dis continuous, although long intervals of normal appearing nuclei were present. An increased amount of glial tissue was present in this layer. The inner nuclear layer looked rela tively well preserved. Large cystoid spaces were present in the outer plexiform and nu clear layers. In areas, small cystoid spaces were confined entirely to the outer nuclear layer. The receptor layer was atrophie. The outer segments, shortened and of varying width, were greatly reduced in number with interspersed macrophages. Scattered areas of remaining inner segments appeared short and thickened (Fig. 9). An interrupted nonvascular membrane was present on the inner retinal surface. This was primarily a single-layered mem
brane, consisting partly of flattened cells and occasionally of cells similar in appearance to pigment epithelium with a homogeneous inner part (Fig. 10). Proliferation of cells of the pigmented layer of the pars plana was present on both sides of the globe when the unpigmented cells were detached. The only remaining vit reous structure consisted of a single fibrillar layer, corresponding to the anterior hyaloid membrane, which extended into the vitreous cavity from the ora serrata. The pigment epithelium showed both pro tuberant cells and larger flattened cells. A homogenous inner part was always present regardless of morphologic changes of the cellular components. DISCUSSION
The technique for producing retinal de tachment in the owl monkey, as described by
644
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Fig. 3 (Aaberg and Machemer). Naturally occurring detachment: Relatively intact retinal structure. Reduction of cell number in photoreceptor layer (PAS, χ!60). Machemer and Norton, 1 has provided an ex perimental model which is thought to be sim ilar in appearance and behaviour to that of human retinal detachments. The histologie correlation of experimental with naturally
occurring detachments in the owl monkey and human detachments previously undemonstrated, is therefore necessary to increase the validity of inferences made to clinical situations.
Fig. 4 (Aaberg and Machemer). Naturally occurring detachment: Cystoid spaces affecting outer plexiform and outer nuclear layer (PAS, X160).
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Fig. S (Aaberg and Machemer). Naturally ocurring detachment: Retinal tear folded over by preretinal proliferation in connection with the edge of the tear (arrow), causing puckering of internal retinal surface (PAS, X64).
Retinal detachment has been documented by Roberts 3 to occur naturally in dogs, cats, horses, swine, cattle and other mammals, and birds. Recently heredo-familial rhegmatogenous retinal detachments have been reported in the collie by Freeman and associates.4 No report, however, of naturally occurring ret inal detachment in lower primates was found in the literature. The owl monkey observed with a natur ally occurring detachment had not been sub jected to any artifactual techniques, presum ably sustaining a traumatic detachment with out apparent ocular perforation. The retinal detachment was of long duration, as evi denced by the lens changes, the great varia bility in pigment epithelial structure and the retinal changes. The histologie findings are similar to those described by Machemer2 in retinal detachments of 12 to 14 weeks' dura tion and with the long-term experimental de tachments described in this paper. Both types of long-term owl monkey reti
nal detachments, the naturally occurring and the experimental, show a continuation in the spectrum of histologie change occurring in the detached retina. Following resolution of early transient generalized edema, the inner layers continue to be rather well preserved. The location of cystoid formation moves in creasingly toward the outer layers as the age of the detachment increases. A new state of equilibrium is attained, maintaining the in tegrity of the inner layer. The posterior lay ers, void of a capillary network and sepa rated from nourishment through the pigment epithelium, do not reach such an equilibrium. Generalized atrophy of the detached retina is greatest in the retinal layers where cystoid formation is pronounced, i.e., the outer lay ers. As the duration of detachment increases, the cystoid change shifts toward the outer layers. Concomitantly, a change in the size of the cystoid spaces occurs, enlarging often to form huge cavities before eventually de creasing in size as glial tissue begins to accu-
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Fig. 6 (Aaberg and Machemer). Naturally occurring detachment: Another area of preretinal pro liferation with puckering of internal retinal layers (PAS, X400).
mulate. As mentioned previously by Mache mer,2 the atrophy and cystoid formation are most likely expressions of metabolic abnor malities. Mechanical destruction of sur rounding structures by the increasing cyst size may be a contributing factor to retinal atrophy. The retinal atrophy is a slow con tinuous process, beginning with scattered
pyknotic nuclei in the outer nuclear layer. Generalized atrophy is barely recognizable until the detachment is of considerable dura tion. The free-floating retinal cyst, present in the naturally occurring detachment, is some what in discord with this formulation. De void of all vascular supply, there is an aston-
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Fig. 7 (Aaberg and Machemer). Naturally occurring detachment: Intravitreal floating cyst. (A) Cyst wall consists of fairly well preserved retina; ganglion cells gone; cystoid space formation present with remnants of inner (i) nuclear and outer (o) nuclear layers best preserved (PAS, Xl60). (B) Another section with more extensive degeneration and membrane formation (PAS, X64).
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Fig. 8 (Aaberg and Machemer). Naturally occurring detachment: Pigment epithelium with broad flat multinucleated cells and highly protuberant cells. Typical for pigment epithelium in retinal detachment is the homogeneous part of the cell (arrow) consisting of apical processes (PAS, X400). ishing preservation of structure. Although the ganglion cell layer is absent, as would be expected after complete severance of the nerve fiber layer, the inner nuclear layer is preserved well enough to be a recognizable structure. In many areas the outer nuclear layer is also well preserved. It would there fore appear that retinal tissue can survive for a considerable period of time without
blood supply. A discrepancy does exist with the recent histologie description by Kroll5 of experimental central retinal artery occlusion. In the latter study, necrosis of all inner reti nal layers occurred after 16 hours with eventual destruction of even the Müller cells. An explanation for the variance of these findings is not possible at this time. The duration of retinal detachment seems
Fig. 9 (Aaberg and Machemer). Experimental detachment, 13 months: Cystoid spaces of the outer plexiform layer affecting the inner and outer nuclear layers. Compare with Figure 4 (PAS, X400).
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Fig. 10 (Aaberg and Machemer). Experimental detachment, 13 months: Preretinal cells simulating pigment epithelial cells. Note homogeneous part of cells (arrow) and compare with Figure 8 (PAS X400).
to be poorly correlated with the presence, or extent, of preretinal membranes. This is ap parent from the differing extent of mem brane formation in the two long-term exper imental detachments. Furthermore, the cellu lar morphology has great variation. In some areas the cells resemble fibrocytes, while in others they resemble even pigment epithe lium (Fig. 10). The origin of these prereti nal cells is uncertain at present. Prolifera tion originating at the retina wound suggests retinal origin, whereas pigment epithelium like cells raise the possibility of an origin in the pigment epithelium. It is impressive that the pigment epithe lium, although separated from its contiguous neuroepithelial structures, does not signifi cantly atrophy for a long time. On the con trary, the layers show morphologic evidence of activity. Some individual protuberant cells become binucleated. Adjacent cells appear to hypertrophy in the plane of the original layer, not inward toward the detached retina, and become multinucleated. Even the apical processes persist as identifiable structures. The histologie appearance of the naturally occurring and long-term experimental owl monkey detachments bear a strong resem blance to that seen in the long-term human
retinal detachment. In the past, when only short-term experimental detachments were present, it was unclear as to whether a difference in cystoid space location existed between the human and experimental detach ments. In long-term human detachment, the cystoid spaces are seen in the outer plexiform layer, whereas in the short-term exper imental detachments they were found in the inner nuclear layer. The present long-term experimental detachments show there is no difference—it is merely a question of dura tion as to where the cystoid spaces are lo cated. As the human detachment increases in age, the cystoid spaces tend to decrease to gether with a clinical appearance of a thinned retina. A corresponding histologie appearance of an atrophie inner and outer nuclear layer develops. Preretinal membrane formation is almost universally present, al though quite variable. Pigment epithelium shows changes very similar to that described in the owl monkey. There are areas of indi vidual protuberant cells together with mul tinucleated, flattened cells. It therefore appears that the histologie and clinical appearance of experimental reti nal detachment in the owl monkey does not differ from detachments occurring naturally
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in the same species. It can furthermore be stated that both the naturally occuring and the long-term experimentally produced reti nal detachment in the owl monkey have his tologie appearances which are not signifi cantly different from long-term human reti nal detachment.
tachments, is presented as evidence for the validity of the experimental model.
SUMMARY
1. Machemer, R., and Norton, E. W. D. : Experi mental retinal detachment in the owl monkey. I. Methods of production and clinical picture. Am. J. Ophth. 66:388, 1968. 2. Machemer, R.: Experimental retinal detach ment in the owl monkey. II. Histology of retina and pigment epithelium. Am. J. Ophth. 66:396, 1968. 3. Roberts, S. R. : Detachment of the retina in animals. J. Am. Vet. Med. Ass. 135:423, 1959. 4. Freeman, H. M., Donovan, R. H., and Schepens, C. L. : Retinal Detachment, chorioretinal changes, and staphyloma in the collie. Arch. Ophth. 76 :412, 1966. 5. Kroll, A. J. : Experimental central retinal ar tery occlusion. Arch. Ophth. 79 :453, 1968.
The retina of a long-term naturally oc curring retinal detachment in an owl monkey shows cystoid degeneration of the outer plexiform layer with accompanying degeneration of the outer and inner nuclear layers. Pig ment epithelial cells often appear flat and multinucleated. Preretinal and intravitreal cellular proliferation is common. The excel lent agreement between the naturally occur ring and experimental states, in addition to close correlation with long-term human de
ACKNOWLEDGMENTS
We thank Mrs. M. Halley for her assistance during the operative procedures and in the prepara tion of histologie sections. REFERENCES
EFFECT O F COMPLEXED SYNTHETIC RNA ANALOGUES ON H E R P E S SIMPLEX VIRUS INFECTION IN RABBIT CORNEA RALPH POLLIKOFF, P H . D . , PATRICIA CANNAVALE, B . S C , PAUL DIXON, B . S C , AND ANTHONY D I P U P P O , B . S C .
Philadelphia, Pennsylvania
in 1967, Field, Tytell, Lampson, and Hilleman1 demonstrated in mice that the an tiviral efficacy of complexed polyribonucleotides—notably that derived from polycytidylic (PC) and polyinosinic ( P I ) acids— was based on induction of inter feron ( I T F ) . These results provided a promising approach to therapy of virus infection. Since our own studies on rabbit corneas concerning the effect of induction of I T F by endotoxin on herpetic keratitis 2 and a similar effect by From the Wills Eye Hospital and Research Insti tute, Philadelphia, Pennsylvania. This investigation was supported in part by USPHS Research Grant NB-AI 07013, from the National Institute of Neu rological Diseases and Blindness. The study was also aided by a grant from the National Society for the Prevention of Blindness, Inc. Reprint requests to Ralph Pollikoff, Ph.D., Wills Eye Hospital, 1601 Spring Garden Street, Philadelphia, Pennsylvania 19130.
statolon on vesicular stomatitis virus (VSV) keratitis were also promising,3'4 it was thought that treatment with the complexed polyribonucleotide ( P C : P I ) , another inducer of I T F formation, would also be a most likely method of therapy of virus ker atitis in the rabbit eye. An initial study by Pollikoff, DiPuppo, and Cannavale4 showed that the complexed copolymer was highly effective in topical treatment of rabbit cor nea infected with VSV. In addition, the re sults of Park and Baron 5 have also indi cated that there was great promise in ther apy of herpetic keratitis by this method. In the present report, data are presented which extend preliminary reported observa tions and records in full the efficacy of the copolymer alone and in combined therapy with dexamethasone or idoxuridine in rabbit eyes infected with herpes simplex virus.3·6