Dominandy Inherited Cystoid Macular Edema A Histopathologic Study Karin U. Loeffler, MD, Zi-Liang Li, MD, Gerald A. Fishman, MD, Mark O. M. Tso, MD Background: Dominantly inherited cystoid macular edema was described as a clinically distinct form of macular dystrophy with an onset at approximately age 30 years with slow progression over the ensuing decades. This is the first report of the light and electron microscopic findings in two donor eyes of one of the patients with this clinical entity. Methods: Both eyes were obtained after death and fixed within 24 hours in a buffered 4% formaldehyde-1 % glutaraldehyde solution. For light microscopy, tissue was embedded in paraffin and stained with hematoxylin-eosin, periodic acid-Schiff, colloidal iron for mucopolysaccharides, and an antibody to glial fibrillar acidic protein. For ultrastructural investigation, several blocks of choroidal/retinal tissues from the posterior pole, including both maculae, were embedded in epoxy resin and processed for transmission electron microscopy. Results: Major findings included large retinal cysts in the macula, atrophy and marked disorganization of the inner nuclear layer, advanced degeneration of Muller cells with nodular aggregates of basement membrane-like material, and a preretinal membrane. The retinal vasculature did not show excessive endothelial alterations but was surrounded by deposits of multilayered basement membrane in the perivascular space. Conclusion: The authors believe that the pathologic features of dominantly inherited cystoid macular edema are different from those of macular edema caused by other disease processes. The predominant pathologic changes affected mainly the inner nuclear layer. The possibility of a primary disease of the Muller cell is suggested. Ophthalmology 1992;99: 1385-1392
In previous reports from the Netherlands l ,2 and from our clinic,3,4 autosomal dominantly inherited cystoid macular edema was established as a distinct form of macular dystrophy. Clinical features included cystic changes in the macula associated with fluorescein leakage from retinal capillaries. Electroretinographic findings were generally
normal, especially in the early stages, but subnormal electro-oculographic light peak/dark trough ratios and abnormal dark adaptation curves were observed. I ,2,s Decreased visual acuity usually was first noted around the age of 30 and slowly progressed to moderate to severe visual loss over a period of years. In the advanced stage,
Originally received: February 18, 1992, Revision accepted: April 9, 1992, From the Georgiana Dvorak Theobald Ophthalmic Pathology laboratory, Department of Ophthalmology and Visual Sciences, Lions ofIllinois Eye Research Institute, UIC Eye Center, University of Illinois at Chicago College of Medicine, Chicago, Supported in part by grant Lo 453/1-1 from the Deutsche Forschungsgemeinschaft; grant RO I EYO 1903 and core grant EYO 1792 from the National Eye Institute, Bethesda, Maryland; gifts from the Lions of Illinois
Foundation, Maywood, Illinois; the Clifford Sawyer Estate; a grant from the McGraw Foundation, Arlington Heights, Illinois; and by the National Retinitis Pigmentosa Foundation Fighting Blindness, Baltimore, Maryland, Reprint requests to Mark 0, M, Tso, MD, the Georgiana Dvorak Theobald Ophthalmic Pathology Laboratory, Department of Ophthalmology, Lions of Illinois Eye Research Institute, UIC Eye Center, University of Illinois at Chicago, College of Medicine, 1855 W Taylor St, Chicago, IL 60612,
1385
Ophthalmology
Volume 99, Number 9, September 1992
fluorescein angiography showed atrophic-appearing macular lesions associated with both window defects and mild leakage from peri macular capillaries. To our knowledge, no histopathologic report of this disease has been published. We examined two eyes of one of the patients previously described in a clinical study3.4 by light and electron microscopy and postulate a possible cellular mechanism for the retinal changes observed in this disease.
Histopathologic Study
Case Report
Macroscopic Findings
A Greek woman first noted poor central vision at approximately 35 years of age, which slowly worsened during the next 35 years. She did not experience nyctalopia or photophobia. When she first presented at our clinic at age 70 years, her best-corrected visual acuity was 2/120 in the right eye and 2/200 in the left. On slit-lamp examination, no significant pathologic changes were seen in the anterior segment of either eye, but trace cells were noted in the vitreous. Intraocular pressure was normal. Ophthalmoscopy showed bilateral macular lesions that included both atrophic and cystoid changes. Fluorescein angiography showed extensive leakage from retinal capillaries (Fig I). The optic discs appeared to be normal, while the retinal vessels were mildly attenuated. Pigmentary clumping was not conspicuous, but two localized areas of hard exudates were seen within the posterior pole of the right eye. Goldmann perimetry showed bilateral central scotomas with a 11-4e target. There was no known history of diabetes or systemic hypertension. Three other family members were known to be affected by the same retinal disease. 3,4 The patient died of pneumonia at 78 years of age. Both eyes were obtained after death and fixed within 24 hours in a buffered 4% formaldehyde-l % glutaraldehyde solution. For light microscopy, blocks from the anterior and posterior segments were processed for paraffin embedding (specimens 86-30 and 86-31), and sections were stained with hematoxylin-eosin, periodic acidSchiff, colloidal iron for mucopolysaccharides, and an antibody to glial fibrillar acidic protein. For the ultrastructural study, four blocks of choroidal/retinal tissue from the posterior pole of the right eye and seven blocks from the posterior pole of the left
Figure 1. Fluorescein angiogram shows marked leakage from retinal vessels at the posterior pole.
1386
eye, including the macula (specimens B775 and B776), were postfixed in osmium, dehydrated in a graded series of alcohol, and embedded in epoxy resin. Sections were cut with a ReichertJung microtome, and semithin sections were stained with methylene blue-azure II. Ultrathin sections were stained with uranyl acetate-lead citrate and examined with an electron microscope (Hitachi 600, Tokyo, Japan).
Both eyes were of normal size. Dissection along the equator showed unremarkable anterior segments and a grossly clear vitreous. The optic nerve heads showed myelin artifact, and both maculae appeared to be atrophic. A pigmentary disturbance with hyper- and hypopigmentation and lattice degeneration was noted in the retinal periphery anterior to the equator in both eyes.
Microscopic Findings Paraffin sections of the anterior segments showed no notable pathologic changes. The posterior segment, however, showed similar pathologic features in both eyes. At the macula, all retinal layers appeared to be disorganized (Fig 2A). Anterior to the inner limiting membrane was a preretinal membrane consisting of multiple layers of glial cells and collagen (Fig 2B). The nerve fiber layer appeared to be vacuolated due to partial loss of Muller cell footplates at the inner limiting membrane (Fig 2B). The inner nuclear layer was markedly distorted and thickened. Glial fibers insinuated into the inner nuclear layer, thus separating it focally into an anterior and a posterior layer (Fig 2A). Nodules of basal lamina-like material with the appearance of multilaminar basement membrane 6 were occasionally seen within these proliferating glial fibers (Fig 2C), which contained numerous intermediate filaments of approximately 10 nm in diameter. Also within the inner nuclear layer, extending into the outer plexiform layer, large cyst-like spaces were present (Fig 3A), surrounded by Muller cell fibers and pigment-laden cells with remnants of photoreceptor segments projecting anteriorly into the cavity (Fig 3A, inset). Some cell junction formation was observed between surrounding Muller cell fibers (Figs 3B and 3C). The "lumen" of the glial cyst contained some proteinaceous material, small fibrin deposits, and lipid-laden macrophages. Some of these foamy macrophages also were present in the surrounding retinal tissue (Fig 4A). The retinal vessels observed in these sections appeared to be fairly normal. Their endothelial cells had apparently intact cell junctions and were surrounded by pericytes, the basal lamina of which was multilayered and thickened in a widened perivascular space (Figs 4B and 4C). Thus, the perivascular cells were no longer in close apposition with the vessel wall, compatible with previous leakage of plasma components into the surrounding tissue. The photoreceptor layer in the macular area was markedly thinned with loss of photoreceptor inner and outer segments resulting in apposition
Loeffler et al . Cystoid Macular Edema
into an cells (P) and a distorted inner nuclear layer that seems to be separated Figure 2. A, advanced gliosis of the macula with loss of photorec eptor plexiform layer (IPL), inner (OPL), layer plexiform outer of presence the Notice (G). anterior and posterior portion (INL 1 and INL 2) by glial cells nerve magnification, X180). B, electron microgra ph shows vacuolation of and preretina l membran e (arrowheads) (methylene blue-azure II; original appearing Muller cell necroticd condense and (ILM) e membran limiting inner the from fiber layer with partial separatio n of Muller cell footplates ganglion l membran e (curved arrows) toward the vitreous cavity. (G) indicates cytoplasm (thin arrows). Notice the collagen depositio n (e) and preretina e-like material (asterisk) membran t basemen of nodules focal shows layer nuclear inner cell (bar indicates 5 /Lm). C, electron microscopy of the distorted (bar and adjacent cell junction (arrow) are shown at higher magnification surround ed by glial cells. Inset, laminar arrangem ent of nodule material indicates 10 /Lm).
1387
Ophthalmology
Volume 99, Number 9, September 1992
Figure 3. A, large macular cyst (C) located in the area of the inner nuclear layer (INL). Notice atrophy of photoreceptors and patchy loss of retinal pigment epithelium (arrows) (methylene blue-azure II; original magnification, X200). Inset, remnants of photoreceptor elements (arrow) projecting into the cyst cavity and adjacent pigment-laden macrophage (M). B, C, electron microscopy of cyst lining shows glial cells (0) and axons (A). Notice the several cell junctions (single arrows) and elongated cell processes resembling the fiber baskets of Schultze (double arrow). C indicates cyst lumen (bar indicates 1 I'm).
of the outer limiting membrane, formed mainly by adjacent Miiller cells, to the retinal pigment epithelium (Fig 5). Focal loss of the retinal pigment epithelium also was observed. Another notable feature in the macular area was the formation of numerous nodular drusen. In some places, the retinal pigment epithelial cells showed loss of pigment and basal infoldings, but their basal lamina and cell junctions often were still unremarkable. Bruch's membrane showed changes considered to be consistent with the patient's age; these included accumulation of vesicular and tubular structures, deposition of "curly" wide-spacing collagen, and intercapillary thickening. Beneath and within Bruch's membrane, numerous macrophages with various morphologic features were seensome showed typical membranous inclusions and con-
1388
tained lysosomal bodies; others were packed with electronlucent vesicles, some of which contained osmophilic granules; and others had a watery cytoplasm and appeared to be of pericytic origin. Only a few remaining choriocapillaries were seen in this area, and they were lined by thickened endothelial cells without focal cytoplasmic attenuations while the pericytes appeared to be oriented toward Bruch's membrane (Fig 5B). Near the optic nerve head, small cysts filled with proteinaceous exudate were observed in the outer plexiform layer. A few corpora amylacea also were found within the retina in this area. The optic nerve head of the left eye appeared to be edematous and was infiltrated by a few macrophages and polymorphonuclear leukocytes compatible with a partial infarct.
Loeffler et al . Cystoid Macular Edema
Figure 4. A, retina at posterior pole with marked photoreceptor atrophy and invasion of lipid-laden macrophages (M). Retinal vessels (arrows) appear to be normal (methylene blue-azure II; original magnification, X600). B, C, transmission electron microscopy shows retinal vessels surrounded by multilayered basal lamina (arrows). Endothelial cells appear to be well junctioned (arrowheads), but the perivascular space is widened, and surrounding cells show features of degeneration (bar indicates 1 JLm).
1389
Ophthalmology
Volume 99, Number 9, September 1992 Toward the periphery, the inner retina showed several displaced ganglion cells within an atrophic inner nuclear layer (Fig 6) and cytoid bodies, indicating microinfarction of the nerve fiber layer (Fig 6, inset). In contrast, the peripheral photoreceptor layer was well preserved, and the retinal pigment epithelium showed only mild pigmentary changes. Near the pars plana were hyalinized retinal vessels, peripheral microcystoid, and lattice degeneration. The choroid showed no inflammatory infiltrates. Patchy loss of choriocapillaries as evidenced by marked widening of the collagenous intercapillary pillars could be seen throughout all sections examined in both eyes, but there was no definite indication of either a break in Bruch's membrane or subretinal neovascularization. The walls of some of the larger choroidal vessels were rather thickened and sclerotic. The endothelial cells in some veins appeared to be fenestrated and showed intercellular widenings filled by a plasma-like substance. Toward the posterior pole, numerous foamy macrophages with small electron-dense lipid like inclusions similar to those in the retina and Bruch's membrane were found in the vicinity of these vessels. Staining for glial fibrillar acidic protein showed moderate immunoreactivity in the inner retinal layers, with particular staining of the inner limiting membrane but not the perivascular space. Staining for acid mucopolysaccharides with colloidal iron showed a strong reaction in the interphotoreceptor matrix, a moderate reaction in the inner limiting membrane and around blood vessels, and patchy deposits in the sclera.
Discussion To our knowledge, this is the first histopathologic study of a case of "dominantly inherited cystoid macular edema," a slowly progressive macular dystrophy that has been established as a distinct clinical entity. 1-3 In patients with this disease, a gradual decrease in visual acuity is usually noted during the third decade oflife. On ophthalmoscopic examination, multilobulated cysts are seen in
Figure 5. A, retinal pigment epithelium beneath the macular cyst (C) is elevated from Bruch's membrane by loose collagenous tissue (asterisks), remnants of basement membrane (long arrow), and macrophages. Arrowheads point to outer limiting membrane, which is formed mainly by cell junctions between adjacent Muller cells. Only a few normal-appearing photoreceptor cell nuclei are present (short arrows). Notice also the loss of choriocapillaries and foamy macrophages in the choroid (methylene blue-azure II; original magnification, X320). B, electron micrograph of a comparable area shows retinal pigment epithelium/Muller cell apposition (arrowheads indicate cell junctions of outer limiting membrane) and macrophagic infiltration (arrows) in more detail. Bruch's membrane (BM) shows accumulation of tubular and vesicular structures and is eroded by cellular processes (arrowheads). CC indicates choriocapillary (bar indicates 5/L m ).
1390
Figure 6. Light micrograph shows that the inner nuclear layer is reduced in thickness to 2 to 3 nuclei while ganglion cells are still present (methylene blue-azure II; original magnification, XlOO). Inset, microinfarction of nerve fiber layer with formation of cytoid bodies (asterisk).
Loeffler et al . Cystoid Macular Edema the macula. fluorescein angiography shows leakage from the retinal vessels, with petaloid accumulation offluorescein in the macula. An abnormal electro-oculogram also may be seen. Our patient had clinical features typical of this disease. The major histopathologic features of her eyes included large macular cysts (Fig 3), disorganization and gliosis of the inner nuclear layer (Fig 2A), focal Muller cell necrosis and reactive proliferation (Figs 2B, 2C, 3B, and 3C), multilayered deposit of basement membrane in the perivascular space (Figs 4B and 4C), and a preretinal membrane (Figs 2A and 2B). The retinal capillary endothelial cells appeared unremarkable. In addition, there were degenerative changes of photoreceptor and retinal pigment epithelial cells within the macula. In most photoreceptor degenerative diseases, the outer retinal layers are affected, and the inner nuclear layer is spared. In most of the degenerative diseases of the ganglion cells, the inner nuclear layer also is preserved. However, in our patient, the inner nuclear layer showed a prominent loss of cells and disorganization in the presence of relatively intact normal ganglion cell and photoreceptor layers, except in the macula. To our knowledge, no known disease process has been described that specifically affects the inner nuclear layer of the retina. Furthermore, in the macular area, advanced gliosis was seen within the inner nuclear layer, splitting the nuclei into an anterior and posterior sheet. Glial processes with abnormal basement membrane intertwined to form nodules within the inner nuclear layer. Similar glial nodules have been observed in juvenile X-linked retinoschisis and in a patient with autosomal dominant vitreoretinal choroidopathy.7,8 A primary disease process of the Muller cells has been proposed in these entities. 7,8 In addition, large extracellular cysts localized within the inner nuclear layer were seen in the macula of our patient. The glial processes lining these cysts were joined by zonulae adherens, suggesting that they were of Muller cell origin. Marked vacuolation and necrosis of Muller cell footplates along the internal limiting membrane further suggest Muller cell disease in our patient. The above observations indicate that the Muller cell appears to be one of the primary cells involved in this disease process. The preretinal membrane of our patient consisted mostly of spindle glial cells. Epiretinal membranes have been ascribed to develop from macrophages, fibrocytes, fibrous astrocytes, myofibroblast-like cells, and retinal pigment epithelium. 9 In other degenerative diseases, preretinal membranes have been suggested to derive from Muller cells because of the presence of neurotubules and zonulae adherens-like cell junctions. 8,10,II Although the precise origin of the preretinal membrane in our patient could not be determined, the possibility of a Muller cell origin also is considered. It might be instructive to contrast the histopathologic features of the retina of our patient with three entities involving a disease process of Muller cells. Juvenile retinoschisis is a disorder in which diseased Muller cells have been suggested to be a primary cause. 7 Condon and co-
workers7 found the inner layers of the retinoschisis to consist of Muller cells occasionally connected by maculae adherens-like cell junctions. In their patients with juvenile sex-linked retinoschisis, the perivascular space of the retinal vessels was thickened, with deposition of multilaminar basement membrane and fine filaments that were assumed to be derived from Muller cells. In addition, nodules of basement membrane material were seen lined by glial cells within the retinal nuclear layers. Both the vascular changes and these glial nodules resembled those observed in our patient. In an animal model in which rats and rabbits received intravitreal injections of aminoadipic acid, a known Muller cell toxin, large cystic cavities in the retina were lined by Muller cell processes. 12 In our patient, similar large extracellular macular cysts were observed, and they were lined by Muller cell processes. In autosomal dominant vitreoretinochoroidopathy, retinal glial cells formed multilaminar basement membrane in a nodular fashion .8 A preretinal membrane showing Muller cell features also was seen. These glial nodules and the preretinal membrane are comparable with those seen in our patient. Our patient was clinically diagnosed as having cystoid macular edema with vascular leakage based on fluorescein angiographic findings. With the exception of an increased deposit of basement membrane material in the perivascular space, large extracellular macular cysts lined by Muller cell processes, and lipid-laden macrophages, no overt pathologic changes were observed along the retinal vasculature. Those perivascular changes, however, are consistent with chronic vascular leakage, and the absence of a light or electron microscopic evidence of pathology within the endothelium does not contradict the clinical observation of fluorescein leakage from retinal capillaries. The fluorescein molecule is extremely small, and the pathophysiologic changes of the vasculature can be so subtle that morphologic changes might not be seen. The cystoid macular edema in our patient might be compared with cystoid macular edema caused by other disease processes and with peripheral cystoid degeneration ofthe retina. 13.14 Fine and Brucker 13 described swelling and necrosis of Muller cells in two patients with cystoid macular edema secondary to peripheral choroidal melanoma. In contrast, Gass et al, 15 in their study of a patient with aphakic cystoid macular edema, observed extracellular edema sparing Muller cells. In addition, in cystoid macular edema associated with diabetes, exudate and leakage from retinal vasculature have been reported. In cystoid macular edema secondary to retinal vein occlusion, liquefaction necrosis of retinal structures with microinfarction and subsequent cyst formation was seen. 16.17 In contrast, the macular cysts in our patient consisted of large extracellular spaces lined by Muller cell processes. Lipid-laden macrophages were seen in the adjacent retinal tissue. These features are not comparable with the cystoid macular edema caused by other disease processes. The retinal cystic spaces in peripheral cystoid retinal degeneration are believed to be lined by Muller cells. These
1391
Ophthalmology
Volume 99, Number 9, September 1992
cysts have been shown to be surrounded by cell processes joined by zonulae adherens-like cell junctions. IS In this respect, they bear some resemblance to the macular cysts seen in our patient. However, the pathogenetic mechanism of the development of these peripheral retinal cysts has not yet been determined. Other complicating factors, however, have to be taken into account for interpretation of the histopathologic observations in our patient. Consideration must be given to histopathologic changes caused by aging that are not necessarily part of the dominantly inherited cystoid macular edema. Indeed, localized atrophy of the retinal pigment epithelium and photoreceptor complex was seen in the macula of our patient. Although these changes were likely secondary to the presence of chronic macular edema, they may, at least in part, have been related to the patient's age. In conclusion, we believe that the pathologic features of dominantly inherited cystoid macular edema are unique and appear to be different from those of macular edema caused by other disease processes. The possibility of a primary cellular disease mechanism of the Muller cells is suggested.
References 1. Deutman AF, Pinckers AJLG, Aan De Kerk AL. Dominantly inherited cystoid macular edema. Am J Ophthalmol 1976;82:540-8. 2. Notting JGA, Pinckers AJLG. Dominant cystoid macular dystrophy. Am J Ophthalmol 1977;83:234-41. 3. Fishman GA, Goldberg MF, Trautmann Jc. Dominantly inherited cystoid macular edema. Ann Ophthalmol 1979; 11: 21-7. 4. Fishman GA, Goldberg MF, Trautmann Jc. Dominantly inherited cystoid macular edema. Perspect Ophthalmol 1979;3:29-35.
1392
5. Pinckers A, Deutman AF, Notting JGA. Retinal functions in dominant cystoid macular dystrophy (DCMD). Acta Ophthalmol 1976;54:579-90. 6. Fine BS, Yanoff M. Ocular Histology: A Text and Atlas, 2nd ed. Hagerstown: Harper & Row, 1979; 42-50. 7. Condon GP, Brownstein S, Wang N-S, et al. Congenital hereditary (juvenile X-linked) retinoschisis. Histopathologic and ultrastructural findings in three eyes. Arch Ophthalmol 1986; 104:576-83. 8. Goldberg MF, Lee F-L, Tso MOM, Fishman GA. Histopathologic study of autosomal dominant vitreoretinochoroidopathy. Peripheral annular pigmentary dystrophy of the retina. Ophthalmology 1989;96: 1736-46. 9. Kampik A, Kenyon KR, Michels RG, et al. Epiretinal and vitreous membranes. Comparative study of 56 cases. Arch Ophthalmol 1981;99:1445-54. 10. Nork TM, Ghobrial MW, Peyman GA, Tso MOM. Massive retinal gliosis. A reactive proliferation of Muller cells. Arch Ophthalmol 1986;104:1383-9. II. Nork TM, Wallow IHL, Sramek SJ, Anderson G. Muller's cell involvement in proliferative diabetic retinopathy. Arch Ophthalmol 1987;105:1424-9. 12. Ishikawa Y, Mine S. Aminoadipic acid toxic effects on retinal glial cells. Jpn J Ophthalmol 1983;27:107-18. 13. Fine BS, Brucker AJ. Macular edema and cystoid macular edema. Am J Ophthalmol 1981 ;92:466-81. 14. YanoffM, Fine BS, Brucker AJ, Eagle RC Jr. Pathology of human cystoid macular edema. Surv Ophthalmol 1984;28: 505-11. 15. Gass JDM, Anderson DR, Davis EB. A clinical, fluorescein angiographic, and electron microscopic correlation of cystoid macular edema. Am J Ophthalmol 1985;100:82-6. 16. Tso MOM. Pathology of cystoid macular edema. Ophthalmology 1982;89:902-15. 17. Wallow IHL, Danis RP, Bindley C, Neider M. Cystoid macular degeneration in experimental branch retinal vein occlusion. Ophthalmology 1988;95: 1371-9. 1.8. Spitznas M, Luciano L, Reale E. Occluding junctions surrounding cystoid spaces in the human peripheral retina. A thin-section and freeze-fracture study. Albrecht Von Graefes Arch Klin Exp Ophthalmol 1981;217:155-65.
In previous reports from the Netherlands l ,2 and from our clinic,3,4 autosomal dominantly inherited cystoid macular edema was established as a distinct form of macular dystrophy. Clinical features included cystic changes in the macula associated with fluorescein leakage from retinal capillaries. Electroretinographic findings were generally
normal, especially in the early stages, but subnormal electro-oculographic light peak/dark trough ratios and abnormal dark adaptation curves were observed. I ,2,s Decreased visual acuity usually was first noted around the age of 30 and slowly progressed to moderate to severe visual loss over a period of years. In the advanced stage,
Originally received: February 18, 1992, Revision accepted: April 9, 1992, From the Georgiana Dvorak Theobald Ophthalmic Pathology laboratory, Department of Ophthalmology and Visual Sciences, Lions ofIllinois Eye Research Institute, UIC Eye Center, University of Illinois at Chicago College of Medicine, Chicago, Supported in part by grant Lo 453/1-1 from the Deutsche Forschungsgemeinschaft; grant RO I EYO 1903 and core grant EYO 1792 from the National Eye Institute, Bethesda, Maryland; gifts from the Lions of Illinois
Foundation, Maywood, Illinois; the Clifford Sawyer Estate; a grant from the McGraw Foundation, Arlington Heights, Illinois; and by the National Retinitis Pigmentosa Foundation Fighting Blindness, Baltimore, Maryland, Reprint requests to Mark 0, M, Tso, MD, the Georgiana Dvorak Theobald Ophthalmic Pathology Laboratory, Department of Ophthalmology, Lions of Illinois Eye Research Institute, UIC Eye Center, University of Illinois at Chicago, College of Medicine, 1855 W Taylor St, Chicago, IL 60612,
1385
Ophthalmology
Volume 99, Number 9, September 1992
fluorescein angiography showed atrophic-appearing macular lesions associated with both window defects and mild leakage from peri macular capillaries. To our knowledge, no histopathologic report of this disease has been published. We examined two eyes of one of the patients previously described in a clinical study3.4 by light and electron microscopy and postulate a possible cellular mechanism for the retinal changes observed in this disease.
Histopathologic Study
Case Report
Macroscopic Findings
A Greek woman first noted poor central vision at approximately 35 years of age, which slowly worsened during the next 35 years. She did not experience nyctalopia or photophobia. When she first presented at our clinic at age 70 years, her best-corrected visual acuity was 2/120 in the right eye and 2/200 in the left. On slit-lamp examination, no significant pathologic changes were seen in the anterior segment of either eye, but trace cells were noted in the vitreous. Intraocular pressure was normal. Ophthalmoscopy showed bilateral macular lesions that included both atrophic and cystoid changes. Fluorescein angiography showed extensive leakage from retinal capillaries (Fig I). The optic discs appeared to be normal, while the retinal vessels were mildly attenuated. Pigmentary clumping was not conspicuous, but two localized areas of hard exudates were seen within the posterior pole of the right eye. Goldmann perimetry showed bilateral central scotomas with a 11-4e target. There was no known history of diabetes or systemic hypertension. Three other family members were known to be affected by the same retinal disease. 3,4 The patient died of pneumonia at 78 years of age. Both eyes were obtained after death and fixed within 24 hours in a buffered 4% formaldehyde-l % glutaraldehyde solution. For light microscopy, blocks from the anterior and posterior segments were processed for paraffin embedding (specimens 86-30 and 86-31), and sections were stained with hematoxylin-eosin, periodic acidSchiff, colloidal iron for mucopolysaccharides, and an antibody to glial fibrillar acidic protein. For the ultrastructural study, four blocks of choroidal/retinal tissue from the posterior pole of the right eye and seven blocks from the posterior pole of the left
Figure 1. Fluorescein angiogram shows marked leakage from retinal vessels at the posterior pole.
1386
eye, including the macula (specimens B775 and B776), were postfixed in osmium, dehydrated in a graded series of alcohol, and embedded in epoxy resin. Sections were cut with a ReichertJung microtome, and semithin sections were stained with methylene blue-azure II. Ultrathin sections were stained with uranyl acetate-lead citrate and examined with an electron microscope (Hitachi 600, Tokyo, Japan).
Both eyes were of normal size. Dissection along the equator showed unremarkable anterior segments and a grossly clear vitreous. The optic nerve heads showed myelin artifact, and both maculae appeared to be atrophic. A pigmentary disturbance with hyper- and hypopigmentation and lattice degeneration was noted in the retinal periphery anterior to the equator in both eyes.
Microscopic Findings Paraffin sections of the anterior segments showed no notable pathologic changes. The posterior segment, however, showed similar pathologic features in both eyes. At the macula, all retinal layers appeared to be disorganized (Fig 2A). Anterior to the inner limiting membrane was a preretinal membrane consisting of multiple layers of glial cells and collagen (Fig 2B). The nerve fiber layer appeared to be vacuolated due to partial loss of Muller cell footplates at the inner limiting membrane (Fig 2B). The inner nuclear layer was markedly distorted and thickened. Glial fibers insinuated into the inner nuclear layer, thus separating it focally into an anterior and a posterior layer (Fig 2A). Nodules of basal lamina-like material with the appearance of multilaminar basement membrane 6 were occasionally seen within these proliferating glial fibers (Fig 2C), which contained numerous intermediate filaments of approximately 10 nm in diameter. Also within the inner nuclear layer, extending into the outer plexiform layer, large cyst-like spaces were present (Fig 3A), surrounded by Muller cell fibers and pigment-laden cells with remnants of photoreceptor segments projecting anteriorly into the cavity (Fig 3A, inset). Some cell junction formation was observed between surrounding Muller cell fibers (Figs 3B and 3C). The "lumen" of the glial cyst contained some proteinaceous material, small fibrin deposits, and lipid-laden macrophages. Some of these foamy macrophages also were present in the surrounding retinal tissue (Fig 4A). The retinal vessels observed in these sections appeared to be fairly normal. Their endothelial cells had apparently intact cell junctions and were surrounded by pericytes, the basal lamina of which was multilayered and thickened in a widened perivascular space (Figs 4B and 4C). Thus, the perivascular cells were no longer in close apposition with the vessel wall, compatible with previous leakage of plasma components into the surrounding tissue. The photoreceptor layer in the macular area was markedly thinned with loss of photoreceptor inner and outer segments resulting in apposition
Loeffler et al . Cystoid Macular Edema
into an cells (P) and a distorted inner nuclear layer that seems to be separated Figure 2. A, advanced gliosis of the macula with loss of photorec eptor plexiform layer (IPL), inner (OPL), layer plexiform outer of presence the Notice (G). anterior and posterior portion (INL 1 and INL 2) by glial cells nerve magnification, X180). B, electron microgra ph shows vacuolation of and preretina l membran e (arrowheads) (methylene blue-azure II; original appearing Muller cell necroticd condense and (ILM) e membran limiting inner the from fiber layer with partial separatio n of Muller cell footplates ganglion l membran e (curved arrows) toward the vitreous cavity. (G) indicates cytoplasm (thin arrows). Notice the collagen depositio n (e) and preretina e-like material (asterisk) membran t basemen of nodules focal shows layer nuclear inner cell (bar indicates 5 /Lm). C, electron microscopy of the distorted (bar and adjacent cell junction (arrow) are shown at higher magnification surround ed by glial cells. Inset, laminar arrangem ent of nodule material indicates 10 /Lm).
1387
Ophthalmology
Volume 99, Number 9, September 1992
Figure 3. A, large macular cyst (C) located in the area of the inner nuclear layer (INL). Notice atrophy of photoreceptors and patchy loss of retinal pigment epithelium (arrows) (methylene blue-azure II; original magnification, X200). Inset, remnants of photoreceptor elements (arrow) projecting into the cyst cavity and adjacent pigment-laden macrophage (M). B, C, electron microscopy of cyst lining shows glial cells (0) and axons (A). Notice the several cell junctions (single arrows) and elongated cell processes resembling the fiber baskets of Schultze (double arrow). C indicates cyst lumen (bar indicates 1 I'm).
of the outer limiting membrane, formed mainly by adjacent Miiller cells, to the retinal pigment epithelium (Fig 5). Focal loss of the retinal pigment epithelium also was observed. Another notable feature in the macular area was the formation of numerous nodular drusen. In some places, the retinal pigment epithelial cells showed loss of pigment and basal infoldings, but their basal lamina and cell junctions often were still unremarkable. Bruch's membrane showed changes considered to be consistent with the patient's age; these included accumulation of vesicular and tubular structures, deposition of "curly" wide-spacing collagen, and intercapillary thickening. Beneath and within Bruch's membrane, numerous macrophages with various morphologic features were seensome showed typical membranous inclusions and con-
1388
tained lysosomal bodies; others were packed with electronlucent vesicles, some of which contained osmophilic granules; and others had a watery cytoplasm and appeared to be of pericytic origin. Only a few remaining choriocapillaries were seen in this area, and they were lined by thickened endothelial cells without focal cytoplasmic attenuations while the pericytes appeared to be oriented toward Bruch's membrane (Fig 5B). Near the optic nerve head, small cysts filled with proteinaceous exudate were observed in the outer plexiform layer. A few corpora amylacea also were found within the retina in this area. The optic nerve head of the left eye appeared to be edematous and was infiltrated by a few macrophages and polymorphonuclear leukocytes compatible with a partial infarct.
Loeffler et al . Cystoid Macular Edema
Figure 4. A, retina at posterior pole with marked photoreceptor atrophy and invasion of lipid-laden macrophages (M). Retinal vessels (arrows) appear to be normal (methylene blue-azure II; original magnification, X600). B, C, transmission electron microscopy shows retinal vessels surrounded by multilayered basal lamina (arrows). Endothelial cells appear to be well junctioned (arrowheads), but the perivascular space is widened, and surrounding cells show features of degeneration (bar indicates 1 JLm).
1389
Ophthalmology
Volume 99, Number 9, September 1992 Toward the periphery, the inner retina showed several displaced ganglion cells within an atrophic inner nuclear layer (Fig 6) and cytoid bodies, indicating microinfarction of the nerve fiber layer (Fig 6, inset). In contrast, the peripheral photoreceptor layer was well preserved, and the retinal pigment epithelium showed only mild pigmentary changes. Near the pars plana were hyalinized retinal vessels, peripheral microcystoid, and lattice degeneration. The choroid showed no inflammatory infiltrates. Patchy loss of choriocapillaries as evidenced by marked widening of the collagenous intercapillary pillars could be seen throughout all sections examined in both eyes, but there was no definite indication of either a break in Bruch's membrane or subretinal neovascularization. The walls of some of the larger choroidal vessels were rather thickened and sclerotic. The endothelial cells in some veins appeared to be fenestrated and showed intercellular widenings filled by a plasma-like substance. Toward the posterior pole, numerous foamy macrophages with small electron-dense lipid like inclusions similar to those in the retina and Bruch's membrane were found in the vicinity of these vessels. Staining for glial fibrillar acidic protein showed moderate immunoreactivity in the inner retinal layers, with particular staining of the inner limiting membrane but not the perivascular space. Staining for acid mucopolysaccharides with colloidal iron showed a strong reaction in the interphotoreceptor matrix, a moderate reaction in the inner limiting membrane and around blood vessels, and patchy deposits in the sclera.
Discussion To our knowledge, this is the first histopathologic study of a case of "dominantly inherited cystoid macular edema," a slowly progressive macular dystrophy that has been established as a distinct clinical entity. 1-3 In patients with this disease, a gradual decrease in visual acuity is usually noted during the third decade oflife. On ophthalmoscopic examination, multilobulated cysts are seen in
Figure 5. A, retinal pigment epithelium beneath the macular cyst (C) is elevated from Bruch's membrane by loose collagenous tissue (asterisks), remnants of basement membrane (long arrow), and macrophages. Arrowheads point to outer limiting membrane, which is formed mainly by cell junctions between adjacent Muller cells. Only a few normal-appearing photoreceptor cell nuclei are present (short arrows). Notice also the loss of choriocapillaries and foamy macrophages in the choroid (methylene blue-azure II; original magnification, X320). B, electron micrograph of a comparable area shows retinal pigment epithelium/Muller cell apposition (arrowheads indicate cell junctions of outer limiting membrane) and macrophagic infiltration (arrows) in more detail. Bruch's membrane (BM) shows accumulation of tubular and vesicular structures and is eroded by cellular processes (arrowheads). CC indicates choriocapillary (bar indicates 5/L m ).
1390
Figure 6. Light micrograph shows that the inner nuclear layer is reduced in thickness to 2 to 3 nuclei while ganglion cells are still present (methylene blue-azure II; original magnification, XlOO). Inset, microinfarction of nerve fiber layer with formation of cytoid bodies (asterisk).
Loeffler et al . Cystoid Macular Edema the macula. fluorescein angiography shows leakage from the retinal vessels, with petaloid accumulation offluorescein in the macula. An abnormal electro-oculogram also may be seen. Our patient had clinical features typical of this disease. The major histopathologic features of her eyes included large macular cysts (Fig 3), disorganization and gliosis of the inner nuclear layer (Fig 2A), focal Muller cell necrosis and reactive proliferation (Figs 2B, 2C, 3B, and 3C), multilayered deposit of basement membrane in the perivascular space (Figs 4B and 4C), and a preretinal membrane (Figs 2A and 2B). The retinal capillary endothelial cells appeared unremarkable. In addition, there were degenerative changes of photoreceptor and retinal pigment epithelial cells within the macula. In most photoreceptor degenerative diseases, the outer retinal layers are affected, and the inner nuclear layer is spared. In most of the degenerative diseases of the ganglion cells, the inner nuclear layer also is preserved. However, in our patient, the inner nuclear layer showed a prominent loss of cells and disorganization in the presence of relatively intact normal ganglion cell and photoreceptor layers, except in the macula. To our knowledge, no known disease process has been described that specifically affects the inner nuclear layer of the retina. Furthermore, in the macular area, advanced gliosis was seen within the inner nuclear layer, splitting the nuclei into an anterior and posterior sheet. Glial processes with abnormal basement membrane intertwined to form nodules within the inner nuclear layer. Similar glial nodules have been observed in juvenile X-linked retinoschisis and in a patient with autosomal dominant vitreoretinal choroidopathy.7,8 A primary disease process of the Muller cells has been proposed in these entities. 7,8 In addition, large extracellular cysts localized within the inner nuclear layer were seen in the macula of our patient. The glial processes lining these cysts were joined by zonulae adherens, suggesting that they were of Muller cell origin. Marked vacuolation and necrosis of Muller cell footplates along the internal limiting membrane further suggest Muller cell disease in our patient. The above observations indicate that the Muller cell appears to be one of the primary cells involved in this disease process. The preretinal membrane of our patient consisted mostly of spindle glial cells. Epiretinal membranes have been ascribed to develop from macrophages, fibrocytes, fibrous astrocytes, myofibroblast-like cells, and retinal pigment epithelium. 9 In other degenerative diseases, preretinal membranes have been suggested to derive from Muller cells because of the presence of neurotubules and zonulae adherens-like cell junctions. 8,10,II Although the precise origin of the preretinal membrane in our patient could not be determined, the possibility of a Muller cell origin also is considered. It might be instructive to contrast the histopathologic features of the retina of our patient with three entities involving a disease process of Muller cells. Juvenile retinoschisis is a disorder in which diseased Muller cells have been suggested to be a primary cause. 7 Condon and co-
workers7 found the inner layers of the retinoschisis to consist of Muller cells occasionally connected by maculae adherens-like cell junctions. In their patients with juvenile sex-linked retinoschisis, the perivascular space of the retinal vessels was thickened, with deposition of multilaminar basement membrane and fine filaments that were assumed to be derived from Muller cells. In addition, nodules of basement membrane material were seen lined by glial cells within the retinal nuclear layers. Both the vascular changes and these glial nodules resembled those observed in our patient. In an animal model in which rats and rabbits received intravitreal injections of aminoadipic acid, a known Muller cell toxin, large cystic cavities in the retina were lined by Muller cell processes. 12 In our patient, similar large extracellular macular cysts were observed, and they were lined by Muller cell processes. In autosomal dominant vitreoretinochoroidopathy, retinal glial cells formed multilaminar basement membrane in a nodular fashion .8 A preretinal membrane showing Muller cell features also was seen. These glial nodules and the preretinal membrane are comparable with those seen in our patient. Our patient was clinically diagnosed as having cystoid macular edema with vascular leakage based on fluorescein angiographic findings. With the exception of an increased deposit of basement membrane material in the perivascular space, large extracellular macular cysts lined by Muller cell processes, and lipid-laden macrophages, no overt pathologic changes were observed along the retinal vasculature. Those perivascular changes, however, are consistent with chronic vascular leakage, and the absence of a light or electron microscopic evidence of pathology within the endothelium does not contradict the clinical observation of fluorescein leakage from retinal capillaries. The fluorescein molecule is extremely small, and the pathophysiologic changes of the vasculature can be so subtle that morphologic changes might not be seen. The cystoid macular edema in our patient might be compared with cystoid macular edema caused by other disease processes and with peripheral cystoid degeneration ofthe retina. 13.14 Fine and Brucker 13 described swelling and necrosis of Muller cells in two patients with cystoid macular edema secondary to peripheral choroidal melanoma. In contrast, Gass et al, 15 in their study of a patient with aphakic cystoid macular edema, observed extracellular edema sparing Muller cells. In addition, in cystoid macular edema associated with diabetes, exudate and leakage from retinal vasculature have been reported. In cystoid macular edema secondary to retinal vein occlusion, liquefaction necrosis of retinal structures with microinfarction and subsequent cyst formation was seen. 16.17 In contrast, the macular cysts in our patient consisted of large extracellular spaces lined by Muller cell processes. Lipid-laden macrophages were seen in the adjacent retinal tissue. These features are not comparable with the cystoid macular edema caused by other disease processes. The retinal cystic spaces in peripheral cystoid retinal degeneration are believed to be lined by Muller cells. These
1391
Ophthalmology
Volume 99, Number 9, September 1992
cysts have been shown to be surrounded by cell processes joined by zonulae adherens-like cell junctions. IS In this respect, they bear some resemblance to the macular cysts seen in our patient. However, the pathogenetic mechanism of the development of these peripheral retinal cysts has not yet been determined. Other complicating factors, however, have to be taken into account for interpretation of the histopathologic observations in our patient. Consideration must be given to histopathologic changes caused by aging that are not necessarily part of the dominantly inherited cystoid macular edema. Indeed, localized atrophy of the retinal pigment epithelium and photoreceptor complex was seen in the macula of our patient. Although these changes were likely secondary to the presence of chronic macular edema, they may, at least in part, have been related to the patient's age. In conclusion, we believe that the pathologic features of dominantly inherited cystoid macular edema are unique and appear to be different from those of macular edema caused by other disease processes. The possibility of a primary cellular disease mechanism of the Muller cells is suggested.
References 1. Deutman AF, Pinckers AJLG, Aan De Kerk AL. Dominantly inherited cystoid macular edema. Am J Ophthalmol 1976;82:540-8. 2. Notting JGA, Pinckers AJLG. Dominant cystoid macular dystrophy. Am J Ophthalmol 1977;83:234-41. 3. Fishman GA, Goldberg MF, Trautmann Jc. Dominantly inherited cystoid macular edema. Ann Ophthalmol 1979; 11: 21-7. 4. Fishman GA, Goldberg MF, Trautmann Jc. Dominantly inherited cystoid macular edema. Perspect Ophthalmol 1979;3:29-35.
1392
5. Pinckers A, Deutman AF, Notting JGA. Retinal functions in dominant cystoid macular dystrophy (DCMD). Acta Ophthalmol 1976;54:579-90. 6. Fine BS, Yanoff M. Ocular Histology: A Text and Atlas, 2nd ed. Hagerstown: Harper & Row, 1979; 42-50. 7. Condon GP, Brownstein S, Wang N-S, et al. Congenital hereditary (juvenile X-linked) retinoschisis. Histopathologic and ultrastructural findings in three eyes. Arch Ophthalmol 1986; 104:576-83. 8. Goldberg MF, Lee F-L, Tso MOM, Fishman GA. Histopathologic study of autosomal dominant vitreoretinochoroidopathy. Peripheral annular pigmentary dystrophy of the retina. Ophthalmology 1989;96: 1736-46. 9. Kampik A, Kenyon KR, Michels RG, et al. Epiretinal and vitreous membranes. Comparative study of 56 cases. Arch Ophthalmol 1981;99:1445-54. 10. Nork TM, Ghobrial MW, Peyman GA, Tso MOM. Massive retinal gliosis. A reactive proliferation of Muller cells. Arch Ophthalmol 1986;104:1383-9. II. Nork TM, Wallow IHL, Sramek SJ, Anderson G. Muller's cell involvement in proliferative diabetic retinopathy. Arch Ophthalmol 1987;105:1424-9. 12. Ishikawa Y, Mine S. Aminoadipic acid toxic effects on retinal glial cells. Jpn J Ophthalmol 1983;27:107-18. 13. Fine BS, Brucker AJ. Macular edema and cystoid macular edema. Am J Ophthalmol 1981 ;92:466-81. 14. YanoffM, Fine BS, Brucker AJ, Eagle RC Jr. Pathology of human cystoid macular edema. Surv Ophthalmol 1984;28: 505-11. 15. Gass JDM, Anderson DR, Davis EB. A clinical, fluorescein angiographic, and electron microscopic correlation of cystoid macular edema. Am J Ophthalmol 1985;100:82-6. 16. Tso MOM. Pathology of cystoid macular edema. Ophthalmology 1982;89:902-15. 17. Wallow IHL, Danis RP, Bindley C, Neider M. Cystoid macular degeneration in experimental branch retinal vein occlusion. Ophthalmology 1988;95: 1371-9. 1.8. Spitznas M, Luciano L, Reale E. Occluding junctions surrounding cystoid spaces in the human peripheral retina. A thin-section and freeze-fracture study. Albrecht Von Graefes Arch Klin Exp Ophthalmol 1981;217:155-65.
