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Clinicopathologic Correlation of Surgically Removed Macular Hole Opercula
Clinicopathologic Correlation of Surgically Removed Macular Hole Opercula STEVEN A. MADREPERLA, MD., BROOKS W. McCUEN II, M.D., DYSON HICKINGBOTHAM, AND W. R. GREEN, M.D.
A
recognized that most macular holes occur in the absence of antecedent injury and are referred to as idiopathic. Theories for the pathogenesis of idiopathic macular holes have included progressive thinning of the foveal tissue4 and prehole cyst formation.5,6 A primary role for the vitreous was suggested by studies indicating a decrease in the relative risk for macular hole formation in eyes with complete posterior vitreous detachment.4,5·7 Gass8 and Johnson and Gass9 proposed a theory of idiopathic macular hole formation whereby shrinkage of adherent cortical vitreous first causes a circumscribed foveolar detachment (stage I) followed by early retinal dehiscence (stage II), then enlargement of the macular hole with vitreofoveal separation (stage III), and finally complete posterior vitreous detachment (stage IV). Guyer and Green 10 proposed the theory of tangential traction of the cortical vitreous by fluid movements. They proposed that, with enlargement of the premacular bursa and its continuity with the central area of vitreous, fluid countercurrents occurring with eye movements create tangential traction via the cortical vitreous at the fovea.
Accepted for publication Feb. 7, 1995. From the Duke Eye Center, Durham, North Carolina (Drs. Madreperla and McCuen and Mr. Hickingbotham); and the Wilmer Eye Institute, Baltimore, Maryland (Dr. Green). Dr. Madreperla was a 1993-94 Heed Ophthalmic Fellow. Reprint requests to W. R. Green, M.D., Eye Pathology Laboratory, Maumenee 427, Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD 21287-9278; fax: (410) 614-3457.
A n overlying opacity is sometimes seen in association with macular holes and, as such, has been termed an operculum, since it is thought to represent the tissue that once occupied the hole. It is not surprising that reports of the frequency of an associated operculum have varied widely (20% to 60%), as the operculum is often difficult to visualize clinically.4,7,9,11'15 Such an operculum, when observed just anterior to the plane of the macular hole, moves minimally with respect to the retina. Substantial evidence now suggests that the operculum at this time
• PURPOSE: To determine the ultrastructural characteristics of the operculum associated with macular holes. • METHODS: We developed instrumentation and a technique to capture the operculum observed with macular holes. Two opercula were studied by transmission electron microscopy. • RESULTS: The two specimens were attached to a layer of native collagen identified as cortical vitreous and were composed primarily of Mueller cells and fibrous astrocytes without adjacent inner limiting membrane. N o distinct retinal neuronal tissue was present. • CONCLUSIONS: Our findings indicate that proliferation of fibrous astrocytes and Mueller cells occurs with the formation of a macular hole, that this reparative tissue may be dislodged, and it is the reparative tissue that previously has been interpreted as an operculum. LTHOUGH MACULAR HOLES HAVE BEEN CONSIDered an untreatable condition, recent development of surgical approaches to improve vision after macular hole formation has led to renewed interest in this entity.1 Since the first description in 1871,2 the clinical characterization and theories on the pathogenesis of macular hole have continued to evolve. Although originally they were thought to be the result of trauma, 3 it is now
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(stage III according to Gass) is suspended by a thin layer of tapered cortical vitreous. This presumed vitreofoveal separation is often impossible to visualize with a slit lamp, but membranous attachments to the operculum can be visualized by ultrasonography.11 Interestingly, an opacity suspended just anterior to a normal appearing fovea, which is otherwise clinically indistinguishable from an operculum, has been termed a pseudo-operculum. Appearance of a pseudo-operculum has been documented after presumed aborted macular hole formation.16 Because of the absence of an associated retinal hole, these structures have been proposed to represent a condensation of cortical vitreous.816 To shed more light on this subject, we developed a method to remove safely and selectively tissue identified at macular hole surgery as an operculum and to examine the intact tissue by electron microscopy.
PATIENTS AND METHODS PATIENTS WITH STAGE III MACULAR HOLES WERE OPER-
ated on by using a modification of previously published techniques.1 Standard three-port vitrectomy was performed by using transscleral cannulas (Greishaber, Kennesaw, Georgia). A minimal core vitrectomy was performed with a light pipe and vitreous cutter. These instruments were exchanged for a lighted pick and a fiberoptic tissue manipulator (Greishaber, Kennesaw, Georgia) attached to manual suction. Suction was applied while the manipulator tip was held just anterior to the retina, temporal to the optic nerve head. The surgeon engaged a layer of nearly transparent tissue (presumed cortical vitreous) with the manipulator and gently lifted. Concurrently, the pick was used to enter the hole in the cortical vitreous corresponding to the space occupied by the optic disk, helping to elevate the cortical vitreous. As this layer was further elevated, the apparently attached operculum lifted with it. The operculum, attached to the cortical vitreous, was then suspended in the midvitreous cavity, and there was an adjacent hole in the cortical vitreous at the site corresponding to the optic disk. The vitreous cutter was used to enlarge the opening in the detached posterior hyaloid beginning through the hole in the cortical vitreous. 198
Fig. 1 (Madreperla and associates). View of cup-shaped jaws of microbiopsy forceps in open position.
The cutter was exchanged for specially designed microbiopsy forceps (Fig. 1). Coming from the space opened between the hole in the cortical vitreous and the operculum, the surgeon gently captured the operculum with the forceps without crushing the tissue. By coaxial illumination, the cortical vitreous was cut from around the biopsy forceps and the operculum was removed. The forceps and the operculum were immersed in 10% sucrose for 30 seconds and then placed in 2% buffered glutaraldehyde. The operation was completed by using the vitreous cutter to remove the remainder of the peripheral vitreous. A soft-tipped cannula was used to perform a fluid-air exchange. A drop of autologous serum was placed on the macular hole. The air was exchanged for 20% C3F8. Postoperatively, the patient maintained a facedown position until the gas bubble resorbed. After fixation for 24 hours, the operculum was removed from the microbiopsy forceps under a dissecting microscope and placed in 0.1 M sodium cacodylate, pH 7.6, then transferred to 1% tannic acid for 30 minutes. After being rinsed in sodium cacodylate, the tissue was transferred to 1% Os0 4 for 60 minutes, rinsed in H 2 0, and placed in 2% uranyl acetate overnight. After rinsing in H 2 0, the tissue was sequentially dehydrated in ethanol (50% to 100%), then infiltrated with and embedded in Araldite 506.
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CASE REPORTS • CASE l: A 72-year-old woman seen on Oct. 1, 1992, had visual acuity of R.E.: 20/400 secondary to a full-thickness macular hole. She had a one-month history of yellow-colored blurring in the left eye. Visual acuity was L.E.: 20/60. Examination disclosed an area of cystic-appearing retina centered at the fovea with a possible full-thickness defect at the nasal aspect of the lesion, which was thought to represent an early stage II macular hole. On return visit, April 15, 1993, six months after initial examination, visual acuity was L.E.: 20/70, and the retinal examination disclosed a slightly larger full-thickness retinal defect. No operculum was noted. The patient returned May 26, 1994, 13 months later, complaining of further decrease in vision. Visual acuity was L.E.: 20/80, and fundus examination disclosed a 700- μιη full-thickness macular hole with a surrounding cuff of subretinal fluid approximately 1,000 μιη in diameter (Fig. 2, left). An operculum was noted clinically. The patient underwent vitreous surgery on May 27, 1994, at which time a definite operculum was observed and retrieved. By July 25, 1994, the macular hole was closed, and visual acuity was 20/80 (Fig. 2, left). • CASE 2: A 66-year-old woman with a history of cataract extraction with intraocular lens placement in
the right eye five years and an Nd:YAG capsulotomy three years before the present examination had gradual but progressive decrease in visual acuity in her right eye during the one year before examination. On examination, visual acuity was R.E.: 20/80 and L.E.: 20/25. Slit-lamp examination of the right eye disclosed a posterior chamber intraocular lens with a central opening in the posterior capsule. The left eye was phakic with mild nuclear sclerosis. Fundus biomicroscopy of the right eye disclosed no Weiss's ring. There was a full-thickness macular hole estimated to be 350 μιτι in diameter with a surrounding cuff of detached retina of approximately 800 μπι in diameter (Fig. 3, left). A round opacity appeared to be suspended immediately anterior to the hole and was interpreted to be an operculum. Fundus examination of the left eye disclosed a normal fovea and no Weiss's ring. There was no operculum. Vitreous surgery was performed with retrieval of the operculum as described previously. Two months later visual acuity had improved to R.E.: 20/50 and the macular hole was no longer visible (Fig. 3, right).
RESULTS THE OPERCULUM FROM CASE 1 WAS APPROXIMATELY 270
μπι long (Fig. 4). Along most of one surface was a
Fig. 2 (Madreperla and associates). Case 1. Left, Large, full-thickness macular hole. Right, Postoperative appearance of healed macular hole. VOL.120, No. 2
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Fig. 3 (Madreperla and associates). Case 2. Left, Full-thickness macular hole (arrow) before treatment. Right, Normal-appearing macula without hole after treatment.
layer of native collagen with 11-nm fibrils (Figs. 5 and 6), which represented the attached cortical vitreous, thereby identifying the inner surface of the opercu-
lum. In only one folded area could definite internal limiting membrane of the retina be identified (circle in Figs. 4 and 7).
Fig. 4 (Madreperla and associates). Case 1. Composite, low-power view of operculum. Thicker, cellular ends are connected by a thinner segment. A thin coUagenous layer along this region (cortical vitreous) identifies the inner, vitreal surface (arrows) of the operculum. A short segment of internal limiting membrane (circle) is present in an area of folding (X550). 200
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Fig. 5 (Madreperla and associates). Case 1. Higher power view of thicker, end section of operculum (see Figure 4). A thin cortical vitreous layer is present on inner surface (arrow). A nucleus and numerous cell processes of Mueller cells are present (X2,500).
The operculum from Case 1 was nonuniform, with thicker ends connected by a thinner segment. A higher-power view of one of the thicker ends (Fig. 5) shows a nucleus and several cell processes, demonstrating the cellularity of the tissue. A higher-power view of the inner surface demonstrated the close association between the cell processes and the cortical vitreous (Fig. 6). No intervening internal limiting membrane of the retina was identified here. The cell processes displayed numerous profiles of smooth endoplasmic reticulum and prominent intercellular junctions, which are characteristic of Mueller cells. Only a small segment of internal limiting membrane of the retina was identified between the cortical vitreous and cellular processes (Fig. 7). Figure 8 demonstrates the two types of cells found in the VOL.120, No. 2
operculum from Case 1. Mueller cell processes displayed much smooth endoplasmic reticulum and prominent intercellular junctions (Fig. 8, top). Fibrous astrocytes with densely packed 10-nm, intermediate filaments and surrounding basement membrane were also present (Fig. 8, bottom). In only one area, a single cross section of a membrane-bound array of regularly arranged microtubules was noted and thought to represent a nerve fiber, but this was not a consistent feature of the operculum. The operculum from Case 2 was more regular in shape with a length of about 280 μηι and a uniform thickness of approximately 12 μιη (Fig. 9). Similar to that of Case 1, only one side had a layer of adjacent native collagen fibrils (cortical vitreous) identifying the internal surface of the operculum (Fig. 10). A
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Fig. 6 (Madreperla and associates). Higher power view of inner aspect of operculum of Case 1 with 11-nm thick collagen fibrils (asterisks). Processes of adjacent Mueller cells have much smooth endoplasmic reticulum (arrows) and some cell junctions (arrowheads) (X20,000).
higher-power view of the adjacent cell processes showed them to be filled with 10-nm, intermediate filaments, characteristic of fibrous astrocytes.
DISCUSSION WE OBSERVED TWO PATIENTS WHO HAD OPACITIES Suspended anterior to stage III macular holes that had the characteristics typically described for operculum. No definite membranous attachments to the operculum could be seen clinically, although they were assumed to be present because of the relative immobility of the operculum. Both patients underwent surgery as described, and each operculum was re-
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moved atraumatically with a specially designed instrument. During surgery, the operculum appeared tightly adherent to the cortical vitreous layer that was elevated from the surface of the retina in both cases. In both cases, histologie examination disclosed a thin layer of native collagen (cortical vitreous) adherent to one surface. We presumed this to represent the inner, or vitreal, surface of the operculum. Perhaps surprisingly, no area of either operculum had an arrangement of cells typical of retina. There were virtually no neural elements, and, although Mueller cell processes were present, they were not organized as would be expected in retinal tissue. Also, although cellular processes were tightly opposed to the cortical vitreous, there was generally absence of internal
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Fig. 7 (Madreperla and associates). Magnified views of folded area of operculum identified by circle in Figure 4 illustrate a segment of internal limiting membrane (arrows) and adjacent cortical vitreous (asterisk) (top, X 4,000; bottom, X 10,000).
limiting membrane of the retina. In the normal arrangement, internal limiting membrane would lie between cortical vitreous and Mueller cell processes. It seems that there are two possible explanations for the findings: it is either a true avulsion of retinal tissue or an avulsion of reparative tissue. As mentioned, a single nerve process was found in the operculum of
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Case 1, and, additionally, a small segment of internal limiting membrane was noted. These observations suggest that a small portion of the tissue can be identified as retina, per se. Lack of identifiable neural elements and typical retinal organization in the specimen might be the result of neuronal degeneration and glial hyperplasia occurring after detachment
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Fig. 8 (Madreperla and associates). The operculum from Case 1 consists of Mueller cell process (top) with abundant profiles of smooth endoplasmic reticulum (arrows) and intercellular junctions (arrowheads). Fibrous astrocyte processes (bottom) were present and were identified by large bundles of cytoplasmic 10-nm filaments (asterisk) and basement membrane (arrowheads) (top and bottom, X 40,000).
of the operculum from the surrounding retina. Neuronal processes might be expected to degenerate once detached from afferent and efferent connections. In this situation, we would also have to assume that the 204
internal limiting membrane of the retina degenerated nearly completely after formation of the operculum. Fibrous astrocytes and Mueller cells have been shown to be involved in the repair of experimental
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Fig. 9 (Madreperla and associates). Case 2. Low-power view of 12^m-thick operculum with numerous layers of interdigitating cell processes (X 12,000). retinal wounds17 without regeneration of the internal limiting membrane. In two postmortem studies of treated, healed macular holes, fibrous astrocytes and Mueller cells were involved in sealing the macular holes.1819 Finally, these cells have been identified in an epiretinal membrane that developed after successful closure of a macular hole, leading to reopening of the hole.20 The epiretinal membrane was postulated to result from the healing process, involving fibrous astrocytes and Mueller cells, gone awry. By analogy, a second interpretation of our data is that the majority of the operculum in both patients studied here VOL.
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represents the result of attempted (albeit eventually unsuccessful) healing. Indeed, in Case 1 the patient was followed up for more than one year from the time a probable small retinal dehiscence was noted, to the time a definite, classic stage III hole was found. Perhaps during the process of macular hole formation, fibrous astrocytes and Mueller cell proliferation and migration occurred, and this tissue was interpreted as the operculum. If this situation is true, then this tissue might be better termed a pseudo-operculum. The latter hypothesis fits with other clinical and histologie observations. For instance, a so-called
HiSTOLOGic CHARACTERISTICS OF MACULAR HOLE OPERCULUM
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Fig. 10 (Madreperla and associates). Case 2. Higher power view of internal margin of operculum with 10-nm native collagen fibrils (cortical vitreous) (arrow) along the internal surface and cell processes of fibrous astrocytes containing 10-nm filaments (asterisks) (x60,000). pseudo-operculum appears clinically similar to an operculum, except for the absence of an associated macular hole. That a pseudo-operculum represents a condensation of cortical vitreous816 seems an inadequate explanation, as no such condensation has been demonstrated histologically in the fovea. The cortical 206
vitreous and internal limiting membrane are thinnest in the fovea.21 A n alternate interpretation, on the basis of our observations, is that the process of aborted or successful macular hole formation (for example, a small retinal dehiscence) allows for fibrous astrocyte and Mueller cell proliferation and migra-
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tion. It is even possible that aborted macular hole formation actually represents successful repair of a small retinal
dehiscence
and
that
the
pseudo-
operculum represents excess glial tissue avulsed at the time of vitreofoveal separation. Such a situation is possible, because a healed retinal dehiscence would presumably be as undetectable, clinically, as treated macular holes are. Second, the actual size of the treated macular holes examined postmortem is less than 50 μπι.18,19 T h e pretreatment macular hole may appear as large as it does (approximately 500 μπι in diameter) because of inherent retinal elasticity, tangential traction, or both, but the piece of missing retinal tissue is much smaller. T h e opercula from both eyes studied by us were more than 200 μπι in diameter, much larger than the healed macular holes studied post mortem. Finally, in a recent, prospective, natural history study of patients with macular holes, the operculum was observed to reattach to the retina in three cases in which macular holes spontaneously closed after complete vitreofoveal separation.22 T h e authors speculated that these were stage II holes in which the flap of retina (the developing operculum) was reincorporated into the hole after vitreous traction was relieved. We find this difficult to understand because flap tears elsewhere in the retina do not behave in this way. We do find the observation interesting, however, and suggest that release of vitreous traction on the glial operculum (or pseudooperculum) could allow it to seal the macular hole. Our data do confirm the attachment of cortical vitreous to the tissue previously identified as an operculum, as suspected from clinical and intraoperative observations. However, these studies show that the operculum is composed largely of hyperplastic glial cells, rather than retina, per se. We cannot be certain from these data whether the findings are the result of secondary changes occurring after detachment of the operculum or whether the fibrous astrocytes and Mueller cells are actively involved during macular hole formation, perhaps in an attempt to seal the hole. O n the basis of previous studies,17'20 we favor the latter hypothesis over the former.
REFERENCES
2. Noyés HD. Detachment of the retina, with laceration of the macula lutea. Trans Am Ophthalmol Soc 1871;1:128-9. 3. Lister W. Holes in the retina and their clinical significance. Br J Ophthalmol 1924;8:1-5. 4. Morgan CM, Schatz H. Idiopathic macular holes. Am J Ophthalmol 1985;99:437-44. 5. McDonnell PJ, Fine SL, Hillis AI. Clinical features of idiopathic macular cysts and holes. Am J Ophthalmol 1982;93:777-86. 6. Kornzweig AL, Feldstein M. Studies of the eye in old age, II: hole in the macula: a clinical-pathologic study. Am J Ophthalmol 1950;33:243-7. 7. Trempe CL, Weiter JJ, Furukawa H. Fellow eyes in cases of macular hole: biomicroscopic study of the vitreous. Arch Ophthalmol 1986;104:93-5. 8. Gass JDM. Idiopathic senile macular hole: its early stages and pathogenesis. Arch Ophthalmol 1988;106:629-39. 9. Johnson RN, Gass JDM. Idiopathic macular holes: observations, stages of formation, and implications for surgical intervention. Ophthalmology 1988;95:917-24. 10. Guyer DR, Green WR. Idiopathic macular holes and precursor lesions. In: Franklin RM, editor. Proceedings of the symposium on retina and vitreous, New Orleans Academy of Ophthalmology, New Orleans. New York: Kugler Publications, 1993:135-62. 11. Dugel PU, Smiddy WE, Byrne SF, Hughes JR, Gass JDM. Macular hole syndromes: echographic findings with clinical correlation. Ophthalmology 1994;101:815-21. 12. Ogura Y, Shahidi M, Mori MT, Blair NP, Zeimer R. Improved visualization of macular hole lesions with laser biomicroscopy. Arch Ophthalmol 1991;109:957-61. 13. Avila MP, Jalkh AE, Murakami K, Trempe CL, Schepens CL. Biomicroscopic study of the vitreous in macular breaks. Ophthalmology 1983;90:1277-83. 14- Aaberg TM, Blair CJ, Gass JDM. Macular holes. Am J Ophthalmol 1970;69:555-62. 15. Gass JDM, Van Newkirk M. Xanthic scotoma and yellow foveolar shadow caused by a pseudo-operculum after vitreofoveal separation. Retina 1992;12:242-4. 16. Wiznia RA. Reversibility of the early stages of idiopathic macular holes. Am J Ophthalmol 1989;107:241-5. 17. Miller B, Miller H, Patterson R, Ryan SJ. Retinal wound healing: cellular activity at the vitreoretinal interface. Arch Ophthalmol 1986;104:281-5. 18. Funata M, Wendel RT, de la Cruz Z, Green WR. Clinicopathologic study of bilateral macular holes treated with pars plana vitrectomy and gas tamponade. Retina 1992;12:28998. 19. Madreperla SA, Geiger GL, Funata M, de la Cruz Z, Green WR. Clinicopathologic correlation of a macular hole treated by cortical vitreous peeling and gas tamponade. Ophthalmology 1994;101:682-6. 20. Fekrat S, Wendel RT, de la Cruz Z, Green WR. Clinicopathologic correlation of an epiretinal membrane associated with a recurrent macular hole. Retina 1995;15:53-7. 21. Foos RY. Vitreoretinal juncture: topographical variations. Invest Ophthalmol 1972;11:801-8. 22. Yuzawa M, Watanabe A, Takahashi Y, Matsui M. Observation of idiopathic full-thickness macular holes: follow-up observation. Arch Ophthalmol 1994;112:1051-6.
1. Kelly NE, Wendel RT. Vitreous surgery for idiopathic macular holes: results of a pilot study. Arch Ophthalmol 1991; 109:654-9. VOL.120, No. 2
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A
recognized that most macular holes occur in the absence of antecedent injury and are referred to as idiopathic. Theories for the pathogenesis of idiopathic macular holes have included progressive thinning of the foveal tissue4 and prehole cyst formation.5,6 A primary role for the vitreous was suggested by studies indicating a decrease in the relative risk for macular hole formation in eyes with complete posterior vitreous detachment.4,5·7 Gass8 and Johnson and Gass9 proposed a theory of idiopathic macular hole formation whereby shrinkage of adherent cortical vitreous first causes a circumscribed foveolar detachment (stage I) followed by early retinal dehiscence (stage II), then enlargement of the macular hole with vitreofoveal separation (stage III), and finally complete posterior vitreous detachment (stage IV). Guyer and Green 10 proposed the theory of tangential traction of the cortical vitreous by fluid movements. They proposed that, with enlargement of the premacular bursa and its continuity with the central area of vitreous, fluid countercurrents occurring with eye movements create tangential traction via the cortical vitreous at the fovea.
Accepted for publication Feb. 7, 1995. From the Duke Eye Center, Durham, North Carolina (Drs. Madreperla and McCuen and Mr. Hickingbotham); and the Wilmer Eye Institute, Baltimore, Maryland (Dr. Green). Dr. Madreperla was a 1993-94 Heed Ophthalmic Fellow. Reprint requests to W. R. Green, M.D., Eye Pathology Laboratory, Maumenee 427, Johns Hopkins Hospital, 600 N. Wolfe St., Baltimore, MD 21287-9278; fax: (410) 614-3457.
A n overlying opacity is sometimes seen in association with macular holes and, as such, has been termed an operculum, since it is thought to represent the tissue that once occupied the hole. It is not surprising that reports of the frequency of an associated operculum have varied widely (20% to 60%), as the operculum is often difficult to visualize clinically.4,7,9,11'15 Such an operculum, when observed just anterior to the plane of the macular hole, moves minimally with respect to the retina. Substantial evidence now suggests that the operculum at this time
• PURPOSE: To determine the ultrastructural characteristics of the operculum associated with macular holes. • METHODS: We developed instrumentation and a technique to capture the operculum observed with macular holes. Two opercula were studied by transmission electron microscopy. • RESULTS: The two specimens were attached to a layer of native collagen identified as cortical vitreous and were composed primarily of Mueller cells and fibrous astrocytes without adjacent inner limiting membrane. N o distinct retinal neuronal tissue was present. • CONCLUSIONS: Our findings indicate that proliferation of fibrous astrocytes and Mueller cells occurs with the formation of a macular hole, that this reparative tissue may be dislodged, and it is the reparative tissue that previously has been interpreted as an operculum. LTHOUGH MACULAR HOLES HAVE BEEN CONSIDered an untreatable condition, recent development of surgical approaches to improve vision after macular hole formation has led to renewed interest in this entity.1 Since the first description in 1871,2 the clinical characterization and theories on the pathogenesis of macular hole have continued to evolve. Although originally they were thought to be the result of trauma, 3 it is now
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(stage III according to Gass) is suspended by a thin layer of tapered cortical vitreous. This presumed vitreofoveal separation is often impossible to visualize with a slit lamp, but membranous attachments to the operculum can be visualized by ultrasonography.11 Interestingly, an opacity suspended just anterior to a normal appearing fovea, which is otherwise clinically indistinguishable from an operculum, has been termed a pseudo-operculum. Appearance of a pseudo-operculum has been documented after presumed aborted macular hole formation.16 Because of the absence of an associated retinal hole, these structures have been proposed to represent a condensation of cortical vitreous.816 To shed more light on this subject, we developed a method to remove safely and selectively tissue identified at macular hole surgery as an operculum and to examine the intact tissue by electron microscopy.
PATIENTS AND METHODS PATIENTS WITH STAGE III MACULAR HOLES WERE OPER-
ated on by using a modification of previously published techniques.1 Standard three-port vitrectomy was performed by using transscleral cannulas (Greishaber, Kennesaw, Georgia). A minimal core vitrectomy was performed with a light pipe and vitreous cutter. These instruments were exchanged for a lighted pick and a fiberoptic tissue manipulator (Greishaber, Kennesaw, Georgia) attached to manual suction. Suction was applied while the manipulator tip was held just anterior to the retina, temporal to the optic nerve head. The surgeon engaged a layer of nearly transparent tissue (presumed cortical vitreous) with the manipulator and gently lifted. Concurrently, the pick was used to enter the hole in the cortical vitreous corresponding to the space occupied by the optic disk, helping to elevate the cortical vitreous. As this layer was further elevated, the apparently attached operculum lifted with it. The operculum, attached to the cortical vitreous, was then suspended in the midvitreous cavity, and there was an adjacent hole in the cortical vitreous at the site corresponding to the optic disk. The vitreous cutter was used to enlarge the opening in the detached posterior hyaloid beginning through the hole in the cortical vitreous. 198
Fig. 1 (Madreperla and associates). View of cup-shaped jaws of microbiopsy forceps in open position.
The cutter was exchanged for specially designed microbiopsy forceps (Fig. 1). Coming from the space opened between the hole in the cortical vitreous and the operculum, the surgeon gently captured the operculum with the forceps without crushing the tissue. By coaxial illumination, the cortical vitreous was cut from around the biopsy forceps and the operculum was removed. The forceps and the operculum were immersed in 10% sucrose for 30 seconds and then placed in 2% buffered glutaraldehyde. The operation was completed by using the vitreous cutter to remove the remainder of the peripheral vitreous. A soft-tipped cannula was used to perform a fluid-air exchange. A drop of autologous serum was placed on the macular hole. The air was exchanged for 20% C3F8. Postoperatively, the patient maintained a facedown position until the gas bubble resorbed. After fixation for 24 hours, the operculum was removed from the microbiopsy forceps under a dissecting microscope and placed in 0.1 M sodium cacodylate, pH 7.6, then transferred to 1% tannic acid for 30 minutes. After being rinsed in sodium cacodylate, the tissue was transferred to 1% Os0 4 for 60 minutes, rinsed in H 2 0, and placed in 2% uranyl acetate overnight. After rinsing in H 2 0, the tissue was sequentially dehydrated in ethanol (50% to 100%), then infiltrated with and embedded in Araldite 506.
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CASE REPORTS • CASE l: A 72-year-old woman seen on Oct. 1, 1992, had visual acuity of R.E.: 20/400 secondary to a full-thickness macular hole. She had a one-month history of yellow-colored blurring in the left eye. Visual acuity was L.E.: 20/60. Examination disclosed an area of cystic-appearing retina centered at the fovea with a possible full-thickness defect at the nasal aspect of the lesion, which was thought to represent an early stage II macular hole. On return visit, April 15, 1993, six months after initial examination, visual acuity was L.E.: 20/70, and the retinal examination disclosed a slightly larger full-thickness retinal defect. No operculum was noted. The patient returned May 26, 1994, 13 months later, complaining of further decrease in vision. Visual acuity was L.E.: 20/80, and fundus examination disclosed a 700- μιη full-thickness macular hole with a surrounding cuff of subretinal fluid approximately 1,000 μιη in diameter (Fig. 2, left). An operculum was noted clinically. The patient underwent vitreous surgery on May 27, 1994, at which time a definite operculum was observed and retrieved. By July 25, 1994, the macular hole was closed, and visual acuity was 20/80 (Fig. 2, left). • CASE 2: A 66-year-old woman with a history of cataract extraction with intraocular lens placement in
the right eye five years and an Nd:YAG capsulotomy three years before the present examination had gradual but progressive decrease in visual acuity in her right eye during the one year before examination. On examination, visual acuity was R.E.: 20/80 and L.E.: 20/25. Slit-lamp examination of the right eye disclosed a posterior chamber intraocular lens with a central opening in the posterior capsule. The left eye was phakic with mild nuclear sclerosis. Fundus biomicroscopy of the right eye disclosed no Weiss's ring. There was a full-thickness macular hole estimated to be 350 μιτι in diameter with a surrounding cuff of detached retina of approximately 800 μπι in diameter (Fig. 3, left). A round opacity appeared to be suspended immediately anterior to the hole and was interpreted to be an operculum. Fundus examination of the left eye disclosed a normal fovea and no Weiss's ring. There was no operculum. Vitreous surgery was performed with retrieval of the operculum as described previously. Two months later visual acuity had improved to R.E.: 20/50 and the macular hole was no longer visible (Fig. 3, right).
RESULTS THE OPERCULUM FROM CASE 1 WAS APPROXIMATELY 270
μπι long (Fig. 4). Along most of one surface was a
Fig. 2 (Madreperla and associates). Case 1. Left, Large, full-thickness macular hole. Right, Postoperative appearance of healed macular hole. VOL.120, No. 2
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Fig. 3 (Madreperla and associates). Case 2. Left, Full-thickness macular hole (arrow) before treatment. Right, Normal-appearing macula without hole after treatment.
layer of native collagen with 11-nm fibrils (Figs. 5 and 6), which represented the attached cortical vitreous, thereby identifying the inner surface of the opercu-
lum. In only one folded area could definite internal limiting membrane of the retina be identified (circle in Figs. 4 and 7).
Fig. 4 (Madreperla and associates). Case 1. Composite, low-power view of operculum. Thicker, cellular ends are connected by a thinner segment. A thin coUagenous layer along this region (cortical vitreous) identifies the inner, vitreal surface (arrows) of the operculum. A short segment of internal limiting membrane (circle) is present in an area of folding (X550). 200
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Fig. 5 (Madreperla and associates). Case 1. Higher power view of thicker, end section of operculum (see Figure 4). A thin cortical vitreous layer is present on inner surface (arrow). A nucleus and numerous cell processes of Mueller cells are present (X2,500).
The operculum from Case 1 was nonuniform, with thicker ends connected by a thinner segment. A higher-power view of one of the thicker ends (Fig. 5) shows a nucleus and several cell processes, demonstrating the cellularity of the tissue. A higher-power view of the inner surface demonstrated the close association between the cell processes and the cortical vitreous (Fig. 6). No intervening internal limiting membrane of the retina was identified here. The cell processes displayed numerous profiles of smooth endoplasmic reticulum and prominent intercellular junctions, which are characteristic of Mueller cells. Only a small segment of internal limiting membrane of the retina was identified between the cortical vitreous and cellular processes (Fig. 7). Figure 8 demonstrates the two types of cells found in the VOL.120, No. 2
operculum from Case 1. Mueller cell processes displayed much smooth endoplasmic reticulum and prominent intercellular junctions (Fig. 8, top). Fibrous astrocytes with densely packed 10-nm, intermediate filaments and surrounding basement membrane were also present (Fig. 8, bottom). In only one area, a single cross section of a membrane-bound array of regularly arranged microtubules was noted and thought to represent a nerve fiber, but this was not a consistent feature of the operculum. The operculum from Case 2 was more regular in shape with a length of about 280 μηι and a uniform thickness of approximately 12 μιη (Fig. 9). Similar to that of Case 1, only one side had a layer of adjacent native collagen fibrils (cortical vitreous) identifying the internal surface of the operculum (Fig. 10). A
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Fig. 6 (Madreperla and associates). Higher power view of inner aspect of operculum of Case 1 with 11-nm thick collagen fibrils (asterisks). Processes of adjacent Mueller cells have much smooth endoplasmic reticulum (arrows) and some cell junctions (arrowheads) (X20,000).
higher-power view of the adjacent cell processes showed them to be filled with 10-nm, intermediate filaments, characteristic of fibrous astrocytes.
DISCUSSION WE OBSERVED TWO PATIENTS WHO HAD OPACITIES Suspended anterior to stage III macular holes that had the characteristics typically described for operculum. No definite membranous attachments to the operculum could be seen clinically, although they were assumed to be present because of the relative immobility of the operculum. Both patients underwent surgery as described, and each operculum was re-
202
moved atraumatically with a specially designed instrument. During surgery, the operculum appeared tightly adherent to the cortical vitreous layer that was elevated from the surface of the retina in both cases. In both cases, histologie examination disclosed a thin layer of native collagen (cortical vitreous) adherent to one surface. We presumed this to represent the inner, or vitreal, surface of the operculum. Perhaps surprisingly, no area of either operculum had an arrangement of cells typical of retina. There were virtually no neural elements, and, although Mueller cell processes were present, they were not organized as would be expected in retinal tissue. Also, although cellular processes were tightly opposed to the cortical vitreous, there was generally absence of internal
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Fig. 7 (Madreperla and associates). Magnified views of folded area of operculum identified by circle in Figure 4 illustrate a segment of internal limiting membrane (arrows) and adjacent cortical vitreous (asterisk) (top, X 4,000; bottom, X 10,000).
limiting membrane of the retina. In the normal arrangement, internal limiting membrane would lie between cortical vitreous and Mueller cell processes. It seems that there are two possible explanations for the findings: it is either a true avulsion of retinal tissue or an avulsion of reparative tissue. As mentioned, a single nerve process was found in the operculum of
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Case 1, and, additionally, a small segment of internal limiting membrane was noted. These observations suggest that a small portion of the tissue can be identified as retina, per se. Lack of identifiable neural elements and typical retinal organization in the specimen might be the result of neuronal degeneration and glial hyperplasia occurring after detachment
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Fig. 8 (Madreperla and associates). The operculum from Case 1 consists of Mueller cell process (top) with abundant profiles of smooth endoplasmic reticulum (arrows) and intercellular junctions (arrowheads). Fibrous astrocyte processes (bottom) were present and were identified by large bundles of cytoplasmic 10-nm filaments (asterisk) and basement membrane (arrowheads) (top and bottom, X 40,000).
of the operculum from the surrounding retina. Neuronal processes might be expected to degenerate once detached from afferent and efferent connections. In this situation, we would also have to assume that the 204
internal limiting membrane of the retina degenerated nearly completely after formation of the operculum. Fibrous astrocytes and Mueller cells have been shown to be involved in the repair of experimental
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Fig. 9 (Madreperla and associates). Case 2. Low-power view of 12^m-thick operculum with numerous layers of interdigitating cell processes (X 12,000). retinal wounds17 without regeneration of the internal limiting membrane. In two postmortem studies of treated, healed macular holes, fibrous astrocytes and Mueller cells were involved in sealing the macular holes.1819 Finally, these cells have been identified in an epiretinal membrane that developed after successful closure of a macular hole, leading to reopening of the hole.20 The epiretinal membrane was postulated to result from the healing process, involving fibrous astrocytes and Mueller cells, gone awry. By analogy, a second interpretation of our data is that the majority of the operculum in both patients studied here VOL.
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represents the result of attempted (albeit eventually unsuccessful) healing. Indeed, in Case 1 the patient was followed up for more than one year from the time a probable small retinal dehiscence was noted, to the time a definite, classic stage III hole was found. Perhaps during the process of macular hole formation, fibrous astrocytes and Mueller cell proliferation and migration occurred, and this tissue was interpreted as the operculum. If this situation is true, then this tissue might be better termed a pseudo-operculum. The latter hypothesis fits with other clinical and histologie observations. For instance, a so-called
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Fig. 10 (Madreperla and associates). Case 2. Higher power view of internal margin of operculum with 10-nm native collagen fibrils (cortical vitreous) (arrow) along the internal surface and cell processes of fibrous astrocytes containing 10-nm filaments (asterisks) (x60,000). pseudo-operculum appears clinically similar to an operculum, except for the absence of an associated macular hole. That a pseudo-operculum represents a condensation of cortical vitreous816 seems an inadequate explanation, as no such condensation has been demonstrated histologically in the fovea. The cortical 206
vitreous and internal limiting membrane are thinnest in the fovea.21 A n alternate interpretation, on the basis of our observations, is that the process of aborted or successful macular hole formation (for example, a small retinal dehiscence) allows for fibrous astrocyte and Mueller cell proliferation and migra-
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tion. It is even possible that aborted macular hole formation actually represents successful repair of a small retinal
dehiscence
and
that
the
pseudo-
operculum represents excess glial tissue avulsed at the time of vitreofoveal separation. Such a situation is possible, because a healed retinal dehiscence would presumably be as undetectable, clinically, as treated macular holes are. Second, the actual size of the treated macular holes examined postmortem is less than 50 μπι.18,19 T h e pretreatment macular hole may appear as large as it does (approximately 500 μπι in diameter) because of inherent retinal elasticity, tangential traction, or both, but the piece of missing retinal tissue is much smaller. T h e opercula from both eyes studied by us were more than 200 μπι in diameter, much larger than the healed macular holes studied post mortem. Finally, in a recent, prospective, natural history study of patients with macular holes, the operculum was observed to reattach to the retina in three cases in which macular holes spontaneously closed after complete vitreofoveal separation.22 T h e authors speculated that these were stage II holes in which the flap of retina (the developing operculum) was reincorporated into the hole after vitreous traction was relieved. We find this difficult to understand because flap tears elsewhere in the retina do not behave in this way. We do find the observation interesting, however, and suggest that release of vitreous traction on the glial operculum (or pseudooperculum) could allow it to seal the macular hole. Our data do confirm the attachment of cortical vitreous to the tissue previously identified as an operculum, as suspected from clinical and intraoperative observations. However, these studies show that the operculum is composed largely of hyperplastic glial cells, rather than retina, per se. We cannot be certain from these data whether the findings are the result of secondary changes occurring after detachment of the operculum or whether the fibrous astrocytes and Mueller cells are actively involved during macular hole formation, perhaps in an attempt to seal the hole. O n the basis of previous studies,17'20 we favor the latter hypothesis over the former.
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