ACTA O P H T H A L M O L O G I C A VOL. 5 4 1 9 7 6
The Department
of Ophthalmology (Head: E. Linnkr), University of GGteborg, Sweden
THE EPIPAPILLARY MEMBRANE AND THE GLAUCOMATOUS OPTIC DISC BY
TORD JERNDAL
The frequent presence of an epipapillary membrane as a glial covering of the optic disc is a common source of error when evaluating the cupping of the optic disc in glaucoma. Four instructive cases are documented with colour photographs and field charts.
Key words: optic disc - cup/disc ratio - glaucoma - glaucomatous cupping - glaucomatous field defect - congenital anomalies - Bergmeister membrane - epipapillary membrane.
I n 1877 Bergmeister described a glial membrane a t the optic nerve head of the rabbit embryo (Fig. 1) a n d this structure is of current interest in the evaluation of glaucomatous cupping of t h e optic disc. According to Seefelder (1910) the glial covering of the optic disc in adult humans is a rudiment of the fetal glial coating of the disc described by Bergmeister. Therefore it is called t h e Bergmeister membrane in t h e following text. This term is chosen to point out its relationship to the fetal Bergmeister papilla and to strees its congenital nature. A s the hyaloid vascular system involutes a n d normally disappears in the 8-9th Received January 3, 1976. 185
Tord Jerndal
5
7 Fig. 1. Schematic illustration of a section through the ocular anlage of a rabbit, 18 days of fetal age. Re-drawn after Bergmeister (1877). 1. Outer layer of optic cup. 2. Inner layer of optic cup. 3. Lens. 4. Rim of optic cup. 5. Hyaloid vascular cup. 6. Optic stalk. 7. Fetal optic papilla. 8. Cylindric cell layer (future Bergmeister membrane).
A
B
Fig. 2. Fig. 2A. Late fluorescence pattern (36 seconds after injection) of the optic disc and the peripapillary region. The bright fluorescence of the temporal part is in strong contrast to the nasal part, where a Bergmeister membrane is situated. At the peripapillary border between 8 and 12 o’clock a crescentic area of fluorescence is apparent outside the membrane. Fig. 2B. Still later phase of the same sequence (44 seconds after injection). T h e fluorescence has subsided but the outline of the Bergmeister membrane is still clearly seen as a darker covering of the nasal optic disc. (Reproduced with permission from “Fluoreszenzangiographie der Retina” by Achim Wessing 1968. Georg Thieme, Stuttgart, West Germany). 186
Epipn@illary Membrane
Fig. 3.
Schematic drawing ol central horizontal section through a glaucomatous optic disc. The marginal cupping is evident on the left (temporal) side but concealed by the Bergmeister membrane on the right (nasal) side. 1. Apparent cupping of the disc. 2. Bergmeister's membrane supported by arterial branch. 3. Nerve fiber layer of the retina. 4. Choroid. 5 . Sclera. 6. Cribriform plate. 7. Dural sheath of optic nerve.
fetal month, the glial remnants form epipapillary strand or membranes usually confined to the optic disc, and particularly the nasal half (Samuels 1931). This involutional process is not terminated until after birth. Therefore the optic nerve head of the newborn displays a dull glial surface of greyish appearance, sometimes without a clearcut central cupping. In the adult eye discrete glial sheaths are usually seen around the arteries on the disc and rarely also in the immediately peripapillary area. A close relationship of the glial sheaths to the retinal arteries is natural in view of the common origin of the hyaloid and the retinal arteries.
Surface of the Normal Optic Disc The surface of the adult optic disc is to a variable extent covered by a layer of glia (astrocytes) forming the Bergmeister membrane which at the edge of the disc tapers off into the internal limiting membrane (Samuels 1931). The physiological excavation and the temporal half of the disc is practically free from the Bergmeister membrane. Roth & Foos (1972) in a post-mortem material of 504 eyes, found on gross examination epipapillary glial membranes in 139 (27.6 O/O) and thus confirmed the findings of Samuels (1931). The epipapillary membrane was mainly situated on the nasal and nasoinferior aspect of the nerve head and seemed to disappear gradually toward the optic cup. Histological verification of the gross observation was obtained in 33 eyes of 34 (Roth & Foss 1972). The membrane consisted of 187
4A
5A
5B
6A
6B
7A
8A
188
Efiipapillary Membrane Fig. 4. Case 1, I. A. Female, age 54. Exfoliation glaucoma, 0. D. was diagnosed at 53. On first examination IOP was 56 mm by applanation and a grave defect was found in the superior nasal visual field. A succesful trabeculectomy normalized the IOP. The optic disc 0. D. is seen in Fig. 4A. The excavation is more pronounced inferiorly and the arteries are CUNed along the nasal aspect of the cup. A grey glial sheath surround the central stem of the arteries and conceals the nasal undermining. An annular membrane of greyish orange encircles the periphery of the disc and mingles with the arterial sheath. Also on the superior aspect of the paracentral disc is a thinner glial membrane, best seen with biomicroscopy. suspended between the fine arteries running across the disc and its superior edge. Comment: The glial structure described mask the true extent of the excavation but a slit-lamp microscopy revealed the pathologic anatomy. Visual field shown in Fig. 48. Fig. 5. Case 1. I. A. The nonglaucomatous disc of 0. S. is seen in Fig. 5A, and the corresponding field in Fig. 58. The tiny excavation is central and demarcated by an annular Bergmeister membrane of orange colour. A fine arterial branch is actually outlining the superior rim of the excavation. (Biomicroscopic ObSeNatiOn). Comment: The appearance of the right optic disc (Fig. 4A) would hardly have been associated with grave field defect had not the extension of the treacherous Bergmeister membrane been identified. Fig. 6. Case 2 , N. P. Male age 59. Chronic narrow angle glaucoma was diagnosed at 54 with moderately impaired visual function of 0. S. Because of recurring peaks of IOP a trabeculectomy was performed on this eye. The optic disc of 0. S. is seen in Fig. 6A. The disc is pale and has a distinctly marginal excavation on the temporal aspect. The true width of the excavation is very difficult to assess, because of an impressive glial membrane which covers the nasal third of the disc and ends abruptly with a sharp concave margin in the arterial bifurcation. The Bergmeister membrane is supported by several arterial branches and is thereby suspended at a considerable distance from the bottom of the excavation. (Biomicroscopic ObSeNatiOn). The membrane in this case is greyish yellow and thick enough to conceal the entry of the retinal vessels. The excavation is an extreme example of the "vertically oval cup" described by Kirsch and Anderson (1973). The visual field is demonstrated in Fig. 66. The true condition of the optic nerve head was established on slitlamp microscopy: a 3600 marginal cupping with a probable nasal undermining. Comment: The presence of a thick Bergmeister membrane covering the nasal third of the optic disc obscured the severity of the glaucomatous cupping. Fig. 7 . Case 3 , A. 0. Male, age 60. Bilateral late congenital glaucoma was diagnosed at 57. 0. S. was blind since childhood due to multiple malformation: microcornea, goniodysgenesis and coloboma of the iris with complicated cataract, glaucoma and retinal detachment. 0. D. displayed typical goniodysgenesis and a minute choroidal coloboma. IOP between 18 and 22 mm by applanation on miotics and epinephrine. Very slow progress of a superior Bjerrum scotoma. The optic disc of 0. D. is seen in Fig. 7A. The entire disc is covered by a continuous glial membrane as seen with the microscope. No excavation can be identified, but a deeper orange colour of the disc nasal to the vessels is observed. The nasal position of the vascular tree suggests the possibility of a glaucomatous excavation underneath the membrane. The glial covering of the margin in the 7 o'clock position is thin enough to let back lumps of choroidal pigment shimmer through. An inferior peripapillary halo is seen as well as the minute choroidal coloboma at 6 o'clock. The visual field is demonstrated in Fig. 88. Comment: Maldeveloped eye with complete covering of the disc by the Bergmeister membrane. Impossible to evaluate the true excavation of the disc in spite of a growing Bjerrum scotoma. Fig. 8. Case 4, M. M. Female, age 61. Dominant late congenital glaucoma 0. U. was diagnosed at 53 and topical treatment was started. Because of uncontrolled tension in the forties, trabeculectomy was performed bilaterally at 59 with lasting control of tension. The ophthalmoscopic appearance of the optic disc 0. S. (Fig. 8A) is "completely normal" with a tiny central excavation and good colour. The colour is of the deep orange hue, however, and a closer microscopic look will reveal an annular concave membraneous cover of the disc. Comment: Once again it is helpful to study the fine arterial branches which suspend the membrane over the excavation of the disc. The characteristic arcuate scotomas found on perimetry 0. S. (Fig. 86) were at first a surprise in view of the "normal" appearance of the optic disc.
189
Tord Jerndal
one or several layers of flattened glial cells constituting a tenuous covering, or rarely, a heavy sheet. I n addition, 29 eyes without any evidence of gross epipapillary membranes were examined and on histological examination 5 of these did show a membrane. These membranes were more tenuous than those which had been observed microscopically, but were otherwise identical. The Bergmeister membrane is often fairly distinct in the shape of a nasal crescent or a n annular meniscus (personal observation) and as a rule carries small arteries radiating from the center of the disc. T h e colour of this membrane is more greyish orange than the “normal appearance” of the disc with its rosy pink hue. There is another subtle characteristic of the membrane which is appreciable by ophthalmoscopy, but is best demonstrated by slit-lamp biomicroscopy. This sign is the “sandy dry” character of the surface of the membrane or a reduced translucency of the surface when illuminated with a narrow slit. The different appearance of the nasal half of the disc compared with the temporal one is also demonstrated by fluorescence papillography (Fig. 2). The fine vessels and diffuse fluorescence of the true surface of the nasal disc are mainly concealed by the Bergmeister membrane.
The Glaucomatous Optic Disc The optic disc in a glaucomatous eye undergoes a characteristic, gradual atrophy due to a chronic relative ischemia (for review see Hayreh 1974). This vascular disturbance is beleived to cause an initially reversible but eventually irreversible damage of the axons in front of the lamina cribosa. If the glaucoma is uncontrolled, a successive degeneration of axons will occur with a resulting loss of nerve tissue in the prelaminar area. I n glaucoma the astroglial membrane of Bergmeister does not always participate in the atrophic cupping of the optic nerve head. So, in many eyes of advanced glaucoma with a marginal or even undermined cupping, a sickle-shaped edge of the Bergmeister membrane is seen. As a rule it is most evident on the nasal aspect of the disc and as a sheathing of the arteries (Fig. 3).
Case Reports Given in legends to Figs. 4-8 on spread with colour plates and field charts.
Discussion Much has been written on the size and shape of the glaucomatous cupping without due consideration to the Bergmeister membrane which is obviously little, 190
Efiipapillary Membrane
if at all, affected by the advancing glaucomatous atrophy of the disc. The most likely reason for the resistance of this membrane to the ischemic degeneration of the optic nerve head is the dual vascularization of this area. ? h e degenerating axons in the prelaminar area are served by the vulnerable choroidal vascular bed which is more easily disturbed by an elevated IOP (Hayreh 1974). The Bergmeister membrane, on the other hand, is vascularized by the hyaloid-retinal circulation. The recognition of the epipapillary membrane on the glaucomatous optic disc is a finding of great practical significance. The cup/disc ratio or the volume of the cup becomes a poor measure of the health condition of the optic disc if a study glial lid is masking a rodent excavation underneath. This pitfall is clearly demonstrated by the case reports presented. T h e vertically oval shape of the glaucomatous cupping reported by Kirsch & Anderson (1973) is interpreted by me as due to a Bergmeister membrane covering the nasal part of the disc. I n spite of their astute observations, however, these authors did not express their recognition of this anatomic structure. The difference in coloration between the nasal and the temporal half of the optic disc on ophthalmoscopic examination has recently been studied by Hayreh (1972). H e demonstrated that the relatively pale temporal half of the disc was paradoxically more vascular than the nasal half as judged by fluorescence angiography. The pale impression on ophthalmoscopy was explained by a more abundant glial tissue in the temporal part of the disc, since according to Hayreh, glial tissue is opaque on ophthalmoscopy but transparent on fluorescence angiography. T h e statement by Hayreh that glial tissue (unspecified) is transparent to fluorescent light a t first contradicts the observations that the Bergmeister glial membrane may extinguish fluorescence from the corresponding nasal part of the optic disc (Fig. 2). On closer study, however, these findings are not opposed to one another. Hayreh evidently describes only the “deeper” prelaminar glial structures in the nerve head but not the superficial membrane of Bergmeister. Furthermore, he has not made a clear distinction between congenital and proliferative glial tissue. In Hayreh’s case (1972) showing glial proliferation with “glial veils in front of the retina”, the histological picture is most likely one of combined mesenchymal and glial proliferation with a preponderance of the former.
Conclusion A n epipapillary glial membrane - the Bergmeister membrane - situated on the nasal aspect of the optic disc is a normal finding on ophthalmoscopy, but 191
Tord Jerndal
is best studied with slit-lamp microscopy. I n advancing glaucoma this membrane may fail to share the degree of atrophy of the underlying axonal tissue, as demonstrated by the four presented cases. Thus, the presence of a Bergmeister membrane will often mask the development of the glaucomatous cupping and may even simulate a normal cup in moderately advanced glaucoma by reflecting a falsely low cup/disc ratio. Therefore in the presence of a dubious excavation, a slit-lamp biomicroscopic examination becomes necessary for a proper evaluation of the glaucomatous cupping.
References Bergmeister 0. (1877) Entwicklungsgeschichte des Saugetier-Auges. Mitteilzingen aus dem embryologischen Institute, Wien, H e f t I , 64-89. Hayreh S. S. (1974) Pathogenesis of cupping of the optic disc. Brit. J. Ophthal. 58, 863-876. Hayreh S. S. (1972) Colour and fluorescence of the optic disc. Ophthalmologica 165, 1 00-1 08. Kirsch R. E. & Anderson D. R. (1973) Clinical recognition of glaucomatous cupping. Amer. J . Ophthal. 75, 442-454. Roth A. M. & Foos R. Y. (1972) Surface structure of the optic nerve head. 1 . Epipapillary membranes. Amer. J . Ophthal. 7 4 , 977-985. Samuels B. (1931) Epipapillary tissues. Arch. Ophthal. 6, 704-723. Seefelder R. (1910) Beitrage zur Histogenese und Histologie der Netzhaut des Pigmentepithels und des Sehnerves. Graefes Arch. Ophthal. 73, 419-537.
Author’s address: Tord Jerndal, M.D., Ugonkliniken, Sahlgrenska sjukhuset, S-413 45 Goteborg, Sweden.
192
The Department
of Ophthalmology (Head: E. Linnkr), University of GGteborg, Sweden
THE EPIPAPILLARY MEMBRANE AND THE GLAUCOMATOUS OPTIC DISC BY
TORD JERNDAL
The frequent presence of an epipapillary membrane as a glial covering of the optic disc is a common source of error when evaluating the cupping of the optic disc in glaucoma. Four instructive cases are documented with colour photographs and field charts.
Key words: optic disc - cup/disc ratio - glaucoma - glaucomatous cupping - glaucomatous field defect - congenital anomalies - Bergmeister membrane - epipapillary membrane.
I n 1877 Bergmeister described a glial membrane a t the optic nerve head of the rabbit embryo (Fig. 1) a n d this structure is of current interest in the evaluation of glaucomatous cupping of t h e optic disc. According to Seefelder (1910) the glial covering of the optic disc in adult humans is a rudiment of the fetal glial coating of the disc described by Bergmeister. Therefore it is called t h e Bergmeister membrane in t h e following text. This term is chosen to point out its relationship to the fetal Bergmeister papilla and to strees its congenital nature. A s the hyaloid vascular system involutes a n d normally disappears in the 8-9th Received January 3, 1976. 185
Tord Jerndal
5
7 Fig. 1. Schematic illustration of a section through the ocular anlage of a rabbit, 18 days of fetal age. Re-drawn after Bergmeister (1877). 1. Outer layer of optic cup. 2. Inner layer of optic cup. 3. Lens. 4. Rim of optic cup. 5. Hyaloid vascular cup. 6. Optic stalk. 7. Fetal optic papilla. 8. Cylindric cell layer (future Bergmeister membrane).
A
B
Fig. 2. Fig. 2A. Late fluorescence pattern (36 seconds after injection) of the optic disc and the peripapillary region. The bright fluorescence of the temporal part is in strong contrast to the nasal part, where a Bergmeister membrane is situated. At the peripapillary border between 8 and 12 o’clock a crescentic area of fluorescence is apparent outside the membrane. Fig. 2B. Still later phase of the same sequence (44 seconds after injection). T h e fluorescence has subsided but the outline of the Bergmeister membrane is still clearly seen as a darker covering of the nasal optic disc. (Reproduced with permission from “Fluoreszenzangiographie der Retina” by Achim Wessing 1968. Georg Thieme, Stuttgart, West Germany). 186
Epipn@illary Membrane
Fig. 3.
Schematic drawing ol central horizontal section through a glaucomatous optic disc. The marginal cupping is evident on the left (temporal) side but concealed by the Bergmeister membrane on the right (nasal) side. 1. Apparent cupping of the disc. 2. Bergmeister's membrane supported by arterial branch. 3. Nerve fiber layer of the retina. 4. Choroid. 5 . Sclera. 6. Cribriform plate. 7. Dural sheath of optic nerve.
fetal month, the glial remnants form epipapillary strand or membranes usually confined to the optic disc, and particularly the nasal half (Samuels 1931). This involutional process is not terminated until after birth. Therefore the optic nerve head of the newborn displays a dull glial surface of greyish appearance, sometimes without a clearcut central cupping. In the adult eye discrete glial sheaths are usually seen around the arteries on the disc and rarely also in the immediately peripapillary area. A close relationship of the glial sheaths to the retinal arteries is natural in view of the common origin of the hyaloid and the retinal arteries.
Surface of the Normal Optic Disc The surface of the adult optic disc is to a variable extent covered by a layer of glia (astrocytes) forming the Bergmeister membrane which at the edge of the disc tapers off into the internal limiting membrane (Samuels 1931). The physiological excavation and the temporal half of the disc is practically free from the Bergmeister membrane. Roth & Foos (1972) in a post-mortem material of 504 eyes, found on gross examination epipapillary glial membranes in 139 (27.6 O/O) and thus confirmed the findings of Samuels (1931). The epipapillary membrane was mainly situated on the nasal and nasoinferior aspect of the nerve head and seemed to disappear gradually toward the optic cup. Histological verification of the gross observation was obtained in 33 eyes of 34 (Roth & Foss 1972). The membrane consisted of 187
4A
5A
5B
6A
6B
7A
8A
188
Efiipapillary Membrane Fig. 4. Case 1, I. A. Female, age 54. Exfoliation glaucoma, 0. D. was diagnosed at 53. On first examination IOP was 56 mm by applanation and a grave defect was found in the superior nasal visual field. A succesful trabeculectomy normalized the IOP. The optic disc 0. D. is seen in Fig. 4A. The excavation is more pronounced inferiorly and the arteries are CUNed along the nasal aspect of the cup. A grey glial sheath surround the central stem of the arteries and conceals the nasal undermining. An annular membrane of greyish orange encircles the periphery of the disc and mingles with the arterial sheath. Also on the superior aspect of the paracentral disc is a thinner glial membrane, best seen with biomicroscopy. suspended between the fine arteries running across the disc and its superior edge. Comment: The glial structure described mask the true extent of the excavation but a slit-lamp microscopy revealed the pathologic anatomy. Visual field shown in Fig. 48. Fig. 5. Case 1. I. A. The nonglaucomatous disc of 0. S. is seen in Fig. 5A, and the corresponding field in Fig. 58. The tiny excavation is central and demarcated by an annular Bergmeister membrane of orange colour. A fine arterial branch is actually outlining the superior rim of the excavation. (Biomicroscopic ObSeNatiOn). Comment: The appearance of the right optic disc (Fig. 4A) would hardly have been associated with grave field defect had not the extension of the treacherous Bergmeister membrane been identified. Fig. 6. Case 2 , N. P. Male age 59. Chronic narrow angle glaucoma was diagnosed at 54 with moderately impaired visual function of 0. S. Because of recurring peaks of IOP a trabeculectomy was performed on this eye. The optic disc of 0. S. is seen in Fig. 6A. The disc is pale and has a distinctly marginal excavation on the temporal aspect. The true width of the excavation is very difficult to assess, because of an impressive glial membrane which covers the nasal third of the disc and ends abruptly with a sharp concave margin in the arterial bifurcation. The Bergmeister membrane is supported by several arterial branches and is thereby suspended at a considerable distance from the bottom of the excavation. (Biomicroscopic ObSeNatiOn). The membrane in this case is greyish yellow and thick enough to conceal the entry of the retinal vessels. The excavation is an extreme example of the "vertically oval cup" described by Kirsch and Anderson (1973). The visual field is demonstrated in Fig. 66. The true condition of the optic nerve head was established on slitlamp microscopy: a 3600 marginal cupping with a probable nasal undermining. Comment: The presence of a thick Bergmeister membrane covering the nasal third of the optic disc obscured the severity of the glaucomatous cupping. Fig. 7 . Case 3 , A. 0. Male, age 60. Bilateral late congenital glaucoma was diagnosed at 57. 0. S. was blind since childhood due to multiple malformation: microcornea, goniodysgenesis and coloboma of the iris with complicated cataract, glaucoma and retinal detachment. 0. D. displayed typical goniodysgenesis and a minute choroidal coloboma. IOP between 18 and 22 mm by applanation on miotics and epinephrine. Very slow progress of a superior Bjerrum scotoma. The optic disc of 0. D. is seen in Fig. 7A. The entire disc is covered by a continuous glial membrane as seen with the microscope. No excavation can be identified, but a deeper orange colour of the disc nasal to the vessels is observed. The nasal position of the vascular tree suggests the possibility of a glaucomatous excavation underneath the membrane. The glial covering of the margin in the 7 o'clock position is thin enough to let back lumps of choroidal pigment shimmer through. An inferior peripapillary halo is seen as well as the minute choroidal coloboma at 6 o'clock. The visual field is demonstrated in Fig. 88. Comment: Maldeveloped eye with complete covering of the disc by the Bergmeister membrane. Impossible to evaluate the true excavation of the disc in spite of a growing Bjerrum scotoma. Fig. 8. Case 4, M. M. Female, age 61. Dominant late congenital glaucoma 0. U. was diagnosed at 53 and topical treatment was started. Because of uncontrolled tension in the forties, trabeculectomy was performed bilaterally at 59 with lasting control of tension. The ophthalmoscopic appearance of the optic disc 0. S. (Fig. 8A) is "completely normal" with a tiny central excavation and good colour. The colour is of the deep orange hue, however, and a closer microscopic look will reveal an annular concave membraneous cover of the disc. Comment: Once again it is helpful to study the fine arterial branches which suspend the membrane over the excavation of the disc. The characteristic arcuate scotomas found on perimetry 0. S. (Fig. 86) were at first a surprise in view of the "normal" appearance of the optic disc.
189
Tord Jerndal
one or several layers of flattened glial cells constituting a tenuous covering, or rarely, a heavy sheet. I n addition, 29 eyes without any evidence of gross epipapillary membranes were examined and on histological examination 5 of these did show a membrane. These membranes were more tenuous than those which had been observed microscopically, but were otherwise identical. The Bergmeister membrane is often fairly distinct in the shape of a nasal crescent or a n annular meniscus (personal observation) and as a rule carries small arteries radiating from the center of the disc. T h e colour of this membrane is more greyish orange than the “normal appearance” of the disc with its rosy pink hue. There is another subtle characteristic of the membrane which is appreciable by ophthalmoscopy, but is best demonstrated by slit-lamp biomicroscopy. This sign is the “sandy dry” character of the surface of the membrane or a reduced translucency of the surface when illuminated with a narrow slit. The different appearance of the nasal half of the disc compared with the temporal one is also demonstrated by fluorescence papillography (Fig. 2). The fine vessels and diffuse fluorescence of the true surface of the nasal disc are mainly concealed by the Bergmeister membrane.
The Glaucomatous Optic Disc The optic disc in a glaucomatous eye undergoes a characteristic, gradual atrophy due to a chronic relative ischemia (for review see Hayreh 1974). This vascular disturbance is beleived to cause an initially reversible but eventually irreversible damage of the axons in front of the lamina cribosa. If the glaucoma is uncontrolled, a successive degeneration of axons will occur with a resulting loss of nerve tissue in the prelaminar area. I n glaucoma the astroglial membrane of Bergmeister does not always participate in the atrophic cupping of the optic nerve head. So, in many eyes of advanced glaucoma with a marginal or even undermined cupping, a sickle-shaped edge of the Bergmeister membrane is seen. As a rule it is most evident on the nasal aspect of the disc and as a sheathing of the arteries (Fig. 3).
Case Reports Given in legends to Figs. 4-8 on spread with colour plates and field charts.
Discussion Much has been written on the size and shape of the glaucomatous cupping without due consideration to the Bergmeister membrane which is obviously little, 190
Efiipapillary Membrane
if at all, affected by the advancing glaucomatous atrophy of the disc. The most likely reason for the resistance of this membrane to the ischemic degeneration of the optic nerve head is the dual vascularization of this area. ? h e degenerating axons in the prelaminar area are served by the vulnerable choroidal vascular bed which is more easily disturbed by an elevated IOP (Hayreh 1974). The Bergmeister membrane, on the other hand, is vascularized by the hyaloid-retinal circulation. The recognition of the epipapillary membrane on the glaucomatous optic disc is a finding of great practical significance. The cup/disc ratio or the volume of the cup becomes a poor measure of the health condition of the optic disc if a study glial lid is masking a rodent excavation underneath. This pitfall is clearly demonstrated by the case reports presented. T h e vertically oval shape of the glaucomatous cupping reported by Kirsch & Anderson (1973) is interpreted by me as due to a Bergmeister membrane covering the nasal part of the disc. I n spite of their astute observations, however, these authors did not express their recognition of this anatomic structure. The difference in coloration between the nasal and the temporal half of the optic disc on ophthalmoscopic examination has recently been studied by Hayreh (1972). H e demonstrated that the relatively pale temporal half of the disc was paradoxically more vascular than the nasal half as judged by fluorescence angiography. The pale impression on ophthalmoscopy was explained by a more abundant glial tissue in the temporal part of the disc, since according to Hayreh, glial tissue is opaque on ophthalmoscopy but transparent on fluorescence angiography. T h e statement by Hayreh that glial tissue (unspecified) is transparent to fluorescent light a t first contradicts the observations that the Bergmeister glial membrane may extinguish fluorescence from the corresponding nasal part of the optic disc (Fig. 2). On closer study, however, these findings are not opposed to one another. Hayreh evidently describes only the “deeper” prelaminar glial structures in the nerve head but not the superficial membrane of Bergmeister. Furthermore, he has not made a clear distinction between congenital and proliferative glial tissue. In Hayreh’s case (1972) showing glial proliferation with “glial veils in front of the retina”, the histological picture is most likely one of combined mesenchymal and glial proliferation with a preponderance of the former.
Conclusion A n epipapillary glial membrane - the Bergmeister membrane - situated on the nasal aspect of the optic disc is a normal finding on ophthalmoscopy, but 191
Tord Jerndal
is best studied with slit-lamp microscopy. I n advancing glaucoma this membrane may fail to share the degree of atrophy of the underlying axonal tissue, as demonstrated by the four presented cases. Thus, the presence of a Bergmeister membrane will often mask the development of the glaucomatous cupping and may even simulate a normal cup in moderately advanced glaucoma by reflecting a falsely low cup/disc ratio. Therefore in the presence of a dubious excavation, a slit-lamp biomicroscopic examination becomes necessary for a proper evaluation of the glaucomatous cupping.
References Bergmeister 0. (1877) Entwicklungsgeschichte des Saugetier-Auges. Mitteilzingen aus dem embryologischen Institute, Wien, H e f t I , 64-89. Hayreh S. S. (1974) Pathogenesis of cupping of the optic disc. Brit. J. Ophthal. 58, 863-876. Hayreh S. S. (1972) Colour and fluorescence of the optic disc. Ophthalmologica 165, 1 00-1 08. Kirsch R. E. & Anderson D. R. (1973) Clinical recognition of glaucomatous cupping. Amer. J . Ophthal. 75, 442-454. Roth A. M. & Foos R. Y. (1972) Surface structure of the optic nerve head. 1 . Epipapillary membranes. Amer. J . Ophthal. 7 4 , 977-985. Samuels B. (1931) Epipapillary tissues. Arch. Ophthal. 6, 704-723. Seefelder R. (1910) Beitrage zur Histogenese und Histologie der Netzhaut des Pigmentepithels und des Sehnerves. Graefes Arch. Ophthal. 73, 419-537.
Author’s address: Tord Jerndal, M.D., Ugonkliniken, Sahlgrenska sjukhuset, S-413 45 Goteborg, Sweden.
192
