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Pathogenic Implications of Subretinal Gas Migration Through Pits and Atypical Colobomas of the Optic Nerve
T. Mark Johnson, MD, FRCSC;
Mark W. Johnson, MD
Arch Ophthalmol. 2004;122:1793-1800.
ABSTRACT
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Objective To describe subretinal migration of gas and silicone oil in a series of patients with congenital cavitary optic disc anomalies and to further clarify the pathogenesis of the associated maculopathy.
Methods Medical records of 4 female patients, aged 8 to 34 years, who developed subretinal gas migration after vitreous surgery for macular detachment associated with cavitary optic disc anomalies were reviewed. A theoretical model was used to calculate the pressure differential required to induce subretinal gas migration through an optic pit.
Results The 4 patients had bilateral atypical optic nerve colobomas or a unilateral large optic pit. A definite defect in the tissue overlying the disc excavation could be seen in one eye, and intraoperative drainage of subretinal fluid through the disc anomaly was possible in all cases. Subretinal migration of gas or silicone oil was seen intraoperatively in one case and first appeared between 1 and 17 days postoperatively in the remaining cases. Theoretical calculations suggest that the pressure differential required for migration of gas through a small defect in the roof of a cavitary disc lesion is within the range of expected fluctuations in cerebrospinal fluid pressure.
Conclusions These observations provide clinical confirmation of a defect in tissue overlying cavitary optic disc anomalies and imply interconnections between the vitreous cavity, subarachnoid space, and subretinal space. We theorize that intermittent pressure gradients resulting from normal variations in intracranial pressure play a critical role in the pathogenesis of retinopathy associated with cavitary disc anomalies.
INTRODUCTION
Congenital cavitary anomalies of the optic nerve that may be associated with serous detachments of the macula include optic disc pit, optic nerve coloboma (typical and atypical), and morning glory disc anomaly.1-4 Frank macular detachment appears to be preceded by the accumulation of intraretinal fluid emanating from the disc anomaly and constituting an unusual form of retinoschisis-like separation.5 Subsequently there is breakthrough of fluid into the subretinal space leading to detachment of the macula and occasionally larger areas of the retina. The origin of the fluid and precise pathogenesis of macular detachment associated with cavitary optic disc anomalies remain unclear.
We present 4 cases of retinal detachment associated with excavated optic disc anomalies in which vitreous surgery was complicated by subretinal migration of gas and silicone oil. This rare and unexpected event cannot readily be explained by the principles known to govern the behavior of intraocular gas and silicone oil. We believe that our clinical observations, coupled with recent optical coherence tomographic findings and consideration of cerebrospinal fluid (CSF) dynamics, provide important new insights into the pathogenesis of the maculopathy complicating optic pits and related disc anomalies.
METHODS
We retrospectively identified 4 patients who developed subretinal gas migration after vitreous surgery for macular detachment associated with cavitary optic disc anomalies. The patients were derived from the practices of 4 retina specialists at 3 centers. One patient (case 1) was described in a previous report.6 The medical records and available fundus photographs were reviewed. Although institutional review board oversight was not required for this chart review, each patient gave written informed consent before undergoing surgical intervention. Using the physical principles governing the behavior of intraocular gas, we calculated the theoretical pressure differential required for gas migration into an optic pit and compared this with information derived from a model of CSF pressure dynamics.
REPORT OF CASES
CASE 1
A 24-year-old woman was examined because of decreased and darkened vision in the central visual field of the right eye. The ocular history was significant for mild myopia. The maternal family history was notable for glaucoma.
The visual acuity measured 6/200 OD and 20/20 OS. The anterior segment was normal in each eye. Examination of the right fundus demonstrated retinal detachment involving the macula and superotemporal midperiphery and extending to the temporal border of the optic nerve (Figure 1). A stellate outer foveal defect was present, with a tiny full-thickness defect at the center of the fovea. The retina between the optic nerve and the fovea had an appearance suggesting retinal thickening or schisis. Examination of the optic disc demonstrated nasalization of the vessels with a deep, large, horizontally oval cup and a notch in the temporal neuroretinal rim. The left disc was anomalous, with a large cup and nasalization of disc vessels but no evidence of associated maculopathy (Figure 1). B-scan ultrasonography of the right eye showed no evidence of posterior vitreous detachment. Orbital ultrasound and computed tomographic scans were normal bilaterally.
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Figure 1. Case 1 fundus photographs. A, Right eye, showing anomalous optic disc with associated retinal detachment and outer lamellar foveal break. B, The left optic disc is also anomalous, but without an associated maculopathy.
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The patient underwent pars plana vitrectomy with removal of the attached posterior hyaloid, subretinal fluid drainage through a small retinotomy, fluid-gas exchange with 20% sulfur hexafluoride, and 10 days of postoperative face-down positioning. Two months postoperatively, a moderate posterior subcapsular cataract was evident, along with a small macular hole and shallow subretinal fluid in the macula extending nasally to the optic disc. Contact lens examination demonstrated a defect in the tissue overlying the temporal aspect of the disc cavitation.
When the subretinal fluid persisted 2 months later, krypton red laser burns were placed in 3 rows in the temporal juxtapapillary area. The patient then underwent phacoemulsification with placement of an intraocular lens followed by repeat vitrectomy with fluid-gas exchange and postoperative prone positioning. Seven days postoperatively, several gas bubbles were noted in the subretinal space between the optic disc and central macula (Figure 2). There was also gas trapped under neural tissue overlying the deep optic disc cavitation. The gas resolved during the subsequent 3 weeks.
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Figure 2. Case 1, 7 days after fluid-gas exchange. Fundus photograph of the right eye shows gas bubbles under the retina and trapped within the disc cavity beneath a neural tissue layer. A small hole (arrow) in this tissue could be seen on biomicroscopy.
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Two months later, the patient noted an abrupt decline in vision in the right eye. Examination showed extensive detachment of the macular region and fluid communication with the small hole in the neural tissue over the optic disc. A 50% fluid-gas exchange using 20% perfluoropropane was performed. After 7 days of face-down positioning, the macula was flat and supplemental krypton laser was applied to the temporal aspect of the optic disc. After 10 additional days of face-down positioning, the patient noted an abrupt decline in vision and was found to have recurrent detachment of the posterior retina. Numerous small subretinal gas bubbles were located in the superior aspect of the detachment (Figure 3). An additional cluster of bubbles appeared to be located within the schisis cavity in the papillomacular bundle area. No intraocular pressure measurement greater than 25 mm Hg was recorded at any postoperative examination.
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Figure 3. Fundus photograph of the right eye of case 1, 17 days after the second fluid-gas exchange. Numerous subretinal gas bubbles have appeared in the superior aspect of the detachment. A smaller cluster of bubbles appears to be located within the schisis-like cavity in the papillomacular bundle.
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Two months later, a total and highly bullous retinal detachment developed, obscuring a view of the optic disc and macula. No peripheral retinal breaks were found. The patient underwent repeat vitrectomy. During fluid-air exchange, subretinal fluid was drained through a small macular hole and over the optic disc. Moderately heavy laser photocoagulation was applied around the entire optic nerve, and lighter burns were placed in the papillomacular bundle and at the edge of the macular hole. Two weeks postoperatively, the visual acuity had improved to 20/100 and the retina was completely flat (Figure 4). During the subsequent 10 years, the visual acuity remained stable and the retina remained attached in the right eye.
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Figure 4. Fundus photograph of the right eye of case 1, 2 weeks after the final vitrectomy procedure, shows retinal reattachment and extensive laser scarring around the optic disc.
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CASE 2
An 8-year-old girl was diagnosed as having an optic pit in her left eye on routine ophthalmologic examination. The visual acuity was 20/20 OU. Several months later, she returned for evaluation of central visual blurring in the left eye. The ocular and medical histories were notable only for mild myopia. The visual acuity was 20/20 OD and 20/70 OS. The anterior segment was normal bilaterally. Fundus examination of the right eye showed a normal optic disc and retina, with a cup-disc ratio of 0.5. Examination of the left eye showed detachment of the macula associated with a deep excavation in a large optic disc (Figure 5). No Weiss ring was present.
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Figure 5. Photograph of the left optic disc of case 2 shows deep pitlike excavation in a slightly enlarged optic nerve head.
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The patient underwent pars plana vitrectomy with removal of the posterior hyaloid. During fluid-air exchange, subretinal fluid was drained through the optic pit. Argon green laser was placed around the temporal juxtapapillary area. The vitreous cavity was filled with 10% perfluoropropane gas and the patient was positioned face down. One week postoperatively, a subretinal gas bubble was noted in the macular region. This was allowed to resorb spontaneously.
One month later, a bullous retinal detachment was noted superiorly, with shallow detachment of the macula. Repeat vitrectomy with lensectomy, fluid-gas exchange, and scleral buckle was performed. No retinal breaks could be found. Recurrent retinal detachment inferiorly was noted 2 weeks postoperatively and treated with repeat vitrectomy followed by injection of silicone oil.
Ten days postoperatively, the patient was found to have extensive silicone oil in the subretinal space (Figure 6). She underwent repeat vitrectomy with silicone oil aspiration through the pit and placement of autologous blood over the optic pit. Endolaser treatment was performed for 360° around the optic nerve. Six months postoperatively, the visual acuity in the left eye was no light perception. The retina was completely attached, but extensive optic atrophy was present.
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Figure 6. Fundus photographs of case 2, 10 days postoperatively, show extensive silicone oil in the subretinal space posteriorly (A) and inferiorly (B).
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CASE 3
A 34-year-old woman had a 3-month history of central visual distortion and darkening in the left eye. The ocular and medical histories and family ocular history were unremarkable. Visual acuity was 20/20 OD and 20/50 OS. The anterior segments were normal.
The right fundus was normal apart from a large optic cup with a small amount of fibroglial tissue and nasalization of disc vessels. There was a large, deep, sharply delimited, and inferiorly decentered excavation in the left disc, with a possible slitlike defect in the neural rim nasally (Figure 7). Biomicroscopy of the left macula showed evidence of retinoschisis and retinal striae in the papillomacular bundle and fovea, with a small serous outer-layer detachment in the central macula (Figure 8). No evidence of a posterior vitreous detachment was present.
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Figure 7. Photographs of the right (A) and left (B) optic disc of case 3 show large and deep anomalous excavations.
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Figure 8. Photograph of the left fundus of case 3 shows evidence of retinoschisis and retinal striae in the papillomacular bundle and fovea, with a small outer-layer detachment in the central macula. The schisis-like changes are contiguous with the optic disc.
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Laser photocoagulation was performed along the temporal aspect of the optic nerve. Four months later, the visual acuity was 20/60 OS and a persistent macular detachment was noted. The patient underwent pars plana vitrectomy. During fluid-air exchange, a portion of the subretinal fluid was aspirated through the optic disc cavitation. At the conclusion of the procedure, subretinal gas was noted. The fluid-air exchange was repeated and the subretinal air was removed.
At the 7-year follow-up examination, the visual acuity was 20/30 OS. The macula was attached with mild residual retinal striae, and laser scars were present along the temporal margin of the optic nerve.
CASE 4
A 33-year-old woman had sudden loss of vision in her left eye. The family history was notable for glaucoma. The visual acuity was 20/20 OD and 20/200 OS. Results of anterior segment examination were normal. Fundus examination showed a large anomalous optic disc with a large cup (cup-disc ratio, 0.7) bilaterally. In addition, there was a small pit in the temporal aspect of the left disc accompanied by a large serous detachment of the macula.
The patient underwent pars plana vitrectomy. During fluid-air exchange it was noted that the subretinal fluid could be aspirated via the optic pit. Endolaser photocoagulation was applied to the temporal juxtapapillary retina. On the first postoperative day, the macula was completely flat and additional laser treatment was performed along the temporal margin of the disc.
Three weeks postoperatively, the visual acuity was 20/30 OS. Recurrent subretinal fluid was noted adjacent to the optic pit. Pure perfluoropropane gas was injected into the vitreous cavity and the patient was placed in a prone position. One day later, multiple small gas bubbles were noted in the submacular space. The intraocular pressure was 14 mm Hg. The subretinal gas resolved during the subsequent month.
The patient returned 6 weeks later with an acute decline in vision to the level of counting fingers. Examination demonstrated extensive retinal detachment over the temporal half of the fundus, with no peripheral retinal breaks. The patient underwent repeat vitrectomy with fluid-air exchange, laser, and subretinal fluid drainage through a retinotomy. Additional laser treatment was applied along the temporal margin of the optic disc. Two years postoperatively, the visual acuity was 20/50 OS and the retina was completely attached.
RESULTS
PRESSURE DIFFERENTIAL CALCULATION
For a bubble of gas to pass through a retinal break, the force pushing the bubble through the hole must exceed the surface tension of the gas bubble on the edges of the hole.7 The force tending to push the bubble through the hole is the product of the area of the hole ( R2) and the pressure difference across the hole ( p). The force opposing prolapse is the surface-tension force, which is the product of 3 factors: the coefficient of surface tension ( = 0.073 N/m for a gas-water interface), the length of the margin of prolapse (circumference of the hole = 2R), and the cosine of the contact angle ( ). When a gas bubble is about to pass through the hole, the radius of curvature of the bubble equals the radius of the retinal hole. At this point the angle of contact is 0° and cos = 1. Therefore, the equation for the pressure difference (in pascals) across the hole at the time of gas migration simplifies to Pa = 2/R.7 Assuming a hole 200 µm in diameter, Pa = 2(0.073 N/m)/0.0001 m = 1460 Pa = 148 mm H2O. Thus, the pressure gradient required to push a gas bubble through a hole of this size is at least 148 mm H2O (approximately 11 mm Hg).
MODEL OF CSF PRESSURE
Normal CSF pressure in the lateral recumbent position typically varies from 100 to 250 mm H2O.8 In a case series of 58 patients ranging in age from 15 to 83 years, the mean CSF pressure was 141 ± 19 mm H2O.8 Intracranial pressure also appears to vary significantly over time. Studies of patients with pseudotumor cerebri have demonstrated intracranial pressures varying from 50 to 500 mm H2O during 24-hour periods.8 There are few studies examining intracranial pressure over time in otherwise normal patients.
Cerebrospinal fluid pressure is dependent in part on body position. The CSF can be modeled as a closed tube 700 mm in length with a pressure of 140 mm H2O in the horizontal position.9 When the tube is reoriented vertically, the pressure within different parts of the tube is altered substantially (Figure 9). Although this model is not an exact replica of the human condition, it demonstrates that changes in body position cause significant alterations in intracranial pressure. The magnitude of these changes easily exceeds the pressure gradient required for gas migration calculated in the previous subsection.
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Figure 9. A model of cerebrospinal fluid as a closed tube 700 mm in length with a pressure of 140 mm H2O in the horizontal position. When the tube is reoriented vertically, the pressure within different parts of the tube is changed.
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COMMENT
Typical coloboma of the optic disc is a congenital excavation, located inferonasally, that is believed to result from malclosure of the embryonic ocular fissure.2, 4 Optic disc pits are classically small and temporally located, but they appear to exist along a spectrum of congenital cavitary disc anomalies that are often referred to as atypical optic nerve colobomas.1-3,10 The embryologic basis for atypical optic nerve head colobomas, including optic pits, is unclear. Although our patients had negative family histories, their disc anomalies are similar to those previously described in several autosomal dominant pedigrees of atypical optic nerve colobomas and pits that were often associated with nonrhegmatogenous detachments of the macula or more extensive areas of retina.1, 3, 10 The optic disc abnormalities in case 3 also bear some resemblance to those described in the papillorenal syndrome, an autosomal dominant condition occasionally associated with serous retinal detachment.11 Our patient had no personal or family history of renal disease.
Careful biomicroscopy and optical coherence tomographic imaging have demonstrated that edema or a schisis-like separation in the outer retina appears to be the initial pathogenic step in the development of serous macular detachment complicating congenital cavitary optic disc anomalies.5, 12-14 Fluid from the disc excavation first accumulates within the retinal stroma, most prominently in the outer plexiform layer. When severe, the edema mimics a retinoschisis cavity, but with intact vertical bridging retinal elements. The fluid later enters the subretinal space, either through an obvious outer lamellar foveal hole5, 12-13 or possibly through minute invisible breaks in the outer retina. The schisis-like separation has been shown both to precede macular detachment and to invariably communicate with the optic disc, even when the associated macular detachment does not.12-14 The presence of schisis-like outer retinal edema most likely explains the high frequency of treatment failure after photocoagulation to the juxtapapillary retina in these eyes, although separation of the outer retina from the retinal pigment epithelium may also be a factor.
The most plausible sources of fluid responsible for the retinopathy associated with optic pits and other cavitary disc anomalies are the vitreous cavity and the subarachnoid space. Evidence confirming a communication through the pit between the vitreous cavity and the subretinal space includes the following: (1) india ink studies performed on collie dogs with cavitary disc anomalies similar to human optic pits demonstrated leakage of ink from the vitreous cavity (but not from the subarachnoid space) into the subretinal space via the optic pit.15 (2) During vitrectomy, intraoperative drainage of subretinal fluid through cavitary disc anomalies was possible in our cases and in previously reported cases.6, 16-17 (3) In addition to the cases reported in this study, rare cases of subretinal migration of vitreous substitutes through anomalous disc excavations have been reported previously. These include the migration of gas through an optic pit after outpatient perfluoropropane injection,18 the migration of both gas and silicone oil through a morning glory disc after vitrectomy,16 and the intraoperative migration of perfluorodecalin through a morning glory disc.19
Vitreous fluid is thought to gain access to anomalous disc cavitations through small holes or breaks in overlying diaphanous membranes or neuroectodermal tissue. In our case 1, a gas bubble was observed trapped within the disc excavation, having passed through a small visible break in overlying neural tissue (Figure 2). Similar breaks have also been documented in other series.6, 16-18,20 The possibility of vitreous traction associated with these breaks has been suggested by clinical observations in several cases,6, 17-18,21 but its pathogenic role remains unclear. Obviously, vitreous traction played no role in the subretinal gas migration seen in our patients, since the migration occurred in each case after vitrectomy and peeling of the posterior cortical vitreous layer.
Several authors have suggested that CSF from the perineural subarachnoid space may be responsible for the retinopathy complicating optic pits and related anomalies.22-25 Histologically, optic nerve pits are herniations of dysplastic retina into a collagen-lined sac or pocket, which often extends posteriorly into the subarachnoid space through a defect in the lamina cribrosa.22, 26 The posterior aspect of the sac is typically a multiloculated fluid-filled space. Optical coherence tomographic studies have suggested a communication between the schisis-like intraretinal space and a perineural space associated with the optic pit.12-13 Furthermore, communications between the subarachnoid space and subretinal space and between the subarachnoid space and vitreous cavity have been proved clinically in patients with the morning glory anomaly. In one case, metrizamide dye injected into the subarachnoid space migrated into the subretinal space but not into the vitreous.23 In a second case, gas injected into the vitreous at the time of optic nerve sheath fenestration for extensive retinal detachment was noted to migrate into the perineural subarachnoid space.24 Finally, the finding of relative hypotony in an eye with an optic pit was attributed by the authors to drainage of intraocular fluid through the pit and into the subarachnoid space.25
Our cases of gas and silicone oil migration from the vitreous into the subretinal space clearly prove a communication between these 2 spaces through the cavitary disc anomalies. However, this phenomenon also suggests an unusual and complex pathogenesis, since surface tension considerations dictate that migration of a large intravitreal gas bubble through a small defect is impossible without a large pressure gradient. Assuming a generous hole in the roof of an optic pit of 200-µm diameter, we calculate that a pressure differential across the defect of at least 148 mm H2O (11 mm Hg) is necessary to force a gas bubble into the optic pit and then subretinal space. However, a significant pressure differential between the vitreous cavity and subretinal space does not normally exist. We propose that the pressure differential required for the subretinal migration of gas observed in our patients derives from pressure fluctuations in CSF that are transmitted to the optic pit via the perineural subarachnoid space.
Large fluctuations in intracranial and CSF pressure have been measured in both normal and pathologic situations. Factors such as changes in body position and venous pressure contribute to these fluctuations. Our calculations, based on the simplified models described in this report, suggest that the pressure differential required for migration of gas through a small defect in the roof of a cavitary disc lesion is well within the range of expected fluctuations in CSF pressure. Such pressure alterations would be transmitted to the sac of the pit by CSF migration across the connective-tissue capsule in cases where the porous capsule is permeable to fluid (Figure 10). In pits with an impermeable capsule, we speculate that pressure transmission could occur by small pressure-induced movements of the capsule causing deformation of the pit sac (Figure 10). Thus, the pit conceivably functions like a bulb syringe, "sucking" fluid (or gas or silicone oil) into the pit sac during a drop in intracranial pressure and then, with a rise in pressure, ejecting it from the sac. The fluid or gas exiting the pit would be expected to divide, part into the vitreous cavity and part into the retinoschisis cavity and eventually the subretinal space (Figure 3). The existence of such transient pressure gradients is suggested by the observation in one patient that vitreous debris overlying an optic pit was intermittently sucked into the pit and later dislodged back into the posterior vitreous.25
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Figure 10. Schematic illustration of the anatomy of an optic pit and associated maculopathy. The herniated dysplastic tissue and pit capsule vary in porosity from one eye to another. In eyes with an impermeable capsule, the pit functions like a bulb syringe, "sucking" vitreous fluid into the pit sac during a drop in intracranial pressure (ICP) (A) and then, during a rise in pressure, expelling it from the sac (B). In eyes with a permeable capsule, fluctuations in ICP are transmitted to the pit by cerebrospinal fluid migration across the capsule (C).
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Our model demonstrates that normal fluctuations in intracranial pressure can theoretically produce forces that are capable of exceeding the surface tension of gas at a small break overlying an optic pit. The pressure gradient required for subretinal migration of materials with lower surface tension, such as silicone oil, perfluorocarbon liquid, and hyaluronic acid,27 is lower, such that subretinal migration could occur more easily and through smaller defects in the dysplastic tissue overlying the pit. Furthermore, since intravitreal gas can occasionally migrate through cavitary disc anomalies into the subarachnoid space,24 silicone oil or perfluorocarbon liquid could potentially do so more easily and with unknown pathologic consequences. It may therefore be prudent to avoid the use of liquid vitreous substitutes in the surgical management of cavitary optic disc anomalies.16, 19
A substantial pressure difference between the vitreous cavity and subretinal space cannot develop in an eye with a mobile retina.7 However, fluctuations in intraocular pressure do affect the pressure differential between the vitreous cavity and spaces outside the globe, such as the pit sac and perioptic subarachnoid space. Indeed, high intraocular pressure during fluid-air exchange likely contributed to the gas migration observed intraoperatively in case 3. In the remaining cases, migration occurred postoperatively and without an apparent contribution by elevated intraocular pressure.
We believe that a pathogenic model that incorporates transient pressure gradients derived from the subarachnoid space is necessary to explain the unusual phenomenon of subretinal gas migration through cavitary disc anomalies. A unifying model must also include the observation that the anatomy of cavitary disc anomalies varies from one eye to another. On the basis of the studies previously referred to, it seems clear that cavitary lesions communicate openly with the vitreous cavity in some eyes, with the subarachnoid space in other eyes, and with both spaces in yet others. As Irvine et al24 suggested, the vitreous, subarachnoid, and subretinal spaces may all be variably interconnected because of the incomplete differentiation and porous nature of the herniated tissues composing the optic nerve anomaly (Figure 10). It follows that the subretinal fluid in a given case might be vitreous fluid, CSF, or an admixture of the two fluids. We speculate that the age at symptom onset in patients with congenital excavated disc lesions may depend in part on the anatomy of these interconnections. The typical age at onset, in the third and fourth decades of life, may reflect the age at which sufficient liquid vitreous is available to be drawn into the pit.6, 18, 20 On the other hand, CSF is more likely involved when the onset occurs in patients too young to have liquefied vitreous, especially when the associated retinal detachment is extensive.
The concept of a cavitary disc anomaly functioning as a mechanical pump driven by fluctuations in CSF pressure might also explain the peculiar retinoschisis-like separation and associated retinal detachment seen in these cases. Fluid moving passively from the vitreous cavity through a pit would unlikely be driven into the retinal stroma with sufficient force to cause a large schisis-like split and subsequent macular detachment. However, it is plausible that alterations in CSF pressure, transmitted to the pit sac as described previously, would pump small aliquots of fluid under pressure into the retinal stroma. This fluid might be expected to gradually dissect a schisis cavity in the outer retina and eventually break into the subretinal space, often through a stellate outer foveal defect that has the appearance of having been created under force.
Subretinal migration of gas or silicone oil through cavitary disc anomalies is an uncommon phenomenon. On the basis of our cases and those previously reported,16-17,19, 24 it appears that patients with large cavitary anomalies may be at greatest risk for this complication. Although these eyes tend to develop large and recurrent retinal detachments, anatomic success is ultimately possible with the creation of a sufficient laser barrier in the juxtapapillary retina. Caution must be exercised in the application of this laser barrier, since the optic atrophy and poor visual outcome seen in case 2 may have resulted from overly intense laser treatment extending 360° around the nerve head. A unifying model of pathogenesis that we believe accounts for subretinal gas migration and other peculiar features of the retinopathy associated with cavitary disc anomalies includes 2 critical features: (1) variable interconnections between the vitreous, subarachnoid, and subretinal spaces and (2) transmission of intracranial pressure fluctuations to the pit via the perineural subarachnoid space.
AUTHOR INFORMATION
Correspondence: Mark W. Johnson, MD, Kellogg Eye Center, 1000 Wall St, Ann Arbor, MI 48105 (markwj{at}umich.edu).
Submitted for Publication: September 17, 2003; final revision received February 27, 2004; accepted May 27, 2004.
Previous Presentation: This study was presented in part at the annual meeting of the Association for Research in Vision and Ophthalmology; May 4, 2000; Fort Lauderdale, Fla; and at the 18th Annual Meeting of the Vitreous Society; January 10, 2001; Cancun, Mexico.
Acknowledgment: We thank the following individuals for providing case history material for this study: Susan G. Elner, MD, Robert R. Francis, MD, Brian T. Perkovich, MD, and Todd E. Schneiderman, MD.
Financial Disclosure: None.
Author Affiliations: Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan School of Medicine, Ann Arbor. Dr T. M. Johnson is now with the National Retina Institute and George Washington University, Chevy Chase, Md.
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