Pathogenic Implications of Subretinal Gas Migration Through Pits Andatypical Colobomas of the Optic Nerve

CLINICAL SCIENCES Pathogenic Implications of Subretinal Gas Migration Through Pits and Atypical Colobomas of the Optic Nerve

T. Mark Johnson, MD, FRCSC; Mark W. Johnson, MD

Objective: To describe subretinal migration of gas and cases. Subretinal migration of gas or silicone oil was seen silicone oil in a series of patients with congenital cavi- intraoperatively in one case and first appeared between tary optic disc anomalies and to further clarify the patho- 1 and 17 days postoperatively in the remaining cases. genesis of the associated maculopathy. Theoretical calculations suggest that the pressure differential required for migration of gas through a small de- Methods: Medical records of 4 female patients, aged 8 fect in the roof of a cavitary disc lesion is within the range to 34 years, who developed subretinal gas migration af- of expected fluctuations in cerebrospinal fluid pressure. ter vitreous surgery for macular detachment associated with cavitary optic disc anomalies were reviewed. A theo- Conclusions: These observations provide clinical con- retical model was used to calculate the pressure differ- firmation of a defect in tissue overlying cavitary optic disc ential required to induce subretinal gas migration through anomalies and imply interconnections between the vit- an optic pit. reous cavity, subarachnoid space, and subretinal space. We theorize that intermittent pressure gradients result- Results: The 4 patients had bilateral atypical optic nerve ing from normal variations in intracranial pressure play colobomas or a unilateral large optic pit. A definite de- a critical role in the pathogenesis of retinopathy associ- fect in the tissue overlying the disc excavation could be ated with cavitary disc anomalies. seen in one eye, and intraoperative drainage of subretinal fluid through the disc anomaly was possible in all Arch Ophthalmol. 2004;122:1793-1800

ONGENITAL CAVITARY havior of intraocular gas and silicone oil. anomalies of the optic We believe that our clinical observa- nerve that may be associ- tions, coupled with recent optical coher- ated with serous detach- ence tomographic findings and consider- ments of the macula in- ation of cerebrospinal fluid (CSF) cludeC optic disc pit, optic nerve coloboma dynamics, provide important new in- (typical and atypical), and morning glory sights into the pathogenesis of the macu- disc anomaly.1-4 Frank macular detach- lopathy complicating optic pits and re- ment appears to be preceded by the accu- lated disc anomalies. mulation of intraretinal fluid emanating from the disc anomaly and constituting an unusual form of retinoschisis-like separa- METHODS tion.5 Subsequently there is breakthrough of fluid into the subretinal space leading to We retrospectively identified 4 patients who detachment of the macula and occasion- developed subretinal gas migration after vit- ally larger areas of the retina. The origin of reous surgery for macular detachment associ- Author Affiliations: Kellogg the fluid and precise pathogenesis of macu- ated with cavitary optic disc anomalies. The pa- Eye Center, Department of lar detachment associated with cavitary op- tients were derived from the practices of 4 retina Ophthalmology and Visual specialists at 3 centers. One patient (case 1) was tic disc anomalies remain unclear. 6 Sciences, University of We present 4 cases of retinal detach- described in a previous report. The medical Michigan School of Medicine, ment associated with excavated optic disc records and available fundus photographs were Ann Arbor. Dr T. M. Johnson is reviewed. Although institutional review board now with the National Retina anomalies in which vitreous surgery was oversight was not required for this chart re- Institute and George complicated by subretinal migration of gas view, each patient gave written informed con- Washington University, Chevy and silicone oil. This rare and unex- sent before undergoing surgical intervention. Chase, Md. pected event cannot readily be explained Using the physical principles governing the be- Financial Disclosure: None. by the principles known to govern the be- havior of intraocular gas, we calculated the

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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.

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 com- puted tomographic scans were normal bilaterally. The patient underwent pars plana vitrectomy with re- moval 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 Figure 2. Case 1, 7 days after fluid-gas exchange. Fundus photograph of the examination demonstrated a defect in the tissue overlying right eye shows gas bubbles under the retina and trapped within the disc the temporal aspect of the disc cavitation. cavity beneath a neural tissue layer. A small hole (arrow) in this tissue could When the subretinal fluid persisted 2 months later, be seen on biomicroscopy. krypton red laser burns were placed in 3 rows in the temporal juxtapapillary area. The patient then underwent theoretical pressure differential required for gas migration into phacoemulsification with placement of an intraocular lens an optic pit and compared this with information derived from followed by repeat vitrectomy with fluid-gas exchange a model of CSF pressure dynamics. and postoperative prone positioning. Seven days postoperatively, several gas bubbles were noted in the sub- REPORT OF CASES retinal space between the optic disc and central macula (Figure 2). There was also gas trapped under neural tis- CASE 1 sue overlying the deep optic disc cavitation. The gas resolved during the subsequent 3 weeks. A 24-year-old woman was examined because of decreased Two months later, the patient noted an abrupt de- and darkened vision in the central visual field of the right cline in vision in the right eye. Examination showed ex- eye. The ocular history was significant for mild myopia. The tensive detachment of the macular region and fluid com- maternal family history was notable for glaucoma. munication with the small hole in the neural tissue over The visual acuity measured 6/200 OD and 20/20 OS. The the optic disc. A 50% fluid-gas exchange using 20% per- anterior segment was normal in each eye. Examination of fluoropropane was performed. After 7 days of face- the right fundus demonstrated retinal detachment involv- down positioning, the macula was flat and supplemen- ing the macula and superotemporal midperiphery and ex- tal krypton laser was applied to the temporal aspect of tending to the temporal border of the optic nerve the optic disc. After 10 additional days of face-down po- (Figure 1). A stellate outer foveal defect was present, with sitioning, the patient noted an abrupt decline in vision a tiny full-thickness defect at the center of the fovea. The and was found to have recurrent detachment of the pos- retina between the optic nerve and the fovea had an ap- terior retina. Numerous small subretinal gas bubbles were pearance suggesting retinal thickening or schisis. Exami- located in the superior aspect of the detachment nation of the optic disc demonstrated nasalization of the (Figure 3). An additional cluster of bubbles appeared vessels with a deep, large, horizontally oval cup and a notch to be located within the schisis cavity in the papillomacu-

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/26/2021 Figure 4. Fundus photograph of the right eye of case 1, 2 weeks after the Figure 3. Fundus photograph of the right eye of case 1, 17 days after the final vitrectomy procedure, shows retinal reattachment and extensive laser second fluid-gas exchange. Numerous subretinal gas bubbles have appeared scarring around the optic disc. 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.

lar bundle area. No intraocular pressure measurement greater than 25 mm Hg was recorded at any postoperative examination. 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 postop- Figure 5. Photograph of the left optic disc of case 2 shows deep pitlike eratively, the visual acuity had improved to 20/100 and excavation in a slightly enlarged optic nerve head. the retina was completely flat (Figure 4). During the subsequent 10 years, the visual acuity remained stable and the Repeat vitrectomy with lensectomy, fluid-gas exchange, retina remained attached in the right eye. and scleral buckle was performed. No retinal breaks could be found. Recurrent retinal detachment inferiorly was CASE 2 noted 2 weeks postoperatively and treated with repeat vitrectomy followed by injection of silicone oil. An 8-year-old girl was diagnosed as having an optic pit Ten days postoperatively, the patient was found to have in her left eye on routine ophthalmologic examination. extensive silicone oil in the subretinal space (Figure 6). The visual acuity was 20/20 OU. Several months later, She underwent repeat vitrectomy with silicone oil aspi- she returned for evaluation of central visual blurring in ration through the pit and placement of autologous blood the left eye. The ocular and medical histories were no- over the optic pit. Endolaser treatment was performed table only for mild myopia. The visual acuity was 20/20 for 360° around the optic nerve. Six months postopera- OD and 20/70 OS. The anterior segment was normal bi- tively, the visual acuity in the left eye was no light per- laterally. Fundus examination of the right eye showed a ception. The retina was completely attached, but exten- normal optic disc and retina, with a cup-disc ratio of 0.5. sive optic atrophy was present. Examination of the left eye showed detachment of the macula associated with a deep excavation in a large op- CASE 3 tic disc (Figure 5). No Weiss ring was present. The patient underwent pars plana vitrectomy with re- A 34-year-old woman had a 3-month history of central moval of the posterior hyaloid. During fluid-air ex- visual distortion and darkening in the left eye. The ocu- change, subretinal fluid was drained through the optic lar and medical histories and family ocular history were pit. Argon green laser was placed around the temporal unremarkable. Visual acuity was 20/20 OD and 20/50 OS. juxtapapillary area. The vitreous cavity was filled with The anterior segments were normal. 10% perfluoropropane gas and the patient was posi- The right fundus was normal apart from a large optic tioned face down. One week postoperatively, a subreti- cup with a small amount of fibroglial tissue and nasaliza- nal gas bubble was noted in the macular region. This was tion of disc vessels. There was a large, deep, sharply de- allowed to resorb spontaneously. limited, and inferiorly decentered excavation in the left disc, One month later, a bullous retinal detachment was with a possible slitlike defect in the neural rim nasally noted superiorly, with shallow detachment of the macula. (Figure 7). Biomicroscopy of the left macula showed evi-

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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).

A B

Figure 7. Photographs of the right (A) and left (B) optic disc of case 3 show large and deep anomalous excavations.

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 re- sidual 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 ex- Figure 8. Photograph of the left fundus of case 3 shows evidence of amination showed a large anomalous optic disc with a retinoschisis and retinal striae in the papillomacular bundle and fovea, with a small outer-layer detachment in the central macula. The schisis-like changes large cup (cup-disc ratio, 0.7) bilaterally. In addition, there are contiguous with the optic disc. was a small pit in the temporal aspect of the left disc ac- companied by a large serous detachment of the macula. dence of retinoschisis and retinal striae in the papillomacu- The patient underwent pars plana vitrectomy. Dur- lar bundle and fovea, with a small serous outer-layer de- ing fluid-air exchange it was noted that the subretinal fluid tachment in the central macula (Figure 8). No evidence could be aspirated via the optic pit. Endolaser photoco- of a posterior vitreous detachment was present. agulation was applied to the temporal juxtapapillary retina. Laser photocoagulation was performed along the tem- On the first postoperative day, the macula was com- poral aspect of the optic nerve. Four months later, the pletely flat and additional laser treatment was per- visual acuity was 20/60 OS and a persistent macular de- formed along the temporal margin of the disc. tachment was noted. The patient underwent pars plana Three weeks postoperatively, the visual acuity was vitrectomy. During fluid-air exchange, a portion of the 20/30 OS. Recurrent subretinal fluid was noted adjacent

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/26/2021 to the optic pit. Pure perfluoropropane gas was injected 140 – (700/2) = –210 mm H O into the vitreous cavity and the patient was placed in a 2 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. Exami- 140 mm H O nation demonstrated extensive retinal detachment over 2 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 140 + (700/2) = 490 mm H O the retina was completely attached. 2

Figure 9. A model of cerebrospinal fluid as a closed tube 700 mm in length

RESULTS 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. PRESSURE DIFFERENTIAL CALCULATION

For a bubble of gas to pass through a retinal break, the force onstrates that changes in body position cause signifi- pushing the bubble through the hole must exceed the sur- cant alterations in intracranial pressure. The magnitude face tension of the gas bubble on the edges of the hole.7 of these changes easily exceeds the pressure gradient re- The force tending to push the bubble through the hole is quired for gas migration calculated in the previous sub- the product of the area of the hole (␲R2) and the pressure section. difference across the hole (⌬p). The force opposing pro- lapse is the surface-tension force, which is the product of COMMENT 3 factors: the coefficient of surface tension (␥=0.073 N/m for a gas-water interface), the length of the margin of pro- Typical coloboma of the optic disc is a congenital exca- lapse (circumference of the hole=2␲R), and the cosine of vation, located inferonasally, that is believed to result from the contact angle (␪). When a gas bubble is about to pass malclosure of the embryonic ocular fissure.2,4 Optic disc through the hole, the radius of curvature of the bubble pits are classically small and temporally located, but they equals the radius of the retinal hole. At this point the angle appear to exist along a spectrum of congenital cavitary of contact is 0° and cos ␪=1. Therefore, the equation for disc anomalies that are often referred to as atypical optic the pressure difference (in pascals) across the hole at the nerve colobomas.1-3,10 The embryologic basis for atypical time of gas migration simplifies to ⌬Pa=2␥/R.7 Assuming optic nerve head colobomas, including optic pits, is un- a hole 200 µm in diameter, ⌬Pa=2(0.073 N/m)/0.0001 clear. Although our patients had negative family histo- m=1460 Pa=148 mm H2O. Thus, the pressure gradient re- ries, their disc anomalies are similar to those previously quired to push a gas bubble through a hole of this size is at described in several autosomal dominant pedigrees of least 148 mm H2O (approximately 11 mm Hg). atypical optic nerve colobomas and pits that were often associated with nonrhegmatogenous detachments of the MODEL OF CSF PRESSURE macula or more extensive areas of retina.1,3,10 The optic disc abnormalities in case 3 also bear some resemblance Normal CSF pressure in the lateral recumbent position to those described in the papillorenal syndrome, an au- 8 typically varies from 100 to 250 mm H2O. In a case se- tosomal dominant condition occasionally associated with ries of 58 patients ranging in age from 15 to 83 years, serous retinal detachment.11 Our patient had no per- 8 the mean CSF pressure was 141±19 mm H2O. Intracra- sonal or family history of renal disease. nial pressure also appears to vary significantly over time. Careful biomicroscopy and optical coherence tomo- Studies of patients with pseudotumor cerebri have dem- graphic imaging have demonstrated that edema or a schi- onstrated intracranial pressures varying from 50 to 500 sis-like separation in the outer retina appears to be the 8 mm H2O during 24-hour periods. There are few studies initial pathogenic step in the development of serous macu- examining intracranial pressure over time in otherwise lar detachment complicating congenital cavitary optic disc normal patients. anomalies.5,12-14 Fluid from the disc excavation first ac- Cerebrospinal fluid pressure is dependent in part on cumulates within the retinal stroma, most prominently body position. The CSF can be modeled as a closed tube in the outer plexiform layer. When severe, the edema mim- 700 mm in length with a pressure of 140 mm H2Ointhe ics a retinoschisis cavity, but with intact vertical bridg- horizontal position.9 When the tube is reoriented verti- ing retinal elements. The fluid later enters the subreti- cally, the pressure within different parts of the tube is nal space, either through an obvious outer lamellar foveal altered substantially (Figure 9). Although this model hole5,12,13 or possibly through minute invisible breaks in is not an exact replica of the human condition, it dem- the outer retina. The schisis-like separation has been

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/26/2021 shown both to precede macular detachment and to in- nal detachment was noted to migrate into the perineural variably communicate with the optic disc, even when the subarachnoid space.24 Finally, the finding of relative hy- associated macular detachment does not.12-14 The pres- potony in an eye with an optic pit was attributed by the ence of schisis-like outer retinal edema most likely ex- authors to drainage of intraocular fluid through the pit and plains the high frequency of treatment failure after pho- into the subarachnoid space.25 tocoagulation to the juxtapapillary retina in these eyes, Our cases of gas and silicone oil migration from the although separation of the outer retina from the retinal vitreous into the subretinal space clearly prove a com- pigment epithelium may also be a factor. munication between these 2 spaces through the cavitary The most plausible sources of fluid responsible for the disc anomalies. However, this phenomenon also sug- retinopathy associated with optic pits and other cavitary gests an unusual and complex pathogenesis, since sur- disc anomalies are the vitreous cavity and the subarach- face tension considerations dictate that migration of a large noid space. Evidence confirming a communication through intravitreal gas bubble through a small defect is impos- the pit between the vitreous cavity and the subretinal space sible without a large pressure gradient. Assuming a gen- includes the following: (1) india ink studies performed on erous hole in the roof of an optic pit of 200-µm diam- collie dogs with cavitary disc anomalies similar to human eter, we calculate that a pressure differential across the optic pits demonstrated leakage of ink from the vitreous defect of at least 148 mm H2O (11 mm Hg) is necessary cavity (but not from the subarachnoid space) into the sub- to force a gas bubble into the optic pit and then subreti- retinal space via the optic pit.15 (2) During vitrectomy, in- nal space. However, a significant pressure differential be- traoperative drainage of subretinal fluid through cavitary tween the vitreous cavity and subretinal space does not disc anomalies was possible in our cases and in previ- normally exist. We propose that the pressure differen- ously reported cases.6,16,17 (3) In addition to the cases re- tial required for the subretinal migration of gas ob- ported in this study, rare cases of subretinal migration of served in our patients derives from pressure fluctua- vitreous substitutes through anomalous disc excavations tions in CSF that are transmitted to the optic pit via the have been reported previously. These include the migra- perineural subarachnoid space. tion of gas through an optic pit after outpatient perfluo- Large fluctuations in intracranial and CSF pressure have ropropane injection,18 the migration of both gas and sili- been measured in both normal and pathologic situations. cone oil through a morning glory disc after vitrectomy,16 Factors such as changes in body position and venous pres- and the intraoperative migration of perfluorodecalin sure contribute to these fluctuations. Our calculations, through a morning glory disc.19 based on the simplified models described in this report, Vitreous fluid is thought to gain access to anomalous suggest that the pressure differential required for migra- disc cavitations through small holes or breaks in overly- tion of gas through a small defect in the roof of a cavitary ing diaphanous membranes or neuroectodermal tissue. In disc lesion is well within the range of expected fluctua- our case 1, a gas bubble was observed trapped within the tions in CSF pressure. Such pressure alterations would be disc excavation, having passed through a small visible break transmitted to the sac of the pit by CSF migration across in overlying neural tissue (Figure 2). Similar breaks have the connective-tissue capsule in cases where the porous also been documented in other series.6,16-18,20 The possi- capsule is permeable to fluid (Figure 10). In pits with bility of vitreous traction associated with these breaks has an impermeable capsule, we speculate that pressure trans- been suggested by clinical observations in several mission could occur by small pressure-induced move- cases,6,17,18,21 but its pathogenic role remains unclear. Ob- ments of the capsule causing deformation of the pit sac viously, vitreous traction played no role in the subretinal (Figure 10). Thus, the pit conceivably functions like a bulb gas migration seen in our patients, since the migration oc- syringe, “sucking” fluid (or gas or silicone oil) into the pit curred in each case after vitrectomy and peeling of the pos- sac during a drop in intracranial pressure and then, with terior cortical vitreous layer. a rise in pressure, ejecting it from the sac. The fluid or gas Several authors have suggested that CSF from the peri- exiting the pit would be expected to divide, part into the neural subarachnoid space may be responsible for the reti- vitreous cavity and part into the retinoschisis cavity and nopathy complicating optic pits and related anoma- eventually the subretinal space (Figure 3). The existence lies.22-25 Histologically, optic nerve pits are herniations of of such transient pressure gradients is suggested by the ob- dysplastic retina into a collagen-lined sac or pocket, which servation in one patient that vitreous debris overlying an often extends posteriorly into the subarachnoid space optic pit was intermittently sucked into the pit and later through a defect in the lamina cribrosa.22,26 The posterior dislodged back into the posterior vitreous.25 aspect of the sac is typically a multiloculated fluid-filled Our model demonstrates that normal fluctuations in space. Optical coherence tomographic studies have sug- intracranial pressure can theoretically produce forces that gested a communication between the schisis-like intrareti- are capable of exceeding the surface tension of gas at a nal space and a perineural space associated with the optic small break overlying an optic pit. The pressure gradi- pit.12,13 Furthermore, communications between the sub- ent required for subretinal migration of materials with arachnoid space and subretinal space and between the sub- lower surface tension, such as silicone oil, perfluorocar- arachnoid space and vitreous cavity have been proved clini- bon liquid, and hyaluronic acid,27 is lower, such that sub- cally in patients with the morning glory anomaly. In one retinal migration could occur more easily and through case, metrizamide dye injected into the subarachnoid space smaller defects in the dysplastic tissue overlying the pit. migrated into the subretinal space but not into the vitre- Furthermore, since intravitreal gas can occasionally mi- ous.23 In a second case, gas injected into the vitreous at the grate through cavitary disc anomalies into the subarach- time of optic nerve sheath fenestration for extensive reti- noid space,24 silicone oil or perfluorocarbon liquid could

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Subretinal Fluid

Herniation of Dysplastic Tissue

Pit Sac

Pit Capsule

Subarachnoid Space

ICP ICP

A B C

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).

potentially do so more easily and with unknown patho- operatively and without an apparent contribution by el- logic consequences. It may therefore be prudent to avoid evated intraocular pressure. the use of liquid vitreous substitutes in the surgical man- We believe that a pathogenic model that incorporates agement of cavitary optic disc anomalies.16,19 transient pressure gradients derived from the subarach- A substantial pressure difference between the vitre- noid space is necessary to explain the unusual phenom- ous cavity and subretinal space cannot develop in an eye enon of subretinal gas migration through cavitary disc with a mobile retina.7 However, fluctuations in intraocu- anomalies. A unifying model must also include the obser- lar pressure do affect the pressure differential between vation that the anatomy of cavitary disc anomalies varies the vitreous cavity and spaces outside the globe, such as from one eye to another. On the basis of the studies pre- the pit sac and perioptic subarachnoid space. Indeed, high viously referred to, it seems clear that cavitary lesions com- intraocular pressure during fluid-air exchange likely con- municate openly with the vitreous cavity in some eyes, with tributed to the gas migration observed intraoperatively the subarachnoid space in other eyes, and with both spaces in case 3. In the remaining cases, migration occurred post- in yet others. As Irvine et al24 suggested, the vitreous, sub-

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©2004 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/26/2021 arachnoid, and subretinal spaces may all be variably inter- Acknowledgment: We thank the following individuals connected because of the incomplete differentiation and for providing case history material for this study: Susan porous nature of the herniated tissues composing the op- G. Elner, MD, Robert R. Francis, MD, Brian T. Perkov- tic nerve anomaly (Figure 10). It follows that the subreti- ich, MD, and Todd E. Schneiderman, MD. nal fluid in a given case might be vitreous fluid, CSF, or an admixture of the two fluids. We speculate that the age at REFERENCES symptom onset in patients with congenital excavated disc lesions may depend in part on the anatomy of these inter- 1. Savell J, Cook JR. Optic nerve colobomas of autosomal-dominant heredity. Arch connections. 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The etiology and treatment The concept of a cavitary disc anomaly functioning as of macular detachment associated with optic nerve pits and related anomalies. a mechanical pump driven by fluctuations in CSF pres- Trans Am Ophthalmol Soc. 1998;96:73-93. sure might also explain the peculiar retinoschisis-like sepa- 7. Wilkinson CP, Rice TA. Appendix 7-A: surface tension of intraocular bubbles. In: ration and associated retinal detachment seen in these cases. Wilkinson CP, Rice TA, eds. Michels Retinal Detachment. 2nd ed. St Louis, Mo: CV Mosby Co; 1997:462-465. Fluid moving passively from the vitreous cavity through a 8. Ekstedt J. CSF hydrodynamic studies in man, 2: normal hydrodynamic variables pit would unlikely be driven into the retinal stroma with related to CSF pressure and flow. J Neurol Neurosurg Psychiatry. 1978;41: sufficient force to cause a large schisis-like split and sub- 345-353. sequent macular detachment. However, it is plausible that 9. Bradbury MWB. 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Optical coherence to- Subretinal migration of gas or silicone oil through cavi- mography of macular lesions associated with optic nerve head pits. Ophthalmology. tary disc anomalies is an uncommon phenomenon. On 1996;103:1047-1053. 13. Krivoy D, Gentile R, Liebmann J, et al. Imaging congenital optic disc pits and the basis of our cases and those previously re- associated maculopathy using optical coherence tomography. Arch Ophthalmol. 16,17,19,24 ported, it appears that patients with large cavi- 1996;114:165-170. tary anomalies may be at greatest risk for this complica- 14. Lincoff H, Schiff W, Krivoy D, Ritch R. Optic coherence tomography of optic disk tion. Although these eyes tend to develop large and pit maculopathy. Am J Ophthalmol. 1996;122:264-266. recurrent retinal detachments, anatomic success is ulti- 15. Brown GC, Shields JA, Patty BE, Goldberg RE. Congenital pit of the optic nerve head, I: experimental studies in collie dogs. 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