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Show Journal of Neuro- Ophthalmology 18( 2): 121- 123, 1998. © 1998 Lippincott- Raven Publishers, Philadelphia Unilateral Optic Disc Edema Following Trabeculectomy Aki Kawasaki, M. D., and Valerie Purvin, M. D. Two cases of a benign form of optic disc edema after successful trabeculectomy are reported. In both patients, optic disc edema was noted 2 to 4 weeks after trabeculectomy. The edema occurred without loss of visual acuity or field. The absolute intraocular pressure and intracranial pressure were normal- that is, the edema was not a syndrome of hypotony or pseudotumor cerebri. However, both patients had intracranial pressure in the high- normal range. The decrease in intraocular pressure into the low- normal range after trabeculectomy may have altered the intracranial pressure: intraocular pressure ratio at the lamina cribrosa enough to produce optic disc edema. Key Words: Optic nerve- Increased intracranial pressure- Papilledema- Trabeculectomy. Optic disc edema with good optic nerve function after trabeculectomy may have several causes. We describe two patients and speculate on the mechanism of their disc edema. CASE REPORTS Case 1 This 24- year- old obese, nondiabetic woman had chronic mixed glaucoma. Despite topical intraocular pressure- ( IOP) lowering agents, her intraocular pressure was 25 to 35 mm Hg. She underwent trabeculectomy with mitomycin in her left eye. Two weeks after surgery, left optic disc edema was noted and was initially attributed to hypotony, although the IOP never measured below 7 mm Hg. Follow- up IOP in her left eye ranged between 7 and 14 mm Hg, and optic disc edema persisted for 4 months. She was subsequently referred for neuro-ophthalmic evaluation. At our consultation, the patient reported a 10- month history of headache with intermittent pulsatile tinnitus. She had no visual blur, diplopia, or transient visual obscurations. Her medical history was significant for asthma, chronic obesity, amenorrhea, and hypertension, Manuscript received September 2, 1997; accepted January 28, 1998. From the Midwest Eye Institute, Clarian Hospitals of Indiana ( A. K.), and the Departments of Ophthalmology and Neurology, Indiana University Medical Center Indianapolis ( V. P.), Indiana, U. S. A. The authors have no proprietary interest in any of the products named in this manuscript. Address correspondence and reprint requests to Aki Kawasaki, M. D., 201 Pennsylvania Parkway, Indianapolis, Indiana 46280- 1381, U. S. A. without history of malignant hypertension. On examination, her weight was 246 pounds and blood pressure was 124/ 94. She had visual acuity of 20/ 20 OD and 20/ 25 OS, with normal color vision and pupillary responses. Results of Goldmann perimetry in her right eye were normal and in her left eye showed mild central depression and baring of the blind spot inferiorly. Biomicroscopy of her left eye showed an avascular bleb superiorly and a peripheral iridectomy. Intraocular pressure was 24 mm Hg OD and 7 mm Hg OS. The right optic disc was flat with a 0.6 cup- to- disc ratio. The left optic disc was moderately edematous, and the cup was obliterated. The posterior poles were clear. A magnetic resonance scan of the head and orbits produced normal findings. Lumbar puncture revealed an opening pressure of 250 mm H2 0 with normal cerebrospinal fluid ( CSF) constituents ( normal CSF opening pressure is less than 250 mm H2 0 in obese people) ( 1). A tentative diagnosis of pseudotumor cerebri syndrome was made, based on her symptom profile, obese body habitus, and borderline normal CSF opening pressure. She opted for observational management and 6 months later, her headache and left optic disc edema had completely resolved. Her IOP was consistently in the mid teens. During this interval, she had lost 15 pounds. Case 2 A 51- year- old mildly overweight woman had chronic open- angle glaucoma, which had been treated medically for 14 years. In 1987, she underwent a trabeculectomy in her left eye, but the filtering bleb closed shortly thereafter. In 1991, she underwent a trabeculectomy with administration of supplemental subconjunctival 5- fluorouracil in her right eye. Two years later in 1993, a second trabeculectomy with administration of mitomycin in her left eye was performed for persistently elevated IOP and development of a shallow inferior arcuate scotoma. Intraocular pressure was 19 mm Hg OD and 28 mm Hg OS before surgery and 20 mm Hg OD and 10 mm Hg OS 1 week after surgery. One month later, she noted transient visual obscurations in her left eye on arising from bed each morning. She reported no headache, pulsatile tinnitus, or diplopia. Her medical history was significant for hypertension and hyperthyroidism, which had been treated with radioactive iodine. On examination, her weight was 207 pounds 121 122 A. KAWASAKI AND V. PURV1N and blood pressure was 152/ 90. She had visual acuity of 20/ 20 OD and 20/ 30 OS with normal color vision in each eye. Goldmann perimetry in her right eye produced normal results and in her left eye showed mild generalized constriction of isopters and enlarged blind spot. There was a trace of relative afferent pupillary defect in the left eye ( 0.3 log units). Biomicroscopy showed bilateral superior blebs, notably larger in the left eye than in the right, with adjacent peripheral iridectomies. Intraocular pressure was 19 mm Hg OD and 12 mm Hg OS. Ocular motility was normal. The right optic disc was flat with a 0.3 cup- to- disc ratio and sloping of the inferotemporal neuroretinal rim. The left optic disc was moderately hy-peremic and edematous ( Figure 1). A computed tomographic scan of the head and orbit, without and with contrast, serum protein electrophoresis, complete blood count, Westergren sedimentation rate, antinuclear antibodies, test results for syphilis, fluorescent treponemal antibody absorption results, and glucose concentration were normal. Lumbar puncture performed in the lateral decubitus position showed a CSF opening pressure of 195 mm H20. Findings in cerebrospinal fluid analysis were normal. No specific treatment was instituted. At serial follow- ups, there was no change in her left optic disc edema or optic nerve function. The IOP in her left eye ranged between 8 to 12 mm Hg. One year later, magnetic resonance imaging of the head and orbit yielded normal findings, and a second determination of CSF opening pressure was 210 mm H20. A trial of acetazolamide was considered but rejected because of concern about potential hypotony. Surgical closure of the filtering bleb in her left eye was not considered because the IOP was finally controlled and stable. Optic nerve sheath fenestration was not undertaken because optic nerve function was stable. Therefore, observational management was continued and 3 years later, her vision and left optic disc edema remained unchanged. DISCUSSION Our two patients with chronic glaucoma developed unilateral optic disc edema with good optic nerve function after uncomplicated trabeculectomy for persistently elevated IOP. One cause of unilateral optic disc edema after trabeculectomy is ocular hypotony ( hypotony is defined as IOP less than 6.5 mm Hg) ( 2). Our patients had no recorded postoperative IOP in the hypotonous range. Another cause of unilateral optic disc edema after trabeculectomy is coexisting pseudotumor cerebri syndrome. Greenfield and Liebmann ( 3) recently described such a case. A 41- year- old obese woman who had juvenile primary open- angle glaucoma and was treated with topical lOP- lowering agents and oral acetazolamide eventually underwent a trabeculectomy with supplemental subconjunctival 5- fluorouracil injections in her left eye. All preoperative medications were discontinued. The lowest recorded IOP in the left eye in the first postoperative week was 9 mm Hg. Two months later optic disc edema developed only in the left eye, which had undergone surgery. Neuroimaging was normal and ICP was elevated at 410 mm HzO, consistent with a diagnosis of pseudotumor cerebri. It has been proposed that the lamina cribrosa sclerae represents an interface at which the ICP in the subarachnoid space behind it is countered by the IOP in front of it. In their patient with pseudotumor cerebri and glaucoma, Greenfield and Leibmann ( 3) hypothesized that the absence of papilledema before trabeculectomy was caused by a balanced ICP- IOP gradient across the lamina cribrosa- that is, increased ICP countered by high IOP. The lowered postoperative IOP disturbed this ICP- IOP gradient and allowed manifestation of papilledema. Likewise, the authors suggest that continued elevation of IOP in the patient's nonoperated right eye protected the optic disc from development of papilledema. Unlike the patient of Greenfield and Liebmann, our patients who developed optic disc edema after trabeculectomy did not have a markedly increased ICP or markedly decreased ( hypotonous) IOP. They had ICP in the high- normal range without history of papilledema, although patient 1 may have had symptoms ( headache, tinnitus) related to her borderline ICP. Both had postoperative IOP in the low- normal range. If the structural state of the optic disc is reflective of the ICP- IOP gra- FIG. 1. Fundus photograph of the right ( A) and left ( B) optic discs. The left optic disc is moderately edematous. Chorioretinal folds and engorgement of the retinal veins are noted. ./ Neuro- Ophtlmlmol, Vol. 18. No. 2, 1998 OPTIC DISC EDEMA 123 dient across the lamina cribrosa sclerae, then perhaps a relative increase in ICP alone or a relative decrease in IOP alone may result in optic disc edema, regardless of the absolute ICP or IOP measurements. In our patients, we believe that altering the ratio of ICP to IOP ( caused by decreased TOP after trabeculectomy) was more important than the absolute ICP or IOP values in contributing to postoperative optic disc swelling. This hypothesis may also explain why patient 2 who had had bilateral trabeculectomy had development of only left optic disc edema. We postulate that the relatively higher IOP in her right eye compared with that in her left eye resulted in a smaller alteration of the ICP- IOP ratio- apparently not enough of an alteration to produce a structural change in the lamina cribrosa sclerae. We also wondered whether differences in the magnitude of the ICP- IOP ratio between the two eyes might partly explain the asymmetric degree of disc edema seen in some patients with pseudotumor cerebri. We reviewed the charts of 280 patients diagnosed by us with pseudotumor cerebri and noted no patients who had asymmetric papilledema and asymmetric IOP. This suggests that other pressures ( systemic arterial, orbital venous) and mechanical factors ( small scleral opening, crowded disc) also play a role in the development of disc edema ( 4,5). In conclusion, optic disc edema after trabeculectomy may result from decreasing the IOP into the low- normal range in the setting of a high- normal ICP. The absolute ICP and IOP measurements seem less important than the change in ICP- IOP ratio. The natural course of this entity appears benign. REFERENCES 1. Corbett JJ, Mehta MP. Cerebrospinal fluid pressure in normal obese subjects with pseudotumor cerebri. Neurology 1983; 33: 1386- 8. 2. Pedcrson . IE. Ocular hypotony. In: Ritch R, Shields MB, Krupin T, eds. The Glaucomas. St. Louis: C. V. Mosby, 1989: 281- 90. 3. Greenfield DS, Liebmann JM. Pseudotumor cerebri appearing with unilateral papilledema after trabeculectomy. Arch Ophthalmol 1997; 115: 423- 6. 4. Hedges TR, Zaren HA. The relationship of optic nerve tissue pressure to intracranial and systemic arterial pressure. Am .1 Ophthalmol 1973; 75: 90- 8. 5. Gordon RN, Burdc RM, Slamovits T. Asymptomatic oplic disc edema. ./ Neuro- Ophthalmol 1997; 17: 29- 32. ./ Neum- Ophtlwlmol, Vol. IS, No. 2, 1998 |
