What should doctors be watchful for after a pars plana vitrectomy (PPV)? Dr. Sahebaan Sethi takes us through an insightful overview surrounding PPV with research and from her own experience in the field. The clinical pearls shared below highlight the importance of working with retinal specialists to effectively address secondary glaucoma post-PPV.
Because of increased retinal comorbidities in the older population, it’s crucial that glaucoma specialists work in close collaboration with retinal surgeons. Often, there are patients with increased pressure following vitreoretinal surgeries, and this can happen anytime during the postoperative period. Moreover, detecting glaucomatous damage may be difficult when the underlying retinal disorder precludes accurate assessments of visual fields or the optic nerve.
PPV is done for several reasons — vitreous hemorrhage, macular holes, epiretinal membranes, retinal detachment repair and proliferative diabetic retinopathy. During the procedure, substitutes like heavy liquid (perfluorocarbon), intraocular gases, or silicone oil (SO) may be used. Heavy liquid is usually removed at the time of the surgery; however, other internal tamponade agents may be present for weeks to several months.
Often, patients with high risk of redetachment may require the tamponade for longer periods of time and the retinal surgeon might opt not to remove it – thus, compromising the aqueous outflow in several ways, which results in increased intraocular pressure (IOP).
Incidence
IOP elevation is the most common complication following PPV surgery. The reported incidence of postoperative glaucoma ranges from 20%-26%.1,2,3 In a prospective study of 222 cases, an IOP rise of 5 to 22 mm Hg during the first 24 hours occurred in 61% of eyes and an increase of 30 mm Hg occurred in 35%.4 Koreen et al.5 observed a 11.6% incidence in late- onset open angle glaucoma among 285 vitrectomized eyes, although rates were higher in eyes that had undergone cataract extraction (15.0%) versus phakic eyes (1.4%). These rates are similar to those reported by Luk et al.6 More recently, a retrospective study by Wu et al.7 examined 198 patients and found that elevated IOP incidences were 19.2% in vitrectomized eyes, compared with 4.5% in the unoperated fellow eye. It’s safe to say that these findings show PPV is a risk factor for secondary glaucoma.
Evaluation
It is important to routinely monitor patients’ postoperative IOP, which is best done by applanation tonometry (indentation tonometers are unreliable due to scleral surgery and intraocular gas interfering with scleral rigidity). One study found that pneumatic tonometry and indentation tonometry underestimated the elevated IOP by 25% and 79% respectively (Poliner LS and Schoch LH, 1987). Tonopen is also an acceptable means, although it underestimates the IOP if it’s above 30 mm Hg.
Pathogenesis
We approach glaucoma according to its presentation, which could either be open-angle or closed-angle glaucoma. The possibilities for open-angle include gas expansion without angle closure — this is the most common cause of acute post-vitrectomy IOP elevation, along with inflammation, silicone oil (sans pupillary block), corticosteroid response and blood mediated mechanism (hyphema, ghost cell or hemolytic).8 The mechanisms for closed-angle glaucoma include ciliary body edema causing pupillary block (the most common mechanism), followed in descending order by pupillary block secondary to fibrin, gas, and lastly silicone oil.9
Secondary glaucoma due to intraocular gas injection
The incidence of high IOP after PPV and long-acting gas tamponade was established by a report that found a 43% incidence of pressures greater than 25 mmHg.9
Sulfur hexafluoride can remain in the eye for 10 to 14 days and up to 55 to 65 days for perfluoropropane.10 Elevated IOP is generally due to an intraocular gas bubble, which causes open-angle glaucoma. Frequently, there is a secondary angle closure pathology – this is due to posterior pressure of the gas on the iris, which causes the angle to narrow. This is well demonstrated in the aphakic patient, who can relieve the pupillary block by posturing face down. It could also be a result of ciliary body edema and iridocorneal apposition.
Risk factors that would predispose a patient to an acute increase in IOP after gas tamponade include the concentration of the gas; patient’s older age; post-operative fibrin in the anterior chamber; concurrent use of a scleral buckle; and use of intraoperative endophotocoagulation.11,12
There are a few points of caution when dealing with this type of patient. They should avoid inhaling any of the nitrous oxide anesthetic during a dental visit or with general anesthesia. This gas diffuses rapidly and causes rapid expansion of the gas bubble, causing IOP to skyrocket as high as 70 mmHg, leading to retinal artery occlusion and ischemia. Generally, it’s suggested that these patients do not increase their elevation by 2,500 feet or travel by air where changes in the cabin pressure can instantaneously cause severe elevation of IOP.13
In Dr. Sethi’s experience, any immediate acute rise in IOP post-operatively can be controlled with topical anti-glaucoma medications and oral carbonic anhydrase inhibitors. However, if the IOPs remain uncontrolled, an anterior chamber paracentesis may help, or a small volume of gas may be aspirated from the vitreal cavity with a 27G needle and a 1ml syringe. Prudent vitreo-retinal surgeons use prophylactic treatment with intraoperative carbonic anhydrase, as this may control the post-operative pressure spike.
Elevated IOP and silicon oil
Reported rates of chronic elevated IOP following use of silicone oil vary enormously—from 2.2 percent to 56 percent.14-16
Risk factors for developing high pressure after silicone oil include: silicone oil in the anterior chamber; preexisting glaucoma; aphakia; early postoperative pressure spike; trauma; diabetes; and postoperative neovascularization of the iris.
Elevated IOP can occur via several mechanisms− acute angle closure with or without pupillary block; open-angle glaucoma with emulsified or non-emulsified silicone oil in the anterior chamber; continuing rubeosis of the iris leading to secondary angle closure; or simple idiopathic open-angle glaucoma.
The incidence of acute angle closure with pupillary block has dropped dramatically since retinal surgeons have begun creating a prophylactic inferior peripheral iridotomies (PI) at the time of surgery. However, these iridotomies may still close spontaneously.17,18
Also, angle closure with pupillary block is more likely if the patient is aphakic. If the PI closes it may be reopened with the Nd YAG. However, Nd YAG laser PI can have a high rate of failure of 78% in reopening inferior PIs (Reddy, 1995).
At one time, it was thought that whenever silicone oil made it into the anterior chamber, IOP would surely rise; however, various studies have shown that high IOP may occur with or without oil in the anterior chamber.19, 20, 21, 22
Management of these patients can be quite tricky. Frequently, removal of the silicone oil may not be enough to resolve the underlying problem; for that reason, it remains a controversial way to control glaucoma. It was reported that removal of the emulsified oil didn’t change the IOP in 91% of subjects.23 In another study, silicone oil removal and medications produced pressure control in only 25% of patients.17 Another study found that patients who underwent silicone oil removal, with or without glaucoma surgery, and those who underwent glaucoma surgery alone, experienced satisfactory IOP control.24
Surgical management of these patients should be closely discussed with retinal surgeons. This is because removing the silicone oil may not always be possible as it’s associated with re-detachment in 11 to 33% eyes.17 If the retina surgeon feels that it’s safe to remove the oil, then, Dr. Sethi says she would proceed with its removal and simultaneous placement of a glaucoma drainage device; glaucoma drainage implants can control the IOP in the majority of eyes after PPV and silicone oil injection.25 Removal of silicone oil alone does not allow eyes to achieve normal IOP. If the retinal surgeon feels the oil needs to remain in the eye for a longer period, and aqueous suppressants are not effective, a glaucoma drainage implant in an inferior quadrant or a trans-scleral diode cycloablation could be considered.
According to Kim and Baumal, topical and systemic anti-glaucoma medications controlled IOP in 30% of eyes (mean number of medications: 1.5), with oral acetazolamide required in 7/18 cases.26 Fifty percent of the eyes required chronic glaucoma treatment. Removal of SO and medical therapy (25%) achieved normal IOPs. Control of IOPs were achieved in 10/14 eyes that underwent surgical intervention. Five of 14 that underwent trabeculectomy with mitomycin C achieved normal IOP (two cases with additional medical therapy and one with surgery alone, post ROSO).
In the same study, one patient had an anterior chamber tube shunt to the encircling band (ACTSEB) and achieved normal IOP with additional medical therapy. Three patients underwent cyclocryotherapy, with 33% achieving normal IOP without and 33.3% with medical therapy. Four patients underwent transcleral cyclophotocoagulation with a 75% success rate of controlling the IOP. In patients with SO induced glaucoma, removal of the oil may reduce the IOP. If the oil is not removed before tube glaucoma surgery, migration of oil into tube can occur, even if it is placed inferiorly, with the hope that the oil will float and not occlude the tube.
Transscleral cyclophotocoagulation has shown successful IOP control in 74-82% of patients after 1 year although the visual function was poor in these patients (Bloom et al 1997 and Han et al, 1999).27 Early removal of silicone oil has been noted to have reduced risk of secondary glaucoma and similar re-detachment rates (Han et al., 1998).
Conclusion
Secondary glaucoma post-PPV may be one of the most refractory cases to deal with and presents a challenge to both glaucoma and retinal specialists. The causes may be multi-factorial and management depends entirely on the mechanism of glaucoma. Patients with whom aggressive medical management is unsatisfactory, may benefit from silicone oil removal, glaucoma drainage devices or cyclodestructive procedures.
References:
1 Faulborn J, Conway BP, Machemer R. Surgical complications of pars plana vitreous surgery. Ophthalmology. 1978;85(2):116-125.
2 Aaberg TM, Van Horn DL. Late complications of pars plana vitreous surgery. Ophthalmology. 1978;85(2):126-140.
3 Ghartey KN, Tolentino FI, Freeman HM, et al. Closed vitreous surgery XVII.Results and complications of pars plana vitrectomy. Arch Ophthalmol. 1980;98:1248-1252.
4 Han DP, Lewis H, Lambrou FH Jr, et al. Mechanism of intraocular pressure elevation after pars plana vitrectomy. Ophthalmology. 1989;96:1357-1362.
5 Koreen L, Yoshida N, Escariao P, et al. Incidence of, risk factors for, and combined mechanism of late-onset open-angle glaucoma after vitrectomy. Retina. 2012;32:160–167.
6 Luk FO, Kwok AK, Lai TY, et al. Presence of crystalline lens as a protective factor for the late development of open angle glaucoma after vitrectomy. Retina. 2009;29:218–224.
7 Wu L, Berrocal MH, Rodriguez FJ, et al. Intraocular pressure elevation after uncomplicated pars plana vitrectomy: results of the Pan American Collaborative Retina Study Group. Retina. 2014;34:1985–1989.
8 Han DP, Lewis H, Lambrou FH Jr, et al. Mechanisms of intraocular pressure elevation after pars plana vitrectomy. Ophthalmology. 1989;96:1357.
9 Ichhpujani P, Jindal A, Katz JL. Silicone oil induced glaucoma: a review. Graefes Arch Clin Exp Ophthalmol. 2009;247(12):1585-1593.
10 Chang S. Intraocular gases. In: Ryan SJ, ed. Retina. vol. 3. St. Louis: CV Mosby, 1989:245.
11 Han DP, Lewis H, Lambrou FH, Mieler WF. Mechanisms of intraocular pressure elevation after pars plana vitrectomy. Ophthalmology. 1989;96:1357-1362.
12 Chen PP, Thompson JT. Risk factors for elevated intraocular pressure after the use of intraocular gases in vitreoretinal surgery. Ophthalmic Surg Lasers. 1997;28:37-42.
13 Mills MD, Devenyi RG, Lam WC, et al. An assessment of intraocular pressure rise in patients with gas-filled eyes during simulated air flight. Ophthalmology. 2001;108:40-44.
14 Cibis PA. Recent methods in the surgical treatment of retinal detachments: intravitreal procedures. Trans Ophthalmol Soc U K. 1965;85:111-127.
15 De Corral LR, Cohen SB, Peyman GH. Effect of intravitreal silicone oil on intraocular pressure. Ophthalmic Surgery. 1987;18:446-449.
16 Nguyen QH, Lloyd MA, Heuer DK, et al. Incidence and management of glaucoma after intravitreal silicone oil injection for complicated retinal detachments. Ophthalmology. 1992;99:1520-1526.
17 Honavar SG, Goyal M, Majji AB, et al. Glaucoma after pars plana vitrectomy and silicone oil injection for complicated retinal detachments. Ophthalmology. 1999;106:169-177.
18 Federman JL, Schubert HD. Complications associated with the use of silicone oil in 150 eyes after retina-vitreous surgery. Ophthalmology. 1988;95:870-876.
19 Haut J, Ullern M, Chermet M, Van Effenterre G. Complications of intraocular injections of silicone combined with vitrectomy. Ophthalmologica. 1980;180:29-35.
20 Watzke RC. Silicone retinopiesis for retinal detachment. A long-term clinical evaluation. Arch Ophthalmol. 1967;77:186-196.
21 Valone J, McCarthy M. Emulsified anterior chamber silicone oil and glaucoma. Ophthalmology. 1994;101:1908-1912.
22 Nguyen QH, Lloyd MA, Heuer DK, Baerveldt G, Minckler DS, Lean JS, Ligett PE. Incidence and management of glaucoma after intravitreal silicone oil injection for complicated retinal detachments. Ophthalmology. 1992;99:1520-1526.
23 Moisseiev J, Barak A, Manaim T, Triester G. Removal of silicone oil in the management of glaucoma in eyes with emulsified silicone. Retina. 1993;13:290-295.
24 Budenz DL, Taba KE, Feuer WJ, Eliezer R, Cousins S, Henderer J, Flynn HW. Surgical management of secondary glaucoma after pars plana vitrectomy and silicone oil injection for complex retinal detachment. Ophthalmology. 2001;108:1628-1632.
25 Ishida K, Ahmed I, Netland PA. Ahmed Glaucoma Valve surgical outcomes in eyes with and without silicone oil endotamponade. J Glaucoma. 2009;18:325-330.
26 Kim RW, Baumal CR. Anterior segment complications related to vitreous substitutes. Ophthalmol Clin North Am. 2004;17(4):569-576.27 Han L, Cairns, JD, Campbell WG, et al. Use of silicone oil in the treatment of complicated retinal detachment: Results from 1981 to 1994. Aust N Z J Ophthalmol. 1998;26:299-304.
