Performance of Retinal Procedures in Previously Vitrectomized Eyes

Unique challenges can arise in these patients.

ANKIT DESAI, MD · LEVENT AKDUMAN, MD

Previously vitrectomized eyes have aqueous humor instead of vitreous humor in the vitreous cavity. Aqueous humor lacks the viscous and semicompact nature of the vitreous humor. Modifications to retinal surgical techniques and anticipation of tissue response in previously vitrectomized eyes are dependent on the surgeon’s awareness of the distinct properties of these ocular substances.

AQUEOUS VS VITREOUS

One must take into account the chemical properties of the aqueous vs vitreous humor when injecting intravitreal substances (bevacizumab, ranibizumab, aflibercept, antibiotics, steroids, etc.) into a previously vitrectomized eye. If prior surgery involved the removal of the vitreous base, one should expect a high incidence of leakage due to a lack of a vitreous plug to the injection site (Figure). The 23-gauge tunnel required for the injection of a dexamethasone intravitreal implant will have an even greater chance of leakage.

Another aspect to consider when injecting intraocular substances is the increased rate of clearance in the aqueous compared to the vitreous humor. A study presented at the Association for Research in Vision and Ophthalmology in 2011 showed that the half-life of intravitreally injected bevacizumab in vitrectomized macaque eyes was reduced by 60%.¹ Chin et al. studied the pharmacokinetics of intravitreal triamcinolone in 84 rabbit eyes and demonstrated that its half-life nearly doubled in nonvitrectomized eyes compared to vitrectomized eyes (2.89 days vs 1.57 days).²

For cases of endophthalmitis, one may perform a vitreous tap with relative ease in previously vitrectomized eyes. Because the aqueous humor replaces the vitreous cavity, a sample is relatively easier to obtain than it is in a nonvitrectomized eye. The viscous nature of vitreous could preclude it from being drawn into a 25-g needle, thus requiring OR time and vitrectomy.

As mentioned earlier, injected drugs have enhanced clearance from the aqueous in post-vitrectomized eyes. However, cases of endophthalmitis can also arise in the presence of silicone tamponades. The surgeon should be cautious when injecting intravitreal medications into silicone-filled eyes and should be aware of the dosage adjustments necessary to avoid inadvertent retinal toxicity.

Hegazy et al. demonstrated that a full non-toxic dose of various antibiotics (ceftazidime, vancomycin, and ganciclovir), recommended for eyes without silicone oil, caused retinal toxicity secondary to drugs trapped in the retrosilicone-preretinal space, leading to prolonged retinal exposure. Their study concluded that a significant decrease in original dosing, 75% in this case, is required to avoid toxicity.³

PARS PLANA VITRECTOMY

When planning pars plana vitrectomy in previously vitrectomized eyes, it is well known that all 20-, 23-, and 25-g procedures can be performed. Most surgeons place single sutures at the sclerotomy site at the conclusion of 20-g PPV cases. This, for the most part, eliminates the risk of postoperative leakage and hypotony. The sutureless technique employed with 23- and 25-g PPV has a higher incidence of leakage from sclerotomy sites postoperatively in previously vitrectomized eyes compared to naïve eyes.

Figure. Subconjunctival bleb formation in a previously vitrectomized eye immediately following an injection of intravitreal bevacizumab.

Amato et al. conducted a retrospective review of 25-g transconjunctival sutureless vitrectomy cases in 43 eyes of 38 patients. Six eyes had previous vitrectomies, all of which had postoperative leakage, while two of the six had hypotony with choroidal detachments. The authors hypothesized that the increased incidence of leakage could possibly have been related to the lack of a plugging effect from the peripheral vitreous.⁴

Woo et al. found similar findings when performing 23-g transconjunctival sutureless vitrectomy. They concluded that risk factors for intraoperative leakage were prior vitrectomy, age, and vitreous base dissection.⁵

Suture closure of the sclerotomy sites at the conclusion of the case will minimize the risk of leakage in previously vitrectomized eyes. This virtually eliminates the risk of postoperative hypotony secondary to leakage, and it possibly decreases the risk of infection. From personal experience, the most commonly encountered problem is the complaint of irritation or foreign body sensation with the suture.

Rhegmatogenous retinal detachment repair in previously vitrectomized eyes can be approached in much the same way as repair in nonvitrectomized eyes. For detachments that begin from superior tears, the approach remains the same. The surgeon can choose to perform a second vitrectomy with gas tamponade and either cryotherapy or laser vs a scleral buckle. The vitrectomy time is usually decreased, and often these eyes require little to no additional incision.

With detachments that have inferior origins, one might believe that a second vitrectomy with a full gas or oil tamponade is required for repair because the viscous support of the vitreous is lost, so external indenting procedures, with or without external draining, might not be as successful.

The role of vitreous in buckling procedures was addressed by Mester et al. in a study published in 2002. They conducted a retrospective review of 718 buckled eyes with an analysis of a subset of 41 previously vitrectomized eyes. They found no statistically significant difference in the reattachment rate between vitrectomized (71.2%) and nonvitrectomized eyes (82.9%), and they concluded that the choice of surgical technique for previously vitrectomized eyes should be based on the number and extent of breaks or the presence and stage of posterior vitreoretinopathy.⁶

With regard to PVR, the amount and stage may vary depending on the degree of the previous vitrectomy. If the vitreous base has been fully shaved, the amount of anterior traction associated with PVR will likely be less. However, if extensive PVR is present, a thorough vitrectomy of the vitreous base is required, along with some degree of retinectomy in severe cases.

The need for additional surgery can arise when a vitrectomized eye still contains an intraocular tamponade of gas or silicone oil. Recurrent retinal detachments can occur as a gas tamponade is reabsorbed, and the time frame for recurrence depends on the type of gas used.

Of the commonly used gases, sulfur hexafluoride (SF₆) usually resorbs in one to two weeks and perfluoropropane (C₃F₈) in six to eight weeks.⁷ During the resorption process, a recurrent RD can manifest from a missed or new tear or secondary to PVR.

Due to the buoyant nature of the gas, detachments most frequently begin inferiorly. If the detachment is a result of undrained fluid from the initial repair, it is reasonable to observe and see if fluid is pumped out by the retinal pigment epithelium. However, if a detachment develops secondary to a new tear or PVR, immediate intervention is preferred.

The approach with a silicone oil tamponade differs. Because oil does not decrease in size, the area not under-tamponade usually develops the worst preretinal membrane proliferation. Due to the fluid density of silicone oil vs vitreous, the former compartmentalizes the eye and floats atop the vitreous. Given these innate properties, one can deduce that this may be why preretinal proliferation commonly occurs in the inferior periphery.

Macular epiretinal membranes are also commonly seen and are usually correlated with patients who habitually sleep on their backs. These membranes can usually be peeled at the time of oil removal. In cases of recurrent detachments with an oil tamponade, the oil needs to be removed and the detachment repaired, followed by replacement of the oil or gas tamponade.

OTHER TECHNIQUES

Epiretinal membrane peeling and macular hole repair are two procedures that are routinely performed in vitrectomized eyes. ERMs arise following retinal breaks, and they can reoccur after previous peeling. Macular holes may occur following vitreous collapse and macular traction in nonvitrectomized eyes, and they can persist or reoccur in vitrectomized eye regardless of whether internal limiting membrane peeling was performed during the initial surgery.

Prior to surgery, macular optical coherence tomography provides visual confirmation of the presence of preretinal membranes, while intraoperatively, staining techniques can be used to enhance visualization. “Positive” staining is achieved with trypan blue (TB) for ERMs and indocyanine green (ICG) for the ILM. (Other options are available; however, these are the most commonly employed.⁸⁾

One can assume that the decrease in fluid density would have effects on the dispersion, clearance, and concentration of the staining chemical. Veckeneer et al. tested the effects of varying concentration of TB in vitrectomized rabbit eyes and found no signs of retinal toxicity, as seen by electroretinogram testing and histologically, following prolonged exposure to 0.06% TB. They did, however, find toxicity associated with prolonged exposure to 0.2% TB in the lower retinal layers, mainly the photoreceptor layer.⁹

Chao et al. investigated the retinal effects of intravitreal ICG in macular hole surgery in rabbit eyes. Varying concentrations of ICG were injected into three groups: intravitreal injection of ICG in vitrectomized eyes; nonvitrectomized eyes followed by fluid-fluid exchange after three minutes; and nonvitrectomized eyes. Their study determined that a 0.05% concentration with minimal exposure time (less than three minutes) would offer the intraoperative benefit of ICG staining while avoiding irreversible retinal toxicity.¹⁰

If the surgeon is utilizing injectable stains, technique plays a critical role is minimizing complications.

Previously vitrectomized eyes produce more turbulent flow if infusion is running during dye injection. To avoid staining the posterior capsule in phakic patients and wide dispersion, one should lower the rate of flow or briefly turn off the infusion. Effective staining is usually achieved in one minute or less, after which infusion can be restarted and excess dye can be aspirated.

Also when injecting dye, care must be taken to direct the needle toward the area of interest, particularly in ILM staining with ICG in macular hole repair. If retinal breaks are present or suspected, the surgeon should forgo the use of dyes, particularly ICG, as studies have shown their toxic effects on the RPE.

Triamcinolone is another viable option for ILM enhancement as the particulate matter of triamcinolone provides a three-dimensional view of the ILM as it sits on the ILM. However, one drawback is difficult visualization secondary to the increased turbulent flow in vitrectomized eyes. Lower infusion rates can decrease this; however, prolonged low rates would not be recommended given the high risk of hypotony, which can also make visualization more difficult.

CONCLUSION

When planning additional surgery in previously vitrectomized eyes, several adjustments must be made when managing new or ongoing pathologies. Anticipating potential complications and implementing modified techniques will help minimize any unwanted outcomes. RP

REFERENCES

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2. Chin HS, Park TS, Moon YS, Oh JH. Difference in clearance of intravitreal triamcinolone acetonide between vitrectomized and nonvitrectomized eyes. Retina. 2005;25:556-560.

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4. Amato JE, Akduman L. Incidence of complications in 25-gauge transconjunctival sutureless vitrectomy based on the surgical indications. Ophthalmic Surg Lasers Imaging. 2007;38:100-102.

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6. Mester U, Anterist N, Kroll P, Brieden-Azvedo S. The role of the vitreous in retinal detachment surgery with external buckling. Ophthalmologica. 2002; 216:242-245.

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9. Veckeneer M, van Overdam K, Monzer J, et al. Ocular toxicity study of trypan blue injected into the vitreous cavity of rabbit eyes. Graefes Arch Clin Exp Ophthalmol. 2001;239:698-704.

10. Chao AN, Chen SN, Kuo YH. Retinal function and histologic changes following intravitreal injection of indocyanine green in a rabbit model. J Ocul Pharmacol Ther. 2004;20:373-374.