Vitrectomy may be indicated for complications of diabetic retinopathy, including vitreous hemorrhage and retinal detachment. It may also be indicated for persons with traumatic penetrating ocular injury, non-diabetic vitreous hemorrhage, rapidly progressing infectious endophthalmitis, and cataract extractions complicated by a vitreous loss or an underlying inflammatory condition.
Wide fluctuations in intra-ocular pressure (IOP) have been documented during vitrectomy in animal models. Such fluctuations in IOP are posited to have potential adverse effects on retinal and optic nerve function and visual acuity recovery, especially for patients with compromised retinal or optic nerve blood flow and decreased ocular perfusion pressure.
An indirect method of monitoring IOP during vitrectomy surgery has been developed (Armoor Ophthalmics, Houston, TX), which involves placing disposable blood pressure transducers into the line tubing used for vitrectomy infusion. Moorhead et al (2005) reported on a clinical study in which this indirect method of IOP measurement was compared to direct measurement during vitrectomy procedures in 10 patients. Intra-ocular pressure was directly measured by inserting a catheter pressure transducer by an extra pars plana incision directly into the vitreous. During various maneuvers of vitrectomy, including air-fluid exchange and gas-forced fusion, pressure measurements were taken simultaneously from the indwelling pressure transducer and the disposable blood pressure sensors in the infusion line. The directly measured IOP varied between 0 and 120 mm Hg during vitrectomy. The investigators reported in each case how indirectly measured IOP during fluid flow, calculated from infusion line pressures, correlated with the directly measured IOP. The investigators commented that the variation in pressures encountered during these vitrectomy surgeries weree similar to measurements reported during cataract surgery. The investigators stated that it is likely that pressure variations documented in this study may be detrimental, but the physiological significance of these findings requires further study.
Following vitrectomy surgery (e.g., repair of macular hole, retinal detachment), face-down positioning may be required for several weeks to maximize retinal tamponade and, subsequently, hole closure or retinal attachment. The vitrectomy face-down positioning system (also known as a vitrectomy chair or a vitrectomy support system) is a device that may be appropriate in selected cases to assist the patient in maintaining a face down position. The rental of a vitrectomy face support may be necessary for up to 6 weeks after vitrectomy surgery.
Ishikawa et al (2009) evaluated the safety and effectiveness of intra-vitreal injection of bevacizumab (IVB) advanced to vitrectomy for severe proliferative diabetic retinopathy (PDR). A total of 8 eyes of 6 patients (33 to 64 years old, all male subjects) with severe PDR were investigated. An intra-vitreal injection of 1.25 mg bevacizumab was carried out 3 to 30 days before planned vitrectomy. All cases showed minimum bleeding during surgical dissection of fibro-vascular membrane. Two cases receiving bevacizumab 7 days before the surgery showed strong fibrosis and adhesion of fibro-vascular membrane, resulted in some surgical complications. The cases having IVB for shorter time did not show extensive fibrosis. The authors concluded that pre-treatment of bevacizumab is likely effective in the vitrectomy for severe PDR. The appropriate timing of vitrectomy after bevacizumab injection should be further evaluated.
In a review on diabetic retinopathy (DR), Cheung et al (2010) noted that although anti-vascular endothelial growth factor (VEGF) therapy has promising clinical applications for the management of DR, its long-term safety in patients with diabetes has not yet been established. Local adverse events of IVB include cataract formation, infection, retinal detachment, vitreous hemorrhage, as well as potential loss of neural retinal cells. Furthermore, a significant portion of anti-VEGF agents injected into the eye could pass into the systemic circulation. Thus, systemic inhibition of angiogenesis is a potential risk. Also, although clinical trials on the use of intra-vitreal anti-VEGF therapy for the treatment of age-related macular degeneration generally show low (0.6 to 1.2 %) rates of stroke, this risk could be increased in patients with DR because of pre-existing diabetes-related vascular disease.
Nicholson and Schachat (2010) stated that many observational and pre-clinical studies have implicated VEGF in the pathogenesis of DR, and recent successes with anti-VEGF therapy for age-related macular degeneration have prompted research into the application of anti-VEGF drugs to DR. These investigators reviewed the numerous early studies that suggest an important potential role for anti-VEGF agents in the management of DR. The authors concluded that for diabetic macular edema, phase II trials of intra-vitreal pegaptanib and intra-vitreal ranibizumab have shown short-term benefit in visual acuity. Intra-vitreal bevacizumab also has been shown to have beneficial short-term effects on both visual acuity and retinal thickness. For PDR, early studies suggest that IVB temporarily decreases leakage from diabetic neovascular lesions, but this treatment may be associated with tractional retinal detachment. Furthermore, several studies indicate that bevacizumab is likely to prove a helpful adjunct to diabetic pars plana vitrectomy for tractional retinal detachment. Finally, 3 small series suggest a potential beneficial effect of a single dose of bevacizumab to prevent worsening of DME after cataract surgery. The authors noted that use of anti-VEGF medications for any of these indications is off-label. Despite promising early reports on the safety of these medications, the results of large, controlled trials to substantiate the safety and efficacy of anti-VEGF drugs for diabetic retinopathy are eagerly awaited.
In a prospective, comparative case series, El-Sabagh and colleagues (2011) evaluated the effects of intervals between pre-operative IVB and surgery on the components of removed diabetic fibro-vascular proliferative membranes. A total of 52 eyes of 49 patients with active diabetic fibro-vascular proliferation with complications necessitating vitrectomy were included in this study. Participant eyes that had IVB were divided into 8 groups in which vitreo-retinal surgery was performed at days 1, 3, 5, 7, 10, 15, 20, and 30 post-injection. A group of eyes with the same diagnosis and surgical intervention without IVB injection was used for comparison. In all eyes, proliferative membrane specimens obtained during vitrectomy were sent for histopathologic examination using hematoxylin-eosin stain, immunohistochemistry (CD34 and smooth muscle actin), and Masson's trichrome stain. Main outcome measure was comparative analysis of different components of the fibro-vascular proliferation (CD34, smooth muscle actin, and collagen) among the study groups. Pan-endothelial marker CD34 expression levels starting from day 5 post-injection were significantly less than in the control group (p < 0.001), with minimum expression (1+) in all specimens removed at or after day 30 post-injection. Positive staining for smooth muscle actin was barely detected in the control eyes at day 1, and consistently intense at day 15 and beyond (p < 0.001). The expression level of trichrome staining was significantly high at day 10, compared with control eyes (p < 0.001), and continued to increase at subsequent surgical time points. The author concluded that a pro-fibrotic switch was observed in diabetic fibro-vascular proliferation after IVB, and these findings suggest that at approximately 10 days post-IVB the vascular component of proliferation is markedly reduced, whereas the contractile components (smooth muscle actin and collagen) are not yet abundant. Moreover, the authors noted that their histologic findings are in agreement with many published clinical findings and might be predictive of an optimal time interval for the pre-operative use of adjunctive IVB, which makes surgery more successful with less intra-operative bleeding and complications; thus resulting in better visual outcomes. However, such favorable outcomes need validation from large-scale clinical studies.