Vascular endothelial growth factor (VEGF) has been implicated in the etiology of various diseases of the retina including diabetic macular edema (DME) and diabetic retinopathy (DR), exudative age-related macular degeneration (AMD), retinal vein occlusions (RVO), myopic choroidal neovascularization, radiation retinopathy, and others. The use of anti-VEGF intravitreal injections has profoundly impacted the treatment and visual outcomes in many of these entities, including macular edema (ME) secondary to RVOs.
Historically, ME and neovascularization secondary to RVO have been treated with macular grid and peripheral scatter photocoagulation, respectively. In the past decade, various clinical trials have repeatedly demonstrated the superior visual acuity results and outcomes with anti-VEGF treatments. The aim of this article is to provide an update to the relevant studies pertinent to the treatment of RVOs.
EPIDEMIOLOGY AND ETIOLOGY
Retinal vein occlusions include branch retinal vein occlusions (BRVO), central retinal vein occlusions (CRVO), and occasionally hemiretinal vein occlusions (HRVO). The Blue Mountains Eye Study reported a 10-year incidence of RVOs at 1.6%.1 The Beaver Dam Eye Study reported a 15-year cumulative incidence of 2.3% for RVOs, with 1.8% for BRVOs and 0.5% for CVRO.2 Both studies demonstrated increased prevalence with advancing age.1,2
Most commonly, BRVO is associated with systemic hypertension, though other risk factors than age also include cardiovascular disease, increased body mass index, hyperviscosity syndromes, and autoimmune conditions.3,4 Sharing a common adventitial sheath and compression of the vein at the arterio-venous (AV) crossing increased by arteriorsclerosis can lead to abnormal flow, endothelial damage, and thrombus of the vein.5-7 The anterior position of the artery to the vein may also play a role in pathogenesis as 99-100% of BRVOs occur at the AV crossing with an anterior artery crossing over the vein compared with 61-67% in controls.6-9 Macular edema related to BRVO continues to be the leading source of vision loss in affected patients occurring in 5-15% of patients over 1 year.10 Macular ischemia, complications of neovascularization, and epiretinal membrane are other secondary complications that may impact vision.
Similarly, CRVO has been associated with increasing age, hypertension, diabetes mellitus, race, hyperlipidemia, and glaucoma.11,12 The etiology of CRVO is thought to be secondary to thrombus formation of the central retinal vein at the level of or posterior to the lamina cribosa.13 The contribution of hypertension and atherosclerosis/arteriosclerosis in the setting of a common adventitial sheath is thought to increase the risk of compression of the central retinal vein by the central retinal artery. Factors including inflammation, hypercoaguability, and other systemic conditions have also been presented as important risk factors, especially in young patients, in the formation of CRVO.14,15 Overall the visual prognosis of CRVO is worse than that of BRVO, particularly in the ischemic subset, and largely depends on vision at presentation. The definition of ischemia varies in the literature but generally relies on a combination of clinical and angiographic findings.16,17 Macular edema is also a leading cause of visual decline in CRVO patients but can resolve in up to 30% of patients in the nonischemic subtype.18 In a study by Hayreh and colleagues (2012),19 they found in their series of patients with ischemic CRVOs that the cumulative incidence of any neovascularization and neovascular glaucoma at 9 months was 52% and 34%, respectively. In the Central Vein Occlusion Study (CVOS), neovascularization of the iris or angle occurred in 16% of eyes with 10-29 disc areas of nonperfusion and in 52% in eyes with ≥75 disc areas of nonperfusion.20 Conversion from the nonischemic to the ischemic type generally occurs in about a third of patients over 3 years and can have a dramatic impact on vision.
TREATMENTS BEFORE ANTI-VEGF THERAPY
Before the anti-VEGF era, 2 landmark multicenter randomized clinical trials helped guide management of ME and neovascularization secondary to RVO for the past quarter century.
The Branch Vein Occlusion Study (BVOS) established the standard of care for nearly 25 years in the treatment of ME secondary to BRVO. The results of this study demonstrated nearly twice as many patients in the treatment arm (65%) gaining 2 or more lines of vision in comparison to the control arm (37%) in 3 years of follow-up.21 The recommendation from this trial suggested waiting 3 months after diagnosis (for possible spontaneous improvement), followed by grid laser if there was presence of persistent ME and vision worse than 20/40. This study also provided guidance in its finding that scatter peripheral photocoagulation can be applied after development of neovascularization to decrease rates of vitreous hemorrhage.22
The CVOS was a multipart study assessing the benefits of panretinal photocoagulation (PRP) in ischemic CRVOs in preventing and treating anterior segment neovascularization along with the impact of grid photocoagulation on visual acuity in patients with ME secondary to CRVOs. The authors recommended careful observation of ischemic CRVOs as the preventative PRP group still had 20% of patients developing iris neovascularization, which needed more treatment.16 In regards to ME, the CVOS did not demonstrate a benefit for grid laser on visual acuity in patients with CRVO and vision 20/50 or worse secondary to ME, though there was a trend toward improvement in younger patients.23
Treatment of RVO markedly changed with the advent of anti-VEGF therapy in the mid-2000s (see next section).
TREATMENT WITH ANTI-VEGF THERAPY
Ranibizumab (Genentech, San Francisco) is a 48 kD recombinant humanized monoclonal antibody with affinity toward all isotypes of VEGF-A, inhibiting its biological activity. It was first approved in the United States for intraocular use in 2006 after 2 phase 3 studies (MARINA and ANCHOR) demonstrating its safety and efficacy in limiting vision loss and disease progression in neovascular AMD.24,25
The use of ranibizumab for treatment of ME secondary to BRVO was approved by the US Food and Drug Administration (FDA) after a phase 3 randomized clinical trial (BRAVO) in 2010.26 The study randomized 397 patients with ME secondary to BRVO into 2 ranibizumab groups (0.3 mg and 0.5 mg) and sham injection group, with each receiving scheduled monthly injections for 6 months, with rescue grid photocoagulation if indicated. The primary endpoint, mean change in best corrected visual acuity (BCVA) at 6 months, demonstrated a 16.6 and 18.3 letter gain in 0.3 mg and 0.5 mg, respectively, versus a 7.3 letter gain in the sham group (P < 0.0001). Reduction in central foveal thickness (CFT), rapidity of vision improvement, percentage of patients with at least 20/40 BCVA or at least 15 letter gain, and the effect of visual function on activities of daily life (ADL) were all outcomes that favored the ranibizumab treatment groups. The strongly positive outcomes of this study allowed for the clinical use of ranibizumab 0.3 mg in the treatment of ME secondary to BRVO. It also vastly aided the eventual approval of the drug by the FDA for clinical usage in the setting of RVO in the United States.
Concurrent to BRAVO, a sister phase 3 randomized clinical trial (CRUISE) was also published in 2010 studying patients with ME secondary to CRVO.27 This study similarly randomized 392 patients into scheduled monthly injections for 6 months of 0.3 mg ranibizumab, 0.5 mg ranibizumab, or sham medication. At 6 months, the mean letter gains in BCVA from baseline were 12.7 in the 0.3 mg group, 14.9 in the 0.5 mg group, and 0.8 in the sham group (P < 0.0001). The study also similarly demonstrated the percentage of patients with at least 20/40 BCVA, at least 15 letter gain, effect on ADL, reduction in CFT, and brevity of vision improvement in the treatment groups as in BRAVO. Also shown was the statistically significant difference in patients with BCVA of 20/200 or less at the 6-month primary endpoint.
These 2 studies, BRAVO and CRUISE, were the first large randomized controlled trials studying the safety and efficacy of ranibizumab on ME in patients with RVOs. These studies also both incorporated a 6-month observation period (after the 6-month scheduled treatment regimen) in which patients were seen monthly but only treated for BCVA of at least 20/40 or CFT of at least 250 μm. The exception was that the previous sham treatment arm received 0.5 mg ranibizumab. On average, patients received fewer injections than during the initial 6-month treatment period yet were able to maintain their visual gains. The previously treated sham group had an expected, yet significant, increase in visual outcomes but they did not fully catch up with patients in the original treatment groups at the end of the 12-month period. The results of these studies paved the way for FDA approval of ranibizumab 0.3 mg for the treatment of RVOs in 2010, as was noted above.
Other studies of significance included an open-label extension (HORIZON) of these 2 studies with 205 and 181 patients who completed BRAVO and CRUISE, respectively. This was a 12-month study with at least 3-month follow-up intervals with retreatment criteria of BCVA of at least 20/40 or CFT of at least 250 μm. This study demonstrated that for BRVOs the visual gains were largely retained but that there was a definite worsening of visual outcomes in patients with CRVOs under this study’s treatment protocol. It was noted that a significant percentage of patients with BRVOs in BRAVO and some in HORIZON had received grid laser, possibly stabilizing their disease process. The results led the authors to conclude that patients with CRVOs likely need to be seen more frequently than every 3 months.
In another multicenter open-label single arm extension of patients who completed the HORIZON study (RETAIN), 34 BRVO patients and 32 CRVO patients were followed for a mean of 49 months.28 Patients were initially seen monthly for 1 year and then every 3 months (with the option to be seen as frequent as monthly) for another year. They were treated with ranibizumab if there was intraretinal fluid in the fovea and also received scatter photocoagulation if 2 consecutive visits required injections. The study showed 17/34 (50%) of BRVO and 12/27 (43.8%) of CRVO patients at photocoagulation follow-up had resolution of ME (no intraretinal fluid for 6 months) at last visit. In the other half of patients with unresolved ME, they still required an average of 3 injections over their last year whereas the 56% of unresolved CRVO-related ME patients required 6 injections over their last year of follow-up. This study provided evidence that although resolution occurs in about half of patients with RVO with treatment, a substantial number continue to need frequent injections even years after initial treatment, particularly in CRVO patients. Figure 1 illustrates an example of a patient with CRVO where periodic injections of both anti-VEGF along with corticosteroids were periodically administered for the treatment of ME even years after initial presentation.
Aflibercept (Regeneron, Tarrytown, NY) is a 115 kD fusion VEGF trap with high affinity for VEGF-A along with VEGF-B and placental growth factor. It was the first FDA approved medication for wet AMD in 2011 after 2 parallel phase 3 studies (VIEW1 and VIEW2) showed its efficacy and safety.29 There was also suggestion that injections every 2 months with this VEGF trap may be equivalent to the gold standard at the time, ranibizumab.
A phase 3 randomized, double masked trial (VIBRANT) compared monthly aflibercept with focal photocoagulation in a 52-week period in patients with ME secondary to BRVO. A total of 183 patients were randomized 1:1 to receiving either 6 injections of 2 mg of aflibercept every 4 weeks and maintenance injections every 8 weeks from weeks 24 to 48 or photocoagulation at baseline with sham injections up until week 48. Both groups had availability of rescue treatments if specific criterion were met including rescue injections in the photocoagulation group at week 24 with 3 injections every 4 weeks (q4) followed by q8 week injections until week 48.
The primary outcome was the percentage of patients with at least 15 letter BCVA gain at the 24-week time point, which was 52.7% in the aflibercept group and 26.7% in the photocoagulation group. At the 52-week time point, 57.1% and 41.1% in the aflibercept and the photocoagulation groups, respectively, gained at least 15 letters in BCVA with 80.7% of the photocoagulation group receiving rescue injections at a mean of 4.4 treatments from weeks 24 to 48. The mean change in letters was 17.0 versus 6.9 at 24 weeks and 17.1 versus 12.2 at 52 weeks in the aflibercept versus the photocoagulation groups, respectively.
These differences all reached statistical significance. The study helped demonstrate the effectiveness of aflibercept in regaining visual acuity in patients with BRVO and ME. Notably, the results tended to favor the early treatment of BRVO with aflibercept as opposed to grid photocoagulation as patients in the photocoagulation group with rescue aflibercept still had inferior visual outcomes at 52 weeks compared with the initial aflibercept cohort.
Two parallel phase 3, randomized, clinical trials (COPERNICUS and GALILEO) conducted in North America, Europe, and Asia evaluated the use of aflibercept versus sham in the treatment of ME secondary to CRVO.30,31 The design of the 2 trials compared 2 mg aflibercept injections q4 weeks for 6 injections and as needed afterwards according to prespecified study criteria. After the 24-week endpoint, sham group patients in the COPERNICUS study could also receive aflibercept if they fit retreatment criteria.
At the primary endpoint of 24 weeks, the COPERNICUS study demonstrated that 56.1% of patients in the aflibercept group versus 12.3% of the sham group achieved at least 15 letter gain compared with baseline. Similarly, there was a mean +17.3 letter gain versus -4.0 letter loss in the treatment and sham groups, respectively. There were also no cases where neovascularization developed in the aflibercept group and no patients received photocoagulation at 24 weeks. At the 52-week endpoint, 55.3% versus 30.1% of patients in the treatment and the sham groups achieved ≥15 letter gain from baseline, respectively.32 The aflibercept group and sham groups demonstrated a mean +16.2 and +3.8 letter gain, respectively. This study also showed anatomical improvement on optical coherence tomography (OCT) and quality of life (at the 24-week endpoint) favoring aflibercept. The results also noted that in sham patients receiving rescue treatment, at the 52-week endpoint, all the visual outcomes were still statistically inferior to patients in the original treatment group. The authors concluded that this delay in treatment may have deleterious effects on visual potential secondary to chronic ME and advocated early treatment.
In the GALILEO study, at 24 weeks, 60.2% and 22.1% of treatment and sham patients had at least 15 letter gain. At week 52, this proportion was unchanged in the treatment group but increased to 32.4% in the sham group.33 In the treatment versus sham groups, the mean letter gain was +18.0 versus +3.3 letters at 24 weeks and +16.9 versus +3.8 letters at 52 weeks. There was a mean of 2.5 pro re nata (PRN) injections in week 24 to 52 for the treatment group.
Both these studies demonstrated the effectiveness of aflibercept in improving anatomical and visual outcomes of CRVO patients with ME. Additionally, these studies helped show the benefits of treatment compared with natural history but also superior outcomes with early treatment of CRVO-related ME with aflibercept. After the COPERNICUS study, aflibercept gained FDA approval for CRVO-related ME in 2012. In 2014, FDA approval was granted for BRVO-related ME after the 1-year results of the VIBRANT study were presented.
Bevacizumab (Genetech, San Francisco, CA) is a humanized monoclonal antibody 148 kD with activity against VEGF that was first approved by the FDA for the treatment of metastatic colorectal cancer.34 The use of intravitreal bevacizumab dramatically changed the treatment landscape of ocular diseases that involved VEGF as an etiological factor. Starting in 2005, bevacizumab had been shown to improve vision in addition to resolving subretinal fluid and decreasing ME in patients with neovascular AMD and RVO, respectively.35,36 However, at this time, there remains no FDA approval of bevacizumab for any intraocular indication given the lack of large randomized clinical trial data. Still, treatment is within the realm of an accepted “standard of care.”
Numerous early studies have demonstrated the improvement in visual acuity, regression of neovascularization, decrease in central retinal thickness (CRT), and cystoid macula edema (CME) in BRVO patients treated with bevacizumab.37-42 Subsequently, several small prospective studies confirmed the efficacy of bevacizumab in the treatment of ME. Jaisse et al43 (2009) reported a prospective case series of 23 patients with perfused macula edema secondary to BRVO, previously untreated, that were followed every 6 weeks for 1 year and treated if visual acuity (VA) was 20/32 or worse or there was presence of CME on OCT exam. The study showed a statistically significant improvement in CRT on OCT and increase in VA with 57% of patients gaining over 3 Early Treatment Diabetic Retinopathy Study (ETDRS) lines over the 1-year follow-up. A subsequent larger prospective series included 63 untreated eyes with BRVO-related ME that were treated if VA was greater than 20/40 or CRT was at least 250 μm.44 Results showed improvement of logarithm of the minimum angle of resolution (logMAR) BCVA from 0.82 at baseline to 0.40 at 12 months (P < 0.001) and in CRT of 515.3 μm at baseline to 233.6 μm at 12 months (P < 0.001). Several other large retrospective studies confirmed and supported these findings.42,45,46 Although significant visual gains are possible, the presence of macular ischemia continues to be a negative prognostic factor in determining improvement in visual acuity with treatment.47
The efficacy of bevacizumab likewise has been strongly demonstrated in patients with VA secondary to CRVO-related ME. An early small retrospective study with 16 eyes showed halving of the visual angle in 14/16 (87.5%) eyes with a decrease from 887 μm to 372 μm in central foveal thickness at 1-month follow-up.48 A larger multicenter retrospective study included 44 eyes receiving 1.25 mg of bevacizumab every 4-8 weeks for any presence of CME in 2 years of follow-up.49 There was a mean improvement of 3.5 lines at 24 months with 25/44 (56.8%) eyes gaining at least 3 ETDRS lines in BCVA. Central macular thickness decreased from 635 μm at baseline to 364 μm at 24 months in this cohort. Several other prospective studies have also demonstrated the efficacy of bevacizumab in improving BCVA and CRT in CRVO-related ME.50,51
Although the majority of studies have shown a significant increase in visual acuity from baseline, several studies did not see a functional visual gain. Beutel et al52 (2010) reported a retrospective series of 21 eyes with nonischemic CRVOs and showed a significant decrease in CRT without significant improvement in BCVA with an average of 3.7 injections per eye over 12 months. A larger retrospective study (BERVOLT) with 24 months of follow-up looked at 65 patients with CRVO-related ME and stratified patients into presenting BVCA of less than 1.25 and at least 1.25 logMAR units.53 With a mean of 9.7 injections, there was no significant change in either of the subgroups despite a significant improvement in CRT in both groups that was sustained through 24 months. The authors concluded the high incidence of poor VA at baseline (suggestive of ischemic CRVO) may have contributed to the lack of improvement seen.
TREATMENT WITH CORTICOSTEROIDS
With the emergence of anti-VEGF medications, corticosteroids (triamcinolone and/or dexamethasone) are now mainly a second-line treatment given the potential adverse effects including elevation of intraocular pressure and cataract development. Nonetheless, corticosteroids have been shown to decrease vessel permeability, inflammation, and expression of VEGF-A levels and have played an important role in the treatment of ME secondary to retinal vein occlusion.54 The efficacy and safety of intravitreal corticosteroids was shown in the Standard Care vs Corticosteroid for Retinal Vein Occlusion Study (SCORE), a prospective multicenter clinical trial, which randomized patients into standard care, 1 mg, and 4 mg intravitreal triamcinolone treatment arms for patients with BRVO- or CRVO-related ME.
In the SCORE-BRVO trial, patients were randomized into the observation followed by grid photocoagulation and 1 mg and 4 mg triamcinolone dosage groups.55 Retreatment was offered at 4-month follow-up unless retreatment deferral criteria was met. The primary efficacy endpoint was visual gain of 15 or more letters (VALS) at 12 months of follow-up. The study showed 28.9%, 25.6%, and 27.2% of the standard care group, 1 mg, and 4 mg triamcinolone groups achieved this endpoint, respectively. There was a greater VALS mean gain at 4 months in the 4 mg triamcinolone group that was not present at month 12. The visual outcomes and the anatomical OCT of the treatment groups were similar to standard care. In months 12-36, the mean change in VALS score from baseline was greatest in the standard of care group.
In the SCORE-CRVO trial, randomization of patients with CRVO-related ME included an observation group and 1 mg and 4 mg triamcinolone groups.56 At the primary efficacy endpoint, 6.8% of the observation group, 26.5% in the 1 mg triamcinolone group, and 25.6% in the 4 mg triamcinolone group achieved a gain of 15 of more VALS at 12 months of follow-up. The OCT center point thickness decrease from baseline was greater in the 4 mg triamcinolone group than the other groups, but the proportion of patients with 250 μm or less center point thickness was similar across all groups at the 12-month endpoint.
In both the BRVO and CRVO subsets of the SCORE trial, there was a significant difference in patients requiring intraocular pressure (IOP) lowering medications between each of the treatments arms versus standard care.55,56 There was also a significant difference in the progression/development of lens opacities in the BRVO subset as well.55 In the CRVO subset, cataract surgery was significantly more frequent in the 4 mg treatment group versus the 1 mg treatment and observation groups.56
The use of an intravitreal biodegradable dexamethasone implant (Ozurdex, Allergan, Irvine, CA) was investigated in a multicenter, prospective, sham-controlled clinical trial (GENEVA) in patients with ME secondary to BRVO and CRVO.57 The trial randomized patients into 0.35 mg (n = 414), 0.70 mg (n = 427), and sham treatment (n = 426) arms. The study showed a statistically significant difference in eyes achieving at least 15 letter BCVA improvement from baseline in the 2 treatment groups with the greatest response rate of 29% at day 60 compared with 11% in the sham group. The statistical significance was seen in days 30-90 but was not demonstrated at the 180-day endpoint. Mean change in BCVA in letters was superior in both treatment groups compared with sham at all time points. Mean decrease in central subfield thickness was greater in both treatment groups at 90 days but did not achieve statistical significance at day 180. Cataract progression differences between the groups were not statistically significant at 6 months, whereas ocular hypertension was reported in significantly more eyes in both the 0.7 mg (4.0%) and 0.35 mg (3.9%) treatment groups than the sham group (0.7%). The changes in IOP peaked, however, at day 60 and were not significantly different at day 180.
In a 6-month open-label extension of the study that included retreatment with the 0.7 mg dexamethasone implant, there was a predictable and similar pattern of IOP rise and resolution with an additional 10.3% of patients that received two 0.7 mg treatments needing IOP-lowering medications.58 At the end of 12 months, there was a statistically significant difference in incidence of cataract development with retreatment with 0.7 mg dexamethasone (29.8%) versus the delayed treatment group (10.5%), with 1.3% (4/302) of phakic eyes receiving cataract extraction by 12 months in the 0.7 mg retreatment group.
Overall, the SCORE trial was a pivotal trial that demonstrated not only the efficacy of triamcinolone in the treatment of RVOs but also the potential secondary side effects of its use. In the BRVO subset, this study continued to demonstrate the durability of grid photocoagulation for the treatment of ME. In both BRVO and CRVO, this study showed that the use of triamcinolone has a role in the treatment of ME and is likely superior to the natural history of the disease. Additionally, the GENEVA trial showed the effectiveness of a long-term dexamethasone implant, which has added to the variety of treatments already available.
NEOVASCULARIZATION AND/OR RETINAL NONPERFUSION
Although the rate of neovascularization remains low in nonischemic CRVOs, the incidence can exceed 52% in some studies with ischemic CRVO.19 In a small prospective phase 1/2 study clinical trial, 20 patients at high risk for sequelae of neovascularization were injected with 9 monthly injections of ranibizumab, observed for 3 months, then treated pro re nata for 24 months.59 There was a 50% rate (n = 9/18) of development of any sort of neovascularization at mean of 24 months of follow-up.
Nonperfusion in the macula often limits the visual potential of RVO patients undergoing treatment, but there is short-term evidence to suggest stabilization of ischemia with anti-VEGF treatment.60 In a retrospective analysis of the BRAVO and CRUISE data, monthly treated ranibizumab patients compared with sham had a significantly higher percentage without retinal nonperfusion at 6 months.61 There was also reperfusion seen of previously nonperfused areas. Once injections became less frequent at 6 months, the percentage of patients without retinal nonperfusion decreased in the treatment groups. Other long-term studies have shown that intermittent injections may not be able to stop the progression of nonperfusion in RVO patients and can lead to vision loss.62
INITIATION OF TREATMENT
The BVOS provided guidance in observing patients with ME secondary to BRVO for 3 months before anti-VEGF treatment, as a number of these patients improved without treatment. Similarly, in nonischemic CRVOs, ME can also resolve over time. However, there is now a compelling amount of evidence that advocates for early treatment in RVO patients with ME. Figure 2 is a representative example of macular edema in BRVO where treatment is initiated with anti-VEGF upon initial presentation. In 1 prospective study with 1:1 randomization of CRVO ME patients to q6 week bevacizumab versus sham versus 6 months followed by q6 week bevacizumab in both groups, the authors found a significant difference in the percentage of patients achieving 15-letter visual gain.50 At 12 months, 18/30 (60.0%) in the treatment group versus 10/30 (33.3%) in the original sham group were able achieve this primary outcome. This inferiority of visual outcomes was also seen in the phase 3 aflibercept trial in which the sham groups receiving rescue treatments did not obtain equal visual outcomes as the original treatment group at 52 weeks.32,33
COMPARISON OF ANTI-VEGF AGENTS
In recent years, several studies have been performed to compare the efficacy of the available anti-VEGF agents in the treatment of RVOs. One prospective randomized study compared the use of bevacizumab and aflibercept in the treatment of CRVOrelated ME. The study randomized 39 patients into the aflibercept group and 40 patients into the bevacizumab group. Treatment was initiated at baseline and retreatment was performed if there was a worsening of BCVA associated with macular thickening on OCT that had previously resolved. This study showed no statistically significant difference in improvement of BCVA or CFT between the 2 groups at 12 months. However, the mean number injections was 3.72 with aflibercept and 5.44 with bevacizumab, indicating the necessity for slightly more frequent injections in the latter group.
A subsequent, large multicenter prospective randomized clinical trial (SCORE2) also compared aflibercept and bevacizumab in the treatment of CRVO- or HRVO-related ME.63 A total of 182 patients and 180 patients were randomized 1:1 into the bevacizumab and aflibercept groups, respectively. Patients received 6 monthly injections and were evaluated at month 6 using VALS with a margin of 5 to demonstrate noninferiority. The study showed the noninferiority of bevacizumab when compared with aflibercept at the primary outcome in terms of VALS. However, there was a significantly lower odds of complete resolution of fluid and CME with bevacizumab when compared when aflibercept [odds ratio (OR), 2.8; 95% confidence interval (CI), 0.20-0.39; P < 0.001].35
Narayanan et al64 (2016) published a prospective randomized study comparing bevacizumab with ranibizumab, with injection at baseline followed by PRN injection based on increase in CRT or loss of vision for patients with BRVO-related ME. Although there was only a 2.5 letter difference in VA between the 2 groups at 6 months, they were not able to demonstrate noninferiority statistically. Rajagopal and colleagues65 (2015) also performed a prospective study (CRAVE) that randomized BRVO and CRVO patients 1:1 into 2 treatment arms with bevacizumab and ranibizumab with 6 monthly injections. The authors did not find a significant difference in visual acuity (0.33 logMAR gain for bevacizumab versus 0.34 logMAR gain for ranibizumab, P = 0.38) or CFT at 6 months. A recent retrospective study compared PRN aflibercept and bevacizumab treatment in BRVO-related ME and found no significant difference in BCVA and CFT at all time points up to 1 year of follow-up with similar injection numbers in the 2 groups.66
Overall, the trend in recent studies seems to favor no significant difference in visual acuity outcomes between the different anti-VEGF agents in the treatment of RVOs. There have been findings that show that aflibercept has higher likelihood of anatomical resolution of ME with potentially decreased treatment burden.34,35 As of this current review, there has not been a large prospective randomized controlled trial directly comparing all 3 available anti-VEGF medications in the treatment of RVOs similar to what has been performed with DME in protocol T of the Diabetic Retinopathy Clinical Research Network (DRCR.net).67 Such a study may help guide treatment choice by ophthalmologists when considering treatment cost burden and likelihood of significant improvement with one agent over another.
The use of anti-VEGF intravitreal injections has generally been well tolerated with relatively low risks of ocular and systemic complications. Regarding the rate of endophthalmitis with intravitreal injections, Cheung et al68 (2012) published a retrospective study demonstrating a per injection incidence of 0.046% (n = 7/14,960) for endophthalmitis in patients receiving anti-VEGF injections. In the MARINA study, there were 5 cases of presumed endophthalmitis in 477 (1.0%) patients with a per injection incidence of 0.05% (n = 5/10,443)24 with ranibizumab. In all the phase 3 studies for ranibizumab and aflibercept for RVOs combined through 1 year, there were 2 cases of endophthalmitis reported.32,33,69-71 The rate of endophthalmitis with anti-VEGF intravitreal injections remains low and the risks of treatment are significantly outweighed by the benefits.
The advent of anti-VEGF intravitreal medications has been one of the pivotal developments in ophthalmology in the treatment of exudative AMD, diabetic macular edema and retinopathy, RVOs, myopic choroidal neovascularization, and radiation retinopathy, among other indications. Despite the advances in vision gain achieved with the treatment of RVOs with anti-VEGF agents, challenges remain such as macular ischemia, high treatment burden, and progression to neovascular glaucoma. Currently, an individually tailored combination of anti-VEGF therapy and possible corticosteroid treatment, along with comprehensive systemic medical control, can provide a successful pathway toward visual rehabilitation in patients with RVOs.
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