eyes vs. only 10% of the untreated eyes. Cataract surgery was performed in 54% of the treated eyes and none of the untreated eyes. This study showed the potential benefits of intravitreal triamcinolone, but it did not directly compare this treatment to laser.

AmajorrandomizedclinicaltrialoftheDiabeticRetinopathyClinicalResearchNetwork (DRCR) recently compared laser and intravitreal triamcinolone for the treatment of DME [22]. Eight hundred and forty eyes received either focal/grid photocoagulation, 1 mg of intravitreal triamcinolone, or 4 mg of intravitreal triamcinolone. Additional treatments were given every 4 months for persistent or new edema. This study found that after 2 years of follow-up, laser was superior to triamcinolone in preventing vision loss and caused less complications. However, the differences in vision were modest. The average change in visual acuity at 2 years was 1 ± 17 letters for the laser group, −2 ± 18 letters for the 1-mg triamcinolone group, and −3 ± 22 letters for the 4-mg triamcinolone group. This statistically significant difference was not caused by steroid-induced cataract; an analysis of patients that were pseudophakic or without clinically relevant lens changes did not show a benefit of triamcinolone over laser. Greater than or equal to 15 letters of improvement was seen in 18% of the laser group, 14% of the 1-mg triamcinolone group, and 17% of the 4-mg triamcinolone group. Overall, this study emphasized that laser treatment remains the gold standard of treatment for DME. When considering these treatments, potential drawbacks are that triamcinolone is limited by complications of glaucoma and cataract, and both treatments lead to a relatively modest amount of vision improvement. These issues set the stage for ranibizumab treatment. The use of ranibizumab for DME can avoid the potential complications of triamcinolone while potentially providing significant vision improvement.

RANIBIZUMAB FOR DME

Ranibizumab is the Fab fragment of a humanized monoclonal antibody that binds all isoforms of VEGF-A, thereby inhibiting its signaling pathway. To produce ranibizumab, the portion of an anti-VEGF murine monoclonal antibody that binds VEGF was mass produced and then altered by affinity maturation [27, 28] (Fig. 2A). Ranibizumab was originally developed for the treatment of AMD. The MARINA and ANCHOR clinical trials demonstrated that after 2 years of follow-up, ranibizumab prevents moderate visual loss in approximately 95% of patients [29, 30]. Moderate vision gain was seen in approximately one-third of patients. While demonstrating the efficacy of ranibizumab for AMD, these studies also established the safety profile of this treatment. The most severe complications are endophthalmitis and retinal detachment, which have a risk of only 1.3% and less than 1.0%, respectively [29]. With the proven safety and efficacy of ranibizumab for neovascular AMD, it was logical to consider whether ranibizumab could improve DME.

Nguyen et al. first studied ranibizumab for DME in a nonrandomized clinical trial involving ten patients [31]. The investigation has been referred to as the READ-1 study (Ranibizumab for Edema of the mAcula in Diabetes). In this study, each patient received 0.5 mg of ranibizumab at baseline and at 1, 2, 4, and 6 months. One week after the first injection, the median and mean reductions in foveal thickness were 88 and 130 mm, respectively. At the study’s primary end point of 7 months, the schedule of ranibizumab

Fig. 2. Ranibizumab and bevacizumab were both created from an anti-VEGF murine monoclonal antibody (Anti-VEGF-A MAb). To create ranibizumab (A), the portion that binds VEGF was inserted into a human FAb framework and mass produced using an Escherichia coli vector to produce rhuFAb version 1. Through affinity maturation, rhuFAb V1 is modified to increase its binding ability by approximately 140-fold. The final product is ranibizumab. To create bevacizumab (B), the portion of the murine antibody that binds to VEGF was inserted into a different humanized Fab variant. This antibody was then mass produced in Chinese hamster ovary (CHO) cells to produce bevacizumab (courtesy of Genentech, Inc.).

injections led to median and mean reductions in foveal thickness of 261 and 246 mm, respectively. This was a mean reduction in excess foveal thickening of 85%. While READ-1 was not a masked, placebo-controlled trial, the visual acuity at 7 months also improved from baseline with a median and mean of 11 and 12.3 letters gained, respectively. Another study by Chun et al. evaluated five patients treated with 0.3 mg of ranibizumab and another five patients treated with 0.5 mg of ranibizumab [32]. The patients received injections at baseline, 1 and 2 months. At 3 months, both doses were associated with an improvement in visual acuity and a decrease in central retinal thickness. The 0.3-mg group gained an average of 12 ± 20 letters, and the 0.5-mg group gained a mean of 7.8 ± 8.1 letters. For central retinal thickness at 3 months, the 0.3-mg group had an average decrease of 45.3 ± 196.3 mm, and the 0.5-mg group had an average decrease of 197.8 ± 85.9 mm. Because of the small sample size, no conclusions can be drawn about any potential differences of the dosing regimens. Interestingly, for both groups, the mean amount of improvement in visual acuity fell after 3 months as the patients were followed out to 6 months, while the mean central retinal thickness continued to improve from month 3 to 6. With regard to the safety of ranibizumab injections for these patients, Nguyen et al. found no adverse systemic or ocular side effects. Chun et al. also did not see adverse systemic side effects, although five of the patients did have intraocular inflammation that resolved within several weeks. The ranibizumab used in

Change from Baseline in Best Corrected Visual Acuity

Fig. 3. Changes in visual acuity from baseline in patients with DME treated in the READ-2 study with ranibizumab, focal/grid laser, or a combination of ranibizumab and laser. The mean (±standard error of the mean) change from baseline in number of letters read at 4 m at 3 and 6 months was significantly greater for ranibizumab alone vs. focal/grid laser alone. The combination group was not significantly different from the other two groups at either time point. *P = 0.01; †P = 0.0003 by one-way analysis of variance and Bonferroni post hoc analysis. RBZ ranibizumab; ETDRS Early Treatment Diabetic Retinopathy Study [33].

the study by Chun et al. has been reformulated since then, with the ranibizumab used in the READ-1 study and subsequent studies in DME and AMD having not induced any reported inflammation. Thus, these studies suggested that ranibizumab is safe and can play a key role in DME. However, the study also raised a question regarding the optimal dosing schedule for ranibizumab and pointed to the need for a larger, double-masked, randomized, controlled trial.

The READ-2 study took this next step. READ-2 is a prospective, controlled, multicenter trial involving 126 patients with DME to be conducted over 36 months, with the primary end point at 6 months [33]. Subjects were randomized 1:1:1 into three groups: (group 1) 0.5 mg of ranibizumab at baseline and months 1, 3, and 5; (group 2) focal/grid laser photocoagulation at baseline and month 3 if needed; and (group 3) a combination of 0.5 mg of ranibizumab and focal/grid laser at baseline and month 3. Group 2 thus provided a comparison to the current standard of care. Group 3 was designed because it has been hypothesized that, in cases of extensive retinal thickening, laser may be more effective if ranibizumab is first administered to reduce the retinal thickening. In turn, the more effective laser treatment may then enable less frequent administration of ranibizumab.

The primary end point for the READ-2 study was the change from baseline visual acuity at 6 months [33]. Study subjects who received ranibizumab only (group 1) had the most improvement in visual acuity at 6 months with a mean gain of 7.24 letters (Fig. 3). This was statistically significant from those that received laser only (group 2), as this group had a mean loss of 0.43 letters. Those that received both ranibizumab and laser (group 3) had a mean gain of 3.80 letters, and this was not statistically significant from group 1 or 2. The mean reduction in excess foveal thickness was 50, 33, and 45% in groups 1, 2, and 3, respectively. Thus, the OCT measurements showed similar trends between the groups. However, it should be noted that the laser only group had no improvement in visual acuity despite a 33% mean reduction in excess foveal thickness. It is well known that a reduction in macular edema after laser photocoagulation is not always accompanied by an improvement of visual acuity [34].

The randomized, controlled READ-2 clinical trial demonstrated that ranibizumab may be superior to focal/grid laser. Nevertheless, this conclusion should be considered carefully as the follow-up for the study was only 6 months and only included up to two laser treatments. Patients in the READ-2 study are being followed until month 36. It is certainly possible that longer follow-up may yield different results in the future, which was exemplified by the previously mentioned DRCR study comparing focal/grid laser with intravitreal triamcinolone acetonide [22]. In this study, 4 mg of triamcinolone led to a greater improvement in mean visual acuity than the laser treated group after 4 months. But as discussed earlier, the laser group had a superior visual acuity outcome compared to triamcinolone at 2 years. The differences in visual acuity shifted in favor of the laser group with longer follow-up. While the results of the READ-2 study are noteworthy, it will be important to see the results of more extensive follow-up. The larger RISE and RIDE phase III trials sponsored by Genentech (South San Francisco, CA) evaluate monthly injections of ranibizumab (0.3 and 0.5 mg) with a 2-year primary end point; patients in the control arm received sham injections. Rescue therapy with laser photocoagulation began at month 3 of these studies. The primary outcome measure for these studies is the proportion of patients who gain 15 letters in BCVA compared to baseline. These two studies have completed recruitment and should have completed data collection for the primary outcome by October 2012.

Yet another consideration highlighted by the READ-2 study is the optimal dosing regimen of ranibizumab for DME. While it was a study with only ten patients, the READ-1 trial had a more aggressive regimen of injections (baseline, 1, 2, 4, and 6 months) compared to the READ-2 study (baseline, 1, 3, and 5 months) [31]. This resulted in an 85% reduction of excess foveal thickness as compared to the 50% achieved by the READ-2 study. The RISE and RIDE trials may help determine if monthly dosing of ranibizumab for DME is more effective. Ultimately, it will be important to devise an effective antiVEGF treatment that is longer lasting.

PEGAPTANIB FOR DME

Ranibizumab is one of the several anti-VEGF treatments that have been studied for the treatment of DME. The first anti-VEGF medication that was delivered by intravitreal injection was pegaptanib, an aptamer that specifically inhibits the VEGF 165 isoform