Navigated Laser In Branch Retinal Vein Occlusion Study

Purpose of the study

In a 12-month prospective, randomized 1:1 study of patients with branch retinal vein occlusion (BRVO) and macular edema, the investigators aim to

1. Examine the treatment response of patients treated with intravitreal aflibercept (Eylea®) and navigated retinal laser (Navilas®)(Group 1) as compared to patients treated with intravitreal aflibercept only (Group 2), and
2. Identify non-invasive retinal biomarkers (retinal oxygen saturation, macular ischemia and retinal vascular arteriolar and venular calibre) for successful treatment outcome.

Problem statement

Severe visual loss or blindness in BRVO is often caused by macular edema. Until a few years ago, treatment included observation or macular grid pattern laser photocoagulation. With this treatment it was often possible to stabilize the disease in a few treatment sessions. However, in recent years better visual outcome has been demonstrated with intravitreal injections of vascular endothelial growth factor (VEGF) inhibitors like ranibizumab or aflibercept. Even though this is encouraging, patients on average need nine injections in the first 12 months. The high number of repetitive treatments is a concern for patients as well as society due to the invasiveness of the treatment and the price of the drug. Hence, it is warranted to develop newer treatment regimens combining the efficacy of intravitreal anti-VEGF with the potential stabilizing effect of macular laser photocoagulation. This would be an approach that might minimize the number of injections and its side effects while still providing acceptable visual outcomes for the patients.

In addition to providing the optimal treatment, it is important to identify non-invasive markers of disease activity and treatment outcome in order to enable individualised and personalised treatment while providing novel research opportunity in this potentially blinding disease.

Theoretical foundation (Literature background)

Retinal vein occlusion (RVO) is a common cause of visual loss in the elderly with a 15-year incidence of 2.3% of the population. The condition is classified anatomically according to the site of the occlusion. Seventy eight percent of patients have an occlusion of a branch vein, which is often complicated by macular edema, leading to visual impairment.

Branch retinal vein occlusion is diagnosed based on intraretinal hemorrhages in the retinal sector drained by the affected vein. In time, hemorrhages often resorb, but vision-threatening complications may arise. The common link for these is ischemia, that leads to an upregulation of VEGF, which then causes neovascularization, vasodilation and increased vascular permeability, leading to macular edema, the most common reason for vision loss in BRVO.

With ischemia in mind, measurements of retinal oxygen saturation could provide important information regarding the metabolic status of the inner retina. The vascular oxygen saturation of the inner retina is a functional marker, that can be measured non-invasively by a spectrophotometric retinal oximeter. Even though this has only been studied on a very limited basis in BRVO, proof-of-concept has been established by Lin et al. and Hardarson et al., demonstrating cross-sectional changes in retinal oxygen saturation. However, they did not correlate these to treatment outcome.

Ischemia can also be evaluated as a structural marker. The most reliable way of evaluating this is to measure the area of retinal non-perfusion by fundus fluorescein angiography. Non-perfusion has been demonstrated as a strong marker of disease severity, but it is still uncertain if this is reversible, and if so, if this surrogate marker of VEGF-activity can potentially be used to guide the treatment.

Retinal vascular calibre is another non-invasive method of evaluating the retinal vascular system. The research unit have performed validated, semiautomatic measurements of the retinal arteriolar and venular diameters in studies of diabetic retinopathy, and demonstrated cross-sectional associations as well as longitudinal predictions of intra- and extraocular microvascular complications of type 1 diabetes. For instance, Broe et al. demonstrated that patients with narrower arterioles and wider venules had an independently higher risk of developing various microvascular complications in a 16-year prospective study. This emphasizes the importance of structural retinal changes in relation to the metabolic function. In BRVO, Youm et al. demonstrated that patients with BRVO had narrowing of retinal arterioles and venules, but any potential correlation to treatment outcome has not been examined.

Current state of the art In 1984 the Branch Vein Occlusion Study for macular edema demonstrated that 63% of patients treated with macular laser gained two or more lines of vision, compared to 36% of untreated eyes. Based on this, the standard treatment for many years was to perform macular laser photocoagulation if vision had not improved after 3-6 month of observation. However, the introduction of VEGF-inhibitors within the last decade has changed the landscape dramatically. Randomized, controlled studies like BRAVO and VIBRANT demonstrated a higher efficacy of ranibizumab and aflibercept versus sham and laser with 53-61% of patients gaining at least three lines of vision.

In Denmark, the present guidelines for treatment of BRVO with macular edema has been set in September 2015 by "Rådet for Anvendelse af Dyr Sygehusmedicin". The council recommended that intravitreal aflibercept or ranibizumab should be used as first line of treatment. However, the council also raised concern, stating that they expected an annual increment of approximately 600 new patients with RVO in Denmark putting both financial and societal burden on the individual and the healthcare system. With the chronic nature of the disease in mind, this is expected to put a significant weight on the healthcare system for the years to come.

Choice of methods

Navigated laser photocoagulation is the cornerstone of the present study. This is a novel laser delivery system that holds many advantages as compared to traditional macular laser photocoagulation. Navigated laser makes treatment easier to plan, perform and document.

Firstly, it includes an eye tracking system, which makes it safe to treat close to the foveal center. For a traditional laser it is recommended to keep a minimum distance of 500μm from the foveal center in order to limit the risk of severe visual loss. For safety reasons many physicians prefer to keep an even larger distance, which often limits the beneficial effect of the treatment. Secondly, the navigated laser system is automatic which improves the accuracy to target focal lesions by 27%. Thirdly, navigated laser makes it possible to import images from fluorescein angiographys and allows for clear delineation and consequent treatment of the diseased microvasculature.

Hypothesis

The investigators hypothesize that:

1. As compared to intravitreal aflibercept monotherapy, combination treatment with intravitreal aflibercept and navigated laser leads to a lesser number of intravitreal injections needed to stabilise vision in patients with BRVO and macular edema.
2. It is possible to use non-invasive retinal markers to predict disease activity and treatment outcome in patients with BRVO and macular edema. Regardless of treatment regimen, the investigators believe that patients who respond well to treatment will have (1) lower retinal venular oxygen saturation, (2) less macular ischemia, and (3) lower retinal venular calibre.