Diabetic retinopathy is characterized by the retinal non-perfusion areas (the retinal hypoxia), leading to the upregulation of vascular endothelial growth factors (VEGF). Subsequently, VEGF causes increased vascular leakage, retinal vasodilation, and the development of macular edema. Based on these mechanisms, the oxygen saturation in the retinal vessels or retinal oxygen consumption would reflect the degree of underlying retinal hypoxia. Injections of anti-VEGF agents (ranibizumab) reduce the macular edema and may suppress the progression of retinal nonperfusion area. However, so far, limited information is available on the effects of anti-VEGF agents (ranibizumab) to the retinal hypoxic conditions. In addition, baseline conditions of the oxygen saturation in the retinal vessels may provide us the predictive information on the treatment efficacy of anti-VEGF agents (ranibizumab) to the diabetic macular edema.~Recent reports suggest that anti-VEGF agents (ranibizumab) may suppress the progression of retinal nonperfusion area. This protective effect would cause the increase of the oxygen consumption in the diabetic retina. We expect that the current study using the retinal oximetry would show the protective effects of ranibizumab on the hypoxia in the diabetic retina.~In addition, previous studies showed an increased VEGF level in the aqueous humor or the vitreous, depending on the progression of the diabetic retinopathy. The level of VEGF in the aqueous humor would reflect the retinal hypoxia and may be of use for the prediction of the visual prognosis. This study is designed to analyze the effects of ranibizumab (Lucentis) to the retinal oxygen saturation or consumption in eyes with diabetic macular edema.~Each eye will be treated with three initial monthly injections of intravitreal ranibizumab 0.5 mg (Lucentis), followed by retreatment as needed, guided by monthly clinical examinations including biomicroscopy, VA measurement, and optical coherence tomography (OCT) examination. The principal criteria for retreatment are the reduction of VA, foveal and extrafoveal macular edema or serous retinal detachment on OCT.~At each visit, both eyes are scheduled to be examined with VA measurement, OCT examination, oxygen saturation measurement. Just before the first injection of ranibizumab, aqueous humor will be extracted with a pipet.~Retinal oximetry will be performed with Oxymap (Oxymap ehf, Reykjavik, Iceland). Briefly, the device simultaneously acquires digital images at two wavelengths and automatically tracks retinal vessels on both images. Retinal vessel oxygen saturation is estimated by spectrophotometric analysis of light reflected from retinal vessels and from the immediately surrounding retina. Oxygen saturation measurements are made on major temporal arteries and veins. Briefly, the first and second degree vessels are used, with the addition of third degree vessels in images where peripapillary haemorrhage prevented analysis close to the optic disc. Vessel segments chosen for analysis are used consistently for consecutive measurements in the same retina.
Recent reports suggest that anti-VEGF agents (ranibizumab) may suppress the progression of retinal nonperfusion area. This protective effect would cause the increase of the oxygen consumption in the diabetic retina. We expect that the current study using the retinal oximetry would show the protective effects of ranibizumab on the hypoxia in the diabetic retina. This study is designed to analyze the effects of ranibizumab (Lucentis) to the retinal oxygen saturation or consumption in eyes with diabetic macular edema.