Macular edema occurs when fluid and protein deposits collect on or under the macula of the eye (a yellow central area of the retina) and causes it to thicken and swell (edema). The swelling may distort a persons central vision, because the macula holds tightly packed cones that provide sharp, clear, central vision to enable a person to see detail, form, and color that is directly in the centre of the field of view. Cause
The causes of macular edema are numerous and different causes may be inter-related. It is commonly associated with diabetes. Chronic or uncontrolled diabetes type 2 can affect peripheral blood vessels including those of the retina which may leak fluid, blood and occasionally fats into the retina causing it to swell. Age-related macular degeneration may cause macular edema. As individuals age there may be a natural deterioration in the macula which can lead to the depositing of drusen  under the retina sometimes with the formation of abnormal blood vessels. Replacement of the lens as treatment for cataract can cause pseudophakic macular edema. (‘pseudophakia’ means ‘replacement lens’)  also known as Irvine-Gass syndrome The surgery involved sometimes irritates the retina (and other parts of the eye) causing the capillaries in the retina to dilate and leak fluid into the retina. Less common today with modern lens replacement techniques. Chronic uveitis  and intermediate uveitis can be a cause.
Higher frequency use of topical steroids provides benefit in difficult to treat cases.Diabetic macular edema may be treated with laser photocoagulation, reducing the chance of vision loss.In 2010, the US FDA approved the use of Lucentis intravitreal injections for macular edema.Iluvien, a sustained release intravitreal implant developed by Alimera Sciences, has been approved in Austria, Portugal and the U.K. for the treatment of vision impairment associated with chronic diabetic macular edema (DME) considered insufficiently responsive to available therapies. Additional EU country approvals are anticipated.In 2013 Lucentis by intravitreal injection was approved by the National Institute for Health and Care Excellence in the UK for the treatment of macular edema caused by diabetes and/or retinal vein occlusion.On July 29, 2014, Eylea (aflibercept), an intravitreal injection produced by Regeneron Pharmaceuticals Inc., was approved to treat DME in the United States. Research
In 2005, steroids were investigated for the treatment of macular edema due to retinal blood vessel blockage such as CRVO and BRVO.A 2014 Cochrane Systematic Review studied the effectiveness of two anti-VEGF treatments, ranibizumab and pegaptanib, on patients with macular edema caused by CRVO. Participants on both treatment groups showed a reduction in macular edema symptoms over six months.Another Cochrane Review examined the effectiveness and safety of two intravitreal steroid treatments, triamcinolone acetonide and dexamethasone, for patients with from CRVO-ME.