Macular edema occurs when any disease process causes swelling of the macula. The macula is the central vision part of the retina. Edema means: An excessive accumulation of serous fluid in tissue spaces or a body cavity. Since the macula is the part of the retina responsible for central vision, patients with macular edema usually have symptoms of central vision loss. Also, with retinal swelling, many patients will notice distortion.
Macular edema occurs when the small vessels in the retina leak fluid that accumulates in the retinal cells. The retinal vessels leak from:
- Traction: macular pucker, vitreoretinal traction syndrome.
- Inflammation: uveitis, post-surgical, trauma.
- Structural damage: retinal vein occlusion. Diabetic retinopathy.
- Biochemical imbalance: macular degeneration, diabetic retinopathy, retinal vein occlusion, retinal dystrophy.
The treatment of macular edema is guided by the cause of the macular edema.
- Traction: In cases of macular edema caused by traction, surgical release of the traction will usually result in resolution of the macular edema. Vitrectomy surgery within a few years of the onset of the macular edema can reverse the retinal damage and restore vision. When macular edema is present for too long, usually over 3 years, the macula becomes permenantly damaged and surgical treatment of the cause of the macular edema does not usually reverse the damage. This is analogous to a rubber band that is overstretched for a long period of time. When the rubber band is released, it does not always return to its original length. Similarly a swollen retina which is treated after being swollen (edemetaous) for a long period of time will usually not return to its original shape.
- Inflammation: In cases of macular edema caused by inflammation, anti-inflammatory medications can reverse the macular edema. Depending on the situation, many patients can be successfully treated with eyedrops. Usually a combination of a steroid eye drop and a non-steroidal anti-inflammatory eye drop are used. If the macular edema does not respond to topical therapy, posterior subtenon’s injection of steroids, intravitreal injection of steroids, and systemic administration of steroids can be helpful. In complicated cases, for instance in patients with concomitant diabetic retinopathy or macular pucker, some patients will be started on more aggressive therapy in addition or in leu of eye drops.
- Structural damage: Eyes with retinal vein occlusion or diabetic retinpathy can be treated with laser. Even though macular edema in these disease has always been considered secondary to structural damage to the retinal vessels, the macular edema usually does respond to intravitreal injection of steroids or avastin or Lucentis. These drugs all block the effect of vascular endothelial growth factor, a chemical produced by retinal cells in response to hypoxia (low oxygen) that causes retinal vessels to leak. Many retinal specialists prefer treatment with laser to that with injectable drugs because the injectable drugs wear off quickly and the macular edema usually returns.
- Biochemical imbalance: Macular edema caused by excess production of vascular endothelial growth factor (VEGF), usually in response to retinal degeneration or ischemia (low oxygen), can respond to drugs that block the effect of VEGF. Steroids, Avastin, and Lucentis, are all effective against many causes of macular edema. Intravitreal injection of Kenalog, a long acting steroid, can suppress macular edema for three to 12 months. Intravitreal Kenalog can cause cataract formation and elevated intraocular pressure (glaucoma). Intraocular injection of Avastin or Lucentis usually only suppresses macular edema for 1 to 3 months. These drugs do not cause cataract or elevated intraocular pressure, but they can be expensive and are only covered by insurance in cases of age-related macular degeneration.