The retina is a very unusual structure. It is the ‘film’ at the back of the eye and has a very fine blood supply across the front of it. Like all blood supplies, it has an artery and a vein component, with the artery being quite a high pressure system and the vein taking the blood back and out of the eye at lower pressure.
The retina is a little unusual in that blockages occur in the artery and/or the vein. Blockage of the artery occurs from emboli or particulate matter coming off from the inside of the heart or heart valves, or from the inside of the blood vessels going up to the head. Vein blockages occur partly because of kinking of the vein at some point and are related to blood pressure, cholesterol and diabetes, but also to glaucoma in the eye.
As the retina is quite like a brain, and for the most part is not able to repair itself substantially, retinal vascular disease (blockage or reduction of the blood vessels) often has a significant and maybe permanent effect on the retina’s capacity to see.
Vein occlusions can produce some unwanted complications to the rest of the eye: the injured retina produces Vascular Endothelial Growth Factors (VEGFs) in an attempt to recreate the vessels or bypass the blockage. Overall this would seem like a useful endeavor excepting that the VEGFs spread throughout the eye and can produce new blood vessels in very unhelpful places, including the front of the eye. New vessels in the front of the eye produce a form of glaucoma (“Rubeotic”) which requires treatment for the cause (treatment of the retina) as well as the effect (the glaucoma). Rubeotic glaucoma sometimes occurs in very bad diabetic eye disease.
Age Related Macular Degeneration
This is the most common cause of central visual loss in almost every country on earth. It is, as the name suggests, related to increasing age. In addition to getting older, there are some genetics and possibly some lifestyle factors. Although there have been some studies that show there is a nutritional component to macular degeneration, it is not so easy to see a compelling difference between supplementation and no supplementation in people with good diets.
It is noted though that macular degeneration is worse in those people who smoke, and for this as well as many other reasons, smoking should be avoided.
Macular degeneration broadly falls into two categories: “wet” and “dry”. Actually the wet version is a complication of the dry form and although there is treatment available for the wet form, the dry continues to progress. The current treatment for wet macular degeneration is injections of in the back of the eye of medications that turn off new blood vessel growth. Currently there are three agents used – Avastin, Lucentis, and Eylea – and they are all effective at reducing new vessel growth, which is the nature of wet macular degeneration. Unfortunately the injections do not usually last much longer than six weeks, although it is not always needed that injections are required every six weeks or so.
Injections for macular degeneration can be done in the office and not more uncomfortable than a standard injection anywhere.
Diabetic retinopathy means changes in the retina secondary to diabetes. Diabetes causes problems with blood vessels, partly due to sugar making some of the layers of blood vessels more brittle. Microvasculopathy, or blood vessel disease in small blood vessels, occurs in the retina, the kidneys and in the feet.
Diabetic retinopathy is a significant cause of visual loss and occurs over time. Diabetic retinopathy is more common the higher the HbA1c is (the longer term sugar control index), the length of time of diabetes, how high the blood pressure is, and how high the cholesterol is. Diabetic retinopathy can get worse in pregnancy.
There are a lot of treatment strategies for diabetic retinopathy, but they are much better instigated as a prophylactic rather than waiting for the vision to decline. Vision loss from diabetic retinopathy is hard to recover from – much better to prevent it.
The treatment options for diabetic retinopathy include laser, injections of steroids and anti-vascular endothelial growth factors, and sometimes surgery.
Tears in the retina can occur because of a normal event known as “posterior vitreous detachment”. The vitreous generally fills the cavity in the back of the eye, but tends to shrink and detach from its back surface, that which is next to the retina, with age. Shrinking and detachment of the vitreous is normal, but can cause the development of floaters and on occasion flashes of light in the periphery.
The sudden onset of floaters and flashes are things that should be checked out and they can be associated with a tear in the retina. A tear in the retina is unusual but much more important than the “posterior vitreous detachment”.
A tear in the retina where it is relatively new without extension can be relatively easily treated with either laser or cryotherapy.
More extensive detachment of the retina will require more complicated procedures. Retinal detachment surgery has improved dramatically, but it is still preferable not to have one.