Anatomy: The retina is a light-sensitive layer of tissue lining the inner surface of the eye. The optics of the eye create an image of visual world on the retina, which serves the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These impulses are sent to the brain. There are several anatomical structures to be noted in the retina. First, the retina is an energy demanding tissue and it requires its own blood supply. Retinal blood vessels and a network of blood vessels called the choroid provide oxygen and nutrients to the retina. Secondly, there is a special anatomical site called the macula that has the highest concentration of photoreceptors. This region of the retina is responsible for the color and the fine visual acuity (20/20).
Clinical photograph of a normal retina
Specific Retinal Diseases
Age-Related Macular Degeneration
The macula is responsible for your central vision. In Age-Related Macular Degeneration there is damage to this area causing blurring of the vision and distortion. More than 2 million Americans 50 years of age and older have advanced AMD, this stage that can lead to severe vision impairment; it is the leading cause of visual loss in the United States today.
There are two forms of age-related macular degeneration (AMD):
Clinical Photo: "Dry" Age Related Macular Degeneration. OCT of Dry AMD below, Drusen
1. “ Dry” Type (non-neovascular): 90% of all patients with AMD have the “dry” type. It is associated with slight distortion of the vision and it is painless visual loss.. Within the macula drusen are present. AREDS vitamins can reduce the risk of the development of “wet” AMD by 25%. In addition, studies have indicated that cessation of cigarette smoking and control of systemic hypertension are important factors in preventing the development of “wet” AMD and its associated profound visual loss.
Clinical Photograph of AMD and OCT of "Wet".
2. The “wet” Type (vascular) of Age Related Macular Degeneration affects 10% of all individuals that have age related macular degeneration. It occurs when abnormal blood vessel grow into the macula, causing bleeding and swelling. If this process continues it will result in permanent visual loss. Fortunately, there are medications that are injected directly into the eye. Without the injections the visual prognosis is poor. Although it requires perservance by the patient and the physician there is a excellent possibility of stabilizing the visual loss.
Diabetic Retinopathy
Diabetic Retinopathy is damage to the retina caused by complications of diabetes. It can affect 80% of all diabeties who have had diabetes for 10 years or more. Diabetes retinopathy affects more than 4.4 million Americans age 40 or older. Diabetic retinopathy acounts for 12 % of all new cases of blindness and it is the leading cause of blindness for people age 20 to 64 years.
OCT: Diabetic Macular Edema
Diabetes causes damage to your retina in two main ways. First, the macula (responsible for your central vision) may swell causing blurry vision. This is called Diabetic Macular Edema and it is a result of damaged blood vessels leaking fluid and lipids into the macula. This is treated either with medications that are injected into the eye or with light laser performed in the office. OCT is critical to make the diagnosis of Diabetic Macular Edema and to follow the progression of treatment.
Proliferative Diabetic Retinopathy
The second form of Diabetic retinopaty is called Proliferative Diabetic Retinopathy where there is bleeding into the vitreous cavity (the middle portion of the eye). The symptoms include painless loss of vision and floaters. The treatment of this problem is either laser, injections of medications or surgery.
Preventive Measures
Control of your blood glucose, cholesterol, and systemic blood pressure are important factors to minimize diabetic retinopathy. A yearly dilated examination is important to monitor the diabetic patient. The York Eye Institute has the technology, medications, and techniques to manage most diabetic problems.