WHAT IS THE RETINA? WHO DO WE SEE?
Millions of people in North America live with varying degrees of irreversible vision loss because they have an untreatable, degenerative eye disorder, which affects the retina. In these conditions, the delicate layer of tissue that lines the inside back of the eye is damaged, affecting its ability to send light signals to the brain. Retinal degenerative disorders are a large and diverse group of conditions affecting young and old, from many cultures, races and ethnicities.
“When we examine the retina, we are looking into a window of the brain.” The retina is a thin layer of tissue on the inside back wall of your eye. It contains millions of light-sensitive cells and other nerve cells that receive and organize visual information. Your retina sends this information to your brain through your optic nerve, enabling you to see.
Retinal diseases can affect any part of your retina and can cause total blindness. Disease affecting the edge of your retina can affect your side (peripheral) vision. Some diseases affect the part of your retina that serves your central vision (the macula and the fovea –this is what gives you your detailed vision – reading and driving vision). Many retinal diseases share some common symptoms and treatments. The main goals of treatment are to stop or slow the disease and preserve, improve or restore your vision, and the earlier a problem is detected, the better your chance to retain vision.
Age-related macular degeneration is the most common condition, distinguished by its prevalence in the senior population.
Other retinal degenerative disorders are inherited, meaning that they are due to a genetic mutation. An individual can inherit such a mutation, even if they have no clear family history of vision loss. In other instances, many members and generations of a family may experience vision loss. There are many types of inherited retinal degenerations. Here are a few of the more common ones:
- Retinitis Pigmentosa
- Choroideremia (affects males)
- Leber’s Congenital Amaurosis
- Retinoschisis, Juvenile
- Stargardt Disease
- Usher Disease
- Bardet Biedl
- The Retinal Exam
Without a healthy retina, the human eye is like a camera without film. The retina receives light rays from the front of the eye and sends them to the retina, then through the optic nerve to the brain where they are turned into clear, bright, colorful images. Ophthalmologists who specialize in the retina are called Vitreo-Retina Specialists because they also deal with disorders of the vitreous, a clear, jelly like substance that lies between the eye’s natural lens and the retina. When disease or injury causes clouding of the vitreous or damage to the retina, the result is a partial or complete loss of vision.
The retinal exam is focused on the back of the eye. For this reason, Dr Mahl will spend time looking through your pupil at the vitreous, retina and other structures located inside the eye. Most patients can expect to have their eyes dilated so Dr Mahl can get a clear view of these structures.
The following method is used in diagnosing retina problems:
Indirect ophthalmoscopy uses a specialized microscope that allows Dr Mahl to observe the vitreous, retina and other internal structures in the eye.
Diabetes mellitus (DM) is a disease that affects blood vessels throughout the body, particularly vessels in the kidney, heart and in the eye. When the blood vessels of the eye are affected, the condition is called diabetic retinopathy. Diabetes mellitus causes these blood vessels to leak fluid and blood into the retina, disturbing the normal architecture of the retina and patients lose vision and can become blind. Diabetic retinopathy is the leading cause of new blindness among adults in the United States. If untreated, there is a risk of becoming blind. The longer one has DM, the higher the incidence of developing diabetic retinopathy. Approximately 80% of people who have had DM for 15 years or longer have some damage to their retinal vessels. There are two stages of diabetic retinopathy. The first stage is background diabetic retinopathy and the second (later) stage is proliferative diabetic retinopathy. Background diabetic retinopathy is associated with leakage and bleeding within the retina. Diabetes causes retinal blood vessel walls to become incompetent, leading to fluid buildup within the retina. Vision may be unaffected or significantly reduced. If enough retinal blood vessels are destroyed by diabetes, the retina may respond by growing new blood vessels; this is called Proliferative diabetic retinopathy. The vitreous can then fill with blood, leading to rapid vision loss. These new vessels can also promote scarring on the surface of the retina, leading to traction retinal detachment. Both stages of diabetic retinopathy can lead to severe vision loss and need to be diagnosed right away.
Macular degeneration is a disease that affects the center of the retina, called the macula. The macula, which is about the size of the capital letter “0” in this sentence, is the part of the retina that is capable of our most detailed vision. We use the macula for reading, driving, recognizing faces, watching television, and performing fine work. Macular degeneration is the leading cause of legal blindness in people older than 55 (legal blindness means that a person has 20/200 visual acuity with eyeglasses). Even with a loss of central vision, color vision and peripheral vision may remain clear in persons with macular degeneration. There are two basic forms of the disease: wet and dry. The wet form affects one eye at a time and can result in sudden vision loss in that eye. The dry form affects both eyes, gradually disrupting central vision.
FLASHES AND FLOATERS CAN BE AN INDICATION OF A POTENTIALLY SERIOUS PROBLEM WITH THE RETINA. FLASHES AND FLOATERS
Flashes appear as flashing lights or as “lightning strikes” in the field of vision, although no light is actually flashing. Flashes are similar to the sensation of “seeing stars” when one is hit on the head. Flashes are most often noticed at night or in a dark room. Floaters are particles that float in the vitreous and cast shadows on the retina. They appear to be strung together with a web-like thread. Some floaters are formed before birth, while others occur normally with aging. A floater is a small clump of gel that forms in the vitreous, which is the clear jelly like fluid that fills the cavity inside the eye. Floaters may be seen as dots, lines, cobwebs, or spiders and are most often noticed when reading, looking at a blank wall, or gazing at a clear sky. Although floaters seem to be in front of the eye, they are actually floating in the fluid inside the eye. Sometimes floaters do not interfere with vision at all. However, when a floater enters the line of vision, light is blocked and a shadow is cast on the retina. A new onset of flashes or floaters is cause for concern. The vitreous tends to become more liquefied as a person ages. This can lead to mild floaters in one or both eyes, called benign floaters. However, a sudden burst of flashes or floaters in one eye suggests that the vitreous is undergoing an acute change. Benign flashes or flouters must be differentiated from harmful floaters like blood due to a burst blood vessel or harmful flashes that may indicate a tear in the retina has occurred.
Retinal detachments can be caused by disease or injury. Here, a segment of the retina becomes separated or peels away from the back wall of the eye. Unless treated promptly, this condition can result in immediate loss of vision. If the vitreous liquefies sufficiently, the back portion of the vitreous can peel off the surface of the retina. This process (called vitreous detachment) may take up to a couple of weeks. During this time, if the vitreous has tight adhesions to the retina, the retina can tear while the vitreous is detaching. Although flashes and floaters may not fully diminish after 2 weeks, the risk of developing a tear is greatly reduced if 2 weeks pass with the retina still intact.
Retinal detachment occurs when the retina becomes separated from the back wall of the eye. When the retina becomes detached, the blood supply is reduced and its ability to process light rays is impaired. If total detachment occurs and is not repaired, the retina becomes useless (as it can no longer transmit information to the brain) and the eye becomes blind.
Dr Mahl has the knowledge to evaluate and diagnose these conditions and determine the appropriate treatment for you.