Taking aim at the ‘film’ of the eye
The retina is the tissue-paper-thin membrane in the back of the eye that acts like the ‘film’ in a camera. The retina collects information from images projected upon it by the optical parts of the eye and sends it along the optic nerve to the brain, where it is interpreted and experienced as vision. There are many diseases and conditions that can affect the retina and vision, including macular degeneration, diabetic retinopathy and retinal holes and detachments.
The vitreous cavity is the area behind the crystalline lens and in front of the retina that is filled with a clear, jelly-like substance called the vitreous or vitreous gel. The vitreous gel is attached most strongly to the front part of the retina, but also in the back part of the eye to the optic nerve, the macula and the large retinal blood vessels.
The retina is a very thin tissue which lines the inside wall of the eye. It is made up of millions of light-sensitive visual cells that send images along the optic nerve to the brain.
The peripheral retina, which makes up 95% of the total retina, is responsible for our side (peripheral) vision. The central part of our retina, which gives us detailed vision, is called the macula. We use our macula to read, drive and recognize faces.
As a person ages, the vitreous gel becomes more liquefied. As the eyeball moves, the liquefied vitreous also moves around, which can cause the vitreous to pull on the retina. The brain interprets this “pulling” on the retina as flashes of light, thus resulting in a person seeing “flashes.” With time, the vitreous can pull free and separate from the retina and the optic nerve. This is called a posterior vitreous detachment or PVD. A PVD eventually happens in most eyes, but rarely causes a problem. The liquefied vitreous can become somewhat condensed and stringy and will form strands. A person can see these strands appearing as spots, small circles or curvy fine threads in the vision. These spots are called “floaters.”
New floaters, especially those in showers and/or accompanied by flashes that continue for 20 minutes or more, should be evaluated to be sure there is no serious retinal problem (such as a retinal tear or detachment). Most disappear on their own or become less noticeable over time.
Retinal tears or holes can be caused when the vitreous pulls too hard on the thin retina, much like trying to remove adhesive tape from tissue paper. These tears/holes can be a potential problem if left untreated. The vitreous gel can enter the hole and lift more of the retina away from the eye wall, resulting in a retinal detachment. Vision is lost wherever the retina is detached. Since tears often happen in the peripheral retina, a person may notice a dark shadow or a veil coming from one side, above or below. Left untreated, it is probable that the entire retina will eventually detach, resulting in the loss of all useful vision in the eye. If the retina tears across a retinal blood vessel, blood may also enter the vitreous (called a vitreous hemorrhage). Vitreous hemorrhages can be small, resulting in floaters similar to a swarm of flies, or much larger, causing the person’s vision to become very dark.
Systemic health conditions such as diabetes or high blood pressure (hypertension) can also cause retinal problems.
Diabetic retinopathy can be classified as Proliferative (PDR) or Non-Proliferative (NPDR). When the retinal blood vessels develop small leaks it is called NPDR. These leaks can seep fluid or blood under the macula (called macular edema), resulting in blurred central vision. Retinal blood vessels can also become obstructed and the part of the retina being nourished by these vessels will no longer work properly. These areas then foster new blood-vessel growth called neovascularization. These new blood vessels are abnormal and leak, causing bleeding and scar tissue to form, thus resulting in severe vision loss or blindness. PDR is the type of retinopathy characterized by the growth of these abnormal retinal vessels (neovascularization).
Your eye doctor may request photographs of your eyes to better determine the degree of your retinopathy. This could be a simple color photo of the retina (back of your eye), or a dye test called fluorescein angiography. With fluorescein angiography, a small amount of fluorescent dye is injected into your arm and tracked through your retinal vessels with a special camera and filters. Another form of photography may involve technology that shows a cross section of your macula, to measure the amount of edema or swelling present. This is called Optical Coherent Tomography(OCT).
Laser treatment is often used in treatment of both types of diabetic retinopathy, although PDR may often require additional surgery call vitrectomy to remove blood and scar tissue from the eye. Also being used in the treatment of macular edema are medications injected directly into the eye, known as Anti-VEGF Medications (i.e. Avastin® or Lucentis®).
The retinal vessels can also be affected by high blood pressure (hypertensive retinopathy). Prolonged elevated pressure in these small vessels can result in damage that causes leakage and swelling in the retina.
Blood clots can form in the small retinal vessels, sometimes causing permanent vision loss. Depending upon the location and type of vessel occluded, laser or intravitreal injection may be recommended.
Macular degeneration (AMD) is the leading cause of blindness in people over the age of 60. Deposits under the retina, called drusen, are a common feature of AMD. While drusen alone generally does not cause loss of vision, an increase in the number or size of the drusen can indicate an increased risk factor. There are basically two types of AMD: dry and wet. Drusen will likely be present in both forms. The “dry” form is most common and is present when the tissue of the macula becomes thin and damaged. Vision loss is usually gradual. The “wet” form results when abnormal blood vessels form (neovascularization) underneath the retina (the Choroid). These vessels leak fluid or blood and damage the central vision. Vision loss may be sudden, rapid and severe.
Symptoms of AMD are varied and may include: blurriness when reading; a dark or blank spot in the center of vision; distortion (i.e. straight lines look wavy). It may be necessary for your eye doctor to perform a fluorescein angiogram to determine if the condition is wet or dry.
There is no cure for AMD, however laser and Anti-VEGF Medications are possible treatments for the wet form. The dry form is generally monitored by the patient with the aid of an Amsler Grid to check for new distortion or other visual disturbances. Nutrition is also addressed, as well as smoking. Vitamins (AREDS Formula) and supplements may be recommended by your eye doctor to help prevent the change from dry AMD to wet. Smoking causes a constriction of blood vessels and can be detrimental to the health of your retina.
Wrinkling of the macula may also cause distorted or blurred central vision. Surgery called pars planavitrectomy may be recommended to peel the membrane from the surface of the macula if vision is significantly impaired. Sometimes, these membranes can pull on the macula, causing a macular hole. A vitrectomy is also necessary to repair these holes and to aid in healing; a gas bubble may be injected into the vitreous. This will require face-down positioning after surgery for up to two weeks. While the surgery is typically quite successful, each person’s visual outcome is different and will depend on many different factors. It is important for patients to discuss their expectations with their surgeon.
Amsler Grid: Graph used to check for new distortion or other visual disturbances.
Anti-VEGF: medication that blocks the chemical called vascular endothelial growth factor.
AREDS formula vitamins: Vitamin supplement specifically formulated for patient with macular degeneration based on the Age-Related Eye Disease study sponsored by the National Eye Institute (NEI).
Avastin® (Bevacizumab): Anti-VEGF drug developed for the treatment of colon cancer, but used in ophthalmology to treat retinal neovascularization and edema by intravitreal injection.
Choroid: Vascular layer under the retina responsible for nourishment to the retinal pigment epithelium (RPE).
Diabetic retinopathy: Disease of the retina caused by diabetes (see “Proliferative Diabetic Retinopathy” and “Non-Proliferative Diabetic Retinopathy”).
Dilation: Enlarging the pupil.
Drusen: Yellow deposits under the retina.
Eylea®: (aflibercept) Anti-VEGF drug used to treat AMD and other retinal diseases.
Flashes: Flashes of light seen by a patient are often caused when the vitreous gel detaches from and pulls on the retina.
Floaters: Often described as “bugs” or “hairs” that a patient sees in their line of vision. As the vitreous liquefies and detaches from the retina, it can become condensed and stringy allowing the patient to see “floaters.”
Fluorescein angiography: Photography of the retina using fluorescein dye to document abnormal blood vessels or leakage.
Hypertensive retinopathy: Damage to the retina due to high blood pressure (hypertension).
Ischemic Optic Neuropathy (ION): The loss of structure and function of a portion of the optic nerve due to obstruction of blood flow to the nerve. May be “anterior” or “posterior.”
Laser: A highly focused beam of light, which can be used to treat a variety of retinal disorders.
Lucentis®: (ranibizumab) Anti-VEGF drug used to treat AMD and other retinal diseases.
Macula: Central part of retina that gives us detailed vision.
Macular degeneration: A group of diseases characterized by loss of central vision because of death or impairment of the cells in the macula.
Macular edema: Swelling in the macula caused by blood or fluid under the central retina.
Neovascularization: The growth of abnormal blood vessels.
Non-Proliferative Diabetic Retinopathy: Less severe diabetic retinopathy than proliferative, but still involves small blood vessel leaks, which can lead to macular edema and vision loss.
OCT (Optical Coherent Tomography): Imaging technique that uses light waves to measure the retina’s thickness and show the layers of the retina.
Optic nerve: Transmits messages to the brain from the eye.
Proliferative Diabetic Retinopathy: A classification of diabetic retinopathy involving the growth of abnormal blood vessels in the retina (neovascularization), which can lead to severe vision loss.
PVD (Posterior Vitreous Detachment): The separation of the vitreous from the retina and optic nerve.
Retina: Thin tissue which lines the inside wall of the eye.
Retinal detachment: When the retina lifts away from the eye wall.
Retinal artery/vein occlusion: A blockage of a small vein or artery in the retina. Depending upon the location this may be classified as a “branch” or central” retinal artery/vein occlusion (BRAO, BRVO, CRAO, CRVO).
Retinal hole or tear: Small holes or tears in the retina which may or may not lead to retinal detachment.
Retinal Pigment Epithelium (RPE): Pigmented cell layer just under the neurosensory retina that nourishes retinal visual cells and just above the choroid.
Retinopathy: A general term indicating non-inflammatory damage to the retina. Often an ocular manifestation of some systemic disease (i.e. diabetes or hypertension).
VEGF (Vascular Endothelial Growth Factor): A chemical that helps the growth of abnormal blood vessels in the retina.
Vitrectomy: Removal of the vitreous gel.
Vitreous: Clear, jelly-like substance that fills the large posterior cavity of the eye.
Vitreous hemorrhage: Small blood vessels in the retina break and leak blood into the vitreous cavity.