The eye is a complex organ that works much like a camera, focusing light rays and forming an image. On the surface of the eye is the cornea, a thin, spherical layer of tissue that provides a clear window for light to pass through. In a healthy eye, the cornea bends or refracts light rays so they focus precisely on the retina in the back of the eye.
Beneath the cornea is the iris, the colored part of the eye which we refer to when we say a person has brown or blue eyes. In the center of the iris is the pupil, which is the opening of the iris. The iris functions like a shutter, adjusting pupil size to control the amount of light entering the eye.
Located behind the iris is the lens, which works together with the cornea and vitreous to focus light. Like the lens in a camera, it adjusts light rays as vision shifts between nearby and distant objects in a process called accommodation.
Light then passes through the vitreous, the gelatinous substance that fills most of the eye and gives it its shape.
The back of the eye is lined with a thin layer of tissue containing millions of photoreceptor (light-sensitive) cells. This is the retina, where light rays focus into an upside-down image. In the center of the retina is the macula. Less than 1/4 of an inch in diameter, the macula is responsible for clear central vision. The retina converts the image into an electrical signal that travels down the optic nerve to the brain.
Flashes and Floaters
Flashes and floaters are common eye symptoms that occur as a result of age-related changes to the vitreous gel. At birth, the vitreous is firmly attached to the retina and is a thick, gelatinous substance without much movement. But as we age, the vitreous begins to liquefy and debris that was once secure in the gel can now float around, casting shadows on the retina. Floaters can be specks, strands or webs and most visible when looking at a uniform light background like the sky or lightly-colored wall.
Eventually the vitreous gel begins to shrink and separate from the retina. At this point, head or eye movement can cause the vitreous to make intermittent contact with the retina, resulting in occasional light flashes or lightning streaks. As the vitreous continues to peel free, it might reach a point where it is firmly attached to the retina and the traction can cause rapid-fire flashes like a strobe. Sometimes, the vitreous tugs so forcefully that it causes a tear in the retina.
If you experience an increase or onset of floaters of if you see flashing lights, it is important to be examined promptly. Although most eyes with these symptoms do not have a retinal tear, those that do require treatment to seal the tear and prevent a more serious problem; a detached retina.
Farsightedness, or hyperopia, is a condition in which the eye focuses on distant objects better than on objects closer to the eye, so nearby objects appear blurry. This happens when light rays refract, or bend, incorrectly in the eye. The eye is designed to focus images directly on the surface of the retina; when the cornea is incorrectly curved or the eye is small, light rays focus behind the surface of the retina, producing a blurry image.
Hyperopia can be treated in a variety of ways. The most common is with glasses or contact lenses. Hyperopia can also be treated with non-invasive medical procedures, including the laser surgeries PRK (photorefractive keratectomy) and LASIK (laser-assisted in situ keratomileusis).
The macula is a small spot in the center of the retina that focuses light at a sharp point and allows us to see objects in detail. This is especially useful for reading, driving and other everyday activities that require clear vision. A macular hole often develops as part of the natural aging process, when the vitreous gel thins and separates from the macula. This can pull on the macula and cause a hole to form. Macular holes can also develop from injury, inflammation, retinal detachment or other eye diseases.
In its early stages, a macular hole may cause a small blurry or distorted area in the center of vision. As the hole grows over time, central vision progressively worsens, and peripheral vision may also be affected. There are three different stages of macular holes, including foveal detachments, partial-thickness holes and full-thickness holes. Each stage can progress to the next if left untreated.
Most macular holes can be successfully treated through vitrectomy, a surgical procedure to remove the vitreous gel and stop it from pulling on the retina. The doctor then inserts a mixture of air and gas into the area to keep its shape. Vitrectomy is performed on an outpatient basis under local anesthesia and is considered a safe and effective treatment for a macular hole.