- Visual acuity test is the basic test using the standard Snellen chart. Acuity refers to the sharpness of vision and how clearly an object is seen and, with the test, the doctor will determine range of vision. The four most common visual problems are nearsightedness, farsightedness, astigmatism, and presbyopia. They are usually caused by focusing problems of the cornea or the lens or by an abnormal shape of the eye. Most problems can be corrected with eyeglasses, contact lenses, or surgery that will adjust the curvature of the cornea.
Visual field test (perimetry) assesses the field of vision directly in front without eye movement. This field of vision is assessed with the use of a testing screen on which a computerized machine flashes spots of lights. The flashes of light will be at different locations on the screen and of varying brightness. A button is pressed each time a flash of light is seen; and the machine records the responses, mapping the areas where vision is good. Blank holes or gaps may indicate such serious eye disorder as glaucoma or macular degeneration, which often go unnoticed without testing. Another test that is used is the Amsler grid, named after the Swiss ophthalmologist who developed it. The square grid looks like graph paper; and, by the time the test is over, it will look like a “cross-stitch pattern” before it is sewn. In the center of the grid is a black dot. The doctor will cover one eye, ask that you focus the other eye directly on the dot, and then ask if you can see the entire grid clearly. If the tiny squares appear to have different sizes, distortions, or parts missing, this will indicate where, and to what extent, damage to the retina has occurred.
Vitamins are essential nutrients for the health of the eyes and maintenance of vision. (See more separately under Eyes and Nutrition.)
Vitrectomy is a surgical procedure used to remove the clouded vitreous or scar tissue. Occasionally, bleeding or inflammation clouds the vitreous and blocks the surgeon’s view of the detached retina. In other instances, scar tissue makes it impossible to repair a retinal detachment with pneumatic retinopexy or scleral buckling alone. In such cases, the surgeon will use the vitrectomy method, which involves a variety of delicate instruments that are passed into the eyeball through small openings in the sclera. These instruments include a light probe that illuminates the inside of the eye, a cutter to remove vitreous or scar tissue, and an infusion tube that replaces the volume of removed tissue with a balanced salt solution to maintain normal pressure and shape of the eye. After the vitrectomy is completed, the surgeon performs the scleral buckling procedure and may fill the inside of the eye with air, gas, or silicone to help seal the retina against the wall of the eye. Virectomy may also be performed for conditions other than complicated retinal detachments including: vitreous clouding by blood that prevents light from reaching the retina, macular puckers (epiretinal membranes), infection inside the eye (endophthalmitis), or a foreign body inside the eye.
Virectomy surgery usually takes an hour or two, but significantly longer in more complex cases. The complex cases are performed under general anesthesia, while shorter procedures are usually performed under local anesthesia.Complications of vitrectomy surgery include the following: failure to accomplish intent, retinal detachment that may require additional surgery or may be inoperable, vitreous hemorrhage, infection, elevated eye pressure (glaucoma), poor healing or nonhealing corneal defects, corneal clouding and scarring, cataracts (which may require eventual or immediate removal of the lens), double vision, eyelid drooping, loss of circulation to vital tissues in the eye (resulting in a decrease or loss of vision), permanent blindness, loss of the eye, phthisis (disfigurement and shrinkage of the eyeball), optic nerve injury, or closure of the eye’s artery or vein.
- Vitreous cavity extends from the back of the lens to the retina at the back of the eyeball. It is filled with a clear, gelatinous substance called the vitreous humor or simply, vitreous. The average human eye weighs about seven grams or one-quarter ounce. Nearly four grams of that is vitreous. Together with the aqueous humor in the anterior chamber, the vitreous helps maintain the pressure and shape of the eyeball.
Updated October 2012
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