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Technology
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Vision test The vision test is one of the simplest yet most important components of the eye exam. In order for eye doctors to compare results, it's always done at a standardized distance of twenty feet. Today, mirrors are used to reflect the image so the room can be shorter; but the image still looks like it is twenty feet away. The charts are standardized too and doctors around the world use the same basic format. But what do those numbers mean? Each line of the eye chart is assigned a notation in the form of a fraction that represents your visual acuity. The numerator is the distance in feet the patient is from the eye chart. The denominator represents the distance an eye with "normal" vision can read the same line. Interpreting the numbers is simple.
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Eye Chart
Image Source: http://www.stlukeseye.com/eyeq/Vision.asp |
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This simple screening test is used to assess the macula (the center of the retina). The Amsler Grid consists of evenly spaced horizontal and vertical lines printed on black or white paper. A small dot is located in the center of the grid for fixation. While staring at the dot, the patient looks for wavy lines and missing areas of the grid. This test is especially helpful for monitoring vision at home. The doctor is especially interested in the following when testing vision with the Amsler Grid:
Are you able to see the corners and sides of the square?
Do you see any wavy lines?
Are there any holes or missing areas?
If the lines of grid do not appear straight and parallel or there are missing areas, the doctor will examine the back of the eye (macula) very closely. This test is frequently given to patients for home use to monitor macular degeneration. When using the test at home, notify the doctor if any changes in the appearance of the Amsler Grid are detected.
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Amsler Grid
Image Source: http://www.stlukeseye.com/eyeq/Amsler.asp |
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An ophthalmoscope is an instrument used to examine the retina and vitreous. Ophthalmoscopy requires dilating the pupils with drops to give the doctor the best view inside the eye. There are two types of ophthalmoscopes: direct and indirect. The direct is a hand-held instrument with a battery powered light source. It also has a series of lenses that can be dialed in to focus the doctor's view of the retina. The direct ophthalmoscope is useful for examining the central retina. The indirect ophthalmoscope can be used to examine the entire retina. This instrument is worn on the doctor's head. While looking through the instrument's magnifying glasses, a special lens is placed in front of the patient's eye, allowing the doctor to see the retina clearly.
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Don't be surprised if someday, your eye doctor orders photographs of the back of your eye. These pictures are necessary to document the health of the optic nerve, vitreous, macula, retina and its blood vessels. The photographs are used for comparison, documentation, and sometimes to diagnose certain eye conditions. Because fundus photography is a highly specialized form of medical imaging, it can't be done with an ordinary camera. It requires a customized camera that is mounted to a microscope with intricate lenses and mirrors. These high-powered lenses are designed so the photographer can visualize the back of the eye by focusing light through the cornea, pupil and lens. Before beginning, the pupil is dilated with drops. Otherwise, it would automatically constrict from the bright light of the camera flash. The patient is asked to stare at a fixation device so the eyes are still. While the photographer is taking the pictures, the patient will see a series of bright flashes. The entire process usually takes approximately five to ten minutes.
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Fundus Photography
Image Source: http://www.stlukeseye.com/eyeq/FundusPhotography.asp |
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Fluorescein angiography (fluorescein - the type of dye that is used; angiogram - a study of the blood vessels) is an extremely valuable test that provides information about the circulatory system and the condition of the back of the eye. FAs are useful for evaluating many eye diseases that affect the retina.The test is performed by injecting a special dye, called fluorescein, into a vein in the arm. In just seconds, the dye travels to the blood vessels inside the eye. A camera equipped with special filters that highlight the dye is used to photograph the fluorescein as it circulates though the blood vessels in the back of the eye. If there are any circulation problems, swelling, leaking or abnormal blood vessels, the dye and its patterns will reveal these in the photographs. The doctor can then make a determination as to the diagnosis, and possible treatment options for the patient. In many cases, these photos are taken with a digital camera system, allowing the physician to interpret the results immediately.
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Retinal photograph of a patient complaining of decreased vision.
Image Source: http://www.stlukeseye.com/eyeq/FluoresceinAngiogram.asp |
Fluorescein angiogram indicating fluid leakage within the retina
Image Source: http://www.stlukeseye.com/eyeq/FluoresceinAngiogram.asp |
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People have cataract surgery when the cataract has progressed enough to seriously impair your vision and affect your daily life. Many people consider poor vision an inevitable fact of aging, but cataract surgery is a simple, relatively painless procedure to regain vision. Cataract surgery has made extraordinary and exciting advances over the past 20 years. Last year, approximately 2.7 million Americans underwent cataract surgery. Greater than 95% of those patients now enjoy improved sight somewhere between 20/20 and 20/40 vision. State-of-the-art cataract surgery is now a safe, effective, and comfortable procedure performed Most cataract surgeries are now performed using microscopic size incisions, advanced ultrasonic equipment to fragment cataracts into tiny fragments, and foldable intraocular lenses (IOLs) to maintain small incision size. Cataract surgery today is the result of extraordinary technological and surgical advancements that allows millions of people to once again enjoy crisp and clear vision. A true marvel of modern medicine, cataract surgery may restore vision to levels you may have never thought possible. During surgery, the surgeon will remove your clouded lens, and in most cases replace it with a clear, plastic intraocular lens (IOL). New IOLs are being developed all the time to make the surgery less complicated for surgeons and the lenses more helpful to patients. One example is a new IOL that lets patients see at all distances, not just one. Another new IOL blocks both ultraviolet and blue light rays, which research indicates may damage the retina (see illustration).
Cataract Surgery
Image Source: http://www.allaboutvision.com/conditions/cataracts.htm |
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The glaucoma procedures include a variety of surgical and laser procedures designed to treat glaucoma and prevent vision loss. The glaucoma procedures are nearly as varied as the many types of glaucoma. However, the goal of glaucoma procedures is to reduce or stabilize pressures in the eye, thereby preventing vision loss.
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Glaucoma Drainage Device: (Tube Shunt)
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Glaucoma drainage devices, also known as tube shunts, are implanted devices that are designed to maintain an artificial drainage pathway for patients with glaucoma. This procedure is often chosen for patients at high risk of failure with a traditional glaucoma filter procedure (trabeculectomy). Such patients might include those with neovascular glaucoma, glaucoma associated with uveitis (iritis), prior history of failure with a filter procedure, and any patient with glaucoma under 30 years of age. All of these patients are at significant risk for failure of a routine glaucoma filter procedure due to greater inflammation and fibrosis (scarring), which might close off the drainage canal.
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Tube Shunt implantation
Image Source: http://www.eyemdlink.com/EyeProcedure.asp?EyeProcedureID=45 |
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Procedure
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A small incision is made in the conjunctiva, usually towards the top of the eye, however, the surgery may be performed in other quadrants of the eye. The surgeon will then make a tiny incision in the sclera of the eye and will fashion an opening for the drainage implant device. The drainage tube will be placed such that the opening of the tiny tube is inside the anterior chamber of the eye where it is bathed in aqueous fluid. The tube is sutured in place with the drainage device attached to the sclera of the eye. Most surgeons will place an absorbable suture around the tube at the time of surgery to prevent filtration through the device until a fibrous capsule has formed. As such, the device is not expected to function until about 3 to 8 weeks following the procedure. This technique is thought to prevent over-filtration. Once the tube shunt is securely sutured into the desired position, the conjunctiva over the device is closed with tiny sutures, which are considerably finer than human hair.
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A Laser peripheral iridotomy (PI) is performed almost exclusively for patients with narrow angles, narrow angle glaucoma, or acute angle closure glaucoma Laser peripheral iridotomy involves creating a tiny opening in the peripheral iris, allowing aqueous fluid to flow from behind the iris directly to the anterior chamber of the eye. This typically results in resolution of the forwardly bowed iris and thereby an opening up of the angle of the eye. The narrow or closed angle thus becomes an open angle!
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Peripheral iridotomy
Image Source: http://www.eyemdlink.com/EyeProcedure.asp?EyeProcedureID=46 |
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A thin plastic or glass lens that is fitted over the cornea of the eye to correct various vision defects.
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