- Tactile aids provide information that visually impaired individuals access through the sense of touch. These may include braille materials, braille-marked tools, or adaptive aids. Braille materials are read with the fingertips. Braille markings are found on such adaptive aids as rulers, measuring cups, and clocks in place of numbers or letters. Tactile color is a standardized system of twelve distinct colors, each assigned a specific texture. This allows visually impaired persons to participate better in creating or enjoying visual artwork. It is also useful in mapmaking, for labeling, and as an educational resource. Tactile maps and globes are three-dimensional maps used as orientation aids. They contain raised surfaces, textures, and braille markings and are designed to be read with the fingertips. The optacon is a reading machine that converts print into tactile letter configurations. The user scans a small camera over a line of print with the right hand, while resting the left hand on an electronic array. The machine electronically converts each letter into a print letter configuration formed on the array by vibrating pins and read by the left index finger.
Tarsorrhaphy is a surgical procedure in which a section of the eyelids is stitched together at the corner of the eye. The surgery may be performed in the treatment of dendritic ulcers, Bell’s palsy, thyroid disease, or any disorder in which the eye is in danger of overexposure or drying. The procedure is reversible and may be used as a temporary measure.
Tears are much more than just water. They are a complex mixture of water, fatty oils, proteins, electrolytes, bacteria-fighting substances, and growth factors that regulate various cell processes. This mixture helps make the eye surface smooth and clear. Without it, vision would be impossible. Eyelids spread tears across the surface of the eye in a thin film which has three basic layers: mucus, water, and oil. The inner layer consists of mucus produced by the conjuctiva. The middle layer is water with a little bit of salt and makes up about 90% of the tear. This layer is produced by the lacrimal glands and cleanses the eye, washing away any foreign particles or irritants. The outer layer is produced by glands on the edge of the eyelid and contains fatty oils called lipids. These smooth the tear surface and slow the evaporation of the watery layer. As with everything, the balance is sometimes thrown off. An imbalance in the compounds causes the tears to evaporate faster, drying out the eyes. Certain diseases or chemical burns can cause changes in the oily and mucus layers of the tears as can such disorders as blepharitis, rosacea, and other skin diseases. Tear production is measured using the Schirmer tear test in which blotting strips of paper are placed under the lower eyelids. After five minutes, the amount of strip soaked by the tears is measured. Other tests use special dyes in eyedrops to determine the surface condition of the eye. The doctor will look for staining patterns on the cornea and measure how long it takes before the tears evaporate. A mild case of dry eyes can usually be treated with artificial tears which can be used as often as needed. If they are used frequently, preservative-free and mercury-free eyedrops is the best choice in order to avoid allergic or toxic reactions. Ointments can also be used; but, since they blur the vision, it is best to use them only at night.
Thyroid gland can cause problems for the eyes. If it becomes diseased, the body creates antibodies, which are supposed to fight off infection and disease. However, in some cases, including thyroid disease, they attack normal tissue; and, for some reason, the eyes become vulnerable to some of these antibodies, and damage can result. Symptoms of thyroid eye disease are bulging eyes, double vision problems, and damage to the optic nerve. Progression of the disease can be slow or aggressive and eye problems can remain for years even after the thyroid condition has been brought under control.
Tomography is also known as computerized axial tomography. It is a test that records the way tissues react when exposed to X-rays. The computerized process measures the resistance of the soft tissues to the passage of the rays and translates the measurements to pictures on film or video screen. The process intensifies and contrasts sections of the eye, eye orbit, and brain which are indistinguishable with x-rays alone. The computer scan isolates segments of the eye as slight as three millimeters thick. It can outline the crystalline lens apart from the surrounding aqueous fluid and point out tumors to the back of the eye, as in the choroid, which would be invisible to standard x-rays. Computerized axial tomography can often be used as a safer alternative to more expensive and risky procedures that require hospitalization and the injection of air or radiopaque dyes.
Tonography is a painless test to determine the fluid pressure within the eye (intraocular pressure). The test, using a tonometer, is conducted as part of the routine annual eye examination. A tonometer is a small instrument probe that is attached to a biomicroscope or slit lamp. The examiner looks through the biomicroscope as the test is being conducted. The biomicroscope illuminates and magnifies the front part of the eye. Before the test begins, the eyes are prepared by inserting anesthetic drops. The examiner then gently touches a strip of paper laced with fluorescein dye to the inside of each lower lid. The released orange dye mixes with the eye’s tears and covers the cornea. The examiner shines a blue light on each eye and gently touches the cornea with the tonometer. When the probe touches the cornea, a pattern is created in the dye. The intraocular pressure is measured by the amount of force needed to create a pattern. A normal reading varies from 14 to 21. A higher reading may indicate the presence of glaucoma. The test is regularly performed as a glaucoma screening procedure and often is a step in presurgical evaluations to determine whether surgery is immediately prudent.
Tonometry (see Glaucoma Testing.)
Trabeculectomy is a surgical procedure performed to treat open-angle glaucoma. A trabeculectomy bypasses the damaged meshwork drainage systems and creates a new drainage duct from the eye. During the procedure, the sclera is dissected to make a “trapdoor” opening or flap. A block of tissue as thick as the sclera and corneal tissue and containing trabeculum is removed. Often, an iridectomy is then performed. A peripheral iridectomy is the removal of a peripheral section of the iris blocking the anterior angle and deterring aqueous fluid drainage. After the iridectomy, the opening is sutured shut in a loose stitch that will serve as a trapdoor drainage canal for the aqueous and relieve the intraocular buildup. The conjuctival covering of the sclera is then stitched closed. A trabeculectomy is performed with local or general anesthesia in a hospital operating room. The procedure usually takes less than an hour. The patient remains hospitalized for up to three days, and eye drops are prescribed for up to one month. Heavy lifting, bending, or strenuous activity is not permitted for a month. Surgery results vary greatly, depending on such factors as inflammation, scarring, and healing of the drain. Complications associated with the procedure include flattened anterior chambers, scarring of the drainage site (which results in continued glaucoma), infection, inflammation, and hemorrhage. Approximately, one-third of all trabeculectomy patients develop cataracts.
Trachoma is a contagious disease of the eyelids, conjunctiva, and cornea. It is a leading cause of blindness in the world and may affect over 500 million people. Trachoma is caused by the bacteria Chlamydia trachomatisand may be linked to bacterial infections caused by agents Koch-Weeks bacillus, Morax Axenfeld diplobacillus, and the gonococcus bacillus. These, and other such agents, thrive in overcrowded conditions in which a lack of clean water and poor sewage disposal, sanitation, and hygiene exist. Many think that this is restricted to underdeveloped countries, but it is quite prevalent in highly urbanized areas of the industrial nations as well. In such conditions, this highly communicable disease can infect entire communities. Trachoma attacks both eyes, scarring the conjunctiva inside the eyelid and eventually spreading to the cornea. Initial symptoms include pain, oversensitivity to light, and impaired vision. The eye produces a surplus of tears and a discharge. Muscle spasms develop in the eyelids; and the eyelashes turn inward, which further inflames the cornea. As the cornea becomes more scarred, it becomes more opaque, resulting in eventual blindness. In the early stages, trachoma can be successfully treated with sulpha drugs, antibiotics, or surgery. Advances stages of the disease resist treatment, resulting in blindness. Trachoma can be prevented with improved sanitary conditions, hygiene, and clean water supplies.
Transpupillary thermotherapy (TTT) is is a new experimental laser treatment for patients who have the wet form of age-related macular degeneration, especially those who have a condition known as “occult choroidal neovascularization”, in which abnormal blood vessels grow beneath the macula and are hidden beneath layers of tissue. Because a doctor must be able to see the abnormal vessels in order to treat them with traditional laser therapy or photodynamic therapy, patients with OCN are considered unsuitable for those treatments. TTT involves using a low-intensity laser to apply heat to the area in which the abnormal blood vessels are growing. The heat raises the temperature of the retina, causing the blood in the abnormal vessels to clot. This stops them from leaking and reduces the size of the lesions in the area of the blood vessels. This is beneficial because the fluid and blood that leak from these vessels damage the light-sensitive photoreceptor cells in the macula. Trials showed that about 20% of the 15 patients who participated in a pilot study experienced a slight improvement in their vision. All but a few showed a noticeable decline in the thickness of the retina, which doctors say indicates that growth and leakage of new blood vessels had been stopped – at least, temporarily. Research is ongoing, but the procedure appears to be promising.
Trephine is a surgical instrument used in ophthalmologic procedures. The metal instrument looks much like a small, round cookie cutter attached to a handle. The round section comes in various diameter sizes, ranging from three to five millimeters. The size of the trephine is etched onto the handle for identification. The trephine is generally used as a marker. When pressed gently onto the cornea, it makes a distinct, temporary indentation for the surgeon to follow. The trephine is used in corneal transplant surgery to mark duplicate sections of cornea from host and donor, and in radial keratotomy surgery, to mark the optical zone for radial cuts.
Trichiasis is a condition in which the eyelashes grow inward into the eye, causing the lashes to rub against the cornea, producing pain and infection. This may occur spontaneously or be caused by an injury, infection, or such disease such as trachoma. The lashes can be removed with epilating forceps to remedy the disorder immediately. If regrowth is a problem, the lash roots can be destroyed by electrolysis.
