- Interferometer focuses an intense, coherent source of regular or laser light into the eye to establish an approximate idea of the reclaimable vision. The instrument is also practical for predicting the eventual sight attainable after treatment for amblyopia.
Intraocular lens (IOL) implants are small, clear plastic lenses implanted into the eyes during a surgical procedure to replace the section of natural lens lost in cataract removal surgery. As a permanent substitute for the lens, it enables the cornea to focus light onto the retina and produce a distinct image. IOL implants are made up of two parts. The optic is the center portion of the lens that does the job of focusing. It is approximately one-quarter of an inch long and made of PMMA (Polymethyl Methacrylate) plastic. The portion called the haptic holds the lens in place. The power of the IOL is determined by two tests. Keratometry is a test that determines the curvature of the cornea. More curved corneas require incrementally weaker implants. An ultrasonic A-scan determines the length of the eye. The longer (more nearsighted) the eye, the weaker the implant needed. An A-scan may determine that an IOL is unnecessary. IOL implantation can be performed in either intracapsular or extracapsular cataract surgery removal and significant advances have been made in their technology. IOLs are smaller than they used to be and can be folded and placed into the eye through a tiny incision. There are three implantation methods: anterior chamber, posterior chamber, and iris supported. The lens is placed in front of the iris in the anterior method, behind the iris in the posterior method, and is clipped or sewn to the iris in the almost obsolete iris-supported method. Most ophthalmologists prefer the posterior method, claiming the lenses are more secure there and in a better position to help restore eyesight. IOLs provide constant, immediate improvement in vision and require no ongoing care. Patients may require normal glasses or bifocals as a supplement. IOL surgery is often restricted to older patients since long-term side effects are unknown. It is recommended that the surgery not be repeated if an implant was unsuccessful in one eye or in the presence of other serious eye problems.
Iridectomy is the surgical removal of part of the eye’s iris. The procedure is often performed as treatment for narrow-angle glaucoma, a condition in which aqueous fluid builds within the eye as a result of a pupillary block and causes a rise in intraocular pressure. The removal of the section of iris creates a passageway between the posterior and anterior chambers of the eye and eliminates an iris bombe, a condition in which the iris is abnormally bowed forward from the increased intraocular pressure. The procedure, performed under general or local anesthetic, allows aqueous fluid to pass from the posterior to anterior chamber and thus reduces intraocular pressure. Traditionally, a small incision is made at the limbus through the cornea and sclera into the anterior chamber of the eye. Since the iris is malleable (able to be beaten into a thin plate), the incision allows a peripheral portion of the iris to prolapse out of the eye. The prolapsed section is held with forceps and excised with scissors. The iris bombe sinks backward into the eye. Often, the condition or blockage requires only a cut to be made rather than a removal of the iris. The cut is called an iridotomy and may be made surgically or with an argon laser, which burns a hole in the iris through the closed eye. Iridectomy or iridotomy is usually performed at the initial attack of narrow-angle glaucoma after treatment with medication has begun. It is used as a treatment and as a prophylactic measure to prevent recurrent attacks of narrow-angle glaucoma.
Irideremia (See Aniridia.)
Iridocyclitis is a condition of the iris and ciliary body in which these two portions of the eye become inflamed. Because of the close proximity of the ciliary body to the iris, inflammation and infection pass easily from one body to another. Since the iris and ciliary body are located in the front portion of the unveal tract, which also includes the choroid, the condition is also called anterior uveitis, or inflammation of the unveal tract. Symptoms may include pain, especially when focusing on near objects, redness, light sensitivity, and changes in the appearance of the pupil. The inflammation irritates the sphincter muscle of the pupil which causes it to constrict, appear misshapen, or develop spasms. As a result of iridocyclitis, posterior synechiae may occur. This is a condition in which the pupil adheres to the underlying lens. Iridocyclitis may be caused by iritis, which in turn is caused by injuries, viruses, herpes zoster, fungi, parasites, arthritis, and sinus or tooth infections. The condition may be treated with cycloplegic, or dilating drops, local steroids, and medications for underlying causes. The condition may last for two weeks or more and carries a tendency to recur. Several recurrences may raise the possibility of cataract development.
Iridodonesis is a trembling of the iris. This condition is frequently seen with a subluxated (displaced) lens or following cataract surgery. It is also associated with Marfan’s syndrome.
Iris is a circular curtain composed of tiny, radial muscles which contract and relax to shape the size of the pupil. It is better known as the “colored part of the eye.” The color of the eyes depends on the number of pigment cells in the iris. For example, light blue eyes have the least number of pigment cells, while dark brown or black have the most.
Iritis is an inflammation of the iris. Symptoms may include pain, especially when focusing on near objects, redness, light sensitivity, and changes in the appearance of the pupil. While the cornea remains clear, the pupil may appear constricted or misshapen and develop spasms. Because the iris is part of the uveal tract, iritis may be present in uveitis. Other causes may include injuries, viruses, herpes zoster, fungi, parasites, arthritis, and sinus or tooth infections. When the inflammation of iritis spreads to the adjoining ciliary body, the condition is termed iridocyclitis, or anterior uveitis. Iritis is most often treated with cycloplegic, or dilating eye drops and local steroids. The condition may last for two weeks or more and carries a tendency to recur. Several recurrences may increase the possibility of cataract development.
