Any time there is a penetrating wound to the cornea, the iris is often injured as it is directly beneath the cornea in the eye. The injury can be a direct laceration to the cornea or the iris can prolapse through a laceration in the cornea. Blunt trauma can also impact the iris. The most common injuries to the iris include tears in the sphincter and dialysis of the root of the iris. You can also get iridoschisis and atrophy of the iris. Most iris injuries also result in a traumatic hyphema.
Iris injuries are important because, when they are injured, they result in a distorted, nonreactive pupil and photophobia because the iris doesn’t close down when exposed to light. If the pupil is contracted permanently, there can be a loss of full vision. The idea behind treating an iris injury is to preserve as much of the tissue of the iris as possible and to restore its normal architecture.
When a sharp object penetrates the cornea and goes as far as the anterior chamber, the anterior chamber becomes shallower and the iris is the next eye organ in the way. The lens and iris are the next things to be lacerated. The lens rapidly dries out following this type of injury. An external iris prolapse can also occur with this injury. This especially occurs when the laceration is located at the periphery of the cornea. In such cases, the prolapsed iris plugs the wound, leading to a shallower but not flat anterior chamber.
If the iris is incarcerated, it should not be sacrificed and as much of the iris as possible should be spared. The initial sutures following an injury should avoid the incarcerated iris. A very fine, sharp needle should be used so that the wound doesn’t separate when the needle is passed through the tissue. The initial stabilizing sutures may often be temporary because they are too long or too short. They can always be replaced later.
After the wound has been stabilized, the best way to reposition the incarcerated iris is to inject viscoelastic material through the wound in order to deepen the chamber and to draw the iris away from the wound. A high viscosity agent is preferred but if this is not available, a small bubble of air can be injected into the anterior chamber from the periphery of the cornea.
If the iris remains incarcerated, it is important to make sure that some of the sutures haven’t punctured the iris keeping it prolapsed. If this proves not to be the case, a fine cyclodialysis spatula can be passed through the periphery of the cornea in order to be swept across the anterior chamber, freeing up the iris from the wound.
Exposed iris must be carefully evaluated in order to decide whether to excise it or replace it into its natural position. Prolonged prolapse leads to a lack of circulation to the iris and the iris segment can lose its circulation. The exposed iris can also be colonized with bacteria. If the iris is later repositioned, there can be prolonged inflammation and infection of the anterior chamber and iris. Usually, if the iris has been prolapsed only a few hours, it can be saved.
If the decision is made to save the iris, it should be treated with balanced salt irrigation and a cellulose surgical sponge to remove mucus and debris. The cellulose sponge should be sent for culture to see what kind of organisms might have been growing on the prolapsed iris.
Surgical repair of the iris is usually done as a secondary surgery. It is difficult to repair primarily because hemorrhaging can interfere with visualization of the iris in the initial stages after the injury. The reason to surgically repair the iris is to improve the vision and this can’t be accurately assessed until the eye heals from the initial injury.
Frequently other secondary surgery is indicated at the same time, such as penetrating injury to the lens and repair of the iris can be done at the same time. Frequently, an overzealous attempt at primarily closing the iris leads to interference with the critical aspects of diagnoses and treatment postoperatively, such as visualization of the retina or extraction of a cataract.
The presenting signs of a blunt trauma to the iris is transient iritis. The pigment may be freed up and be deposited on the lens, or on the cornea. The sphincter muscle injury may be minimal, resulting in a mild anisocoria (change in the size of the pupil) with retained reactivity of the pupil. More severe cases result in a pupil that is not responsive to light or to agents designed to dilate the pupil. Local sphincter tears can cause a slight teardrop formation of the pupil or a sector of the iris may be deformed. Pigment can migrate from the pupil over the injured iris tissue.
If an attempt is made to stretch the iris root is made, this frequently results in a hyphema. a residual deformity can occur, such as a recession of the anterior angle, dialysis of the iris root, or creation of a cleft in the iris.
Iris Sphincter Tear Treatment
The initial management of a blunt trauma to the iris is usually supportive until the eye has completely recovered from the initial injury. Mild bruising of the iris can result in iritis without any other injury. Treatment with a cycloplegic is usually the only treatment necessary. Topical steroids can also be used to improve comfort and to speed healing of the iris.
If there is a hyphema (blood in the anterior part of the eye), this should be treated in order to avoid increasing the pressure in the eye. This reduces the chances of having an ischemic injury to the iris sphincter muscle or the optic nerve. It also reduces the chance of staining of the cornea from the red blood cells. There should be aggressive use of anti-inflammatory medications to reduce formation of strands of tissue forming in the front and back of the eye so that no more iris sphincter muscle damage is caused.
Conservative measures are usually adequate to manage the long term complications of an iris injury. Cosmetic concerns should be managed with empathy for the patient’s feelings. Iris deformities can be quite pronounced especially among people with light colored irises. These contrast strongly with a dark colored pupil. Tinted contact lenses can be used to hide the deformity of the iris.
There can be complaints about glare from a variety of sources. It can be from a lacerated iris or from corneal scarring. If the pupil is nonreactive, a contact lens with an artificial pupil can be used. Sunglasses can be used for glare from sunlight but can’t help a patient who experiences glare from headlights of oncoming cars at night. If the pupil is not completely round, dilation of the eye should be attempted and long acting agents can be used to treat the problem.
Laser treatment can be done to lyse strands, bands, and adhesions of the iris. A sphincterotomy can improve the appearance of pupils that are not round or are to the side. This can be done in patients who don’t tolerate topical drops to dilate the eye. A sphincterotomy can be used to improve vision if the visual axis can be shifted away from a scar on the cornea toward a clear part of the cornea.
A laser can be used to disrupt the iris stroma so that an adequate sphincterotomy can be performed. Because bleeding usually occurs from the sphincter, treatment should begin at the opening of the iris and should work out toward the edge of the iris, where the sphincter is located. This way bleeding is avoided until the end of the procedure.
Laser treatment can be used to break down strands, bands, and adhesions around the iris. Remnants of lens capsule, strands of tissue or fibrin may adhere to the wound so that there is distortion of the pupil. If there is pigment on the strand, the laser can thermally disrupt the strand.
Lens capsule remnants are usually very delicate and can readily rupture with small pulses of the laser. Vitreous strands need higher energies from the laser. Adhesions can be broken down with varying strengths of the laser, depending on their size. Prolonged strands can cause permanent distortion of the pupil and increased density of the strand, making it difficult to get rid of through laser treatment.
Surgery to sphincter lacerations or tears can be performed. Suture material that absorbs should be used because they degrade less and are less subject to hydrolysis. One must be cautious when stretching the iris to cover a defect in the tissue. Care must be taken to avoid injury to the capsule of the lens, which could result in a cataract. The surgeon can put viscoelastic material between the posterior part of the iris and the lens in order to protect the lens during surgery.
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