After the cornea swelling has subsided and the IOP has been lowered, which is usually 48 hours after an acute angle closure, laser iridotomy can be performed. Pilocarpine is applied topically to the eye to constrict the pupil prior to surgery. When the pupil is constricted, the iris is thinner and it is easier for the surgeon to form a penetrating hole. If the eye is still edematous (swollen)—often the situation when the IOP is extremely high—glycerin is applied to the eye to enable the surgeon to visualize the iris. Apraclonidine, an IOP-lowering drop, is applied one hour before surgery. Immediately prior to surgery, an anesthetic is applied to the eye.
Next, an iridotomy contact lens, to which methylcellulose is added for patient comfort, is placed on the upper part of the front of the eye. This lens increases magnification and helps the surgeon to project the laser beam accurately. The patient is asked to look downwards as the surgeon applies laser pulses to the iris, until a hole is formed. Once the hole has penetrated the iris, iris material bursts through the opening, followed by aqueous fluid. At this point, the surgeon can also see the anterior part of the lens capsule through the opening. The hole, or iridotomy, is formed on the upper section of the iris at an 11:00 or 1:00 position, so that the hole is covered by the eyelid. In an aphakic eye, the hole may be made on the inferior iris. After performing the laser iridotomy, the surgeon may place a gonioscopy lens on the eye if the angle has been opened. There is no pain associated with this surgery, although heat may be felt at the site of the lasering.
If a patient has a tendency to bleed, the argon laser will be used to pre-treat the patient prior to completing the procedure with an Nd:Yag laser, or the argon laser alone may be used. The argon laser is capable of photo-coagulation, and, thus, minimizes any bleeding that occurs as the iris is penetrated. Formation of a hole is more difficult with the argon laser because it operates with a decreased power density and the tissue response to the argon laser has greater variability. The argon laser can be used with more patients who have medium-brown irises, however, since the energy of this laser is readily absorbed by irises of this color.
Martha Reilly OD, The Gale Group Inc., Gale, Detroit,