THE SURGICAL DECISION
The decision to operate on any eye is a serious one that glaucoma surgeons confront in two basic situations. The first is when the intraocular pressure (IOP) is very high and the patient has pain, corneal edema, and rapid deterioration of vision. In this situation, the patient can easily appreciate that vision is immediately threatened and can understand the need for surgery with its attendant risks, discomfort, and inconvenience. The surgeon also understands this, and the decision to operate is clear.
The other situation is one in which the patient may not be experiencing any discomfort or visual impairment. This situation is more typical in patients with chronic open-angle glaucoma or, even more problematic, normal-pressure glaucoma. In this situation, the indication for surgery is progressive or worrisome visual field loss or deterioration of the optic nerve, which the physician can recognize but the patient usually does not. The patient must agree to subject an eye with adequate or even normal vision to a procedure that may actually worsen vision and thus decrease the ability to read, drive, watch television, or recognize family and friends. The surgery poses the potential but very real risk, from the patient’s point of view, of harming the vision rather than saving it.
It is important in this latter situation to remember that the goal of glaucoma therapy is to maintain good vision for the patient’s lifetime. Thus to make the right recommendation to the patient, the surgeon must consider the life expectancy of the patient, the rate of disease progression, and the risks and benefits of other therapies. The surgeon must also weigh the surgical benefit (i.e., the likelihood that the surgery will be successful and prevent further visual loss) against the risks of surgical failure or complications.
It is also important to remember that visual loss from damage to the optic nerve is irreversible, whereas visual loss from the most common complications of glaucoma surgery (cataract or refractive change) can be corrected. Therefore the guiding principle in this situation must be to protect the optic nerve. For each patient, the physician must weigh the evidence of progressive nerve damage against the need for and likelihood of arresting that progression ( Box 33-1 ).
Documented visual field and optic nerve damage, despite maximum tolerated medications and laser therapy, that threatens the patient’s vision.
Anticipated progressive damage (e.g., experience in the same or fellow eye that indicates the current course will lead to loss of vision) or intolerably high IOP. Medication failure because of ineffectiveness, intolerance, poor compliance, or complications.
Intraocular pressure that is high enough to place the future health of the optic nerve at significant risk. This pressure will differ dramatically, depending on the condition of the nerve and the patient’s prior history. For example, if the patient has extensive fixation threatening field loss, pressures in or near the ‘normal’ range may be too high for the nerve to tolerate. If the physician waits for further progression before operating, central vision may be lost.
Dysfunctional ocular tissues (corneal edema or bullous keratopathy, pulsating central retinal artery).
Combined with cataract procedure if there is borderline IOP control, advanced damage, or history of postoperative IOP rise in the fellow eye.
Nothing is more reassuring to a patient than to have complete confidence in his or her physician and the other members of the healthcare team. Preparing a patient for surgery begins with a careful and thorough history and physical examination by the ophthalmologist. The ophthalmologist must know the patient’s medical history as well as his or her current physical status. Consultation with the primary care physician should be a routine part of the preoperative plan. It is important that the surgical decision be made in the context of thepatient’s whole life. Family, social, and work-related issues are import-ant in the patient’s decision to proceed with surgery as well as in the patient’s ability to follow the prescribed postoperative treatment plan. When outpatient or ‘come-and-go’ surgery is performed, rehabilitation takes place away from the traditional healthcare setting. Postoperative care is crucial in glaucoma surgical management. Every effort should be made to ensure that the patient is being discharged to an appropriately supportive environment.
INSTRUCTIONS TO THE PATIENT
The physician should tell the patient what to expect with the surgical experience, including a careful explanation of the expected rehabilitation and recovery period. Successful filtration surgery is often followed by a period of relative hypotony and poor vision, which may last from several days to a few weeks after the procedure. Patients can become needlessly demoralized during this period if they have not been properly counseled to expect that visual recovery will take time. A thorough explanation of potential complications is mandatory.
Physicians are now legally required to provide this information to obtain the patient’s agreement to operate (informed consent). Patients must be warned that they may lose vision or even the eye. They may develop cataracts, infection, and hemorrhage. The risk of these complications for each patient should be estimated using the best available evidence and should be shared with the patient. It is best to give these data as ranges, simple ratios, or approximate percentages so that the patient can understand the risk. The surgery itself and the probability of success can be explained reassuringly so that the patient can develop realistic expectations. It is useful to emphasize the unfortunate fact that glaucoma surgery is rarely intended or expected to improve vision, but rather such surgery is performed in an effort to protect the remaining vision. Patients who expect the operation to restore lost vision can be profoundly disappointed with a result that the surgeon views as completely successful.
It is important to explain to the patient that the local anesthetic will be momentarily painful but that the surgery itself is essentially painless. A well-prepared patient is more calm, less apprehensive, and more cooperative; preoperative sedation is more effective, and the surgery will go more smoothly for both the patient and surgeon.
A history of previous illnesses and a review of symptoms particularly related to the cardiovascular system are in order. Significant findings should be further evaluated by the appropriate physical examination or laboratory tests. Laboratory studies, radiography, electrocardiography, and other diagnostic tests should be ordered when indicated by these findings. Electrolyte levels, including potassium, may be altered, especially in patients using oral carbonic anhydrase inhibitors and thiazide diuretics.
Before the orders are written, the surgeon should question the patient about possible allergy to medications. The patient should take to the hospital any medications he or she routinely uses at home, including systemic medications as well as ophthalmic eyedrops and tablets, and should continue to use these on the same schedule as at home.
OUTPATIENT VERSUS INPATIENT SURGERY
Outpatient surgery has been routine for cataract extraction for many years. Glaucoma surgery leaves a filtering wound that disrupts the integrity of the eye and, unlike cataract surgery, may leave the eye hypotonous and susceptible to injury from external pressure or Valsalva’s maneuvers. Nevertheless, many patients have undergone successful and uncomplicated outpatient filtering surgery, and many patients prefer not to stay in the hospital. In many places, particularly the United States, health plans do not authorize overnight stays for routine glaucoma surgery.
Surgical arrangements should be tailored to each patient’s needs. There may be cardiac, pulmonary, or other systemic problems that require hospitalization either before or after surgery. Hospitalization may be indicated if there is a history of a complication in the other eye, if the patient is one eyed, or if there is risk of hemorrhage or other complication. Patients traveling from long distances may need to stay in a hotel or guest house for some portion of the preoperative or postoperative period. Although this is not as convenient as staying in the hospital, it is preferable to driving long distances for daily follow-up and is much less expensive than the hospital.
With the exception of the strong cholinesterase inhibitors, glaucoma medications should be continued until surgery. The cholinesterase inhibitors demecarium bromide (Humorsol) and echothiophate iodide (Phospholine) caused prolonged postoperative inflammation and possibly increase surgical bleeding. These medications are used rarely today. A weaker miotic (e.g., pilocarpine) should be substituted for these drops 2 or 3 weeks before surgery if time permits.
The cholinesterase inhibitors also lower blood cholinesterase and pseudocholinesterase for weeks. Therefore adjunctive anesthetic agents such as succinylcholine may cause prolonged apnea. The anesthesiologist should be told of all drugs that have been taken recently by the patient. Some surgeons try to discontinue the prostaglandin analogs several days to a week prior to surgery although most do not. Those who discontinue these agents prior to surgery feel that they may contribute to postoperative inflammation or even cystoid macular edema.
Most systemic medications should be continued unless they have the potential to cause bleeding. Aspirin is one such medication and should be discontinued for 10–14 days before surgery if possible. A surprising number of patients fail to list aspirin among the medicines they are taking unless asked specifically. The ophthalmologist should consult with the treating physician for patients who are using coumadin or other antithrombotic therapy such as ticlopidine and clopidogel. Surgery can often be performed safely while the patient is using these agents; however, they do add risk especially for retro- or peribulbar hemorrhage as well as suprachoroidal hemorrhage, periocular intraoperative bleeding, and hyphema; therefore, it may be better whenever possible to delay surgery until their effects can be reduced or stopped.
Preoperative sedation eases the patient’s passage through the operating room. If an anesthesiologist is not in attendance, meperidine (Demerol) and hydroxyzine hydrochloride (Vistaril), each given in a dose of 0.5–1 mg/kg body weight, make an excellent combination of analgesic and tranquilizer. A wide variety of other perianesthetic agents have been used as well, and each physician should be familiar with the appropriate agents and choose the most appropriate medication for the patient.