Cataract Surgery in Glaucoma Patients
Cataract surgery in glaucoma patients presents the ophthalmic surgeon and the afflicted patient with many problems. One of the most important is the misconception that “a cataract extraction is a cataract extraction.” Society’s perception of cataract surgery as a quick-fix operation with a rapid return of splendid vision is often not true for glaucoma patients undergoing “routine” cataract surgery. The management approach in the patient who has both glaucoma and cataract must be in many ways totally different from that of a person with cataract uncomplicated by glaucoma. The failure to appreciate this difference may lead to unnecessary morbidity and visual loss. In years past, patients with both cataract and glaucoma frequently provided overwhelming surgical challenges for the ophthalmologist. Fortunately, surgical techniques for both diseases have improved greatly over the past decade, and surgeons with up-to-date expertise in both subspecialties can provide superior outcomes for their patients. The learning curve may be steep at times, but the fusion of surgical skills slowly falls into place as the surgeon constantly learns and upgrades his or her skills.
The latest advances in small-incision cataract surgery include continuous curvilinear capsulorhexis (CCC), improved management of miotic pupils, divide-and-conquer nucleofractic phacoemulsification, clear cornea lens extraction, and foldable intraocular lenses. These techniques, in combination with antimetabolite-assisted guarded filtration surgery (GFS) and postoperative sclera flap suture lysis, dramatically improve outcomes for most glaucoma patients with surgical cataracts. The ability to combine these two procedures through one small incision and simultaneously modulate would healing dramatically improves success rated, decreases postoperative complications, improves cost-effectiveness, allows for rapid visual recovery, and provides superior outcomes for glaucoma patients.
Small-incision cataract surgery, however, is not appropriate for every glaucoma patient. The surgeon must be facile and maintain skill in all branches of cataract surgery, including intra-capsular cataract extraction (ICCE), manual nuclear expression with extra-capsular cataract extraction (ECCE), and phaco-emulsification of soft and hard nuclei. A fusion of these skills is necessary because a subluxated rock-hard nucleus may require ICCE, the nucleus may be too dense for emulsification, thus requiring manual expression, or the surgeon may find it necessary to convert to ECCE techniques during small-incision surgery.
This page will provide a framework to help the surgeon caring for a patient with both cataract and glaucoma decide when to perform a cataract extraction alone, a glaucoma procedure alone, or a combined cataract-glaucoma procedure. Furthermore, techniques that are especially appropriate when performing cataract extraction in patients with glaucoma will be presented in detail. The theme running through these decisions is based on the following section on guiding principles and on the concept that any additional surgical step carries with it the increased risk of complication.
Guiding Principles of Cataract Surgery
Glaucoma is a disease in which ocular tissues become damaged by intraocular pressure (IOP) that is higher than the tissues can tolerate. Glaucoma is not a single condition; the word encompasses a wide variety of entities of different pathogenesis and different intensity.
Knowledge of the basic principles related to the effects and side effects of cataract extraction in patients with glaucoma is essential of the surgeon is to choose a course that is most appropriate for each individual case. Some of these principles are known by all, and many are established but not known by all, and many are established but not well appreciated. Some of the principles that follow are neither well known nor well established but are based on our personal experience or the experiences of those whose clinical judgment appears to us to be sound. Principles not given a supporting reference usually fall into this category.
Clinical Aspects of Optic Nerve Head Damage
Short-term, moderate elevation of intraocular pressure is not likely to affect a healthy optic nerve.
Optic nerves vary in their ability to resist the damaging effects of intraocular pressure. Healthy optic nerves of adults are not usually damaged by intraocular pressures below the diastolic ophthalmic artery pressure (around 30 to 35 mmHg) unless the pressure persists for a minimum of at least 3 months. The exceptions patients with sickle-cell disease. In addition, healthy optic nerves in adults can withstand short-term (perhaps up to 2 weeks) elevations of IOP below the systolic level of ophthalmic artery blood pressure (average, 70 mmHg) without sustaining apparent damage (with the exception of sickle-cell abnormalities). All optic nerves are damaged permanently by intraocular pressures greater than systolic retinal artery blood pressure when such an elevation persists for more than a few minutes.
Glaucomatous optic nerves are likely to be damaged by elevated intraocular pressure.
Optic discs already compromised by disease (glaucoma or otherwise) are at greater risk for further damage and can be permanently damaged by increases of IOP of relatively small magnitude and short duration. Precise data are lacking, but pressure elevations as small as a 50% increase (i.e., 20 to 30 mmHg) for 1 month can be expected to cause a permanent worsening of disc damage in patients with serious disc damage present prior to the pressure elevation.
Optic discs that are badly damaged by glaucoma (“sick discs”) can be further damaged permanently by pressure elevations as short as: 1 day or less when the pressure elevation is in the range of 50 mmHg or more; 1 day when intraocular pressure is 30 to 50 mmHg: or several days when the spike is in the range of the diastolic ophthalmic artery blood pressure. The visually damaging pressure level of intraocular pressure can be estimated.
The pressure at which a patient has developed a hemorrhage of the optic disc or at which progressive disc damage or visual field loss has been noted to occur prior to cataract extraction gives a rough estimate of the level of IOP the optic nerve is able to tolerate. This pressure provides a baseline to use for predicting future damage. For example, a patient whose intraocular pressures are fairly consistent at about 15 mmHg and who develops an optic disc hemorrhage with pressures in that range, is very likely to be at risk for progressive optic disc deterioration with intraocular pressures above 15 mmHg. In contrast, a patient who develops a disc hemorrhage when intraocular pressures are averaging around 25 mmHg probably has an optic disc that is more resistant to the damaging effects of IOP and may tolerate a pressure up to 25 mmHg. These factors help the comprehensive ophthalmologist decide how high and how long a postoperative intraocular pressure spike is tolerable.
Pseudo-pits of the optic nerve are a sign of a pressure-sensitive optic nerve.
Optic discs in which there is an acquired pit of the optic nerve are probably damaged more rapidly by pressure elevations than are optic discs without pits of the optic nerve.
Visual Field Loss and Its Relation to Cataract and Glaucoma Surgery
Visual field defects of a diffuse type are generally characteristic of patients whose optic nerves are relatively resistant to the damaging effects of intraocular pressure. Dense paracentral defects, however, are characteristic of patients whose optic discs are more sensitive to the damaging effects of intraocular pressure.
Factors affecting the likelihood of visual field damage:
Patients with visual field loss that extends into fixation are more likely to have their visual acuity damaged by postoperative pressure elevations than are patients whose field defects spare the area of fixation. Appropriate preoperative planning, such as combined or staged surgery to eliminate postoperative pressure spikes, is essential for this group of patients. In addition, patients with preoperative visual field defects that split into fixation may experience a sudden decrease in acuity associated with an otherwise uncomplicated intraocular surgery. This phenomenon of wipeout occurs in 1% to 5% of cases. "Wipeout" also appears to be related to severe postoperative hypotony and is more common in patients whose postoperative intraocular pressure measures less than 5 mmHg. This is an entity different from hypotony/maculopathy. Any surgical procedure causing severe hypotony predisposes to wipeout; thus, patients with split fixation having cataract extraction followed later by a filtration procedure are twice as likely to develop wipeout as patients undergoing a combined cataract-glaucoma procedure.
Anterior-Segment Tissue Alterations Secondary to Glaucomatous Disease
The anatomic and physiologic alterations of glaucomatous eyes are protein:
Recognition of these alterations facilitates treatment of the disease process. Patients who have suffered an acute-angle closure glaucoma attack with intraocular pressures of 60mmHg may develop significant corneal endothelial damage, posterior synechiae, and iris necrosis. All of these tissue alterations affect the surgeon's type of cataract surgery. Corneal decomposition after otherwise uncomplicated cataract extraction is common in patients having sustained a severe attack of acute angle-closure glaucoma. Surgeons contemplating cataract extraction in these eyes naturally desire to avoid as much corneal trauma as possible.
The atonic pupil that follows a severe angle-closure attack is fixed and dilated. This pupil alteration may cause the surgeon to choose intraocular lens (IOL) with a larger optic to prevent glare and monocular diplopia associated with the larger pupil. Eyes with short axial lengths typically have a very shallow anterior chamber. This makes it even more difficult for the surgeon to work, especially when introducing any instrument into the eye. In addition, eyes with short axial lengths (Less than 22mm) require different IOL calculation formulas; otherwise, undesirable postoperative hyperopia occurs. another example relates to patients with the exfoliation syndrome who have abnormal zonules and an abnormal capsule, predisposing to rupture.
The iris of glaucoma patients is usually abnormal:
Widespread glaucomatous iris abnormalities include abnormal blood vessels permeability, flaccid iris tone, rigid or atrophic muscles, and friability. the iris of patients with exfoliation syndrome is extremely tender and easily torn. Pigment dispersion, breakdown of the blood-aqueous barrier, and hyphema at the time of surgery and postoperatively are common in these eyes. The lens capsule and zonules tend to be more fragile in patients with glaucoma than in those without glaucoma. The problem is most severe in those with the most advanced glaucoma who have been treated most intensively. Surgery is extremely complicated in the exfoliation syndrome because of zonular dehiscence and loose zonules, and the cortex is unusually sticky and can be extremely difficult to aspirate after nuclear removal. The lenses of patients with long-standing glaucoma and advanced cataracts are often partially "loose" even though they do not appear frankly dislocated.
The conjunctiva of patients with glaucoma is often abnormal:
Long-term parasympathomimetic drug therapy produces leaky iris vessels with breakdown of the blood-aqueous barrier, posterior synechiae, peripheral anterior synechiae, and rigid miotic pupils. Inability to sufficiently dilate the pupil is a leading cause of vitreous loss at the time of cataract surgery. The final outcome of cataract extraction is worsened by preoperative long-term use of parasympathomimetic drugs because the pupil does not dilate well, the iris is more likely to bleed when traumatized breakdown of the blood-aqueous barrier is excessive, and there is an increased likelihood of vitro-retinal interface problems. The tissues of patients with glaucoma who have been treated medically for glaucoma are not as healthy as the tissue of patients who do not have glaucoma. The conjunctiva undergoes several tissue alterations due to topical anti-glaucoma therapy. These tissue alterations lead to higher intra-operative complications and excessive filtration failure.