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Surgical Management for Coexisting Cataract and Glaucoma
Scott M. Walsman M.D. & Lama A. Al-Aswad M.D.
The care and management for patients with a visually significant cataract and coexisting glaucoma place many decisions in front of the physician and patient.
2 Patient Selection
3 Surgical Technique
There are three general approaches that can be considered: (1) cataract extraction alone, which may need to be followed by a filtration surgery later, (2) filtering surgery alone, which will be followed by cataract extraction at a later time, and (3) combined cataract and glaucoma surgery.
In recent years, the intraocular pressure (IOP) lowering effect of glaucoma surgery has been substantially enhanced by the adjunctive use of anti-metabolites1,2. However, vision-threatening complications, including hypotony, maculopathy, flat anterior chamber, and bleb infection, are not uncommon. In particular, an eye with angle-closure glaucoma (ACG) is at risk of developing a flat anterior chamber after filtering surgery3. On the other hand, many studies show that cataract extraction with posterior chamber intraocular lens (IOL) implantation also decreases IOP in eyes with or without glaucoma, although the effect varies considerably depending on the type and severity of glaucoma. In particular, several reports assert that cataract extraction can normalize IOP in eyes with ACG4-6. In these studies, the long-term reduction in IOP in eyes with ACG was attributed to significant widening of the anterior chamber angle. The mechanism of primary ACG may be principally related to an anteriorly positioned lens and a small anterior segment, which leads to relative pupillary block and subsequently permanent closure of the anterior chamber angle. Therefore, it seems reasonable that cataract extraction could improve IOP control in eyes with ACG7. In contrast, although IOP control in primary open-angle glaucoma (POAG) has also been reported to improve after cataract surgery, the mechanisms of the IOP decrease remain unclear. As the trabecular meshwork is compromised in POAG, the IOP reduction after cataract surgery may be transient.
A sound surgical plan is needed to begin a dialogue with the patient to provide better insight into the various options and why a particular course should be chosen. The physician must determine the visual need and visual potential of the patient, severity of the glaucoma, target intraocular pressure (IOP) and current IOP, and the patient’s overall physical health before a surgical discussion can begin.
Determining visual potential in patients with coexisting cataracts and glaucoma can be challenging. It is often hard to discern how much the glaucoma is contributing to the reduced visual acuity. There are several approaches, which can be tried to better predict post-operative visual acuity. The Potential Acuity Meter (PAM) focuses a Snellen acuity chart on the retina to remove lenticular affects and is very useful to show overall macular potential of vision. The physician, however, must also take into account the patient’s visual field, which may be approaching fixation. For those patients with only small central fields of vision and/or a spilt fixation visual field, the idea of a filtering surgery for many Ophthalmologist raises another point of interest in the decision process, which is the possibility of “snuff-out” or loss of the remaining central vision. Snuff-out, however, usually occurs due to an intraoperative event or postoperative complication and is rarely idiopathic. A review by Costa et al. showed that approximately 6% of patients who had glaucoma with advanced preoperative visual field defects who underwent trabeculectomy had a severe reduction in their central visual acuity. Patients who lost central vision had statistically higher rates of surgical complications and higher preoperative IOPs8. Importantly, unexplained snuff-out was not observed. This and the previous mentioned points are important for not only judging the severity of the glaucoma, but also providing the patient with realistic expectations for post-operative visual acuity and an accurate risk-benefit ratio of the surgical options.
A patient is a good surgical candidate for cataract extraction alone when there is only mild glaucomatous damage and the IOP is well controlled on one or possibly two topical medications. Cataract extraction with a posterior chamber intraocular lens (PCIOL) can be associated with a significant IOP rise in the early postoperative course in patients with pre-existing glaucoma9,10. This can be due to retained viscoelastic material, increased intraocular inflammation, steroid response in an already impaired trabecular meshwork.
Physicians need to be aware that in glaucoma patients after phacoemulsification and PCIOL implantation; many studies have shown a significant rise in IOP compared to non-glaucomatous patients. It is possible that up to half of patients may have an IOP of 25mmHg or greater and the greatest asset in the care of these patients is to expect this rise and monitor IOP frequently and aggressively5,9,10. It is important for the physician and patient to also be aware that during the first 2 to 4 months after cataract surgery, many patients with glaucoma will have IOPs above their preoperative baseline, whereas patients without glaucoma will often have unaffected or even lower IOP as stated above. Some studies have shown that patients with pre-existing POAG can have a small drop in IOP and require fewer medications after cataract surgery but this is not common and generally is not seen until 1 to 2 years after surgery9,10. Regardless of the possible late post-operative IOP lowering affects, cataract surgery alone should not be relied upon in treating uncontrolled primary open angle glaucoma, but may be a treatment option in angle closure glaucoma patients.
When glaucoma is uncontrolled despite the use of maximum medical therapy and selective laser trabeculoplasty, when possible, the physician and patient are faced with the fact that glaucoma surgery will be required. The surgery of choice is the surgery that will control the IOP best, and most often this is a filtering operation performed alone. When a patient also has a visually significant cataract, the decision becomes more complicated. In a minority of patients it is possible that glaucoma surgery can reduce the post-operative need for IOP lowering therapy and this may improve the vision and quality of life enough to delay cataract surgery. As an alternative, the cataract can also be removed later, once the filtering bleb is functioning and tissue integrity is sound. This two-stage approach is sometimes preferred, as it has been shown that patients who underwent the two-stage procedure, had a greater percentage of long-term IOP reduction compared to those patients who underwent a combined procedure11. Physicians must also keep in mind that the use of anti-metabolites such as mitomycin-C at the time of combined surgery can lead to more complications such as hypotony, maculopathy, bleb leak, blebitis and possible endopthalmitis10,12-15. Thus, in an eye with incipient cataracts, where visual impairment is mild and the glaucoma is uncontrolled a better surgical outcome may occur with a two staged approach, all the time informing the patient that cataractogenic changes with likely accelerate after surgery and that a 5 year incidence of 87% of cataracts with noted after trabeculectomies16, although recent studies have begun to show similar long-term IOP control with both surgical plans17.
The third approach for surgical care is for those patients in whom you would consider a combined procedure. In those patients, the selection and glaucoma staging is very important. Although a great amount of thought may be needed to determine the correct situation for performing a combined surgery the following situations are some in which a combined approach might be considered: (1) there is adequate IOP control but significant drug-induced side effects; (2) adequate IOP control on maximal medications but advanced glaucomatous optic atrophy; (3) IOP is only under borderline control on maximal medications; or (4) uncontrolled glaucoma on maximal medications and an urgent need to restore vision and two surgeries are not feasible nor in the patient’s best interest. When performing a single surgery the patient will only be exposed to one surgical session and as such there is less risk of IOP spikes just after surgery. This is a powerful factor when dealing with patients with advanced glaucoma and concern of loss of central vision.
Cataract extraction by phacoemulsification and trabeculectomy has been shown to be a safe and effective treatment for patients with coexisting glaucoma and cataract18-20. Recent studies have shown that postoperative complication rates and IOP were lower when cataract surgery was combined with trabeculectomy at a two-year follow up21. Many studies have shown that the early postoperative pressure rise after cataract surgery is significantly less after a combined procedure than after cataract extraction alone18-20. As such, when this is taken into account with good patient selection, the next determination is whether to perform a one-site or two-site surgery.
A single-site surgery is likely faster to perform than a two-site procedure, but more recent studies have begun to show that not only does a two-site procedure produce better post-operative IOP control, but also produce less need for adjunct glaucoma medications18. Wyes et al showed in 1998 that patients who underwent a two-site procedure had a mean IOP of 13.3mmHg and required 0.2glaucoma medications compared to the one-site patients who had a mean IOP of 15.3 and required 0.8 glaucoma medications22. A two- site procedure also has safety advantages over a one-site technique as there is less risk of anti-metabolites entering the anterior chamber, and less manipulation of the conjunctiva.
Regardless of the type of combined procedure performed, recent studies support the claim that a combined procedure can be as effective, if not more effective, than two separate surgeries. As with all patient care issues, a sound surgical plan coupled with patient dialogue will help to set appropriate expectations for the surgery and for the post-operative management. This approach combined with assigning glaucoma patients into one of the three above mentioned approaches would help physicians break down a complicated patient presentation into a manageable and successful treatment plan.
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