Cataracts and the Glaucoma Patient
March 7, 2007
Norma Devine, Editor
On Wednesday, March 7, 2007, Dr. Michael James Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed “Cataracts and the Glaucoma Patient.”
Moderator: Welcome back, Dr. Pro. Tonight’s topic is “Cataracts and the Glaucoma Patient”.
Dr. Pro: Hello, everyone.
Moderator: Please begin by explaining what a cataract is.
Dr. Pro: Okay. A cataract is opacification or clouding of the natural lens, which usually is due to normal aging. Cataract extraction has become one of the most common and successful surgical procedures in the U.S.
Moderator: Are cataracts a risk factor for glaucoma? Is glaucoma a risk factor for cataracts?
Dr. Pro: That question is a bit complicated to answer. First we need to speak of the type of glaucoma. In angle-closure glaucoma (narrow angles), the cataract crowds the anterior chamber, pushing the iris forward. A mature cataract in that condition can actually cause or contribute to angle closure, thus being a risk for that type glaucoma.
However, the most common type of glaucoma in the U.S. is open-angle glaucoma, and here the answer is trickier. CIGTS (Collaborative Initial Glaucoma Treatment Study), an important study sponsored by the NIH (National Institute of Health), compared medically and surgically treated glaucoma patients. “The 4-year interim outcomes noted no significant difference in visual field loss between the medically and surgically treated patients.”
Patients assigned to trabeculectomy had lower intraocular pressures, but demonstrated a greater risk for significant loss of visual acuity and a threefold increased rate of cataract progression.” Other studies have confirmed a higher rate of cataract in surgically treated patients.
Moderator: So trabeculectomy seems to be a risk factor for cataracts?
Dr. Pro: Yes.
P: When you say that surgically treated patients lost visual acuity, are you referring to cataract formation and nothing else as the reason?
Dr. Pro: That, and transient decreased post-op visual acuity. At the end of the CIGTS study, visual acuity was equal in the two groups.
P: Are a “ripe” cataract and a “mature” cataract the same?
Dr. Pro: Yes, but those really aren’t medical terms, in that they hold no diagnostic value. Rather, they are used to describe the condition to the patient: The cataract is affecting the patient’s visual ability, and the patient may benefit from cataract surgery.
P: For a glaucoma patient, when is it deemed necessary to remove a cataract? Are cataracts removed when they are “ripe” or is there a longer waiting period?
Dr. Pro: That depends. First, let’s talk about the broad glaucoma classes again. In patients with narrow angles or angle closure, there are situations where cataract surgery is beneficial: The surgery opens the angle.
In open-angle glaucoma patients who have never had glaucoma surgery, the timing of cataract surgery is usually similar to the timing of cataract surgery in healthy patients. New studies have shown that removing cataracts seems to improve the IOP (intraocular pressure) in many glaucoma patients.
P: Do high IOPs speed up the development of cataracts?
Dr. Pro: Very high IOPs seem to. Certainly, patients who have suffered from angle-closure attacks may develop opacities in the lens. But the drops may increase the rate of cataract formation.
Here are some data from the OHTS (Ocular Hypertension Treatment Study), another large NIH study. “ An increased rate of cataract extraction and cataract filtering surgery was found in the medication group (7.6%) compared with the observation group (5.6%)
(hazard ratio [HR] 1.56; 95% confidence interval [CI] 1.05 to 2.29)”.
P: What are the proposed reasons for the increased progression rate of cataracts in the OHTS medication group, as opposed to the group with similarly high IOPs but no medications?
Dr. Pro: The drops may have a toxic effect on cells within the lenses that lead to cataracts. In that study, there was no difference in visual acuity; rather, the investigators had recorded lens changes in the medicine group.
Moderator: Was the OHTS study controlled for which medications seemed to have the higher cataract rates?
Dr. Pro: No.
P: Can anyone with any type of glaucoma get cataracts?
Dr. Pro: Yes, just like the general population, all types of glaucoma patients are at risk. Some, like uveitic (inflammatory) glaucoma patients, may be at higher risk. Those patients may be using steroid drops, which can lead to cataracts.
P: What are the proposed reasons for the increased rate of cataract progression after a trab?
Dr. Pro: That may possibly be due to post-operative inflammation, or may be influenced by some post-operative complications, such as a shallow or flat anterior chamber.
P: Do the laser therapies for glaucoma also increase the risk for cataracts?
Dr. Pro: A study, which came out one or two years ago, suggested that a laser peripheral Iridotomy (LPI) may increase the risk of a cataract.
P: After a trabeculectomy, I had hypotony for several months and developed a cataract. Is hypotony a risk factor for cataracts?
Dr. Pro: As I mentioned, a shallow or flat anterior chamber increases the risk for a cataract. I don’t know whether hypotony with a deep anterior chamber increases the risk for a cataract.
P: If a person has undergone a trabeculectomy and then cataract surgery, can another cataract grow in the same eye?
Dr. Pro: Once a cataract is removed it never “grows back”. It is possible for the capsule (which holds the cataract), to get cloudy. That condition is called an opacified posterior capsule, or secondary membrane, and is easily removed in the office with a laser.
P: What is an epiretinal membrane (ERM)?
Dr. Pro: An epiretinal membrane is a wrinkle of tissue in the back of the eye, on the retina. It is removed by a retina specialist in the operating room.
P: I had a trabeculectomy in the eye with a cataract and was told that it would be difficult for me to wear a contact lens if the cataract was removed. Is that still true?
Dr. Pro: It is hard to comment precisely on each case like that. In cataract surgery, the cataract (opaque lens) is removed from the capsule and replaced with an artificial lens. That usually eliminates the need for a contact lens.
P: Does cataract removal lower IOP in patients with open-angle glaucoma and normal-tension glaucoma? If so, why?
Dr. Pro: I answered that earlier. The answer may be yes, but we don’t have a really good study to prove it. We think the improved IOP may be due to improved functioning of the trabecular meshwork (drain) after the cataract is removed.
P: My IOP went down a little for more than three years.
P: Do you suggest going to both a cataract surgeon and a glaucoma specialist if the patient has both cataract and glaucoma?
Dr. Pro: You should go to an eye surgeon you trust. As I said, most glaucoma specialists perform cataract surgery. Ask questions about your needs and concerns.
P: Are some medications, such as Seroquel, thought to increase the risk for developing cataracts?
Dr. Pro: That is mentioned in the literature. There are others, but usually those complications are related to higher doses.
P: How is the effect of a cataract on the patient’s visual ability measured?
Dr. Pro: First, that effect is evaluated subjectively, such as what the patient complains about (glare, trouble reading, driving, etc.) Second, that effect is measured by testing objectively with the eye chart.
P: Do glaucoma patients handle cataract surgery as well as patients without glaucoma?
Dr. Pro: I don’t know. I haven’t really noticed a difference.
P: If the lens implanted in cataract surgery is unsatisfactory for the patient, can it be removed and replaced with another?
Dr. Pro: Yes, lens exchanges are sometimes performed, as you described.
P: Is there any evidence that the preservatives in glaucoma medications, rather than the pressure-lowering components, cause changes in the natural lens?
Dr. Pro: Good question. The preservatives are certainly toxic to the surface of the eye, but no study that I know about has found whether they cause cataracts.
P: Thanks, Dr. Pro. Terrific job!
Dr. Pro: Have a great evening, everyone.