Glaucoma and the Natural Lens
Chat Highlights
March 2, 2005

On Wednesday, March 2, 2005, Dr. Courtland Schmidt a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma and the Natural Lens."

Moderator:  Welcome, Dr. Schmidt.  Our topic tonight is glaucoma and the natural lens.  Where in the eye is the natural lens of the eye located?

Dr. Courtland Schmidt:  The lens sits just behind the pupil and focuses light on the retina.  It is clear throughout life, but when it becomes cloudy and distorts vision, it is a cataract.

P:  How does the natural lens work?

Dr. Courtland Schmidt:  The lens is convex on both sides and focuses incoming light rays onto the macula, the focusing point of the retina.  Think of a shape like a piece of M&M's candy.

P:  Are all natural lenses the same size, shape, etc.?

Dr. Courtland Schmidt:  There is some variability, but not as much as there is with the overall length of the eye from front to back.  In a farsighted person, the eye is usually shorter, and the size of the lens relative to the front of the eye somewhat greater.  That is why farsighted people tend to have more angle closure; their lens is relatively larger for their eye and pushes the iris forward toward the cornea.

P:  What are lens-induced glaucomas?

Dr. Courtland Schmidt:  That encompasses several types.  If a cataract becomes very large and swollen (intumescent) it can physically cause angle closure.  That is phacomorphic glaucoma.

Sometimes lens proteins from a cataract leak out through the lens capsule and cause inflammation and glaucoma.  That is phacolytic glaucoma.

The most common involvement of the lens contributing to glaucoma is in angle closure, as noted above.  As a cataract develops, it actually becomes somewhat thicker and gradually pushes the iris forward.  That can cause either chronic or acute angle-closure glaucoma.

Moderator:  Aren't there also glaucoma-induced lens disorders?

Dr. Courtland Schmidt:  Yes. Some older glaucoma medications, like phospholine iodide, can cause cataracts to progress.  Glaucoma surgery, like any intraocular surgery, can hasten the development of cataracts.  Combined cataract and glaucoma surgery is commonly necessary in our patient population, as both are more common with increasing age.

P:  It's my understanding that the lens becomes hard with age.  But a Texas ophthalmologist, Dr. Ronald Schachar, says that's just a story people have been pushing. What do you think?

Dr. Courtland Schmidt:  The natural lens does seem to lose flexibility over time, although some people feel it's loss of muscle tone in the ciliary body, which focuses the lens, that makes this occur.  Certainly the non-cataractous lens is much softer than the common types of cataract that occur with advancing age.

P:  How is "cataract" defined?

Dr. Courtland Schmidt:  Cataract is loss of clarity in the lens in the eye that focuses the light.  Think of Saran™ Premium Wrap turning into wax paper.  It becomes more difficult, or impossible, to see through.

P:  Does everybody get cataracts?

Dr. Courtland Schmidt:  Everybody gets cataracts as they get older, although in many people the cataract in the early stages doesn't affect their vision whatsoever.  That's why the only reason to remove a cataract is when it is affecting a person's quality of life by decreasing visual function. I tell my patients, "I'm not going to tell you it's time for cataract surgery; YOU are going to tell ME it's time for cataract surgery."

P:  Why do people who have had congenital cataracts removed develop secondary glaucoma?

Dr. Courtland Schmidt:  Any previous intraocular surgery increases the risk of glaucoma down the road.  In addition, the condition(s) that led to the congenital cataracts may also have resulted in an abnormal outflow system, which leads to glaucoma later on.

P:  Why is that type of glaucoma harder to treat than primary open-angle glaucoma?

Dr. Courtland Schmidt:  The glaucoma tends to be harder to treat because some drops work less well, laser is often ineffective, and the younger age of the patients makes the drain created by cutting surgery more prone to scar over.

P:  Why is retinal detachment more likely for those patients?

Dr. Courtland Schmidt:  Cataract surgery of any kind increases the risk of retinal detachment.

P:  Would you explain how glaucoma surgery causes cataracts to develop?

Dr. Courtland Schmidt:  The natural lens is metabolically active and requires the eye to produce aqueous humor to remain clear.  If the eye doesn't produce aqueous humor (fluid) during a period of hypotony after glaucoma surgery, or if the lens touches the cornea (flat anterior chamber), a cataract can progress.  Essentially, any mechanical "insult" (which is what even the most uneventful surgery is) can increase the rate at which a cataract develops.  Fixing a retinal detachment, doing a corneal transplant . . . all can make a cataract develop faster than it otherwise might.

P:  How does cataract surgery affect previous glaucoma surgery (trabeculectomy)?

Dr. Courtland Schmidt:  Anything that causes inflammation can cause a trabeculectomy to lose some -- or rarely -- all of its function and scar down.  That can be trauma, severe pink eye, uveitis and, as you noted, cataract surgery.  The chance of needing to use more glaucoma medications increases, as does the chance of needing another trabeculectomy.

P:  What percentage of patients who have a trabeculectomy, followed by cataract removal, need to have a second trabeculectomy?

Dr. Courtland Schmidt:  I believe it's about 5 to 10% over two to three years, depending on luck and the skill of your surgeon. The hard data are indefinite.

P:  Would you please explain the grades of cataracts and how the grades are determined?

Dr. Courtland Schmidt:  They are subjective and variable. Some people use a scale of 1 to 4; others 1 to 10.  To me, the only opinion that really matters about the cataract is how much it's affecting the person's quality of life.

P:  If a patient who is considering having SLT (selective laser trabeculoplasty) or ALT (argon laser trabeculoplasty) has developing cataracts, should the surgeries be done in a particular order?

Dr. Courtland Schmidt:  SLT and ALT don't seem to affect cataract progression if properly performed.  Any laser has the potential to cause cataracts if improperly performed.  SLT can be done before cataract surgery if the glaucoma is mild; with more advanced glaucoma, a better choice may be a combined trabeculectomy and cataract procedure.

P:  Are any adverse effects noted from the accumulation of iris pigment on the lens in pigmentary glaucoma?

Dr. Courtland Schmidt:  I know of no adverse effects on the lens itself from the pigment in pigmentary glaucoma.

P:  When will a camera-like intraocular lens that is capable of both near and far focusing become available?

Dr. Courtland Schmidt:  "Multifocal" intraocular lenses, which allow focusing at both distance and near, have been a goal for some time.  Some are currently on the market.  Patient satisfaction is quite variable, and most glaucoma patients are not good candidates, especially if they have significant field loss.  Most cataract surgery patients still need some optical correction for either distance or near.

P:  I'm 43 years old, acutely myopic since birth.  About two years ago I had trabeculectomies in both eyes. In the right eye, my worst eye, a cataract seems to be advancing fast (grade 2 on the 1 - 4 scale), whereas a cataract in the left eye doesn't seem to be advancing fast.  Is that unusual?

Dr. Courtland Schmidt:  The rate can often be quite different between two eyes, even with identical surgery.  The left may take much longer.  That being said, remember that by selecting an intraocular lens of the correct focusing power, your surgeon can greatly reduce your nearsightedness with cataract surgery.  Usually, though, both eyes of a very nearsighted person need to be done since the brain doesn't like looking out of one very nearsighted eye and one not-so-nearsighted eye.

P:  Will you comment on the effects of cataract surgery on highly myopic patients?

Dr. Courtland Schmidt:  Some of the happiest patients we see are very highly myopic patients who have cataract surgery.  That's because a lot of the visual distortion from high-power glasses or contacts is eliminated.

P:  Could an epiretinal membrane be removed at the same time as a cataract?

Dr. Courtland Schmidt:  Technically, yes.  It usually requires a retinal surgeon at the time of cataract surgery.  However, some retinal surgeons recommend doing just the cataract first to see what kind of visual result is achieved, then removing the membrane later, if need be.

Moderator:  Is it better for glaucoma patients, or suspects, to have a cataract removed even if the cataract is not causing problems and there is little or no visual field damage.

Dr. Courtland Schmidt:  I tell my patients "if the cataract doesn't bother you, don't bother it."  It's one thing to take a cataract out with minimal symptoms if you are already being forced to do a trabeculectomy.   But if you're just using one glaucoma medication, have no cataract symptoms, and your glaucoma is stable, I don't see the point of surgery.

Moderator:  Dr. Schmidt, thanks for taking the time to be here. It's always a pleasure to have you join us.

On March 9, Dr. Wilson discussed "Which Treatment is Best for Me?" in the Chat room. Click here for highlights of that meeting.

Click here for the most recent glaucoma chat highlights and links to the chat archives.

Click here for upcoming glaucoma chat events.