The Cornea
Chat Highlights
May 22, 2002

Norma Devine, Editor

On Wednesday, May 22, 2002, Dr. Christopher Rapuano, a cornea and external disease specialist at Wills, and the glaucoma chat group discussed "The Cornea."

Moderator:  Welcome, Dr. Rapuano.  I see you made it into the room okay.  

Dr. Rapuano:  Hello, everyone.

Moderator:  Doctor, will you please tell us a little about yourself?  

Dr. Rapuano:  I grew up in New Jersey, went to Brown University, then to Columbia University Medical School.  I did my internship in Boston, my residency in ophthalmology at Wills Eye Hospital, and a cornea fellowship in Iowa.  I have been on the staff at Wills since 1991.

P:  Dr. Rapuano, what is the cornea and what is its function?

Dr. Rapuano:  The cornea is the clear covering of the eye, like the crystal on a watch.  The cornea covers the iris, the colored part of the eye.  It focuses much of the light onto the retina.  Any opacity, swelling or irregularity in the cornea can affect visual acuity.

P:  Can eye drops damage the cornea?

Dr. Rapuano:  Some eye drops can damage the cornea, although it isn't common.  Certain drops, especially those with harsh preservatives, can be irritating, especially if used frequently.  Occasionally, carbonic anhydrase inhibitors, such as Trusopt and Azopt, have been associated with corneal swelling.

P:  Doctor, I have had stem cell deterioration in my left eye for a number of years.  What are the chances that I will get it in my right eye?

Dr. Rapuano:  That really depends on why you have the stem cell degeneration.  If it is from multiple surgeries, then you probably won't get it in the other eye, unless the other eye has had multiple surgeries.

P:  I have had multiple surgeries in both eyes.  

Dr. Rapuano:  Well, you may be at risk for stem cell degeneration in the right eye, too.

P:  Could you please explain the loss of corneal endothelial cells?  What causes it, is it permanent and what effects do topical carbonic anhydrase inhibitors, such as Trusopt, Azopt and one part of  Cosopt, have on the number of these cells?

Dr. Rapuano:  You are born with a certain number of endothelial cells on the back surface of the cornea, which keep the cornea clear throughout your life. These cells die off at a natural rate.  Most people have enough cells to last them a lifetime.  However, anything that damages the cells can mean the cornea develops swelling.  Carbonic anhydrase inhibitors, such as Trusopt and Azopt, are thought to decrease the function of these cells, on occasion.  If this occurs, and the drops are stopped, the cells typically regain their function.  There are reported cases of these cells not regaining their function and permanent swelling developing.

P:  I have secondary glaucoma, caused by Chandler's syndrome, which necessitated a trabeculectomy in February.  Will the endothelial cells of the cornea continue to grow?  If they do, how will that  affect the trab?

Dr. Rapuano:  The endothelial cells are the cells on the back of the cornea that pump fluid out of the cornea to keep the cornea clear.  In Chandler's syndrome, the endothelial cells can migrate to cover the trabecular meshwork, causing glaucoma.  Unfortunately, the endothelial cells do not regenerate, so when they die, they are gone forever.  If enough die, the cornea becomes permanently swollen.  These cells can migrate over a trabeculectomy and scar it, but the trabeculectomy hole is usually big.

P:  What would cause a rough cornea, and what can be done about it?  My doctors says my cornea looks like a good mogul ski run.

Dr. Rapuano:  A lot of things can cause a "rough" cornea, including multiple medications, dry eyes, and multiple surgeries, which can affect the stem cells and the tear-producing cells.  Corneal scarring from previous scratched corneas, and corneal infections can also cause a rough cornea.  What can be done depends on the exact cause.  Reducing toxic medications, and plugging tear drainage ducts are two good options.

P:  Is it true that the success rate for corneal transplants is low?  

Dr. Rapuano:  The success rate of corneal transplants is the best of all organ transplants!  However, it really depends on the reason for the transplant.  Some eyes do extremely well, such as those with keratoconus.  Others do poorly, such as those with chemical burns.

P:  I have aniridia and have had a stem cell graft.  How long does it take to settle down?  One doctor said it could take up to a year. 

Dr. Rapuano:  Yes, it can take a long time for stem cell grafts to "settle down."

P:  Are things very different with an aniridic graft?

Dr. Rapuano:  Yes, aniridic grafts tend to reject more often.

P:  When are cyclosporine pills used instead of eye drops?

Dr. Rapuano:  Cyclosporine is a strong immunosuppressive medication most commonly used to prevent heart, lung, liver and kidney transplant rejection.  We use it to prevent rejection of a stem-cell transplant, but not usually with rejection of a corneal transplant, because of the side effects.

P:  What are the symptoms of corneal swelling?

Dr. Rapuano:  The main symptom of corneal swelling is decreased vision.  Severe swelling can cause pain. Your doctor can see the swelling when he uses a slit lamp.  

P:  A glaucoma patient asked on the Bionic Eye where she could get her corneal thickness measured.  She said nobody does only the pachymetry, and her doctor won't give her a referral.  

Dr. Rapuano:  In the past, corneal specialists were the only doctors who had the machines to check cornea thickness.  The most common, and probably the most accurate, method is ultrasound pachymetry.  These machines cost several thousand dollars.  The test is typically considered a part of the standard eye exam, meaning it cannot be billed separately.  It is easy to see why most doctors would not want to buy this piece of equipment.  It is also easy to see why a doctor can't do only that test, as he can't bill for it alone.  Not that doctors only care about money, but we still have to make ends meet, which is tougher and tougher these days.

P:  How important is it for glaucoma patients to get the thickness of their corneas measured?  The question is in reference to the relationship between corneal thickness and the measurement of intraocular pressure.  

Dr. Rapuano:  The thinner the cornea, the lower the IOP measures.  That is, the tendency is to get a falsely low IOP.  In general, the cornea needs to be much thinner or thicker than normal for it to make a big difference. Having said that, it is becoming another piece of information to add to the equation, especially if someone is getting worse when the IOP seems under control.

P:  Not many ophthalmologists have pachymeters, do they?

Dr. Rapuano:  More and more glaucoma specialists are getting pachymeters.  If patients wrote Medicare and told them pachymetry was an important and separate part of the eye exam, which requires special, expensive equipment and expertise, and it could be billed separately, I believe more eye doctors would measure the cornea.  Doctors have already told Medicare, but Medicare isn't listening.

P:  Some studies show that the Tonopen (which indents the cornea) is less sensitive to corneal thickness when measuring intraocular pressure (IOP) than the Goldmann tonometer (which flattens the cornea). Since it's difficult to get corneal thickness checked, would it be worthwhile to  compare the measurements of the two tonometers?  

Dr. Rapuano:  That sounds reasonable.  I really don't know.  You see, Goldmann applanation has been the gold standard, so we have always compared other measurements to it.

P:  My glaucoma specialist alternates between using the Goldman tonometer and the Tonopen to measure my IOP.

P:  When I occlude my tear ducts, I sometimes find myself pressing quite hard.  Can that do any damage to the cornea or the tear duct (or anything else)?

Dr. Rapuano:  When you press on the tear ducts, you should be pressing on the nose side and not the eyeball side.  Still it is pretty hard to damage the eye that way, unless you have a very thin trabeculectomy bleb or perhaps a cornea transplant, but even then it would be rare.

P:  Does a trabeculectomy damage the cornea? 

Dr. Rapuano:  Any eye surgery can damage the cornea.  Generally, trab surgery does minimal damage.  But if the chamber flattens after surgery, that can do considerable damage.

P:  I have Haab's striae, due to congenital glaucoma, on both corneas.  I never had any problems until two years ago, when suddenly I got corneal swelling in my right eye.  I use Muro 128, which helps a lot, but I don't understand why all of a sudden I have these problems with that cornea.  I'm 32 years old and had one surgery on each eye when I was a baby.  My doctor wants me to see a corneal specialist.  Do you think I will need a transplant someday?

Dr. Rapuano:  The Haab's striae are evidence of corneal damage; that is, damage to the endothelial cells I mentioned earlier.  The cells were most likely damaged, but not enough to cause corneal swelling.  Over the last 32 years, a few more cells died off naturally, and it reached a level where the cornea became swollen.  When the Muro 128 doesn't do the trick, you may well need a corneal transplant.

P:  I was wearing hard contact lenses for 30 years.  Little did I know that dry eye was developing in both eyes.  Would wearing a hard contact lens with dry eye make the cornea thinner?

Dr. Rapuano:  Chronic contact lens wear can damage the tear producing cell and make dry eyes worse.  Severe dry eyes can cause corneal thinning, but that isn't typical.

P:  Is it possible to use soft contact lenses for short periods (4 to 5 hours)?  I have never used any contacts.  What kind is best for most patients?

Dr. Rapuano:  I think the best contacts for most patients in the year 2002 is daily wear, disposable, soft contact lenses.  They give most (not all) people excellent vision. You put in a brand new lens each morning, throw it in the trash at night, and open up a new lens the next day.

P:  Are contact lens used for days harmful to the eye?  

Dr. Rapuano:  The use of contact lenses is not without potential complications.  One of the most frequent reasons for cornea infections I see on a day-to-day basis is from contact lenses.  But, overall, they are pretty safe if used properly.

P:  What pathological effect can carbachol have on the cornea?  I've heard some vague concerns about this expressed by some doctors. 

Dr. Rapuano:  In my experience, carbachol doesn't cause much cornea damage.

P:  Years of published research have shown that the preservative in almost all glaucoma and other eye drop medications can injure the eye, including the cornea.  There seem to be more modern alternatives. This area is really obscure to patients.  Do you think eye specialists could help guide the drug companies into using more modern alternatives?

Dr. Rapuano:  Some glaucoma medications (Timoptic, for one, I believe) are available in preservative-free forms.  Generally, a preservative in the eye a few times a day isn't too bad.  Unfortunately, many patients are using several kinds of drops a day and are getting a lot of preservative.  Preservative-free drops would be great, but would be even more expensive than the already outrageously expensive ones.

P:  Are colored haloes a symptom of corneal swelling?

Dr. Rapuano:  Colored halos could indicate corneal swelling, but could also be due a host of other things, such as corneal irregularity and cataract.

P:  Can dual punctal plugs in an eye exacerbate blepharitis?

Dr. Rapuano:  Punctal plugs are typically used for dry eyes, which many patients have along with blepharitis.  But plugs can occasionally exacerbate blepharitis and have to be removed.

P:  Since many cornea surgeons are turning to LASIK, will there be a shortage of skilled cornea surgeons?

Dr. Rapuano:  That is an excellent question.  I know of several excellent corneal surgeons who now do many fewer, even no, corneal transplants.   

P:  How do you feel about a glaucoma patient having a LASIK procedure?

Dr. Rapuano:  That depends on the degree of glaucoma.  Very mild glaucoma is probably not an issue.  For anything but mild glaucoma, LASIK probably is not a great idea. Certainly not after glaucoma surgery.

Moderator:  Thank you for answering our questions, Dr. Rapuano.  

P:  We are also pleased that your being here allowed Dr. Rick to celebrate his birthday tonight.

Dr. Rapuano:  Thank you.  I enjoyed it.  Goodbye.

End of highlights for May 22, 2002.

On May 29, Dr. Werner discussed "Childhood Glaucoma" in the Chat room. Click here for highlights of that meeting.

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