Correcting Vision
Chat Highlights
November 6, 2002

Norma Devine, Editor

On Wednesday, November 6, 2002, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Correcting Vision."

Moderator:  Good evening, Dr. Wilson.  Tonight we will be discussing refraction (contacts, glasses, etc. ). The first question concerns an Ahmed valve. 

P:  Yes, I'm scheduled to have an Ahmed valve implanted in the left eye on December 10th.  I've had success with an Ahmed valve in the right eye.  However, I've been reading on the Internet that other types may be as good or better. What do you think?  

Dr. Rick Wilson:  I rarely use Ahmed valves, because I haven't been able to get as low an IOP (intraocular pressure) with them as I have with bigger shunts.  However, if you have an Ahmed valve in the right eye that is working well, usually that is a good sign that the same kind will work in the other eye.

P:  What is the maximum of  hyper myopia?

Dr. Rick Wilson:  Usually a minus 20 is at the extreme, in my experience.

Moderator:  What is "hyper myopia"?

Dr. Rick Wilson:  I interpreted that to mean very high myopia (near-sightedness). The term may have been misused.  The questioner may have wished to ask about hyperopia, which is far-sightedness.  Plus 20 to 30 diopters can be seen with that.

Moderator:  Should a glaucoma suspect (ocular hypertensive) be cautious about having laser corrective surgery (LASIK).

Dr. Rick Wilson:  Yes, because LASIK will thin the cornea, and tonometry (the way we measure IOP in the eye) will register falsely low.  I tell patients who  feel strongly they want the surgery that I will take their IOPs one morning for four hours and again at the same times after they have healed from the surgery. The readings give me the fudge factor that needs to be applied to their falsely low IOPs after the surgery.

P:  Do most glaucoma specialists perform refractions? 

Dr. Rick Wilson:  Not routinely.  

P:  Can a laser be used to correct astigmatism?

Dr. Rick Wilson:  Yes.

Moderator:  If a cataract is very small, is it possible to extract the part of lens where the cataract is, put in a transplant, and use LASIK for the other part in a single operation.  Would that help to avoid a retinal detachment? 

Dr. Rick Wilson:  The capsule around the cataract cannot be removed without extracting the entire contents. It would be much less accurate to perform both the cataract and the LASIK surgery simultaneously, rather than doing the cataract, possibly with some refractive cuts. It would not help to avoid a retinal detachment.

P:  If a glaucoma patient is using Timoptic and Xalatan drops, won't the drops be absorbed, at least to some extent, by the lens of the eye and cause side effects?  If the patient is also suffering from cataract, won't the drops increase vision problems?  

Dr. Rick Wilson:  We don't know if the lens absorbs any of the drops.  At least, I don't know.  Any blurred vision usually comes from the effect of the drops on the muscle that works the lens, not the lens itself.  Some drops, like steroids and phospholine iodide, can cause posterior cataracts.

P:  How effective are corrective lenses for a person with limited visual fields? If the damage is progressing, does it make sense to get the lenses?

Dr. Rick Wilson:  Lenses will not help with limited visual fields.  However, since central vision is retained to near the end in glaucoma, lenses will help the vision of persons with advanced glaucoma, if the light entering the eye is not focused sharply on the retina.

P:  Is it a better idea for glaucoma patients using several glaucoma eye drops  throughout the day to wear glasses instead of contacts?  In general, are glasses a better way to correct vision for glaucoma patients?  I would think that the fewer foreign objects in the eye, the better.  

Dr. Rick Wilson:  I have many patients taking glaucoma drops who use contact lenses.  Clearly, the drops are slightly toxic or irritating to many eyes.  Adding contacts just adds a little more irritation.  In young eyes with good tear formation, the contacts are usually well tolerated.  Post-menopausal women, whose eyes are starting to make increasingly fewer tears, have more difficulty with contacts, and even with their eye drops.

P:  I had LASIK surgery three years ago.  The left eye never really seemed right after that.  No one at that time mentioned any concern about glaucoma or normal-tension glaucoma (NTG). Last year, two years after the surgery,  I was diagnosed with aggressive NTG, and was already legally blind in that eye.  Could the LASIK surgery have made the NTG more aggressive?

Dr. Rick Wilson:  Have your intraocular pressures been adjusted for your artificially thin corneas? You may well have run-of- the-mill glaucoma, not normal-tension glaucoma, once the pressures are adjusted for the thin corneas.

P:  How long should a glaucoma patient wait after a trabeculectomy to get refracted for new lenses?

Dr. Rick Wilson:  Till the pressures seem stabilized.

P:  An ophthalmologist once told me that myopia causes my natural eye lens to nearly touch the retina.  I rarely had more than a -7.5 D corrective lens.  Is that something I should be concerned about? 

Dr. Rick Wilson:  The first statement makes no sense to me, as myopic eyes are bigger than normal and the lens may be further from the retina. If your lens is pathologically posterior, that would also make you myopic.  But you would usually have a discernable problem.  A minus 7.5 is about what I am, and if your retina is healthy, I would not be overly concerned.

P:  My two-year-old son has glaucoma and wears glasses with a -7 prescription in both eyes.  He stands so close to the TV that he kisses it sometimes, even with his glasses on.  I wonder what his vision is like. 

Dr. Rick Wilson:  Children can comfortably look at things quite close.  The image they then get is bigger.  It is not unusual for children to watch TV from a closer distance than adults would feel comfortable with.  It may also be that your child is more myopic than the minus 7, and the closer distance makes things clearer for him.  

P:  How I can get a better understanding of his myopia? 

Dr. Rick Wilson:  His pediatric ophthalmologist can use a retinoscope, which will reveal the extent of his myopia.

P:  What can be done to correct vision decreased by low eye pressure (hypotony)? 

Dr. Rick Wilson:  Raise the pressure by re-suturing the bleb, a blood injection into the bleb, or a cyclodialysis cleft.  

P:  What is a cyclodialysis cleft?

Dr. Rick Wilson:  It's a split between the middle layer of the eye and the sclera (white outer coat of the eye) in the front chamber.  Aqueous fluid enters this split and is drained off faster than the usual way, resulting in abnormally low intraocular pressures. 

P:  I had a combined trabeculectomy-cataract operation on my right eye.  The vision in my right eye, when healed, will be fuzzy, with a 20/40 lens implant.  The vision in my left eye is 20/200, corrected to 20/ 25 with glasses.  My doctor says I may need a prism lens for my right eye to get both eyes to work together.  Does that happen often?

Dr. Rick Wilson:  That depends on the cause of the prism requirement.  It is not common, in my experience.

P:  How long after shunt surgery should I wait to put my contact lens in the eye that had the shunt?  

Dr. Rick Wilson:  After a shunt insertion, it is usually about a month before I allow my patients to consider using contact lenses again.

P:  Why is it that some eyes can be corrected only so much?  For example, my right eye can only be corrected to 20/70. 

Dr. Rick Wilson:  There are too many reasons to be able to tell you all of them.  The frequent causes are refractive, followed by cataract, nerve damage, or retinal problems (macular degeneration, hypotony maculopathy, etc.).

P:  Can the glare from halos be minimized by corrective lenses?  The glare from auto headlights at night makes crossing the street difficult for me. 

Dr. Rick Wilson:  That depends.  Spokes of white lights radiating from any source of light are common with refractive problems.  However, cataracts and dilated pupils (sometimes from drops) can also cause those spokes.  Colored halos (rings) around lights are usually related to corneal edema or swelling.

P:  I just had glaucoma wick surgery on Monday last week.  Today my glaucoma specialist said I could start wearing my contacts again, starting with an hour a day.  Is that unusual?

Dr. Rick Wilson:  One of the advantages of non-penetrating surgery is that the eye is not opened, so rehabilitation is faster.  The trade-off is that usually  the IOP achieved is not as low as it is with trabeculectomy.  I would usually be slightly more cautious, but would leave the decision up to your doctor since he can see how the eye is healing.

P:  What is glaucoma wick surgery?

Dr. Rick Wilson:  In wick surgery, a very thin membrane is created between the outside of the eye and the anterior chamber.  Fluid leaks through the membrane, lowering the IOP.  A wick can be left over the membrane to maintain a space there as the wick dissolves.  The space acts as a reservoir into which fluid can drain and be absorbed.

P:  I was reading about endoscopic cyclophotocoagulation recently.  Is that performed by many glaucoma specialists, and what do you think of the procedure?  

Dr. Rick Wilson:  It is mostly performed by cataract surgeons who are treating medically controlled glaucoma patients, who want to take fewer medications after cataract surgery.  Very few glaucoma specialists use it.  I personally feel it is much more natural and physiologic to create a bypass drain to encourage fluid to leave the eye than it is to kill the part that makes the fluid so that less fluid is made.

P:  What tests are performed when cataract surgery is contemplated on a glaucoma patient who has Type 2 diabetes, is myopic, and has astigmatism?

Dr. Rick Wilson:  The retina will need to be examined to make sure it is not damaged too much by the diabetes. The curvature and length of the eye will need to be measured to determine the power of the lens to be put in the eye. 

Dr. Rick Wilson:  Hope everyone has a great week. Thanks for attending our chat.

Moderator:  Thank you, Dr. Wilson. 

End of highlights for November 6, 2002.

On November 13, Dr. Wilson discussed "Steroid Use and IOP" in the Chat room. Click here for highlights of that meeting.

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