From: M20614@mwvm.mitre.org (Hugh Pritchard)
Subject: Re: Risks of cataract surgery?
Organization: The MITRE Corporation, McLean VA 22102
Date: Wed, 14 Oct 1992 12:22:52 GMT

In article <1992Oct13.025238.14926@netcom.com>
park@netcom.com (Bill Park) writes:
 
>An article in the local newspaper reports a study by Georgetown U. and
>Johns Hopkins on a risk to cataract sufferers from the cures.
 
Yes, it also appeared in the _The_Washington_Post_ Health section.              sdays.
 
> [synopsis of article reporting risk from prophylactic capsulotomies]
 
>A couple of my relatives may soon have to decide whether to have
>cataract surgery.  What should they do to reduce the risk or estimate
>it more accurately in their cases (80 year old woman, 72 year old man,
>both white and healthy, with low blood pressure for their age).
 
The article said that since there was this risk, that merely
*prophylactic* capsulotomies might not be such a good idea.
 
This is not the same thing as assessing the need for the cataract surgery
in the first place.  We are speaking of two things:
 
   1)  Cataract surgery:  The cataractous lens is removed, leaving behind
       the rear (posterior) portion of the clear wrapping (the capsule)
       that normally surrounds the lens.  Frequently, an acrylic artificial
       lens is placed in the eye, usually right where the old lens was --
       nestled between the iris and the posterior capsule.
 
       Your relatives' ophthalmologists will tell them that cataract
       surgery is indicated only when the cataracts interfere significantly
       with their lives.
 
   2)  Occasionally, the posterior capsule itself becomes cloudy some time
       after the cataract surgery.  This is often referred to as "secondary
       cataract."  The standard treatment for this is to zap the cloudy
       posterior capsule with a laser, blowing open a hole at its center.
       This is called a capsulotomy.
 
       Sometimes this is done as a prophylactic measure, with no evidence
       of secondary cataract.
 
>What causes the clouding?  If it is an allergic reaction to the
>artificial lens material, shouldn't they first test for sensitivity to
>that material?
 
The reasons for the clouding of the posterior capsule are unknown, as are the
reasons for the cataracts.
 
Secondary cataracts have nothing to do with the presence or absence of the
artificial lens (called an IOL, for Intra-Ocular Lens).
 
The IOLs are made of polymethyl methacrylate (PMMA), a kind of acrylic.
During World War II, doctors in Britain noticed that fighter pilots with
shards of shattered airplane canopy in their eyes did NOT develop infections
in their eyes.  The canopies were made of Perspex -- PMMA.  Later, ophthal-
mologists remembered this when they developed IOLs:  PMMA is inert with
respect to the eye.  Since the IOLs are made entirely of PMMA (even the
springy side pieces used to hold the IOL in place), the IOL is inert with
respect to the eye.
 
>Also, why would a laser procedure tend to detach a retina?
 
I don't know.  If the reason(s) were obvious, ophthalmologists would have
twigged to them long ago.  2% risk (as reported in the study) is not 100%
incidence of retinal detachment!
 
> What exactly is the procedure?
 
Patient complains of once again having cloudy vision, even though cataracts
have already been removed.  Ophthalmologist takes a look, and explains
"secondary cataracts" to patient.  Ophthalmologist and patient repair to
hospital or out-patient center at their mutual convenience.  Patient is
sedated; ophthalmologist focusses blue-green laser on the offending
posterior capsule, and blows a hole in the center.  Takes about 10 minutes.
 
Trouble is, some ophthalmologist like to do this *before* any secondary
cataract shows up, because the procedure is so easy and, up 'til now,
so risk-free.
 
[I'm not a physician.  I have, however, had these eye problems:
   1953:  Born with fully developed cataracts in both eyes.
          Also, first IOL implanted in the U.S.
   1956:  Both cataracts removed, in separate operations.
   1962:  Had secondary cataract removed -- this was before laser technology.
   1986:  IOLs implanted in both eyes (anterior chamber), in separate
          operations.  Ophthalmologist trimmed back my remaining posterior
          capsule.
   1989:  Had to have one IOL replaced with one in posterior chamber, as it
          rubbed against inside of cornea, causing corneal edema.
   1990:  Cornea transplant (penetrating keratoplasty).
]
 
**  Hugh Pritchard,  hapritch@mitre.org,  703/883-6616