MadSci Network: General Biology

Re: Why does sclera ingrows into the pupil ?

Date: Wed Jun 28 13:25:12 2000
Posted By: Tom Stickel, Grad student, Optometry, Indiana University School of Optometry
Area of science: General Biology
ID: 961639005.Gb

Hey there,
  The technical name for what your friend has is a 
pterygium (pronounced ter-IH-gee-um).  The plural 
form is pterygia.  The disease is not genetic, as far as 
I could find out.  According to Deborah Pavon-
Langston in her "Manual of Ocular Disease" and Jack 
Kanski in his "Clinical Ophthalmology," pterygia are 
caused by exposure to sun and the elements, e.g. wind 
and dry conditions.  Most pterygia form on the side 
closest to the nose, because the nose reflects a lot of 
sun on the eye. From personal experience, I can tell 
you that as an optometry student in Indiana, I rarely 
ever see a true pterygium.  But I've made several 
service trips to Mexico to do exams on farmers down 
there, and they all have pterygia.  They spend morning 
till night up in the hot desert and thin air of high 
elevations, and that does it every time.  Is your friend 
(and her parents) from a tropical and/or hot climate?
  As far as surgery, you can scrape away a pterygium, 
but they have a tendency to recur.  After scraping, 
some sort of drug such as Mitomycin-C, which inhibits 
cell growth, is put on the eye to keep a new pterygium 
from forming.
  What's actually happening with a pterygium is not 
that the sclera is growing over the pupil.  First, a 
pterygium is not really sclera, but it does look a lot 
like it.  Pterygia are just generic fibrovascular tissue 
that extend from the sclera.  The other thing I 
wanted to mention is that pterygia don't grow into the 
pupil, but they can cover the pupil up.  The pupil is 
that little hole in your iris, the colored part of the 
eye.  Take a good look at your friend's eye and you'll 
see that the pterygium is on her cornea, the clear 
front part of her eye.  You'll also notice that the 
pupil is a few millimeters (usually about 3.5 mm) behind 
her cornea.   When a pterygium grows over the cornea 
far enough to start covering up the pupil, though, 
that's when it starts to hamper vision, and that's 
when they're usually scraped off.
  That's the story.  I hope I've helped to answer your 


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