THIS WEEK:                                                       p18 13 Apr
02
 #30  Visual attraction
          Push detached retinas back into place with the help of a little
          magnetism

 Ian Sample

YOUR eyes are turning to liquid as you read this--it's an
inexorable fact of life. As people age, the transparent gel
called the vitreous humour that fills the eye gradually breaks
down into a liquid. And a detached retina can sometimes follow as
a result.

As the vitreous humour liquefies, the remaining gel may pull away
from the retina, ripping small holes in it. If the liquefied
material then seeps through the holes, it can lift the retina
from the back of the eyeball. Detached retinas cause blurred
vision, and if left untreated can lead to blindness.

Current treatments can repair holes at the top or bottom of the
retina, but not both. Now a new idea using an injectable magnetic
fluid promises to fix detached retinas wherever the damage has
occurred. The technique has not yet been tested, even in animals.
But if successful, it would achieve something surgeons have
always wanted to do, says David Wong, an eye surgeon at the Royal
Liverpool University Hospital.

Today, surgeons treating detached retinas drain liquid from the
eye and replace it with a jelly-like silicone fluid. This viscous
liquid pushes the retina into position against the back of the
eye, and physically blocks the holes in the retina.

The silicone ensures that salty water which seeps into the eye
from a gland behind the iris doesn't flow through the holes and
cause more of the retina to detach. It is normally left in for 3
to 6 months before being drained away. Another technique is to
sew a thin silicone-rubber band around the eye to squeeze it
enough to close up the holes in the retina.

But success is limited. Because silicone floats on the salty
water, it can only plug holes in the upper part of the retina,
says James Dailey, an ophthalmologist at the Erie Retinal Surgery
in Pennsylvania. Other fluids, such as fluorosilicone, sink, so
they won't block holes in the upper part. These limitations mean
that around a third of these treatments fail. And the
silicone-rubber band treatment does not reattach the retina.

So Dailey has teamed up with Judy Riffle, a chemist at Virginia
Tech in Blacksburg, to make a novel liquid that can plug rips in
the retina wherever they are formed.

By adding tiny particles of magnetite, a form of an iron oxide, to
the silicone molecules, Riffle made a viscous biocompatible
liquid that is also magnetic. This allows it to be moved into
place by applying a magnetic field. The magnetite particles are
linked to the silicone molecules, so they don't separate out when
a magnetic field is applied. 'It won't break up, even under much
greater stresses than those seen in the eye,' says Dailey.

Their plan is to inject the magnetic silicone into the eyes of
patients with detached retinas. A magnetic collar sewn around the
outside of the eyeball, across the damaged area, would then
magnetically attract the silicone fluid. This would push the
retina back into place while plugging any holes beneath it. While
the magnetic collar would need to be fitted permanently, it would
not obscure the patient's vision because it doesn't have to block
the eye's main visual field, says Dailey.

The work was described this week at the American Chemical Society
meeting in Orlando, Florida. Animal tests could get the go-ahead
next year.


____________________________________________________________
Copyright 2002 New Scientist, Reed Business Information


VICUG-L is the Visually Impaired Computer User Group List.
To join or leave the list, send a message to
[log in to unmask]  In the body of the message, simply type
"subscribe vicug-l" or "unsubscribe vicug-l" without the quotations.
 VICUG-L is archived on the World Wide Web at
http://maelstrom.stjohns.edu/archives/vicug-l.html