This video-rich presentation focuses on cataracts, the history of surgery, and modern implants used today. Neat stuff!
SCREEN CAPTURES FROM THIS LECTURE:
Using this eye model, I show how the normally clear lens can turn cloudy. This
occurs because of UV light, oxidation reactions, and the accumulation of water
insoluble proteins that cause the tissue to opacify.
The lens/cataract sits immediately underneath or behind the iris (the colored
part of the eye). Normally, you can’t see a cataract externally because the
inner eye is dark … all you can see is the black pupil.
By shining a bright light into the eye, we can see that the cataract lights
up. This cataract is turning brown and glows like muddy water.
We believe that cataract surgery first began in ancient Egypt.
The Egyptian surgeon would chew on an opiate concoction, and spit this anesthetic
mixture into the eye of his patient.
Couching is when the surgeon pushes on the cataract lens with a needle. Eventually,
the supporting zonule "springs" will break, and the lens falls into
the bottom of the eye.
During World War II, fighter pilots had pieces of Plexiglas shrapnel lodge inside
the eye. Amazingly, this plastic didn’t become inflamed or cause infection,
so modern lens implants were considered.
Early cataract surgery was somewhat barbaric, requiring large incisions and
removal of the cataract in one giant piece. It was also hard to find a place
to insert thenew implant that wouldn’t cause damage to the delicate inner structures
of the eye.
One great advance in surgery was the refinement of the surgical microscope.
Most surgeries prior were used with magnified lens loupes like you see here.
The second great advance in surgery was the recognition that the cataract/lens
has three layers like a peanut M&M candy.
In this hypermature cataract, you can see that the cortex (the chocolate of
the cataract) has liquefied and turned white. The inner nucleus (the peanut
of the cataract) has gotten very hard and sunken to the bottom of the capsule
(the outer candy shell).
After removing the inner nucleus and cortex of the original cataract, we now
have a capsular "bag" with a hole in the front. This is like a little
basket, and we can put our new foldable implants directly into this little pocket.
Modern implants are made of flexible acrylic plastic. They have a central "optic"
and little arms called "haptics" that act as springs to center the
implant and hold it in place.
One of the great challenges with vision is astigmatism. It is easy to fix astigmatism
with glasses, as we grind the correction directly into the glass and make sure
it offsets the eye’s refractive error.
New "toric implants" can fix astigmatism as well. After placing the
implant in the eye, I spin it so that is perfectly offsets your natural astigmatism.
One difficulty we have as we get older is the inability to focus at near. We
need "cheater glasses" after age 40, and our dependence upon them
increases with age. After normal cataract surgery, everyone needs cheaters …
but it would be nice if we could make an implant that focusses at both distance
and near. We can look at underwater creatures for clues to making this technology
possible.
Fish can focus at near, despite having rock-hard lenses in their eyes (very
similar to our hard plastic implants) by moving their lens forward and backward.
This focusses just like a telescope.
There is an implant now that does the same thing. The Crystalens implant has
hinges in it that allow the implant rotate forward and backwards. This does
help somewhat with distance and near vision, but I’ve been somewhat underwhelmed
by the results.
The anablep, a South American fish can give us some ideas. This fish is also
called the "four-eyed fish" because it swims at the surface of the
water, with half its eyes out of the water. This allows the fish to see predators
from above, and food below. That’s because this fish has a bifocal built into
its eye. Thus, it has a "multifocal lens" inside the eye.
The Restor lens is an implant we use these days. This implant has concentric
rings that alternate between distance and near focus. This multi-focal lens
gives patients some near vision and distance vision, potentially without the
need for glasses at all. There are some tradeoffs with contrast sensitivity
and mild halos, but if you screen your patients carefully, most people like
it.
To conclude, surgery has improved over the past century, and implant technology
has given our patients many options.
