Presbyopia
What
is presbyopia?
Presbyopia
is an age-related refractive condition
that makes it difficult for the eye
to bring close objects into focus.
Presbyopic eyes gradually lose the
ability to change their lenses’
convexity, which many believe is due
to the lens becoming rigid and the
muscles that control its shape growing
weak.
What
are the treatments for presbyopia?
Up
until recently, treatment
for presbyopia consisted almost
exclusively of the prescription of
corrective glasses – reading
glasses, bifocals, or trifocals –
to help the patient compensate for
the condition’s effects.
However,
some procedures have been developed
that many feel will become viable
solutions to presbyopia. Some are
still being researched, while others
are currently practiced but have yet
to gain widespread acceptance. These
techniques include the production
of monovision, Surgical Reversal of
Presbyopia (SRP), Anterior Ciliary
Sclerotomy (ACS), Laser Presbyopia
Reversal (LAPR), Photophako Reduction
(PPR), Photophako Modulation (PPM),
and lens replacement.
Monovision
One way to combat presbyopia is through
monovision. All individuals have one
eye – typically the dominant
one – that primarily focuses
on distant objects and one eye that
primarily focuses on near objects.
When a patient can no longer adjust
properly to near objects, some doctors
suggest making the non-dominant eye
slightly nearsighted. This relieves
some of the burden on the non-dominant
eye in trying to adjust to a near
field while making distance vision
almost solely the propriety of the
dominant eye. Monovision can be produced
with contacts of different strength;
this may be a permanent solution,
but is also sometimes used before
surgery as a preliminary trial to
see if the patient can adapt to the
condition. If the patient takes to
monovision, then the non-dominant
eye is made slightly nearsighted through
laser vision correction.
Surgical
Reversal of Presbyopia
A technique called Surgical Reversal
of Presbyopia is currently undergoing
clinical tests that are stirring up
interest. In this procedure, four
pieces of plastic – called scleral
expansion bands (SEB) – are
placed just below the surface of the
eye’s sclera, stretching the
muscles that control the lens. The
premise of SRP is that these muscles
have gone slack and that returning
tension to them will increase their
ability to alter the lens for focusing.
Patients in SRP studies have generally
gained some ability to adjust their
eyes’ focus. However, the jury
is still out on the procedure, primarily
because of safety concerns. Some worry
that the plastic bands will have toxic
effects.
Anterior
Ciliary Sclerotomy
Another recently developed procedure
is called Anterior Ciliary Sclerotomy
(ACS). This technique is termed “off-label”:
it uses FDA-approved (U.S. Food and
Drug Administration) devices in a
revolutionary way. Only a few select
doctors perform it. The surgery entails
making eight incisions in a radial
pattern across the surface of the
sclera. ACS is based on an alternative
theory about presbyopia that holds
that a presbyopic lens suffers from
constricted movement because lenses
constantly expand throughout their
lifetime. The incisions in the sclera
are intended to allow the lens more
room to change its convexity; however,
whether or not this actually results
in improved focal ability is still
up for debate.
Laser
Presbyopia Reversal
A procedure that is similar in concept
to Anterior Ciliary Sclerotomy is
Laser Presbyopia Reversal (LAPR).
Instead of using a manual cutting
instrument to make the incisions,
LAPR uses a laser. Early studies of
this technique have been promising.
Photophako
Reduction
There are several even more revolutionary
techniques that use a laser to alter
certain qualities of the lens itself.
Photophako reduction (PPR) uses a
laser to create cavities in the lens
and reduce its size. This is intended
to allow the lens more room to change
shape, much like ACS. Another laser
technique is called Photophako modulation
(PPM). It uses the laser to perforate
the lens so that it may soften and
regain lost flexibility.
Lens
Replacement
One final technique is lens replacement.
This procedure would be similar to
lens replacement for cataracts,
in which the eye’s natural lens
is surgically removed and a synthetic
lens inserted. However, scientists
are still trying to construct a lens
that can change focus.
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