|A shift to farsighted vision after RK can provide poor vision
when combined with presbyopia.
Many individuals who had Radial Keratotomy (RK) years ago are now experiencing fluctuation
in vision quality throughout the day and a shift in visual acuity toward hyperopia (farsighted, longsighted) vision. Some of this shift may be natural.
Natural Hyperopic Shift
Many people become more hyperopic in the fifth and sixth decade
of life. The natural hyperopic shift may not explain all of
the phenomena of hyperopia after RK, however the natural changes
of the eye it may be responsible for some.
RK Corneal Weakening
The process of RK is to make four, eight, twelve, or more radial
incisions through about 90% of the cornea. These incisions weaken
the cornea, causing a flattening of the center of the cornea and
reducing myopic (nearsighted, shortsighted) vision. The healing of the RK incisions
restores some of the cornea's strength and provides stability. Unfortunately
for some, the RK incisions did not provide enough strength to the
cornea for the long term.
Daily Fluctuations and Hyperopic Shift
Because some corneas with previous RK have become unstable, patients
experience fluctuations in visual acuity throughout the day. The
internal pressure of the eye pushes out on the cornea, causing a
central steepening and creating hyperopia. Fluctuations and hyperopic
shift does not occur to everyone who had RK. There appears to be
some correlation between the number of radial incisions and the
probability of corneal instability. Those who had more incisions
tend to be more likely to develop unstable corneas, however instability
or stability can occur with few or multiple incisions. Every individual
Presbyopia and Hyperopia Equal Poor Vision Quality
Presbyopia is when the natural crystalline lens of the eye is less able to change shape to
focus on objects near. Presbyopia usually becomes problematic at
about age 40. The combination of hyperopia and presbyopia often
provides poor quality vision at all distances. The obvious answer
to this problem is to correct the hyperopia and use reading glasses
or bifocals for near vision.
Hyperopic vision can be vastly improved with glasses, but due
to the physics of hyperopic correction, much better correction may
be achieved with contact lenses. New contact lens materials that
allow more air to pass through the lens make contact lens wear much
more comfortable than before. A scleral contact lens can sit over
the cornea, needing to touch only the outer white part of the eye.
New technology rigid gas permeable (RGP) contacts are much more
comfortable than those in the past. An advantage of an RGP lens
is that it can add stability to a fluctuating cornea.
Many former RK patients are appropriate candidates for conventional
or custom wavefront Lasik, Bladeless Lasik, PRK, or LASEK. If the patient is fully presbyopic, an alternative that
may be appropriate is Refractive Lens Exchange (RLE). RLE is the same as cataract
surgery. The natural lens is removed and replaced with an artificial
lens that is calculated to correct the hyperopia. If the cornea
is stable, RLE may be an appropriate method to resolve hyperopia.
Every eye that has had previously surgery is unique. Whether
or not a surgical correction is appropriate will depend upon each
person's individual circumstances. Only a comprehensive evaluation
by a competent doctor will be able to determine what is best.
A very interesting technique that is in the early stages of development
and availability is Corneal Collagen Crosslinking with Riboflavin (CxL).
This is a process of applying light to the cornea while it is protected
with vitamin enriched eye drops to cause the cornea to become stronger
and more stable.
Looking For Best Lasik Surgeon?
If you are ready to choose a doctor to be evaluated for conventional
or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization.
Locate a USAEyes Evaluated & Certified Lasik Doctor.
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