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by monovision may result in decreased binocular vision, contrast
sensitivity, and stereo acuity. After an adaptation period, patients are
often able to see and function normally. Patients who report blurred
vision, diffi culty with night driving, and other visual tasks in low-light
conditions typically do not adapt to monovision and may require an
enhancement on their non-dominant eye so that both eyes are fully
corrected for distant vision. Airmen who seek monovision correction
should consult an eye care practitioner to assist them in compliance
with standards outlined in the “Guide for Aviation Medical Examiners
(see below):
Airmen who opt for monovision LASIK must initially wear correction
(i.e., glasses or contact lens) for near vision eye while operating an
aircraft. After a 6-month period of adaptation, they may apply for a
Statement of Demonstrated Ability (SODA) with a medical fl ight test.
If the airman is successful, the lens requirement is removed from their
medical certifi cate.
Advances in Refractive Surgery
Wavefront LASIK
Eye care specialists have traditionally used standard measurement
techniques that identify and correct lower-order aberrations, such as
nearsightedness, farsightedness, and astigmatism. However, no two
people share the same eye irregularities or have similar refractive
needs. Vision is unique and as personal as fi ngerprints or DNA.
Wavefront technology allows eye surgeons to customize the LASIK
procedure for each eye, providing the possibility of even better vision.
The FDA approved the fi rst system for general use in October 2002.
A laser beam is sent through the eye to the retina and is refl ected
back through the pupil, measuring the irregularities of the light wave
(wavefront) as it emerges from the eye. This process produces a threedimensional
map of the eye’s optical system. Measuring the cornea’s
imperfections or aberrations in this way allows the refractive surgeon
to develop a personalized treatment plan for the patient’s unique
vision needs. Correcting the patient’s specifi c imperfections can result
in sharper vision, better contrast sensitivity, and reduces problems
associated with higher-order aberrations after surgery, such as haloes
and blurred images. Studies indicate that 90-94% of patients receiving
wavefront LASIK achieved visual acuity of 20/20 or better. However,
those with thin corneas, high degrees of aberrations, severe dry eyes,
or conditions affecting the lens and vitreous fl uid inside the eye may
not be good candidates for wavefront LASIK.
Other Advances in Refractive Surgery
The eye’s optical system creates a limit as to how wide and deep the
laser ablation should be, i.e., the wider the ablation, the deeper the
laser must ablate into the cornea, which may result in delayed healing
and prolonged visual recovery. The development of new lasers allows
the creation of a wider ablation zone while removing the least amount
of tissue. Studies have shown that this reduces problems with night
vision and other side effects associated with laser refractive surgery.
Laser technology that provides variable optical zone sizes and beam
shapes with scanning capabilities allows the eye surgeon greater
fl exibility in developing a more personalized laser vision procedure.
A spot laser may be adjusted so minimal spherical aberrations are
produced and a larger optical zone is created. Results from clinical
trials indicate that 67% of eyes had UCVA of 20/16 or better and 25%
had 20/12.5 or better. Additionally, there was an overall improvement
in nighttime visual function and night driving, which is achieved by
preserving the optical zone size and better shaping of the ablation
profi le.
During traditional LASIK, the corneal fl ap is created with a
mechanical microkeratome manipulated by the surgeon’s hand.
While this method has worked well over the years, the performance
of these devices can be unpredictable and is the source of a majority
of surgical complications. These diffi culties result in irregularities in
thickness between the central and peripheral areas of the fl ap that can
induce postoperative astigmatism.
The IntraLase Femtosecond Laser Keratome, which received FDA
approval in December 1999, is the fi rst blade-free technology for
creating the corneal fl ap. The laser keratome beam passes into the
cornea at a predetermined depth, producing a precise cut that is
reportedly more accurate than the microkeratome. Corneal fl aps made
with the laser keratome appear to adhere more tightly to the corneal
bed at the end of the procedure, which may eliminate problems with
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