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not counted in this number and some studies incorrectly include
presbyopes, who also require plus power lenses to see clearly.
Astigmatism is a condition often caused from an irregular curvature
of the cornea. As a result, light is not focused to a single image on the
retina. Astigmatism can cause blurred vision at any distance and may
occur in addition to myopic or hyperopic conditions. Approximately
60% of the population has some astigmatism.
What is Laser Refractive Surgery?
In October 1995, the Food and Drug Administration (FDA) approved
the use of the excimer laser to perform a refractive procedure
called Photorefractive Keratectomy (PRK). PRK improves visual
acuity by altering the curvature of the cornea through a series of
laser pulses. The laser photoablates (vaporizes) the corneal tissue
to a predetermined depth and diameter. PRK can be used to correct
myopia, hyperopia, and astigmatism. Reported PRK problems such
as postoperative pain, prolonged healing period, increased risk of
infection, and glare (halos) at night, has resulted in Laser in situ
Keratomileusis (LASIK) becoming the preferred choice for refractive
surgery by patients and eyecare practitioners. A survey in the United
States found that the percentage of refractive surgeons performing
PRK had decreased from 26% in 1997 to less than 1% in 2002.
LASIK is performed using two FDA approved devices: the
microkeratome and excimer laser. During the LASIK procedure, the
microkeratome slices a thin fl ap from the top of the cornea, leaving
it connected by a small hinge of tissue. The corneal fl ap is folded
aside and the excimer laser is used to reshape the underlying corneal
stroma. The fl ap is then returned to its original position.
Is LASIK an Option for Me?
An eye care specialist should thoroughly evaluate your current
ocular health and correction requirements to determine whether you
are a suitable candidate for refractive surgery. Clinical trials have
established the following selection criteria for LASIK.
Selection Criteria:
4 Age 18 years or older
4 Stable refractive error (less than .50 diopters [D] change within
the last year) correctable to 20/40 or better
4 Less than - 15.00 D of myopia and up to 6 to 7 D of astigmatism
4 Less than + 6.00 D of hyperopia and less than 6 D of
astigmatism
4 No gender restriction, with the exception of pregnancy
4 Pupil size less than or equal to 6 mm (in normal room lighting)
4 Realistic expectations of fi nal results (with a complete
understanding of the benefi ts, as well as the possible risks)
In addition to conforming to the above criteria, it is important that you
possess normal ocular health and be free of pre-existing conditions
that may contraindicate LASIK.
Contraindications:
4 Collagen vascular disease (corneal ulceration or melting)
4 Ocular disease (dry eye, keratoconus, glaucoma, incipient
cataracts, herpes simplex keratitis, corneal edema)
4 Systemic disorders (diabetes, rheumatoid arthritis, lupus, HIV,
AIDS)
4 History of side effects from steroids
4 Signs of keratoconus
4 Use of some acne medication (e.g., Accutane and/or Cordarone)
Is LASIK Safe for Pilots?
Aviators considering LASIK should know that in initial FDA trials
reporting high success rates (> 90%) and low complication rates (<
1%), the criteria for success varied. In most clinical studies, success
was defi ned as 20/40 or better distant uncorrected visual acuity
(UCVA) under normal room lighting with high contrast targets, not
20/20 or better UCVA. While the majority of patients do experience
dramatic improvement in vision after laser refractive surgery,
there is no guarantee that perfect UCVA will be the fi nal outcome.
Even successful procedures may leave many patients with a small
amount of residual refractive error that requires an ophthalmic
device (eyeglasses or contact lenses) to obtain 20/20 visual acuity. If
overcorrection results, patients may need reading glasses.
Compared to its predecessor (PRK), LASIK requires higher technical
skill by the surgeon because a corneal fl ap must be created. Although
rare, loss of best corrected visual acuity (BCVA) can occur when there
are surgical complications such as those summarized below.
Surgical Complications:
4 Decentered or detached corneal fl ap
4 Decentered ablation zone
4 Button-hole fl ap (fl ap cut too thin resulting in a hole)
4 Perforation of the eye
Operation of an aircraft is a visually demanding activity performed
in an environment that is not always user friendly. This becomes
particularly evident if the choice of vision correction is ill-suited for
　
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