for
CATARACTS
Developed for the
Aerospace
Medical Association
by their constituent organization
American
Society of Aerospace Medicine Specialists
Overview:
A
cataract is an opacity of the lens or the surrounding
lens capsule in the eye. It may be
congenital or acquired and can result from multiple etiologies. Congenital cataracts and cataracts that develop
within the first year of life (infantile cataracts) are a fairly common finding
with a prevalence of about 1 in every 2000 births. They can be from multiple causes to include
hereditary, genetic, metabolic, maternal infections, toxic or ocular
anomalies. Often, however, congenital
and infantile cataracts are idiopathic.
They can be bilateral or unilateral and range in severity from complete
opacification of the lens that necessitates an early cataract extraction to
minor opacification without any visual sequelae. Often very minor congenital cataracts will
not be found during childhood examinations and are only noted as incidental
findings on later exams. Other opacities
can exist on the outer surface of the lens capsule, such as embryonic fetal
vasculature remnants but these are not considered cataracts and typically do
not cause visual problems.
Acquired cataracts in
adulthood are the leading age-related cause of blindness and visual impairment
in the world. One study has shown that
visually significant cataracts were present in 2.6% of women and 0.4% of men
ages 43-54. These numbers increase to
10.0% of women and 3.9% of men ages 55-64 and 23.5% of women and 14.3% of men
ages 65-74. An earlier study found even
higher prevalence of visually significant cataracts with 4.7% of women and 4.3%
of men ages 52-64 and 19.3% of women and 16.0% of men ages 65-74.
The lens undergoes
multiple changes as it ages. Since the
lens continuously adds new layers to the outside, the inner nucleus is
compressed and hardened leading to nuclear sclerosis. Other chemical changes increase the pigmentation,
hydration and cause proteins to aggregate, all of which promote scattering of
light. Further, these changes increase
the refractive index leading to slightly induced myopia, and lens hardening
leads to a decrease in the lens' accommodative ability. These nuclear sclerotic changes are a normal
occurrence in adults middle age or older and do not necessarily impair
vision. However, if the changes are
excessive, a nuclear sclerotic cataract can result, which can significantly
impair vision.
Cortical cataracts
arise in the outer layers of the lens but outside the nucleus. These cataracts result from hydration of the
cortex and often start as visible vacuoles.
The cataract progresses to form spoke like opacities from the peripheral
lens inward. These opacities can
significantly impair vision and lead to glare complaints.
A posterior
subcapsular cataract is located between the posterior capsule and the outer
lens cortex. Cells inside the peripheral
lens capsule migrate to the posterior inner surface of the capsule and develop
into granular opacities. This can also
occur in the anterior subcapsular region.
These changes lead to poor vision and glare that worsens in bright
light.
Certain medications
also may lead to cataract formation.
Long term corticosteroid use has been associated with formation of
posterior subcapsular cataracts while other medications such as phenothiazines,
miotics and amiodarone have been associated with other types of cataracts. Finally, either blunt or penetrating trauma
to the lens or eye, ionizing, infrared or ultraviolet radiation and metabolic
diseases, such as, diabetes and Wilson's disease are all associated with
cataract formation.
In addition, to glare
and declining visual acuity, cataracts can cause other visual complaints. Cataracts may cause visual field depressions
or defects. Also, the lenticular color
changes associated with certain cataracts (e.g. the yellowing in nuclear sclerosis)
can cause acquired color vision deficiencies.
To restore vision
compromised from cataract formation, surgery is the best option available. If a cataract and the surrounding lens
capsule are extracted, it is called an intracapsular extraction. This procedure, however, is very rarely
performed. The most common surgery is extraction
of the cataract leaving the lens capsule intact in the eye, an extracapsular
extraction. The modern version of this
procedure is called phacoemulsification.
Phacoemulsification uses an ultrasonic device to break up the cataract
so that it can be removed through a much smaller incision, often in the
cornea. This technology, coupled with
foldable intraocular lenses (IOL) has significantly reduced the size of the
incision and complications associated with the procedure. Multiple techniques for incisions can be used
for these procedures to enter the eye, including entry through the cornea or
the sclera. The cataract is then removed
and usually an intraocular lens (IOL) is implanted. These lenses may be placed either in the
anterior chamber between the iris and cornea or the posterior chamber, behind
the iris. Multiple IOL designs exist of
different materials that are rigid or flexible.
Some designs are sewn into place while most remain in place without the
need for sutures.
After a cataract extraction,
the eye can no longer accommodate, and therefore reading and other near work
becomes difficult without the use of reading glasses. Some IOLs have been designed to help mitigate
this problem. The multifocal lenses have
multiple refractive zones within the lens that attempt to bring images at
distance and near into focus at different times depending on the size of the
pupil. However, neither distance nor
near images are as clear as they would be with a single vision IOL with reading
glasses for near work. Another newer
option involves a hinged IOL, which moves with contraction of the ciliary body
and is thought to provide some accommodative power. Since the natural lens filters ultraviolet
light, some IOLs have been developed with tints added to help filter
ultraviolet light and prevent retinal damage.
Although cataract
surgery is one of the safest surgeries available, it does have complications,
some possibly severe and sight threatening.
By far the most common complication is posterior capsular opacification
(PCO). This occurs when the cells that
are present in the periphery of the lens that usually slowly proliferate
throughout life remain in the lens capsule after extraction and migrate to the
posterior surface. At this location they
can proliferate, cause wrinkling and distortion or cause fibrosis of the
posterior capsule. The posterior
capsular changes can lead to glare and a decline in visual acuity. PCO varies in incidence and severity but
appears to occur at visually significant levels in about 28% of pseudophakic
patients at 5 years after surgery. Newer
IOL materials and surgical techniques have successfully decreased the
incidence. The typical treatment for
visually significant PCO is a Nd:YAG
laser posterior capsulotomy that focuses a laser on
the posterior capsule and creates a hole through which the light can
travel. The procedure is fairly benign
but does increase the risk of retinal detachments, (2.4%-3.2%). About half of these detachments occur within
the first year. In addition to PCO,
there are other, some potentially serious complications of cataract
surgery. Infections can develop in the
post-surgical period that are often serious and can threaten the eye. Retinal detachments can occur, especially when
the posterior capsule is disrupted. The
patient may have a reaction to the IOL after it has been placed or it may
dislocate and require additional surgery.
Further, the cornea, retina, iris and other parts of the eye may have
iatrogenic injury that can result in significant permanent visual impairment.
Phakic, aphakic and
pseudophakic are terms used to describe the status of an individual’s
lens. Phakic refers to a person with an
intact natural lens while a pseudophakic individual had a lens extracted and an
IOL placed. A person is aphakic if the
natural lens was extracted and no IOL was implanted. Leaving an individual aphakic is still an
option; however, often the distortion of vision that accompanies aphakic
spectacles or contact lenses is intolerable.
Aeromedical Concerns: Aeromedically, lens changes are defined as opacities (developmental lens defects that do not progress) and cataracts (lens opacities with the potential to progress and compromise visual function). Developmental opacities of the lens are not disqualifying, whereas cataracts, including congenital polar cataracts, are. Decreased visual acuity, contrast sensitivity or symptoms of glare associated with cataracts have the potential to adversely affect mission effectiveness and flight safety. Even if a lens change does not significantly impact vision at present, any of those defined as cataracts have the potential to progress, some relatively quickly. This progression necessitates, at a minimum, monitoring of any potentially progressive cataract to ensure visual functioning remains unaffected. Some cataractous changes become problematic only under certain environmental conditions, such as in bright lights or at night.
As with
any medical problem in aircrew, medical treatment to meet the current standard
of care is mandated without the necessity to receive permission from applicable
or waiver authorities.
However, there are some complicating issues with cataracts in
aircrew. Typically, civilian patients
are not operated on until the patient deems his or her vision is poor enough to
require surgery. Often this level of
severity is after the patient's vision has declined significantly below the
20/20 Air Force vision standard. Military
aircrew may require surgery at an earlier point than their civilian
counterparts.
Only certain IOLs are
approved for use in military aircrew members.
Referral to specific service medical policy is recommended. Generally, the preferred procedure is an
extracapsular cataract extraction with implantation of a posterior chamber IOL
at either the ciliary sulcus or in the capsular bag. Any IOLs with tints in the visual spectrum
including blue-blocking chromophores have the potential to interfere with
normal color vision perception.
Like any medical
condition, implanted IOLs have additional concerns in the aviation environment
that are not present in typical daily use.
A review of FAA records done in 1993 examined the accident risks for
pseudophakic pilots versus phakic pilots.
This study found a statistically significant increased risk of aviation
mishaps associated with pseudophakic pilots.
The risk was even greater for pseudophakic pilots under the age of
50. When compared to their corresponding
phakic counterparts, pseudophakic pilots under the age of 50 had 3.72 times the
risk of having a mishap while the pseudophakic pilots over the age of 50 had
1.41 times the risk.
Another concern for
IOLs is the theoretical risk of dislocation of IOLs under the extreme G-forces
in the aviation environment. According
to an Air Force database, there has been no known dislocation of an IOL during
flight duties in Air Force aviators.
Further, study animals with implanted IOLs were subjected to G-forces up
to +12 Gz without any signs of dislocation.
A case report in August 2000 demonstrated that IOLs may be stable under
high G-forces when a pilot with an IOL ejected from a T-6A Texan and the IOL
remained stable.
Medical Work-up: A good history, to include all visual
complaints is paramount. The diagnosis of cataracts is made with
direct ophthalmoscopy or slit lamp examination.
Cataract extraction is generally reserved for visually significant
cataracts. The resulting aphakia is then
corrected with either aphakic contact lenses or intraocular lens implants. The operative noted is required as is the
model number and type of intraocular lens utilized; also need to prescription
for any aphakic contact lenses or spectacles if applicable as well as the best
corrected visual acuities at distance and near.
A good dilated retinal exam is also important.
Aeromedical Disposition:
Air Force: Early consultation with a
reliable ophthalmologist is recommended to avoid procedures, which would render
the aviator unwaiverable, and to assure that timely surgery is performed. Because of the potential complications of
iridocyclitis and end-ophthalmitis, close ophthalmological follow-up is usually
required for 3 months after surgery until visual acuity stabilizes and final
corrective lenses are prescribed. All
trained aviators who have had a surgical procedure for a cataract can be
considered for a waiver and will need to be evaluated at the ACS. This evaluation cannot occur any sooner than
90 days after the surgery or 30 days if the only procedure was laser
treatment. Waiver requests for untrained
aviators are not likely.
Army:
Cataracts
are considered disqualifying in AR 40-501 Standards of Medical Fitness. They are discussed in the Cataract
Aeromedical Policy Letter which articulates similar aeromedical concerns as the
USAF. With regard to waivers, initial
applicants with cataract are rarely waivered, even if they are asymptomatic,
because most cataracts are progressive; however applicants are considered on a
case by case basis. Waivers for rated
personnel are usually granted after successful surgical correction. The medical work-up and post operative
evaluation for Army aircrew is similar to that in the USAF. However the Army APL specifies the Mentor
Brightness Acuity Test be performed prior to and after surgery with visual
acuity documented for each eye separately at low, medium and high settings. The Army prefers extracapsular lens extraction
with intraocular lens (IOL) implants as the treatment of choice, but there are
no written limitations on the type of IOL used.
Navy:
The
condition is considered disqualifying. Once
vision has deteriorated to less than 20/20 correctable or the patient has a
positive Glare test, the flier should be disqualified from flying until
successful surgical removal of the cataract. Waiver to Service Group 1 may be considered
after surgery provided the VA returns to 20/20 corrected, is within refraction
limits, and the Glare test is negative (normal).
Civilian: Return to flying status may be considered after surgery provided the visual acuity has stabilized, spectacles prescribed, and the candidate meets appropriate military and/or FAA standards. Adequate history and physical examination to exclude conditions such as Wilson's disease, diabetes mellitus, hypothyroidism, systemic steroid use, and hypoparathyroidism should be accomplished. The airman must meet the vision standards of their respective class. They should not have any side effects that are incompatible with flight, such as glare. . The airman is expected to provide the FAA with an Eye Evaluation on Form 8500-7. All classes of medical certificates are allowed. The airman's visual acuity must correct to standards for the medical class requested and if they do not, corrective lenses are required. For a non-multifocal intraocular lens the AME may issue providing the airman does not have any adverse side-effects and they meet FAA vision standards for the class requested.
In the past several
years the FAA has felt that the multifocal lenses have been perfected enough to
allow them both external and intraocular.
The FAA is also accepting the use of the accommodating lenses described
above. The requirement for these lenses
is that if they were surgically inserted the airman must be grounded for 3
months and then is followed with a special issuance. The airman also must have
a one-month period of grounding in order to adjust to the lenses. If the airman does not meet vision standards
in one or both eyes a medical flight test and Statement of Demonstrated Ability
will be required.
Waiver
Experience:
Air Force: Prior to 1962, the Air Force aviator with visually significant cataract was doomed to be disqualified without waiver. In 1962, the first aphakic aviator was returned to full flight status and in 1979, the first military pilot with an IOL was returned to flying. In 1974, the first aphakic aviator was returned to full flight status and in 1979 the first military pilot with an IOL was returned to flying. A review AIMWTS showed 110 cases of cataracts for initial flying training and active flyers, all aeromedical summaries were reviewed. Twenty-five (25/110 – 23%) were disqualified; seven initial aviation training candidates, eight from the pilot/navigator populations and ten from the non-pilot/navigator population. Of the seven disqualified aviation candidates, six were for cataracts and the seventh was for another eye condition. Of the eight disqualified pilot/navigators, five were for cataracts (initial or not correctable to 20/20) and the other three were for other medical conditions (e.g. rheumatoid arthritis, alcohol abuse). Of the other ten disqualified aviators, four were for cataracts (initial or not correctable to 20/20) and the other six were for other medical conditions. Aviators with IOLs are flying unrestricted in high performance aircraft without complications or difficulty reported.
Army: The Aeromedical
Epidemiological Data Repository (AEDR) catalogs all Army flight physicals since
1960. There have been approximately
160,000 individual aircrew entered in this database. During this period of time, there have been
114 cases of cataract discovered in either one or both eyes. Of those 80 were retained.
Navy: Precise statistics are not available at this time.
Civilian: As of 2010 the FAA had 521 first-, 992
second-, and 4,670 airmen who are currently issued with a cataract that they
were following or who had surgical removal.
The FAA also maintains a Path code for airmen issued who have an
intraocular lens implanted and as of the same time period there were 398
first-, 792 second-, and 3,302 third-class airmen currently issued.
|
ICD9 Code for Cataract |
|
|
366 |
Cataract |
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Nakagawara VB, Wood
KJ. Aviation accident risk for airmen
with aphakia and artificial lens implants.
US Department of Transportation, Federal Aviation
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DJ. Ocular problems in
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Prepared
by Drs. John Gooch and Dan Van Syoc
Date:
September 26, 2010