Clinical Practice Guideline

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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References:

 

Eyeonics.  Crystalens physician labeling.  http://www.crystalens.com/index.htm.  Apr 2006. 

 

Johns KF, Feder RS, Hamill MB, Miller-Meeks MJ, Rosenfeld SI, Perry PE.  Basic and Clinical Science Course:  Lens and Cataract.  American Academy of Ophthalmology.  2003:  26-65.

 

Jacobs DS.  Cataract.  UpToDate.  Online Version 15.1.  December 13, 2006.

 

Klein BE, Klein R, Linton KL.  Prevalence of age-related lens opacities in a population.  The Beaver Dam Eye Study.  Ophthalmology.  1992 Apr; 99(4):  546-52.

 

Leske MC, Sperduto RD.  The epidemiology of senile cataracts:  a review.  Am J Epidemiol.  1983 Aug; 118(2):  152-65.

 

Nakagawara VB, Wood KJ.  Aviation accident risk for airmen with aphakia and artificial lens implants.  US Department of Transportation, Federal Aviation Administration.  DOT/FAA/AM-93/11.  Oklahoma City, OK.  July 1993.

 

Smith P, Ivan D, LoRusso F, MacKersie D, Tredici T.  Intraocular lens and corneal status following aircraft ejection by a USAF aviator.  Aviat Space Environ Med.  1992 Apr; 63(4):  302-7.

 

Tredici TJ, Ivan DJ.  Ocular problems in the aging military aviator.  Presented at the RTO HFM Symposium, RTO MP-33, Toulon France, Oct 1999. 

 

 

 

Prepared by Drs. John Gooch and Dan Van Syoc

Date: September 26, 2010