Good vision depends on many factors. One factor is the transparency of the eye structures in the line of sight. Any disturbance in the clarity may impair best visual acuity or cause problems with glare or cause other visual distortions and distractions. Cataracts cause a clouding with distortions and lack of clarity in the lens of the eye. This is a very common condition with over one million surgical procedures for cataracts performed each year in the United States.
Anatomy of the Eye
The anatomy of the eye is similar in many ways to a camera. Moving from the outer portion of the eye to inner, light passes through several structures before falling on the retina (equivalent to a camera's film), where the brain may process the light as a visual image. First, light passes through the cornea, the clear portion of the outer eye that contact lenses are placed on. This area is sensitive to touch and is similar to a filter placed over a camera's lens. It usually remains clear unless there is an infection with scarring, trauma or vision correction surgery with complications. Underneath the cornea is the anterior chamber filled with a clear fluid called aqueous humor. This aqueous humor is constantly flowing through the anterior chamber except in conditions that may block the outflow. This will cause a rise in the pressure in the anterior chamber and may lead to glaucoma. The lens lies just under the colored iris and forms the back of the anterior chamber and the front of the posterior chamber. The lens is visible through the opening in the iris called the pupil. Behind the lens is the posterior chamber filled with a clear jelly-like protein termed the vitreous humor. The inner lining of the back portion of the eye is the retina.
The lens is a convex disk that is held in place by muscles. The outer lining of the lens is called the capsule. The lens changes shape by contracting and relaxing the ciliary muscles to change the focal distance of the eye by making the lens thicker or thinner. The younger lens can change shapes rather dramatically allowing reading at very close distances when the lens is thicker. Cataracts occur in the lens of the eye.
Aging and Presbyopia
Aging causes several effects in the eye. One is a stiffening of the lens and a progressive loss of the lens' ability to change shapes. The individual finds that reading must be done at greater distances initially and then with the aid of reading glasses. This stiffening of the lens with age is termed presbyopia. Presbyopia is a universal phenomenon.
Cataract formation is also a consequence of aging, although it is by no means a universal finding like presbyopia. There are other causes of cataracts. These may include inherited conditions, trauma or exposure to microwave or UV radiation. Pilots are at risk for microwave radiation-induced lens damage if they were to repeatedly stand in front of an operating weather radar on the ground. Cataracts are irregular collections of protein densities within the lens. These imperfections distort light flow through the lens. This is analogous to imperfections in a diamond or cracks in a clear ice cube. The lens begins to cloud as a cataract grows. Cataracts tend to be progressive in size and density, obscuring vision as they grow. They consolidate in a process called maturation.
Effects on Vision
If the cataract is off the central visual axis, it may not be noticed in daylight when the pupil is small and light passes through the lens without striking the cataract. At night, the pupil opens wider to get more light to the eye. The cataract may bend light entering the periphery of the lens. A person may perceive this as glare or halos around lights at night. If the cataract is on the central visual axis (near the center of the lens), best visual acuity will gradually deteriorate. Glasses do not help overcome the interfering effects of the cataract on light passing through the central portion of the lens.
FAA Vision Standards
A pilot or controller may perform aviation duties with a cataract as long as he/she meets the visual standards for the class of medical certificate applied. The distant standard is 20/20 corrected for First and Second class certification and 20/40 for Third class certificates. Once the standards can not be met, the pilot is grounded. Surgical options with replacement of the lens with an artificial implant offer the best opportunity to meet standards. Intraocular lenses (IOLs) are made of synthetic plastics such as PMMA. Use of IOLs is allowed for all classes of certification. A pilot may have IOLs in both eyes and still be waived for First Class certification.
An ATCS may be granted permission by the Regional Flight Surgeon to continue to control if a cataract degrades vision to 20/25 in one eye. Typically however, unilateral vision loss or field defects are not acceptable for air traffic control operations in a tower. They may be waived for pilots, however.
Surgical Correction and Intraocular Lenses
The surgery to remove a cataract and implant the lens is generally well tolerated. The cataract must be mature enough to allow removal. There are several techniques to use. Most involve making a small incision on the edge of the cornea to access the lens. The contents of the lens within its capsule is emulsified and removed with suction. An artificial lens (IOL) is placed in the capsule and anchored in place with one or two sutures. The cornea is then sutured and heals quickly. The corneal sutures are removed in several days. Most pilots note a dramatic improvement in their distant vision immediately. Because the artificial lens does not change shape, near vision for reading usually requires glasses.
For pilots who have bilateral IOLs inserted with one focusing at distant and one focusing at near, pilots will be denied medical certification for a minimum of six months. If they are able to adapt to the vision adequately, they may be granted a Statement of Demonstrated Ability (SODA) for functional monocularity. The FAA discourages this approach.
In the Fall of 2005, the FAA approved multifocal intraocular lenses. These new self-accommodating IOL (can focus both at distant and near) were approved by the FDA in November 2003. The Crystalens uses the muscles of the eye to move the lens and adjust the focal distance. This new lens may negate the need for reading glasses. The FAA protocol for accomodative or multifocal lenses requires a three month post- operative recovery, no vision defects, and the pilot must be able to meet FAA vision standards (see the FAA protocol in our Information Resources section). Note that with standard "non-accomodating" lenses, a pilot would be able to go back to flying as soon as fully recovered.
FAA Reporting Requirements
Once a pilot meets FAA vision standards, they may return to flying on their current medical. We suggest discussing this with the Aviation Medical Examiner to maker sure they will grant a medical when it comes due without the need to defer. Controllers are required to report to the Regional Flight Surgeon before returning to duty. The pilot or controller should provide the operative report, a statement about what IOL was used and an FAA Form 8500-7, Report of Eye Evaluation completed by the ophthalmologist at the final visit following surgery.
The reports may be mailed by the pilot to the FAA at:
Federal Aviation Administration Aeromedical Certification Division CAMI Bldg./ AAM-300 P.O. Box 26080 Oklahoma City, OK 73126-9922
However, incomplete packages or inadvertant statements by treating specialists sometime trigger undue scrutiny by the FAA. Our VFS physicians may also assist in expediting FAA reporting and clearance, and are trained to recognize and help your physicians properly address any aeromedically significant issues before submission.
VFS Aeromedical Assistance
For a more specific personal explanation to your questions or those concerning aeromedical certification, contact VFS for a private consultation. For help in reporting treatment for and obtaining clearance from the FAA to fly or control with these conditions, refer to the VFS Confidential Questionnaire. If you are a VFS Corporate Member, these services are FREE to you.