Van B. Nakagawara, OD, FAAO
Kathryn J. Wood, Opt TR
Ronald W. Montgomery, BS
Civil aviation is a major commercial and technological industry in the United States. Approximately 1.45 million people rely daily on scheduled air carriers for business and personal travel, while general aviation contributes more than $45 billion annually to the nation's economy and provides more than 540,000 jobs.
Over the past two decades, the demographics of the civil airman population has changed. The percentage of airmen who are > 40 years of age has increased from 39% in 1976 to more than 59% in 1996. The average age of civil airmen in 1996 was 43.0 years of age. A common consequence of aging is an increased prevalence of vision problems. There has been a nearly 30% increase in restrictions associated with visual conditions in civil airmen from 1976 to 1996.
When an eye doctor examines and prescribes for a patient, it is customary to ask the individual about occupational and recreational activities that might influence the use of any ophthalmic correcting devices. In general, a single correcting device is not functional for all activities. For civil airmen, the types of ophthalmic devices recommended are often determined by the flight activities being performed. For example:
- Airmen who do aerobatic flying may be advised to wear soft contact lenses, since they are not as easily dislodged as rigid lenses.
- Agricultural aircraft operators (crop dusters) may be exposed to harmful pesticides. Soft contact lenses, which can absorb chemicals into their matrix, may be contraindicated. Adequate eye protection should be recommended to these pilots.
- Eye protection devices should be recommended for all monocular aviators, since they can receive ocular trauma from flying objects in the cockpit during turbulence or aerobatic maneuvers. Additionally, bird strikes have shattered aircraft windscreens.
- Monovision contact lens wear is not recommended for flying, since it reduces stereopsis and distance visual acuity. Presbyopic airmen who wear contact lenses should be fitted with lenses for distant vision and prescribed eyeglasses to correct for near vision.
- Opaque or translucent colored contact lenses may affect peripheral vision of the pilot, especially at dusk and at night, and should be discouraged.
- The pilot is exposed to many glare sources in aviation and proper eye protection from glare should be recommended. Since color vision is important to the airman, dark tints (i.e., <8% transmittance) and tints that distort color vision (e.g., blue-blocking lenses) should be avoided.
- Polarizing spectacles reveal striations in plastic or tempered glass windscreens that can produce visual fatigue and distortion.
- A thick spectacle frame temple may break the seal of an oxygen mask and interfere with communication headsets. A thick eyewire frame may affect the peripheral field of vision.
- Seating positions (reclining, head forward, or normal) has a major influence on bifocal segment heights. It is recommended that the bifocal segment be set at a height that will enable the pilot to see the instrument panel in front without interfering with distant viewing. To determine correct segment position, the pilot should mark the height on the lens with a grease pencil while seated in the cockpit. Presbyopic pilots who fly multiple aircraft may require different sets of spectacles for each aircraft.
- Smaller segment bifocals (e.g., ST-25) allow for distant peripheral vision around the bifocal segment. However, for more sophisticated aircraft with wide instrument arrays, a wider reading area (e.g., Executive bifocal) may be preferred. (See Figure 1.)
- For presbyopic pilots who view instruments above the line of sight, an occupational or task-specific lens may be recommended, such as the Varilux "Overview" or a double "D" segment lens. The double "D" segment with a standard separation (13 mm) between the segments may reduce the visual field of an aviator. However, special lenses with a wider separation (20 mm) may provide a practical solution. (See Figure 2.)
- Trifocal users may find the normal intermediate segment width (7 mm) too narrow for viewing the complete instrument panel without moving their head. A lens with a modified intermediate segment (14 mm) may resolve the problem (e.g., X-Cel's CRT lens). (See Figure 2.)
- Many pilots advance their seats forward on takeoff and landing to improve their external visibility. In flight, aviators often move their seats back to provide more comfort to their legs and back. Therefore, pilots may be 30+ inches from the instrument panel and 20-36 inches from navigational charts. Lenses for near and intermediate distances should be considered when prescribing for pilots.
- Changes in lens types (single vision to bifocal, bifocal to trifocal or progressive addition) can affect peripheral vision and depth perception. The airman should be advised that new lenses can distort vision and alter visual cues (visual scene appears to slant, objects appear larger or smaller than actual size) while performing flight maneuvers.
- Red light in the cockpit should be avoided since it reduces accommodative ability and contributes to making aviation maps and charts unreadable.
Aviation Medical Examiners (AMEs) can contribute to aviation safety by ensuring that pilots are wearing ophthalmic devices that best serve their particular needs. Knowledge of the unique occupational, recreational, and environmental requirements of the civil airman can assist the AME in suggesting alternate vision corrective devices that are better suited for a particular aviation activity.
Dr. Nakagawara, Ms .Wood, and Mr. Montgomery are members of the Aeromedical Research Division's Vision Research Team at the FAA's Civil Aeromedical Institute.