Volume 2, Number 1 January 2003
TNT FYI:
Effects of LASIK in Aircraft Maintenance
This text is excerpted from an article by occupational health physician James W. Allen, MD, MPH. He explains adjustments to be made when presbyopia (age related changes to the eye) must be considered in combination with LASIK corrections for myopia. Dr. Allen wore glasses to correct myopia for more than 35 years. For three months following his own laser in situ keratomileusis (LASIK) surgery, he kept detailed records of his recovery and the impact of changes to his vision as they related to his participation in owner assisted aircraft maintenance.
Physicians often give patients work restrictions after medical procedures to ensure successful recovery. Similarly, aviation maintenance technicians (AMT) who undergo LASIK should consider placing limitations on themselves to ensure the consistency and safety of their work.
To see clearly, the visual image must focus on the rod and cone cells in the retina, a layer of cells at the back of the eyeball. Structures that refract light are the cornea, or outer layer of the eyeball, and the lens, whose amount of accommodation is controlled by tiny ciliary eye muscles. When both the cornea and lens give the correct refraction, the visual image focuses clearly on the retina.
Myopic (nearsighted) individuals see only near objects and typically need visual correction with a negative diopter (for example, Ð4.25) for distant vision. With this added visual correction plus the existing refraction of their lens, the distant image is in sharp focus at the retina.
Aging reduces the ability of ciliary muscles to change the accommodative power of the lens causing loss of clear vision (presbyopia). Small objects must be held further and further from the eyes to be clearly visualized. By the fifth decade of life, many people need +1.5 to +2.5 diopters of visual correction.
LASIK adds refractive power by reshaping the cornea but doesn't correct presbyopia. In laymen's terms, LASIK grinds the cornea into the same prescription as the myopic individual's glasses. The result is that myopes no longer need visual correction because surgically reshaping the cornea allows images to focus clearly on the retina. The important issue is that LASIK helps only nearsighted individuals. For years, a myopic individual has worn glasses for vision and learned that close objects can be seen without glasses. After LASIK, the reverse will be true. Far objects are now in focus but reading glasses may be necessary to correct presbyopia. No matter when corrective surgery is complete, the age-related effects of presbyopia will eventually require some visual correction to focus on small objects or read newsprint.
My first recommendation is that all employees in safety-sensitive positions who undergo corrective eye surgery report this surgery to their supervisor on the first day back to work. During the postoperative period, the individual is adjusting to new visual effects. My experience indicates that a risk exists to overlooking near-field objects that would have been obvious prior to the surgery. While this policy may apply to only those working in designated safety-sensitive positions, I recommend all AMTs who maintain aircraft to report their surgery to their supervisor.
For the first few days following surgery, supervisors should require the wearing of safety glasses. My surgeon required wearing goggles for two nights after surgery. His reasoning was that inadvertent eye rubbing would displace the cornea flap. In the hangar, the purpose of safety glasses is to prevent inadvertent eye injury.
Depth perception originates from two mechanisms. A different angle of viewing from our two eyes produces depth perception for near vision. The relative difference in sizes produces depth perception for distant vision. My experience with depth perception was variable. I found I could successfully parallel park the car two days after surgery. On the other hand, for two months I consistently missed the hook when I hung my clothes in a closet. My recommendation is to place a two-month restriction on the post-LASIK AMT from taxiing aircraft. This two-month recovery time will permit reacquisition of depth perception and limit scratched or dented wingtips. The cautious post-LASIK AMT will also ask for spotters when maneuvering aircraft with a tow bar.
After LASIK, I noted the importance of proper lighting to visualize objects. Cone cells located in the center of the retina are responsible for color vision and visualizing detail. Rod cells located in the periphery of the retina are responsible for night vision, dark adaptation, and brightness perception. LASIK reshapes the cornea on the surface of the eyeball without touching the retina deep inside the eyeball. Based on this anatomy, I can't explain my sudden recognition for the importance of good lighting. In spite of my lack of a good explanation, I strongly encourage post-LASIK AMTs to use a good light source to visualize a job.
Loss of accommodation is age-related and occurs with very little individual variability. Beyond the age of 35, the post-LASIK AMT should have and use reading glasses. Completing a job requiring fine detail without use of glasses should raise the supervisor's suspicion about the integrity of the job.
Use of the buddy system is a strategy to insure that the post-LASIK AMT doesn't inadvertently miss a screw or other fine detail. Most aircraft repair work requires the use of near vision so any failure to correct the effects of presbyopia will make small items appear invisible. A buddy, with good near vision, can quickly survey a job and provide the added reassurance that nothing was missed.
The length of time to enforce work restrictions depends on how quickly an individual adapts to its effects. Prior to LASIK, the myopic individual used glasses for distant vision but could read objects if brought close enough. After LASIK, reading glasses may be necessary to correct presbyopia but distant objects are best seen without glasses. The AMT must learn these new skills. After two to three months, I had well adapted to my new vision. The restriction could be dropped at that time. n
Adapted from "MedicalCorner: LASIK and the Aircraft Technician" Aviation Maintenance, August 2002 <www.aviationmx.com>
[ The NDT Technician ]
Copyright © 2008 by the American Society for Nondestructive Testing, Inc. ASNT is not responsible for the authenticity or accuracy of information herein. Published opinions and statements do not necessarily reflect the opinion of ASNT. Products or services that are advertised or mentioned do not carry the endorsement or recommendation of ASNT.
IRRSP, NDT Handbook, The NDT Technician and www.asnt.org are trademarks of the American Society for Nondestructive Testing, Inc. ACCP, ASNT, Level III Study Guide, Materials Evaluation, Nondestructive Testing Handbook, Research in Nondestructive Evaluation and RNDE are registered trademarks of the American Society for Nondestructive Testing, Inc.
ASNT exists to create a safer world by promoting the profession and technologies of nondestructive testing.
