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Considerations in Contact Lens Use Under Adverse Conditions: Proceedings of a Symposium An Overview of U.S. Army Aviation and Contact Lens Issues Morris R. Lattimore, Jr. While U.S. Army aircraft can be either fixed- or rotary-wing, this discussion will address the rotary-wing or helicopter segment of the Army aviation community. The Army's arsenal of helicopters encompasses a number of types of aircraft, each designed for a specific mission. These include cargo, observation, utility, and attack helicopters. As an institution, Army aviation has been seriously interested in contact lens wear by its ametropic pilots since the early 1970s, when it was shown that dust and debris did not cause a significant problem for soft contact lens wearers in an aviation environment (Crosley et al., 1974). However, with the soft lenses commercially available then, an unacceptable variation in visual acuity was documented. At present, Army Regulation (AR) 40-63 prohibits contact lens wear by all aircraft crew members; the only waivers to that restriction have been associated with investigative protocols. The advent of new lens materials spurred further interest within the aviation community, leading to the development of a preliminary investigation of extended contact lens wear by a small group of volunteer aviators (Bachman, 1988). The results are in the process of being published, so only a brief summary will be supplied here. PRELIMINARY STUDY In order to develop relative safety patterns in established rotary-wing systems, an initial feasibility study of contact lens wear involved volunteer ametropic aviators qualified in the UH-lH Iroquois utility helicopter and/or AH-1 Cobra attack helicopter. Forty-four volunteer subjects were fitted with six different brands of extended-wear contact lenses, including both hydrophilic and rigid gas-permeable lenses. The mean uncorrected visual acuity was 20/46, with individual acuities ranging from 20/15 to 20/200.
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Considerations in Contact Lens Use Under Adverse Conditions: Proceedings of a Symposium The extended-wear lenses were worn on a 7-day/6-night schedule. That is, after the initial fitting, the lenses were worn continuously for 7 days and 6 nights. The lenses then were removed prior to retiring on the seventh night, and were reapplied the following morning after using an appropriate disinfection and lens care regimen. Postfitting follow-up examinations were provided on day 1, day 8, and every 30 days thereafter. The study ran for 6 months with an 86 percent success rate. Six subjects withdrew from the study because of acuity problems (2) or discomfort (4). Prior to the initial contact lens fitting, the mean flying time for the subject population was 2,136 hours. Over the 6-month period of the study the mean flying time for successful contact-lens-wearing subjects was 294 hours. During the course of the study, there were no groundings for contact-lens-related reasons, and there were no aircraft incidents or accidents related to the wearing of contact lenses. Subjective performance assessments rated the contact lenses used as being superior to spectacle wear by a vast majority of the subjects for preflight (68 percent), takeoffs (83 percent), routine flight (83 percent), nap-of-the-earth flight (89 percent), night vision goggles flight (88 percent), instrument flight (88 percent), and mission-oriented protective posture IV conditions (100 percent). Temporary discontinuances of contact lens wear were incurred by six pilots a total of nine times. Causes of discontinuance were conjunctivitis (8), abrasion (2), foreign body (2), facial trauma (1), and meibomitis (1). Again, none of the contact lens wear discontinuances led to grounding; the affected aviators merely wore their spectacles in lieu of the contact lenses. In summary, this initial feasibility study demonstrated the safe use, both in medical and flight terms, of extended-wear contact lenses by AH-l and UH-l pilots. DRIVING FORCE Immediate interest is being directed at the AH-64 Apache attack helicopter (Figure 1). The Apache's integrated helmet and display sighting system (IHADSS) uses a virtual imaging system to provide visual input to the pilot and copilot from a closed-circuit video system. The image can be in a daytime TV mode or in an infrared-sensitive mode for night flying, with a zoom capability of up to nine times. Aviator input on the helmet display unit (HDU) is always to the right eye only. Superimposed along the periphery of the HDU are essential flight instrument readings, so the pilot can obtain enough basic information to fly the aircraft strictly from IHADSS input. The left eye remains free and unobstructed for direct viewing of the instrument panel or for visualization of the flight environment through the windscreen. Correct placement of the imaging system on the helmet is critical to efficient use. Standard flight frame spectacle wear had caused
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Considerations in Contact Lens Use Under Adverse Conditions: Proceedings of a Symposium FIGURE 1 AH-64 Apache attack helicopter. NOTE: The AH-64 Apache attack helicopter represents the utmost in modern air weaponry. The two-man airframe system is designed to fly in literally any weather conditions. FIGURE 2 U.S. Army helmet display unit. NOTE: The HDU is positioned over the right eye; spectacle-wearing aviators have had some difficulty in obtaining proper positioning for optimal utilization.
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Considerations in Contact Lens Use Under Adverse Conditions: Proceedings of a Symposium FIGURE 3 U.S. Army M-48 protective mask. NOTE: The M-48 protective mask was designed specifically for the Apache system, since the preexisting M-24 protective mask was totally incompatible with HDU positioning. Some difficulty in obtaining correct placement of the system. As a result, a smaller right eyepiece was developed to minimize these difficulties, but it did not solve them (Figure 2). Compounding the IHADSS placement dilemma has been the development of the M-43 protective mask (Figure 3), designed to protect the aviator from chemical contaminants that could be encountered in the modern battlefield. However, no accommodation was made for spectacle-wearing aviators. A proposed amendment to the protective mask consists of glue-on optics bonded
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Considerations in Contact Lens Use Under Adverse Conditions: Proceedings of a Symposium FIGURE 4 U.S. Army M-43 protective mask. NOTE: The M-43 protective mask does not offer an easy means of correcting refractive error; two possible options are glue-on optics and contact lens wear. Each option has its own set of advantages and disadvantages.
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Considerations in Contact Lens Use Under Adverse Conditions: Proceedings of a Symposium onto the external surface of the eye bubble. Visual complications induced by such a revision include image magnification and distortion. In addition, the peripheral HDU symbology is obscured because of a decreased field of view that stems from the increased physical distance imposed on imager placement ( Figure 4). Consequently, ametropic aviators may be unable to fly the AH-64 under chemically contaminated conditions. Contact lens wear constitutes an alternative to the M-43 glue-on optics and represents an attractive short-term solution to the aviation community. However, before even advocating contact lens wear as a viable option, the Army's medical community wishes to ensure that all potential hazards and costs are fully documented so that an informed decision can be reached. REFERENCES Bachman, W.G. 1988 Extended-Wear Soft and Rigid Contact Lenses: Operational Evaluation Among Army Aviators. Contact Lenses in the Aviation Environment. USAARL Technical Report No. 88-17, Fort Rucker, Alabama. Crosley, J.K., E.G. Braun, and R.W. Bailey 1974 Soft (hydrophilic) contact lenses in U.S. Army aviation; an investigative study of the Bausch & Lomb “Soflens.” American Journal of Optometry and Physiological Optics 5:470–477.
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