Aircrew visors and color vision performance: a comparative and preliminary pilot study analysis.

BACKGROUND: A very important aspect of visual performance to consider, for present and future recommendations regarding aircrew visors, concerns their impact on color vision. The literature has remained mostly inconclusive with respect to the human perceptual process of colors during actual mission employment. OBJECTIVE: This study uses active duty military aircrews to provide objective and valuable information on the effects of Short Wavelength Absorbing Filters (SWAFs), such as the High Contrast Visor (HCV), and some selected waveband type Laser Eye Protection (LEP) visors on color vision. It provides a direct comparison of several current and proposed aircrew eye protective visors with respect to their effects on color vision. The data analyzed in this study will also be used to support a recommendation regarding a new optimal visor for aircrew wear during air to air (and ground) engagements, for sun protection, and possible visual enhancement in order to improve user compliance. METHODS: Seven volunteers on active flying status each underwent comprehensive color vision testing with and without seven of the U. S. Air Force's (USAF's) current or proposed aircrew visors/filters. Spectral transmissions of these visors/filters were obtained to identify and determine their individual characteristics which included their ability to induce acquired color vision decrements in "color normal" individuals. RESULTS: The widely utilized USAF HCV significantly degraded color vision more than luminosity matched neutral density visors. Abrupt color vision decrements for specifically fielded LEP visors were also noted. Their objective data supported theoretical and speculated color vision effects. Even though low transmittance neutral density visors did have some effect on color vision, decrement severity was not considered significant enough to affect overall performance during color vision testing. CONCLUSIONS AND DISCUSSION: Because of their ability to significantly affect color vision, concerns regarding the use of HCV and LEP visors should entail age, baseline color vision, environmental, and mission factors. Further testing should be done to evaluate the definitive effects that these visors actually have on the recognition of color symbology of Multi Function and Electronic Flight Information Displays. Findings in this study also support theoretical opinions that encourage the fielding of a neutral density filter (mildly tinted) with an overall transmission of 25-49%. Its use by flyers during low and bright illuminant conditions may greatly enhance visual performance by encouraging wearer compliance while allowing colors to be perceived normally.

The effect of positive pressure breathing for altitude protection on intraocular pressure.

BACKGROUND: The effect of positive pressure breathing for altitude protection (PBA) on intraocular pressure was studied; the behavior of intraocular pressure both during and after PBA exposure was of particular interest. METHODS: Seven subjects were exposed to PBA of up to 60 mmHg at ground-level. The subjects were seated, and wore an aircrew helmet (HGU-55/P), oro-facial mask (M8U-20/P), thoracic counterpressure garment (CSU-17/P) and an extended coverage G-suit (ATAGS). Before, during and after each exposure, intraocular pressure was measured using a Tono-Pen XL applanation tonometer. RESULTS: All 7 subjects completed 10 min of PBA at breathing pressures of 30 and 40 mmHg, and 6 subjects completed 10 min at 50 and 60 mmHg. Mean and SEM increases in intraocular pressure, as compared to pre-exposure baseline measurements, were 7.7 +/- 0.6 mmHg at a breathing pressure of 30 mmHg, 12.0 +/- 0.9 mmHg at 40 mmHg, 18.4 +/- 1.3 mmHg at 50 mmHg and 20.0 +/- 0.6 mmHg at 60 mmHg. The difference between each of these increases was significant (p < 0.05), with the exception of that between 50 and 60 mmHg PBA. CONCLUSIONS: Intraocular pressure increases as breathing pressure increases. It is likely that this change in intraocular pressure would provide some protection to the retinal vasculature during PBA. In addition, it is unlikely that the temporary elevation of intraocular pressure following pressure breathing is of medical concern.

Photorefractive keratectomy (PRK) in the military aviator: an aeromedical perspective.

Refractive surgery to visually rehabilitate refractive errors of the eye continues to evolve at a significant pace and is here to stay. The surgical manipulation of the cornea by carefully planned incisions, as in radial keratotomy, represented the first procedure to evolve for the correction of ametropia and is an area of continued active development and improvement. However, many concerns mitigate against this procedure in the aeromedical arena. More recently, photorefractive keratectomy using laser technology to ablate and recontour the corneal surface has emerged as a viable modality. This paper explores the aeromedical factors surrounding this new revolutionary procedure and discusses the issues relevant to evaluating its applicability to the modern military aviator as well as reviewing results of the latest clinical trials currently in progress. The goal is to provide the aeromedical community with the fundamental information required to formulate aeromedical decisions and policy-making in regard to a new procedure that is certain to have tremendous impact on the selection of future aircrew candidates.