A comparison of stereopsis with ANVIS and F4949 night vision goggles.

BACKGROUND: This study was undertaken to see if the model of NVG affects stereoacuity. METHODS: We tested 13 male and 2 female aircrew with the Aviator's Night Vision Imaging System (ANVIS) and F4949 NVGs. Visual acuity was measured using the NVG Resolution Grid and stereopsis was determined using a modified Howard-Dolman test. RESULTS: In simulated light conditions, average stereoscopic threshold using the F4949 NVG (17.35 arc s) was not significantly better than the ANVIS NVG (18.42 arc s), the mean difference being 1.07 arc s (95% confidence limits, -2.85 to 4.99). CONCLUSIONS: The Howard-Dolman test proved to be effective in eliminating monocular clues, thus validating its use in testing NVG stereopsis. The distribution of visual acuities across subjects and goggle models was too narrow to evaluate the effect of visual acuity on stereoacuity in NVGs. Differences in trial means during the course of the study indicated the presence of a "learning" effect on the Howard-Dolman test.

Corneal response and vision with the Softperm lens in simulated aircraft conditions.

BACKGROUND: Contact lenses are generally more compatible than spectacles with the life-support systems, personal protective devices, and helmet-mounted targeting systems used in modern military aircraft. This study evaluated the Softperm contact lens in a simulated aircraft environment to determine its potential use by USAF aviators. METHODS: Thirteen subjects wearing Softperm lenses were exposed to a simulated aircraft environment for 2 hours. Subjects were evaluated for signs of hypoxic stress by measuring corneal thickness changes and observing changes in corneal staining and conjunctival injection. Changes in visual acuity were also measured. Slit lamp biomicroscopy was used to assess lens movement at the beginning and end of the treatment period to determine if lens fit changed. Over-refractions to determine residual astigmatism were performed to evaluate how well the Softperm lens corrected astigmatic refractive errors. RESULTS: A statistically significant increase in corneal thickness was found after two hours of Softperm wear in the simulated aircraft environment. Several subjects experienced an increase in epithelial staining, which appears to be associated with changes in lens fit (tightening). All subjects experienced conjunctival injection. Residual astigmatism secondary to lens flexure occurred in all but two eyes, but no eyes had greater than 0.75 diopters. CONCLUSIONS: When properly fitted, the Softperm lens can be safely worn in an aircraft environment similar to the one simulated in this study. This lens design may provide an alternative to the lenses presently approved for USAF aviators.

Aircrew soft contact lens wear: a survey of USAF eyecare professionals.

The USAF, when it approved soft contact lens (SCL) wear for aircrew in June 1989, chose a conservative approach that authorizes only daily-wear of extended-wear SCL's. The aircrew SCL program has been perceived as a success, and follow-up data are no longer being collected. A survey was sent to all USAF eyecare professionals to assess the types and extent of SCL-related ocular pathology, the magnitude of environmental SCL problems in the cockpit, and the brands of SCL's that are being fitted. Only two instances of ulcerative keratitis were reported. The most severe inflight problem reported was the dry cockpit environment. CSI-T (Pilkington Barnes-Hind) was the most frequently used spherical lens and the Hydrasoft Toric XW (CoastVision) was the most used toric lens. The USAF aircrew SCL program appears to be progressing successfully. However, the Ophthalmology Branch at Armstrong Laboratory will continue to monitor the program for serious medical complications.