The AN/AVS-9 night vision goggle (NVG) has an eyepiece lens that can be adjusted from +2 to -6 diopters (D). We have shown previously<sup>1,2,3</sup> that on average NVG users tend to select about -1D, with a range of +0.5D to -4D3. This study was designed to evaluate NVG visual acuity (NVG VA) and subjective ratings for a range of diopter settings including user-selected and three fixed settings of -0.25D, -1D and -2D. Twenty-one experienced USAF Special Operations aircrew members, including 15 pilots, served as subjects. The median user-selected setting was -1.25D and ranged from +0.5D to -3.5D. Only 2 of the 21 subjects had user-selected NVG VA significantly better than a fixed setting of -1D. Of those two, one was not wearing prescribed glasses and the other was 49 years old, presbyopic, and could not focus through the -1D lenses. Subjective ratings and NVG VA indicated that most people could fly with a fixed setting of -1D for each eye, although two individuals needed different diopter settings for the right and left eyes. The new Panoramic NVG (PNVG) has a fixed eyepiece focus of -1D. Results suggest the PNVG should have a limited set of accessory lenses available.
Integrated Panoramic Night Vision Goggles (IPNVGs) are the prototype night vision goggles (NVGs) and may be the next generation of NVGs. The AN/AVS-9 (F-4949) NVGs, worn by Air Force aircrews, have continuously adjustable eyepieces (from +2.0 diopters (D) to -6.0 D). Unlike the F-4949s, IPNVGs have a fixed-focus eyepiece at
-1.0 D. However, previous research has shown that some operators are very insistent that their visual acuity is impaired if they do not have eyepiece settings on the order -2.0 D or more, where they are currently setting their NVGs. The proposed solution is to provide “snap-on” lenses to the IPNVGs in order to obtain a selection of settings. The purpose of this study is to determine if NVGs with this discrete number (two) of “snap-on” lenses are acceptable or if additional lenses are required.
The wide field of view night vision goggles (WNVG) are the next generation of night vision goggles (NVGs). They have a significantly increased horizontal field of view and a weight similar to the current AN/AVS-9, which only has a 40 degree circular field-of-view (FOV). Due to complicated optics and weight issues, the WNVG will have a fixed-focus eyepiece; this is different from the AN/AVS-9 (Figure 1), which has a continuously adjustable +2.0 to -6.0 diopter (D) range for each eyepiece. Site visits were made to several Special Operations Squadrons to survey aircrew members about the WNVG with a fixed-focus eyepiece and optional clip-on lenses. This paper addresses aircrew acceptance of the use of snap-on/helper lenses in place of continuously adjustable eyepieces.
Technology is advancing to the point where night vision goggle designs being developed have wider fields of view to help achieve an increase in situational awareness. The appropriate diopter setting for the eyepiece of these goggles needed to be determined. Aircrew members were surveyed to determine the range of diopter settings they were using. In order to determine what fixed setting would work the best, two diopter settings were chosen (-1.0 and -0.5) to preset aircrew members' goggles. The aircrew flew with these presettings and then filled out a 14-question survey about the diopter settings.