Night Vision Goggles In Focus: Revised Procedures Improve Visual Acuity By 25%

Dr. Jean Dyer

"I cant see anything with these!" is a common reaction when a soldier with no training or experience wears night vision goggles (NVGs) for the first time. But with training on proper adjustment procedures, every soldier can learn to eliminate that initial, blurry image. And with additional field experience, soldiers find that the goggles are an invaluable asset during night operations. To provide the ground soldier useable and definitive guidance on adjusting NVGs, we examined the effectiveness of using different field-expedient objects and of instructions on the proper adjustment procedures. These adjustment procedures were adapted from the latest aviation guidelines, which are more complete than those currently available to ground forces. Soldiers need to see the best they can to maximize performance and to operate safely at night. NVGs definitely provide soldiers better vision, but it is not the sharp, 20/20 acuity experienced during daylight. Under optimum illumination conditions, NVGs can provide 20/35 or 20/40 acuity. When the light at night is poor, NVG acuity is decreased. And regardless of the degree of ambient illumination, soldiers will not obtain the best NVG acuity without proper training in NVG adjustment.

Recently, the aviation community took efforts to ensure that pilots adjust their goggles for maximum visual acuity before flight. Their procedures require that NVG controls be adjusted in a specific sequence. These procedures also use NVG test sets or special indoor visual charts when adjusting the diopter setting. But neither of these assessment techniques is feasible for field use by ground soldiers. First, test sets weigh too much. Also, visual acuity charts require a controlled light source. Therefore, there was a need to develop comparable effective procedures for field use.

Field-Expedient Objects and Test Equipment

Instead of using the heavy, expensive test sets, our experimental procedures used objects and equipment readily available to soldiers. After soldiers adjusted their NVGs, we assessed their acuity with a special night vision goggle test set developed by Hoffman Engineering Corporation. The numbers in the center of the squares are the second part of the standard Snellen resolution fraction, for example, the 25 pattern represents Snellen 20/25. The soldier indicated the square with the smallest number where both the vertical and horizontal bars were discernible. This reading was then the visual acuity of the system with the given adjustments.

Recommended Procedures

The recommended procedures which emerged from our experiments are summarized in Figure 3 (see next page). Training and practice on these procedures improved visual acuity by at least 25%. In addition, the variability in acuity readings was reduced by two-thirds. And, there were no soldiers with blurry NVG images (20/70 visual acuity or worse).

The best readings were obtained with the tree trunk, vehicle, vehicle trail, IR and blue chem lights, and stars. Of these six objects, soldiers found that they could most easily and quickly determine when they had a sharp NVG image when viewing a tree trunk or a vehicle. The tree trunk, vehicle, stars, and vehicle trail were rated as the more usable in field environments. The chem lights were rated as less sound tactically because of potential light discipline problems.

Soldiers reacted negatively to red light sources, because of the large bloom produced in the goggles which was extremely hard to reduce. Other intense light sources (e.g., the Phoenix) created similar problems.

Nearly all soldiers (80%) indicated they could see better after using the procedures. They also reported learning something new about either the diopter adjustments or the eye span adjustments. As soldiers gained expertise in making the adjustments, they performed them very quickly.

In summary, good NVG acuity readings can be achieved with field-expedient objects when the soldier selects a high-contrast object or a non-intense light source. Training on proper adjustment procedures consistently eliminates extremely poor visual acuity settings and significantly improves the settings of soldiers with limited NVG experience. Consequently, performance and safety will be improved for every soldier, from vehicle driver to point man to rifleman.