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PubMed1996

Effects of overlay symbology in night vision goggles on accommodation and attention shift.

BACKGROUND: Binocular night vision goggles that have a monocular symbology overlay provide potential conflicts between perceived symbology distance and optical vergence cues for accommodation. HYPOTHESIS: Accommodative response was measured in subjects who perceived symbology nearer than the background to determine if accommodation could respond to the optical stimulus and override the perceptual cues. METHODS: Symbology was presented to the right eye under two conditions (clear and blurred to 20/50 resolution) and the background was presented binocularly with and without added speckle noise that is typical of the NVG at low light levels. RESULTS: On average, subjects accommodated by less than 0.1 diopters (D) to all 4 of the stimulus combinations even though the perceived proximal depth difference between background and symbology was 10 times greater. No perceptible blur resulted from this small change in accommodation because it is well below the depth of focus of the human eye. A control experiment illustrated that an accommodative response, at least as small as 0.25 D, could easily be stimulated optically and detected by the experimental apparatus. In a final experiment, the duration required to shift attention away from the background to a peripheral symbol, acquire critical information, and return attention to the background was 0.69 s which included saccade latency and scan time of the symbol. CONCLUSIONS: These results indicate that small changes in accommodation that occur when pilots shift attention from background to symbology do not produce perceived blur of the symbology or the background and thereby do not impair performance.

Accommodation, Ocular↗
PubMed2002

Computer modeling of airbag-induced ocular injury in pilots wearing night vision goggles.

BACKGROUND: Airbags have saved lives in automobile crashes for many years and are now planned for use in helicopters. The purpose of this study was to investigate the potential for ocular injuries to helicopter pilots wearing night vision goggles when the airbag is deployed. METHODS: A nonlinear finite element model of the human eye was created. Ocular structures such as the fatty tissue, extraocular muscles, and bony orbit were included. The model was imported into Madymo (Mathematical Dynamical Models) and used to determine the worst-case position of a helicopter pilot wearing night vision goggles. This was evaluated as the greatest Von Mises stress in the eye when the airbag was deployed. RESULTS: The worst-case position was achieved by minimizing the distance between the eyes and goggles, having the occupant look directly into the airbag, and making initial contact with the airbag halfway through its full deployment. Simulations with the goggles both remaining fastened to and breaking away from the aviator helmet were performed. Finally, placing a protective lens in front of the eyes was found to reduce the stress to the eye but increase the force experienced by the surrounding orbital bones. CONCLUSION: The finite element model of the eye proved effective for evaluating the experimental parameters.

Accidents, Aviation↗
PubMed1993

Spatial contrast sensitivity through aviator's night vision imaging system.

Visual acuity is often used to assess vision through image intensifying devices such as night vision goggles (NVG's). Fewer attempts have been made to measure contrast sensitivity through NVG's. Such information would be useful to better understand contrast processing through NVG's under various stimulus conditions. In this study, computer-generated letter charts were used to measure contrast sensitivity through third generation NVG's for a range of letter sizes. The red phosphor of a standard color monitor proved to be an effective stimulus for third generation devices. Different night sky conditions were simulated over a 3 log unit range. The results illustrate the profile of contrast sensitivity through third generation NVG's over a range of night sky conditions. Comparison of measurements through NVG's to measurements obtained without the device but at the same luminance and color distinguish between effects of luminance and noise on contrast sensitivity.

Adult↗
PubMed1986

[An electronic visual aid using a luminance amplifier in night vision disorders].

The efficiency of a light amplifier system for the improvement of night vision has been tested on 30 normal subjects and on subjects suffering from night blindness including 36 patients with pigmentary retinopathy, 18 myopic patients with night blindness and 12 patients with senile cataracts. In all cases, the scotopic vision presented a great improvement and it reached up to half of photopic vision. The use of the light amplifier would certainly provide a considerable improvement for subjects suffering from night blindness and mostly for those suffering from pigmentary retinopathy. But two conditions are necessary for this: miniaturization of the device and absence of major macular lesions in the patient.

Cataract↗
PubMed2001

Orotrachial intubation in darkness using night vision goggles.

OBJECTIVE: Securing the airway of a wounded soldier while operating in a light-restricted combat environment may be required of forward-deployed military medical personnel. The best method of obtaining such an airway has not been addressed. In this pilot study, the objective was to examine the use of endotracheal intubation using an infrared filtered laryngoscope and night vision goggles. METHODS: The investigators performed endotracheal intubation, using an infrared filter light source laryngoscope, on patients undergoing elective surgical procedures. All intubations took place in a completely darkened operating room. RESULTS: Twenty-one patients (91.3%) were intubated successfully as defined in the study. No adverse outcomes or complications occurred. CONCLUSIONS: This study demonstrates that endotracheal intubation can be performed using a laryngoscope with an infrared filter and night vision goggles with a high success rate in a select population in a darkened environment.

Adolescent↗
PubMed2004

Evaluation of a prototype Minified Augmented-View device for patients with impaired night vision.

An evaluation was carried out of the first prototype (LV-3) of a new night vision device, which incorporates visual field expansion through minification (Minified Augmented-View), to provide feedback for continuing development. Six subjects with night blindness completed visual function measurements and indoor mobility assessments without a device, with the LV-3 and with a commercially available comparison device (the Multi-Vision) at light levels representative of well lit and poorly lit streets. Device performance and potential benefits in real-world situations were evaluated at four outdoor locations (well lit to very dark). Results indicate that the see-through nature and spectacle-frame mounting of the LV-3 address some of the cosmetic and ergonomic disadvantages of currently available devices; however insufficient light sensitivity of the prototype camera limited LV-3 performance. With improved camera sensitivity and full implementation of the Minified-Contours Augmented-View concept in the next prototype, patients might be able to make better use of the novel field expansion and vision multiplexing features to aid outdoor night mobility.

Adult↗
PubMed2006

Predicting patients' night vision complaints with wavefront technology.

PURPOSE: To evaluate the accuracy of the diagnostic capabilities of optical metrics generated from wavefront measurements in relationship to post-laser-assisted in situ keratomileusis (LASIK) visual complaints as expressed and drawn by patients. DESIGN: Retrospective analysis and observational case series. METHODS: Patient wavefront data from an investigational device exemption study for wavefront-guided ablations were used to derive normative modulation transfer function (MTF), encircled energy (EE), and Strehl ratio. These optical metrics and their point-spread functions (PSF) were compared with data from five postoperative patients with night vision complaints. Patients were asked to draw their symptoms, which were elicited by testing with a Fenthoff muscle light, while using their best-corrected distance vision. RESULTS: The MTF, EE, and Strehl ratio of most patients were markedly different from those of the averages of 208 normal myopic eyes before and after LASIK surgery. The spatial extent of the PSF correlated positively with the severity of the visual complaints. Wavefront-derived PSFs were markedly similar to the patients' drawings. CONCLUSIONS: The results of this study demonstrate the diagnostic capability of the wavefront system in predicting visual symptoms and complaints of patients with high-order aberrations. Objective visual metrics from patients with night vision complaints were different from those of normal myopic eyes that had undergone LASIK procedures.

Adult↗
PubMed2006

Effect of night vision goggles on performance of advanced life support skills by emergency personnel.

Night vision goggles (NVGs) are used by military personnel operating in low-light environments. It is not known whether NVGs can be used by medical personnel to provide emergency care under such conditions. This was a randomized controlled study to determine the effect of NVGs on the performance of intravenous line insertion (IVI) and endotracheal intubation (El) on training manikins. Emergency physicians and paramedics were randomized to perform EI and IVI in ambient light or in total darkness using NVGs. Each skill was repeated three times, and averages were determined. The average times for EI in ambient light and with NVGs were 48.4 and 188.2 seconds, respectively (SE of 13.4 seconds for both; p < 0.0001). The average times for IVI in ambient light and with NVGs were 34.7 and 73.7 seconds, respectively (SE of 4.1 seconds for both; p < 0.0001). Emergency personnel were able to successfully perform these skills using NVGs, but their times were significantly longer than in ambient light.

Advanced Cardiac Life Support↗
PubMed1989

Compatibility of the aviation night vision imaging systems and the aging aviator.

With the advent of the night vision goggle (NVG) mission requirements in the United States Army, the reserve components began training with the second generation (AN/PVS-5 & AN/PVS-5A) systems. These systems prohibit the wear of spectacles by the aviator. Certain modifications on some systems allowed for spectacle wear. However, there still exists a 5-h day filter training minimum in which the full NVG with facemask and cushion must be worn without spectacles. The NVG system corrects up to +2.00 diopters of hyperopia and up to -6.00 diopters of myopia, but only +/- 1.00 diopter of astigmatism. A survey of the reserve component (USAR and NG) aviators in the Southwest was conducted to establish the relative incompatibility of the NVG system among an aviator population older than the active component aviators. All medical record custodians received questionnaires and the flight surgeon followed up replies by telephone or on-site visits. We screened a total of 127 aviator records. The aviator's average age was 39.5 years; 65.3% had 20/20 vision and were emmetropes. Of those that wore spectacles, 82.4% had hyperopia or myopia correctable by the built-in optical adjustments contained in the NVG. The other 17.6%, who had vision that exceeded the correction factors built into the NVG, consisted of astigmats with greater than 2.00 diopters of cylinder. Nearly 20% of the aviators who wore corrective lenses exceeded the corrective limits of the goggles that they used. Further, pilots had no specific prescreening instruction. With the development of more sophisticated aviation optics. Three options exist: modify visual standards, allow contact lens wear, or design future systems to be compatible with spectacles.

Adult↗
PubMed2004

Risk factors for night vision complaints after LASIK for myopia.

PURPOSE: To study the preoperative risk factors for night vision complaints (NVCs) after LASIK in a clinical setting. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Seven hundred ninety-five patients (1488 eyes) who underwent LASIK for myopia up to -9.75 diopters (D) (from January 1 to December 31, 1999). SETTING: Private clinic. METHODS: A complete preoperative examination was performed. Patients had bilateral LASIK surgery using the Nidek EC-5000 non-wavefront guided slit-scanning excimer laser and the Moria LSK One microkeratome. Patients were observed postoperatively for 12 months. MAIN OUTCOME MEASURES: The reported NVCs for each eye were rated on a subjective scale based on functional visual comfort. Clinically important NVC odds ratios (ORs) were calculated. RESULTS: Reports of NVCs decreased considerably from 25.6% at 1 month to 4.7% at 12 months postoperatively, at which time all patients reported similar NVCs in both eyes. Stratification of risk factors at 12 months postoperatively showed a 2.8-times increase in NVCs for initial myopia of >5 D, a 2.5-times increase for an optical zone of </=6.0 mm, and a 2.9-times increase for a postoperative spherical equivalent outside +/-0.5 D of emmetropia. The role of attempted spherical correction, age of the patient, and postoperative spherical equivalent had significant importance in logistic regression of the OR throughout the first postoperative year. In a stepwise logistic regression using 6- and 12-month data, attempted spherical correction and optical zone were the most predictive factors of NVCs (P<0.001). Pupil size at any month postoperatively was not statistically predictive of postoperative NVCs in any differential model involving it. CONCLUSIONS: Attempted degree of spherical correction, age, optical zone, and postoperative spherical equivalent were major risk factors of NVCs throughout the first postoperative year, whereas pupil size was not. Future wavefront studies that characterize higher order aberrations might be helpful for understanding individual visual aberrations while predicting quality of vision.

Adolescent↗
PubMed1987

An automated portable night vision testing system.

This report describes a new testing system designed to assess night vision parameters of the military population in the field, and to quantify the effects of various environmental stress factors, such as extended exposure to high altitude, on the dark adaptation process. The instrument is based on an established procedure for dark adaptation measurement in which the subject continuously adjusts the threshold luminance of a recurrently flashing stimulus. The device described here represents a modernized version of the original technique, which features an automated testing procedure and provides for computerized data translation of the dark adaptation function. It also offers the advantages of rugged construction and field portability not available in clinical style instruments.

Computers↗
PubMed2003

Visual performance with night vision goggles after photorefractive keratectomy for myopia.

OBJECTIVE: To evaluate visual performance and resolution through night vision goggles (NVG) before and after photorefractive keratectomy (PRK). DESIGN: Nonrandomized, comparative (self-controlled) trial. PARTICIPANTS: Nineteen patients (38 eyes) of active-duty US Army Special Forces soldiers. INTERVENTION: PRK for myopia and astigmatism. MAIN OUTCOME MEASURES: Visual acuity with best optical correction was measured preoperatively and postoperatively (3 months) using acuity charts of various contrast (100%, 10%, 2.5%, 1.25%). Preoperative and postoperative (3 month) uncorrected and best-corrected visual resolutions through NVGs were assessed using a high contrast tribar chart presented at four light levels (3.44 x 10(-3), 1.08 x 10(-3), 1.04 x 10(-4), 1.09 x 10(-5) foot Lamberts) simulating a range of night sky conditions. Subjects were trained before testing. RESULTS: Uncorrected visual acuity at the 3-month postoperative assessment was greater than or equal to 20/20 in 33 of 38 (86.8%) eyes. No eyes lost 2 or more lines of best spectacle-corrected visual acuity. Preoperative and 3-month postoperative best-corrected low-contrast acuity measurements showed no significant differences at all levels of resolution. Preoperative visual resolution through NVGs decreased systematically with decreasing night sky condition. Visual acuities before PRK were reduced without optical correction. Postoperative visual performance with NVGs (without optical correction) equaled or exceeded performance preoperatively with best correction. CONCLUSIONS: This prospective case series provides data on the safety and efficacy of PRK with respect to visual performance under night sky conditions using NVGs. There was no significant loss of visual acuity across a range of contrast levels 3 months postoperatively. There was no change in best-corrected NVG visual resolution postoperatively, whereas uncorrected visual resolution was significantly enhanced compared with preoperative levels. This improvement may translate into better function for soldiers who are unable to or choose not to use optical correction in operational environments.

Adult↗
PubMed2001

Light adaptation: night vision goggle effect on cockpit instrument reading time.

BACKGROUND: Light adaptation to the intensified image provided by a night vision device may handicap pilots who have set cockpit instrument luminance too low. METHODS: Under conditions simulating night flying, subjects adapted to an NVG image at 3 or 10 footlamberts (fL), then used a joystick to indicate the position of the horizon in an ADI illuminated by NVIS-compatible light at luminances 2 to 3.5 log units lower than the NVG image. RESULTS: Response times increased no more than a few tenths of a second when the decrease in luminance was only 2 log units. Greater decreases produced correspondingly longer delays in response, reaching as much as 5.5 s for subjects in their twenties and 8-15 s for older subjects. CONCLUSIONS: While a decrease of more than 2 log units is not likely to occur under most operational conditions, it is certainly possible, and pilots should be aware that significant risk can be incurred by setting cockpit instruments to luminance levels below 0.03 fL.

Adaptation, Ocular↗
PubMed1980

A human performance/workload evaluation of the AN/PVS-5 bifocal night vision goggles.

Eight experienced U.S. Army aviators performed various maneuvers in an instrumented helicopter to test the relative usability of two bifocal-configured night vision goggles. Both configurations were statistically better than the unmodified arrangement when looking at a pilot's ability to fly a standard traffic pattern and to hold a precise altitude at night. The subjective data, supported by comparative flight performances with the two bifocals, further suggested that a 24% bifocal version was more desirable than a 14% configuration. The inference is that the reduced inside field of view presented by the 14% bifocal interferes with a pilot's ability to readily locate instruments once he has directed his attention inside the cockpit.

Aerospace Medicine↗
PubMed1998

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.

Adult↗
PubMed1999

Distance estimation with night vision goggles: a little feedback goes a long way.

Immediate feedback was given to correct observers' estimates of distance in an experiment in which those estimates were made outdoors at night while observers wore night vision goggles (NVGs). Initially observers made unguided estimates of distances between marked positions in an open field. Those distances ranged from 7.6 m (25 ft) to 64 m (210 ft). Later the same observers made more estimates. After each of these they were told the measured distance between the positions. During this training, the observers' height from the ground plane was either at a standing position or at an elevated position raised 2.3 m (7 ft 7 in) from standing position. After the training--either immediately after, a week later, or at both times--observers made unguided estimates of distance for a second time. These latter estimates of ground distance made with the NVGs were improved. Average improvement of the observers' estimates persisted for at least one week after training. This training can be applied to improve clearance estimates and estimates of hover height for pilots of rotary-wing aircraft.

Aerospace Medicine↗