[Effect of noise on color vision & night vision].
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Color Perception↗
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Evaluation of the Night Vision Spectacles on patients with impaired night vision.
BACKGROUND: The Night Vision Spectacles (NiViS) were developed by a consortium of European companies to assist individuals who suffer from impaired night vision. They consist of a head-mounted video camera (input) and binocular displays (output) connected to a portable computer processor, which uses an algorithm to enhance the luminance and contrast of the video image. METHODS: Eighteen patients with impaired night vision were tested, including those with retinitis pigmentosa (7), Usher syndrome (2), fundus albipunctatus (1) and complete (4) and incomplete (4) congenital stationary night blindness. Normal trichromats (3) and typical, complete achromats (2) acted as controls. A battery of tests assessed: visual acuity at 5 m (projection unit) and 1 m (chart) and at high and low contrasts; contrast sensitivity; absolute and increment threshold; the influence of glare; contrast motion detection; and hand-eye performance. The tests were performed, with and without the NiViS, at three adaptation levels: low scotopic (10(-3) cd/m2), high scotopic (10(-2) cd/m2) and mesopic (10(-1) cd/m2). RESULTS: At the low and high scotopic levels, the majority of patients showed improved performance on the visual acuity, contrast sensitivity and motion contrast tests with the NiViS. At the mesopic level, the advantage with the NiViS was greatly reduced, but still present for contrast sensitivity. CONCLUSION: Patients with impaired night vision can benefit from the NiViS when performing tasks involving contrast and motion perception. Those with normal visual fields and retaining good photopic vision will benefit more than those with constricted visual fields and impaired cone vision. Recommendations regarding desirable improvements of the NiViS and suitability for the individual patient are given.
Adolescent↗
[Night vision and night combat activities].
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Dark Adaptation↗
Vernier acuity through night vision goggles.
Night vision goggles (NVG's) are being used increasingly in military and civilian environments. Despite the use of these devices, relatively few tests exist to assess visual performance through NVG's. Hyperacuity tasks may provide a sensitive index of performance through night vision devices. In this study, grating vernier acuity was measured through NVG's. As reported previously, a power law relation was observed between vernier acuity and stimulus contrast. Comparison of vernier acuity with and without NVG's indicated that performance is limited by the contrast transfer of the device. Vernier acuity measurements can be used to assess the quality of vision and quantity of contrast transferred through night vision devices.
Adult↗
An assessment of a proposed method for adjusting and focusing ANVIS night vision goggles.
Night vision goggles are becoming an increasingly important tool in military aviation. They provide superior visual capability over unaided night vision, but any reduction in goggle performance can have a serious effect on flight safety and operational effectiveness. This study shows that the use of a standard adjustment procedure in a night vision goggle (NVG) test lane, with a resolution chart, provides an effective method for aircrew to obtain better visual capability than is currently obtained by focusing on distant features of the landscape. Visual acuity (VA) was measured for 20 aircrew representing all crew positions, after using both the current adjustment method and the proposed method for adjusting ANVIS NVGs. The average visual acuity showed an improvement from 6/19 (s.d. = 3.9) with the current method to 6/13 (s.d. = 2.8) with the proposed method. However, NVG test lanes cannot be used with goggles which have fixed infinity objective lenses eg Nite.
Aerospace Medicine↗
An assessment of the ANV 20/20 focusing aid for night vision devices.
Night vision goggles (NVGs) are becoming an increasingly important tool in military aviation. They provide superior visual capability over unaided night vision, but any reduction in goggle performance can have a serious effect on flight safety and operational effectiveness. This study shows that the use of the ANV 20/20 focusing aid provides an effective method for aircrew to obtain a better visual capability than is currently obtained by focusing on distant features of the landscape or distant lights. Visual acuities using the current and proposed focusing methods were compared in 50 aircrew. The visual acuity showed an average improvement of 18% with the proposed method compared with the current method. This was found to be statistically significant (p < 0.01). Using the current method of focusing there was a significant (p < 0.01) difference in the visual acuity achieved between the right and left tubes/eyes. Using the ANV 20/20 there was no difference between tubes/eyes. ANV 20/20 was found to improve visual acuity when using NVG as well as enabling the user to achieve equal visual acuities with both eyes.
Aviation↗
Visual evoked potentials through night vision goggles.
Night vision goggles (NVG's) have widespread use in military and civilian environments. NVG's amplify ambient illumination making performance possible when there is insufficient illumination for normal vision. While visual performance through NVG's is commonly assessed by measuring threshold functions such as visual acuity, few attempts have been made to assess vision through NVG's at suprathreshold levels of stimulation. Such information would be useful to better understand vision through NVG's across a range of stimulus conditions. In this study visual evoked potentials (VEP's) were used to evaluate vision through NVG's across a range of stimulus contrasts. The amplitude and latency of the VEP varied linearly with log contrast. A comparison of VEP's recorded with and without NVG's was used to estimate contrast attenuation through the device. VEP's offer an objective, electrophysiological tool to assess visual performance through NVG's at both threshold and suprathreshold levels of visual stimulation.
Contrast Sensitivity↗
Visual acuity with the ITT Night Vision Aid for patients with night blindness.
The Night Vision Aid is a photomultiplier device developed by International Telephone and Telegraph Co. (ITT) and the Retinitis Pigmentosa Foundation as a mobility aid for those with night blindness. The purpose of this study was to measure visual acuity with and without the Night Vision Aid at a variety of light levels to determine how much visual assistance it provided over a wide range of illuminations. Ten normal subjects and five patients with retinitis pigmentosa (RP) used the aid at nine luminance levels ranging from 10(-6) to 10(2) ml. With the device, visual acuity improved at light levels below 0.1 ml and target visibility was extended about 3 log units further into low luminance. At light levels above 0.1 mL, unassisted visual acuity was better in all normal and most RP subjects. The best visual acuity attained with the Night Vision Aid was 6/15 (20/50). Graphs and dark adaptation curves illustrate our findings.
Adolescent↗
Evaluation of night vision disturbances.
BACKGROUND: Evaluation of night vision disturbances has relied on subjective responses. We designed a test to more objectively measure night vision disturbances. METHODS: The test consisted of projecting a small circle onto a visual acuity screen. The patient is asked to draw exactly what he sees on an Amsler grid. We evaluated 118 eyes in photopic and scotopic conditions and under different conditions of refractive correction. RESULTS: Image degradation increased in scotopic conditions for myopes (p = .0001), hyperopes (p = .005), and emmetropes (p = .01). Myopic refractive error correlated with size of glare response (p = .001). Astigmatism correlated with decentration of glare response (p = .0001). Decentration increased in scotopic compared to photopic conditions (p = .002). CONCLUSION: Our test offers a simple, convenient way to evaluate night vision disturbances and may offer a means of assessing night vision disturbances in patients considering refractive surgery.
Adolescent↗
[Night vision; practical consideration on night flights].
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Aerospace Medicine↗
An evaluation of night vision mobility aids.
Two night vision aids are commercially available to help individuals who have diseases that cause night blindness. The ITT Night Vision Aid (NVA) is a light amplification device; the Wide Angle Mobility Light (WAML) is a wide beam flashlight. The effectiveness of both instruments in helping night-blind, field-restricted subjects to walk a course of residential streets at night was tested. WAML users were also surveyed to determine the usage, applications, and reliability of the device. We found that the WAML significantly reduced error rates and was preferred by most subjects; it was reported to be used regularly by individuals who owned it. The NVA did not significantly improve error scores, and was not effective as an ambulatory night mobility aid for most patients.
Adult↗
The hazard of spatial disorientation during helicopter flight using night vision devices.
INTRODUCTION: Night Vision Devices (NVDs) provide an enormous advantage to the operational effectiveness of military helicopter flying by permitting flight throughout the night. However, compared with daytime flight, many of the depth perception and orientational cues are severely degraded. These degraded cues predispose aviators to spatial disorientation (SD), which is a serious drawback of these devices. METHODS: As part of an overall analysis of Army helicopter accidents to assess the impact of SD on military flying, we scrutinized the class A-C mishap reports involving night-aided flight from 1987 to 1995. The accidents were classified according to the role of SD by three independent assessors, with the SD group further analyzed to determine associated factors and possible countermeasures. RESULTS: Almost 43% of all SD-related accidents in this series occurred during flight using NVDs, whereas only 13% of non-SD accidents involved NVDs. An examination of the SD accident rates per 100,000 flying hours revealed a significant difference between the rate for day flying and the rate for flight using NVDs (mean rate for daytime flight = 1.66, mean rate for NVD flight = 9.00, p < 0.001). The most important factors associated with these accidents were related to equipment limitations, distraction from the task, and training or procedural inadequacies. CONCLUSIONS: SD remains an important source of attrition of Army aircraft. The more than fivefold increase in risk associated with NVD flight is of serious concern. The associated factors and suggested countermeasures should be urgently addressed.
Accidents, Aviation↗
2,3-Diphosphoglycerate and night vision.
Recovery of night vision at altitude has been examined in relationship to changes of 2,3,diphosphoglycerate (DPG). It appears that, if DPG influences night adaptation, its effect is small. Inter-individual variability is large, both in terms of DPG and performance on the MESOP, the device used to measure dark adaptation.
2,3-Diphosphoglycerate↗
Mild hypoxia and visual performance with night vision goggles.
Military night vision goggles (NVGs) are image intensifiers normally used when the human operator's visual capabilities are unimpaired by oxygen deprivation. However, mountain search team members and aviators sometimes operate with NVG augmentation at altitudes where hypoxic visual decrement is documented. The objective of this research was to investigate the effects of mild hypoxia on monocular visual performance with NVGs. It was found that mild oxygen deprivation significantly affects unaided square-wave grating visual acuity but does not significantly affect NVG-augmented performance. Large differences between visual sensitivities at different spatial frequencies were not differentially affected by mild hypoxia. Supplemental oxygen did significantly improve naked-eye but not NVG-augmented night resolution acuity up to a simulated altitude of 13,000 ft (3,962 m) above sea level (ASL).
Aerospace Medicine↗
Testing night vision goggles in a dark outside environment.
BACKGROUND: People with degenerative retinal diseases such as retinitis pigmentosa, may have adequate day vision but suffer from poor night vision. We have tested newly developed night vision goggles (NVG) to help these patients overcome their night blindness, thereby promoting more opportunities for normal activities at night or in the dark. METHODS: A total of 42 subjects with night blindness due to retinitis pigmentosa, choroideremia, cone rod dystrophy, or Bardet Biedl syndrome were recruited and clinically examined (visual acuity, visual field, and contrast sensitivity). Using an experienced mobility trainer, we tested binocular NVG on the subjects in two locations: a dark room and a 1 to 2 h outside course at night that provided different levels of difficulties (i.e., obstacles, brightness, and contrast). The assessment of which patients benefited from the NVG was predominantly based on the subjective evaluation of the mobility trainer, followed by their graded responses on two questionnaires. RESULTS: Based on the evaluation of the mobility trainer, 23 (61%) of the 42 subjects experienced improved mobility and orientation with the NVG outdoors, and 19 (39%) subjects did not. The ophthalmic data demonstrated that a visual acuity better than 20/100 and a visual field > 5 degrees (Goldmann perimetry III4) is necessary to benefit from NVG usage. In addition, subjective responses on increased mobility and independence were positively correlated with successful NVG testing. CONCLUSIONS: Night vision goggles have the ability to improve poor night vision in subjects with visual acuity > 20/100 and a visual field > or = 5 degrees (Goldmann: III4). In so doing, NVG can help overcome the obstacles experienced by many people suffering from night blindness. NVG, therefore, have the potential to greatly improve quality of life.
Adolescent↗
Zinc supplementation might potentiate the effect of vitamin A in restoring night vision in pregnant Nepalese women.
BACKGROUND: Zinc deficiency may result in abnormal dark adaptation or night blindness, a symptom primarily of vitamin A deficiency. During a placebo-controlled trial in Nepal, weekly vitamin A supplementation of women reduced but failed to eliminate the incidence of night blindness during pregnancy, suggesting a role for zinc. OBJECTIVE: The study examined the efficacy of daily zinc supplementation in restoring night vision of pregnant women who developed night blindness while routinely receiving either vitamin A, beta-carotene, or placebo in a field trial. DESIGN: Women (n = 202) who reported to be night blind during pregnancy were randomly assigned in a double-blind manner, stratified on vitamin A, beta-carotene, or placebo receipt, to receive 25 mg Zn or placebo daily for 3 wk. Thus, the 6 groups studied were as follows: beta-carotene + zinc, beta-carotene alone, vitamin A + zinc, vitamin A alone (vitamin A + placebo), zinc alone (zinc + placebo), and placebo (2 placebos: one for the vitamin A or beta-carotene study and one for the zinc study). Women underwent a clinic-based assessment that included pupillary threshold testing and phlebotomy before and after supplementation. Supplement use and daily history of night blindness were obtained at home twice every week. RESULTS: Zinc treatment increased serum zinc concentrations, but alone (zinc alone group), failed to restore night vision or to improve dark adaptation. However, women in the vitamin A + zinc group who had baseline serum zinc concentrations <9.9 micromol/L were 4 times more likely to have their night vision restored (95% CI: 1.1, 17.3) than were women in the placebo group and tended to have a small improvement in pupillary threshold scores (by 0.21 log candela/m2; P = 0.09). CONCLUSION: These data suggest that zinc potentiated the effect of vitamin A in restoring night vision among night-blind pregnant women with low initial serum zinc concentrations.
Adult↗
Head and eye movements in visual search using night vision goggles.
BACKGROUND: Night-vision goggles (NVGs) provide only a restricted field of view and have other characteristics that may affect the head and eye movements used in visual search. METHODS: We measured head scan patterns, the magnitude and duration of gaze saccades, and fixation duration as subjects searched computer generated imagery either with or without NVGs. Subjects searched for either a large (6 degrees) target on a low-detail background (high conspicuity condition) or a small (2 degrees) target on a high-detail background (low conspicuity condition). RESULTS: All subjects displayed head-scan patterns that were qualitatively similar to those reported in the literature. Although both head-scan speed and amplitude were higher for the NVG condition as compared with the no-NVG condition, the difference was not statistically significant. Head-scan speed did vary significantly with target conspicuity, however. Gaze saccade amplitude varied with target conspicuity but only when NVGs were used. Fixation duration did not vary with either NVG use or target conspicuity. A two-parameter (exponent and scaling parameter) power function was fitted to the amplitude-duration data. The power-function exponents varied from about 0.30 to 0.44, but there was a concommitant variation in the scaling parameter, and the result was no significant difference in the form of the power functions fitted to the data. CONCLUSIONS: NVG use did not significantly affect any of the individual head or eye movement variables involved in searching the computer-generated imagery studied here. However, the decrease in gaze-saccade amplitude with increased target conspicuity when NVGs were used is evidence of the sensitivity of the head and eye movement measurement techniques used here, and suggests that all available measures of response efficiency be considered when evaluating NVGs using complex stimuli.
Adult↗
Evaluation of mid-term stability of night vision tests.
BACKGROUND: Dark adaptation rate, scotopic retinal sensitivity and contrast sensitivity under mesopic conditions, but not visual acuity, have been shown to be directly related to the ability to identify military targets at night. These parameters can be used to select personnel for specific military tasks demanding excellent night vision, as well as to assess pharmacological effects on night vision. PURPOSE: To evaluate the mid-term (2 to 6-week period) stability of night vision tests based on assessment of the above parameters. METHODS: Dark adaptation rate, scotopic retinal sensitivity and contrast sensitivity under mesopic conditions were studied in 16 young volunteers during a 6-week period. RESULTS: Tests of scotopic retinal sensitivity (after 30 min of dark adaptation) exhibited high reproducibility and a low fluctuation rate, with a high correlation between values at week 0 and at 2-week intervals during the following 6 weeks of the study (rs (week 0 to week 6) = 0.81, p = 0.0001). The reproducibility of mesopic contrast sensitivity tests (average of 1.5, 3, 6 and 12 cycles per degree, (cpd)) was fair (rs (week 0 to week 2) = 0.67, p = 0.0045), whereas that of dark adaptation rate tests was poor. CONCLUSIONS: In view of the reproducibility characteristics of these night vision tests, assessment of night vision ability in pilots and military personnel, as well as assessment of pharmacological effects on night vision, may be based on scotopic retinal sensitivity (after 30 min of dark adaptation) and contrast sensitivity under mesopic conditions (average of 1.5, 3, 6 and 12 cpd).
Adult↗