Jerome W. Molchany

Accidental human laser retinal injuries from military laser systems

The time course of the ophthalmoscopic and functional consequences of eight human laser accident cases from military laser systems is described. All patients reported subjective vision loss with ophthalmoscopic evidence of retinal alteration ranging from vitreous hemorrhage to retinal burn. Five of the cases involved single or multiple exposures to Q-switched neodymium radiation at close range whereas the other three incidents occur over large ranges. Most exposures were within 5 degrees of the foveola, yet none directly in the foveola. High contrast visual activity improved with time except in the cases with progressive retinal fibrosis between lesion sites or retinal hole formation encroaching the fovea. In one patient the visual acuity recovered from 20/60 at one week to 20/25 in four months with minimal central visual field loss. Most cases showed suppression of high and low spatial frequency contrast sensitivity. Visual field measurements were enlarged relative to ophthalmoscopic lesion size observations. Deep retinal scar formation and retinal traction were evident in two of the three cases with vitreous hemorrhage. In one patient, nerve fiber layer damage to the papillo-macular bundle was clearly evident. Visual performance measured with a pursuit tracking task revealed significant performance loss relative to normal tracking observers even in cases where acuity returned to near normal levels. These functional and performance deficits may reflect secondary effects of parafoveal laser injury.

Laser flash effects on tracking performance and the aversion response

Introduction: For an accidental laser exposure, the duration of the incident radiation on a specific retinal site depends on the initial fixation, the kinetics of the aversion (blink reflex) and the orienting response (eye movement) toward or away from the light image. Pupilary constriction during the exposure will attenuate the retinal irradiance. Methods: In this study, tracking performance was measured in eight volunteers exposed to O1, LO, and 10 second laser flashes while tracking a dynamic target (O28 degs) through a monocular telescope equipped with a miniature video camera to monitor eye response. The collimated 514 nm argon laser beam produced corneal radiant exposures of 0. 16, 0.33, and LO mJ/cm2 for the 0. 1, LO, and 3O second conditions respectively. Total time off target and maximum absolute error scores were measured for bright (430 nits) and dim (43 nits) ambient luminance conditions. Eye response (blink and pupilary response) was assessed by evaluation of the video from the eye camera. Volunteer reports of the visual experience were recorded. Results: Total time off target (> 0.5 mrad) was maximal for the 3 second exposure condition and minimal for the 0. 1 second conditions. Analysis of the data indicated that there was no photic induced blink reflex for the 0. 1 second condition under the bright light condition. For some volunteers, blinks did occur during the longer duration exposures but were not classic reflex blinks. Pupil responses following the laser presentation showed pupil diameters decreased from initial values of approximately 6 mm to 23 mm which reduced the total energy into the eye at that point by a factor of 10. Volunteers reported smeared and multiple afterimages for the 3 second condition, however, only a single, focal, afterimage was reported for the 0. 1 second condition. This information reflects a history of eye movements during the exposure; Summary: For durations of 100 msec or less, physiological mechanisms that would limit the retinal radiant exposure are not operative for the conditions investigated in this study. For the a 1 second exposure condition, fracking performance was not affected for the bright light vials and only minimally affected foe the dim light trials.

Laser-induced afterimages in humans.

Afterimages induced by incoherent light sources have been studied as complex visual perceptions for over 200 years; however, individuals who have viewed a coherent source (a laser) on-axis have reported visual experiences unlike those observed for full-field flashes from incoherent sources. In the present study, 10 volunteers viewed all combinations of blue, green, and red laser light and background colors that matched the wavelengths of the laser sources (a total of 9 conditions). The bright focal (50 μm retinal irradiance diameter) 3-sec. exposures (approximately 9 log trolands-40% of the maximum permissible exposure level) given to the volunteers were administered as they performed a simulator tracking task. A 50/50 mirror (a mirror which reflected 50% of the laser beam into the optical pathway while allowing the 50% of the light from the visual scene to pass through the mirror) permitted simultaneous intrabeam viewing of the laser source and the scene. The volunteers were asked to report what they saw immediately after the laser was turned off and 1-min. postexposure. The immediate reports indicated that the image they observed was the same color as the laser source and not the complementary color. Also, the images were often surrounded by well-defined borders and, regardless of lasers or backgrounds color, were generally red. One minute following presentation of the laser light the images seen were predominantly purple, dark or no longer present; however, the edge color when present generally appeared red. The immediate appearance of the images was inferred to be neural in nature and not photochemical. These results suggest the properties of the laser source, i.e., coherency, monochromaticity, and the lasers capacity to place an intense beam of light in a small retinal area, all contributed to the unique appearance of the postflash images.

Transient disruption of human pursuit-tracking performance for laser exposures below permissible exposure limits

The proliferation of lasers for medical care, laser displays, industrial applications and audio- visual presentations has increased the potential for accidental intrabeam exposure to visible laser radiation. The output of these laser devices may be limited to below permissible exposure limits, but they are perceived as bright and can affect performance. The disruption experienced while viewing a laser is related to factors that include the retinal irradiance level, wavelength, ambient light level and mode (continuous wave (CW) and repetitively pulsed (RP)). This report describes studies where these factors were varied to assess the effects of laser light on tracking performance in a laboratory simulator and in a field study. Disruption was determined by measuring maximum error and total time off target. Performance disruption increased as irradiance levels increased and ambient light levels decreased.Under dawn/dusk conditions, relatively low-level laser energy produced performance disruption. Green laser light at the peak of the photopic sensitivity curve was more disruptive than red laser light. Increased error scores during CW and RP trials were attributed to average rather than peak power effects. More than 1500 laser exposures at levels up to MPE/2 have been given to volunteers. Despite transient performance disruption comparison of the pre- and post- laser visual performance tests and fundus evaluations wee unremarkable.

Preferred retinal location induced by macular occlusion in a target recognition task

Laser-induced central retinal damage not only may diminish visual function, but also may diminish afferent input that provides the ocular motor system with the feedback necessary to move the target to the fovea. Local visual field stabilizations have been used to demonstrate that central artificial occlusions in the normal retina suppress visual function. The purpose of this paper is to evaluate the effect of local field stabilizations on the ocular motor system in a contrast sensitivity task. Five subjects who tested normal in a standard clinical eye exam viewed landolt rings at varying visual angles under three artificial scotoma conditions and a no scotoma condition. The scotoma conditions were a 2 degree(s) and 5 degree(s) stabilized central scotoma and a 2 degree(s) stabilized scotoma positioned 1 degree(s) nasal to the fovea. A Dual Purkinje Eye-Tracker (SRI, version 5) was used to provide eye-position data and to stabilize the artificial scotoma on the retina. The data showed a consistent preference for placing the target in the superior retina under the 2 degree(s) and 5 degree(s) conditions with a strong positive correlation between visual angle and deflection of the eye position into the superior retina. These data suggest that loss of visual function from laser-induced foveal damage may be due in part to a disruption in the ocular motor system. Thus, even if some function remains in the damage site ophthalmoscopically, the ocular motor system may organize around a nonfoveal retinal location, behaviorally suppressing foveal input.

Effects of bilateral and unilateral laser ocular exposure in humans

INTRODUCTION: The amount of visual disruption experienced by individuals exposed to a visible laser source at levels, which are below that, which will damage the cornea or retina will depend on laser exposure parameters and task demands. Previous work has evaluated the effects of wavelength, duration, ambient light level, and target variables. One factor that has not received attention is monocular vs. binocular exposure. Whether the exposure is monocular or binocular may alter pupil dynamics, eyelid closure, and ultimately affect visual performance. METHODS: In this study 10 males and females were exposed to 0.1 and 3.0 sec laser flashes while tracking a dynamic target at 0.28 deg/sec through a scope that was capable of selecting binocular or monocular viewing. Bright (430 nits) and dawn/dusk (4.3 nits) ambient light conditions were simulated using ND filters. A collimated 514.5 nm argon laser beam produced corneal radiant exposures of 0.16 and 1.0 mJ/cm2 for the 0.1 and 3.0 sec conditions respectively. For each flash trial total time off target and maximum absolute error scores were calculated. Eye response (changes in pupil diameter) was assessed by evaluation of videotape from an IR eye camera. Tracking error scores (total time off target) were calculated for each flash trial. RESULTS: Analysis of variance results for the total time off target scores found all three main factors (light level, exposure duration, and monocular/binocular to be significant. Earlier studies have previously shown dawn/dusk flash exposures be more disruptive than bright light trials. Also three sec exposures were more disruptive than one sec exposures. Finally, monocular exposures produced significantly higher error scores than did binocular exposures. For the pupil diameters the post-flash diameters were significantly smaller that the pre-flash diameters and monocular diameters larger that binocular pupil sizes. SUMMARY: The Total Time Off Target error scores for the monocular viewing condition were significantly higher than the binocular viewing condition supporting bilateral summation contributions to binocular tracking. Pupil recovery diameters were approximately 84% of baseline for monocular viewing regardless of ambient light level and flash duration. Binocular viewing conditions yielded an average 75% pupil recovery. Continuing analysis of the pupil data precludes us from making a more definitive statement.

Optimization of neural retinal visual motor strategies in recovery of visual acuity following acute laser induced macula injury

Laser induced damage to the retina may produce immediate and serious loss in visual acuity as well as subsequent recovery of visual acuity over a 1 to 6 month post exposure period. While acuity may recover, full utilization of the foveal region may not return. In one patient, a superior/temporal preferred retinal location (PRL) was apparent, while a second patient demonstrated significant foveal involvement and contrast sensitivity more reflective of foveal than parafoveal involvement. These conditions of injury wee simulated by using an artificial scotoma technique which optically stabilized a 5 degree opacity in the center of the visual field. The transmission of spatially degraded target information in the scotoma was 0 percent, 5 percent and 95 percent. Contrast sensitivity for the 0 percent and 5 percent transmission scotoma showed broad spatial frequency suppression as opposed to a bipartite contrast sensitivity function with a narrow sensitivity loss at 3 cycles/degree for the 95 percent transmission scotoma. A PRL shift to superior temporal retina with a concomitant change in accommodation was noted as target resolution became more demanding. These findings suggest that restoration of visual acuity in human laser accidents may depend upon the functionality of complex retinal and cortical adaptive mechanisms.

Visual Functions Associated With Rhesus Visual Pursuit Tracking.

While numerous investigations of visual function and visual performance exist, the relationship between these measures is largely unexplored. In this study, we have evaluated the receptor input for visual pursuit motor tracking performance using the rhesus monkey as an animal model for the human visual system. Spectral sensitivity functions derived from rhesus spectral intensity tracking performance functions emphasize the role of photopic retinal mechanisms for high fidelity tracking performance criteria. Spectral sensitivity functions under these conditions appear photopic in shape and reflect central retinal long-and middle-wavelength-sensitive cone systems. Scotopic intrusion may occur with lower fidelity performance criteria. Species differences previously reported between rhesus and human long wavelength foveal retinal mechanisms may be reflected for visual performance criteria as well.