Accelerated healing of laser-injured rabbit retina by basic fibroblast growth factor.

PURPOSE: To improve the outcome of injured retina, human recombinant basic fibroblast growth factor (bFGF) was examined for its ability to accelerate healing in laser-injured New Zealand Red rabbits. METHODS: A multi-line argon laser (454 to 514 nm) was used to produce lesions near subretinal hemorrhaging levels. Within 30 minutes after irradiation, eyes were intravitreally injected directly above the lesions with 10 microliters vehicle or 10 micrograms of bFGF in 10 microliters of vehicle. Lesions were evaluated by funduscopy and fluorescein angiography. After 4 days of treatment, animals were killed and eyes examined histologically. RESULTS: On subsequent days, bFGF-treated lesions were less opaque, smaller in diameter, and less leaky to fluorescein than lesions in the control eyes. Eyes treated with bFGF exhibited reduction in lesion diameter (P < or = 0.001) and in the lesion periphery, decreased loss of photoreceptors (P < or = 0.001), and greater numbers of pigmented epithelial cells, compared to controls. By bromodeoxyuridine incorporation, increased proliferation occurred in fibroblasts, retinal pigmented epithelial cells, and inner retinal glial cells. CONCLUSIONS: These results indicate that bFGF both accelerated ocular tissue repair and also prevented photoreceptor loss. The rescue of photoreceptors by bFGF may occur through direct action on the photoreceptors, or indirectly through effects on other cells in the retina.

On the use of schematic eye models to estimate retinal image quality.

The optical performance of the eyes of nine vertebrate species was evaluated using optical system design techniques and schematic eye models. Essential features of eyes, including the modulation transfer function (MTF) and the MTF cutoff frequency are related to the numerical aperture of the eyes. Superior resolution for in vivo imaging of photoreceptors may be achieved by dilating the iris pupil of an eye, minimizing coherence, and using short wavelength illumination. The difference of lateral and axial resolution between a small and a large eye for imaging photoreceptors in vivo.

Near infrared laser ocular bioeffects.

Thresholds for laser chorioretinal injury in the red end of the visible spectrum and the near-infrared (IR-A) spectral regions are presented. An unpredicted wavelength dependence of the injury threshold for single Q-switched pulses is demonstrated. Four lasers were used to determine thresholds at 40 wavelengths between 532 nm and 1064 nm: a ruby laser, a neodymium:YAG-pumped dye laser, an erbium:YLF laser and an alexandrite laser. Despite many careful and repeated efforts to determine a cause for the variation due to possible variations in the lasers or other aspects of the experimental technique and due to biological absorption properties of the eye, there is no complete or obvious explanation for the significant variations of threshold with small changes in wavelength. The implications of these findings for laser safety standards are presented.

Retinal image motion during deliberate fixation: implications to laser safety for long duration viewing.

With the easy attainability of hand-held laser devices and the burgeoning light emitting diode (LED) technology, safety standards for long-term viewing of continuous light sources are being scrutinized. One concern is with quantifying the effect of head and eye movements on the distribution of energy over the retina. This experiment describes target motion over the retina as a result of head and eye movements during a deliberate fixation task. Volunteers deliberately fixated, with (fettered) and without (unfettered) head and chin rest support, on LEDs that subtended a 0.1 min of arc visual angle. A Dual Purkinje Image Eyetracker measured eye position during each 100-s fixation trial. The data showed an elliptical retinal energy distribution, oriented on the temporal/ nasal retinal axis, with a major axis 1.5 times greater than the minor. The average half-maximum diameter for the major axis was 40 microm for the fettered and 107 microm for the unfettered condition. The retinal area illuminated from head and eye movements showed a positive linear relationship with time. Peak retinal radiant exposure at 100 s was reduced by a factor of 10 as a result of eye movements and by a factor of 30 as a result of head and eye movements. Although the net result was a reduction in radiant exposure from a "no-movement" baseline, the distribution of energy over the retina was well within the 200 microm foveal boundary. The data suggest that the laser permissible exposure limits for long term viewing of a small continuous wave source include a factor that adjusts for this reduction in retinal radiant exposure with time.

Laboratory simulator and field pursuit tracking performance with females and males in the presence of laser glare.

BACKGROUND: The developments in laser technology have increased the precision of many tasks and has made the presence of lasers common-place. In the military the pervasive use of laser devices in uncontrolled environments enhances the potential for human exposure. The visual disruption experienced during these exposures could lead to serious injury or disruption of performance. Characterization of changes in visual-motor performance of military personnel exposed to safe levels of laser glare assists in minimizing mission performance decrements. METHODS: There were 18 female and male military personnel who performed a tracking task in the field and in the laboratory. Two systems were used to assess possible gender differences inherent to the operation of each unit. There were six, 3-s laser trials presented at an irradiance of 400 microW.cm-2 during 15 bright light and 15 simulated dawn/dusk trials with each system. The laser beam on the retina was collinear with the image on the sight. Maximum absolute error (MAE) and total time-off-target (TTOT) scores were determined. RESULTS: Analysis showed that after the flash females tended to lead and males lagged behind the target. No significant differences in MAE or TTOT scores attributable to gender were found. Dawn/dusk flash trials produced greater disruption of pursuit tracking than did bright light trials. Repeated flash exposures showed either an adaptive or a cumulative response. CONCLUSIONS: Significant visual disruption was found following exposure to "safe" levels of laser light and this effect was increased during simulated dawn/dusk conditions. The degree of performance decrement was not related to gender.

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 microm 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 of ten surrounded by well-defined borders and, regardless of laser's or background's col or, 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 laser's capacity to place an intense beam of light in a small retinal area, all contributed to the unique appearance of the postflash images.

Spectrophotometry of the canine bladder.

Canine bladders were subjected to spectrophotometric analysis in order to choose a laser for experimental endoscopic use. Percentages of transmission and reflection were obtained; these allowed derivation of an absorption curve throughout the wavelength range of water transparency. We conclude that the argon laser was the most appropriate system available at the present time.

Urokinase-treatment of fresh laser irradiation-induced vitreous hemorrhage.

Using a ruby laser, we induced vitreous hemorrhage in each eye of 12 rabbits. On the following day either 25,000 Ploug units of urokinase or saline were injected into the eyes of each rabbit. Urokinase did not accelerate the absorption of blood from the vitreous but prevented the development of severe vitreous fibrosis which replaced the hemorrhage in seven of the control eyes.

Grating visual evoked cortical potentials in the evaluation of laser bioeffects: instrumentation.

A system was designed to permit simultaneous viewing of the ocular fundus of the rhesus monkey (Macaca mulatta), the accurate placement of laser radiation on the retina, and the stimulation of the site to produce a grating visual evoked cortical potential (VECP). A fundus camera was modified to incorporate a grating whose image was projected onto the retina at specific locations. The evoked potential could thus be obtained for any rate of alternation before, during, and after the exposure of the fovea to any one of many laser sources. An example is shown of the use of this system to monitor the grating VECP before and after exposure of the animal's fundus to a 900 nm gallium arsenide laser source for 60 sec. In this case, changes were observed in the variability of the latency of components of the VECP when compared to the prelaser exposure potentials.

Simultaneous irradiation and imaging of blood vessels during pulsed laser delivery.

BACKGROUND AND OBJECTIVE: Simultaneous irradiation and viewing of 10-120 microm cutaneous blood vessels were performed to investigate the effects of 2-micros 577-nm dye laser pulses. STUDY DESIGN/MATERIALS AND METHODS: A modified scanning laser confocal microscope recorded vessel response to different radiant exposures (J/cm2). Probit analysis determined the 50% probability ("threshold") radiant exposure necessary to cause embolized or partly occluding coagula, coagula causing complete blood flow stoppage, and hemorrhage. RESULTS: A statistically significant difference in the threshold radiant exposure existed for each damage category for blood vessels 10-30 microm in diameter, but not for larger vessels. For vessels over 60 microm, complete flow stoppage was unattainable; increasing laser pulse energy produced hemorrhage. In larger vessels, coagula often were attached to the superficial vessel wall while blood flowed underneath. Monte Carlo optical and finite difference thermal modeling confirmed experimental results. CONCLUSION: These results provide insight into the role of pulse duration and vessel diameter in the outcome of pulsed dye laser irradiation.