Donald A. Gagliano

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.

Accidental human retinal injuries by laser exposure: Implications to laser safety

In the past several years, the USAMRD has evaluated several laser accident/incident cases. The accidents generally occurred at close range from q-switched laser systems and resulted in retinal injury with visual function loss with varying degrees of recovery. The time course of the ophthalmoscopic consequences of the injuries was evaluated by conventional and scanning laser ophthalmoscopy (SLO). Functional evaluations included Snellen visual acuity, Amsler Grid, threshold visual fields, contrast sensitivity, color discrimination tests and performance of a pursuit tracking task. The clinical results and situational assessments of five exposure incidents are described. Five cases involved single or multiple exposures to q-switched neodymium (4) and ruby (1) laser radiation. All exposures were within 5 degrees of the fovea, yet none directly in the foveola. All patients reported subjective central vision loss in the acute phase. 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. Three patients showed little to no recovery measured at 12 months with suppression of both high and low spatial frequency contrast sensitivity. Deep retinal scar formation and retinal traction were evident in two cases with vitreous hemorrhage. Nerve fiber layer damage to the papillo-macular bundle was clearly evident by SLO in one case. Visual performance measured with a pursuit tracking task revealed significant performance loss relative to normal tracking observers. Recovery from accidental laser eye injury depends on the exposure dose and location of the injury site within the retina and the potential for complicating secondary effects (e.g. scar formation, nerve fiber loss). When secondary effects are minimal, recovery to normal or near normal visual acuity may occur modified by ocular-motor processes that shift the preferred retinal location superior and slightly temporal to the fovea.In the past several years, the USAMRD has evaluated several laser accident/incident cases. The accidents generally occurred at close range from q-switched laser systems and resulted in retinal injury with visual function loss with varying degrees of recovery. The time course of the ophthalmoscopic consequences of the injuries was evaluated by conventional and scanning laser ophthalmoscopy (SLO). Functional evaluations included Snellen visual acuity, Amsler Grid, threshold visual fields, contrast sensitivity, color discrimination tests and performance of a pursuit tracking task. The clinical results and situational assessments of five exposure incidents are described. Five cases involved single or multiple exposures to q-switched neodymium (4) and ruby (1) laser radiation. All exposures were within 5 degrees of the fovea, yet none directly in the foveola. All patients reported subjective central vision loss in the acute phase. In one patient the visual acuity recovered from 20/60 at one week to 20/25 in fo...

Macular hole surgery following accidental laser injury with a military rangefinder

An active duty marine corps service member had bilateral full thickness macular holes induced following accidental Q-switched laser exposure from a hand held Neodymium range finder (ANGVS-5). The right eye had a large hole nasal to the fovea, while the left eye had a much smaller hole closer to the fovea centralis. Over the 18 months following the injury, the left eye demonstrated mild progressive degradation in visual function, but retained 20/20 final visual acuity. In contrast, the hole in the right eye increased in size, developed a localized retinal detachment with cystic changes in the fovea, and had atrophy of the retinal pigment epithelium. Within 6 months after injury, acuity declined to 20/100. Macular hole surgery was performed with a goal of sealing the edges of the hole in order to allow resolution of the localized detachment and cystic changes in the fovea. In spite of surgical techniques that are generally successful in the treatment of macular holes associated with other etiologies, the fundus findings remained unchanged and visual acuity declined to 20/400. To the best of our knowledge, this is the first case report of macular hole surgery for this condition.

Confocal scanning laser ophthalmoscopic imaging resolution of secondary retinal effects induced by laser radiation

We have evaluated secondary laser induced retinal effects in non-human primates with a Rodenstock confocal scanning laser ophthalmoscope. A small eye animal model, the Garter snake, was employed to evaluate confocal numerical aperture effects in imaging laser retinal damage in small eyes vs. large eyes. Results demonstrate that the confocal image resolution in the Rhesus monkey eye is sufficient to differentiate deep retinal scar formation from retinal nerve fiber layer (NFL) damage and to estimate the depth of the NFL damage. The best comparison with histological depth was obtained for the snake retina, yielding a ratio close to 1:1 compared to 2:1 for the Rhesus. Resolution in the Garter snake allows imaging the photoreceptor matrix and therefore, evaluation of the interrelationship between the primary damage site (posterior retina), the photoreceptor matrix, and secondary sites in the anterior retina such as the NFL and the epiretinal vascular system. Alterations in both the retinal NFL and epiretinal blood flow rate were observed within several minutes post Argon laser exposure. Unique aspects of the snake eye such as high tissue transparency and inherently high contrast cellular structures, contribute to the confocal image quality. Such factors may be nearly comparable in primate eyes suggesting that depth of resolution can be improved by smaller confocal apertures and more sensitive signal processing techniques.

Functional and ophthalmoscopic observations in human laser accident cases using scanning-laser ophthalmoscopy

A scanning laser ophthalmoscope (SLO) equipped with an acousto- optical modulator (ACM) was used to make focal acuity and contrast sensitivity measurements in individuals with macular damage. The depth of modulation achieved by the ACM was determined by imaging the SLO raster pattern onto a Pulnix TM 745 video camera and evaluating the intensity distribution with a Big Sky BVA10 beam view analyzer. Contrast levels remained approximately constant over the entire range of SLO input raster power settings. A delta Technologies image processing system produced Landolt ring test stimuli at the center of the raster pattern. Contrast thresholds were determined at various retinal locations by having subjects fixate a specific location on a fixed grid imaged on the raster pattern. This procedure insured that the test stimuli were always imaged in the center of the raster pattern thereby avoiding peripheral variations in the raster pattern intensity distribution. Measurements of contrast sensitivity where focal test targets fell within the macular damage area demonstrated elevated contrast thresholds relative to retinal locations where focal test targets evaluated the border regions between normal and pathological retina.

Morphological and functional effects of induced laser retinal fibrosis

Human laser accident exposure cases may involve severe macula retinal injury resulting in long term visual acuity and spatial vision deficit. In order to investigate this problem, we have chosen to model the effects of such long term exposure in the monkey retina for parafoveal Q- switched exposure produced at two parafoveal exposure sites. Our results suggest significant loss of retinal function in and adjacent to the scar region. Recovery occurs in regions with less scar formation, the foveal region, although long term changes in foveal receptor mechanisms are apparent even after 1 year post-exposure, they do not correlate completely with recent human investigations of severe accidental exposure nor with brain enzyme analysis in our monkey model.

Utilization of scanning laser ophthalmoscopy in laser-induced bilateral human retinal nerve fiber layer damage

In this paper, we describe a military laser accident case where bilateral Q-switched laser exposure resulted in bilateral macular damage with immediate visual acuity loss in one eye (OS) and delayed visual acuity loss in the other exposed eye (OD), where retinal damage appeared more parafoveal. At 6 weeks post exposure, OS had recovered to 20/17 and OD had dropped to 20/100 Snellen activity. Retinal nerve fiber damage was observed in both eyes at this time. Contrast sensitivity measurements made in OS were suppressed across all spatial frequencies, even though Snellen acuity measured in the normal range. More severe high spatial frequency loss in contrast was measured in the right eye as well as low spatial frequency loss. Both OS and OD revealed a parafoveal preferred retinal locus with scanning laser ophthalmoscopy contrast sensitivity measurements, suggesting parafoveal retinal compensatory processes.

Confocal scanning laser evaluation of repeated Q-switched laser exposure and possible retinal NFL damage

Repeated extended source Q-switched exposure centered on the macula has been shown to produce a Bullseye maculopathy. This paper provides a confocal scanning laser ophthalmoscopic evaluation with regard to the retinal nerve fiber layer (NFL) and deeper choroidal vascular network. Confocal imaging revealed that the punctate annular appearance of this lesion in the deeper retinal layers is associated with retinal nerve fiber bundle disruptions and small gaps in the retinal NFL. No choroidal dysfunction was noticed with Indocyanine green angiography. It is hypothesized that retinal NFL damage occurs either through disruption of retinal pigment epithelial cell layer support to the NFL or through direct exposure to high spatial peak powers within the extended source beam profile, causing direct microthermal injury to the NFL. The apparent sparring of the fovea reflects central retinal morphology rather than a lack of retinal damage to the fovea.

Nerve fiber layer (NFL) degeneration associated with acute q-switched laser exposure in the nonhuman primate

We have evaluated acute laser retinal exposure in non-human primates using a Rodenstock scanning laser ophthalmoscope (SLO) equipped with spectral imaging laser sources at 488, 514, 633, and 780 nm. Confocal spectral imaging at each laser wavelength allowed evaluation of the image plane from deep within the retinal vascular layer to the more superficial nerve fiber layer in the presence and absence of the short wavelength absorption of the macular pigment. SLO angiography included both fluorescein and indocyanine green procedures to assess the extent of damage to the sensory retina, the retinal pigment epithelium (RPE), and the choroidal vasculature. All laser exposures in this experiment were from a Q-switched Neodymium laser source at an exposure level sufficient to produce vitreous hemorrhage. Confocal imaging of the nerve fiber layer revealed discrete optic nerve sector defects between the lesion site and the macula (retrograde degeneration) as well as between the lesion site and the optic disk (Wallerian degeneration). In multiple hemorrhagic exposures, lesions placed progressively distant from the macula or overlapping the macula formed bridging scars visible at deep retinal levels. Angiography revealed blood flow disturbance at the retina as well as at the choroidal vascular level. These data suggest that acute parafoveal laser retinal injury can involve both direct full thickness damage to the sensory and non-sensory retina and remote nerve fiber degeneration. Such injury has serious functional implications for both central and peripheral visual function.

Laser-induced retinal nerve fiber layer (NFL) damage

Retinal nerve fiber layer (NFL) damage can be induced by retinal laser photocoagulation. This type of thermal injury involves degeneration in both descending and ascending directions from the photic injury site. We have repeated early studies in evaluation of the acute phases of the injury process. Our findings indicate that the ascending or Wallerian portion of the NFL degeneration requires less time than the descending portion; an early neural debris channel occurs in close proximity to retinal vessels and appears to enter the optic disc in close proximity to the retinal vasculature. Angiography of the ascending debris sheath suggests possible capillary pattern modulation associated with this neural debris sheath. Retinal traction evident in with other acute injuries appears at 2 weeks and disappears after 8 weeks suggesting secondary control factors other than retinal hemorrhage in the development of retinal traction bands.