[Clinical and electroretinographic profile of commotio retinae]. / Perfil clínico e eletrorretinográfico da comoção retiniana.

PURPOSE: To investigate clinical, anatomic and electroretinographic changes in eyes that suffered blunt ocular trauma with commotio retinae. METHODS: Patients who presented commotio retinae after unilateral blunt ocular trauma less then 72 hours before were submitted to visual acuity testing, biomicroscopy, binocular indirect ophthalmoscopy, fluorescein angiography, optical coherence tomography and full-field electroretinography. Full-field ERG was repeated after 15 and 30 days. RESULTS: Sixteen patients were included in the study. On the first examination there was a statistically significant difference between affected and fellow eye in all response amplitudes, without b/a ratio alteration, and a delay in single-flash cone response and 30-Hz flicker implicit time. On the second examination, the difference between the eyes remained for oscillatory potentials, but disappeared on the last examination. In fluorescein angiography, all patients presented mottled hyperfluorescence and hypofluorescent areas, due to alterations in the pigment barrier. On optical coherence tomography, we found optically empty spaces at the site of the lesion. CONCLUSION: Found changes suggested photoreceptor and ganglion cells, but not Müller cell functional alterations, as well as pigment mobilization. These changes disappeared 30 days after the trauma.

Increased expression of brain-derived neurotrophic factor preserves retinal function and slows cell death from rhodopsin mutation or oxidative damage.

There are no effective treatments for inherited retinal degenerations, which are prevalent causes of visual disability. Several proteins promote the survival of various types of neurons, and increasing expression of one or more of these survival factors is a promising strategy for a new treatment. Studies examining the effects of intravitreous injections of brain-derived neurotrophic factor (BDNF) in models of inherited retinal degenerations have suggested that BDNF has little survival-promoting activity for photoreceptors. In this study, we generated double transgenic mice with doxycycline-inducible expression of BDNF in the retina. In a model of primary rod photoreceptor degeneration, expression of BDNF resulted in significant delay in photoreceptor cell death and maintenance of retinal function assessed by electroretinogram recordings. Expression of BDNF also caused strong protection of photoreceptors from oxidative damage-induced cell death. These data suggest that continuous expression of BDNF, unlike intravitreous injections, results in morphologic and functional benefit in animal models of inherited retinal degeneration. Double transgenic mice with inducible expression of survival factors provide valuable tools for selection of survival factor candidates for gene therapy.

Antagonistic effects of adrenalectomy and ether/surgical stress on light-induced photoreceptor damage.

Light-induced damage to retinal photoreceptors in influenced by the endocrine status of the animal during the period of exposure. Experimental manipulation of the pituitary gland and of prolactin levels has been shown to affect retinal damage in rats exposed to visible light. When rats are experimentally stressed, prolactin secretion from the pituitary gland occurs as does secretion of adrenocorticotropic hormone (ACTH), which stimulates the release of adrenal cortical hormones. Since prolactin appears to influence retinal damage and since stressed animals have increased serum levels of prolactin, a comparison of photoreceptor damage in animals in which the adrenal glands were removed or which had been experimentally stressed was undertaken in this study. Adrenalectomized rats had thicker outer nuclear layer (ONL) measurements than those found in sham-operated animals. Stressed rats had severely damaged retinas with cystic degeneration and significantly reduced ONL thickness measurements as compared to retinas of unstressed and adrenalectomized rats. Therefore hormones of the pituitary-adrenal system appear to be involved in the damage to the retina by light, and this response may be related to an interaction or synergism between the adrenal gland, stress, and prolactin secretion.

Repair and late degeneration of the primate foveola after injury by argon laser.

Each foveola of nine rhesus monkey eyes was subjected to a single, mild, calibrated exposure from an argon laser (1 to 1.4 mW for 10 to 20 min). Observations from ophthalmoscopy, fundus photography, and fluorescein angiography were correlated with light and electron microscopic studies. The ophthalmoscopic changes consisted of initial whitening and subsequent but persistent depigmentation of the foveola. Fluorescein angiography showed a pattern consistent with "window defect" of the retinal pigment epithelium (RPE). In the first 6 months after injury, the pathologic changes consisted of initial vacuolar changes of the RPE, followed by persistent hypopigmentation and slow development of membranous bodies or lipoidal degeneration in these cells. Initial alteration and subsequent incomplete reformation of cone outer segments were also noted. In animals sacrificed 3 to 4 years after injury, separation of RPE from Bruch's membrane, with production of various abnormal basement membranes and intercellular cystoid changes in the overlying retina, was observed. The morphologic observations suggest that although the mildly injured epithelial cells may recover, they may develop functional incompetence at a later date, resulting in serous detachment of RPE and foveal (macular) edema.

Transpupillary irradiation of the rabbit retina with the cw-Nd:YAG laser. I. Acute morphologic effects produced using two different pulse forms.

The retinas of six pigmented rabbits (12 eyes) were irradiated with a cw-Nd:YAG laser using two different pulse forms, in conjunction with a constant pulse duration of 200 msec and a retinal focus diameter of 200 microns. The first pulse form (a) was characterized by an initial transient, lasting 15-20 msec, with a peak power twice that of the ensuing plateau phase of 180-185 msec. The second pulse form (b) was almost rectangular in shape. Although the average energies (and powers) for each pulse form were identical, almost 20% of this entity was delivered within the first 20 msec for the first pulse form. Impact lesions were examined at the biomicroscopic, light, and electron microscopic levels, and the characteristic morphologic features described for the cw-mode in general. Comparison of the effects produced using each pulse form revealed a number of differences. At low pulse energies (less than 150 mJ) the rectangular pulse form produced a photocoagulation reaction within the outer sensory retina, but when using the pulse form with the initial transient, this effect was superimposed by a degree of mechanical disruption. Ruptures produced within the elastic component of Bruch's membrane first appeared at lower pulse energies (ie, at 75 mJ, as opposed to 150 mJ for the rectangular pulse form) and were more frequent, and choroidal macrohemorrhaging (observed at pulse energies greater than or equal to 200 mJ) occurred only, when this latter pulse form was employed. Each of these phenomena may be attributed to the higher power and energy densities attained during the initial transient, which has disruptive properties. In order to avoid the risk of severe bleeding, these irradiation parameters should be maintained below approximately 6.4 X 10(3) W/cm2 and approximately 0.13 X 10(3) J/cm2.

Retinal damage produced by intraocular fiber optic light.

We exposed the maculas of owl monkey eyes to light from an intraocular fiber optic light source similar to that used for human pars plana vitrectomy. Retinal irradiance was calculated at 0.22 W/cm2. Eyes were exposed for time intervals ranging from 30 minutes to five minutes and were observed after light treatment by fundus photography and fluorescein angiography. Tissue was obtained for light and electron microscopy by animal killing at one hour, 24 hours, one week, and four weeks. Fundus lesions were seen ophthalmoscopically as early as five hours following 30 minutes of light exposure. Significant damage to the photoreceptor layer and less damage to the pigment epithelium was present by light and electron microscopy as early as one hour after 30 minutes of light exposure. By one month complete loss of photoreceptors with Müller cell junctions between inner retina and flattened abnormal retinal pigment epithelium cells was observed. Fluorescein angiography revealed significant staining of the pigment epithelium and outer retina 24 hours after 30 minutes of light exposure. No leakage from retinal vessels occurred. At one month following light treatment, transmission of choroidal fluorescein through window defects in the pigment epithelium was present with no retinal staining. The threshold for ophthalmoscopically visible fundus lesions in this study was 15 minutes of light exposure. Ten minutes of light treatment was the threshold for microscopic changes. Short light exposures damaged the outer retina and spared the pigment epithelium. Removing a substantial amount of the infrared light from our light source did not protect the retina from damage. Removal of light between 400 and 500 nm is probably more helpful in protecting the retina. Intermittent light exposure of the retina seemed as harmful as uninterrupted illumination for the same cumulative period of time. We speculate that the retinal damage caused by intraocular fiber optic light has primarily a photic mechanism. Damage to the retinal pigment epithelium may be secondary to outer retinal damage. The present levels of intraocular light used for human pars plana vitrectomy are probably safe in most instances. Lengthy preretinal membrane stripping procedures during vitrectomy, however, may pose a threat of light damage to the retina. This damage must be appreciated as continued efforts are made to produce brighter sources of intraocular light for human pars plana vitrectomy.

Müller cell GFAP expression exhibits gradient from focus of photoreceptor light damage.

High intensity (ca. 150 foot-candles), cumulative fluorescent light exposure regimes of 40 or 60 minutes to pigmented Long Evans rats were sufficient to elicit glial fibrillary acidic protein immunoreactivity (GFAP-IR) in Müller cells, when the animals are sacrificed 7 days post-exposure. Exposure to only 20 minutes of cumulative light or sacrifice immediately after exposure was not sufficient to initiate GFAP-IR in Müller cells. A gradient of GFAP-IR was observed extending from an approximately circular focus superior to the optic disc to the peripheral retina, whether or not there was morphological damage to the photoreceptors observable at the light microscopic level. Photoreceptor lesions produced by laser photocoagulation elicited the same gradient of GFAP-IR, and showed that GFAP-IR was not a reflection of a central to peripheral gradient of light received by the retina. Excessive light exposure initiated a signal which induced GFAP expression in Müller cells. This signal appeared to require a dark period and may be a diffusible factor that moves through extracellular pathways.

[Histology of retinal lesions after continuous irradiation and selective micro-coagulation of the retinal pigment epithelium]. / Histologie von Netzhautläsionen nach kontinuierlicher Bestrahlung und nach selektiver Mikrokoagulation des retinalen Pigmentepithels.

Mild continuous wave (CW) irradiation (100 ms, 20 mW, 514 nm) and irradiation with 100 repetitive 5 microseconds laser pulses (3 or 6 microJ, 514 nm) at a repetition rate of 500 Hz was performed to the regio macularis of chinchilla rabbits. The angiographically visible lesions were histologically followed up to 4 weeks. With both irradiation modalities the original retinal pigment epithelium (RPE) was replaced by a monolayer of new RPE cells. Only minimal immediate and no subsequent damage to the photoreceptors was found after selective RPE photocoagulation. Only minimal inflammatory response was found after selective RPE photocoagulation in contrast to CW photocoagulation where macrophages, RPE cells and lymphocytes regularly appear in the damaged photoreceptor layer.

[Trauma from light induced by the operating microscope in the rat retina]. / Fototraumatisme induse de microscopul operator pe retina de sobolan.

The study proposes to analyze the lesions show to the retina level of the rat exposes to light of an operate microscope Zeiss Op Mi 220 (without filters). The conditions of the experiment was created such as the photochemical effect of the radiation to predominate more than thermic effect. Rat's retinae was visualized through photonic and electronic microscopy. The images show that the maximal lesions are situated to the level of the retinal pigment epithelium and of photoreceptors cells. The histological aspects presume the action of the free radicals in the production of the lesions.

Photic injury promotes cleavage of p75NTR by TACE and nuclear trafficking of the p75 intracellular domain.

The p75 neurotrophin receptor (p75NTR) is a member of the tumor necrosis factor receptor superfamily that paradoxically mediates neuronal survival and differentiation or apoptotic cell death. Cleavage of p75NTR by a constitutively active metalloprotease could result in shedding of its extracellular domain (p75ECD) and generation of a pro-apoptotic intracellular domain (p75ICD). In this study, we established that exposure of a transgenic mouse photoreceptor cell line to intense light upregulated the expression of p75NTR and of the disintegrin metalloprotease tumor necrosis factor-converting enzyme (TACE) and resulted in apoptotic cell death. Light damage promoted TACE cleavage of p75NTR resulting in shedding of the soluble p75ECD and nuclear translocation of the p75ICD. Overexpression of TACE and p75NTR-induced p75NTR cleavage and secretion of p75ECD, but not nuclear transport of p75ICD. Light-induced cleavage of p75NTR, nuclear localization of p75ICD, and apoptosis were inhibited by IC-3, a metalloprotease inhibitor. Increased levels of p75NTR and TACE were observed in photoreceptor cells of animals with photic injury. Our findings support a role for TACE in the proteolytic cleavage of p75NTR and light-induced apoptosis.

Isolation of components of admittance change in rod outer segments.

1. Rods were separated by equilibration on a bovine serum albumin (BSA) density gradient into two major fractions, differing in their response to light.2. In one fraction the response, measured as a change in the real part of admittance DeltaG, appeared to consist exclusively of component I, while in the other, component II was prominent.3. Evidence is presented that component I arose in damaged rods. This follows from observations on rods which have been deliberately damaged by freezing followed by thawing, or by fragmentation.4. In such damaged rods, component II was absent while component I was increased in amplitude.5. The frequency dependence of component I in isolation was characterized as a positive DeltaG of constant amplitude from low frequencies up to the characteristic frequency f(Y) for the major dispersion of admittance. Above this frequency, it declined to a variable extent.6. The frequency dependence of component II observed in isolation was consistent with the previous analysis.7. A negative-going DeltaG is described which was linear with the amount of rhodopsin bleached and which was frequency independent up to the highest frequency of measurement (17 MHz).8. The origins of component I and the negative component are discussed.

Isolation of temperature-sensitive diphtheria toxins in yeast and their effects on Drosophila cells.

We have isolated temperature-sensitive diphtheria toxins (DT-A(ts)) to develop a method that allows temporal impedement of cellular functions. Four DT-A(ts) genes were isolated in a mutagenesis screen using the yeast, Saccharomyces cerevisiae. When expressed in yeast, these DT-A(ts) arrest growth at 18 degrees C but not at 30 degrees C. Three DT-A(ts) were subsequently tested in the R1-R6 photoreceptor cells of transgenic fruit flies, Drosophila melanogaster. The toxins show similar temperature dependence in both organisms, suggesting that they may be useful in a wide range of non-homeothermic species. DNA sequence analysis revealed that three of the four DT-A(ts) mutations are novel. Interestingly, the fourth DT-A(ts) carries the same point mutation as the extensively characterized CRM197, an ADP ribosyltransferase-defective form of diphtheria toxin.

Localized current field hyperthermia: effect on normal ocular tissue.

Using a 500 kHz radiofrequency electromagnetic heating system, the effects of localized current field hyperthermia in normal rabbit eyes were examined. A specially designed scleral plaque placed on normal rabbit eyes was heated to temperatures of 43 degrees C, 45 degrees C, and 47 degrees C for a period of 45 min. The effects of hyperthermia were monitored by clinical examination, fluorescein angiography, electroretinography and histopathology. A graded effect with increasing temperature was found at the lower temperature, and it was confined to the treatment field. At 47 degrees C the electroretinogram was extinguished due to diffuse photoreceptor damage outside the treatment field, as demonstrated by histopathology and electron microscopy. This study indicates that hyperthermia at 45 degrees C for 45 min is the maximum allowable temperature without causing diffuse retinal damage in the normal rabbit eye.

Therapeutic range of repetitive nanosecond laser exposures in selective RPE photocoagulation.

BACKGROUND: The aim of this study was to investigate whether selective damage the RPE while sparing the adjacent photoreceptors is possible with repetitive 200-ns pulses of Nd:YAG laser (532 nm) and what potential side effects can be expected with higher pulse energies. METHODS: We irradiated the retinas of 19 eyes of 10 chinchilla rabbits with 500 pulses from a Nd:YAG laser, each 200 ns in duration, at a repetition rate of 500 Hz (158 microns, 0-120 microJ). Threshold curves for different effects were established. Representative lesions were investigated by light and transmission electron microscopy. RESULTS: It was possible to produce lesions, which were only visible by fluorescein angiography. The ED50 threshold energy per pulse for visibility by fluorescein angiography was 2.1 microJ per pulse, for visibility by ophthalmoscopy 8.6 microJ. Bubble formation, an uncommon phenomenon in retinal photocoagulation, occurred at energies of 15-25 microJ. Hemorrhage occurred at surprisingly high energy levels of more than 100 microJ. Histology performed on lesions visible only by angiography showed damage primarily to the RPE and outer segments, with very little damage to some inner segments dependent on the energy used. CONCLUSIONS: Selective RPE damage is possible with repetitive 200-ns laser pulses and appropriate energy; however, the collateral damage to the adjacent retina is more pronounced than with repetitive microsecond laser pulses. There is no risk of hemorrhage of retinal photocoagulation with the repetitive 200-ns laser pulses at low energy levels which would be used clinically.

Understanding the origin of visual percepts elicited by electrical stimulation of the human retina.

BACKGROUND: The success of a retinal prosthesis for patients with outer retinal degeneration (ORD) depends on the ability to electrically stimulate retinal cells other than photoreceptors. Experiments were undertaken in human volunteers to ascertain whether electrical stimulation of cells other than photoreceptors will result in the perception of light. METHODS: In two subjects, two areas of laser damage (argon green and krypton red) were created in an eye scheduled for exenteration due to recurrent cancer near the eye. In the operating room prior to exenteration, under local anesthesia, a hand-held stimulating device was inserted via the pars plana and positioned over the damaged areas and normal retina. Subjects' psychophysical responses to electrical stimulation were recorded. RESULTS: In both subjects, electrical stimulation produced the following perceptions. Normal retina: dark oval (subject 1), dark half-moon (subject 2); krypton red laser-treated retina: small, white light (both subjects); argon green laser treated retina: thin thread (subject 1), thin hook (subject 2). Histologic evaluation of the krypton red-treated retina showed damage confined to the outer retinal layers, while the argon green-treated area evinced damage to both the outer and the inner nuclear layers. CONCLUSION: The perception produced by electrical stimulation was dependent on the retinal cells present. Electrical stimulation of the krypton red-ablated area best simulated the electrically elicited visual perceptions of our blind, ORD patients, suggesting that the site of stimulation in blind patients is the inner retinal neurons.

Basic fibroblast growth factor and local injury protect photoreceptors from light damage in the rat.

Injection of basic fibroblast growth factor (bFGF) into the eye, intravitreally or subretinally, delays photoreceptor degeneration in inherited retinal dystrophy in the rat, as does local injury to the retina (Faktorovich et al., 1990). To determine whether this heparin-binding peptide or local injury is effective in any other form of photoreceptor degeneration, we examined their protective roles in light damage. Albino rats of the F344 strain were exposed to 1 or 2 weeks of constant fluorescent light (115-200 footcandles), either with or without 1 microliter of bFGF solution (1150 ng/microliters in PBS) injected intravitreally or subretinally 2 d before the start of light exposure. Uninjected and intravitreally PBS-injected controls showed the loss of a majority of photoreceptor nuclei and the loss of most inner and outer segments after 1 week of light exposure, while intravitreal injection of bFGF resulted in significant photoreceptor rescue. The outer nuclear layer in bFGF-injected eyes was two to three times thicker than in controls, and the inner and outer segments showed a much greater degree of integrity. Following recovery in cyclic light for 10 d after 1 week of constant light exposure, bFGF-injected eyes showed much greater regeneration of photoreceptor inner and outer segments than did the controls. bFGF also increased the incidence of presumptive macrophages, located predominantly in the inner retina, but the evidence suggests they are not directly involved in photoreceptor rescue. Subretinal injection of bFGF resulted in photoreceptor rescue throughout most of the superior hemisphere in which the injection was made, with rescue extending into the inferior hemisphere in many of the eyes. Remarkably, the insertion of a dry needle or injection of PBS into the subretinal space also resulted in widespread photoreceptor rescue, extending through 70% or more of the superior hemisphere, and sometimes into the inferior hemispheres. This implicates the release and widespread diffusion of some endogenous survival-promoting factor from the site of injury in the retina. Our findings indicate that the photoreceptor rescue activity of bFGF is not restricted to inherited retinal dystrophy in the rat, and that light damage is an excellent model for studying the cellular site(s), kinetics, and molecular mechanisms of both the normal function of bFGF and its survival-promoting activity. Moreover, the injury-related rescue suggests that survival-promoting factors are readily available to provide a protective role in case of injury to the retina, presumably comparable to those that mediate the "conditioning lesion" effect in other neuronal systems.

Histopathology of commotio retinae.

The pathogenesis of commotio retinae in animal models has included extracellular edema, intracellular edema, and photoreceptor outer segment disruption. Histopathologic findings obtained within 24 hours of blunt trauma in a human eye with clinically-observed commotio retinae revealed photoreceptor outer segment disruption and damage to the retinal pigment epithelium. The major site of injury in commotio retinae seems to be at the level of the photoreceptor outer segment-retinal pigment epithelium junction.

Repair of outer blood-retinal barrier after severe ocular blunt trauma in rabbits.

Retinal contusion is a leading cause of visual loss in ocular blunt trauma. However, its pathogenesis remains controversial. We established a rabbit model of severe retinal contusion with energy of about 2.87 J. Typical retinal edema and sometimes subretinal hemorrhage reproducibly occurred at the posterior pole after injury. These subsided 1 week later with depigmentation in the lesion. Histopathological examination revealed severe damage of the outer layer of retina, for example, disruption of retinal pigment epithelium (RPE) and photoreceptors. Electroretinography showed a decrease in the b wave by 38-47% in amplitudes (P < 0.01) during the first 3 days and then returned, although not to normal level. To investigate the damage and repair of blood-retinal barrier (BRB), 5 ml 2% lanthanum solution (La) was injected via the common carotid artery 1-2 min before enucleation. La diffused in the interphotoreceptor space through the damaged junctions of RPE 1 h-3 days after injury. La also reached the nuclei level of photoreceptors up to 14 days after injury. Although a glial scar with scattered RPE cells attached to Bruch's membrane in the severely damage area, no La diffusion was found in the retina 4 weeks after trauma. These results showed incomplete repair of outer BRB after severe blunt trauma.