Retinal Threshold Research Articles

Mild Intraocular Pressure Elevation in Mice Reveals Distinct Retinal Ganglion Cell Functional Thresholds and Pressure-Dependent Properties.

Elevation of intraocular pressure (IOP) causes retinal ganglion cell (RGC) dysfunction and death and is a major risk factor for glaucoma. We used a bead injection technique to increase IOP in mice of both genders by an average of ∼3 mmHg for 2 weeks. This level of IOP elevation was lower than that achieved in other studies, which allowed for the study of subtle IOP effects. We used multielectrode array recordings to determine the cellular responses of RGCs exposed to this mild degree of IOP elevation. We found that RGC photopic receptive field (RF) center size and whole-field RGC firing rates were unaffected by IOP elevation. In contrast, we found that the temporal properties of RGC photopic responses in the RF center were accelerated, particularly in ON sustained cells. We also detected a loss of antagonistic surround in several RGC subtypes. Finally, spontaneous firing rate, interspike interval variance, and contrast sensitivity were altered according to the magnitude of IOP exposure and also displayed an IOP-dependent effect. Together, these results suggest that individual RGC physiologic parameters have unique IOP-related functional thresholds that exist concurrently and change following IOP elevation according to specific patterns. Furthermore, even subtle IOP elevation can impart profound changes in RGC function, which in some cases may occur in an IOP-dependent manner. This system of overlapping functional thresholds likely underlies the complex effects of elevated IOP on the retina.SIGNIFICANCE STATEMENT Retinal ganglion cells (RGCs) are the obligate output neurons of the retina and are injured by elevated intraocular pressure (IOP) in diseases such as glaucoma. In this study, a subtle elevation of IOP in mice for 2 weeks revealed distinct IOP-related functional thresholds for specific RGC physiologic parameters and sometimes showed an IOP-dependent effect. These data suggest that overlapping IOP-related thresholds and response profiles exist simultaneously in RGCs and throughout the retina. These overlapping thresholds likely explain the range of RGC responses that occur following IOP elevation and highlight the wide capacity of neurons to respond in a diseased state.

A virtual model of the retina based on histological data as a tool for evaluation of the visual fields

Background: To settle the fundamentals of a numerical procedure that relates retinal ganglion-cell density and threshold sensitivity in the visual field. The sensitivity of a generated retina and visual pathways to virtual stimuli are simulated, and the conditions required to reproduce glaucoma-type defects both in the optic-nerve head (ONH) and visual fields are explored. Methods: A definition of selected structural elements of the optic pathways is a requisite to a translation of clinical knowledge to computer programs for visual field exploration. The program is able to generate a database of normalized visual fields. The relationship between the number of extant receptive fields and threshold sensitivity is plotted for background sensitivity and corresponding automated perimetry. A solution in two planes to the 3D distribution of axons in the ONH is proposed. Visual fields with induced damage in the optic disc are comparable in pattern and quantity to glaucomatous records. Results: The two-level simulation of the ONH facilitates the analysis of optic-cup/retinal defects. We can generate the virtual optic pathways tailored to the age and morphology of the patient’s eye, and it is possible to reproduce glaucomatous damage by “reverse engineering” engineering. The virtual cortical model renders a quantitative relationship between visual defect and neural damage. Conclusions: A two-level computing of the retina/optic nerve facilitates the analysis of neuroretinal defects and can be incorporated to automatic perimeters to facilitate visual field analysis.

Clinical effectiveness study of transcranial direct current stimulation in amblyopic children

to assess the neurophysiological effect and clinical effectiveness of transcranial direct current stimulation in combination with drug therapy in amblyopic children. The study involved 32 healthy children in the age of 5-12 years and 97 patients of the same age with refractive strabismic amblyopia. All study subjects underwent standard examination including ophthalmological (visometry, refractometry in normal conditions and in cycloplegia, biomicroscopy, ophthalmoscopy, type of vision), neurophysiological methods (determination of retinal electric sensitivity threshold, electric lability of optic nerve, amplitude and latency period of visual evoked potentials, electroencephalogram wave amplitudes, localization of peak electrical activity area of the cerebral cortex), assessment of neuropsychic development and estimation of mental development coefficient with age tests. Dynamics of neurophysiological parameters shows that healthy children develop fully functional retina, visual cortex and cortical-subcortical connections by 12 years. Children with refractive strabismic amblyopia in all age groups show statistically significant (р<0.05) deterioration of neurophysiological parameters of the visual analyzer, retardation of cortical-subcortical connections formation and lower electrical activity of the cerebral cortex. Amblyopic children show lower coefficients of mental development accompanied by intellectual deficiency and deterioration of learning ability. Proposed treatment method improved neurophysiological parameters of the visual analyzer in 83.5% of cases and increased visual acuity in 81.4% of cases. Improvement of psychological development resulted in better logical thinking, memory reinforcement and better adaptation to school educational environment in 86.6% of children.

Visual Subfield Progression in Glaucoma Subtypes.

Purpose To investigate visual field progression pattern and factors associated with progression in patients with primary open-angle glaucoma (POAG), normal-tension glaucoma (NTG), and chronic angle-closure glaucoma (CACG). Methods The raw data of the 30-2 Humphrey Field Analyzer from glaucoma patients with definite visual field progression were processed with pointwise linear regression (PLR) analysis. The rate of change of retinal threshold sensitivity in the ten glaucoma hemifield test (GHT) zones, the upper and the lower hemifields, and the whole field was evaluated and was correlated with patients' basic demographic data. Results An average follow-up of 6.94 ± 2.69 years that showed the rate of change of visual field threshold sensitivity was correlated with the peak posttreatment intraocular pressure (IOP) and the long-term IOP fluctuations in all GHT zones except in the inferior arcuate area. The baseline IOP, the trough posttreatment IOP, the refractive status, and the CCT were not correlated with VF progression. Conclusion The rate of visual field progression was correlated with the peak posttreatment IOP and the long-term IOP fluctuation but with subfield differences.

EFFICACY OF NEUROPROTECTIVE SUPPORT OF THE PATIENTS WITH DIABETES MELLITUS DURING PANRETINAL LASER PHOTOCOAGULATION

The purpose of the study was to assess the efficacy of Citicoline influence on morphometric and functional parameters of retina in patients with diabetes mellitus after panretinal laser photocoagulation. We observed 47 patients (79 eyes) with preproliferative diabetic retinopathy which underwent panretinal laser photocoagulation in 3 stages. 28 patients (43 eyes) of main group received Citicoline therapy during 2 months after 1st stage of panretinal laser photocoagulation. The efficacy criteria were the corrected visual acuity changes from baseline, thickness of retinal nerve fiber layer and retinal threshold sensitivity before, after 1, 3, and 6 months after laser photocoagulation. Our results suggest that Citicoline administration after panretinal laser photocoagulation has potential effective influence on retinal nerve fiber layer thickness that allows to recommend it for use as medical support of panretinal laser photocoagulation in patients with diabetes mellitus.

Inner retina changes in hydroxychloroquine patients

PurposeTo study if hydroxychloroquine (HCQ) patients with apparent no retinal toxicity will show lower retinal thickness in inner layers as compared to healthy controls.MethodsRetrospective study of 43 patients (86 eyes) evaluated for HCQ macular toxicity with spectral‐domain OCT (SD‐OCT) and with no OCT signs of maculopathy were subdivided into two groups: (1) no blunting of the foveal contour (foveal splaying), (2) with foveal splaying. Age and sex‐matched controls were used for comparison. Automated retinal layer segmentation at the center of fovea and at a radius of 3 (parafoveal) to 6mm (perifoveal) from the superior, inferior, temporal and nasal sectors was performed. Statistical analysis using two sample t‐test was made to calculate significant results between groups.ResultsCenter macular and internal retinal layers thickness in all parafoveal sectors, particularly in the retinal nerve fibre (RNFL) and ganglion cell layer (GCL), was statistically reduced when compared to control group (p &lt; 0.05) and differed between group 1 and 2. RNFL thickness was also reduced in all perifoveal sectors but temporal sector (p &lt; 0.05) and inner plexiform layer and inner nuclear layer thickness showed only significant reduction in foveal and nasal parafoveal sector (p &lt; 0.05) in HCQ eyes. No significant differences in outer layers was observed between groups.ConclusionsSmall changes in inner retinal layers thickness have been described with HCQ use and conflicting correlation with HCQ toxicity is present in the literature. This study supports that inner retina at the fovea and parafovea is thinner in patients with no outer retinal OCT signs of HCQ toxicity. Further investigation is needed to assess if an inner retinal thickness reduction threshold could serve as valuable tool for identifying patients with increased risk of HCQ maculopathy.

Validation of a computer model to predict laser induced retinal injury thresholds

A computer model was developed for calculating the intraocular energy producing a thermally induced retinal threshold lesion upon exposure to optical radiation. The model parameters were adjusted to best fit the threshold levels reported in the literature in-vivo, with nonhuman primates at wavelengths between 413 and 1338 nm, exposure durations between 100 μs and 50 min, and various retinal spot sizes and exposures to paramacular or macular sites. Comparison of the calculated thresholds with all consistent experimental results published over the past 50 years shows good agreement with a standard deviation of 31%. This validates the model to be used for quantitative predictions of retinal injury thresholds as well as for risk analysis of laser products and supports the development of exposure limits. The spread of data suggests that accuracy cannot be improved much further due to experimental uncertainties and intersubject variability.

Rabbit Retinal Ganglion Cell Activation Thresholds in Response to Various Electrical Stimulation Waveforms using a Different Spatial Resolution Electrode Array

Rabbit Retinal Ganglion Cell Activation Thresholds in Response to Various Electrical Stimulation Waveforms using a Different Spatial Resolution Electrode Array

P189 Transcranial modulation of visually induced gamma power: a concurrent TACS-MEG study

Introduction Alpha oscillations (8–12 Hz) are proposed to mediate ‘attentional gating’ by suppressing neuronal processing in task-irrelevant sensory regions, reflected by ‘pulsed-inhibition’ of stimulus-induced gamma-band activity (40–100 Hz). Concurrent TACS-MEG has the potential to reveal TACS entrainment of alpha oscillations at the stimulation site and thus their causal impact on neuronal activity representing stimulus processing. Objectives We aimed to provide evidence that TACS can entrain the phase of alpha oscillations in the visual cortex by assessing its modulatory impact on the power of visual stimulus-induced gamma oscillations via simultaneous MEG recordings. Materials & methods TACS was applied during MEG in intermingled 5.4s trials either in Oz-Cz or FPz-Cz montage. Montage and stimulation frequency were randomized across trials, applying either individual alpha frequency (IAF), IAF−4 Hz, IAF+4 Hz, or no stimulation, resulting in a 2 (Montage) × 3 (Frequency) design plus a ‘NoStim’ condition. Stimulation intensity for both montages was adjusted separately to 95% retinal phosphene threshold. Participants performed a simple visual detection task, attending an inward moving grating, known to induce strong occipital gamma responses. TACS artifacts were reduced via regression methods, LCMV beamformer time-course extraction from the visual cortex, and high-pass filtering. Importantly, the gamma frequency of interest (∼50–60 Hz) was largely unaffected by TACS artifacts. We compared TACS-to-gamma phase-power coupling (PAC) for the respective experimental conditions. Results We found a rhythmic modulation of stimulus-induced gamma power by TACS at IAF (i.e., TACS-gamma phase-amplitude coupling) for the Oz-Cz montage, but not for the FPz-Cz montage which was introduced to control for subthreshold retinal entrainment effects. Conclusion Our findings (i) demonstrate that concurrent TACS-MEG can principally be used to study cross-frequency-coupling between transcranially entrained slower and spontaneous or stimulus-related faster oscillations, (ii) cannot merely result from subthreshold retinal entrainment, and (iii) suggest that alpha oscillations are indeed a possible means for top-down suppression of bottom-up sensory processing.

Normal values for microperimetry with the MAIA microperimeter: sensitivity and fixation analysis in healthy adults and children.

To establish normative values of retinal sensitivity and parameters describing the fixation pattern using macular analyzer integrity assessment (MAIA) microperimetry (Centervue, Padova, Italy) in adults and children. A sample of 237 eyes of 237 healthy subjects aged between 10 and 70 years (mean age 30.63 ± 16.23 years) was evaluated using the MAIA microperimeter. The following parameters provided by the MAIA device were evaluated: average threshold (AT), macular integrity, fixation indexes (P1% and P2%), bivariate contour ellipse area (BCEA) for 95% and 63% of points, and horizontal (H) and vertical (V) axes of the ellipse of fixation. Differences between different age-related groups were evaluated. Correlation of microperimetric parameters with age was also assessed. Median retinal sensitivity of the overall sample was 32.90 dB (interquartile range 1.80 dB). Median P1 and P2 values were 98.00% (6.00) and 100.00% (1.00), respectively. Median BCEA for 95% and 63% of points were 2.40°2 (4.50) and 0.30°2 (0.50), respectively. Median H and V were 0.90° (0.80) and 0.90° (0.70), respectively. Age was significantly correlated with the following parameters in subjects from 21 to 70 years of age (p<0.01): AT (rho -0.47), P1 (rho -0.37), BCEA95 (rho 0.43), BCEA63 (rho 0.42), H (rho 0.43), and V (rho 0.40). Retinal sensitivity in healthy eyes tends to decrease with age as well as the stability of the pattern of fixation. A normative database in terms of retinal sensitivity threshold and fixation performance can be established in this type of eyes.

Retinal thermal damage threshold dependence on exposure duration for the transitional near-infrared laser radiation at 1319 nm.

The retinal damage effects induced by transitional near-infrared (NIR) lasers have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. In this paper, the in-vivo retinal damage ED50 thresholds were determined in chinchilla grey rabbits for 1319 nm laser radiation for exposure durations from 0.1 s to 10 s. The incident corneal irradiance diameter was fixed at 5 mm. The ED50 thresholds given in terms of the total intraocular energy (TIE) for exposure durations of 0.1, 1 and 10 s were 1.36, 6.33 and 28.6 J respectively. The ED50 thresholds were correlated by a power law equation, ED50 = 6.31t0.66 [J] where t is time [s], with correlation coefficient R = 0.9999. There exists a sufficient safety margin (factor of 28~60) between the human ED50 thresholds derived from the rabbit and the maximum permissible exposure (MPE) values in the current laser safety standards.

Burst Firing in a Motion-Sensitive Neural Pathway Correlates with Expansion Properties of Looming Objects that Evoke Avoidance Behaviors.

The locust visual system contains a well-defined motion-sensitive pathway that transfers visual input to motor centers involved in predator evasion and collision avoidance. One interneuron in this pathway, the descending contralateral movement detector (DCMD), is typically described as using rate coding; edge expansion of approaching objects causes an increased rate of neuronal firing that peaks after a certain retinal threshold angle is exceeded. However, evidence of intrinsic DCMD bursting properties combined with observable oscillations in mean firing rates and tight clustering of spikes in raw traces, suggest that bursting may be important for motion detection. Sensory neuron bursting provides important timing information about dynamic stimuli in many model systems, yet no studies have rigorously investigated if bursting occurs in the locust DCMD during object approach. We presented repetitions of 30 looming stimuli known to generate behavioral responses to each of 20 locusts in order to identify and quantify putative bursting activity in the DCMD. Overall, we found a bimodal distribution of inter-spike intervals (ISI) with peaks of more frequent and shorter ISIs occurring from 1–8 ms and longer less frequent ISIs occurring from 40–50 ms. Subsequent analysis identified bursts and isolated single spikes from the responses. Bursting frequency increased in the latter phase of an approach and peaked at the time of collision, while isolated spiking was predominant during the beginning of stimulus approach. We also found that the majority of inter-burst intervals (IBIs) occurred at 40–50 ms (or 20–25 bursts/s). Bursting also occurred across varied stimulus parameters and suggests that burst timing may be a key component of looming detection. Our findings suggest that the DCMD uses two modes of coding to transmit information about looming stimuli and that these modes change dynamically with a changing stimulus at a behaviorally-relevant time.

Cystoid macular edema after femtosecond laser–assisted versus phacoemulsification cataract surgery

To evaluate the incidence of postoperative clinical cystoid macular edema (CME) associated with femtosecond laser-assisted cataract surgery (Catalys laser system) versus phacoemulsification cataract surgery. Launceston Eye Institute, Launceston, Tasmania, Australia. Nonrandomized, single-surgeon, prospective, comparative cohort case series. Patients who had femtosecond laser-assisted cataract surgery and phacoemulsification cataract surgery between March 2012 and July 2014 were included in the study. The femtosecond laser-assisted cataract surgery group had anterior capsulotomy, lens fragmentation, with or without corneal incisions via femtosecond laser pretreatment. Standard phacoemulsification surgery and foldable acrylic intraocular lens insertion proceeded in all cases. All patients received topical nonsteroidal drops commencing 2 days preoperatively and continuing for 4 weeks postoperatively. The incidence of postoperative clinical CME (confirmed by optical coherence tomography) and comparison between groups were measured. The main outcome measure was the clinical CME rates. Of the eyes, 833 had femtosecond laser-assisted cataract surgery amd 458 had standard phacoemulsification cataract surgery. Both groups had similar baseline parameters. There were 7 cases of postoperative CME (0.8%) in the femtosecond laser-assisted cataract surgery group compared to 1 case (0.2%) in the phacoemulsification cataract surgery group, highlighting a trend toward greater cystoid macular edema in the femtosecond laser-assisted cataract surgery group. This correlated with a change in laser treatment speed (due to a software upgrade), suggesting that retinal safety thresholds need further careful analysis. Increased CME might be a subthreshold retinal injury safety signal after femtosecond laser pretreatment and warrants further study. There are no financial or conflicts of interest for any author.

Effect of Myopic Defocus on Visual Acuity after Phakic Intraocular Lens Implantation and Wavefront-guided Laser in Situ Keratomileusis.

This study aimed to investigate the effect of myopic defocus on visual acuity after phakic intraocular lens (IOL) implantation and wavefront-guided laser in situ keratomileusis (wfg-LASIK). Our prospective study comprised thirty eyes undergoing posterior chamber phakic IOL implantation and 30 eyes undergoing wfg-LASIK. We randomly measured visual acuity under myopic defocus after cycloplegic and non-cycloplegic correction. We also calculated the modulation transfer function by optical simulation and estimated visual acuity from Campbell & Green’s retinal threshold curve. Visual acuity in the phakic IOL group was significantly better than that in the wfg-LASIK group at myopic defocus levels of 0, –1, and –2 D (p < 0.001, p < 0.001, and p = 0.02, Mann-Whitney U-test), but not at a defocus of –3 D (p = 0.30). Similar results were also obtained in a cycloplegic condition. Decimal visual acuity values at a myopic defocus of 0, −1, −2, and -3 D by optical simulation were estimated to be 1.95, 1.21, 0.97, and 0.75 in the phakic IOL group, and 1.39, 1.11, 0.94, and 0.71 in the wfg-LASIK group, respectively. From clinical and optical viewpoints, phakic IOL implantation was superior to wfg-LASIK in terms of the postoperative visual performance, even in the presence of low to moderate myopic regression.

Metanx and early stages of diabetic retinopathy.

l-Methylfolate, pyridoxal 5'-phosphate, and methylcobalamin, individually have been reported to have beneficial effects on diabetes-induced defects. The possibility that combining these therapeutic approaches might have additional benefit led us to investigate the effect of Metanx against development of early stages of diabetic retinopathy in a mouse model. C57BL/6J mice were made diabetic with streptozotocin, and some were given Metanx (a combination food product) mixed in the food at a dose of 5 mg/kg of body weight. Mice were killed at 2 months and 10 months of study for assessment of retinal function, retinal vascular histopathology, accumulation of albumin in neural retina, and biochemical and physiological abnormalities in retina. Two months of diabetes significantly increased leukostasis within retinal vessels and superoxide generation by the retina. Diabetes also significantly increased expression of intercellular adhesion molecule-1 (ICAM-1) and phosphorylation of IκB. Daily consumption of Metanx significantly inhibited all of these abnormalities. Ten months of diabetes significantly increased the degeneration of retinal capillaries and impaired visual function (spatial frequency threshold (SFT) and a parameter of contrast sensitivity) compared to nondiabetic controls. Daily consumption of Metanx for 10 months inhibited impairment of SFT but had no significant beneficial effect on capillary degeneration, pericyte loss, or the estimate of contrast sensitivity. Metanx inhibited a diabetes-induced defect in retinal spatial frequency threshold and inhibited measures of oxidative stress and inflammation. It had no significant effect on contrast sensitivity or retinal capillary degeneration. Nutritional management with Metanx may help inhibit diabetes-induced defects in visual function.

Correlation of papillomacular nerve fiber bundle thickness with central visual function in open-angle glaucoma.

Purpose. To determine the correlation of reduced retinal thickness in the central papillomacular bundle (CPB) to central visual function, including central retinal sensitivity and visual acuity, in glaucoma patients. Methods. This study enrolled 50 eyes of 50 patients with open-angle glaucoma who were carefully screened for comorbid conditions that can cause decreased central visual function, such as cataracts or macular diseases. We used a novel CPB analysis comprising a program for optical coherence tomography that measured RNFL thickness and GCC thickness in the CPB and divided lengthwise into three parts (upper, middle, and lower CPB). The relationship of these parameters, including conventional macular thickness, to visual field sensitivity in four central standard automated perimetry points (the central four thresholds) and BCVA was analyzed. Results. The two parameters most highly correlated with central four thresholds were macular GCCT and macular RNFLT. The two parameters most highly correlated with BCVA were middle CPB (mid-CPB) GCCT and mid-CPB RNFLT. A multiple regression analysis revealed that mid-CPB GCCT was an independent factor impacting central retinal thresholds and BCVA. Conclusions. Our results suggest that mid-CPB RNFLT and GCCT, parameters of a novel papillomacular bundle analysis, are candidate biomarkers of decreased central visual function in glaucomatous eyes.

Results of complex treatment of diabetic retinopathy

Aim. To investigate the results of complex treatment of diabetic retinopathy. Methods and results. Diabetic retinopathy (DR) is a late complication of diabetes mellitus (DM), which leads to severe disability and significantly reduces the quality of life of patients. In the DR peroxidation of proteins with decreased antioxidant activity is enhanced in the blood of patients. These findings point to the desirability of placing products containing short carotenoids into the complex therapy of diabetic patients with DR in order to maintain visual function.Conclusion. In the DR under the influence of short carotenoids in complex treatment decreased severity of microvascular complications, increased total retinal lability by 8-16 Hz on the average are noted, the level of electrical retinal sensitivity phosphene threshold decreased to 87 uA (p &lt;0.05), photosensitivity of the retina increased by 16 dB on the average, the amount of relative scotomas reduced.

Relationships of retinal structure and humphrey 24-2 visual field thresholds in patients with glaucoma.

To determine relationships between spectral-domain optical coherence tomography (SD-OCT) derived regional damage to the retinal ganglion cell-axonal complex (RGC-AC) and visual thresholds for each location of the Humphrey 24-2 visual field, in all stages of open-angle glaucoma. Patients with early, moderate, and advanced glaucoma were recruited from a tertiary glaucoma clinic. Humphrey 24-2 and 9-field Spectralis SD-OCT were acquired for each subject. Individual OCT volumes were aligned, nerve fiber layer (NFL), ganglion cell and inner plexiform layers (GCL+IPL) cosegmented. These layers were then partitioned into 54 sectors corresponding to the 24-2 grid. A Support Vector Machine was trained independently for each sector to predict the sector threshold, using these structural properties. One hundred twenty-two consecutive subjects, 43 early, 39 moderate, and 40 advanced, glaucoma were included (122 eyes). Average correlation coefficient (R) was 0.68 (0.47-0.82), and average root mean square error (RMSE) was 6.92 dB (3.93-8.68 dB). Prediction performance averaged over the entire field, superior hemifield, and inferior hemifield had R (RMSE) values of 0.77 (3.76), 0.80 (5.05), and 0.84 (3.80) dB, respectively. Predicting individual 24-2 visual field thresholds from structural information derived from nine-field SD-OCT local NFL and GCL+IPL thicknesses using the RGC-AC concept is feasible, showing the potential for the predictive ability of SD-OCT structural information for visual function. Ultimately, it may be feasible to complement and reduce the burden of subjective visual field testing in glaucoma patients with predicted function derived objectively from OCT.

Laser-induced retinal damage threshold for repetitive-pulse exposure to 100-μs pulses.

The laser-induced retinal injury thresholds for repetitive-pulse exposures to 100-μs-duration pulses at a wavelength of 532 nm have been determined for exposures of up to 1000 pulses in an in vivo model. The ED50 was measured for pulse repetition frequencies of 50 and 1000 Hz. Exposures to collimated beams producing a minimal retinal beam spot and to divergent beams producing a 100-μm-diameter retinal beam spot were considered. The ED50 for a 100-μs exposure was measured to be 12.8 μJ total intraocular energy for a minimal retinal beam spot exposure and 18.1 μJ total intraocular energy for a 100-μm-diameter retinal beam spot. The threshold for exposures to N > 1 pulse was found to be the same for both pulse repetition frequencies. The variation of the ED50 with the number of pulses is described well by the probability summation model, in which each pulse is considered an independent event. This is consistent with a threshold-level damage mechanism of microcavitation for single-pulse 100-μs-duration exposures. The data support the maximum permissible exposure levels for repetitive-pulse exposure promulgated in the most recent laser safety guidelines.

POFAL Study: «Protection Oculaire Face aux Agressions Lasers», Phase I

AbstractPurpose Risk of laser beam exposure, particularly to laser "pointers" easily available on open sale or on internet increases every year. Many incidents and accidents have been reported over the last three years in France. The purpose of this study is to try to determine a retinal lesion threshold secondary to such exposures.Methods A laser system (532nm) with a power and duration control has been developed specifically for this study to achieve exposure. A first phase was performed in pigmented rodents with different combinations of time ‐ power beam exposure. Powers ranged from 0.5 to 4.5mW and durations from 0.1 to 0.35sec. A second phase was performed in non‐human primates (NPH) with blink reflex time (0.25sec) and 1, 2, 3.5 and 4.5mW. Histological analysis of outer layers and immunoassay to assess tissular damage (GFAP) were performed to each phase.Results A significant correlation between energy and photoreceptor thickness is found in rodents. Histological analysis did not find a structural alteration or combination threshold. Immunoassay confirm tissular damage in inner layers. Photoreceptors alterations are located at foveal zone in NHP. Outer layers thickness is statistically lower when exposure power is greater than 1mW. A significant correlation between energy and photoreceptor thickness is also found only in foveal zone.Conclusion This study reports systematic tissue damage when power exposures correspond to upper limits of the class II lasers (1mW). This is the first in‐vivo study analyzing exposure effects to low power laser beam or easily accessible. These initial results are used to guide and adapt research on protection systems for people exposed.