Restoration of retinal structure and function after selective photocoagulation

Morphology, Fundus Autofluorescence, and Retinal Sensitivity of Photocoagulated Lesions in Proliferative Diabetic Retinopathy

Purpose

To evaluate the relationships among morphology, fundus autofluorescence (FAF), and retinal sensitivity of photocoagulated lesions more than 1 year after panretinal photocoagulation in patients with proliferative diabetic retinopathy and good vision.

Methods

This retrospective cohort study included patients with proliferative diabetic retinopathy who had undergone panretinal photocoagulation more than 1 year ago. The photocoagulated lesions were classified according to FAF levels: group A, no FAF; group B, diffuse FAF; group C, white-dotted centers with diffuse FAF; group D, white-dotted centers without FAF; and group E, controls. The main outcome measures were FAF, retinal sensitivity, and morphology of the photocoagulated lesions.

Results

The median sensitivity values and number of photocoagulated lesions in groups A (n = 37), B (n = 39), C (n = 4), D (n = 15), and E (n = 39) were 0 dB, 18.0 dB, 13.9 dB, 0.3 dB, and 21.5 dB, respectively. EZ lines were absent in 93.5%, 18.1%, 50%, 93.3%, and 0% of lesions in groups A, B, C, D, and E, respectively. The inner retinal layer was damaged in 45.2%, 3.0%, 50%, 73.3%, and 0% lesions in groups A, B, C, D, and E, respectively. Statistically significant between-group differences were observed in the retinal sensitivities of the photocoagulated lesions, presence of EZ lines, and damage to the inner retinal layer (p < 0.05).

Conclusions

The photoreceptors in most photocoagulated lesions with diffuse FAF retain their morphology and function.

Translational Relevance

Using fundus autofluorescence, the damage to photoreceptors after panretinal photocoagulation in patients with diabetes can be estimated in a noninvasive manner. This process can help in determining the need for additional panretinal photocoagulation.

Modeling complex age-related eye disease

Modeling complex eye diseases like age-related macular degeneration (AMD) and glaucoma poses significant challenges, since these conditions depend highly on age-related changes that occur over several decades, with many contributing factors remaining unknown. Although both diseases exhibit a relatively high heritability of >50%, a large proportion of individuals carrying AMD- or glaucoma-associated genetic risk variants will never develop these diseases. Furthermore, several environmental and lifestyle factors contribute to and modulate the pathogenesis and progression of AMD and glaucoma. Several strategies replicate the impact of genetic risk variants, pathobiological pathways and environmental and lifestyle factors in AMD and glaucoma in mice and other species. In this review we will primarily discuss the most commonly available mouse models, which have and will likely continue to improve our understanding of the pathobiology of age-related eye diseases. Uncertainties persist whether small animal models can truly recapitulate disease progression and vision loss in patients, raising doubts regarding their usefulness when testing novel gene or drug therapies. We will elaborate on concerns that relate to shorter lifespan, body size and allometries, lack of macula and a true lamina cribrosa, as well as absence and sequence disparities of certain genes and differences in their chromosomal location in mice. Since biological, rather than chronological, age likely predisposes an organism for both glaucoma and AMD, more rapidly aging organisms like small rodents may open up possibilities that will make research of these diseases more timely and financially feasible. On the other hand, due to the above-mentioned anatomical and physiological features, as well as pharmacokinetic and -dynamic differences small animal models are not ideal to study the natural progression of vision loss or the efficacy and safety of novel therapies. In this context, we will also discuss the advantages and pitfalls of alternative models that include larger species, such as non-human primates and rabbits, patient-derived retinal organoids, and human organ donor eyes.

Natural Course of Solar and Laser-Associated Retinal and Macular Injuries at a Primary Care Hospital in Switzerland

BACKGROUND

Solar and laser-associated retinopathies are rare occurrences. The two retinopathies are both photo-induced but differ in the involved intensity and duration of exposure. The purpose of this study was to evaluate the clinical features and natural course of these two entities, with a focus on the changes in the outer retina over time.

PATIENTS AND METHODS

This retrospective analysis assessed patients with solar or laser maculopathy seen at the Department of Ophthalmology of the University Hospital Zurich in Switzerland over the last 10 years. Visual acuity (VA; Snellen) and optical coherence tomography (OCT) findings were reviewed and analyzed at baseline and last follow-up visit. Areas of damaged outer retina, identified on en face OCT images as hyporeflective areas, were tagged and compared between visits. Descriptive analysis was performed by calculating mean values ± standard deviation (SD). Statistical evaluation was done using the Wilcoxon signed rank test. A p value < 0.05 was considered statistically significant.

RESULTS

Five patients with solar retinopathy and six patients with laser-associated retinopathy were identified. In the solar retinopathy group, mean VA at baseline was 0.80 (SD ± 0.37) and improved to 0.90 (SD ± 0.36). This was not statistically significant (p = 0.066). In the laser-associated retinopathy group, mean VA at baseline was 0.89 (SD ± 0.18) and improved to 1.03 (SD ± 0.09), which was not statistically significant either (p = 0.063). At baseline, in OCT cross-sections, initial changes were observed in the interdigitation, myoid, and ellipsoid zone, as well as the outer nuclear layer and the Henle fiber layer. At follow-up, most cases presented an alteration in the residual ellipsoid zone, with the degree of the aforementioned alterations depending on the size of the initial defect. A decrease of the hyporeflective alterations measured in en face OCT scans was observed in both groups but was only statistically significant in the laser-associated retinopathy group (p = 0.018 versus p = 0.172).

CONCLUSIONS

OCT can help to detect and monitor solar and laser-associated retinal injuries. Most injuries are minor, with good functional restitution. Minor changes in the ellipsoid zone often persist, even in cases with full visual recovery.

Homeostatic plasticity in the retina

Vision begins in the retina, whose intricate neural circuits extract salient features of the environment from the light entering our eyes. Neurodegenerative diseases of the retina (e.g., inherited retinal degenerations, age-related macular degeneration, and glaucoma) impair vision and cause blindness in a growing number of people worldwide. Increasing evidence indicates that homeostatic plasticity (i.e., the drive of a neural system to stabilize its function) can, in principle, preserve retinal function in the face of major perturbations, including neurodegeneration. Here, we review the circumstances and events that trigger homeostatic plasticity in the retina during development, sensory experience, and disease. We discuss the diverse mechanisms that cooperate to compensate and the set points and outcomes that homeostatic retinal plasticity stabilizes. Finally, we summarize the opportunities and challenges for unlocking the therapeutic potential of homeostatic plasticity. Homeostatic plasticity is fundamental to understanding retinal development and function and could be an important tool in the fight to preserve and restore vision.

Nestin contributes to laser choroidal and retinal neovascularization

PURPOSE

Choroidal and retinal neovascularization plays an essential role in various ocular diseases. In this study, we examined the role of nestin in this process. Nestin is an intermediate filament protein known to play several roles, including as a marker of neural progenitor and proliferating endothelial cells.

METHODS

We used Brown Norway rats, in which choroidal and retinal neovascularization was induced using intraocular laser impacts. The role of nestin was examined using angiography, western blot from the second to the 14th day after laser impacts, and intraocular injection of nestin siRNA. The localization of the protein was specified by co-immunoreactivity with glial fibrillary protein (GFAP), glutamine synthetase (GS), and von Willebrand factor (vWF).

RESULTS

In the control retina, nestin was found principally in glial structures in the ganglion cell layer, as confirmed by nestin/GFAP immunolabeling. Two days after the laser impacts, the nestin expression extended to numerous radial processes at the site of the impacts. With Bruch's membrane ruptured, these processes penetrated into the choroid. Nestin immunolabeling remained high from the third to the seventh day but appeared reduced on the 14th day. The nature of these processes was not clearly defined, but co-immunolabeling with GFAP suggested that they were principally in activated Müller cells from the third day after the laser impacts. However, the co-immunoreactivity of nestin and GS, a marker of mature functional Müller cells, could be observable only from the seventh day. Nestin was also observed in some vascular cells, as demonstrated by the co-immunoreactivity of the protein with vWF in the choroid and retina. As observed on angiography, the numbers of choroidal and retinal blood vessels were significantly increased (principally on the seventh day) after the laser impacts. An intraocular injection of nestin siRNAs led to a significant decrease in the number of blood vessels.

CONCLUSIONS

Our results confirmed the presence of nestin in glial (e.g., astrocytes), reactive Müller, and endothelial cells. They demonstrated their critical involvement in a rat model of retinal and choroidal neovascularization experimentally induced using ocular laser impacts.

The effect of pegcetacoplan treatment on photoreceptor maintenance in geographic atrophy monitored by AI-based OCT analysis

PURPOSE

To investigate the therapeutic effect of intravitreal pegcetacoplan on the inhibition of photoreceptor (PR) loss and thinning in geographic atrophy (GA) on conventional spectral domain-optical coherence tomography (SD-OCT) imaging by deep learning-based automated PR quantification.

DESIGN

Post-hoc analysis of a prospective, multicenter, randomized, sham-controlled, masked phase II trial investigating the safety and efficacy of pegcetacoplan for the treatment of GA due to age-related macular degeneration.

PARTICIPANTS

Study eyes of 246 patients, randomized 1:1:1 to monthly (AM), bimonthly (AEOM) and sham (SM) treatment.

METHODS

We performed fully automated, deep learning-based segmentation of retinal pigment epithelium (RPE) loss and PR thickness on SD-OCT volumes acquired at baseline, month 2, 6 and 12. The difference in the change of PR loss area was compared between treatment arms. Change in PR thickness adjacent to the GA borders and in the whole 20 degrees scanning area was compared between treatment arms.

MAIN OUTCOME MEASURES

Square root transformed PR loss area in μm or mm, PR thickness in μm, PR loss/RPE loss ratio.

RESULTS

A total of 31,556 B-Scans of 644 SD-OCT volumes of 161 study eyes (AM: 52, AEOM: 54, SM: 56) were evaluated from baseline to month 12. Comparison of mean change in PR loss area revealed statistically significantly less growth in the AM group at month 2, 6 and 12 compared to SM (-41μm ± 219 vs. 77μm ± 126, p=0.0004; -5μm ± 221 vs. 156μm ± 139, p<0.0001; 106μm ± 400 vs. 283μm ± 226 p=0.0014). PR thinning was significantly reduced under monthly treatment compared to sham within the GA junctional zone as well as throughout the 20 degrees area. A trend towards greater inhibition of PR loss compared to RPE loss was observed under therapy.

CONCLUSIONS

Distinct and reliable quantification of PR loss using deep learning-based algorithms offers an essential tool to evaluate therapeutic efficacy in slowing disease progression. PR loss and thinning are reduced by intravitreal complement C3 inhibition. Automated quantification of PR loss/maintenance based on OCT images is an ideal approach to reliably monitor disease activity and therapeutic efficacy in GA management in clinical routine and regulatory trials.

Pascal short-pulse plus subthreshold endpoint management laser therapy for diabetic macular edema: the "sandwich technique"

Background

Diabetic macular edema (DME) is the main cause of visual loss in diabetic patients. Despite the use of anti-VEGF therapy as first-line treatment, there are many patients whose response to treatment is poor or transient at best. Sophisticated laser techniques have emerged aiming at low-intensity retinal damage, avoiding excessive heat that causes tissue necrosis and related collateral effects.

Objective

To evaluate the effect of combined sublethal laser modalities from short-pulse duration (SPD) with endpoint management (EpM) subthreshold laser [named the “sandwich technique” (SWiT)] on central subfield thickness (CST) and best-corrected visual acuity (BCVA) in patients with DME.

Material and methods

In this consecutive retrospective study, 37 patients (37 eyes) with center-involved (CI) DME were treated with SWiT laser therapy from April 2017 to June 2021. The technique consisted of a mean number of 200 (range number 50–400) SPD laser burns OCT-guided thickened area performed on the juxta- and perifoveal area 500 µm away from the foveal center, overlapping with a mean number of 1000 (range number 800–1200) EpM laser burns focused on 6 mm macular diameter area but saving 300 µm toward the foveal center. All patients underwent ophthalmological evaluations, including BCVA and CST measurement by spectral-domain optical coherence tomography (SD-OCT), before and after SWiT laser therapy. The mean follow-up time was 19.2 months (range 2–60 months).

Results

Thirty-five out of 37 cases showed an improvement in CST and BCVA following treatment. At baseline, mean CST (µm) ± standard error (SE) and mean BCVA (logMAR) ± SE was 456.95 ± 37.00 and 0.71 ± 0.29, respectively. After a mean follow-up of 19.2 months, mean CST (µm) ± SE and BCVA (logMAR) ± SE were 272.09 ± 9.10 (p < 0.0001) and 0.54 ± 0.26 (p = 0.003), respectively. A statistically significant reduction in CST and improvement in BCVA was noted after laser therapy application. The anti-VEGF injection frequency was reduced during the mean 19.2 months of the study period.

Conclusions

The novel “sandwich” laser therapy aid reduced CST and improved BCVA in this retrospective case series. Further prospective studies are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40942-022-00381-5.

AMIGO1 Promotes Axon Growth and Territory Matching in the Retina

Dendrite and axon arbor sizes are critical to neuronal function and vary widely between different neuron types. The relative dendrite and axon sizes of synaptic partners control signal convergence and divergence in neural circuits. The developmental mechanisms that determine cell-type-specific dendrite and axon size and match synaptic partners' arbor territories remain obscure. Here, we discover that retinal horizontal cells express the leucine-rich repeat domain cell adhesion molecule AMIGO1. Horizontal cells provide pathway-specific feedback to photoreceptors-horizontal cell axons to rods and horizontal cell dendrites to cones. AMIGO1 selectively expands the size of horizontal cell axons. When Amigo1 is deleted in all or individual horizontal cells of either sex, their axon arbors shrink. By contrast, horizontal cell dendrites and synapse formation of horizontal cell axons and dendrites are unaffected by AMIGO1 removal. The dendrites of rod bipolar cells, which do not express AMIGO1, shrink in parallel with horizontal cell axons in Amigo1 knockout (Amigo1 KO) mice. This territory matching maintains the function of the rod bipolar pathway, preserving bipolar cell responses and retinal output signals in Amigo1 KO mice. We previously identified AMIGO2 as a scaling factor that constrains retinal neurite arbors. Our current results identify AMIGO1 as a scaling factor that expands retinal neurite arbors and reveal territory matching as a novel homeostatic mechanism. Territory matching interacts with other homeostatic mechanisms to stabilize the development of the rod bipolar pathway, which mediates vision near the threshold.SIGNIFICANCE STATEMENT Neurons send and receive signals through branched axonal and dendritic arbors. The size of these arbors is critical to the function of a neuron. Axons and dendrites grow during development and are stable at maturity. The mechanisms that determine axon and dendrite size are not well understood. Here, we identify a cell surface protein, AMIGO1, that selectively promotes axon growth of horizontal cells, a retinal interneuron. Removal of AMIGO1 reduces the size of horizontal cell axons without affecting the size of their dendrites or the ability of both arbors to form connections. The changes in horizontal cell axons are matched by changes in synaptic partner dendrites to stabilize retinal function. This identifies territory matching as a novel homeostatic plasticity mechanism.

Impact of Photoreceptor Loss on Retinal Circuitry

Our sense of sight relies on photoreceptors, which transduce photons into the nervous system's electrochemical interpretation of the visual world. These precious photoreceptors can be disrupted by disease, injury, and aging. Once photoreceptors start to die, but before blindness occurs, the remaining retinal circuitry can withstand, mask, or exacerbate the photoreceptor deficit and potentially be receptive to newfound therapies for vision restoration. To maximize the retina's receptivity to therapy, one must understand the conditions that influence the state of the remaining retina. In this review, we provide an overview of the retina's structure and function in health and disease. We analyze a collection of observations on photoreceptor disruption and generate a predictive model to identify parameters that influence the retina's response. Finally, we speculate on whether the retina, with its remarkable capacity to function over light levels spanning nine orders of magnitude, uses these same adaptational mechanisms to withstand and perhaps mask photoreceptor loss.

Laser Therapy in the Treatment of Diabetic Retinopathy and Diabetic Macular Edema

PURPOSE OF REVIEW

This review highlights indications and evidence on laser therapy in the management of diabetic retinopathy and diabetic macular edema. Particular focus is placed upon the benefits and limitations of conventional laser photocoagulation versus more modern laser photocoagulation techniques, as well as the role of laser photocoagulation in treatment of diabetic retinopathy and diabetic macular edema with the frequent utilization of pharmacologic, including anti-vascular endothelial growth factor (VEGF), therapy.

RECENT FINDINGS

Laser photocoagulation remains the gold-standard therapy for the effective, definitive treatment of PDR, and also is highly effective in the management of DME. However, numerous recent studies have demonstrated the clinical efficacy and improved functional and anatomic outcomes of combination therapy with pharmacologic treatment. Continuing innovations in laser technology and improved understanding of laser-retinal interactions and pathophysiology demonstrate that laser therapy will continue to play a critical role in the treatment of diabetic retinopathy and diabetic macular edema for many years to come.

Mature Retina Compensates Functionally for Partial Loss of Rod Photoreceptors

Loss of primary neuronal inputs inevitably strikes every neural circuit. The deafferented circuit could propagate, amplify, or mitigate input loss, thus affecting the circuit’s output. How the deafferented circuit contributes to the effect on the output is poorly understood because of lack of control over loss of and access to circuit elements. Here, we control the timing and degree of rod photoreceptor ablation in mature mouse retina and uncover compensation. Following loss of half of the rods, rod bipolar cells mitigate the loss by preserving voltage output. Such mitigation allows partial recovery of ganglion cell responses. We conclude that rod death is compensated for in the circuit because ganglion cell responses to stimulation of half of the rods in an unperturbed circuit are weaker than responses after death of half of the rods. The dominant mechanism of such compensation includes homeostatic regulation of inhibition to balance the loss of excitation.

Care et al. ablate half of the rods in mature mouse retina and find that primary neuron loss is functionally compensated for by balanced inhibition and excitation at the secondary neuron. Changes in cone-mediated, but not rod-mediated, output neuron spikes are recapitulated by half stimulation, demonstrating independent regulation of pathways.

FUNCTIONAL AND STRUCTURAL EFFECTS OF NONDAMAGING RETINAL LASER THERAPY FOR MACULAR TELANGIECTASIA TYPE 2: A Randomized Sham-Controlled Clinical Trial

PURPOSE

Macular telangiectasia (MacTel) Type 2 is a progressing neurovascular disease of the macula, currently lacking effective treatment. This study assessed the effect of nondamaging retinal laser therapy (NRT) compared with sham.

METHODS

Twelve MacTel patients were enrolled in this double-masked, controlled, randomized clinical trial. For the nine patients with both eyes eligible, one eye was randomized to NRT or sham and the other received alternate treatment. For three patients with only one eye eligible, that eye was randomly assigned either NRT or sham. Ellipsoid zone disruption, best-corrected visual acuity, and macular automated perimetry at 12 months served as structural and functional measures.

RESULTS

Eleven eyes were randomized to sham and 10 to NRT. Baseline best-corrected visual acuity was 66 letters (20/50) for sham and 72 letters (20/40) for NRT (P = 0.245). Ellipsoid zone disruption area was 298 µm2 in sham and 368 µm2 in NRT (P = 0.391). At 12 months, ellipsoid zone disruption increased by 24% in sham and decreased by 34% in NRT (P < 0.001). Best-corrected visual acuity measures remained stable during follow-up compared with baseline. At 1 year, the mean macular sensitivity was 28 dB in the NRT group, compared with 26 dB in sham.

CONCLUSION

Nondamaging retinal laser therapy was safe and well tolerated in patients with MacTel and resulted in structural and functional improvements, which could represent a protective effect of laser-induced hyperthermia. Longer follow-up and larger number of patients should help corroborate these effects.

Continuous wave milipulse yellow laser treatment for perifoveal exudative vascular anomalous complex-like lesion: A case report

INTRODUCTION

Perifoveal exudative vascular anomalous complex (PEVAC) is an underdiagnosed macular entity. A striking feature of this entity is the unresponsiveness to anti-VEGF treatment. Continuous wave milipulse yellow laser 577 nm (CWMYL-577) has a high absorption peak for oxyhaemoglobin, which allows for low power density use.

PURPOSE

To report a case of a PEVAC-like lesion unresponsive to anti-VEGF and corticosteroids, successfully treated with a single session of minimally invasive focal laser, using CWMYL-577.

METHODS

A diabetic patient with a symptomatic PEVAC-like lesion in the right eye, presented with decreased vision (20/100) and cystoid edema that had persisted for the last 18 months, despite multiple intraocular injections of anti-VEGF and long acting corticosteroids. Three spots of low power density CWMYL-577 (100 mW, 25 ms and 100 µm, using lens with no amplification factor) over the lesion were successfully performed in one laser session. One month and three months after the laser procedure, a gradual decrease of edema and lipid exudates was observed and at a 6-month follow-up, the retina had recovered its normal anatomy with visual acuity of 20/20 that have persisted for 4 years after treatment.

CONCLUSIONS

Minimal invasive focal laser using the CWMYL-577 can be considered an effective therapeutic strategy for symptomatic nonresponding PEVAC-like lesion in patients with DM without DR.

Partial Cone Loss Triggers Synapse-Specific Remodeling and Spatial Receptive Field Rearrangements in a Mature Retinal Circuit

Resilience of neural circuits has been observed in the persistence of function despite neuronal loss. In vision, acuity and sensitivity can be retained after 50% loss of cones. While neurons in the cortex can remodel after input loss, the contributions of cell-type-specific circuits to resilience are unknown. Here, we study the effects of partial cone loss in mature mouse retina where cell types and connections are known. At first-order synapses, bipolar cell dendrites remodel and synaptic proteins diminish at sites of input loss. Sites of remaining inputs preserve synaptic proteins. Second-order synapses between bipolar and ganglion cells remain stable. Functionally, ganglion cell spatio-temporal receptive fields retain center-surround structure following partial cone loss. We find evidence for slower temporal filters and expanded receptive field surrounds, derived mainly from inhibitory inputs. Surround expansion is absent in partially stimulated control retina. Results demonstrate functional resilience to input loss beyond pre-existing mechanisms in control retina.

Care et al. find that photoreceptor ablation causes structural rearrangement of bipolar cell input synapses while output synapses endure. Functionally, recipient ganglion cells show altered receptive field sizes, an effect not seen after partial stimulation of control retina, demonstrating de novo changes that occur in inhibitory circuitry after photoreceptor loss.

Homeostatic Plasticity Shapes the Retinal Response to Photoreceptor Degeneration

Homeostatic plasticity stabilizes input and activity levels during neural development, but whether it can restore connectivity and preserve circuit function during neurodegeneration is unknown. Photoreceptor degeneration is the most common cause of blindness in the industrialized world. Visual deficits are dominated by cone loss, which progresses slowly, leaving a window during which rewiring of second-order neurons (i.e., bipolar cells) could preserve function. Here we establish a transgenic model to induce cone degeneration with precise control and analyze bipolar cell responses and their effects on vision through anatomical reconstructions, in vivo electrophysiology, and behavioral assays. In young retinas, we find that three bipolar cell types precisely restore input synapse numbers when 50% of cones degenerate but one does not. Of the three bipolar cell types that rewire, two contact new cones within stable dendritic territories, whereas one expands its dendrite arbors to reach new partners. In mature retinas, only one of four bipolar cell types rewires homeostatically. This steep decline in homeostatic plasticity is accompanied by reduced light responses of bipolar cells and deficits in visual behaviors. By contrast, light responses and behavioral performance are preserved when cones degenerate in young mice. Our results reveal unexpected cell type specificity and a steep maturational decline of homeostatic plasticity. The effect of homeostatic plasticity on functional outcomes identify it as a promising therapeutic target for retinal and other neurodegenerative diseases.

En Face Optical Coherence Tomography Imaging Ellipsoid Zone Regeneration in Laser-Induced and Solar Maculopathies

The purpose of the study was to analyze imaging findings in spectral domain en face optical coherence tomography (SD OCT) in patients with laser-induced and solar maculopathies focusing on the possible regeneration of the ellipsoid zone. In a retrospective case series of 3 patients (4 eyes) with solar maculopathy and 2 patients (3 eyes) with laser-induced maculopathy who underwent a comprehensive ocular examination, ellipsoid zone (EZ) was segmented from SD OCT data. Evaluation of EZ in en face OCT revealed a hyporeflective lesion surrounded by a hyperreflective border. The area of EZ alteration was measured manually in en face OCT. All patients showed partial EZ regeneration. Mean EZ alteration decreased from 0.12 mm² (range: 0.05-0.32) at baseline to 0.07 mm² (range: 0.01-0.22) at last follow-up (p = 0.018, mean follow-up: 372 days; range: 115-592). Mean best visual acuity (BVA) improved from 20/36 at baseline to 20/30 (p = 0.018). In conclusion, en face OCT imaging clearly delineated the area of EZ alteration in patients with laser-induced and solar maculopathies. Follow-up showed significant reformation of the EZ as well as improvement of BVA.

Development of a Spatial Model of Age-Related Change in the Macular Ganglion Cell Layer to Predict Function From Structural Changes

PURPOSE

To develop location-specific models of normal, age-related changes in the macular ganglion cell layer (GCL) from optical coherence tomography (OCT). Using these OCT-derived models, we predicted visual field (VF) sensitivities and compared these results to actual VF sensitivities.

DESIGN

Retrospective cohort study.

METHODS

Single eyes of 254 normal participants were retrospectively enrolled from the Centre for Eye Health (Sydney, Australia). Macular GCL measurements were obtained using Spectralis OCT. Cluster algorithms were performed to identify spatial patterns demonstrating similar age-related change. Quadratic and linear regression models were subsequently used to characterize age-related GCL decline. Forty participants underwent additional testing with Humphrey VFs, and 95% prediction intervals were calculated to measure the predictive ability of structure-function models incorporating cluster-based pooling, age correction, and consideration of spatial summation.

RESULTS

Quadratic GCL regression models provided a superior fit (P value <.0001-.0066), establishing that GCL decline commences in the late 30s across the macula. The equivalent linear rates of GCL decline showed eccentricity-dependent variation (0.13 μm/yr centrally vs 0.06 μm/yr peripherally); however, average, normalized GCL loss per year was consistent across the 64 macular measurement locations at 0.26%. The 95% prediction intervals describing predicted VF sensitivities were significantly narrower across all cluster-based structure-function models (3.79-4.99 dB) compared with models without clustering applied (5.66-6.73 dB, P < .0001).

CONCLUSIONS

Combining spatial clustering with age-correction based on regression models allowed the development of robust models describing GCL changes with age. The resultant superior predictive ability of VF sensitivity from ganglion cell measurements may be applied to future models of disease development to improve detection of early macular GCL pathology.

Morphological alterations of intrinsically photosensitive retinal ganglion cells after ablation of mouse photoreceptors with selective photocoagulation

In this work, we investigated changes in the morphology of intrinsically photosensitive retinal ganglion cells (ipRGCs), M1 subtype, and pupillary light reflex following local and selective ablation of photoreceptors in mice. Laser photocoagulation was used to selectively destroy four patches of photoreceptors per eye at around 4 papillary diameters from the optic disc and at the 3, 6, 9, and 12 o'clock positions between the retinal vessels in the adult mouse retina, leaving cells in the inner retina intact. Morphological parameters of individual M1 cells specifically labeled by the antibody against melanopsin (PA1-780), including dendritic field size, total dendritic length, and dendritic branch number, were examined 1, 2, 4, and 8 weeks after photocoagulation with Neurolucida software. A considerable reduction in these parameters in M1 cells in the "lesioned areas" was found at all the four time points after photocoagulation, as compared with those in the "unlesioned areas". Although M1 cells in the lesioned areas showed significant changes as early as 1 week after laser treatment and the changes gradually increased, reaching a peak value at 2 weeks, morphological restoration was clearly seen in these cells over time. However, no difference in the morphological parameters of M1 cells was observed between the unlesioned areas of laser-treated mice and the corresponding areas of age-matched normal mice without laser lesions. Fluorescence intensity of the somata of melanopsin-positive M1 cells located inside the lesioned areas was significantly decreased at all the four time points after photocoagulation, whereas no changes in pupillary light reflex were detected at different light irradiations, indicating that photocoagulation-induced local photoreceptor loss and alterations of ipRGCs may be insufficient to cause abnormalities in non-image-forming (NIF) visual functions. The results suggest that intact photoreceptors could be crucial for maintaining the expression levels of melanopsin and normal morphology of M1 cells.

In vivo imaging reveals transient microglia recruitment and functional recovery of photoreceptor signaling after injury

Microglia, the resident macrophages of the central nervous system, are critical for synaptic pruning and maintenance and for mitigating injury and neurodegeneration. Determining whether microglia–neuron interactions are beneficial in specific instances has been difficult, largely because of the local and transient nature of the interactions. Using simultaneous optical coherence tomography/scanning laser ophthalmoscopy (SLO) and adaptive optics SLO retinal imaging in mice, we show interactions of microglia and photoreceptors over time scales from seconds to months during injury, degeneration, and repair. In vivo optical assessment of photoreceptor signaling in a large neuronal field encompassing the injured area allows us to relate the time course of these microglia movements to that of the tissue remodeling and functional recovery.

Microglia respond to damage and microenvironmental changes within the central nervous system by morphologically transforming and migrating to the lesion, but the real-time behavior of populations of these resident immune cells and the neurons they support have seldom been observed simultaneously. Here, we have used in vivo high-resolution optical coherence tomography (OCT) and scanning laser ophthalmoscopy with and without adaptive optics to quantify the 3D distribution and dynamics of microglia in the living retina before and after local damage to photoreceptors. Following photoreceptor injury, microglia migrated both laterally and vertically through the retina over many hours, forming a tight cluster within the area of visible damage that resolved over 2 wk. In vivo OCT optophysiological assessment revealed that the photoreceptors occupying the damaged region lost all light-driven signaling during the period of microglia recruitment. Remarkably, photoreceptors recovered function to near-baseline levels after the microglia had departed the injury locus. These results demonstrate the spatiotemporal dynamics of microglia engagement and restoration of neuronal function during tissue remodeling and highlight the need for mechanistic studies that consider the temporal and structural dynamics of neuron–microglia interactions in vivo.

Activation of Rod Input in a Model of Retinal Degeneration Reverses Retinal Remodeling and Induces Formation of Functional Synapses and Recovery of Visual Signaling in the Adult Retina

A major cause of human blindness is the death of rod photoreceptors. As rods degenerate, synaptic structures between rod and rod bipolar cells disappear and the rod bipolar cells extend their dendrites and occasionally make aberrant contacts. Such changes are broadly observed in blinding disorders caused by photoreceptor cell death and are thought to occur in response to deafferentation. How the remodeled retinal circuit affects visual processing following rod rescue is not known. To address this question, we generated male and female transgenic mice wherein a disrupted cGMP-gated channel (CNG) gene can be repaired at the endogenous locus and at different stages of degeneration by tamoxifen-inducible cre-mediated recombination. In normal rods, light-induced closure of CNG channels leads to hyperpolarization of the cell, reducing neurotransmitter release at the synapse. Similarly, rods lacking CNG channels exhibit a resting membrane potential that was ~10 mV hyperpolarized compared to WT rods, indicating diminished glutamate release. Retinas from these mice undergo stereotypic retinal remodeling as a consequence of rod malfunction and degeneration. Upon tamoxifen-induced expression of CNG channels, rods recovered their structure and exhibited normal light responses. Moreover, we show that the adult mouse retina displays a surprising degree of plasticity upon activation of rod input. Wayward bipolar cell dendrites establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings demonstrate remarkable plasticity extending beyond the developmental period and support efforts to repair or replace defective rods in patients blinded by rod degeneration.SIGNIFICANCE STATEMENT Current strategies for treatment of neurodegenerative disorders are focused on the repair of the primary affected cell type. However, the defective neurons function within a complex neural circuitry, which also becomes degraded during disease. It is not known whether rescued neurons and the remodeled circuit will establish communication to regain normal function. We show that the adult mammalian neural retina exhibits a surprising degree of plasticity following rescue of rod photoreceptors. The wayward dendrites of rod bipolar cells re-establish contact with rods to support normal synaptic transmission, which is propagated to the retinal ganglion cells. These findings support efforts to repair or replace defective rods in patients blinded by rod cell loss.

Non-Therapeutic Laser Retinal Injury

BACKGROUND:

As lasers have become an increasingly important component of commercial, industrial, military, and medical applications, reported incidents of non-therapeutic laser eye injuries have increased. The retina is particularly vulnerable due to the focusing power and optical transparency of the eye. Continued innovations in laser technology will likely mean that lasers will play an increasingly important and ubiquitous role throughout the world. Critical evaluation should thus be paid to ensure that non-therapeutic injuries are minimized, recognized, and treated appropriately.

METHODS:

A comprehensive literature review on the PubMed database was conducted to present case reports and case series representative of the variety of laser eye injuries in different injury circumstances, tissue types, and biological damage mechanisms.

RESULTS:

A general summary of non-therapeutic laser retina injuries is presented, including information about growth of the industry, increasingly accessible online markets, inconsistent international regulation, laser classifications, laser wavelengths, and laser power, mechanisms of tissue injury, and a demonstration of the variety of settings in which injury may occur. Finally, 68 cases found in the literature are summarized to illustrate the presentations and outcomes of these patients.

CONCLUSIONS:

As non-therapeutic laser eye injuries increase in frequency, there is a greater need for public health, policy, diagnosis, and treatment of these types of injuries.

Long-term Rescue of Photoreceptors in a Rodent Model of Retinitis Pigmentosa Associated with MERTK Mutation

MERTK mutation reduces the ability of retinal pigment epithelial (RPE) cells to phagocytize the photoreceptor outer segments, which leads to accumulation of debris separating photoreceptors from RPE cells, resulting in their degeneration and loss of vision. In a rat model of Retinitis Pigmentosa due to MERTK mutation, we demonstrate that surgical removal of debris performed when about half of photoreceptors are lost (P38), allows the remaining photoreceptor cells to renew their outer segments and survive for at least 6 months - 3 times longer than in untreated eyes. In another set of experiments, patterned laser photocoagulation was performed before the debris formation (P19-25) to destroy a fraction of photoreceptors and thereby reduce the phagocytic load of shed outer segment fragments. This treatment also delayed the degeneration of the remaining photoreceptors. Both approaches were assessed functionally and morphologically, using electroretinography, optical coherence tomography, and histology. The long-term preservation of photoreceptors we observed indicates that MERTK-related form of inherited retinal degeneration, which has currently no cure, could be amenable to laser therapy or subretinal surgery, to extend the visual function, potentially for life.

Comparison of pre-retinal oxygen pressure changes after selective retina therapy versus conventional photocoagulation in the rabbit eye

PURPOSE

To evaluate oxygen consumption by photoreceptors, we estimated changes in pre-retinal oxygen pressure (PO₂) after selective retina therapy (SRT) compared with conventional photocoagulation (PC) in rabbits.

METHODS

One eye of each of 10 Chinchilla Bastard rabbits received both 144 laser SRT spots and 144 laser PC spots. Color fundus photography, optical coherence tomography (OCT), and fluorescein angiography were used to evaluate the lesions after treatment. Fiber-optic sensors (optodes) were used to determine the pre-retinal PO₂ levels of untreated, SRT-treated, and PC-treated areas of laser-damaged eyes 7 days after treatment. The pre-retinal PO₂ was measured in the other five eyes (controls). The same procedures were applied to these remaining five eyes 4 weeks after treatment. Light microscopy (LM) was used to evaluate histological changes 7 days and 4 weeks after treatment.

RESULTS

We found no significant difference in the mean pre-retinal PO₂ values among untreated, SRT-treated, and control eyes 7 days after treatment. However, the mean pre-retinal PO₂ value in PC-treated regions (24.3 ± 4.9 mmHg; mean ± SD) was higher than those in untreated regions (17.0 ± 1.8 mmHg; P = 0.019), SRT-treated regions (16.7 ± 2.6 mmHg; P = 0.015), and controls (16.9 ± 2.4 mmHg; P = 0.018). Similarly, the mean pre-retinal PO₂ of only PC-treated regions (25.2 ± 4.7 mmHg) was higher than those of the untreated regions (16.3 ± 2.5 mmHg; P = 0.006), SRT-treated regions (17.7 ± 3.1 mmHg; P = 0.023), and controls (16.4 ± 2.4 mmHg; P = 0.007) 4 weeks after treatment. OCT and LM revealed selective retinal pigment epithelium damage with the sparing of photoreceptors in SRT lesions.

CONCLUSIONS

SRT treatment did not induce changes in the oxygen consumption of photoreceptors, or the pre-retinal PO₂.

Evolution of Concepts and Technologies in Ophthalmic Laser Therapy

Ophthalmology was the first medical specialty to adopt lasers right after their invention more than 50 years ago, and they gradually revolutionized ocular imaging, diagnostics, therapy, and surgery. Challenging precision, safety, and selectivity requirements for ocular therapeutic and surgical procedures keep advancing the laser technologies, which in turn continue enabling novel applications for the preservation and restoration of sight. Modern lasers can provide single-cell-layer selectivity in therapy, submicrometer precision in three-dimensional image-guided surgery, and nondamaging retinal therapy under optoacoustic temperature control. This article reviews the evolution of laser technologies; progress in understanding of the laser-tissue interactions; and concepts, misconceptions, and accidental discoveries that led to modern therapeutic and surgical applications of lasers in ophthalmology. It begins with a brief historical overview, followed by a description of the laser-tissue interactions and corresponding ophthalmic applications.

Regenerative medicine in the retina: from stem cells to cell replacement therapy

Following the fast pace of the growing field of stem cell research, retinal cell replacement is finally emerging as a feasible mean to be explored for clinical application. Although neuroprotective treatments are able to slow the progression of retinal degeneration caused by diseases such as age-related macular degeneration and glaucoma, they are insufficient to fully halt disease progression and unable to recover previously lost vision. Comprehensive, technological and intellectual advances over the past years, including the in vitro differentiation of retinal cells at manufacturing scale from embryonic stem (ES) cell and induced pluripotent stem (iPS) cell cultures, progress within the area of retinal disease modeling, and the first clinical trials have started to shape the way towards addressing this treatment gap and translating retinal cell replacement to the clinic. Here, summarize the most recent advances within retinal cell replacement from both a scientific and clinical perspective, and discuss the remaining challenges towards the delivery of the first retinal cell products.

Experimental verification of subthreshold laser therapy using conventional pattern scan laser

Purpose

Leading-edge therapeutic laser technologies are not available at every medical facility; therefore, alternative approaches incorporating novel advances in digital and laser technology into more readily available conventional methods have generated significant research interest. Using a rabbit model, this study investigated whether the algorithm used in the Endpoint Management (EM) software system of the latest devices could enable subthreshold laser treatment in conventional retinal tissue laser therapy systems.

Materials and methods

Two types of devices were used, the PASCAL Streamline 577 and the MC 500-Vixi™, and the laser method was classified into three categories: EM; single-shot using PASCAL with arbitrary energy settings (PSS-SDM); and MC500-Vixi^TM (VX-SDM), which were performed in eight eyes from four Dutch-Belted rabbits. In EM, 100 mW (100%) was set as a landmark, and the laser energy parameters were gradually decreased to 80%, 60%, 50%, 40%, 30%, 20%, and 10%, using a 2 × 3 square pattern. In PSS-SDM and VX-SDM, as control, the laser energy was gradually decreased to 100, 80, 60, 50, 40, 30, 20, and 10 mW. The laser settings were fixed at 200 μm, 20 ms, and a wavelength of 577 μm. To identify and compare the extent of tissue damage at each spot size, optical coherence tomography (OCT) and histological findings were used to construct a three-dimensional histopathology image using a confocal laser scanning fluorescence microscope.

Results

The spot size at 50% setting on EM was 7183 μm²; PSS-SDM required 50 mW (5503 μm²) to 60 mW (10279 μm²) and VX-SDM required 50 mW (7423 μm²) to create the approximate spot size. Furthermore, at 50 mW of PSS-SDM and VX-SDM, the extent of tissue damage in all three methods was generally in accord with the outer nuclear layer by OCT and inner nuclear layer by histopathological imaging.

Conclusion

These findings suggest that it may be possible to perform subthreshold laser therapy using approximations from the EM algorithm.

Deafferented Adult Rod Bipolar Cells Create New Synapses with Photoreceptors to Restore Vision

Upon degeneration of photoreceptors in the adult retina, interneurons, including bipolar cells, exhibit a plastic response leading to their aberrant rewiring. Photoreceptor reintroduction has been suggested as a potential approach to sight restoration, but the ability of deafferented bipolar cells to establish functional synapses with photoreceptors is poorly understood. Here we use photocoagulation to selectively destroy photoreceptors in adult rabbits while preserving the inner retina. We find that rods and cones shift into the ablation zone over several weeks, reducing the blind spot at scotopic and photopic luminances. During recovery, rod and cone bipolar cells exhibit markedly different responses to deafferentation. Rod bipolar cells extend their dendrites to form new synapses with healthy photoreceptors outside the lesion, thereby restoring visual function in the deafferented retina. Secretagogin-positive cone bipolar cells did not exhibit such obvious dendritic restructuring. These findings are encouraging to the idea of photoreceptor reintroduction for vision restoration in patients blinded by retinal degeneration. At the same time, they draw attention to the postsynaptic side of photoreceptor reintroduction; various bipolar cell types, representing different visual pathways, vary in their response to the photoreceptor loss and in their consequent dendritic restructuring.SIGNIFICANCE STATEMENT Loss of photoreceptors during retinal degeneration results in permanent visual impairment. Strategies for vision restoration based on the reintroduction of photoreceptors inherently rely on the ability of the remaining retinal neurons to correctly synapse with new photoreceptors. We show that deafferented bipolar cells in the adult mammalian retina can reconnect to rods and cones and restore retinal sensitivity at scotopic and photopic luminances. Rod bipolar cells extend their dendrites to form new synapses with healthy rod photoreceptors. These findings support the idea that bipolar cells might be able to synapse with reintroduced photoreceptors, thereby restoring vision in patients blinded by retinal degeneration.

Multi-Modal Longitudinal Evaluation of Subthreshold Laser Lesions in Human Retina, Including Scanning Laser Ophthalmoscope-Adaptive Optics Imaging

BACKGROUND AND OBJECTIVE

Subthreshold retinal laser therapy is efficacious for a variety of retinovascular disorders. Currently, it is unknown which laser parameters can ensure no detectable damage to human retina tissue.

MATERIALS AND METHODS

One informed physician participant with a normal retina was treated with three levels (75%, 50%, and 25%) of subthreshold 577-nm laser (PASCAL; Topcon, Santa Clara, CA) at 20-millisecond (ms) duration and 100 µm spot size. Several high-resolution retinal imaging modalities, including spectral-domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscope-adaptive optics (SLO-AO), were used to longitudinally image retinal laser lesions during a 9-month period.

RESULTS

SLO-AO and SD-OCT imaging of subthreshold laser therapy in human retina showed no cone cell or RPE damage at all time points during a 9-month period using the 25% threshold power 577-nm laser in the human retina.

CONCLUSION

It is likely that subthreshold laser therapy with 577-nm laser at 20-ms duration in the human retina is safe at the 25% of threshold power level.

Rapid Recovery of Visual Function Associated with Blue Cone Ablation in Zebrafish

Hurdles in the treatment of retinal degeneration include managing the functional rewiring of surviving photoreceptors and integration of any newly added cells into the remaining second-order retinal neurons. Zebrafish are the premier genetic model for such questions, and we present two new transgenic lines allowing us to contrast vision loss and recovery following conditional ablation of specific cone types: UV or blue cones. The ablation of each cone type proved to be thorough (killing 80% of cells in each intended cone class), specific, and cell-autonomous. We assessed the loss and recovery of vision in larvae via the optomotor behavioural response (OMR). This visually mediated behaviour decreased to about 5% or 20% of control levels following ablation of UV or blue cones, respectively (P<0.05). We further assessed ocular photoreception by measuring the effects of UV light on body pigmentation, and observed that photoreceptor deficits and recovery occurred (p<0.01) with a timeline coincident to the OMR results. This corroborated and extended previous conclusions that UV cones are required photoreceptors for modulating body pigmentation, addressing assumptions that were unavoidable in previous experiments. Functional vision recovery following UV cone ablation was robust, as measured by both assays, returning to control levels within four days. In contrast, robust functional recovery following blue cone ablation was unexpectedly rapid, returning to normal levels within 24 hours after ablation. Ablation of cones led to increased proliferation in the retina, though the rapid recovery of vision following blue cone ablation was demonstrated to not be mediated by blue cone regeneration. Thus rapid visual recovery occurs following ablation of some, but not all, cone subtypes, suggesting an opportunity to contrast and dissect the sources and mechanisms of outer retinal recovery during cone photoreceptor death and regeneration.

Nondamaging Retinal Laser Therapy: Rationale and Applications to the Macula

PURPOSE

Retinal photocoagulation and nondamaging laser therapy are used for treatment of macular disorders, without understanding of the response mechanism and with no rationale for dosimetry. To establish a proper titration algorithm, we measured the range of tissue response and damage threshold. We then evaluated safety and efficacy of nondamaging retinal therapy (NRT) based on this algorithm for chronic central serous chorioretinopathy (CSCR) and macular telangiectasia (MacTel).

METHODS

Retinal response to laser treatment below damage threshold was assessed in pigmented rabbits by expression of the heat shock protein HSP70 and glial fibrillary acidic protein (GFAP). Energy was adjusted relative to visible titration using the Endpoint Management (EpM) algorithm. In clinical studies, 21 eyes with CSCR and 10 eyes with MacTel were treated at 30% EpM energy with high spot density (0.25-diameter spacing). Visual acuity, retinal and choroidal thickness, and subretinal fluid were monitored for 1 year.

RESULTS

At 25% EpM energy and higher, HSP70 was expressed acutely in RPE, and GFAP upregulation in Müller cells was observed at 1 month. Damage appeared starting at 40% setting. Subretinal fluid resolved completely in 81% and partially in 19% of the CSCR patients, and visual acuity improved by 12 ± 3 letters. Lacunae in the majority of MacTel patients decreased while preserving the retinal thickness, and vision improved by 10 letters.

CONCLUSIONS

Heat shock protein expression in response to hyperthermia helps define the therapeutic window for NRT. Lack of tissue damage enables high-density treatment to boost clinical efficacy, therapy in the fovea, and retreatments to manage chronic diseases.

Transplantation of human embryonic stem cell-derived retinal tissue in two primate models of retinal degeneration

Retinal transplantation therapy for retinitis pigmentosa is increasingly of interest due to accumulating evidence of transplantation efficacy from animal studies and development of techniques for the differentiation of human embryonic stem cells (hESCs) and induced pluripotent stem cells into retinal tissues or cells. In this study, we aimed to assess the potential clinical utility of hESC-derived retinal tissues (hESC-retina) using newly developed primate models of retinal degeneration to obtain preparatory information regarding the potential clinical utility of these hESC-retinas in transplantation therapy. hESC-retinas were first transplanted subretinally into nude rats with or without retinal degeneration to confirm their competency as a graft to mature to form highly specified outer segment structure and to integrate after transplantation. Two focal selective photoreceptor degeneration models were then developed in monkeys by subretinal injection of cobalt chloride or 577-nm optically pumped semiconductor laser photocoagulation. The utility of the developed models and a practicality of visual acuity test developed for monkeys were evaluated. Finally, feasibility of hESC-retina transplantation was assessed in the developed monkey models under practical surgical procedure and postoperational examinations. Grafted hESC-retina was observed differentiating into a range of retinal cell types, including rod and cone photoreceptors that developed structured outer nuclear layers after transplantation. Further, immunohistochemical analyses suggested the formation of host-graft synaptic connections. The findings of this study demonstrate the clinical feasibility of hESC-retina transplantation and provide the practical tools for the optimization of transplantation strategies for future clinical applications.

Alterations in Kainate Receptor and TRPM1 Localization in Bipolar Cells after Retinal Photoreceptor Degeneration

Photoreceptor degeneration differentially impacts glutamatergic signaling in downstream On and Off bipolar cells. In rodent models, photoreceptor degeneration leads to loss of glutamatergic signaling in On bipolar cells, whereas Off bipolar cells appear to retain glutamate sensitivity, even after extensive photoreceptor loss. The localization and identity of the receptors that mediate these residual glutamate responses in Off bipolar cells have not been determined. Recent studies show that macaque and mouse Off bipolar cells receive glutamatergic input primarily through kainate-type glutamate receptors. Here, we studied the impact of photoreceptor degeneration on glutamate receptor and their associated proteins in Off and On bipolar cells. We show that the kainate receptor subunit, GluK1, persists in remodeled Off bipolar cell dendrites of the rd10 mouse retina. However, the pattern of expression is altered and the intensity of staining is reduced compared to wild-type retina. The kainate receptor auxiliary subunit, Neto1, also remains in Off bipolar cell dendrites after extensive photoreceptor degeneration. Similar preservation of kainate receptor subunits was evident in human retina in which photoreceptors had degenerated due to serous retinal detachment. In contrast, photoreceptor degeneration leads to loss of synaptic expression of TRPM1 in mouse and human On bipolar cells, but strong somatic expression remains. These findings demonstrate that Off bipolar cells retain dendritic glutamate receptors during retinal degeneration and could thus serve as a conduit for signal transmission from transplanted or optogenetically restored photoreceptors.

Development of Animal Models of Local Retinal Degeneration

PURPOSE

Development of nongenetic animal models of local retinal degeneration is essential for studies of retinal pathologies, such as chronic retinal detachment or age-related macular degeneration. We present two different methods to induce a highly localized retinal degeneration with precise onset time, that can be applied to a broad range of species in laboratory use.

METHODS

A 30-μm thin polymer sheet was implanted subretinally in wild-type (WT) rats. The effects of chronic retinal separation from the RPE were studied using histology and immunohistochemistry. Another approach is applicable to species with avascular retina, such as rabbits, where the photoreceptors and RPE were thermally ablated over large areas, using a high power scanning laser.

RESULTS

Photoreceptors above the subretinal implant in rats degenerated over time, with 80% of the outer nuclear layer disappearing within a month, and the rest by 3 months. Similar loss was obtained by selective photocoagulation with a scanning laser. Cells in the inner nuclear layer and ganglion cell layer were preserved in both cases. However, there were signs of rewiring and decrease in the size of the bipolar cell terminals in the damaged areas.

CONCLUSIONS

Both methods induce highly reproducible degeneration of photoreceptors over a defined area, with complete preservation of the inner retinal neurons during the 3-month follow-up. They provide a reliable platform for studies of local retinal degeneration and development of therapeutic strategies in a wide variety of species.

Adult cortical plasticity studied with chronically implanted electrode arrays

The functional architecture of adult cerebral cortex retains a capacity for experience-dependent change. This is seen after focal binocular lesions as rapid changes in receptive field (RF) of the lesion projection zone (LPZ) in the primary visual cortex (V1). To study the dynamics of the circuitry underlying these changes longitudinally, we implanted microelectrode arrays in macaque (Macaca mulatta) V1, eliminating the possibility of sampling bias, which was a concern in previous studies. With this method, we observed a rapid initial recovery in the LPZ and, during the following weeks, 63-89% of the sites in the LPZ showed recovery of visual responses with significant position tuning. The RFs shifted ∼3° away from the scotoma. In the absence of a lesion, visual stimulation surrounding an artificial scotoma did not elicit visual responses, suggesting that the postlesion RF shifts resulted from cortical reorganization. Interestingly, although both spikes and LFPs gave consistent prelesion position tuning, only spikes reflected the postlesion remapping.

Photoreceptor ablation initiates the immediate loss of glutamate receptors in postsynaptic bipolar cells in retina

Structural changes underlying neurodegenerative diseases include dismantling of synapses, degradation of circuitry, and even massive rewiring. Our limited understanding of synapse dismantling stems from the inability to control the timing and extent of cell death. In this study, selective ablation of cone photoreceptors in live mouse retina and tracking of postsynaptic partners at the cone-to-ON cone bipolar cell synapse reveals that early reaction to cone loss involves rapid and local changes in postsynaptic glutamate receptor distribution. Glutamate receptors disappear with a time constant of 2 h. Furthermore, binding of glutamate receptors by agonists and antagonists is insufficient to rescue glutamate receptor loss, suggesting that receptor allocation depends on the physical presence of cones. These findings demonstrate that the initial step in synapse disassembly involves postsynaptic receptor loss rather than dendritic retraction, providing insight into the early stages of neurodegenerative disease.

The evolution of laser therapy in ophthalmology: a perspective on the interactions between photons, patients, physicians, and physicists: the LXX Edward Jackson Memorial Lecture

PURPOSE

To present the evolution of laser therapy in modern ophthalmic practice.

DESIGN

Review of published experimental and clinical studies.

METHODS

A review was undertaken of the work of multiple investigators leading to the invention of the laser, its biophysical effects on ocular tissues from which it derives its name (light-amplified stimulation of emitted radiation), and the development of various laser-based devices and methods to treat common ophthalmologic disorders, with particular emphasis on new and emerging retinal and anterior segment applications.

RESULTS

Because the eye is optimized for the transmission of light and its transduction into neural signals, lasers are particularly well suited for ophthalmic therapy. This fact and the high demands for precision in therapy have inspired the development of highly sophisticated laser systems that have impacted the treatment of common diseases. These include diabetic retinopathy, age-related macular degeneration, retinal venous occlusive disease, retinopathy of prematurity, and optical aberrations including ametropia, cataract, and glaucoma, among others. Recent developments in scanning laser systems, including image-guided systems with eye tracking, real-time feedback, and ultra-short pulse durations, have enabled increased selectivity, precision, and safety in ocular therapy. However, improved outcomes have been associated with increased cost of medical care, and attention to and optimization of their cost effectiveness will continue to be required in the future.

CONCLUSIONS

The invention and evolution of modern ophthalmic lasers have enhanced therapeutic options and can serve as a heuristic model for better understanding the process of innovation, including the societal benefits and also unintended consequences, including increased costs.

Transplantation of embryonic and induced pluripotent stem cell-derived 3D retinal sheets into retinal degenerative mice

In this article, we show that mouse embryonic stem cell- or induced pluripotent stem cell-derived 3D retinal tissue developed a structured outer nuclear layer (ONL) with complete inner and outer segments even in an advanced retinal degeneration model (rd1) that lacked ONL. We also observed host-graft synaptic connections by immunohistochemistry. This study provides a "proof of concept" for retinal sheet transplantation therapy for advanced retinal degenerative diseases.

Focal damage to macaque photoreceptors produces persistent visual loss

Insertion of light-gated channels into inner retina neurons restores neural light responses, light evoked potentials, visual optomotor responses and visually-guided maze behavior in mice blinded by retinal degeneration. This method of vision restoration bypasses damaged outer retina, providing stimulation directly to retinal ganglion cells in inner retina. The approach is similar to that of electronic visual protheses, but may offer some advantages, such as avoidance of complex surgery and direct targeting of many thousands of neurons. However, the promise of this technique for restoring human vision remains uncertain because rodent animal models, in which it has been largely developed, are not ideal for evaluating visual perception. On the other hand, psychophysical vision studies in macaque can be used to evaluate different approaches to vision restoration in humans. Furthermore, it has not been possible to test vision restoration in macaques, the optimal model for human-like vision, because there has been no macaque model of outer retina degeneration. In this study, we describe development of a macaque model of photoreceptor degeneration that can in future studies be used to test restoration of perception by visual prostheses. Our results show that perceptual deficits caused by focal light damage are restricted to locations at which photoreceptors are damaged, that optical coherence tomography (OCT) can be used to track such lesions, and that adaptive optics retinal imaging, which we recently used for in vivo recording of ganglion cell function, can be used in future studies to examine these lesions.