A role for photoreceptors in retinal oedema and angiogenesis: an additional explanation for laser treatment?

Bone Marrow-Derived Cell Recruitment to the Neurosensory Retina and Retinal Pigment Epithelial Cell Layer Following Subthreshold Retinal Phototherapy

Purpose

We investigated whether subthreshold retinal phototherapy (SRPT) was associated with recruitment of bone marrow (BM)–derived cells to the neurosensory retina (NSR) and RPE layer.

Methods

GFP chimeric mice and wild-type (WT) mice were subjected to SRPT using a slit-lamp infrared laser. Duty cycles of 5%, 10%, 15%, and 20% (0.1 seconds, 250 mW, spot size 50 μm) with 30 applications were placed 50 to 100 μm from the optic disc. In adoptive transfer studies, GFP⁺ cells were given intravenously immediately after WT mice received SRPT. Immunohistochemistry was done for ionized calcium-binding adapter molecule-1 (IBA-1⁺), CD45, Griffonia simplicifolia lectin isolectin B4, GFP or cytokeratin). Expression of Ccl2, Il1b, Il6, Hspa1a, Hsp90aa1, Cryab, Hif1a, Cxcl12, and Cxcr4 mRNA and flow cytometry of the NSR and RPE-choroid were performed.

Results

Within 12 to 24 hours of SRPT, monocytes were detected in the NSR and RPE-choroid. Detection of reparative progenitors in the RPE occurred at 2 weeks using flow cytometry. Recruitment of GFP⁺ cells to the RPE layer occurred in a duty cycle–dependent manner in chimeric mice and in mice undergoing adoptive transfer. Hspa1a, Hsp90aa1, and Cryab mRNAs increased in the NSR at 2 hours post laser; Hif1a, Cxcl12, Hspa1a increased at 4 hours in the RPE-choroid; and Ccl2, Il1b, Ifng, and Il6 increased at 12 to 24 hours in the RPE-choroid.

Conclusions

SRPT induces monocyte recruitment to the RPE followed by hematopoietic progenitor cell homing at 2 weeks. Recruitment occurs in a duty cycle–dependent manner and potentially could contribute to the therapeutic efficacy of SRPT.

Association of serum N(ε)-Carboxy methyl lysine with severity of diabetic retinopathy

PURPOSE

To correlate serum levels of N-epsilon-carboxy methyl lysine (N(ε)-CML) with severity of retinopathy, in vivo macular edema and disruption of external limiting membrane (ELM) and photoreceptor ellipsoid zone in type 2 diabetes mellitus (DM).

METHODS

Consecutive cases of type 2 DM [diabetes mellitus with no retinopathy (No DR) (n=20); non- proliferative diabetic retinopathy (NPDR) with diabetic macular edema (n=20); proliferative diabetic retinopathy with diabetic macular edema (PDR) (n=20)] and healthy controls (n=20) between the ages of 40 and 65 years were included (power of study=93.8%). In vivo histology of retinal layers was assessed using spectral domain optical coherence tomography. Every study subject underwent macular thickness analysis using the macular cube 512×128 feature. Disruption of ELM and photoreceptor ellipsoid zone was graded: grade 0, no disruption of ELM and ellipsoid zone; grade 1, ELM disrupted and ellipsoid zone intact; grade 2, both ELM and ellipsoid zone disrupted. Data were statistically analyzed.

RESULTS

The mean levels of N(ε)-CML were 31.34±21.23 ng/ml, 73.88±35.01 ng/ml, 91.21±66.65 ng/ml, and 132.08±84.07 ng/ml in control, No DR, NPDR and PDR respectively. N(ε)-CML level was significantly different between the study groups (control, No DR, NPDR and PDR) (p<0.001). Mean logMAR visual acuity decreased with increased levels of N(ε)-CML (p<0.001). The association of N(Ɛ)CML with the grades of disruption was found to be statistically significant (F value=18.48, p<0.001). Univariate analysis was done with N(Ɛ)-CML as a dependent variable. The values of N(Ɛ)-CML were normalized (log10) and were subjected to univariate analysis with fasting blood glucose level, glycosylated hemoglobin, central subfield macular thickness and cube average thickness among the diseased groups (NPDR and PDR) that act as confounders. It was found that none of the variables had significant effect on N(Ɛ)-CML (fasting blood glucose p=0.12, HBA1c p=0.65, central subfield macular thickness p=0.13, cube average thickness p=0.19). N(Ɛ)-CML tends to be a significant and important predictor of grade of ELM and ellipsoid zone disruption in diabetic retinopathy.

CONCLUSIONS

Increased N(ε)-CML levels are associated with increased severity of diabetic retinopathy, macular edema and structural changes in macula that is ELM and ellipsoid zone disruption, which serves as a prognosticator of visual outcome.

Recent developments in laser treatment of diabetic retinopathy

Laser photocoagulation has been the mainstay of diabetic retinopathy treatment since its development in mid-20^th century. With the advent of antivascular endothelial growth factor therapy, the role of laser therapy appeared to be diminished, however many advances in laser technology have been developed since. This review will describe recent advances in laser treatment of diabetic retinopathy including pattern scan laser, short-pulse duration and a reduced fluence laser, and navigated laser system for proliferative diabetic retinopathy and macular edema.

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.

Association between myopia and diabetic retinopathy: a review of observational findings and potential mechanisms

A protective, but inconsistent association between myopia and a decreased risk of diabetic retinopathy (DR) has been suggested in several studies. However, it is unclear whether the structural, or the refractive components of myopia; or both, is the main contributor to this protective relationship. This paper provides a comprehensive review of existing evidence on the association between myopia, and its structural (axial length [AL], anterior chamber depth [ACD]) and refractive (lens biometry and corneal curvature [CC]) components, with DR. 11 studies consisting of 7230 subjects from 1960 to April 2012, were reviewed. A longer AL was the only variable associated with a lower risk and severity of DR. Therefore, the available evidence suggests that AL is the main contributor to the protective influence of myopia on DR observed in earlier studies. Further investigations are now needed to determine the mechanisms by which AL protects against DR.

Notch signaling pathway regulates proliferation and differentiation of immortalized Müller cells under hypoxic conditions in vitro

Previous studies have indicated that Müller glia in chick and fish retinas can re-enter the cell cycle, express progenitor genes, and regenerate neurons via the Notch signaling pathway in response to retinal damage or growth factors. Here, we investigated the role of Notch signaling and the effect of hypoxia, as a means to induce retinal damage, on the proliferation of an immortalized Müller cell line (rMC-1 cells). Our data showed that rMC-1 cells expressed Müller glia and neural and retinal progenitor markers but did not express neuronal or retinal markers. Hypoxia increased rMC-1 cell proliferation by activating the positive cell-cycle regulators, cyclins A and D1, as well as the neural and retinal progenitor markers, Notch1, Hes1, nestin, Sox2, Msi1, Pax6, and NeuroD1. However, hypoxia did not significantly influence the expression of Müller glial markers GS, CRALBP, and cyclin D3 or the death of the rMC-1 cells. The increase in cell proliferation induced by hypoxia was greatly attenuated by blocking Notch signaling with the inhibitor DAPT, resulting in the reduced expression of positive cell-cycle regulators (cyclins A and D1) and neural and retinal progenitor markers (Notch1, Hes1, Sox2, Pax6, and NeuroD1). Blockade of the Notch signaling pathway by DAPT after hypoxia promoted the differentiation of rMC-1 cells to neurons, as demonstrated by the induction of neural marker (Tuj1), retinal amacrine (Syntaxin1), and retinal ganglion cell (Brn3b) markers, although the expression of the latter marker was low. Taken together, our data indicate that Notch signaling is required for proliferation under hypoxic conditions either by activating the positive cell-cycle regulators or by skewing their de-differentiation towards a neural progenitor lineage. These findings indicate that the Notch signaling pathway regulates hypoxia-induced proliferation and differentiation of Müller glia.

Optimal current and future treatments for diabetic macular oedema

Diabetic retinopathy is the most common cause of vision loss in working-age adults. Both inflammation and vascular endothelial growth factor (VEGF) play a critical role, modern and emerging treatments have centred on both laser photocoagulation and new pharmacologic strategies to improve the prognosis. Focal and grid photocoagulation, as described in the ETDRS trials, remain the gold standard of treatment. New classes of agents include long-acting steroid formulations delivered as intravitreal injections and also anti-VEGF agents. In addition, studies are under way to evaluate potential benefits from other novel agents, including those acting on the mammalian target of rapamycin pathway. In limited numbers of direct head-to-head comparisons, both steroids and anti-VEGF agents appear to be superior to conventional photocoagulation in reducing macular oedema in the first 4-6 months after treatment, although laser photocoagulation appears to be superior at time points of 1-2 years. In addition, there appear to be significant potential long-term complications of steroids including cataracts and glaucoma that may limit their use in certain patients. New methods of the laser delivery including shorter pulse durations and pattern scanning may also improve the effectiveness and risk profile of laser from the patient prospective. Finally, multi-modality therapy may play an increasingly important role.