The Blood-ocular Barriers and their Dysfunction: Anatomy, Physiology, Pathology

Complex barriers comprise the blood-aqueous (BAB) and the blood-retinal barrier (BRB), and separate anterior and posterior eye chambers, vitreous body, and sensory retina from the circulation. They prevent pathogens and toxins from entering the eye, control movement of fluid, proteins, and metabolites, and contribute to the maintenance of the ocular immune status. Morphological correlates of blood-ocular barriers are tight junctions between neighboring endothelial and epithelial cells, which function as gatekeepers of the paracellular transport of molecules, thereby limiting their uncontrolled access to ocular chambers and tissues. The BAB is composed of tight junctions between endothelial cells of the iris vasculature, endothelial cells of Schlemm's canal inner wall, and cells of the nonpigmented ciliary epithelium. The BRB consists of tight junctions between endothelial cells of the retinal vessels (inner BRB) and epithelial cells of the retinal pigment epithelium (outer BRB). These junctional complexes respond rapidly to pathophysiological changes, thus enabling vascular leakage of blood-derived molecules and inflammatory cells into ocular tissues and chambers. Blood-ocular barrier function, which can be clinically measured by laser flare photometry or fluorophotometry, is compromised in traumatic, inflammatory, or infectious processes, but also frequently contributes to the pathophysiology of chronic diseases of the anterior eye segment and the retina, as exemplified by diabetic retinopathy and age-related macular degeneration.

Blast Exposure Induces Ocular Functional Changes with Increasing Blast Over-pressures in a Rat Model

Purpose: Blast-related brain and ocular injuries can lead to acute and chronic visual dysfunction. The chronic visual consequences of blast exposure and its progression remain unclear. The goal of this study is to analyze ocular functional response to four levels of blast exposure and identify a threshold of blast exposure leading to acute and chronic visual dysfunction. Methods: Anesthetized adult male Long-Evans rats received a single-blast exposure at a peak overpressure of 78, 117, 164 or 213 kPa, delivered by a compressed air-driven shock tube. Clinical eye examination, intraocular pressure (IOP), flash electroretinography (fERG) and spectral-domain optical coherence tomography (SD-OCT) images were assessed prior to, and at multiple time points post exposure. Results: No abnormal fERG were observed for the two lowest-level blast groups (78 kPa or 117 kPa). For the 164 kPa group, the a- and b-wave amplitudes of the fERG were decreased at 3 days postexposure (p = 0.009 for a-wave, p = 0.010 for b-wave), but recovered to baseline levels by 7 days post-exposure. The IOP was unchanged for the 117 kPa and 164 kPa groups. The 78 kPa group demonstrated a small transient increase during week one (p = 0.046). For the highest blast group (213 kPa), the IOP was significantly elevated immediately post-exposure (p = 0.0001), but recovered by 24 hr. A bimodal depression in the fERG a- and b-wave amplitudes was observed for this group: the amplitudes were depressed at day 3 post-exposure (p = 0.007 for a-wave, p = 0.012 for b-wave), and recovered by day 7 post-exposure. However, the fERG amplitudes were once again depressed at week 8 post-exposure, suggesting a chronic retinal dysfunction. All retinae appeared normal in SD-OCT images. Conclusions: Our study demonstrates that a single-blast exposure may result in acute and chronic fERG deficit, and traumatic IOP elevation. Noninvasive functional tests may hold promise for identifying individuals with a risk for developing chronic visual deficits, and indicating a time window for early clinical diagnosis, rehabilitation, and treatment.

Contribution of prostanoid FP receptor and prostaglandins in transient inflammatory ocular hypertension

We explored the involvement of FP receptor and endogenous prostaglandins (PGs) in transient ocular hypertension (OH) induced by PGE2 or PGF2α in mouse eyes. PGE2 and PGF2α were topically applied to induce transient OH in Wild-type (WT) and FP-, EP1-, EP2-, and EP3-deficient (knockout [KO]) mice. To suppress endogenous PG production, the non-steroidal anti-inflammatory drug nepafenac was applied topically before treatment. PGE2 and PGF2α induced significant OH in the WT, FPKO, and EP1–3KO mice compared to the control 30 min after instillation, and the increase in IOP at 30 or 60 min after instillation in FPKO mice was significantly higher than that in the WT mice. The effects of PGF2α on the increase in IOP were significantly weaker than those of PGE2, especially in EP1KO and EP3KO mice. Transient OH induced by PGE2 and PGF2α was significantly attenuated by nepafenac treatment in FPKO mice. Transient OH was induced by PGE2 and PGF2α in WT, FPKO, and EP1–3KO mice, which was enhanced in FPKO mice. This OH was significantly diminished by nepafenac treatment in FPKO mice, suggesting that FP receptor may have an important naïve physiological role in the eye, and could regulate IOP elevation during PG-associated ocular inflammation.

The potential impact of recent insights into proteomic changes associated with glaucoma

INTRODUCTION

Glaucoma, a major ocular neuropathy, is still far from being understood on a molecular scale. Proteomic workflows revealed glaucoma associated alterations in different eye components. By using state-of-the-art mass spectrometric (MS) based discovery approaches large proteome datasets providing important information about glaucoma related proteins and pathways could be generated. Corresponding proteomic information could be retrieved from various ocular sample species derived from glaucoma experimental models or from original human material (e.g. optic nerve head or aqueous humor). However, particular eye tissues with the potential for understanding the disease's molecular pathomechanism remains underrepresented. Areas covered: The present review provides an overview of the analysis depth achieved for the glaucomatous eye proteome. With respect to different eye regions and biofluids, proteomics related literature was found using PubMed, Scholar and UniProtKB. Thereby, the review explores the potential of clinical proteomics for glaucoma research. Expert commentary: Proteomics will provide important contributions to understanding the molecular processes associated with glaucoma. Sensitive discovery and targeted MS approaches will assist understanding of the molecular interplay of different eye components and biofluids in glaucoma. Proteomic results will drive the comprehension of glaucoma, allowing a more stringent disease hypothesis within the coming years.