Effects of visible-light irradiation on vitreous structure in the presence of a photosensitizer

Laser-induced nanobubbles safely ablate vitreous opacities in vivo

In myopia, diabetes and ageing, fibrous vitreous liquefaction and degeneration is associated with the formation of opacities inside the vitreous body that cast shadows on the retina, appearing as 'floaters' to the patient. Vitreous opacities degrade contrast sensitivity function and can cause notable impairment in vision-related quality of life. Here we introduce 'nanobubble ablation' for safe destruction of vitreous opacities. Following intravitreal injection, hyaluronic acid-coated gold nanoparticles and indocyanine green, which is widely used as a dye in vitreoretinal surgery, spontaneously accumulate on collagenous vitreous opacities in the eyes of rabbits. Applying nanosecond laser pulses generates vapour nanobubbles that mechanically destroy the opacities in rabbit eyes and in patient specimens. Nanobubble ablation might offer a safe and efficient treatment to millions of patients suffering from debilitating vitreous opacities and paves the way for a highly safe use of pulsed lasers in the posterior segment of the eye.

Radiotherapy-induced alterations in vitreous humor: A new potential critical structure

Vitreous humor (VH) is not considered as a critical structure in the radiotherapy planning process. In the present study, an experimental animal model was performed to examine the effects of radiotherapy on VH. The right eyes of twelve New Zealand rabbits were irradiated to 60 Gy in 3 fractions in accordance with the scheme used in the treatment of uveal melanoma in our clinic, and contralateral (left) eyes were considered as control. Weekly ophthalmologic examination was performed after irradiation, for three months. At the end of the third month, enucleation and vitreous collection were conducted. The vitreous samples were subjected to metabolomic analyses, ELISA analyses, viscosity measurements, and electron microscopic examination. In control and experimental vitreous samples, 275 different metabolites were identified, and 34 were found to differ significantly between groups. In multivariate analyzes, a clear distinction was observed between control and irradiated vitreous samples. Pathway analysis revealed that nine pathways were affected, and these pathways were mainly related to amino acid metabolism. A significant decrease was observed in the expressions of type II, V, and XI collagens in protein level in the ELISA. There was a non-significant decrease in type IX collagen and viscosity. Electron microscopic examination revealed disrupted collagen fibrillar ultra-structure and dispersed collagen fragments in the experimental vitreous. An intact vitreous is essential for a healthy eye. In this study, we observed that radiation causes changes in the vitreous that may have long-term consequences.

Systemic oxidative stress biomarkers in patients with vitreomacular traction syndrome

PURPOSE

To evaluate whether the systemic oxidative stress biomarkers increased in patients with vitreomacular traction syndrome (VMT).

METHODS

This study compared 25 patients diagnosed with VMT with 20 healthy controls. As a biomarker of systemic oxidative stress, malondialdehyde (MDA) was measured. Total oxidant status (TOS) and total antioxidant status (TAS) were measured to evaluate the systemic oxidant status.

RESULTS

Serum MDA values were significantly higher among the patients (p < 0.001). The ideal cut-off value for MDA was determined to be 22.1 µmol/L, with 80% sensitivity and 75% specificity. The between-group differences were not statistically significant for TOS or TAS (p = 0.326 and p = 0.698, respectively).

CONCLUSION

Increased MDA levels suggest that systemic oxidative stress may play a role in VMT.

Hyaluronic acid-lipid binding

Background

Phospholipid (PL)–hyaluronic acid (HA) interactions are relevant to aging-associated vitreous humor liquefaction, therapies for dry eye disease, skin-care products and synovial joint lubrication. Phosphatidyl choline–HA interactions have been well characterized. However, other major lipids found in tears, vitreous humor and synovial joints have not. The purpose of this study was to bridge this gap of knowledge.

Methods

HA (1600 kDa) at 5 mg/mL, was mixed with various lipids ranging in concentration from 0.1 to 10 mg/mL in D₂O. HA–PL binding was measured from the decrease in HA proton resonance intensity with binding using a nuclear magnetic resonance spectrometer.

Results

Cholesterol weakly bound to HA, followed by monoglyceride and palmitoyl palmitate < phosphatidyl choline, phosphatidic acid and sphingomyelin. The maximum amount of PL bound was 14 ± 1 µmoles inferring a 1 to 1 molar ratio of bound PL to HA dimer. Monoglyceride and palmitoyl palmitate required two to three times more lipid to achieve 100% bound HA compared to PL.

Conclusions

Physiological levels of HA, phosphatidyl choline and sphingomyelin would result in only 4% of the hydrophobic hydrogens of HA to be bound. HA–PL binding interactions could be important for therapeutic use of HA in eye drops in future studies to treat dry eye and to trap PL entering the VH to keep them from forming light scattering micelles. HA–lipid binding may also be relevant to the therapeutic effects of topical skin-care products. Both head group and hydrocarbon chain moieties influence HA–lipid interactions.

Vitreous Antioxidants, Degeneration, and Vitreo-Retinopathy: Exploring the Links

The transparent vitreous body, which occupies about 80% of the eye’s volume, is laden with numerous enzymatic and non-enzymatic antioxidants that could protect the eye from oxidative stress and disease. Aging is associated with degeneration of vitreous structure as well as a reduction in its antioxidant capacity. A growing body of evidence suggests these age-related changes may be the precursor of numerous oxidative stress-induced vitreo-retinopathies, including vision degrading myodesopsia, the clinically significant entoptic phenomena that can result from advanced vitreous degeneration. Adequate intravitreal antioxidant levels may be protective against vitreous degeneration, possibly preventing and even improving vision degrading myodesopsia as well as mitigating various other vitreo-retinopathies. The present article is, therefore, a review of the different antioxidant molecules within vitreous and the inter-relationships between vitreous antioxidant capacity and degeneration.

Oxidative Stress, Lipid Peroxidation, and Loss of Hyaluronic Acid in the Human Vitreous Affected by Synchysis Scintillans

The aim of this study was to assess the oxidative stress status in eyes affected by synchysis scintillans and to compare it to vitreoretinal disorders without synchysis scintillans. Human aqueous and vitreous humors were obtained during vitrectomy from thirty-seven otherwise healthy patients that were randomly chosen among patients that had to undergo a 25-gauge pars plana vitrectomy from the central vitreous cavity, for either synchysis scintillans (n = 16) or vitreoretinal disorders without synchysis scintillans (n = 21), such as idiopathic epimacular membrane (n = 12), macular hole (n = 5), or rhegmatogenous retinal detachment (n = 4). The redox parameters thiobarbituric acid reactive substances (TBARS), a measurement of lipid peroxidation, nitrite concentration, an estimate of nitric oxide (NO) production, 4-hydroxynonenal (4-HNE)-protein conjugates, a structural protein modification by lipid peroxidation product 4-HNE, and the antioxidative activities of Cu,Zn-superoxide dismutase (SOD), and catalase were measured in aqueous and vitreous humors and compared between synchysis scintillans affected and not-affected patients. TBARS and nitrite levels of the vitreous humor were significantly higher in patients with synchysis scintillans as compared to patients affected by vitreoretinal disorders without synchysis scintillans. Synchysis scintillans patients had significantly lower activities of SOD and catalase both in aqueous and vitreous humors than patients with vitreoretinal disorders without synchysis. The consequently higher lipoperoxide-dependent 4-HNE production in synchysis scintillans was detectable in aqueous and vitreous humors as a significant increased accumulation of 4-HNE-protein conjugates vs nonsynchysis vitreoretinal disorders. Additionally, hyaluronic acid (HA) was significantly decreased in the vitreous body of synchysis scintillans patients. The data consistently show that synchisis scintillans is accompanied by a redox imbalance with increased oxidative modifications of 4-HNE proteins and loss of HA, both of likely importance for remote damages of the retina. It remains to be proven whether a therapeutic strategy which targets oxidative stress may be effective in the treatment of synchysis patients.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Evaluation of posterior vitreous detachment after uneventful phacoemulsification surgery by optical coherence tomography and ultrasonography

BACKGROUND

The aim was to investigate the effect of uneventful phacoemulsification on vitreoretinal interface evaluated by optical coherence tomography (OCT) and ultrasound.

METHODS

One hundred and fifty eyes were evaluated for the presence or absence of posterior vitreous detachment by ultrasound and OCT prior to cataract surgery. Only those eyes with intact vitreoretinal adhesion were included in the study. All patients underwent cataract surgery. At one month, three months and six months, all patients were assessed with OCT and ultrasound. The data were analysed for statistical significance.

RESULTS

The study was carried out on 30 of 31 patients with no posterior vitreous detachment. The mean age of patients was 62.63 ± 7.15 years (range 49 to 75 years) and 15 were female. Posterior vitreous detachment developed in 17 patients (56.66 per cent) at one month, 21 patients (70 per cent) at three months and 22 patients (73.33 per cent) at six months following the surgery. No complications or acute symptoms were detected associated with posterior vitreous detachment.

CONCLUSION

Vitreoretinal interface changes and vitreoretinal separations and progression of separation can be easily evaluated by OCT. The current study confirms that posterior vitreous detachment occurs commonly soon after cataract surgery.

From the analysis of pharmacologic vitreolysis to the comprehension of ocriplasmin safety

INTRODUCTION

Pharmacologic vitreolysis is a strategy used to treat anomalous posterior vitreous detachment, by weakening vitreoretinal adhesion with an intravitreal drug. Pharmacologic vitreolysis facilitates surgery, and abnormalities of the vitreoretinal interface including vitreomacular traction (VMT) and early stage macular hole (MH) could be resolved. Ocriplasmin is a recombinant protease, active against fibronectin and laminin, which are important components of the vitreoretinal interface. Ocriplasmin has been approved for symptomatic treatment of VMT and MH with visible traction, and it functions by dissolving the proteins that link the vitreous to the macula, thereby creating a complete posterior vitreous detachment (PVD).

AREAS COVERED

This paper reviews the current knowledge and status of investigations regarding the use of ocriplasmin for pharmacologic vitreolysis and its safety.

EXPERT OPINION

Ocriplasmin is a non-specific enzyme; therefore, it dissolves vitreal proteins as well as possibly proteins associated with visual function in the retina, choroid, and lens. Ocular adverse events (OAEs) of ocriplasmin include transient visual loss, intraocular inflammation, vitreous floaters, lens opacification, zonular instability of the lens, and intraocular hemorrhage. The prevalence of the OAEs is very low; however, on rare occasions, they can result in widespread retinal dysfunction. Research into the acute and long-term safety of ocriplasmin is required.

Evolution of early changes at the vitreoretinal interface after cataract surgery determined by optical coherence tomography and ultrasonography

PURPOSE

To evaluate the onset of posterior vitreous detachment (PVD) including early changes at the vitreoretinal interface after uneventful phacoemulsification in nonmyopic eyes using optical coherence tomography (OCT) and ultrasound.

DESIGN

Prospective consecutive study.

METHODS

Patients undergoing cataract surgery at our unit between January and October 2010 were recruited and examined with OCT and ultrasound preoperatively. Inclusion criteria were complete vitreoretinal attachment, no ocular pathology other than cataract, and no previous ocular surgery. All patients underwent phacoemulsification with intraocular lens implantation. Postoperatively, OCT and ultrasound were performed 1 month and 3 months after surgery. Exclusion criteria were axial length≥25 mm, lattice degeneration, intraoperative complications, and incomplete follow-up.

RESULTS

Forty-nine eyes of 49 patients could be enrolled in the study. Some degree of PVD was noted in 29 eyes (59.2%) 1 month after surgery and in 35 eyes (71.4%) 3 months after surgery. Moreover, a significant decrease in prevalence of initial PVD and a corresponding increase of more advanced PVD stages throughout the duration of the study was observed. In patients older than 70 years some degree of PVD was diagnosed in 92.3% compared to 47.8% in patients younger than 70 years (P=.002).

CONCLUSION

OCT facilitates the detection of early vitreoretinal separation that indicates initial PVD. After phacoemulsification the prevalence of some degree of PVD is consequently more frequent when supplementary OCT is used. Furthermore, OCT discloses a significant progression of PVD in the postoperative course. Patients older than 70 years are more likely to develop pseudophakic PVD.

Emerging nonsurgical methods for the treatment of vitreomacular adhesion: a review

With the dissemination of optical coherence tomography over the past two decades, the role of persistent vitreomacular adhesion (VMA) in the development of numerous macular pathologies - including idiopathic macular hole, vitreomacular traction syndrome, cystoid and diabetic macular edema, neovascularization in diabetic retinopathy and retinal vein occlusion, exudative age-related macular degeneration, and myopic traction maculopathy - has been established. While invasive vitreoretinal procedures have long been utilized to address complications related to these disorders, such an approach is hampered by incomplete vitreoretinal separation and vitreous removal, surgical complications, and high costs. In light of such limitations, investigators have increasingly looked to nonsurgical means for the treatment of persistent pathologic VMA. Chief among these alternative measures is the intravitreal application of pharmacologic agents for the induction of vitreous liquefaction and/or vitreoretinal separation, an approach termed pharmacologic vitreolysis. This article aims to review the available evidence regarding the use of pharmacologic agents in the treatment of VMA-related pathology. In addition, a discussion of vitreous molecular organization and principles of physiologic posterior vitreous detachment is provided to allow for a consideration of vitreolytic agent mode of action and molecular targets.

Axillary and rectal temperature measurements poorly agree in newborn infants

AIM

Evaluation of the agreement between axillary temperature measurements and rectal temperature measurements in neonates.

METHODS

Rectal and axillary body temperatures were simultaneously measured for 3 min in 33 neonates (gestational age 25-42 weeks, weight 840-4,005 g). Two investigators performed paired measurements, one in each neonate. A single type of thermometer was used in this study: one thermometer for each rectal and another thermometer for each axillary measurement. The Bland-Altman method was used (95% 'limits of agreement': mean +/- 2 SD) to determine the level of agreement between axillary and rectal measurements.

RESULTS

The axillary temperature was significantly lower than the rectal temperature (mean +/- SD 0.27 +/- 0.20 degrees C, p < 0.05). The '95% limits of agreement' ranged from -0.13 to +0.67 degrees C. Increasing postnatal age (days) showed a significant increase in temperature difference (rectal minus axillary; r = 0.54; p < 0.05).

CONCLUSIONS

The mean difference between axillary and rectal temperature shows a wide variation. Axillary temperature measurements cannot be used interchangeably with rectal measurements in neonates.

Effects of Advanced Glycation End Products on Hyaluronan Photolysis: A New Mechanism of Diabetic Vitreopathy

PURPOSE

To test the effects of advanced glycation end products (AGEs), which are increased in vitreous of diabetic patients, on photolysis of hyaluronan.

METHODS

Pullulan standards were used as molecular weight (MW) markers to obtain a calibration curve. 0.02% hyaluronan solutions were divided into AGE-added and AGE-free samples; each sample was irradiated using a xenon lamp or kept in the dark. Retention time (RT) was measured for each sample using high-performance liquid chromatography.

RESULTS

RTs and logarithm of MW of pullulan standards were negatively correlated. In hyaluronan samples exposed to light, RT increased significantly for both AGE-added and AGE-free samples compared with samples kept in the dark. RT in AGE-added samples was greater by 3% than that in AGE-free samples (p = 0.02).

CONCLUSIONS

Exposure to light decreases MW of hyaluronan; addition of AGEs promotes this change. The photosensitizer activity of AGEs may be associated with accelerated depolymerization of hyaluronan in diabetic patients.

Variations of posterior vitreous detachment

AIMS

To identify variations in posterior vitreous detachment (PVD) and establish a clinical classification system for PVD.

METHODS

400 consecutive eyes were examined using biomicroscopy and vitreous photography and classified the PVD variations-complete PVD with collapse, complete PVD without collapse, partial PVD with thickened posterior vitreous cortex (TPVC), or partial PVD without TPVC.

RESULTS

In each PVD type, the most frequently seen ocular pathologies were as follows: in complete PVD with collapse (186 eyes), age related changes without vitreoretinal diseases (77 eyes, 41.4%) and high myopia (55 eyes, 29.6%); in complete PVD without collapse (39 eyes), uveitis (23 eyes, 59.0%) and central retinal vein occlusions (8 eyes, 20.5%); in partial PVD with TPVC (64 eyes), proliferative diabetic retinopathy (30 eyes, 46.9%); and inpartial PVD without TPVC (111 eyes), age related changes without vitreoretinal diseases (62 eyes, 55.9%). This PVD categorisation was significantly associated with the prevalence of each vitreoretinal disease (p < 0.0001, chi 2 test on contingency table).

CONCLUSIONS

PVD variations can be classified into four types, which is clinically useful because each type corresponds well to specific vitreoretinal changes.

Serum-induced collagen gel contraction

PURPOSE

To understand the molecular events underlying disease-related vitreous gel contraction, the effect of serum components on collagen was investigated.

METHODS

Bovine vitreous or dermal collagen was incubated with a mixture of transglutaminase (TG; factor XIIIa) and fibronectin (FN), and the biochemical changes of collagen were monitored by gel electrophoresis. In addition, serum-induced changes in the volume of the collagen gel were monitored.

RESULTS

Gel electrophoresis revealed a new high-molecular-weight band (M(r) 240,000) presumably due to intermolecular cross-links of collagen peptides and FN. The serum components also were shown to cause a significant decrease in the volume of the collagen gel. CONCLUSION. Collagen gel contraction could be attributed to the collagen-FN-collagen cross-links catalyzed by TG.

Mechanisms of photo-induced vitreous liquefaction

To understand the mechanisms of photo-induced vitreous liquefaction, this study investigated the effects of free radicals on collagen and hyaluronic acid (HA). Bovine vitreous collagen or HA was irradiated by visible light in the presence of riboflavin (RF) as a photosensitizer. The changes in the molecular weight of collagen and HA were monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography, respectively. Free radicals were shown to cause an increase in the high-molecular-weight components and insolubilization of the vitreous collagen and a decrease in the molecular weight of HA. The change in molecular properties of the vitreous collagen could be attributed to extensive crosslinks of the molecules. Since RF is present in the vitreous, which is irradiated by visible light over a lifetime, both cross-links of vitreous collagen and degradation of HA may contribute to age-related vitreous liquefaction.

Molecular mechanisms of posterior vitreous detachment

To determine a molecular mechanism for posterior vitreous detachment and contraction of vitreous gel, the effects of serum components on bovine vitreous were systematically studied. Incubation of vitreous gel with calf serum caused a contraction of the gel accompanied by the release of a waterlike liquid. The low molecular weight fraction (M(r) < 10,000) of serum was ineffective in this process, whereas incubation of the vitreous with the high molecular weight fraction resulted in changes in the gel structure similar to those caused by serum alone. Individually, transglutaminase (factor XIIIa) was found to be most effective in inducing gel contraction. The effect was more pronounced when transglutaminase was used with fibronectin. Since transglutaminase is known to promote collagen-collagen or collagen-fibronectin-collagen cross-links, the contraction of the vitreous in this case can be attributed to the formation of similar cross-links.

Liquefaction of human vitreous in model aphakic eyes by 300-nm UV photolysis: monitoring liquefaction by fluorescence

After the lens is removed in cataract surgery, the vitreous presumably receives all of the ambient 300-nm light that has filtered through the cornea. Using this model for aphakic eyes, we progressively irradiated intact vitreous samples of a 49-year-old human with 300-nm light and monitored changes in absorption, fluorescence, and circular dichroism (CD) properties. CD and fluorescence measurements of unirradiated vitreous samples showed a) a strong tryptophan fluorescence band of non-collagenous protein at 336 nm and a very weak band around 430 nm due to N-formylkynurenine (N-FK), a photoproduct of tryptophan, and b) a strong, negative CD band below 250 nm representing a composite spectrum of hyaluronic acid, collagen, and non-collagenous protein. Upon irradiation, the tryptophan emission band at 336 nm progressively decreased with time and the band maximum was concomitantly red-shifted; the N-FK fluorescence band at 430 nm, on the other hand, continually increased with the time of irradiation. A significant increase in the fluidity (liquefaction) of the vitreous gel also was noted upon irradiation, a change that was monitored successfully by measuring the progressive decrease in the polarization value of tryptophan fluorescence. The extent of liquefaction, measured spectroscopically, was found to be 40% upon irradiation for 10 hr. In addition, CD measurements indicated a partial loss in the secondary structure of the non-collagenous protein.

Ageing of the vitreous

Changes that occur in the vitreous during ageing contribute to a variety of vitreo-retinal disorders. These age-related changes are rheologic, biochemical, and structural in nature. Our current knowledge of these ageing changes is reviewed. Hypotheses for the mechanisms of liquefaction (synchisis senilis) and posterior vitreous detachment are proposed.