Lower intraocular oxygen tension in diabetic patients: possible contribution to decreased incidence of nuclear sclerotic cataract

In vivo measurement of T1 in the vitreous humor of patients with ischemic retinal disease

PURPOSE

To demonstrate MR T1 mapping in vivo as a method to non-invasively estimate vitreous oxygen concentration in ischemic eye disease.

METHODS

Patients with ischemic eye disease (central retinal vein occlusion, ocular ischemic syndrome, and proliferative diabetic retinopathy) were prospectively recruited. MRI was performed on each patient before any treatment, with T1 mapping acquired using an inversion recovery TrueFISP sequence at several inversion times, from a single slice positioned through the center of both eyes in the axial oblique plane. A phantom study measuring seven different concentrations of vitronectin, a protein released in ischemic eye disease, was undertaken to determine its potential confounding effect on T1 .

RESULTS

Ten participants were recruited (eight central retinal vein occlusion, one ocular ischemic syndrome, and one proliferative diabetic retinopathy). Of the eight central retinal vein occlusion cases, there was a statistically different vitreous T1 in the diseased eye compared to the healthy control eye (4.306 vs. 4.518 s, p = 0.008). T1 times did not significantly alter across the range of vitronectin concentrations.

CONCLUSIONS

Ischemic eye disease decreases vitreous T1 , potentially implying an increase in vitreous partial pressure of oxygen (pO2 ) concentration given what is known from the relationship between 1/T1 and pO2 . Potential theories for this unexpected result are discussed. This study provides further data on this technique, with potential clinical application in eye disease.

Electron, Photon, and Neutron Dose Conversion Coefficients of Lens and Non-Lens Tissues Using a Multi-Tissue Eye Model to Assess Risk of Cataracts and Retinitis

Previous publications describe the estimation of the dose from ionizing radiation to the whole lens or parts of it but have not considered other eye tissues that are implicated in cataract development; this is especially critical for low-dose, low-ionizing-density exposures. A recent review of the biological mechanisms of radiation-induced cataracts showed that lenticular oxidative stress can be increased by inflammation and vascular damage to non-lens tissues in the eye. Also, the radiation oxygen effect indicates different radiosensitivities for the vascular retina and the severely hypoxic lens. Therefore, this study uses the Monte Carlo N-Particle simulations to quantify dose conversion coefficients for several eye tissues for incident antero-posterior exposure to electrons, photons, and neutrons (and the tertiary electron component of neutron exposure). A stylized, multi-tissue eye model was developed by modifying a model by Behrens etal. (2009) to include the retina, uvea, sclera, and lens epithelial cell populations. Electron exposures were simulated as a single eye, whereas photon and neutron exposures were simulated employing two eyes embedded in the ADAM-EVA phantom. For electrons and photons, dose conversion coefficients are highest for either anterior tissues for low-energy incident particles or posterior tissues for high-energy incident particles. Neutron dose conversion coefficients generally increase with increasing incident energy for all tissues. The ratio of the absorbed dose delivered to each tissue to the absorbed dose delivered to the whole lens demonstrated the considerable deviation of non-lens tissue doses from lens doses, depending on particle type and its energy. These simulations demonstrate that there are large variations in the dose to various ocular tissues depending on the incident radiation dose coefficients; this large variation will potentially impact cataract development.

Intraoperative oxygen tension and redox homeostasis in Pseudomyxoma peritonei: A short case series

Introduction

Pseudomyxoma peritonei (PMP) is a rare malignant disease characterized by a massive multifocal accumulation of mucin within the peritoneal cavity. The current treatment option is based on complete cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy. However, the recurrence is frequent with subsequent progression and death. To date, most of the studies published in PMP are related to histological and genomic analyses. Thus, the need for further studies unveiling the underlying PMP molecular mechanisms is urgent. In this regard, hypoxia and oxidative stress have been extensively related to tumoral pathologies, although their contribution to PMP has not been elucidated.

Methods

In this manuscript, we have evaluated, for the first time, the intratumoral real-time oxygen microtension (pO2mt) in the tumor (soft and hard mucin) and surrounding healthy tissue from five PMP patients during surgery. In addition, we measured hypoxia (Hypoxia Inducible Factor-1a; HIF-1α) and oxidative stress (catalase; CAT) markers in soft and hard mucin from the same five PMP patient samples and in five control samples.

Results

The results showed low intratumoral oxygen levels, which were associated with increased HIF-1α protein levels, suggesting the presence of a hypoxic environment in these tumors. We also found a significant reduction in CAT activity levels in soft and hard mucin compared with healthy tissue samples.

Discussion

In conclusion, our study provides the first evidence of low intratumoral oxygen levels in PMP patients associated with hypoxia and oxidative stress markers. However, further investigation is required to understand the potential role of oxidative stress in PMP in order to find new therapeutic strategies.

Lower Blood Oxygen Saturation is Associated With Microvascular Complications in Individuals With Type 1 Diabetes

CONTEXT

Blood oxygen saturation (SpO2) is lower in type 1 diabetes (T1D) compared with nondiabetic controls. Hypoxia (low tissue oxygenation) is thought to be a risk factor for progression of diabetic complications, but it is unknown whether hypoxemia (low SpO2) is associated with diabetic complications.

OBJECTIVE

To test if hypoxemia is associated with presence of diabetic complications in T1D.

DESIGN, SETTING, AND METHODS

Cross-sectional study in persons with T1D divided by a previously suggested threshold in low (<96%) and high (≥96%) SpO2, measured in the supine position with pulse oximetry. Complications included albuminuria (2 of 3 consecutive measurements ≥30 mg/g), any diabetic retinopathy, neuropathy, and history of cardiovascular disease (CVD). Odds ratios were adjusted for age, diabetes duration, sex, smoking, physical activity, body mass index, systolic blood pressure, and blood hemoglobin.

RESULTS

We included 659 persons, 23 (3.5%) with low and 636 (96.5%) with high SpO2. In total, 151 (23%) had albuminuria, 233 (36%) had retinopathy, 231 (35%) had neuropathy, and 72 (11%) had CVD. The adjusted odds ratio (95% CI, P value) for low vs high SpO2 was 3.4 (1.3-8.7, P = 0.01) for albuminuria, 2.8 (1.0-7.5, P = 0.04) for retinopathy, 5.8 (1.8-18.6, P < 0.01) for neuropathy, and nonsignificant for CVD (0.6 [0.2-2.4, P = 0.51]).

CONCLUSIONS

SpO2 below 96% was associated with increased presence of albuminuria, retinopathy, and neuropathy in T1D, but not with CVD. Whether hypoxemia could be a target of intervention to prevent progression in microvascular disease in type 1 diabetes should be investigated.

The Postvitrectomy Cataract

To review the recent literature regarding risk factors for cataract formation after vitrectomy, the challenges and management strategies for anterior segment surgeons when facing post-vitrectomy cataract surgery, and the visual outcomes of patients undergoing post-vitrectomy cataract surgery. Cataract surgery after vitrectomy can be safely performed to significantly improve the visual outcome in most post-vitrectomy patients, although final visual acuity is primarily limited by the patient’s underlying vitreoretinal pathology.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Retinal Oxygen Delivery and Metabolism Response to Hyperoxia During Bilateral Common Carotid Artery Occlusion in Rats

Purpose

The purpose of the current study was to test the hypothesis that responses of total retinal blood flow (TRBF), inner retinal oxygen delivery (DO₂), metabolism (MO₂), and extraction fraction (OEF) to hyperoxia are higher after minutes of bilateral common carotid artery occlusion (BCCAO) as compared to days of BCCAO.

Methods

Twenty-eight rats were subjected to BCCAO for 30 minutes (n = 12), 1 day (n = 8), or 3 days (n = 8). Eight of the 12 rats were also evaluated at baseline, prior to BCCAO. During room air breathing (RA) and 100% O₂ inspiration (hyperoxia), blood flow and phosphorescence lifetime imaging were performed to measure TRBF and vascular O₂ contents, respectively. DO₂, MO₂, and OEF were calculated from these measurements.

Results

After 30 minutes or 3 days of BCCAO, TRBF did not differ between RA and hyperoxia conditions (P ≥ 0.14) but decreased under hyperoxia after 1 day (P = 0.01). Compared to RA, DO₂ and MO₂ were increased under hyperoxia after 30 minutes of BCCAO (P ≤ 0.02). Additionally, MO₂ was decreased under hyperoxia after 1 day of BCCAO (P = 0.04). OEF was decreased under hyperoxia compared to RA (P < 0.001). Under hyperoxia, TRBF and DO₂ were reduced after all BCCAO durations compared to baseline (P ≤ 0.04), whereas MO₂ did not differ from baseline after 30 minutes of BCCAO (P = 1.00).

Conclusions

The findings indicate that hyperoxia introduced minutes after ischemia can reduce DO₂ impairments and potentially return MO₂ to approximately normal values. This information contributes to the knowledge of the effect of supplemental oxygen intervention on TRBF, DO₂, MO₂, and OEF outcomes after variable durations of ischemia.

Predicting speed of progression of lens opacification after pars plana vitrectomy with silicone oil

Purpose

An increasing number of posterior segment disorders is routinely managed with pars plana vitrectomy (PPV). In older, phakic patients cataract formation is expected within the first two years after surgery. For younger patients its progression is individually fluctuating. This study uses an objective quantitative measurement for lens-status-monitoring after PPV with silicone oil to derive predictions for progression and severity of post-operative lens opacification evaluated in patients with rhegmatogenous retinal detachment (RRD).

Methods

Data acquisition was performed prospectively between March 2018 and March 2021. PentacamHR® Nucleus Staging mode (PNS) was used to objectively gather data about nuclear cataracts after PPV at different time points. Data was grouped into training and test sets for a mathematical prediction model. Via backward variable selection method a mathematical formula was set up by means of which predictions about lens densitometry (LD) can be calculated.

Results

20 males [58.8%] and 14 females [41.2%] matched the inclusion criteria (mean age 50.6 years [23–75; ±12.3]). Average follow-up was 8.1 months (3,4–17.4; ±3.4). Mean baseline LD of the treated and fellow eye before surgery was 11.1% (7.7%-17.6%; ±2.0) and 11.2% (7.7%-14.8%; ±1.5), respectively. Predicted LD values by the model for five pre-selected patients closely match the observed data with an average deviation of 1.06%.

Conclusions

Using an objective parameter like LD delivered by the PentacamHR® PNS mode additionally to the patient’s age allows us to make an individual prediction for any time after PPV with silicone oil due to RRD for all ages. The accuracy of the model was stronger influenced by baseline LD as cofactor in the equation than patient’s age. The application for the prediction lens opacification [which can be accessed for free under the following link (https://statisticarium.com/apps/sample-apps/LensDensityOil/)] can help vitreoretinal surgeons for patient consultation on the possibility to combine PPV with cataract surgery.

Vitrectomy for diabetic macular edema and the relevance of external limiting membrane

PURPOSE

To evaluate the relevance of external limiting membrane (ELM) on the visual and morphological results in eyes with diabetic macular edema (DME) that underwent pars plana vitrectomy (PPV) with epiretinal membrane (ERM) and internal limiting membrane (ILM) peeling.

METHODS

Medical records of patients with DME who underwent PPV at our unit between January 2017 and December 2019 were reviewed. We assessed preoperative and postoperative best-corrected visual acuity (BCVA), central macular thickness (CMT) using spectral domain OCT (optical coherence tomography). Exclusion criteria were previous PPV; incomplete data; concomitant diseases including retinal vein occlusion, age-related macular degeneration, uveitis; and a follow-up of less than 12 months. The surgeries were performed using 23- or 27-gauge vitrectomy. The ELM was graded depending on its configuration (grade 0 = intact, grade 1 to 3: disruption of varying extent).

RESULTS

Ninety-nine eyes were enrolled. The postoperative follow up averaged 23.7 months. The preoperative and final BCVA averaged 0.71 ± 0.28 and 0.52 ± 0.3 logMAR, respectively (p = 0.002). The CMT averaged 515.2 ± 209.1 μm preoperatively and 327 ± 66.1 μm postoperatively (p = 0.001). Eyes with intact ELM (n = 8) had a significantly better BCVA compared to those with ELM disruption (0.28 ± 0.14 vs. 0.7 ± 0.25 logMAR, p = 0.01). The final CMT was similar among the groups (intact ELM: 317 ± 54.6 μm; ELM disruption: 334 ± 75.2, p = 0.31).

CONCLUSIONS

PPV with ERM and ILM peeling is an effective treatment of DME. Eyes with intact ELM preoperatively had a significantly better final visual outcome. To maximize the benefit for patients with DME we recommend early PPV as long as ELM is intact.

Lens densitometry for assessment and prediction of cataract progression after pars plana vitrectomy with C3F8-gas for retinal detachment

Purpose

Lens opacification is a common complication after pars plana vitrectomy (PPV) and knowing its progression would facilitate consulting patients. The purpose of this study was to evaluate a quantitative model for lens-status-monitoring after PPV with C3F8 gas. Our model was evaluated in rhegmatogenous retinal detachment (RRD) patients of various age and lens densitometry (LD).

Methods

Data between March 2018 and March 2020 were evaluated retrospectively. LD measurements of the PentacamHR® Nucleus Staging mode (PNS) were used to quantify lens opacification over time. A mixed-effect regression model was designed, to enable LD predictions at any time postoperatively. Calculations were based on patient’s age and baseline LD as dependent variables. Six patients were randomly excluded during model development, to be used for testing its power afterwards.

Results

34 patients (male 19 [55.9%], female 15 [44.1%]) matched the inclusion criteria. Average age was 58.5 years (32–77;±4.3) and average follow-up was 7.2 months (3,4–23.1;±1,8). Mean baseline LD of the treated and fellow eye before surgery were 10.9% (8.7%-14.8%;±0.8) and 10.7% (8.5%-14.1%;±0.6), respectively. Using our prediction model, LD values for the six pre-selected patients closely match the observed data with an average deviation of 1.07%.

Conclusions

Evaluation of age and baseline LD using a mixed-effect regression model might predict cataract progression in RRD patients treated with PPV and C3F8-gas. Such a tool could be considered during cataract surgery consultation in these patients.

In vivo Oxygen Condition of Human Nasal Inferior Turbinate-Derived Stem Cells in Human Nose

BACKGROUND AND OBJECTIVE

Human nasal inferior turbinate-derived stem cells (hNTSCs) have been considered as a potent and useful source for regenerative medicine. To most effectively mimic the native environment of inferior turbinate could be very effective to hNTSCs biology. Thus, the purpose of this study was to evaluate partial pressure of oxygen (ppO2) and temperature in inferior turbinate.

METHODS

Ten patients were enrolled who underwent endoscopic endonasal transsphenoidal skull base tumor surgery between January 2014 and December 2015. The commercially available OxyLab pO2 monitor gauges the ppO2 and temperature using a fluorescence quenching technique. Also, hNTSCs were isolated from 10 patients and cultivated under hypercapnic condition (5, 10, and 15%) to mimic hypoxic intranasal conditions.

RESULTS

The measured oxygen concentration in submucosa tissue was higher than that at the surface of the inferior turbinate and the temperature in submucosa tissue was higher than the value at the surface of inferior turbinate. The patterns of proliferation were significantly different according to hypercapnic cultivation conditions and there were statistically significant decreased proliferation rates after the exposure of higher CO2 over a period of 5 days.

CONCLUSIONS

Intranasal turbinate tissue showed the hypoxia state in concordance with the result of the other tissues or organs. However, indirectly induced hypoxia influenced the influence on the hNTSCs proliferation negatively. Further study is needed to mimic the real hypoxic state, but our results could be used to optimize the culture environment of hNTSCs, thereby producing the stem cells for regenerative therapies.

The Influence of Diabetes Status on the Rate of Cataract Surgery Following Pars Plana Vitrectomy

PURPOSE

We aimed to evaluate the association between diabetic status and the rates of cataract extraction (CE) following pars plana vitrectomy (PPV).

DESIGN

Retrospective cohort, multicenter database study.

PARTICIPANTS

Patients were selected from an insurance claims database (PharMetrics LifeLink) that included persons who had filed claims between 2006 and 2015 in the United States.

METHODS

We analyzed the records of 22 146 patients who underwent PPV performed by 2705 retina physicians. The vitrectomy group included patients ≥18 years of age who had undergone PPV. The control group included patients who were matched to the vitrectomy group 1:2 based on sex, diabetes mellitus (DM) status, region of the United States, and Charleston Comorbidity Index.

MAIN OUTCOME MEASURES

Hazard ratios (HRs) and rates of cataract surgery in patients with and without diabetes who had undergone prior PPV.

RESULTS

The hazard ratio for post-PPV CE was lower among patients with diabetes (3.307; 95% confidence interval [CI], 3.051-3.583) than among patients without diabetes (4.889; 95% CI, 4.670-5.119). This association was significant for all subgroups of patients with diabetes except in patients with diabetes and without retinopathy (4.086; 95% CI, 3.511-4.754). There was a significantly longer time between PPV and CE in patients with diabetes (537 days; 95% CI, 459-677 days) compared with those without diabetes (295 days; 95% CI, 278-312 days). The type of DM (type 1 vs. type 2) did not influence the rate of post-PPV cataract surgery. In persons with diabetes who underwent PPV, we observed a trend for a lower HR of cataract surgery in eyes with proliferative retinopathy (0.903; 95% CI, 0.725-1.124), and nonproliferative retinopathy (0.965; 95% CI, 0.721-1.290) compared with eyes with no retinopathy.

CONCLUSIONS

Eyes of patients with diabetes had a significantly decreased risk of undergoing CE after PPV surgery compared with eyes of patients without diabetes.

Intraocular Oxygen and Antioxidant Status: New Insights on the Effect of Vitrectomy and Glaucoma Pathogenesis

PURPOSE

The purpose of this study was to investigate correlations of partial pressure of oxygen (pO₂) in the ocular anterior segment of human eyes and aqueous humor antioxidant levels of ascorbate (AsA) and total reactive antioxidant potential (TRAP) with glaucoma and vitreous status.

METHODS

This prospective, cross-sectional study stratified patients (n = 288 eyes) by lens and vitreous status and the presence of primary open-angle glaucoma for statistical analyses. Intraocular pO₂ concentrations were measured using a fiberoptic probe in patients at the beginning of planned glaucoma and/or cataract surgery. Aqueous humor specimens were obtained for antioxidant analysis of AsA and TRAP.

RESULTS

Following prior pars plana vitrectomy, pO₂ levels were significantly higher than in the reference group of cataract surgery in the anterior chamber angle (16.2 ± 5.0 vs. 13.0 ± 3.9 mm Hg; P = .0171) and in the posterior chamber (7.6 ± 3.1 vs. 3.9 ± 2.7 mm Hg; P < .0001). AsA and TRAP levels were significantly lower (1.1 ± 0.4 vs. 1.4 ± 0.5 mM, respectively; 403.3 ±116.5 vs. 479.0 ± 146.7 Trolox units, respectively; P = .004 and P = .024, respectively) in patients after vitrectomy. In patients with an intact vitreous, neither pO₂ nor antioxidant status correlated with lens status or glaucoma.

CONCLUSIONS

Increased pO₂ and antioxidant depletion following vitrectomy suggests an alteration of the intraocular oxidant-antioxidant balance. Our study links physiologic factors such as increased pO₂ in the anterior chamber angle and the posterior chamber to decreased antioxidant levels in aqueous humor following vitrectomy. Oxidative stress/damage to the trabecular meshwork in such post-vitrectomy cases may contribute to intraocular pressure elevation and increased risk of glaucoma. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Surgical management of diabetic tractional retinal detachments

Tractional retinal detachment is an end-stage form of diabetic retinopathy that occurs when contractile forces in the vitreous and neovascular tissue lead to the detachment of the neurosensory retina. We review the literature related to the management of this disease. Preoperative planning includes appropriate patient selection, diagnostic and prognostic imaging, and medical optimization with reduction of systemic risk factors. Use of antivascular endothelial growth factor for preoperative treatment has had significant benefits for tractional retinal detachment repair in improving surgical efficiency and outcomes. Advances in microsurgical instrumentation are discussed, with attention to small-gauge vitrectomy with improved flow dynamics, viewing strategies, and lighting allowing bimanual surgery. Special emphasis is placed on bimanual surgical technique, choice of tamponade, and the avoidance of iatrogenic damage. Complications and special considerations are further explored. Based on our compilation of relevant literature, we propose a surgical algorithm for the management of these complex patients.

The Different Facades of Retinal and Choroidal Endothelial Cells in Response to Hypoxia

Ocular angiogenic diseases, such as proliferative diabetic retinopathy and neovascular age-related macular degeneration, are associated with severe loss of vision. These pathologies originate from different vascular beds, retinal and choroidal microvasculatures, respectively. The activation of endothelial cells (EC) plays pivotal roles in angiogenesis, often triggered by oxygen deficiency. Hypoxia-inducible factors in ECs mediate the transcription of multiple angiogenic genes, including the canonical vascular endothelial growth factors. ECs show notable heterogeneity in function, structure, and disease, therefore the understanding of retinal/choroidal ECs (REC; CEC) biochemical and molecular responses to hypoxia may offer key insights into tissue-specific vascular targeting treatments. The aim of this review is to discuss the differences spanning between REC and CEC, with focus on their response to hypoxia, which could provide innovative and sustainable strategies for site specific targeting of ocular neovascularization.

Preliminary results from the use of intraoperative real-time biliary oxygen monitoring in liver transplantation

BACKGROUND AND AIMS

Biliary anastomosis is a frequent area of complications after liver transplantation (LT) and a potential area of "microangiopathy". The concept of a "marginal bile duct" is unexplored. The main aim was to make a preliminary evaluation of the utility of an innovative real-time oxygen microtension (pO2mt) testing device for the assessment of bile duct viability during LT and to correlate these pO2mt values with microvascular tissue quality by histopathology and outcomes.

PATIENTS AND METHODS

Observational prospective cohort study with 23 patients. Oxygen microtension measurements were made placing a micropO2 probe in different areas of recipient and donor's bile duct intraoperative.

RESULTS

Mean pO2mt in the graft bile duct at the level of the anastomosis 103.82 (31-157) mm Hg, being 121.52 (55-174) mm Hg 1.5 cm proximal to the hilar plate (P < 0.001). Mean pO2mt in the recipient's bile duct was 117.87 (62-185) mm Hg, while a value of 137.30 (81-198) mm Hg was observed 1.5 cm distal to the anastomosis (P < 0.001). Cystic duct resection (12 cases) was also related with higher pO2mt values at anastomosis [117.8 (93-157) vs 88.54 (31-124) mm Hg] and distal to anastomosis [135.6 (111-174) vs 106.2 (55-133) mm Hg; P < 0.001]. Patients with 1-, 3-, and 12-month biliary complications had significantly lower pO2mt in the intraoperative measurements.

CONCLUSION

Our preliminary results show that distal borders of donor and recipient bile ducts may be low-vascularized areas. Tissue pO2mt is significantly higher in areas close to the hilar plate and to the duodenum in donor and recipient's sides, respectively. Bile duct injury and biliary complications are associated with worse tissue pO2mt.

Visual outcome and complications of cataract extraction after pars plana vitrectomy

Purpose

To evaluate the visual outcomes and complications of phacoemulsification in previously vitrectomized eyes.

Patients and methods

A retrospective analysis of 87 consecutive vitrectomized eyes (87 patients) which had undergone phacoemulsification with intraocular lens implantation between 2013 and 2016.

Results

The mean interval from pars plana vitrectomy (PPV) to cataract surgery (CS) was 18.8 months. Mean age at CS was 61.5 years. Intraoperative complications included anterior rhexis tear (1 eye) and hyphema (1 eye). Postoperative complications included macular edema (17.2%, mean 42 days), posterior capsule opacification (13.8%, mean 14 months), ocular hypertension (11.5%), and anterior uveitis (1.1%). Preoperative mean best-corrected visual acuity improved from 20/50 to 20/25. Ninety-one percent of the eyes gained 2 or more lines, and 95% achieved visual acuity ≥20/40 after CS. Preoperative mean spherical equivalent improved from -4.35 to -0.17. Eyes with clear lens prior to the PPV had later CS (clear lens 27.1 vs no clear lens 9.7 months; p=0.016). Patients >55 years with clear lens at PPV (n=21) had earlier CS than younger ones with clear lens (n=24) (11.8 vs 40.5 months; p=0.033). Mean follow-up was 14.5 months.

Conclusion

Phacoemulsification is a safe procedure in vitrectomized eyes, with substantial gains in vision in most cases. Patients of advanced age and eyes without clear lens prior to the PPV had earlier CS.

Postoperative Complications of Pars Plana Vitrectomy for Diabetic Retinal Disease

Despite recent advances in the medical management of diabetic retinal disease, there remain established indications for vitreoretinal surgery in the treatment of severe proliferative diabetic retinopathy. These include non-clearing vitreous hemorrhage and tractional retinal detachment. Advances in surgical instrumentation, technique, and experience have led to improved visual outcomes, as well as a corresponding decrease in the incidence of postoperative complications. However, the presence of systemic and ocular factors in diabetic patients increases the risk of adverse events compared to non-diabetic individuals. This review will focus on the most important postoperative complications following pars plana vitrectomy, with specific considerations for the diabetic patient.

The quantitative assessment of alterations in lens transparency after transconjunctival 27-gauge microincision vitrectomy surgery

PurposeTo evaluate the baseline and post-vitrectomy lens densitometry values by a Scheimpflug camera in eyes with epiretinal membrane that were treated with 27-G microincision vitrectomy surgery (MIVS) without tamponade and to compare the results with those in fellow healthy eyes.Patients and methodsProspective case series. The lens densitometry measurements of 24 patients, who underwent 27-G MIVS without any tamponade for the treatment of epiretinal membrane, were taken preoperatively and on the first week, first month, and third month postoperatively with Pentacam HR-Scheimpflug imaging system.ResultsThe mean lens densitometry values at Zone 1 and average lens densitometry values significantly increased in the study eyes on the first month when compared with the preoperative values (P=0.011, P=0.033, respectively). Additionally, there were statistically significant differences regarding the mean lens densitometry values of Zone 1 and Zone 2, and also average lens densitometry values between the preoperative and third month postoperative values (P=0.003, P=0.021, P=0.009, respectively). However, the densitometry values of fellow eyes were similar at preoperatively and all the postoperative follow-up periods (P>0.05 for all).ConclusionsThis study suggests that 27-G MIVS might cause post-surgical lens density changes even in early postoperative months and vitreous may play an important role in protecting the transparency of the lens.

Nrf2 as a target for prevention of age-related and diabetic cataracts by against oxidative stress

Cataract is one of the most important causes of blindness worldwide, with age-related cataract being the most common one. Agents preventing cataract formation are urgently required. Substantial evidences point out aggravated oxidative stress as a vital factor for cataract formation. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/Kelch-like erythroid-cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1) system is considered as one of the main cellular defense mechanisms against oxidative stresses. This review discusses the role of Nrf2 pathway in the prevention of cataracts and highlights that Nrf2 suppressors may augment oxidative stress of the lens, and Nrf2 inducers may decrease the oxidative stress and prevent the cataract formation. Thus, Nrf2 may serve as a promising therapeutic target for cataract treatment.

Refractive changes after lens-sparing vitrectomy for macular hole and epiretinal membrane

Purpose

Cataract progression after lens-sparing vitrectomy might differ according to original posterior segment diseases. Our objective was to analyze the refractive values after lens-sparing vitrectomy for macular hole (MH) and epiretinal membrane (ERM).

Materials and methods

We reviewed the medical records of 25 MH patients (25 eyes) and 23 ERM patients (23 eyes) who underwent lens-sparing vitrectomy. Refractive changes in both groups were compared. All patients underwent 20-gauge three-port pars plana vitrectomy. Fluid–air exchange was performed during vitrectomy only in the MH group. The results were analyzed using the unpaired t-test, chi-square test, or Fisher exact probability test, and multivariate analysis.

Results

There were no significant differences in the patient’s age (P=0.45). The myopia progression rate (D/month) was higher in the MH group after surgery than that in the ERM group (P=0.035). MH group had more females (P=0.043), longer surgical time (P<0.001), and higher frequencies of surgical adjuvants use (triamcinolone acetonide, P=0.019; brilliant blue G, P<0.001). The myopia progression rate in the MH group (R=0.568, P<0.001) correlated with female gender. However, no correlation was observed between longer surgical time and the use of surgical adjuvants.

Conclusion

The rate of myopia progression was higher in the MH group. Fluid–air exchange and gender may affect the rate of myopia progression.

Pars plana vitrectomy with partial tamponade of filtered air in Rhegmatogenous retinal detachment caused by superior retinal breaks

BACKGROUND

To investigate the anatomic and functional outcomes of pars plana vitrectomy (PPV) with partial tamponade of filtered air for rhegmatogenous retinal detachment (RRD) caused by superior retinal breaks.

METHODS

Retrospective, comparative, consecutive case series study. Patients with RRD caused by superior retinal breaks undergone PPV with partial tamponade (Group A) and whole tamponade (Group B) of filtered air were included. The main outcomes were primary and final success rates, best corrected visual acuity (BCVA), and rate of postoperative cataract surgery.

RESULTS

Forty-one patients (41 eyes) were included in Group A and 36 patients (36 eyes) were included in Group B. There were no significant differences in primary or final success rates between Groups A and B (P = 0.618 and P = 1.000, respectively). The patients in Group A experienced quicker postoperative vision improvement (from the Week 1 follow-up) than the patients in Group B (from the Month 3 follow-up). The postoperative cataract surgery rate of Group A (7/31) was lower than that of Group B (13/26) (P = 0.031).

CONCLUSIONS

PPV with partial tamponade of air is effective in achieving a high anatomic success rate, quicker postoperative vision improvement, and lower rate of postoperative cataract surgery in RRD caused by superior retinal breaks.

Retinal oximetry in humans using visible-light optical coherence tomography [Invited]

We measured hemoglobin oxygen saturation (sO₂) in the retinal circulation in healthy humans using visible-light optical coherence tomography (vis-OCT). The measurements showed clear oxygenation differences between central retinal arteries and veins close to the optic nerve head. Spatial variations at different vascular branching levels were also revealed. In addition, we presented theoretical and experimental results to establish that noises in OCT intensity followed Rice distribution. We used this knowledge to retrieve unbiased estimation of true OCT intensity to improve the accuracy of vis-OCT oximetry, which had inherently lower signal-to-nose ratio from human eyes due to safety and comfort limitations. We demonstrated that the new statistical-fitting sampling strategy could reduce the estimation error in sO₂ by three percentage points (pp). The presented work aims to provide a foundation for using vis-OCT to achieve accurate retinal oximetry in clinical settings.

Retinal oxygen: from animals to humans

This article discusses retinal oxygenation and retinal metabolism by focusing on measurements made with two of the principal methods used to study O₂ in the retina: measurements of PO₂ with oxygen-sensitive microelectrodes in vivo in animals with a retinal circulation similar to that of humans, and oximetry, which can be used non-invasively in both animals and humans to measure O₂ concentration in retinal vessels. Microelectrodes uniquely have high spatial resolution, allowing the mapping of PO₂ in detail, and when combined with mathematical models of diffusion and consumption, they provide information about retinal metabolism. Mathematical models, grounded in experiments, can also be used to simulate situations that are not amenable to experimental study. New methods of oximetry, particularly photoacoustic ophthalmoscopy and visible light optical coherence tomography, provide depth-resolved methods that can separate signals from blood vessels and surrounding tissues, and can be combined with blood flow measures to determine metabolic rate. We discuss the effects on retinal oxygenation of illumination, hypoxia and hyperoxia, and describe retinal oxygenation in diabetes, retinal detachment, arterial occlusion, and macular degeneration. We explain how the metabolic measurements obtained from microelectrodes and imaging are different, and how they need to be brought together in the future. Finally, we argue for revisiting the clinical use of hyperoxia in ophthalmology, particularly in retinal arterial occlusions and retinal detachment, based on animal research and diffusion theory.

Preliminary investigation of multispectral retinal tissue oximetry mapping using a hyperspectral retinal camera

Oximetry measurement of principal retinal vessels represents a first step towards understanding retinal metabolism, but the technique could be significantly enhanced by spectral imaging of the fundus outside of main vessels. In this study, a recently developed Hyperspectral Retinal Camera was used to measure relative oximetric (SatO2) and total hemoglobin (HbT) maps of the retina, outside of large vessels, in healthy volunteers at baseline (N = 7) and during systemic hypoxia (N = 11), as well as in patients with glaucoma (N = 2). Images of the retina, on a field of view of ∼30°, were acquired between 500 and 600 nm with 2 and 5 nm steps, in under 3 s. The reflectance spectrum from each pixel was fitted to a model having oxy- and deoxyhemoglobin as the main absorbers and scattering modeled by a power law, yielding estimates of relative SatO2 and HbT over the fundus. Average optic nerve head (ONH) saturation over 8 eyes was 68 ± 5%. During systemic hypoxia, mean ONH saturation decreased by 12.5% on average. Upon further development and validation, the relative SatO2 and HbT maps of microvasculature obtained with this imaging system could ultimately contribute to the diagnostic and management of diseases affecting the ONH and retina.

Lens density measurement with Scheimpflug camera in vitrectomised eyes

OBJETIVE

To determine whether vitrectomised eyes have a higher lens optical density, when measured with a Scheimpflug camera, compared to non-vitrectomised eyes.

METHOD

The peak and linear Scheimpflug optical density (DOS), and area of both eyes were measured in a sample size of 81 vitrectomised phakic patients. A comparison was made between the DOS of the vitrectomised eye lens and the contralateral non-vitrectomised eye using the Student-t test.

RESULTS

A significantly higher linear DOS and area was obtained in the 81 vitrectomised phakic eyes when compared to the non-vitrectomised eyes (P<.001). The peak DOS is not significantly increased in respect to non-vitrectomised eyes (P=.59).

CONCLUSIONS

The lens DOS in vitrectomised eyes is higher than in non-vitrectomised eyes. The importance of the vitreous in the maintenance of lens transparency is emphasised.

Hypoxia and Dark Adaptation in Diabetic Retinopathy: Interactions, Consequences, and Therapy

In diabetes, retinal blood flow is compromised, and retinal hypoxia is likely to be further intensified during periods of darkness. During dark adaptation, rod photoreceptors in the outer retina are maximally depolarized and continuously release large amounts of the neurotransmitter glutamate-an energetically demanding process that requires the highest oxygen consumption per unit volume of any tissue of the body. In complete darkness, even more oxygen is consumed by the outer retina, producing a steep fall in the retinal oxygen tension curve which reaches a nadir at the depth of the mitochondrial-rich rod inner segments. In contrast to the normal retina, the diabetic retina cannot meet the added metabolic load imposed by the dark-adapted rod photoreceptors; this exacerbates retinal hypoxia and stimulates the overproduction of vascular endothelial growth factor (VEGF). The use of nocturnal illumination to prevent dark adaptation, specifically reducing the rod photoreceptor dark current, should ameliorate diabetic retinopathy.

LONG-TERM FOLLOW-UP OF INTRAOCULAR PRESSURE AFTER VITRECTOMY IN EYES WITHOUT PREEXISTING GLAUCOMA

PURPOSE

To identify whether vitrectomy is associated with an increased risk of elevated intraocular pressure (IOP) and to report the incidence of open-angle glaucoma after vitrectomy.

METHODS

In this retrospective case series of 234 consecutive patients without a history of glaucoma or diabetes undergoing primary unilateral vitrectomy for an idiopathic epiretinal membrane or macular hole with a minimum of 2 years follow-up, mean IOP in operative and fellow eyes were compared at baseline and multiple postoperative times. Eyes were also assessed for the development of open-angle glaucoma.

RESULTS

The mean baseline IOP was 14.91 mmHg, and the mean final IOP was 14.6 (P = 0.278) in the operative eyes. Linear regression analysis of IOP in operative eyes from baseline to the final visit found an increase of 0.000047 mmHg per year compared with -0.00027 mmHg per year in the fellow eyes with no significant difference in the slope of the 2 regression lines (P = 0.27). Six vitrectomy eyes were diagnosed with new-onset open-angle glaucoma during a mean follow-up of 4.4 years; however, only one was not also diagnosed with glaucoma or ocular hypertension in the fellow unoperated eye.

CONCLUSION

Vitrectomy does not seem to be correlated with increased risk of IOP elevation or glaucoma development in comparison with fellow control eyes.

Strategy for the management of diabetic macular edema: the European vitreo-retinal society macular edema study

Objective. To compare the efficacy of different therapies in the treatment of diabetic macular edema (DME). Design. Nonrandomized, multicenter clinical study. Participants. 86 retina specialists from 29 countries provided clinical information on 2,603 patients with macular edema including 870 patients with DME. Methods. Reported data included the type and number of treatment(s) performed, the pre- and posttreatment visual acuities, and other clinical findings. The results were analyzed by the French INSEE (National Institute of Statistics and Economic Studies). Main Outcome Measures. Mean change of visual acuity and mean number of treatments performed. Results. The change in visual acuity over time in response to each treatment was plotted in second order polynomial regression trend lines. Intravitreal triamcinolone monotherapy resulted in some improvement in vision. Treatment with threshold or subthreshold grid laser also resulted in minimal vision gain. Anti-VEGF therapy resulted in more significant visual improvement. Treatment with pars plana vitrectomy and internal limiting membrane (ILM) peeling alone resulted in an improvement in vision greater than that observed with anti-VEGF injection alone. In our DME study, treatment with vitrectomy and ILM peeling alone resulted in the better visual improvement compared to other therapies.

Increased intraretinal PO2 in short-term diabetic rats

In diabetic retinopathy, neovascularization is hypothesized to develop due to hypoxia in the retina. However, evidence for retinal hypoxia is limited, and the progressive changes in oxygenation are unknown. The objective of this study was to determine if retinal hypoxia occurs early in the development of diabetes. Intraretinal oxygen (PO2) profiles were recorded with oxygen-sensitive microelectrodes in control and diabetic Long-Evans rats at 4 and 12 weeks after induction of diabetes. Diabetes did not affect oxygen consumption in the photoreceptors in either dark or light adaptation. Oxygenation of the inner retina was not affected after 4 weeks of diabetes, although vascular endothelial growth factor levels increased. At 12 weeks, average inner retinal PO2, normalized to choriocapillaris PO2, was higher in diabetic rats than in age-matched controls, which was opposite to what was expected. Thus retinal hypoxia is not a condition of early diabetes in rat retina. Increased inner retinal PO2 may occur because oxygen consumption decreases in the inner retina.

Associations of retinal oximetry in persons with diabetes

BACKGROUND

There are limited data available on the variables that might affect retinal vessel oxygen saturation (SO₂) in diabetes. Therefore, the aim of this study is to assess factors associated with retinal oximetry values in persons with diabetes.

DESIGN

Clinic-based cross-sectional study.

PARTICIPANTS

Fifty-eight persons with diabetes aged 18+ years, recruited from the University of Melbourne, the Royal Victorian Eye and Ear Hospital, and St. Vincent's Hospital (Melbourne), Australia.

METHODS

Retinal oximetry was performed using the oximetry module of the Vesselmap system (Imedos UG, Jena, Germany) in 92 diabetic eyes. Generalized estimating equation models were used to estimate the associations between candidate variables (age; gender; retinal capillary flow; duration of diabetes; hypertension; smoking status; presence of diabetic retinopathy [DR]; glycated haemoglobin; triglyceride; total cholesterol; finger SO₂ and ocular perfusion pressure) with retinal oximetry measures.

MAIN OUTCOME MEASURE

Arteriolar SO₂, venular SO₂ and the arterio-venous (A-V) difference.

RESULTS

Of the candidate factors assessed, only the presence of DR was significantly associated with increased venular SO₂ and decreased A-V difference in unadjusted analyses. In models adjusting for age and gender and significant variables from unadjusted analyses, compared with no DR, the presence of DR was significantly associated with greater retinal venular SO₂ values (β = 3.65%, 95% confidence interval: 0.67-6.63%) and decreased A-V difference (β = -2.00%, 95% confidence interval: -3.46 to -0.53%).

CONCLUSION

In patients with diabetes, eyes with DR were associated with increased venular SO₂ and decreased A-V difference compared with eyes without DR, suggesting an altered metabolic state in DR.

Progression of nuclear sclerosis based on changes in refractive values after lens-sparing vitrectomy in proliferative diabetic retinopathy

Background

Nuclear sclerosis (NS) based on the Emery–Little classification and refractive values after lens-sparing vitrectomy was compared between proliferative diabetic retinopathy (DR) patients and nondiabetic patients.

Methods

Progression of NS based on the Emery–Little classification and changes in refractive values were compared between 13 proliferative DR patients (14 eyes, DR group) and 14 nondiabetic patients (14 eyes, non-DR group) who underwent lens-sparing vitrectomy. All patients revealed grade I NS based on the Emery–Little classification. Mean patient age and refractive value just after surgery were 56.07 years and −0.33 diopters (D) in the DR group, and 57.06 years and −0.96 D in the non-DR group.

Results

The Emery–Little classification in the DR group at 6 and 24 months postoperative were grade I (13 eyes)/grade II (one eye) and grade I (eleven eyes)/grade II (three eyes), respectively. Mean refractive values in the DR group at 6, 12, and 24 months postoperative were +0.28 D, +0.27 D, and +0.37 D, respectively. The Emery–Little classification in the non-DR group at 6 and 24 months (or preoperative for patients undergoing cataract surgery) were grade I (five eyes)/grade II (eight eyes) and grade I (zero eyes)/grade II (eight eyes)/grade III (five eyes), respectively. The mean refractive value in the non-DR group at 6 months postoperative was −3.20 D. All eyes exhibited myopic changes and progression of NS.

Conclusion

The findings of this study show that the progression of NS postvitrectomy is mild, even for DR patients 50 years of age or older, thus suggesting the need to reconsider the indications for simultaneous cataract surgery with vitrectomy.

Retinal oxygen metabolism in exudative age-related macular degeneration

PURPOSE

To determine whether retinal vessel oxygen saturation in patients with exudative age-related macular degeneration (AMD) is different from that of a healthy population.

METHODS

Oxygen saturation was measured in retinal arterioles and venules in 46 eyes of 46 treatment-naïve exudative AMD patients and 120 eyes of 120 healthy controls. Simple and multiple linear regression analyses were used to compare the two study groups.

RESULTS

Oxygen saturation in retinal venules increases with age in patients with exudative AMD (0.45 ± 0.19% per year; p = 0.026), while it decreases with age in healthy individuals (-0.13 ± 0.03% per year; p = 0.0002). The slopes are statistically different (ANCOVA; p = 0.0003). The reverse is true for the arteriovenous difference in oxygen saturation, which decreases with age in AMD patients (-0.29 ± 0.16% per year; p = 0.065) and increases in healthy individuals (0.12 ± 0.03% per year; p < 0.0001). At age 80 years, AMD patients have 2.7 percentage points higher venous oxygen saturation than healthy persons and 4.2 percentage points less arteriovenous difference.

CONCLUSIONS

The data suggest that retinal oxygen metabolism may be altered in exudative AMD. The arteriovenous difference is smaller in exudative AMD than in a healthy cohort, consistent with reduced oxygen extraction by retinal vessels in AMD patients. Further studies are needed to fully understand the role of retinal oxygen metabolism in the pathophysiology of exudative AMD.

Aging and age-related diseases of the ocular lens and vitreous body

Reduced quality of life and financial burden due to visual impairment and blindness begin to increase dramatically when individuals reach the age of 40. The major causes of age-related vision loss can be traced to changes to the structure and function of the lens, one of the tissues responsible for focusing light on the retina. Age-related nuclear cataracts, which are caused by aggregation and condensation of proteins, diminish vision because they impede the transmission and focusing of light on the retina. In addition to the slow-developing age-related form, cataracts often develop rapidly as a complication of ocular surgery, such as following vitrectomy or as a consequence of vitreous gel degeneration. Posterior capsular opacification, which can develop following cataract removal, is caused by proliferation and inappropriate accumulation of lens epithelial cells on the surfaces of intraocular lenses and the posterior lens capsule. Presbyopia is a loss of accommodative amplitude and reduced ability to shift focus from far to near objects. Onset of presbyopia is associated with an increase in lens hardness and reduced ability of the lens to change shape in response to ciliary muscle contraction. Avenues of promising research that seek to delay or prevent these causes of low vision are discussed in light of our current understanding of disease pathogenesis and some challenges that must be met to achieve success.

Computational model for oxygen transport and consumption in human vitreous

PURPOSE

Previous studies that measured liquefaction and oxygen content in human vitreous suggested that exposure of the lens to excess oxygen causes nuclear cataracts. Here, we developed a computational model that reproduced available experimental oxygen distributions for intact and degraded human vitreous in physiologic and environmentally perturbed conditions. After validation, the model was used to estimate how age-related changes in vitreous physiology and structure alter oxygen levels at the lens.

METHODS

A finite-element model for oxygen transport and consumption in the human vitreous was created. Major inputs included ascorbate-mediated oxygen consumption in the vitreous, consumption at the posterior lens surface, and inflow from the retinal vasculature. Concentration-dependent relations were determined from experimental human data or estimated from animal studies, with the impact of all assumptions explored via parameter studies.

RESULTS

The model reproduced experimental data in humans, including oxygen partial pressure (Po2) gradients (≈15 mm Hg) across the anterior-posterior extent of the vitreous body, higher oxygen levels at the pars plana relative to the vitreous core, increases in Po2 near the lens after cataract surgery, and equilibration in the vitreous chamber following vitrectomy. Loss of the antioxidative capacity of ascorbate increases oxygen levels 3-fold at the lens surface. Homogeneous vitreous degeneration (liquefaction), but not partial posterior vitreous detachment, greatly increases oxygen exposure to the lens.

CONCLUSIONS

Ascorbate content and the structure of the vitreous gel are critical determinants of lens oxygen exposure. Minimally invasive surgery and restoration of vitreous structure warrant further attention as strategies for preventing nuclear cataracts.

Long-term intraocular pressure changes after vitrectomy for epiretinal membrane and macular hole

Background

To investigate long-term intraocular pressure (IOP) changes after vitrectomy for epiretinal membrane (ERM) or macular hole (MH).

Methods

We retrospectively reviewed the medical records of 57 eyes with ERM and 61 eyes with MH that underwent vitrectomy. IOP levels and changes at 1, 3, 6, 12 months, and the final visit from baseline were evaluated in vitrectomized eyes and non-vitrectomized fellow eyes.

Results

In the ERM group, the mean follow-up period was 29.3 months; the mean preoperative IOP in the operated eyes was 12.9 ± 2.5 mmHg and the final IOP was 13.2 ± 2.9 mmHg. In the MH group, the mean follow-up period was 25.6 months; the mean preoperative IOP in the operated eyes was 13.3 ± 2.5 mmHg and the final IOP was 14.0 ± 3.2 mmHg. The mean final IOP of the fellow unoperated eyes was 13.0 ± 2.5 mmHg in the ERM group and it was 12.9 ± 3.2 mmHg in the MH group. A significant difference was found between the operated eyes and fellow eyes at the final visit in the MH group (P < 0.01) but not in the ERM group (P = 0.40). MH group was significantly at high risk of IOP increase after vitrectomy (P < 0.01).

Conclusions

IOP increase after vitrectomy was found in some eyes with MH during long-term follow-up but it was unlikely in eyes with ERM.

Hypoxia-inducible factor-1 (HIF-1): a potential target for intervention in ocular neovascular diseases

Constant oxygen supply is essential for proper tissue development, homeostasis and function of all eukaryotic organisms. Cellular response to reduced oxygen levels is mediated by the transcriptional regulator hypoxia-inducible factor-1 (HIF-1). It is a heterodimeric complex protein consisting of an oxygen dependent subunit (HIF-1α) and a constitutively expressed nuclear subunit (HIF-1β). In normoxic conditions, de novo synthesized cytoplasmic HIF-1α is degraded by 26S proteasome. Under hypoxic conditions, HIF-1α is stabilized, binds with HIF-1β and activates transcription of various target genes. These genes play a key role in regulating angiogenesis, cell survival, proliferation, chemotherapy, radiation resistance, invasion, metastasis, genetic instability, immortalization, immune evasion, metabolism and stem cell maintenance. This review highlights the importance of hypoxia signaling in development and progression of various vision threatening pathologies such as diabetic retinopathy, retinopathy of prematurity, age-related macular degeneration and glaucoma. Further, various inhibitors of HIF-1 pathway that may have a viable potential in the treatment of oxygen-dependent ocular diseases are also discussed.

Oxidative responses induced by pharmacologic vitreolysis and/or long-term hyperoxia treatment in rat lenses

PURPOSE

The aim of the study was to investigate the protective effects of intact vitreous gel on the lens after pharmacologic vitreolysis and hyperoxia exposure in rats in vivo.

METHODS

Eyes of Sprague-Dawley rats were induced to posterior vitreous detachment (PVD) by pharmacologic vitreolysis, and the rats with and without PVD were treated with hyperoxia 3 h per day for 5 months. Lens transparency was monitored by a slit-lamp biomicroscope. A series of biochemical measurements were made in extracts of the lens cortex and nucleus. Ascorbate levels were measured in the aqueous and vitreous humors.

RESULTS

No significant differences in lens transparency or morphology were observed in all groups, and no significant biochemical changes were observed in the cortex or nucleus of lenses of the PVD group. In the lens nucleus, the values of water-soluble protein concentration in PVD + hyperoxia group were lower than that of the PVD group. The levels of water-soluble proteins, glutathione (GSH) and ascorbate decreased in the hyperoxia group with an intact vitreous body. Vitreolysis enhanced the effect of hyperoxia, decreasing soluble protein, GSH and ascorbate below the levels seen in eyes with vitreolysis alone. The levels of antioxidants and soluble proteins were lower in the lens nucleus, and the effects of vitreolysis plus hyperoxia were more significant in the nucleus. Hyperoxia and hyperoxia plus vitreolysis reduced catalase activity and increased oxidized GSH to a greater extent in the lens cortex, although these treatments increased protein-GSH mixed disulfides in both regions. Long-term hyperoxia also lowered ascorbate levels in the vitreous and aqueous humors, an effect that was enhanced by vitreolysis.

CONCLUSIONS

Exposure to excess molecular oxygen produces significant oxidative damage to the lens, especially the lens nucleus. These effects were enhanced by pharmacologic vitreolysis, indicating that intact vitreous gel protects the lens from oxidative damage.

Retinal oximetry

ABSTRACT.:

PURPOSE

Malfunction of retinal blood flow or oxygenation is believed to be involved in various diseases. Among them are retinal vessel occlusions, diabetic retinopathy and glaucoma. Reliable, non-invasive technology for retinal oxygen measurements has been scarce and most of the knowledge on retinal oxygenation comes from animal studies. This thesis describes human retinal oximetry, performed with novel retinal oximetry technology. The thesis describes studies on retinal vessel oxygen saturation in (1) light and dark in healthy volunteers, (2) central retinal vein occlusion, (3) branch retinal vein occlusion, (4) central retinal artery occlusion, (5) diabetic retinopathy, (6) patients undergoing glaucoma surgery and (7) patients taking glaucoma medication.

METHODS

The retinal oximeter (Oxymap ehf., Reykjavik, Iceland) is based on a fundus camera. An attached image splitter allows the simultaneous capture of four images of the same area of the fundus. Two images are used for further analysis, one acquired with 586 nm light and one with 605 nm light. Light absorbance of retinal vessels is sensitive to oxygen saturation at 605 nm but not at 586 nm. Measurement of reflected light at these wavelengths allows estimation of oxygen saturation in the main retinal vessels. This is performed with custom-made analysis software.

RESULTS

LIGHT AND DARK: After 30 min in the dark, oxygen saturation in retinal arterioles of healthy volunteers was 92 ± 4% (mean ± SD, n = 15). After 5 min in 80 cd/m(2) light, the arteriolar saturation was 89 ± 5%. The decrease was statistically significant (p = 0.008). The corresponding values for retinal venules were 60 ± 5% in the dark and 55 ± 10% in the light (p = 0.020). Similar results were found after alternating 5 min periods of darkness and light. In a second experiment (n = 19), a significant decrease in retinal vessel oxygen saturation was found in 100 cd/m(2) light compared with darkness but 1 and 10 cd/m(2) light had no significant effect. CENTRAL RETINAL VEIN OCCLUSION: In patients with central retinal vein occlusion, the mean saturation in affected retinal venules was 49 ± 12%, while the mean value for venules in the fellow eye was 65 ± 6% (mean ± SD, p = 0.003, n = 8). The retinal arteriolar saturation was the same in affected (99 ± 3%) and the unaffected (99 ± 6%) eyes. The venous oxygen saturation showed much variation between affected eyes. BRANCH RETINAL VEIN OCCLUSION: Median oxygen saturation in venules affected by branch retinal vein occlusion was 59% (range, 12-93%, n = 22), while it was 63% (23-80%) in unaffected venules in the affected eye and 55% (39-80%) in venules in the fellow eye. The difference was not statistically significant (p > 0.05). There was a significant difference between affected arterioles (median 101%; range, 89-115%) and unaffected arterioles (95%, 85-104%) in the affected eye (p < 0.05, n = 18). CENTRAL RETINAL ARTERY OCCLUSION: In a patient with a day's history of central retinal artery occlusion due to temporal arteritis, the mean arteriolar saturation was 71 ± 9% and 63 ± 9% in the venules. One month later, after treatment with prednisolone, the mean arteriolar saturation was 100 ± 4% and the venous saturation 54 ± 5%. DIABETIC RETINOPATHY: When compared with healthy volunteers (n = 31), patients with all categories of diabetic retinopathy had on average 7-10 percentage points higher saturation in retinal arterioles (p < 0.05 for all categories, n = 6-8 in each category). In venules, the saturation was 8-12 percentage points higher (p < 0.05 for all categories). GLAUCOMA SURGERY: Oxygen saturation in retinal arterioles increased by 2 percentage points on average (p = 0.046, n = 19) with surgery, which lowered intraocular pressure from 23 ± 7 mmHg (mean ± SD) to 10 ± 4 mmHg (p < 0.0001). No other significant changes were found (p ≥ 0.35). DORZOLAMIDE: A significant reduction of 3 percentage points was found in arterioles (p < 0.01) and venules (p < 0.05) when patients with glaucoma or ocular hypertension changed from dorzolamide-timolol combination eye drops to timolol alone (n = 6). No change was found in patients, who started on timolol and switched to the combination therapy (p > 0.05, n = 7).

CONCLUSIONS

Dual wavelength oximetry can be used to non-invasively measure retinal vessel oxygen saturation in health and disease. The results indicate that retinal vessel oxygen saturation is (1) increased in the dark, (2) lower in venules affected by central retinal vein occlusions, (3) variable in branch retinal vein occlusion, (4) lower in retinal arterioles in central retinal artery occlusion, (5) increased in diabetic retinopathy, (6-7) mildly affected by glaucoma surgery or dorzolamide.

Retinal oximetry using ultrahigh-resolution optical coherence tomography

BACKGROUND

The purpose of this study was to investigate the repeatability of retinal oximetry using slit-lamp adapted ultrahigh-resolution optical coherence tomography (SL-UHR-OCT).

METHODS

SL-UHR-OCT was developed and fringe patterns were obtained for a major retinal artery and a major retinal vein. A-scans at the central wavelengths of 805 nm and 855 nm were analyzed for calculating optical density ratios (ODRs), from which the percentage oxygen saturation was calculated. Measurements were made on two occasions for each person. Repeatability and coefficients of repeatability were calculated.

RESULTS

The mean ODRs of the artery were 0.79 ± 0.86 and 0.88 ± 0.97 in sessions 1 and 2, respectively. The mean ODRs of the vein were -0.08 ± 0.69 and 0.14 ± 0.77 between the two sessions, and were significantly lower than that of the artery (P < 0.05). The coefficients of repeatability were 1.44 and 1.81 for the artery and vein, respectively. The mean oxygen saturation of the major retinal artery was 94% ± 45% and 98% ± 51% in sessions 1 and 2, respectively, and the mean oxygen saturation of the major retinal vein was 48% ± 36% and 60% ± 40% between sessions.

CONCLUSION

Optical coherence tomographic oximetry for evaluating retinal oxygen saturation was subject to variation, although the averaged measurements in repeated sessions were matched. Further work on reducing variation will be needed.

Combination therapy in diabetic macular oedema and retinal vein occlusion--past and present

This paper summarizes the recent evidence for combined therapies in the intravitreal medical treatment of diabetic macular oedema or macular oedema, secondary to retinal vein occlusion. Since the introduction of anti-inflammatory or anti-VEGF drugs combined with or used alternatively to laser, visual acuity can be stabilized or improved in a significant number of patients. However, there is an ongoing debate regarding the safety, efficiency and economic concerns related to these intravitreal monotherapies because they warrant frequent repetition to maintain the clinical effect. In the literature, the combination of photolasercoagulation, intravitreal steroids or VEGF-inhibitors, or both, shows early compelling evidence that some patients may benefit from less retreatment compared to monotherapy. To provide a conceptual and perspective approach for a first-line combined therapy, this paper also summarizes own results of pilot interventional case series of a 1.5 cc core pars plana vitrectomy and intravitreal substitution with balanced salt solution (BSS), 1.25 mg bevacizumab and 8 mg triamcinolone.

Small-gauge vitrectomy does not protect against nuclear sclerotic cataract

PURPOSE

To determine whether the gauge of vitrectomy instrumentation is associated with the progression of nuclear sclerotic cataract.

METHODS

A prospective interventional and observational study of patients undergoing vitrectomy surgery for various retinal conditions. Patients had Scheimpflug lens photography in the operated and fellow eye at baseline and at 6 months and 12 months after vitrectomy surgery.

RESULTS

Of 42 eyes included in the analysis, 11 had 20-gauge surgery, 22 had 23-gauge surgery, and 9 had 25-gauge surgery. In all operated eyes, vitrectomy surgery led to the significant progression of nuclear sclerotic cataract, compared with the fellow, unoperated eye. This small study was unable to detect a difference in nuclear sclerotic progression when comparing small-gauge surgery (23 and 25 gauge) with standard 20-gauge surgery.

CONCLUSION

Removal of the vitreous gel using any-gauge vitrectomy surgery leads to significant progression of nuclear sclerotic cataract at 6 months and 12 months. The findings are consistent with the hypothesis that the vitreous gel is important in protecting the lens from increased exposure to oxygen that leads to the formation of nuclear sclerotic cataract. This increased exposure to oxygen occurs as a result of removing the vitreous gel and is independent of the gauge of vitrectomy instrumentation.