Visual prognosis and vitreous cytokine levels after arteriovenous sheathotomy in branch retinal vein occlusion associated with macular oedema

The long-term mediation role of cytokines on the causal pathway from maternal gestational age to offspring eye diseases: Lifecourse-Network Mendelian randomization

BACKGROUND

Gestational duration has a significant impact on eye diseases. A large number of evidences suggest that cytokines are associated with gestational duration and eye diseases. However, the causal relationships among cytokines, maternal gestational impairment and offspring eye diseases remain unclear.

METHODS

We performed lifecourse-network Mendelian randomization (MR) to explore the causal relationships between maternal gestational duration (from the Early Growth Genetics (EGG) Consortium and the Lundbeck Foundation Initiative for Integrative Psychiatric Research (iPSYCH) study, N = 84,689), neonatal/adult cytokines (from the NHGRI-EBI Catalog, N = 764/4,618), and adult eye diseases (from FinnGen consotium, N = 309,154) using summary-level data from large genome-wide association studies. Multiplicative random effects inverse variance weighted (IVW) and multivariable-IVW methods were the main analysis methods, and the other 15 pleiotropy-robust methods, weak IV-robust methods, and outliers-robust methods were used as auxiliary methods.

RESULTS

Maternal gestational age (early preterm birth, preterm birth, gestational duration, and post-term birth) had a causal relationship with 42 eye diseases. Four neonatal cytokines, Tumor Necrosis Factor-α(TNF-α), IL10, GROA, and CTACK, as well as four adult cytokines, CTACK, IL10, IL12p70 and IL6 are mediators in the causal relationships between early preterm birth and preterm birth in eight eye diseases. However, after adjusting for these mediators, a null direct causal effect of early preterm birth and preterm birth on eight eye diseases was found. In addition, there was no mediator in the causal relationship between gestational duration and post-term birth to eye diseases.

CONCLUSION

The effects of maternal gestational duration on offspring eye diseases through cytokines are long-term and life-course effects.

Emerging applications of bioinformatics and artificial intelligence in the analysis of biofluid markers involved in retinal occlusive diseases: a systematic review

PURPOSE

To review the literature on the application of bioinformatics and artificial intelligence (AI) for analysis of biofluid biomarkers in retinal vein occlusion (RVO) and their potential utility in clinical decision-making.

METHODS

We systematically searched MEDLINE, Embase, Cochrane, and Web of Science databases for articles reporting on AI or bioinformatics in RVO involving biofluids from inception to August 2021. Simple AI was categorized as logistics regressions of any type. Risk of bias was assessed using the Joanna Briggs Institute Critical Appraisal Tools.

RESULTS

Among 10,264 studies screened, 14 eligible articles, encompassing 578 RVO patients, met the inclusion criteria. The use and reporting of AI and bioinformatics was heterogenous. Four articles performed proteomic analyses, two of which integrated AI tools such as discriminant analysis, probabilistic clustering, and string pathway analysis. A metabolomic study used AI tools for clustering, classification, and predictive modeling such as orthogonal partial least squares discriminant analysis. However, most studies used simple AI (n = 9). Vitreous humor sample levels of interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), and aqueous humor levels of intercellular adhesion molecule-1 and IL-8 were implicated in the pathogenesis of branch RVO with macular edema. IL-6 and VEGF may predict visual acuity after intravitreal injections or vitrectomy, respectively. Metabolomics and Kyoto Encyclopedia of Genes and Genomes enrichment analysis identified the metabolic signature of central RVO to be related to lower aqueous humor concentration of carbohydrates and amino acids. Risk of bias was low or moderate for included studies.

CONCLUSION

Bioinformatics has applications for analysis of proteomics and metabolomics present in biofluids in RVO with AI for clinical decision-making and advancing the future of RVO precision medicine. However, multiple limitations such as simple AI use, small sample volume, inconsistent feasibility of office-based sampling, lack of longitudinal follow-up, lack of sampling before and after RVO, and lack of healthy controls must be addressed in future studies.

The role of IL-6-174 G/C polymorphism and intraocular IL-6 levels in the pathogenesis of ocular diseases: a systematic review and meta-analysis

Interleukin-6 (IL-6) is one of the key regulators behind the inflammatory and pathological process associated with ophthalmic diseases. The role of IL-6-174 G/C polymorphism as well as intraocular IL-6 levels among various eye disease patients differ across studies and has not been systematically reviewed. Thus, this study aims to provide a summary to understand the relationship between IL-6 and ophthalmic disease. In total, 8,252 and 11,014 subjects for IL-6-174 G/C and intraocular levels of IL-6, respectively, were retrieved from PubMed, Scopus and Web of Science. No association was found between IL-6-174 G/C polymorphisms with ocular diseases. Subgroup analyses revealed a suggestive association between the GC genotype of IL-6-174 G/C with proliferative diabetic retinopathy (PDR). Further, the level of intraocular IL-6 among ocular disease patients in general was found to be higher than the control group [standardized mean difference (SMD) = 1.41, 95% confidence interval (CI) 1.24-1.58, P < 0.00001]. Closer examination through subgroup analyses yielded similar results in several ocular diseases. This study thus indicates that the IL-6-174 G/C polymorphism does not predispose patients to ocular disease, although the GC genotype is likely to be a genetic biomarker for PDR. Moreover, intraocular IL-6 concentrations are related to the specific manifestations of the ophthalmic diseases. Further studies with larger sample sizes are warranted to confirm this conclusion.

Changes in Aqueous and Vitreous Inflammatory Cytokine Levels in Retinal Vein Occlusion: A Systematic Review and Meta-analysis

Purpose:

Evidence suggests that inflammatory cytokines not only play a role in the pathogenesis of retinal vein occlusion (RVO) but also may be useful as biomarkers to predict disease severity and response to treatment. We aimed to quantitatively summarize data on inflammatory cytokines associated with RVO.

Methods:

A systematic search of peer-reviewed English-language articles was performed without year limitation up to August 19, 2019. Studies were included if they provided data on aqueous or vitreous cytokine concentrations in patients with RVO. Data were extracted from 116 studies that encompassed 3242 study eyes with RVO and 1402 control eyes. Effect sizes were generated as standardized mean differences (SMDs) of cytokine concentrations between patients with RVO vs controls.

Results:

Among the 4644 eyes in 116 studies, aqueous and vitreous concentrations (SMD, 95% CI, and P value) of interleukin (IL)-6 (aqueous: 1.23, 0.65 to 1.81, P < .001 vitreous: 0.70, 0.49 to 0.90, P < .001), IL-8 (aqueous: 1.11, 0.73 to 1.49, P < .001; vitreous: 1.19, 0.73 to 1.65, P < .001), monocyte chemoattractant protein 1(aqueous: 1.22, 0.72 to 1.72, P < .001; vitreous 1.42, 0.92 to 1.91, P < .001), vascular endothelial growth factor (VEGF) (aqueous: 1.52, 1.09 to 1.94, P < .001; vitreous: 0.99, 0.78 to 1.21, P < .001) were significantly higher in patients with RVO than in healthy controls. Only aqueous concentrations of IL-10 (0.81, 0.45 to 1.18, P < .001), angiopoietin 4 (1.96, 0.92 to 3.00, P < .001), and platelet-derived growth factor (PDGF)-AA (0.82, 0.35 to 1.30, P < .001) were significantly higher in patients with RVO than in healthy controls. Only the vitreous concentration of soluble intercellular adhesion molecule-1 (sICAM-1) (1.23, 0.83 to 1.63, P < .001) was significantly higher in patients with RVO. No differences, failed sensitivity analyses, or insufficient data were found between patients with RVO and healthy controls for the concentrations of the remaining cytokines.

Conclusions:

Several cytokines in addition to VEGF have the potential to be useful biomarkers and therapeutic targets in RVO.

Potential antiedematous effects of intravitreous anti-VEGF, unrelated to VEGF neutralization

The intravitreous injection of therapeutic proteins that neutralize vascular endothelial growth factor (VEGF) family members is efficient to reduce macular edema associated with wet age-related macular degeneration (AMD), retinal vein occlusion (RVO) and diabetic retinopathy (DR). It has revolutionized the visual prognosis of patients with macular edema. The antiedematous effect is dependent on an intravitreous dose of drug, which varies between patients and requires frequent and repeated injections to maintain its effects. At the time when optimizing the duration of anti-VEGF effects is a major challenge, understanding how anti-VEGF reduces macular edema is crucial. We discuss herein how anti-VEGF exerts antiedematous effects and raise the hypothesis that mechanisms, unrelated to VEGF neutralization, might have been underestimated.

New Developments in the Classification, Pathogenesis, Risk Factors, Natural History, and Treatment of Branch Retinal Vein Occlusion

For years, branch retinal vein occlusion is still a controversial disease in many aspects. An increasing amount of data is available regarding classification, pathogenesis, risk factors, natural history, and therapy of branch retinal vein occlusion. Some of the conclusions may even change our impression of branch retinal vein occlusion. It will be beneficial for our doctors to get a deeper understanding of this disease and improve the treatment skills. The aims of this review is to collect the information above and report new ideas especially from the past a few years.

Idiopathic Choroidal Neovascularization: Intraocular Inflammatory Cytokines and the Effect of Intravitreal Ranibizumab Treatment

Idiopathic choroidal neovascularization (ICNV) is a disorder that primarily affecting patients younger than 50 years and can cause severe loss of vision. Choroidal abnormalities, especially choroidal inflammation, have been thought to be involved in the pathophysiology of ICNV. However, the exact pathogenesis of ICNV remains unclear. The aim of our study was investigate the levels of 27 inflammatory cytokines in the aqueous humor of eyes with ICNV, and to determine the effect of intravitreal injection of ranibizumab (IVR) on cytokine levels. Significantly higher levels of IL-2, IL-10, IL-15, IL-17, basic FGF, and GM-CSF were observed in patients with ICNV compared with controls. However, only IL-17 levels were significantly higher in patients with ICNV compared with controls after adjusting for axial length. Furthermore, there were significant correlations between the levels of IL-10, IL-17, GM-CSF, and VEGF and the lesion area. Significant changes in visual acuity and central retinal thickness were observed after IVR. Besides VEGF, IVR also significantly reduced the levels of IL-2, IL-10, basic FGF, and IL-12, however, the IL-6 levels were significantly increased. Our results suggest that there may be an involvement of IL-17-related inflammatory processes in the etiology of ICNV.

Importance of Central Retinal Sensitivity for Prediction of Visual Acuity after Intravitreal Bevacizumb in Eyes with Macular Edema Associated with Branch Retinal Vein Occlusion

Objective

To determine whether the baseline retinal sensitivity can predict the best-corrected visual acuity (BCVA) at 1 month after intravitreal bevacizumab (IVB) in eyes with macular edema (ME) associated with a branch retinal vein occlusion (BRVO).

Subjects and Methods

We evaluated 16 eyes of 16 patients who had ME associated with a BRVO. The mean ± standard deviation age was 69.1 ± 8.9 years, and all had a single IVB injection. The BCVA, central macular thickness (CMT), integrity of the ellipsoid zone (EZ) of the photoreceptors, and retinal sensitivity were determined before (baseline) and at 1 day, 1 week, and 1 month following the IVB. The average threshold retinal sensitivity (AT) within the central 10° was determined by Macular Integrity Assessment. The correlations between the BCVA at 1 month and the CMT, integrity of the EZ, and AT at each visit were determined.

Results

One month after IVB, the BCVA improved significantly from 0.56 ± 0.27 logMAR units to 0.32 ± 0.28 logMAR units, and the CMT from 611.4 ± 209.3 μm to 258.7 ± 64.0 μm (P <0.05). The AT improved significantly from 17.9 ± 5.3 dB to 21.2 ± 5.0 dB (P <0.05). At 1 day after the treatment, both the integrity of the EZ (r = 0.59) and the retinal sensitivity (r = 0.76) were moderately correlated with the BCVA at 1 month.

Conclusion

These results indicate that both the integrity of the EZ and the AT at 1 day after the IVB can predict the BCVA after treatment for ME associated with BRVO. There is a possibility that these parameters will predict the effectiveness of IVB for each case.

Experimental Application of Piezoelectric Actuator-Driven Pulsed Water Jets in Retinal Vascular Surgery

PURPOSE

To report on the effectiveness and safety of an ophthalmic piezoelectric actuator-driven pulsed water jet (ADPJ) system adapted for intraocular use.

METHODS

First, we determined the highest ADPJ flow rate that did not cause an unsafe rise in intraoperative intraocular pressure (IOP) in rabbits (n = 4). Next, we determined the most effective ADPJ frequency (in hertz) at that flow rate. Finally, we visualized the ADPJ stream, measured its pressure, and determined the minimum voltage and distance between the ADPJ needle and retinal veins to induce intravenous displacement of the blood column (DBC) through massage of the outer retinal vessels (n = 3) while not causing retinal tearing or hemorrhage.

RESULTS

We found that a 0.05 mL/min ADPJ flow rate caused IOP to rise above 40 mm Hg after 1 minute, but that at 0.025 mL/min, IOP stayed below 40 mm Hg even after 3 minutes. Moreover, we found that a 0.025 mL/min ADPJ stream was stable at a pulse frequency of 10 Hz and that at this flow rate/frequency the ADPJ pressure was closely correlated with the applied voltage (P < 0.001, r² = 0.9991). The minimum voltage and distance to achieve intravenous DBC without causing retinal tearing or hemorrhage were 40 V and 0.5 mm, respectively.

CONCLUSIONS

With an appropriate flow rate and surgical time, ADPJ successfully induced massage of the retinal vessels and intravenous DBC while maintaining safe IOP and not causing retinal complications.

TRANSLATIONAL RELEVANCE

The ADPJ system has promise as a safe and minimally invasive instrument for the intraocular surgical treatment of human retinal vascular diseases.

The effect of intravitreal bevacizumab on ocular blood flow in diabetic retinopathy and branch retinal vein occlusion as measured by laser speckle flowgraphy

Background

This study evaluated the effect of intravitreal injection of bevacizumab (IVB) on macular edema associated with diabetic retinopathy (DME) or branch retinal vein occlusion (BRVOME) using laser speckle flowgraphy.

Methods

A comparative interventional study of 25 eyes from 22 patients with macular edema (DME group: 12 eyes; BRVOME group: 13 eyes) who underwent IVB. Mean blur rate (MBR) was measured in the retinal artery, retinal vein, optic nerve head (ONH), and choroid before and after IVB.

Results

In the BRVOME group, there was no significant change in MBR in the retinal artery, retinal vein or ONH, but choroidal MBR decreased significantly (P=0.04). In the DME group, the MBR in the retinal artery, retinal vein, ONH, and choroid decreased significantly (P=0.02, P=0.04, P<0.001, and P=0.04, respectively). In the DME group, pre-IVB MBR in the ONH was significantly correlated with post-IVB foveal thickness (R= −0.71, P=0.002). There was no such correlation in the BRVOME group in the ONH.

Conclusion

IVB had a suppressive effect on circulation in eyes with DME but not in those with BRVOME. This suggests that this noninvasive and objective biomarker may be a useful part of pre-IVB evaluations and decision-making in DME.

Branch retinal vein occlusion: treatment modalities: an update of the literature

BACKGROUND

Retinal vein occlusion is the second most common retinal vascular disorder after diabetic retinopathy and is considered to be an important cause of visual loss. In this review, our purpose is to update the literature about the treatment alternatives for branch retinal vein occlusion.

METHODS

Eligible papers were identified by a comprehensive literature search of PubMed, using the terms "branch retinal vein occlusion," "therapy," "intervention," "treatment," "vitrectomy," "sheathotomy," "laser," "anti-VEGF," "pegaptanib," "bevacizumab," "ranibizumab," "triamcinolone," "dexamethasone," "corticosteroids," "non-steroids," "diclofenac," "hemodilution," "fibrinolysis," "tPA," and "BRVO." Additional papers were also selected from reference lists of papers identified by the electronic database search.

RESULTS

Treatment modalities were analyzed.

CONCLUSIONS

There are several treatment modalities for branch retinal vein occlusion and specifically for its complications, such as macular edema, vitreous hemorrhage, retinal neovascularization, and retinal detachment, including anti-aggregative therapy and fibrinolysis, isovolemic hemodilution, vitrectomy with or without sheathotomy, peripheral scatter and macular grid retinal laser therapy, non-steroid agents, intravitreal steroids, and intravitreal anti-vascular endothelial growth factors (anti-VEGFs).

Intravitreal ranibizumab for macular oedema secondary to retinal vein occlusion: a retrospective study of 34 eyes

PURPOSE

To evaluate the efficacy and the safety of intravitreal ranibizumab injection (Lucentis) in eyes with macular oedema secondary to central retinal vein occlusion (CRVO) or branch retinal vein occlusion (BRVO).

METHODS

The files of consecutive patients (34 eyes, 15 CRVO, 19 BRVO) were retrospectively analysed. Intravitreal injections of 0.5 mg ranibizumab were administered; retreatment was based on acuity visual changes and optical coherence tomography findings. Patients received 2-4 injections (mean, 2.1). Mean follow-up was 7 months.

RESULTS

After the first injection, mean best-corrected visual acuity (BCVA) improved from 20/160 to 20/80 and mean central retinal thickness (CRT) decreased significantly from 549 to 301 μm (p < 0.01). For each injection, BCVA improvement was on average nine letters (p < 0.01) and macular oedema reduction was 195 μm CRT (p < 0.01). The decrease in CRT was similar in CRVO and BRVO, but the improvement in BCVA was larger in BRVO. No local or systemic adverse effect was detected. Final visual acuity was correlated to initial visual acuity and to visual acuity measured after the first injection. The change in CRT was correlated to the number of injections and to initial CRT.

CONCLUSION

Intravitreal injections of ranibizumab appeared to be a safe and effective option in the treatment of macular oedema secondary to retinal vein occlusion. Nevertheless, because the natural course has demonstrated a possible improvement in vision in almost one quarter of affected eyes at 3 years, further controlled and prospective studies are necessary to compare this treatment to the natural course with a longer follow-up.

Chemokines in aqueous humour before and after intravitreal triamcinolone acetonide in eyes with macular oedema associated with branch retinal vein occlusion

PURPOSE

To determine the aqueous humour levels of chemokines before and after an intravitreal injection of triamcinolone acetonide (IVTA) in eyes with macular oedema associated with a branch retinal vein occlusion (ME-BRVO).

DESIGN

  Single-centre, prospective, consecutive interventional case series.

PARTICIPANTS

Seventeen eyes of 17 consecutive patients with ME-BRVO who underwent IVTA were studied. Seven eyes without retinal vascular disease served as control.

INTERVENTION

All patients with ME-BRVO underwent IVTA.

MAIN OUTCOME MEASURES

The optical coherence tomographically determined foveal thickness (FT) and the aqueous humour levels of inflammatory chemokines of the C-C subfamily, including eotaxin, monocyte chemotactic protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), β (MIP-1β), and RANTES was determined before the IVTA (baseline) and at 1 week after the IVTA.

RESULTS

At the baseline, only MCP-1 and MIP-1β were detected in the aqueous, and MIP-1β was significantly higher in eyes with a ME-BRVO than in controls (p = 0.004). The level of both of these chemokines was not correlated with the FT (p = 0.654 and p = 0.608, respectively). One week after IVTA, the FT was significantly decreased (p < 0.001), and the levels of MCP-1 and MIP-1β were also significantly reduced (p < 0.001 and p = 0.044, respectively). The decrease in the FT was correlated with the decrease in only MIP-1β (r = 0.58, p = 0.020).

CONCLUSIONS

Alterations of the aqueous level of MIP-1β reflect the improvement of the macular oedema after IVTA in eyes with ME-BRVO. This indicates that the steroid-dependent ME-BRVO was closely related with the level of MIP-1β.

Levels of VEGF but not VEGF(165b) are increased in the vitreous of patients with retinal vein occlusion

PURPOSE

To determine the concentration of the pro-angiogenic vascular endothelial growth factor VEGF(165) (VEGF) and the anti-angiogenic VEGF(165b) in vitreous samples of patients with branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO) in comparison to patients without retinal occlusive disease.

DESIGN

Experimental laboratory investigation.

METHODS

Vitreous samples were collected from patients undergoing surgery for arteriovenous dissection after BRVO, radial optic neurotomy after CRVO in the occlusion group, or macular pucker or macular hole in the control group. Concentrations of VEGF and VEGF(165b) were determined by ELISA and an ELISA-type antibody microarray.

RESULTS

Average vitreal concentration of VEGF was 8.6 ng/mL in the CRVO group and 2.0 ng/mL in the BRVO group as compared to 0.26 ng/mL in the control group. Average vitreal concentration of VEGF(165b) was 27 pg/mL in the CRVO group, 42 pg/mL in the BRVO group, and 49 pg/mL in the control group. In patients with CRVO and BRVO, the angiogenic balance was shifted towards angiogenic stimulation.

CONCLUSION

The severity of RVO from BRVO to CRVO correlates with an increase of VEGF and the decrease of VEGF(165b), indicating a pro-angiogenic shift. Altering the ratio of VEGF(165b)/VEGF(165) might be a feasible approach for treating retinal occlusive diseases.

Long-term study of vascular perfusion effects following arteriovenous sheathotomy for branch retinal vein occlusion

PURPOSE

To evaluate the perfusion effects and long-term visual outcome of pars plana vitrectomy (PPV) combined with arteriovenous sheathotomy (AVS) with or without triamcinolone for nonischaemic branch retinal vein occlusion (NI-BRVO).

METHODS

Prospective, interventional case series of eight patients with NI-BRVO and haemorrhagic macular oedema. Patients underwent PPV and AVS (n = 5), or PPV, AVS and intravitreal triamcinolone (IVT, n = 3). A masked grading technique assessed fundus photographs and fluorescein angiography (FFA) following surgery. Scanning laser ophthalmoscopy/optical coherence tomography (SLO/OCT) evaluated macular oedema and outer retinal architecture. Main outcomes examined included visual acuity (VA), retinal reperfusion, collateral vessel regression, vascular dilatation, cystoid macular oedema (CMO), and ocular neovascularization.

RESULTS

Seven of eight patients underwent uncomplicated surgery, with increased intraretinal perfusion and reduced engorgement of distal retinal veins. The mean pre-logMAR VA was 0.8 (SD 0.17) and did not improve significantly after surgery (post-logMAR 0.6, SD 0.38; p = 0.11, paired t-test). SLO/OCT showed persistent CMO in four patients, and subfoveal thinning of the photoreceptor layer. Collateral vessels disappeared at the blockage site post-AVS in 7/8 eyes, and this was associated with improved retinal perfusion. Six of eight patients developed epiretinal membrane. No patients developed ocular neovascularization. The average follow-up was 34.5 months.

CONCLUSIONS

PPV with AVS is a safe procedure, and adjunctive IVT had no additional effects on vascular perfusion. Successful decompressive surgery was followed by disappearance of collateral vessels at the BRVO blockage site and was a clinical marker for intravascular reperfusion. Long-term epiretinal gliosis and subfoveal photoreceptor atrophy limited functional and visual recovery.

Visual acuity and foveal thickness after vitrectomy for macular edema associated with branch retinal vein occlusion: a case series

Background

The mechanism by which vitrectomy improves macular edema in patients with branch retinal vein occlusion remains unclear, although intraocular levels of vascular endothelial growth factor have been suggested to influence the visual prognosis and macular edema.

Methods

A series of 54 consecutive patients (54 eyes) with branch retinal vein occlusion was studied prospectively. All patients underwent pars plana vitrectomy for treatment of macular edema. Best corrected visual acuity and retinal thickness (examined by optical coherence tomography) were assessed before and after surgery. The level of vascular endothelial growth factor in vitreous fluid harvested at operation was determined. Patients were followed for at least 6 months postoperatively.

Results

Both the visual acuity and the retinal thickness showed significant improvement at 6 months postoperatively (P = 0.0002 and P < 0.0001, respectively). The vitreous level of vascular endothelial growth factor was significantly higher in patients who showed less improvement of visual acuity compared with those who had a better visual prognosis (p = 0.0135). In contrast, a high vitreous level of vascular endothelial growth factor was associated with greater improvement of macular edema (p = 0.0064).

Conclusions

These results suggest that the vitreous level of vascular endothelial growth factor might influence the visual prognosis and the response of macular edema to vitrectomy in patients with branch retinal vein occlusion.

Physiology of vitreous surgery

Vitreous surgery has various physiological and clinical consequences, both beneficial and harmful. Vitrectomy reduces the risk of retinal neovascularization, while increasing the risk of iris neovascularization, reduces macular edema and stimulates cataract formation. These clinical consequences may be understood with the help of classical laws of physics and physiology. The laws of Fick, Stokes-Einstein and Hagen-Poiseuille state that molecular transport by diffusion or convection is inversely related to the viscosity of the medium. When the vitreous gel is replaced with less viscous saline, the transport of all molecules, including oxygen and cytokines, is facilitated. Oxygen transport to ischemic retinal areas is improved, as is clearance of VEGF and other cytokines from these areas, thus reducing edema and neovascularization. At the same time, oxygen is transported faster down a concentration gradient from the anterior to the posterior segment, while VEGF moves in the opposite direction, making the anterior segment less oxygenated and with more VEGF, stimulating iris neovascularization. Silicone oil is the exception that proves the rule: it is more viscous than vitreous humour, re-establishes the transport barrier to oxygen and VEGF, and reduces the risk for iris neovascularization in the vitrectomized-lentectomized eye. Modern vitreous surgery involves a variety of treatment options in addition to vitrectomy itself, such as photocoagulation, anti-VEGF drugs, intravitreal steroids and release of vitreoretinal traction. A full understanding of these treatment modalities allows sensible combination of treatment options. Retinal photocoagulation has repeatedly been shown to improve retinal oxygenation, as does vitrectomy. Oxygen naturally reduces VEGF production and improves retinal hemodynamics. The VEGF-lowering effect of photocoagulation and vitrectomy can be augmented with anti-VEGF drugs and the permeability effect of VEGF reduced with corticosteroids. Starling's law explains vasogenic edema, which is controlled by osmotic and hydrostatic gradients between vessel and tissue. It explains the effect of VEGF-induced vascular permeability changes on plasma protein leakage and the osmotic gradient between vessel and tissue. At the same time, it takes into account hemodynamic changes that affect the hydrostatic gradient. This includes the influence of arterial blood pressure, and the effect oxygen (laser treatment) has in constricting retinal arterioles, increasing their resistance, and thus reducing the hydrostatic pressure in the microcirculation. Reduced capillary hydrostatic pressure and increased osmotic gradient reduce water fluxes from vessel to tissue and reduce edema. Finally, Newton's third law explains that vitreoretinal traction decreases hydrostatic tissue pressure in the retina, increases the pressure gradient between vessel and tissue, and stimulates water fluxes from vessel into tissue, leading to edema.