Impact of preocular and ocular circulatory dynamics on the vascular density of retinal capillary plexuses and choriocapillaris.

PURPOSE: To highlight the influence of preocular and ocular vascular circulatory dynamics on the vascular density (VD) of retinal capillary plexuses (RCPs) and choriocapillaris (CC) in patients with and without cardiovascular risk (CVR) factors. METHODS: A retrospective observational study in patients with and without CVR factors (type 1 and 2 diabetes, arterial hypertension, and hypercholesterolemia). Fluorescein (FA) and indocyanine (ICGA) angiography circulatory times were arterial time (FAAT), start (FAstartLF) and end (FAendLF) of laminar flow, and arterial time (ICGAAT), respectively. OCT angiography VDs were superficial (VDSCP) and deep (VDDCP) RCPs and CC (VDCC) VDs. Correlation and regression analysis were performed after adjusting for confounding factors. RESULTS: 177 eyes of 177 patients (mean age: 65.2 ± 15.9 years, n = 92 with and 85 without CVR) were included. VDSCP and VDDCP were significantly inversely correlated with FAAT, FAstartLF and FAendLF likewise VDCC with ICGAAT. Correlations were stronger in patients without CVR than with CVR. CVR, FAAT, FAstartLF and FAendLF were more strongly correlated with VDDCP than VDSCP. FAAT, FAstartLF and FAendLF significantly impacted VDSCP and VDDCP, likewise ICGAAT impacted VDDCP. VDDCP was most strongly impacted by FAAT and FAstartLF. CONCLUSION: Ocular and pre-ocular circulatory dynamics significantly impacted RCPs and CC VDs, especially deep RCP.

Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency.

In a consanguineous Pakistani family with two affected individuals, a homozygous variant Gly399Val in the eighth transmembrane domain of the taurine transporter SLC6A6 was identified resulting in a hypomorph transporting capacity of ~15% compared with normal. Three-dimensional modeling of this variant has indicated that it likely causes displacement of the Tyr138 (TM3) side chain, important for transport of taurine. The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels. Oral taurine supplementation of 100 mg/kg/day resulted in maintenance of normal blood taurine levels. Following approval by the ethics committee, a long-term supplementation treatment was introduced. Remarkably, after 24-months, the cardiomyopathy was corrected in both affected siblings, and in the 6-years-old, the retinal degeneration was arrested, and the vision was clinically improved. Similar therapeutic approaches could be employed in Mendelian phenotypes caused by the dysfunction of the hundreds of other molecular transporters.

Bi-allelic Loss-of-Function Variants in DNMBP Cause Infantile Cataracts.

Infantile and childhood-onset cataracts form a heterogeneous group of disorders; among the many genetic causes, numerous pathogenic variants in additional genes associated with autosomal-recessive infantile cataracts remain to be discovered. We identified three consanguineous families affected by bilateral infantile cataracts. Using exome sequencing, we found homozygous loss-of-function variants in DNMBP: nonsense variant c.811C>T (p.Arg271∗) in large family F385 (nine affected individuals; LOD score = 5.18 at θ = 0), frameshift deletion c.2947_2948del (p.Asp983∗) in family F372 (two affected individuals), and frameshift variant c.2852_2855del (p.Thr951Metfs∗41) in family F3 (one affected individual). The phenotypes of all affected individuals include infantile-onset cataracts. RNAi-mediated knockdown of the Drosophila ortholog still life (sif), enriched in lens-secreting cells, affects the development of these cells as well as the localization of E-cadherin, alters the distribution of septate junctions in adjacent cone cells, and leads to a ∼50% reduction in electroretinography amplitudes in young flies. DNMBP regulates the shape of tight junctions, which correspond to the septate junctions in invertebrates, as well as the assembly pattern of E-cadherin in human epithelial cells. E-cadherin has an important role in lens vesicle separation and lens epithelial cell survival in humans. We therefore conclude that DNMBP loss-of-function variants cause infantile-onset cataracts in humans.

JNK Inhibition Reduced Retinal Ganglion Cell Death after Ischemia/Reperfusion In Vivo and after Hypoxia In Vitro.

Mitogen-activated protein kinases (MAPKs) are key regulators that have been linked to cell survival and death. Among the main classes of MAPKs, c-jun N-terminal kinase (JNK) has been shown to mediate cell stress responses associated with apoptosis. In Vitro, hypoxia induced a significant increase in 661W cell death that paralleled increased activity of JNK and c-jun. 661W cells cultured in presence of the inhibitor of JNK (D-JNKi) were less sensitive to hypoxia-induced cell death. In vivo, elevation in intraocular pressure (IOP) in the rat promoted cell death that correlated with modulation of JNK activation. In vivo inhibition of JNK activation with D-JNKi resulted in a significant and sustained decrease in apoptosis in the ganglion cell layer, the inner nuclear layer and the photoreceptor layer. These results highlight the protective effect of D-JNKi in ischemia/reperfusion induced cell death of the retina.

Autophagy induction does not protect retina against apoptosis in ischemia/reperfusion model.

The role played by autophagy after ischemia/reperfusion (I/R) in the retina remains unknown. Our study investigated whether ischemic injury in the retina, which causes an energy crisis, would induce autophagy. Retinal ischemia was induced by elevation of the intraocular pressure and modulation of autophagic markers was analyzed at the protein levels in an early and late phase of recovery. Following retinal ischemia an increase in LC3BII was first observed in the early phase of recovery but did not stay until the late phase of recovery. Post-ischemic induction of autophagy by intravitreal rapamycin administration did not provide protection against the lesion induced by the ischemic stress. On the contrary, an increase in the number of apoptotic cells was observed following I/R in the rapamycin treated retinas.

Preretinal partial pressure of oxygen gradients before and after experimental pars plana vitrectomy.

PURPOSE: To evaluate preretinal partial pressure of oxygen (PO2) gradients before and after experimental pars plana vitrectomy. METHODS: Arteriolar, venous, and intervascular preretinal PO2 gradients were recorded in 7 minipigs during slow withdrawal of oxygen-sensitive microelectrodes (10-µm tip diameter) from the vitreoretinal interface to 2 mm into the vitreous cavity. Recordings were repeated after pars plana vitrectomy and balanced salt solution (BSS) intraocular perfusion. RESULTS: Arteriolar, venous, and intervascular preretinal PO2 at the vitreoretinal interface were 62.3 ± 13.8, 22.5 ± 3.3, and 17.0 ± 7.5 mmHg, respectively, before vitrectomy; 97.7 ± 19.9, 40.0 ± 21.9, and 56.3 ± 28.4 mmHg, respectively, immediately after vitrectomy; and 59.0 ± 27.4, 25.2 ± 3.0, and 21.5 ± 4.5 mmHg, respectively, 2½ hours after interruption of BSS perfusion. PO2 2 mm from the vitreoretinal interface was 28.4 ± 3.6 mmHg before vitrectomy; 151.8 ± 4.5 mmHg immediately after vitrectomy; and 34.8 ± 4.1 mmHg 2½ hours after interruption of BSS perfusion. PO2 gradients were still present after vitrectomy, with the same patterns as before vitrectomy. CONCLUSION: Preretinal PO2 gradients are not eliminated after pars plana vitrectomy. During BSS perfusion, vitreous cavity PO2 is very high. Interruption of BSS perfusion evokes progressive equilibration of vitreous cavity PO2 with concomitant progressive return of preretinal PO2 gradients to their previtrectomy patterns. This indicates that preretinal diffusion of oxygen is not altered after vitrectomy. The beneficial effect of vitrectomy in ischemic retinal diseases or macular edema may be related to other mechanisms, such as increased oxygen convection currents or removal of growth factors and cytokines secreted in the vitreous.

Retinal blood flow evaluation.

Much of our basic knowledge of retinal blood flow regulation is based on data obtained from animal experiments through the use of invasive techniques. However, during the last decades, major developments in the field of optics and lasers have led to a variety of noninvasive techniques, which have been applied to the human eye for the investigation of retinal hemodynamics, and more specifically the regulation of retinal blood flow in response to a number of physiological and pharmacological stimuli. The Retinal Vessel Analyzer has markedly simplified the measurement of the diameter of retinal vessels, as well as the change in this diameter evoked by various physiological stimuli (dynamic measurements). Bidirectional laser Doppler velocimetry allows the measurement of absolute red blood cell centerline velocity, which, when combined with the diameter allows the calculation of retinal blood flow in the main retinal vessels. Laser Doppler flowmetry and laser speckle flowgraphy are techniques that measure the velocities of blood in discrete areas of the retinal tissue microcirculation. Adding a scanning capability, a spatial map of velocities across the retinal tissue is obtained. The blue-field simulation technique allows the quantification of the velocity, number and velocity pulsatility of leukocytes moving in the retinal capillaries of the macular region. With color Doppler imaging, the peak systolic and end-diastolic values of blood velocity in the ophthalmic and central retinal artery are measured, from which a resistivity index is obtained. These techniques may help better understand the role of altered retinal blood flow and its regulation in the pathogenesis of retinal diseases of vascular origin.

Safety of 20-gauge transconjunctival sutureless vitrectomy.

PURPOSE: To study the safety of 20-gauge transconjunctival sutureless vitrectomy. METHODS: Clinical data of patients who underwent 20-gauge transconjunctival sutureless vitrectomy for the first time, for various disorders, were reviewed retrospectively. The main outcome measures were the number of sclerotomies requiring suturing as well as the intra- and postoperative complications. RESULTS: A total of 179 operations were performed. Indications for vitrectomy included 68 idiopathic epiretinal membranes, 26 macular holes, 23 phakic and 16 pseudophakic retinal detachments, and 46 various other, less common etiologies. Of these 179 operations, 166 (93%) were sutureless. Of the 537 sclerotomies created, 25 (5%) received a single transconjunctival-scleral suture. Intraoperative complications included premature dislodging of the cannulas in 2 sclerotomies and an iatrogenic horseshoe tear at 1 sclerotomy site. Postoperative complications comprised transient hypotony in 14 cases, subconjunctival gas in 2 cases, and choroidal effusion in 1 case. No serious complications (such as endophthalmitis) were observed. CONCLUSION: 20-gauge transconjunctival sutureless vitrectomy can be considered safe, as the intra- and postoperative complications observed are neither numerous nor significant. Sclerotomies appear to be safe and relatively easy to perform, without compromising the advantages of sutureless surgery.

The rationale of retinal endovascular fibrinolysis in the treatment of retinal vein occlusion: from experimental data to clinical application.

PURPOSE: We describe a retinal endovascular fibrinolysis technique to directly reperfuse experimentally occluded retinal veins using a simple micropipette. METHODS: Retinal vein occlusion was photochemically induced in 12 eyes of 12 minipigs: after intravenous injection of 10% fluorescein (1-mL bolus), the targeted retinal vein segment was exposed to thrombin (50 units) and to Argon laser (100-200 mW) through a pars plana approach. A beveled micropipette with a 30-µm-diameter sharp edge was used for micropuncture of the occluded vein and endovascular microinjection of tissue plasminogen activator (50 µg/mL) in 11 eyes. In one control eye, balanced salt solution was injected. The lesion site was examined histologically. RESULTS: Retinal vein occlusion was achieved in all cases. Endovascular microinjection of tissue plasminogen activator or balanced salt solution led to reperfusion of the occluded retinal vein in all cases. Indicative of successful reperfusion were the following: continuous endovascular flow, unaffected collateral circulation, no optic disk ischemia, and no venous wall bleeding. However, balanced salt solution injection was accompanied by thrombus formation at the punctured site, whereas no thrombus was observed with tissue plasminogen activator injection. CONCLUSION: Retinal endovascular fibrinolysis constitutes an efficient method of micropuncture and reperfusion of an experimentally occluded retinal vein. Thrombus formation at the punctured site can be prevented by injection of tissue plasminogen activator.

A COVID-19-Related Retinopathy Case Report.

The recent outbreak of the severe acute respiratory syndrome coronavirus-2 has been declared a worldwide pandemic by the WHO. Within various multi-organ involvements, several ocular manifestations have been described. We report the case of a patient diagnosed with COVID-19 who presented with a progressive increase of bilateral cotton wool spots over a 1-week period, despite quick and complete recovery of systemic signs of the disease and no ocular symptoms. We followed the evolution of such lesions over a 3-month period. Here, we underline the importance of retinal screening even if no ocular symptom is reported. Furthermore, we demonstrate the essential role of fundus examination as a reflection of systemic vascular changes.

Retinal vessel analyzer measurements of the effect of panretinal photocoagulation on the retinal arteriolar diameter in diabetic retinopathy.

PURPOSE: The purpose of this study was to investigate the effect of panretinal photocoagulation (PRP) on the retinal arteriolar diameter in patients with diabetic retinopathy using a retinal vessel analyzer. METHODS: Ten eyes of 6 consecutive patients with type II diabetes and severe nonproliferative or proliferative diabetic retinopathy were studied prospectively. Measurements of the retinal arteriolar diameter were performed before the first photocoagulation session and after the end of the PRP treatment. RESULTS: Retinal arteriolar diameter before PRP was 131 +/- 15 arbitrary units and decreased to 112 +/- 14 arbitrary units after PRP (P = 0.012). There was a significant vasoconstriction of 13.8% +/- 8.3% following PRP. Mean visual acuity before and after PRP was 0.31 +/- 0.36 logarithm of the minimal angle of resolution and 0.28 +/- 0.30 logarithm of the minimal angle of resolution, respectively (P = 0.68). There was no significant change in mean arterial pressure before and after PRP (P = 0.89). There was no correlation between the visual acuity change or the number of laser burns and the percentage change in the retinal arteriolar diameter (P > 0.1). CONCLUSION: Panretinal photocoagulation has a vasoconstrictive effect on retinal arterioles in patients with severe nonproliferative or proliferative diabetic retinopathy. These results are consistent with an autoregulatory response of the retinal circulation to increased inner retinal oxygen tension after PRP. The retinal vessel analyzer is a fast, accurate, noninvasive, online measuring system for the study of the retinal vascular response to PRP in patients with diabetic retinopathy.

Retinal ischemia-induced apoptosis is associated with alteration in Bax and Bcl-x(L) expression rather than modifications in Bak and Bcl-2.

PURPOSE: Apoptosis is known to play a key role in cell death after retinal ischemia. However, little is known about the kinetics of the signaling pathways involved and their contribution to this process. The aim of this study was to determine whether changes in the expression of molecules in the mitochondrial apoptotic pathway might explain the progression of retinal damage following ischemia/reperfusion. METHODS: Retinal ischemia was induced by elevating intraocular pressure in the vitreous cavity to 150 mmHg for a period of 60 min. At time 0, 3 h (early phase), and 24 h (late phase) after reperfusion, the retinas were harvested and modifications in the expression of Bax, Bak, Bcl-2, and Bcl-x(L) as well as caspase-3 and -7, were examined by qPCR and, in some cases, by western blot. RESULTS: qPCR analysis performed at the early phase after ischemia revealed a time dependent decrease in Bax, Bak, and Bcl-x(L) and no alteration in Bcl-2 mRNA expression in response to retinal ischemia. At the protein level, proapoptotic Bax and Bak were not modulated while Bcl-2 and Bcl-x(L) were significantly upregulated. At this stage, the Bax per Bcl-2 and Bax:Bcl-x(L) ratios were not modified. At the late phase of recovery, Bax and Bcl-x(L) mRNAs were downregulated while Bak was increased. Increased Bax:Bcl-2 and Bax:Bcl-x(L) ratios at both the mRNA and protein levels were observed 24 h after the ischemic insult. Analysis of caspases associated with mitochondria-mediated apoptosis revealed a specific increase in the expression of caspase-3 in the ischemic retinas 24 h after reperfusion, and a decrease in the expression of caspase-7. CONCLUSIONS: This study revealed that Bcl-2-related family members were differently regulated in the early and late phases after an ischemic insult. We showed that the Bax:Bcl-2 and Bax:Bcl-x(L) balances were not affected in the initial phases, but the Bax:Bcl-x(L) ratio shifted toward apoptosis during the late phase of recovery. This shift was reinforced by caspase-3 upregulation.

Intravitreal ranibizumab may induce retinal arteriolar vasoconstriction in patients with neovascular age-related macular degeneration.

OBJECTIVE: To study the effect of intravitreal (IVT) ranibizumab (Lucentis; Genentech, Inc, San Francisco, CA) on the retinal arteriolar diameter in patients with neovascular age-related macular degeneration (AMD). DESIGN: Prospective consecutive interventional case series. PARTICIPANTS: Eleven eyes of eleven patients with previously untreated neovascular AMD. METHODS: All eyes had 3 monthly IVT injections of ranibizumab. The diameter of the retinal arterioles was measured in vivo with a retinal vessel analyzer (RVA) before the first IVT injection and then 7 and 30 days after the first, second, and third injections. MAIN OUTCOME MEASURES: Primary end points were changes in retinal arteriolar diameter and mean arterial pressure (MAP) after IVT ranibizumab. Secondary end points were changes in best-corrected visual acuity (BCVA), central retinal thickness, and intraocular pressure after IVT ranibizumab, and appearance of adverse events during the follow-up period. RESULTS: A significant decrease of the retinal arteriolar diameter was observed after each IVT injection of ranibizumab. Thirty days after the first, second, and third injections, there was a mean decrease of 8.1+/-3.2%, 11.5+/-4.4%, and 17.6+/-7.4%, respectively, of the retinal arteriolar diameter compared with baseline values (P<0.01). There was no significant change in MAP during the period of follow-up (P>0.05). Thirty days after the third IVT injection of ranibizumab, mean BCVA improved by 6.5+/-4.9 Early Treatment Diabetic Retinopathy Study (ETDRS) letters, and central retinal thickness decreased by 91+/-122 microm (P = 0.03). CONCLUSIONS: These results suggest that IVT ranibizumab may induce retinal arteriolar vasoconstriction in patients with neovascular AMD after IVT ranibizumab. Further studies evaluating larger sample sizes are needed to confirm these results and potential adverse effects on the retinal circulation in patients with AMD and retinal vascular diseases. FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Regulation of retinal blood flow in health and disease.

Optimal retinal neuronal cell function requires an appropriate, tightly regulated environment, provided by cellular barriers, which separate functional compartments, maintain their homeostasis, and control metabolic substrate transport. Correctly regulated hemodynamics and delivery of oxygen and metabolic substrates, as well as intact blood-retinal barriers are necessary requirements for the maintenance of retinal structure and function. Retinal blood flow is autoregulated by the interaction of myogenic and metabolic mechanisms through the release of vasoactive substances by the vascular endothelium and retinal tissue surrounding the arteriolar wall. Autoregulation is achieved by adaptation of the vascular tone of the resistance vessels (arterioles, capillaries) to changes in the perfusion pressure or metabolic needs of the tissue. This adaptation occurs through the interaction of multiple mechanisms affecting the arteriolar smooth muscle cells and capillary pericytes. Mechanical stretch and increases in arteriolar transmural pressure induce the endothelial cells to release contracting factors affecting the tone of arteriolar smooth muscle cells and pericytes. Close interaction between nitric oxide (NO), lactate, arachidonic acid metabolites, released by the neuronal and glial cells during neural activity and energy-generating reactions of the retina strive to optimize blood flow according to the metabolic needs of the tissue. NO, which plays a central role in neurovascular coupling, may exert its effect, by modulating glial cell function involved in such vasomotor responses. During the evolution of ischemic microangiopathies, impairment of structure and function of the retinal neural tissue and endothelium affect the interaction of these metabolic pathways, leading to a disturbed blood flow regulation. The resulting ischemia, tissue hypoxia and alterations in the blood barrier trigger the formation of macular edema and neovascularization. Hypoxia-related VEGF expression correlates with the formation of neovessels. The relief from hypoxia results in arteriolar constriction, decreases the hydrostatic pressure in the capillaries and venules, and relieves endothelial stretching. The reestablished oxygenation of the inner retina downregulates VEGF expression and thus inhibits neovascularization and macular edema. Correct control of the multiple pathways, such as retinal blood flow, tissue oxygenation and metabolic substrate support, aiming at restoring retinal cell metabolic interactions, may be effective in preventing damage occurring during the evolution of ischemic microangiopathies.

Primary vitrectomy without scleral buckling for pseudophakic rhegmatogenous retinal detachment.

PURPOSE: To report the anatomic and functional results of primary vitrectomy without scleral buckling for the treatment of pseudophakic rhegmatogenous retinal detachment (PsRD). DESIGN: Prospective, nonrandomized surgical technique study. METHODS: One hundred eyes of 98 patients with PsRD were operated by vitrectomy alone. Internal subretinal fluid drainage, cryocoagulation and/or endolaser and fluid-air exchange with sulfur hexafluoride 20% was applied in all cases. The preoperative and postoperative characteristics were analyzed. Main outcome measures were anatomic success rates after initial surgical intervention and after reoperation for primary failures, visual outcome at the last follow-up visit, and complications. RESULTS: Mean follow-up +/- standard deviation (SD) was 12 +/- 6.3 months (range, seven to 36 months). Mean final visual acuity +/- SD was 0.42 +/- 0.45 logarithm of the minimum angle of resolution (logMAR) compared with 0.95 +/- 0.73 logMAR before surgery (P < .01). Mean number +/- SD of retinal breaks found before surgery was 1.36 +/- 1.12 (range, zero to five), and an additional 1.58 +/- 2.26 (range, zero to 15) retinal breaks were found during surgery. The retina was reattached successfully after a single surgery in 92 eyes (92%). Recurrence of retinal detachment occurred in eight eyes (8%), caused by proliferative vitreoretinopathy in six eyes (75%) and by new breaks in two eyes (25%). Final anatomic reattachment was obtained in these cases after a mean of 1.75 subsequent operations. Three eyes required permanent silicone oil tamponade so that final anatomic success was achieved in 97 eyes (97%). The most common postoperative complication was ocular hypertonia of more than 21 mm Hg, observed in 36 (36%) eyes, which was managed successfully. CONCLUSIONS: Primary vitrectomy without scleral buckling provides a high anatomic success rate in eyes with PsRD and is associated with few complications.

Optical coherence tomography and multifocal electroretinogram findings in chronic solar retinopathy.

PURPOSE: To correlate the structural and functional retinal defects, which are induced photochemically in chronic solar retinopathy. DESIGN: Observational case report. METHODS: Four emmetropic eyes of two patients, previously diagnosed with chronic solar retinopathy, were evaluated by optical coherence tomography (OCT), multifocal electroretinography, and fluorescein angiography. RESULTS: Visual acuity ranged from 20/80 to 20/50 and all subjects had central and steady fixation. In all eyes, OCT demonstrated a hyporeflective space at the level of outer retinal and retinal pigment epithelium (RPE) layers, which was limited to the fovea. The foveal contour was preserved with normal vitreoretinal interface. Multifocal electroretinogram (mfERG) trace array of the first-order kernel demonstrated attenuated responses extending to a larger area, the para- and perifovea. A foveal RPE window defect was angiographically evident in all cases. CONCLUSIONS: A model of centrifugal neuronal damage is proposed for chronic solar retinopathy, with more functional than structural neuroretinal defects.

Regulation of subfoveal choroidal blood flow in age-related macular degeneration.

PURPOSE: To assess the capability of the subfoveal choroidal circulation to regulate its blood flow in response to an acute increase in ocular perfusion pressure in the eyes of healthy elderly persons or of subjects with neovascular age-related macular degeneration (AMD). METHODS: Changes of subfoveal choroidal blood velocity (ChBVel), volume (ChBVol), and flow (ChBF) induced by isometric exercise were determined using laser Doppler flowmetry (LDF) in 19 young healthy volunteers (group 1), 24 elderly healthy volunteers with mild macular pigment distribution changes (group 2), and 23 subjects with subfoveal classic neovascularization caused by AMD (group 3). RESULTS: Isometric exercise induced significant increases in mean ocular perfusion pressure (PPm) of 19.5% +/- 4.9%, 20.2% +/- 3.8%, and 23.2% +/- 4.2%, for groups 1, 2, and 3, respectively (mean +/- 95% confidence interval). In groups 1 and 2, the increase in PPm did not induce significant changes in the mean values of the different LDF parameters. In group 3, however, ChBF increased significantly by 12.4% +/- 5.0%. No significant correlations were found between age and the changes of each of the LDF parameters and of PPm at the end of squatting for the young and elderly healthy groups. CONCLUSIONS: In response to an acute, moderate increase in PPm induced by isometric exercise, subfoveal choroidal blood flow behaves similarly in young and elderly healthy persons and is not significantly different from its value at rest. In contrast, in patients with neovascular AMD, this flow increases, indicating altered regulation in response to the increase in PPm.

Effect of carbogen breathing and acetazolamide on optic disc PO2.

PURPOSE: Acetazolamide was previously shown to increase optic disc partial pressure of oxygen (PO(2)). The study was conducted to evaluate optic disc PO(2) variations during normoxia, hyperoxia (100% O(2)), and carbogen breathing (95% O(2), 5% CO(2)), before and after intravenous administration of acetazolamide. METHODS: PO(2) measurements were obtained at intervascular areas of the optic disc in nine anesthetized minipigs using oxygen-sensitive microelectrodes (10-microm tip diameter) placed at <50 microm from the optic disc. PO(2) was measured continuously during 10 minutes under normoxia, hyperoxia, or carbogen breathing. Oxygen measurements were repeated under these conditions after intravenous injection of acetazolamide (500-mg bolus). RESULTS: In hyperoxia, optic disc PO(2) increased moderately (DeltaPO(2) = 4.81 +/- 1.16 mm Hg (mean +/- SD; 24%; P < 0.001) after a much larger increase in systemic PaO(2). Carbogen breathing induced a significant increase in both systemic PaO(2) and PaCO(2), which resulted in a large increase in optic disc PO(2) (DeltaPO(2) = 13.17 +/- 2.18 mm Hg; 67%; P < 0.001). Acetazolamide induced a slow and progressive increase in both systemic PaCO(2) and optic disc PO(2) (30 minutes DeltaPO(2) = 4.24 +/- 2.45 mm Hg; 24%; P < 0.04). However, it was when carbogen was simultaneously administered that optic disc PO(2) increased most substantially (DeltaPO(2) = 18.91 +/- 5.23 mm Hg; 90%; P < 0.002). CONCLUSIONS: Carbogen breathing increases optic disc Po(2) significantly in minipigs, more than hyperoxia. The association of acetazolamide injection with carbogen breathing could induce an additional increase in optic disc PO(2) through the effect of higher systemic PaCO(2).

Light-induced retinal vascular damage by Pd-porphyrin luminescent oxygen probes.

PURPOSE: The phosphorescence lifetime of certain metalloporphyrins dissolved in a physiological medium provides an optical signature for local oxygen concentration (pO(2)). This effect is used for measuring physiological pO(2) levels in various tissues. However, the phosphorescence quenching of certain metalloporphyrin triplet states by oxygen also creates singlet oxygen, which is highly reactive and capable of inducing tissue damage. In the current study, the Pd-meso-tetra(4-carboxyphenyl) porphyrin dye (PdTCPP) was simultaneously used as an oxygen sensor and a photosensitizer. Phototoxicity was assessed in the eye fundus and correlated with tissue oxygenation, drug-light dose, and severity of tissue damage. METHODS: The kinetics of photochemical oxygen depletion during PdTCPP excitation was measured in vivo on the optic disc of piglets by phosphorescence lifetime imaging. Blood-retinal barrier breakdown and tissue damage were assessed by confocal and electron microscopy. RESULTS: For a retinal irradiance of 5 mW/cm(2) at 532 nm and an injected PdTCPP dose of 20 mg/kg, the mean phosphorescence lifetime measured at the optic disc increased from 100 to 600 micros within 8 minutes of continuous illumination. This corresponds to a decrease of pO(2) from 25 to 0 mm Hg, induced by a light dose of only 2.4 J/cm(2). An exposure time of 6 minutes (1.8 J/cm(2)) generated an increase in phosphorescence lifetime from 100 to 400 micros, corresponding to a decrease in pO(2) from 25 to 4 mm Hg. This caused edema in all retinal layers, whereas irradiation of 2 minutes (0.6 J/cm(2)) damaged blood vessels and induced edema in the inner nuclear layer only. Heavy redistribution of occludin occurred after a 30-minute exposure time (9 J/cm(2)). CONCLUSIONS: PdTCPP is potentially phototoxic under certain experimental conditions and can induce damage in peripapillary retina and optic nerve head after light exposure. The severity of tissue damage correlates with the phosphorescence measurements.

Occult anterior-chamber metallic fragment post-phacoemulsification masquerading as chronic recalcitrant postoperative inflammation.

PURPOSE: To report a case of an occult, metallic, anterior-chamber intraocular foreign body after uneventful phacoemulsification that was masquerading as chronic recalcitrant postoperative inflammation. DESIGN: Interventional case report. METHODS: A 73-year-old patient was referred to us for recalcitrant anterior-chamber inflammation after uneventful phacoemulsification; the patient presented with visual disturbances, anterior-chamber inflammation, and macular epiretinal membrane with concomitant cystoid macular edema. RESULTS: After meticulous evaluations and repeated clinical examinations, a metallic intraocular foreign body was discovered on the iris, which was surgically removed and analyzed. Chemical analysis revealed copper, aluminum, and zinc. Pars plana vitrectomy with epiretinal membrane and indocyanine-green-assisted internal limiting membrane peeling followed, with subsequent improvement of visual acuity. CONCLUSIONS: Intraocular foreign bodies should always be considered in the differential diagnosis of recalcitrant inflammation post-phacoemulsification. However, in the absence of intraocular inflammation, surgical removal of such particles is questionable.