[Hazards posed by LEDs? : A comparative study]. / Gefahr durch LED-Licht? : Eine vergleichende Untersuchung.

BACKGROUND: The increasing use of light-emitting diodes (LEDs) for lighting applications and displays is giving rise to public and professional concern that blue LED emissions could damage the retina or via the proven influence on the melatonin levels disrupt the human day-night rhythm. OBJECTIVE: The study aimed to measure the emission of LEDs and other relevant light sources and evaluate the results comparatively with the help of suitable evaluation functions in order to recognize whether LEDs differ considerably from other light sources in their hazard potential. MATERIAL AND METHODS: The spectra of a cold white and a warm white LED, a white tablet LED display, a fluorescent tube and a halogen lamp were measured and evaluated together with a sunlight spectrum relative to each other using the blue light hazard retina weighting function and the circadian action function. RESULT: Since LEDs can be very different, relative LED ratings also vary greatly. The warm white LED is the one with the lowest risk of blue light retinal damage and the lowest potential for inhibition of melatonin formation and in this respect even gentler than halogen lamps. For cold white LEDs, the values for photochemical retinal danger as well as for the expected inhibition of melatonin formation are much greater. The values for the tablet LED display are even higher. CONCLUSION: Not only LEDs but all examined light sources emit in the blue spectral range, so that in principle they represent a retinal hazard. Depending on the employed LED type, this hazard may be greater or less compared to conventional light sources but even cold white LEDs are rated slightly better than sunlight at noon. To support consumers it might be helpful to classify LEDs and other illuminants by their potential hazard to the eye, as they are already labelled with respect to their energy efficiency.

The efficacy and safety outcomes of the 0.19 mg fluocinolone acetonide implant after prior treatment with the 0.7 mg dexamethasone implant in patients with diabetic macular edema.

PURPOSE: There are little or no published data comparing the outcomes of ILUVIEN® (0.19 mg fluocinolone acetonide [FAc]) and OZURDEX® (0.7 mg dexamethasone [DEX]) implants in patients with diabetic macular edema (DME), and this case sought to compare their outcomes. METHODS: This case was extracted from a monocentric audit involving a pool of 25 patients (33 eyes) with DME and treated with a single FAc implant between October 2013 and December 2016. This case, a 61-year-old male with a pseudophakic lens, is from a patient that had received 4 intravitreal injections of a DEX implant prior to FAc implant and then was monitored for 3 years until re-treatment with a second FAc implant. Parameters measured included visual acuity (VA), central retinal thickness (CRT), and intraocular pressure (IOP). RESULTS: After the DEX implants, CRT transiently improved. In March 2014, the decision was taken to administer an FAc implant, and this led to a reduction in CRT below 300 µm (from a baseline of 748 µm), and this was sustained for 30 months. VA remained above 65 Early Treatment Diabetic Retinopathy Study letters to month 36, after which time a second FAc implant (in April 2017) was administered due to recurrence of edema and CRT decreased to below 300 µm and VA improved to 70 letters. Side effects included elevated IOP, which was effectively managed with IOP-lowering drops. CONCLUSION: A single injection of FAc implant led to sustained improvements in CRT and VA that lasted for between 30 and 36 months, which is in contrast to the DEX implant where re-treatment was generally required within 6-7 months. After 36 months, re-treatment with the FAc implant again led to improved VA and CRT, and responses that were similar to those achieved with the first FAc implant.

[Proteome analysis of undiluted vitreous humor in patients with branch retinal vein occlusion]. / Proteomanalyse unverdünnter Glaskörperflüssigkeit bei Patienten mit einem Venenastverschluss.

BACKGROUND: The pathophysiological mechanisms of macular edema secondary to branch retinal vein occlusion (BRVO) remain unclear. OBJECTIVES: To analyze the protein profile of human vitreous of patients with BRVO and to identify specific dysregulated proteins. MATERIALS AND METHODS: Undiluted vitreous humor samples from patients with treatment naïve BRVO and 15 controls with idiopathic floaters were analyzed in this clinical-experimental study using capillary electrophoresis coupled to a mass spectrometer (CE-MS) and tandem mass spectrometry (MS/MS). Quantitative analysis of the dysregulated proteins was performed with enzyme-linked immunosorbent assay (ELISA). Protein-protein interactions were depicted with the STRING database. RESULTS: A total of 84 proteins were found in the human vitreous samples of 15 patients with BRVO and 15 controls. In all, 14 proteins were significant when comparing the signal intensities of BRVO and control samples. Six significant dysregulated proteins with p < 0.001 were further verified with ELISA. Clusterin, complement factor C3, prostaglandin-H2 D­isomerase and vitronectin were significantly upregulated in the BRVO group and opticin was downregulated. The protein interactions analysis showed associations with inflammatory cascades, matrix changes, mechanisms of cell survival und death. CONCLUSIONS: The results of the study reveal that the proteomic composition of vitreous humor differed significantly between the patients with BRVO and the controls. Whether the identified proteins may serve as potential biomarkers for pathophysiology, diagnostics or therapy should be examine in further studies.

[Ophthalmic diaphanoscopy]. / Diaphanoskopie am Auge.

Diaphanoscopy is an almost 150-year-old diagnostic procedure based on the transillumination of the wall of the eyeball. One of the most important fields of application is the detection of tumors, which can be distinguished from the rest of the tissue by their reduced light transmission. Other fields of application include the diagnosis of retinal tears and holes, the detection of foreign bodies in the vitreous body and the control of coagulative measures in the ciliary body. In comparison to other techniques, diaphanoscopy requires only little effort and is very gentle on patients.

[Fiberless miniature chandelier LED endoilluminator for pars plana vitrectomy]. / Faserloser Miniatur-Chandelier-LED-Endoilluminator für die Pars-plana-Vitrektomie.

BACKGROUND: Currently available chandelier endoilluminators for pars plana vitrectomy consist of conventional optical fibers coupled to a light source. The light probes of these fibers now provide wide emittance angles but it is still often not possible to illuminate the whole intraocular space via just one incision. Therefore, several light probes or additional handheld endoilluminators have to be used simultaneously or the lights have to be repositioned during surgery. OBJECTIVE: The presented prototype of a fiberless chandelier light-emitting diode (LED) endoilluminator aims at illuminating the whole intraocular space with just one incision while reducing the risk of harming the retina. MATERIAL AND METHODS: The light source is a white LED with a conical tip that allows stable fixation within an incision. The physical properties of these LEDs were determined and used for calculating the relevant irradiance to assess the risk of causing harm to the eye. The illumination of the intraocular space was investigated using porcine eyes. RESULTS: The illumination of porcine eyes with the modified LEDs was bright and homogeneous. Measurements and subsequent calculations proved that the expected thermal load and photochemical hazard were very low for human eyes. CONCLUSION: The hitherto existing experimental results on porcine eyes and the theoretical considerations on human eyes were found to be positive; therefore, it is expected that this new fiberless chandelier LED endoilluminator will prove to be advantageous for human patients. It promises a reduced number of incisions with a simplified handling and need to add handheld light sources only if minimal intensity oblique illumination is helpful together with the chandelier illumination. This contributes to a significant reduction of phototoxicity risks and additionally there is a chance for a cost reduction because expensive xenon or mercury lamps are no longer necessary. These expectations have to be verified by further studies on human eyes.

Managing outbreaks of invasive species--a new method to prioritize preemptive quarantine efforts across large geographic regions.

In pest risk assessment it is frequently necessary to make time-critical decisions regarding management of expanding pest populations. When an invasive pest outbreak is expanding rapidly, preemptive quarantine of areas that are under imminent threat of infestation is one of only a few available management tools that can be implemented quickly to help control the expansion. The preemptive quarantine of locations that surround an infested area also acts as a safeguard to counteract the risk of failed detections of the pest in field surveys. In this paper, we present a method that assesses the suitability of preemptive quarantine measures at the level of small geographical subdivisions (U.S. counties). The cost of a preemptive quarantine in a given county is weighed against the protective benefit of delaying the spread of an outbreak to other neighboring counties. We demonstrate the approach with a decision support model that estimates the suitability of preemptive quarantine across multiple counties that surround areas infested with the emerald ash borer (Agrilus planipennis Fairmaire (EAB), Coleoptera: Buprestidae), an emerging major threat to ash tree species (Fraxinus spp.) in North America. The model identifies the U.S. counties where the installation of preemptive quarantine would most effectively slow the spread of EAB populations and reduce risk to high-value areas.

[Cytokine determination from vitreous samples in retinal vascular diseases]. / Zytokinbestimmung aus Glaskörperproben bei retinalen Gefäßerkrankungen.

PURPOSE: The aim of this study was to determine cytokine levels from vitreous samples of treatment-naive patients with diabetic retinopathy (DRP), retinal vein occlusion (RVO) and exudative age-related macular degeneration (ARMD). METHODS: In this study 187 patients (median age 67 years, 101 males) were treated with a combined drug therapy including a 23-gauge core vitrectomy. Interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1) and intravitreal vascular endothelial growth factor (VEGF-A) levels were determined a using cytometric bead assay (CBA) and compared to those of the control group. RESULTS: Compared to the control group all diseases had significantly elevated cytokine levels, except VEGF in ARMD. In DRP samples of patients with diffuse diabetic macula edema (DME) higher VEGF-A and MCP-1 levels were found than in patients with focal DME. Ischemic DRP had higher VEGF levels than non-ischemic DRP. All measured cytokines were significantly higher in central retinal vein occlusion (CRVO) than in branch retinal vein occlusion (BRVO). CONCLUSIONS: Differences in intravitreal cytokine levels in DRP, RVO and ARMD could be demonstrated. The knowledge of depicted specific characteristic dysregulation of cytokines could allow more targeted future therapies.

Subthreshold diode laser micropulse photocoagulation versus intravitreal injections of bevacizumab in the treatment of central serous chorioretinopathy.

PURPOSE: To evaluate the treatment of central serous chorioretinopathy (CSC) with either subthreshold diode laser MicroPulse (SDM) or intravitreal bevacizumab (BCZ). METHODS: This comparative, controlled, prospective study conducted over a period of 10 months examined 52 eyes of 52 patients with (a) treatment with SDM at the active leakage site guided by fluorescein angiography (FA) (n=16 eyes), (b) intravitreal injection of 1.25 mg BCZ (n=10 eyes), or (c) observation (n=26 eyes). Outcome measures included changes in retinal pigment epithelium (RPE) leakage at FA, central macular thickness (CMT), best-corrected visual acuity (BCVA), and 10° macular perimetry. RESULTS: At the end of the study, there was 12.5% persistent leakage in the SDM, compared with 60% in the BCZ and 92% in the control group. Mean CMT decreased by 94 µm in the SDM, 38 µm in the BCZ, and did not change in the control group. Mean BCVA improved more than 6 early treatment of diabetic retinopathy study letters in the SDM, decreased by one letter in the BCZ, and by two letters in the control group. In the SDM group, mean perimetric deficit improved by 1.5 decibels and corrected lost variance by 2.6. In the BCZ, it improved by 0.6, and in the control group by 0.5. Retreatment was required in 7/16 eyes of the SDM group (43.75%), and in 5/10 eyes of the BCZ group (50%). CONCLUSION: SDM photocoagulation was superior to intravitreal injections of 1.25 mg BCZ in the treatment of CSC, which resulted in enhanced visual acuity and macular perimetry.

Inflammatory and angiogenic protein detection in the human vitreous: cytometric bead assay.

Introduction. To evaluate clinical feasibility and reproducibility of cytometric bead assay (CBA) in nondiluted vitreous samples of patients with age-related macular degeneration (ARMD), diabetic macular edema (DME), and central retinal vein occlusion (CRVO). Methods. Twelve patients from a single clinics day qualified for intravitreal injections (ARMD n = 6, DME n = 3, CRVO n = 3) and underwent a combination treatment including a single-site 23 gauge core vitrectomy which yielded a volume of 0.6 mL undiluted vitreous per patient. Interleukin-6 (IL-6), vascular endothelial growth factor isoform A (VEGF-A), and monocyte chemo-attractant protein-1 (MCP-1) were assessed directly from 0.3 mL at the same day (fresh samples). To assess the reproducibility 0.3 ml were frozen for 60 days at -80°, on which the CBA was repeated (frozen samples). Results. In the fresh samples IL-6 was highest in CRVO (median IL-6 55.8 pg/mL) > DME (50.6) > ARMD (3.1). Highest VEGF was measured in CRVO (447.4) > DME (3.9) > ARMD (2.0). MCP-1 was highest in CRVO (595.7) > AMD (530.8) > DME (178). The CBA reproducibility after frozen storage was examined to be most accurate for MCP1 (P = 0.91) > VEGF (P = 0.68) > IL-6 (P = 0.49). Conclusions. CBA is an innovative, fast determining, and reliable technology to analyze proteins in fluids, like the undiluted vitreous, which is important to better understand ocular pathophysiology and pharmacology. There is no influence of intermittent storage at -80° for the reproducibility of the CBA.

Combined intravitreal pharmacosurgery in patients with occult choroidal neovascularization secondary to wet age-related macular degeneration.

AIM: The aim was to investigate the efficacy and safety of combined intravitreal therapy in patients with occult choroidal neovascularization (CNV) secondary to wet age-related macular degeneration (AMD) over 6 months. METHODS: In this prospective pilot study of a case series, 106 patients (mean age 75.4 years) with predominantly occult CNVs were treated with a 1.5-ml core pars plana vitrectomy with intravitreal injections of triamcinolone (8 mg), bevacizumab (1.25 mg) and balanced salt solution. The best-corrected visual acuity (BCVA; logMar), central macular thickness (optical coherence tomography), and intraocular pressure (IOP; Goldmann tonometry) were assessed at baseline and follow-up visits. RESULTS: Statistically significant increases in BCVA (vs. baseline) were observed at 2 months (mean +0.9; standard deviation +/-0.6 lines), 4 months (+1.3; +/-0.7), and 6 months (+1.2; +/-0.7) after the initial combined intravitreal therapy in 96/106 patients. At 6 months, BCVA had deteriorated in 20 of 96 (20.8%) patients by <2.5 lines, remained stable in 38 of 96 (39.6%) and improved in 31 (32.3%) patients by 1-3 lines, and in 7 (7.3%) patients by >3 lines. The mean central retinal thickness decreased by -41.2% (-195; +/-46 microm) over 6 months. 55% demanded intravitreal anti-vascular endothelial growth factor (VEGF) treatment after initial therapy. Increases in IOP were managed by eye drops in 11 (10%) patients with no other adverse event occurring. CONCLUSION: After the combined intravitreal therapy, including two drugs and a limited core vitrectomy, a significant and sustained improvement in vision of patients with occult CNVs was observed over 6 months. In 45% of the initially treated patients, anti-VEGF therapy did not have to be continued, which might be attributed to both the pharmacological effects of the drugs and the physiological changes induced by the vitrectomy (posterior vitreous detachment, liquefaction, and oxygen redistribution).

Spatio-temporal analysis of Xyleborus glabratus (Coleoptera: Curculionidae [corrected] Scolytinae) invasion in eastern U.S. forests.

The non-native redbay ambrosia beetle, Xyleborus glabratus Eichhoff (Coleoptera: Curculionidae: Scolytinae), has recently emerged as a significant pest of southeastern U.S. coastal forests. Specifically, a fungal symbiont (Raffaelea sp.) of X. glabratus has caused mortality of redbay (Persea borbonia) and sassafras (Sassafras albidum) trees in the region; several other Lauraceae species also seem susceptible. Although the range of X. glabratus continues to expand rapidly, little is known about the species' biology and behavior. In turn, there has been no broad-scale assessment of the threat it poses to eastern U.S. forests. To provide a basic information framework, we performed analyses exploiting relevant spatio-temporal data available for X. glabratus. First, we mapped the densities of redbay and sassafras from forest inventory data. Second, we used climate matching to delineate potential geographic limits for X. glabratus. Third, we used county infestation data to estimate the rate of spread and modeled spread through time, incorporating host density as a weighting factor. Our results suggest that (1) key areas with high concentrations of redbay have yet to be invaded, but some are immediately threatened; (2) climatic conditions may serve to constrain X. glabratus to the southeastern U.S. coastal region; and (3) if unchecked, X. glabratus may spread throughout the range of redbay in <40 yr. Disruption of anthropogenic, long-distance dispersal could reduce the likelihood of this outcome.

Intravitreous injection of tissue plasminogen activator and gas in the treatment of submacular hemorrhage under various conditions.

OBJECTIVE: To investigate the efficacy and safety of treating submacular hemorrhages secondary to age-related macular degeneration (ARMD) with intravitreous recombinant tissue plasminogen activator (rt-PA) and gas under various conditions. DESIGN: Prospective, noncomparative case series. PARTICIPANTS: Forty-three consecutive eyes of 42 patients with recent (range, 2-28 days) subfoveal hemorrhage secondary to ARMD were included in this study. The size of subretinal hemorrhage ranged from 0.25 to 30 disc areas. METHODS: All patients were treated with intravitreous injections of rt-PA (50 microg) and sulfur hexafluoride (0.5 ml). Postoperative prone positioning was maintained for 24 to 72 hours. Patient follow-up ranged from 4 to 18 months (mean, 6 months). MAIN OUTCOME MEASURES: Best and final postoperative visual acuity in relation to size and onset of hemorrhage, displacement of subretinal blood, and surgical complications. RESULTS: Best postoperative visual acuity compared with preoperative visual acuity was improved two or more Snellen lines in 19 eyes (44%) and stable in 24 eyes (56%). Final visual acuity was improved two or more lines in 13 eyes (30%), stable in 26 (61%), and two or more lines worse in 4 eyes (9%). Duration of hemorrhage

Vitreous concentrations of TPA and plasminogen activator inhibitor are associated with VEGF in proliferative diabetic vitreoretinopathy.

PURPOSE: In angiogenesis, matrix degradation is an important step in endothelial cell migration and proliferation. There is evidence that serine proteases, such as tissue plasminogen activator (TPA), urokinase-type plasminogen activator (UPA), and plasminogen activator inhibitor (PAI), are involved in this process. We hypothesized that in eyes in which neovascularization is active, such as in proliferative diabetic vitreoretinopathy (PDVR), vitreous levels of these proteases are increased. Furthermore, correlation was sought between intraocular concentrations of serine proteases and vascular endothelial growth factor (VEGF), a multifunctional cytokine that has been shown to play a major part in mediating active neovascularization in patients with ischemic retinal diseases. METHODS: Undiluted samples of vitreous fluid were obtained from patients who underwent vitreoretinal surgery for PDVR or retinal detachment. Vitreous levels of VEGF, TPA, UPA, and PAI were determined by enzyme-linked immunosorbent assay. RESULTS: We found a statistically significant correlation between levels of VEGF and TPA (P<0.01) and VEGF and PAI (P<0.026) in the vitreous fluid of patients with PDVR. Concentrations of VEGF (P<0.03), TPA (P<0.042), and PAI (P<0.0098) in diabetic eyes were significantly higher than in nondiabetic eyes. Of 14 eyes with PDVR, 6 contained detectable levels of UPA. CONCLUSIONS: A correlation between increased levels of VEGF and TPA or PAI in the vitreous fluid of eyes with PDVR reflects the possible role of plasminogen activators in the progression of this disease. An understanding of the endogenous inhibition of matrix degradation in ocular angiogenesis may be useful in the development of new treatment strategies.

Visual outcome after treatment with low-dose recombinant tissue plasminogen activator or hemodilution in ischemic central retinal vein occlusion.

The ischemic type of central retinal vein occlusion (CRVO) is associated with a poor visual and ocular prognosis. Although several reports have indicated that hemodilution or thrombolytic therapy may be of benefit, there is still no consensus among ophthalmologists about the management of this disorder. In our study, we retrospectively evaluated the visual outcome after medical treatment in 58 patients with ischemic CRVO and severe visual loss (< or = 20/50). We separately investigated three different groups, depending on the following criteria: onset of symptoms within 11 days prior to admission and thrombolytic treatment with 50 mg of recombinant tissue plasminogen activator (rtPA) and intravenous heparinization (n = 23) or hemodilution therapy (n = 22) or onset of symptoms >11 days before the initial visit and hemodilution (n = 13). An advancement of 2 or more lines on the logarithmic visual acuity chart was noted in 10 cases (44%) in the rtPA group and in 3 subjects (14%) in the early-phase hemodilution group, whereas only 1 patient in the late-phase hemodilution group showed a comparable improvement. Our findings suggest that treatment with low-dose rtPA or hemodilution aimed at early restoration of blood flow has the potential to improve the visual prognosis in ischemic CRVO. The finding that thrombolysis had a favorable outcome supports the hypothesis that specific subgroups of patients may benefit from this therapeutic approach. Further investigation will be required to definitively prove the effectiveness of fibrinolytic agents.

Complications after implantation of intraocular devices in patients with cytomegalovirus retinitis.

PURPOSE: The authors report their surgical experience after sustained-release ganciclovir treatment, as well as replacing empty ganciclovir implants in patients with acquired immune deficiency syndrome (AIDS) and cytomegalovirus (CMV) retinitis. METHODS: Between November 1995 and August 1998, 79 eyes of 49 patients received 99 intravitreal ganciclovir implants. Patients were examined monthly after implant surgery. Follow-up periods ranged from 6 to 128 weeks. RESULTS: At the first 3-week postoperative visit, 73 eyes (97.2%) of 46 patients exhibited stable conditions. In 6 eyes (3.8%) of 3 patients, further progression was noted due to resistance to ganciclovir. The most common early complication (within 6 weeks after implantation) was cystoid macular edema, observed in 7 eyes receiving implants. Retinal detachment was the most common late complication (over 6 weeks after implantation) in 11 eyes. In almost all eyes with CMV retinitis and retinal detachment, involvement of more than 25% of the retina was observed. Additional severe complications included extrusion of the first pellet in 2 eyes and cataract as a late complication in 5 eyes. A total of 28 eyes (35.4%) of 16 patients receiving a second implant did not experience significant three-line loss by the end of the follow-up period. CONCLUSION: In the treatment of CMV retinitis, sustained-release ganciclovir implantation seems to be an alternative to intravenous ganciclovir. Early implantation and additional replacement of the device has the potential to decrease the risk of developing retinal detachment. We would recommend additional systemic antiviral CMV therapy to avoid infection of the fellow eye and CMV disease.

[Intravitreal endoscopic visualization of intraocular ganciclovir devices: improved long-term treatment of CMV retinitis]. / Endoskopische Kontrolle von Pars plana implantierten Ganciclovir-Medikamententrägern zur Verbesserung der Langzeitprognose bei der Behandlung der Cytomegalievirusretinitis.

BACKGROUND: The recent development of 20- and 19-gauge diameter endoscopes allows an excellent direct intravitreal visualization of intraocular morphology. A gradient index (GRIN) endoscope (Insight Instruments, Lake Mary, FL, USA), which combines a small diameter (0.89 mm, 20 gauge) and an exceptional optical resolution, can be used as a diagnostic tool for the assessment of the safety and vitreous interaction of sustained release intraocular devices which have been designed to deliver ganciclovir (Vitrasert) over a period of 8-12 months and were successively implanted in several eyes. PATIENTS AND METHODS: 78 eyes of 49 patients received 100 ganciclovir implants between November 1995 and July 1998. In six patients who received additional implants, the GRIN endoscope was used as an optical control of wound healing processes and Vitrasert positioning after implantation of prior devices (two-point suturing technique). RESULTS: In all of these six eyes, a clinical stabilization of the cytomegalovirus retinitis was noted. Endoscopic observation of the scleral 5-mm incision revealed no gaps after two-point suturing of the device. Only one of six eyes showed significant vitreous tractions around the Vitrasert. However, the struts of all pellets were completely covered by a fibrous membrane. Occasional fibrous plaques were noted on the surface of devices which presumably had been damaged by surgical manipulations. In one case, the endoscopic examination disclosed the suprachoroidal implantation of a device. In this eye, no signs of retinal toxicity or recurrence of CMV retinitis were observed. CONCLUSIONS: High resolution endoscopy of the vitreous cavity appears to be an effective method for the control of intraocular drug delivery devices. Basically, the repeated implantation of intraocular ganciclovir implants can be considered a safe method in the management of relapsing CMV retinitis. However, the endoscopic observation of fibrous membranes covering the struts suggest that the explanation of an intraocular device has the potential for various intraoperative complications (e.g. hemorrhages, traction, tears, retinal detachment). Therefore, we would recommend the additional implantation of further implants rather than a replacement.

Subretinal microsurgery with gradient index endoscopes.

State-of-the-art subretinal surgery involves a standard three-port pars plana entry, followed by an iatrogenic retinotomy to access the subretinal space. Subretinal manipulations through a small retinotomy are made possible by specially designed instruments. As the surgeon looks through the vitreous cavity, all subretinal maneuvers are obscured by the overlying retina. Consequently, the surgeon is operating 'blindly' and has to rely on 'feeling' rather than direct visualization. Micro-endoscopic viewing systems are the ideal solution for visualization during subretinal surgery. Until now, such endoscopes were either too large for intraocular use or lacked sufficient resolution, especially at a short working distance. Recently, a gradient index (GRIN) endoscope was developed (Insight Instruments, Inc., Lake Mary, Fla., USA) combining a small diameter (0.89 mm, 20 gauge) and incorporating excellent optical resolution, even at extremely close working distances. After ballooning a limited part of the retina without creating a retinal hole, the 20-gauge GRIN endoscope can be introduced into the subretinal space through the sclera and choroid, posterior to the pars plana. Surgical instruments can then be introduced into the subretinal space through a second neighboring sclerotomy. Thus, subretinal surgery can be performed under direct endoscopic control. As a result of direct visualization, the surgeon may perform certain surgical procedures with greater accuracy, i.e., subretinal neovascular membranes may be dissected meticulously from the neurosensory retina and retinal pigment epithelium, minimizing damage to both structures. The feeding choroidal vessel can be identified and directly coagulated, which is usually very difficult during conventional subretinal surgery. Endoscopic subretinal surgery is thus a significant improvement over conventional methods, avoiding the need for a retinotomy and increasing the safety and facility of the surgery itself.

The influence of intraocular pressure and systemic oxygen tension on the intravascular pO2 of the pig retina as measured with phosphorescence imaging.

The intravascular oxygen tension (pO2) of the pig retina was determined by measuring the phosphorescence lifetime of an intravenously injected dye. Pseudocolor images of the intravascular retinal pO2 were obtained. The method is noninvasive except for the application of the dye. The measurement system was adapted to a fundus camera. The systemic arterial oxygen pressure (PaO2) as well as the intraocular pressure (IOP) were altered. In the measurements the pO2 of the choriocapillaris was close to the systemic PaO2. Under normoxia, the retinal veins showed a lower pO2 of about 40 mm Hg. We found evidence of an autoregulation of the retinochoroidal pO2. The retina and the optic nerve head showed an autoregulation of the intravascular pO2 at low IOP, but were more sensitive to a moderate elevation of the IOP of about 40 mm Hg, as compared to the choroidal pO2. The pO2 of the choriocapillaris seemed to change little until the considerably high IOP value of about 50 mm Hg was attained. This behavior is due to either the high perfusion reserve capacity of the choroid or to autoregulation. Although our experiments refer to the perfusion of the pig eye, the results provide indirect evidence that even during a glaucoma attack the human choroid might be able to maintain a reasonable oxygen supply to the retina, whereas the intravascular pO2 of the retinal vessels and of the optic nerve head decrease strongly. The adaptation to a fundus camera facilitates a future clinical application if a nontoxic dye can be developed.