Evaluation of a Force-Sensing Handheld Robot for Assisted Retinal Vein Cannulation.

Approximately 16.4 million people are affected by retinal vein occlusion (RVO) resulting from hypercoagulability, low blood flow or thrombosis in the central or the branched retinal veins. Most common current treatments for RVO aim to limit the damage. In recent years, an experimental procedure, retinal vein cannulation (RVC) has been studied in animal models as well as human eye models. RVC is a procedure for targeted delivery of a therapeutic agent into the occluded retinal vein for dissolving the thrombi. Although effective treatment has been demonstrated via RVC, performing this procedure manually still remains at the limits of human skills. RVC requires to precisely insert a thin cannula into a delicate thin retinal vein, and to maintain it inside the vein throughout the infusion. The needle-vein interaction forces are too small to sense even by an expert surgeon. In this work, we present an evaluation study of a handheld robotic assistant with a force-sensing microneedle for RVC. The system actively cancels hand tremor, detects venous puncture based on detected tool-tissue forces, and stabilizes the needle after venous puncture for reduced trauma and prolonged infusion. Experiments are performed cannulating the vasculature in fertilized chicken eggs. Results show 100% success in venous puncture detection and significantly reduced cannula position drift via the stabilization aid of the robotic system.

In-Human Robot-Assisted Retinal Vein Cannulation, A World First.

Retinal Vein Occlusion (RVO) is a blinding disease caused by one or more occluded retinal veins. Current treatment methods only focus on symptom mitigation rather than targeting a solution for the root cause of the disorder. Retinal vein cannulation is an experimental eye surgical procedure which could potentially cure RVO. Its goal is to dissolve the occlusion by injecting an anticoagulant directly into the blocked vein. Given the scale and the fragility of retinal veins on one end and surgeons' limited positioning precision on the other, performing this procedure manually is considered to be too risky. The authors have been developing robotic devices and instruments to assist surgeons in performing this therapy in a safe and successful manner. This work reports on the clinical translation of the technology, resulting in the world-first in-human robot-assisted retinal vein cannulation. Four RVO patients have been treated with the technology in the context of a phase I clinical trial. The results show that it is technically feasible to safely inject an anticoagulant into a [Formula: see text]-thick retinal vein of an RVO patient for a period of 10 min with the aid of the presented robotic technology and instrumentation.

[Treatment of Retinal Vein Occlusion - Is There Still a Role for Vitreoretinal Surgery?] / Behandlung des retinalen Venenverschlusses ­ Welche Rolle spielt die Vitrektomie heute noch?

Surgical manoeuvres for the treatment of retinal vein occlusion peaked at the turn of the century. The first overwhelming reports could not be confirmed in prospective studies. Furthermore, the functional success was never comparable to intravitreal drug therapy, and the manoeuvres are no longer used in clinical routine. The procedures, the surgical theory and the criticism on vitrectomy, radial optic neurotomy (RON), retinal endovascular fibrinolysis (REVL) and arteriovenous dissection (AVD) will be discussed in this paper. Surgical manoeuvres for the treatment of retinal vein occlusion had a peak by the end of the last and the beginning of the present century. The first overwhelming reports could not be confirmed in prospective studies. Furthermore, the functional success was never comparable to the intravitreal drug therapy and the manoeuvres are no longer used in clinical routine. The procedures, the surgical theory and the criticism on vitrectomy, radial optic neurotomy (RON), retinal endovascular fibrinolysis (REVL), and arteriovenous dissection (AVD) will be discussed in this paper.

Robot-assisted retinal vein cannulation in an in vivo porcine retinal vein occlusion model.

PURPOSE: To evaluate the feasibility of robot-assisted retinal vein cannulation for retinal vein occlusion. METHODS: Prospective experimental study performed in in vivo porcine eyes. A standard three port pars plana vitrectomy was followed by laser-induced branch retinal vein occlusion. Consequently, a retinal vein cannulation with the help of a surgical robot and a microneedle was performed. Complete success was defined as a stable intravenous position of the needle tip confirmed by blood washout for at least 3 min. Secondary outcomes were the occurrence of intra-operative complications and technical failures. RESULTS: Cannulation was successful in 15 of 18 eyes with a complete success rate (duration of infusion of more than 3 min) of 73% after exclusion of two eyes from analysis due to failure in establishing a blood clot. There were no technical failures regarding the robotic device. The intravessel injections of ocriplasmin in two of two eyes led to a clot dissolution. In a subset of five eyes, a second cannulation attempt at the border of the optic disc resulted in a stable intravessel position and infusion during 362 (±138) seconds. CONCLUSION: Robot-assisted retinal vein cannulation with prolonged infusion time is technically feasible. Human experiments are required to analyse the clinical benefit of this new therapy.

TECHNIQUE OF LASER CHORIORETINAL ANASTOMOSIS CREATION IN CENTRAL RETINAL VEIN OCCLUSION AND SUCCESS RATE WITH A NEW PHOTOCOAGULATOR SYSTEM.

PURPOSE: To evaluate the success rate of laser chorioretinal anastomosis (L-CRA) creation with a new laser photocoagulator system capable of 5 watts (W) power in patients with central retinal vein occlusion (CRVO). METHODS: Patients with a treatment-naive CRVO were enrolled as part of an ongoing trial combining L-CRAs with anti-vascular endothelial growth factor treatment. RESULTS: Thirty-three patients were treated with an L-CRA developing in 29 (88%). Mean power was 2.7 W and mean time for development was 1.8 months. Each patient had two potential sites created. Eighteen patients developed 2 L-CRAs and the remaining 11 patients, one each. Of the 66 potential sites, successful L-CRAs developed at 47 sites (71%). Additional Nd:YAG laser applications were used in 39% of sites. Mean follow-up was 23 months and no significant complications were seen. CONCLUSION: An L-CRA as a means of permanently bypassing the obstruction to venous outflow in CRVO may become more relevant as not all patients respond well to intravitreal therapy. The limitation to this technique in the past has been lack of availability of a laser system with the power necessary to create the L-CRA. The success rate with the new system has improved to 88% representing a significant improvement over our original success rate of 33%.

In Vivo Retinal Vein Bypass Surgery in a Porcine Model.

PURPOSE: To evaluate the feasibility of retinal vein bypass surgery for induced branch retinal-vein occlusion (BRVO) in the living porcine eye. METHODS: Fifteen minipigs were used in the study. Seven days before vascular surgery, hyaluronidase and plasmin were intravitreally injected for induction of posterior vitreous detachment. Aspirin and warfarin were oral administered daily starting 5 d prior to vascular surgery for anti-coagulation. The minipigs were anethetized with an intraperitoneal injection of 300 mg/kg chloral hydrate for intravitreal injection procedure and vascular surgery. Temporary keratoprosthesis vitrectomy was performed, and intraoperative video fluorescein angiography (VFA) was possible. The central and posterior vitreous was removed together with the posterior hyaloid membrane to facilitate vascular maneuvers. BRVO was induced by bipolar diathermy on the vein at the main vein's first branching. Polyimide tubes (50.8-µm internal diameter and 7.6-µm wall thickness) were used as artificial vessels. Vascular manipulation was performed in a bimanual manner. Both end of a prepared tubing was inserted into venous lumen by puncturing and catheterization, and the vein bypass bridging the occlusion was created. Then, the patency of the bypass graft was assessed by intraoperative VFA. RESULTS: The retinal vein bypass surgery was surgically accomplished in 33% (5/15) of the eyes, and the immediate graft patency was confirmed by intraoperative VFA only in one eye. We observed and recorded fluorescein flow from the branch vein to the main vein through the bypass graft which bridging the occlusive vein segment. CONCLUSIONS: We demonstrated the feasibility of retinal vein bypass for induced BRVO in the living porcine eye, and the immediate graft patency was successfully evaluated by intraoperative VFA. Despite the potential, there are still some significant hurdles in vivo retinal vein bypass surgery, and modification of both surgical instruments and maneuvers is needed for further study.

Macular hole formation following intravitreal injection of ranibizumab for branch retinal vein occlusion: a case report.

BACKGROUND: Macular hole formation after anti-vascular endothelial growth factor therapy is a rare complication. We report macular hole formation after intravitreal ranibizumab injection for branch retinal vein occlusion. CASE PRESENTATION: A 63-year-old Asian male was treated with intravitreal ranibizumab injection for chronic macular edema with branch retinal vein occlusion in his right eye. Before treatment, best-corrected visual acuity in his right eye was 20/200. Nine days after injection, a full thickness macular hole developed with reduction of macular edema. After pars plana vitrectomy combined with cataract surgery, the macular hole was successfully closed, and the best-corrected visual acuity in his right eye improved to 20/40. CONCLUSION: The possibility of an infrequent complication like macular hole should be considered for intravitreal ranibizumab for macular edema with branch retinal vein occlusion.

Quantitative assessment of manual and robotic microcannulation for eye surgery using new eye model.

BACKGROUND: Microcannulation, a surgical procedure for the eye that requires drug injection into a 60-90 µm retinal vein, is difficult to perform manually. Robotic assistance has been proposed; however, its effectiveness in comparison to manual operation has not been quantified. METHODS: An eye model has been developed to quantify the performance of manual and robotic microcannulation. The eye model, which is implemented with a force sensor and microchannels, also simulates the mechanical constraints of the instrument's movement. Ten subjects performed microcannulation using the model, with and without robotic assistance. RESULTS: The results showed that the robotic assistance was useful for motion stability when the drug was injected, whereas its positioning accuracy offered no advantage. CONCLUSIONS: An eye model was used to quantitatively assess the robotic microcannulation performance in comparison to manual operation. This approach could be valid for a better evaluation of surgical robotic assistance.

Role of hypoxia-inducible factor-1α in preconditioning-induced protection of retinal ganglion cells in glaucoma.

PURPOSE: We recently demonstrated in a mouse model of glaucoma that endogenous epigenetic mechanisms can be activated by a repetitive hypoxic preconditioning (RHP) stimulus to provide robust retinal ganglion cell (RGC) protection. Although we also provided evidence that RHP prevents or delays the apoptotic demise of the RGC soma, the mechanisms responsible for signaling this epigenetic response, as well as the effectors of the glaucoma-tolerant phenotype at the somatic and axonal levels, remain unidentified. In the present study, we used conditional mutant mice lacking hypoxia-inducible factor-1α (HIF-1α) in RGCs (HIF-1α RGC-knockout [KO] mice) to test the hypothesis that RHP-mediated activation of this transcription factor in these cells protects them from glaucomatous injury. METHODS: Adult HIF-1α RGC-KO mice, generated by mating floxed HIF-1α mice with math5-Cre mice, were used. Experimental glaucoma was induced unilaterally in the HIF-1α RGC-KO mice and matched wild-types by elevating the intraocular pressure to 16-20 mmHg for 3 consecutive weeks, secondary to episcleral vein ligation. Mice of each genotype were randomized to either an RHP protocol (six total exposures to systemic hypoxia [11% oxygen], interspersed over a 2-week period, completed 3 days before ligation surgery) or to an untreated group. RGC soma and axon injury was quantified with Neuronal Nuclei (NeuN) immunohistochemistry in retinal flat mounts and SMI32 immunohistochemistry in cross sections of the post-laminar optic nerve, respectively. RESULTS: HIF-1α RGC-KO mice exhibited normal retinal function and morphology, and crosses of math5-Cre mice with floxed ROSA26 reporter mice confirmed Cre recombinase activity was confined to the RGC axons and soma. Untreated wild-type mice exhibited a 30±2% loss of RGC soma and a 31±3% loss of RGC axons after 3 weeks of intraocular hypertension (both p<0.05 versus fellow eye). The 90% and 81% improvement in soma and axon survival, respectively, observed in the wild-type mice treated with RHP (both p<0.05 versus the glaucoma eye in the untreated mice) was still observed to a near identical extent in the RHP-treated HIF-1α RGC-KO mice. RHP had no effect on the magnitude of intraocular pressure elevation in either the KO or wild-type groups, indicating that protection was realized in both genotypes in the face of ongoing intraocular hypertension. CONCLUSIONS: These findings indicate that the robust, glaucomatous protection of the RGC soma and axons induced by RHP does not require HIF-1α-mediated transcription of survival genes and other adaptive responses within the RGCs themselves. Rather, we infer that RGC survival is augmented secondary to the activation of other hypoxia-sensitive transcription factors in RGCs and/or the action of diffusible HIF-1α target gene proteins released from neighboring retinal cells. Ideally, the involvement of such autocrine- and/or paracrine-based mechanisms would be confirmed in future studies, but distinct components of the integrated, pleiotropic, and multicellular basis of this endogenous epigenetic response may prove difficult to demonstrate experimentally, as we found in the present study.

Pars plana vitrectomy with multiple transvenous chorioretinotomies for macular edema due to retinal vein occlusion.

BACKGROUND AND OBJECTIVE: To review results of vitreous surgery for branch and central retinal vein occlusion (BRVO and CRVO). PATIENTS AND METHODS: All cases of vitrectomy with multiple transvenous chorioretinotomies for retinal vein occlusion at a vitreoretinal subspecialty practice were reviewed. RESULTS: Twenty eyes of 20 patients (four with BRVO and 16 with CRVO) were included. Mean time from diagnosis to surgery was 15 months, and mean postoperative follow-up was 22 months. Injections of bevacizumab or ranibizumab decreased postoperatively (P < .0001; Poisson regression model), while log-MAR visual acuity improved (P = .0396; Wilcoxon signed-rank test). Ten eyes required no further injections postoperatively, and three eyes required one postoperative injection. Macular edema expressed as OCT maximum macular thickness was significantly reduced postoperatively at 6 months and 12 months (P = .0077 and .0093, respectively). CONCLUSION: In a pilot study of retinal vein occlusion treatment, multiple transvenous chorioretinotomy surgery significantly improved visual acuity and macular edema and reduced intravitreal drug dependency. Further study is warranted.

Evaluation of the ability of a photocoagulator to rupture the retinal vein and Bruch's membrane for potential vein bypass in retinal vein occlusion.

BACKGROUND AND OBJECTIVE: To evaluate the laser power required to rupture both the retinal vein and Bruch's membrane in a porcine model using a new laser system for treatment of retinal vein occlusion. MATERIALS AND METHODS: The retina was treated in areas with and without an overlying vein. Sections through the laser sites were stained for light and transmission electron microscopy. The percentage of the laser sites with rupture of the retinal vein and Bruch's membrane, the degree of tissue damage, and the diameter of the rupture in Bruch's membrane were determined. RESULTS: The rate of vein rupture was 75% at 3 W, and rupture of Bruch's membrane was achieved at all powers tested. The mean diameter of the rupture in Bruch's membrane increased with laser power. CONCLUSION: The Integre Duo laser system (Ellex Medical Lasers, Adelaide, Australia) is capable of rupturing the retinal vein and Bruch's membrane at lower powers than prior laser systems.

Factors promoting success and influencing complications in laser-induced central vein bypass.

PURPOSE: To evaluate the factors influencing the successful creation of a laser-induced chorioretinal venous anastomosis (L-CRA) and those involved in the development of complications. DESIGN: Interventional cohort study. PARTICIPANTS: Fifty-five patients with a nonischemic central retinal vein occlusion (CRVO) who were randomized to receive an L-CRA from the total of 108 who completed the follow-up period of the Central Vein Bypass Study. METHODS: Patients who were randomized to L-CRA were followed up for an 18-month period. They were stratified in 2 sets of 2 cohorts: those who did or did not demonstrate an L-CRA and those who did or did not demonstrate neovascular complications at the site of the L-CRA. Subgroup analysis was performed to determine what factors influenced the creation of an L-CRA and the development of complications at each individual laser site. MAIN OUTCOME MEASURES: Identification of systemic and local ocular factors associated with increased success rates of L-CRA creation and those involved with an increased risk of neovascular complications. RESULTS: Younger age (P = 0.03), better baseline visual acuity (P = 0.04), and the absence of hypertension (P = 0.001) were systemic features associated with an increased chance of demonstrating a successful L-CRA at each site, whereas sex and duration of the CRVO were not. The position of the L-CRA site did not influence the outcome; however, evidence of rupture of the vein wall at the time of the attempt was associated with a higher chance of success (P = 0.008). Increased risk of neovascularization, which occurred at 12 sites in 10 eyes, was associated with higher central venous pressure before treatment (P = 0.03), prolonged fluorescein transit time (P = 0.0001), and the presence of some capillary nonperfusion (P = 0.01). CONCLUSIONS: Younger age, better baseline visual acuity, and the absence of hypertension were associated with an improved success rate, as was evidence of rupture of the vein wall. High baseline central venous pressure, prolonged fluorescein transit time, and the presence of any retinal ischemia were associated with a higher incidence of neovascular complications. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

An experimental study of retinal endovascular surgery with a microfabricated needle.

PURPOSE: To study the feasibility of performing retinal endovascular surgery with a microfabricated needle-based cannulation system at the level of the retinal microvasculature. METHODS: A total of 40 retinal vein vessels, and 40 porcine eyes were used, and the eyecups were prepared under an operating microscope. Twenty retinal veins each were pierced with a microfabricated needle having an outer diameter of 50 µm and with a micropipette having an outer diameter of 50 µm, respectively, and each vessel that was successfully pierced was injected with a solution. The piercing success rates and injection success rates were calculated, and a histologic examination of the site was performed in each eye. RESULTS: Piercing and injection with the microneedle were successful in all 20 eyes (100%). Histologic examination showed that the retinal vasculature was well preserved in all eyes in which piercing had been performed with the microneedle. Piercing with the micropipette, on the other hand, was successful in only 8 eyes (40%), and injection with the micropipette was successful in only 5 eyes (25%). The tip of the micropipette broke in 12 vessels during piercing and in 3 vessels during injection. CONCLUSIONS; The feasibility of performing microvascular piercing and intravascular injection of retinal veins with a microneedle was demonstrated in porcine eyes. It may be possible to administer solutions into retinal vessels more effectively with a microfabricated needle, and that may contribute to improving retinal endovascular surgery in human eyes.

The Central Retinal Vein Bypass Study: a trial of laser-induced chorioretinal venous anastomosis for central retinal vein occlusion.

PURPOSE: To evaluate the effectiveness of a laser-induced chorioretinal venous anastomosis (L-CRA) as a treatment for nonischemic central retinal vein occlusion (CRVO). DESIGN: Prospective, randomized, controlled, multicenter clinical trial. PARTICIPANTS: A total of 113 consecutive patients with a nonischemic CRVO of >3 months' duration and visual acuity of < or =20/50. METHODS: Patients were randomized to L-CRA (58 patients) or conventional care (55 patients). They underwent standardized retinal photography, fluorescein angiography, and ophthalmic examinations, together with standardized assessments of best-corrected visual acuity, performed by masked visual acuity assessors using Early Treatment Diabetic Retinopathy Study protocols. Analysis was performed by intention-to-treat. MAIN OUTCOME MEASURES: The primary outcome measure was change in visual acuity at 18 months. Secondary outcomes were progression of retinal ischemia and rates of adverse events. RESULTS: A total of 53 control patients and 55 treatment patients completed the study. The 2 groups were comparable for age, age- and gender-adjusted mean visual acuity, and most other parameters. In the treated group of 55 patients, 42 (76.4%) developed an L-CRA. Over the 18-month follow-up period, treated eyes had an 8.3 letter mean improvement from baseline compared with control eyes (P = 0.03). Treated eyes that developed a functional L-CRA achieved an 11.7 letter mean improvement from baseline over the control group after 18 months (P = 0.004). Conversion to the ischemic CRVO category occurred in 20.8% of control eyes and in 9.6% of treated eyes overall (P = 0.33). Of the treated group who developed an L-CRA where the retinal ischemia was due to progression of the CRVO, 4.9% progressed to the ischemic category (P = 0.03). Neovascularization developed at the site of the L-CRA in 10 of 55 treated eyes (18.2%). Vitrectomy surgery was required by 5 of 55 treated eyes (9.1%) because of macular traction or nonresolving vitreous hemorrhage. CONCLUSIONS: Chorioretinal venous anastomosis was created in 76.4% of eyes with nonischemic CRVO in this study. Eyes that developed an anastomosis had a significant improvement (11.7 letters) in final visual acuity after 18 months, compared with eyes in the control group (P = 0.004). Complications were managed successfully with careful follow-up and early intervention.

Venous retinal flow reperfusion mechanisms following radial optic neurotomy with adjunctive intraocular triamcinolone in central retinal vein occlusion.

BACKGROUND: To evaluate retinal reperfusion, anastomosis, and compensation following radial optic neurotomy for ischemic nonperfused central retinal vein occlusion. METHODS: Prospective, non-comparative, interventional case series of 13 patients with ischemic, nonperfused central retinal vein occlusion who underwent decompression surgery with a radial optic neurotomy and adjunctive intraocular triamcinolone. Patients were followed for 1 year after surgery, and were analyzed in the preoperative and postoperative stages determining: visual acuity by ETDRS chart (LogMar) and retinal thickness with optical coherence tomography. Fluorescein angiography was performed at regular intervals to evaluate the capillary perfusion grade. Intraocular pressure was measured and fundus was examined. RESULTS: Visual acuity and retinal thickness improved in 10/13 (77%) patients after surgery at 1-year follow-up. Adequate retinal reperfusion was achieved in ten of the 13 eyes. Acute reperfusion occurred in six eyes within 2 weeks of surgery and a shunt vessel at the optic disk developed in four eyes within 4 months. In the remaining three eyes, retinal reperfusion was not observed by fluorescein angiography. No complications were noted in any of the patients. CONCLUSION: Surgical decompression promoted mechanical reperfusion of the occluded vessel in 10/13 (77%) cases. In 6/13 patients (46%) reperfusion occurred within 2 weeks of surgery, and in 4/13 patients (31%) collateral vessels formed within 4 months.

Comparison of surgical treatments for central retinal vein occlusion; RON vs. cannulation of tissue plasminogen activator into the retinal vein.

PURPOSE: To compare the surgical outcomes and evaluate the effectiveness of two treatments for central retinal vein occlusion: radial optic neurotomy (RON) and cannulation of tissue plasminogen activator (tPA) into the retinal vein (tPA). METHODS: This study consisted of 22 eyes. The inclusion criterion was a best-corrected visual acuity of < or =20/60 due to central retinal vein occlusion. The exclusion criteria were previous treatment and the presence of ocular neovascularization. Patients were randomized into RON or tPA groups (n = 11 each). Best-corrected visual acuity, macular thickness, and complications were recorded. RESULTS: The mean best-corrected visual acuity changed from 16/200 at baseline to 20/167 at 12 months in RON (P = 0.217) and from 10/200 to 20/200 in tPA (P = 0.051). The preoperative macular thicknesses decreased from 1,059 microm to 406 microm 12 months postoperatively in RON (P < 0.001) and from 1,121 microm to 271 microm (P < 0.001) in tPA. Neovascular glaucoma developed in 2 eyes (18%) in RON and in 4 eyes (40%) in tPA. Visual field defects associated with surgery were seen in 2 eyes (18%) in RON. CONCLUSION: There was no significant difference in surgical outcomes between the two procedures. Although best-corrected visual acuity and macular edema improved, the incidence of neovascular glaucoma was high. It is, therefore, still uncertain whether these treatments are effective.

Anatomy of the superior ophthalmic vein approach for direct endovascular access to vascular lesions of the orbit and cavernous sinus.

OBJECTIVE: The superior ophthalmic vein (SOV) provides an alternative venous access for the treatment of carotid-cavernous fistulae. Its direct surgical exposure and cannulation can be difficult. This study was performed to identify anatomic landmarks to facilitate localization and exposure of the SOV. METHODS: The vascular tree of 6 formalin-fixed human cadaveric heads was injected with colored silicone. The SOV was exposed using a periorbital incision. The diameter of the SOV, its distance to the inferior border of the incision, and the angle formed by the SOV and sagittal midpupillary line were measured. The tributaries of the SOV and its orbital anatomy and relationship to the supraorbital notch/foramen were evaluated. RESULTS: The SOV was located in the superomedial quadrant of the orbit. Its mean diameter was 2.2 mm (standard deviation, +/-1.2 mm). The mean distance from the SOV to the superior sulcus of the eyelid nasally was 5.9 mm (standard deviation, +/-2.0 mm). The mean angle formed by the SOV and the sagittal midpupillary line was 27.9 degrees (standard deviation, +/-5.4 degrees). The tributaries of the SOV were the angular vein and supraorbital vein (SPOV). The SPOV, identified in all 12 dissections, could be followed to the SOV within the orbit. The SPOV was always located inside the supraorbital notch/foramen when the latter was present. CONCLUSION: The SOV is located at the superomedial quadrant of the orbit. The SPOV is a reliable reference during surgical exposure. A lid crease or subbrow incision centered over the supraorbital notch simplifies identification of the SOV.

In vitro noncontact intravascular femtosecond laser surgery in models of branch retinal vein occlusion.

PURPOSE: To investigate intravenous femtosecond laser surgery in models of branch retinal vein occlusion. MATERIALS AND METHODS: Non-amplified near infrared femtosecond laser was used to ablate polyamide sutures and human hairs inserted into the vascular lumina of porcine retinal veins in vitro. Specimens were subjected to multiphoton laser scanning microscopy and electron microscopy. RESULTS: Regular laser cuts within sutures and hairs were detected with laser microscopy and electron microscopy. Neither laser microscopy nor histology revealed collateral damage of the vascular wall. CONCLUSIONS: Non-amplified femtosecond lasers may allow precise atraumatic non-contact intravenous retinal surgery controlled by high-resolution imaging of the target.