Force and Velocity Based Puncture Detection in Robot Assisted Retinal Vein Cannulation: in-vivo Study

OBJECTIVE

Retinal vein cannulation is a technically demanding surgical procedure and its feasibility may rely on using advanced surgical robots equipped with force-sensing microneedles. Reliable detection of the moment of venous puncture is important, to either alert or prevent the clinician from double puncturing the vessel and damaging the retinal surface beneath. This paper reports the first in-vivo retinal vein cannulation trial on rabbit eyes, using sensorized metal needles, and investigates puncture detection.

METHODS

We utilized total of four indices including two previously demonstrated ones and two new indices, based on the velocity and force of the needle tip and the correlation between the needle-tissue and tool-sclera interaction forces. We also studied the effect of detection timespan on the performance of detecting actual punctures.

RESULTS

The new indices, when used in conjunction with the previous algorithm, improved the detection rate form 75% to 92%, but slightly increased the number of false detections from 37 to 43. Increasing the detection window improved the detection performance, at the cost of adding to the delay.

CONCLUSION

The current algorithm can supplement the surgeons visual feedback and surgical judgment. To achieve automatic puncture detection, more measurements and further analysis are required. Subsequent in-vivo studies in other animals, such as pigs with their more human like eye anatomy, are required, before clinical trials.

SIGNIFICANCE

The study provides promising results and the criteria developed may serve as guidelines for further investigation into puncture detection in in-vivo retinal vein cannulation.

Chorioretinal Anastomosis for Central Retinal Vein Occlusion: A Review of Its Development, Technique, Complications, and Role in Management

Treatments for central retinal vein occlusion (CRVO) have improved dramatically with the advent of intravitreal agents aimed at blocking the effects of the dominant hypoxia-induced upreglulated cytokine, which is vascular endothelial growth factor (VEGF). This cytokine breaks down the capillary endothelial barriers and is a major component of the macular edema in this condition. These treatments although impressive only address some of the sequelae of CRVO and have no effect on the underlying cause which is an obstruction to venous outflow leading to retinal blood flow stagnation and an elevation of the retinal central venous pressure (CVP). The creation of a laser-induced chorioretinal anastomosis (L-CRA) between the obstructed high pressure retinal venous circulation and the unobstructed low pressure choroidal venous circulation is a means addressing the causal pathology. The L-CRA will help lower the elevated CVP, which has been up until now an unaddressed component of the macular edema in this condition.This article reviews the preclinical and clinical development of the L-CRA and the results of the studies into its effect on the natural history of CRVO. It now can be used in combination with existing anti-VEGF treatments with the intravitreal agents addressing the component of the CRVO-induced macular edema due to the cytokine dysregulation, and the L-CRA addressing the component due to the elevated CVP and retinal venous stagnation. Improvements in laser technology have led to higher success rates in L-CRA creation and potential complications are now minimized and better controlled. The combination of L-CRA with intravitreal anti-VEGF agents offers the potential of a permanent cure with a significant reduction in the burden of therapy and improved visual outcomes in this condition.

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.

Comparative Study of Vitrectomy with and without Vein Decompression for Branch Retinal Vein Occlusion: A Pilot Study

Purpose

To report the clinical outcomes in patients undergoing pars plana vitrectomy with and without vein decompression for treatment of branch retinal vein occlusion (BRVO).

METHODS

Thirty-five eyes with macular edema and visual acuity worse than 20/100 secondary to BRVO were prospectively evaluated. Vitrectomy with posterior hyaloid removal and vein decompression at the arteriovenous crossing was performed on 15 eyes (Group 1); consecutively, the same technique without vein decompression was performed on 20 eyes (Group 2). Primary outcome was visual acuity and secondary outcomes were resolution of macular edema and development of neovascularization.

Results

No differences were found between groups in either patient age (p=0.566) or preoperative visual acuity (p=0.505). No differences were found in visual acuity at 3 (p=0.651), 6 (p =0.697), 9 (p =0.763), 12 (p=0.881), or 18 (p=0.748) months. Mean time for macular edema resolution and visual acuity improvement was 9 months in both groups, with a mean improvement of 3.5 ± 2.35 lines in Group 1 and 3.2 ± 2.97 lines in Group 2. No eyes in either group developed new vessels.

CONCLUSIONS

Results suggest that vitrectomy with posterior hyaloid removal without vein decompression can resolve macular edema, improve vision, and prevent development of new vessels in BRVO.

Ocular Hypertension/Glaucoma in Minipigs: Episcleral Veins Cauterization and Microbead Occlusion Methods

Two methods to induce elevation of the intraocular pressure (experimental glaucoma) are described in the present chapter. The first method is based on increasing the post-trabecular resistance to aqueous outflow by cauterizing the episcleral veins (EVC). This method allows the observation of ultrastructural changes in the trabecular meshwork (TM) without interfering with any structure within the eye such as TM, ciliary body, and/or the Retina. The second method is the multiple injection of microbeads into the anterior chamber, as a pre and intra-trabecular method that induce secondary effects on the TM cells. Both methods lead to an increase in IOP.

Towards Robot-Assisted Retinal Vein Cannulation: A Motorized Force-Sensing Microneedle Integrated with a Handheld Micromanipulator †

Retinal vein cannulation is a technically demanding surgical procedure where therapeutic agents are injected into the retinal veins to treat occlusions. The clinical feasibility of this approach has been largely limited by the technical challenges associated with performing the procedure. Among the challenges to successful vein cannulation are identifying the moment of venous puncture, achieving cannulation of the micro-vessel, and maintaining cannulation throughout drug delivery. Recent advances in medical robotics and sensing of tool-tissue interaction forces have the potential to address each of these challenges as well as to prevent tissue trauma, minimize complications, diminish surgeon effort, and ultimately promote successful retinal vein cannulation. In this paper, we develop an assistive system combining a handheld micromanipulator, called "Micron", with a force-sensing microneedle. Using this system, we examine two distinct methods of precisely detecting the instant of venous puncture. This is based on measured tool-tissue interaction forces and also the tracked position of the needle tip. In addition to the existing tremor canceling function of Micron, a new control method is implemented to actively compensate unintended movements of the operator, and to keep the cannulation device securely inside the vein following cannulation. To demonstrate the capabilities and performance of our uniquely upgraded system, we present a multi-user artificial phantom study with subjects from three different surgical skill levels. Results show that our puncture detection algorithm, when combined with the active positive holding feature enables sustained cannulation which is most evident in smaller veins. Notable is that the active holding function significantly attenuates tool motion in the vein, thereby reduces the trauma during cannulation.

Robot-assisted retinal vein cannulation with force-based puncture detection: Micron vs. the steady-hand eye robot

Retinal vein cannulation is a demanding procedure where therapeutic agents are injected into occluded retina veins. The feasibility of this treatment is limited due to challenges in identifying the moment of venous puncture, achieving cannulation and maintaining it throughout the drug delivery period. In this study, we integrate a force-sensing microneedle with two distinct robotic systems: the handheld micromanipulator Micron, and the cooperatively controlled Steady-Hand Eye Robot (SHER). The sensed tool-to-tissue interaction forces are used to detect venous puncture and extend the robots' standard control schemes with a new position holding mode (PHM) that assists the operator hold the needle position fixed and maintain cannulation for a longer time with less trauma on the vasculature. We evaluate the resulting systems comparatively in a dry phantom, stretched vinyl membranes. Results have shown that modulating the admittance control gain of SHER alone is not a very effective solution for preventing the undesired tool motion after puncture. However, after using puncture detection and PHM the deviation from the puncture point is significantly reduced, by 65% with Micron, and by 95% with SHER representing a potential advantage over freehand for both.

Branch retinal vein occlusion

Retinal vein occlusions (RVO) are the second commonest sight threatening vascular disorder. Branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO) are the two basic types of vein occlusion. Branch retinal vein occlusion is three times more common than central retinal vein occlusion and- second only to diabetic retinopathy as the most common retinal vascular cause of visual loss. The origin of branch retinal vein occlusion undoubtedly includes both systemic factors such as hypertension and local anatomic factors such as arteriovenous crossings. Branch retinal vein occlusion causes a painless decrease in vision, resulting in misty or distorted vision. Current treatment options don't address the underlying aetiology of branch retinal vein occlusion. Instead they focus on treating sequelae of the occluded venous branch, such as macular oedema, vitreous haemorrhage and traction retinal detachment from neovascularization. Evidences suggest that the pathogenesis of various types of retinal vein occlusion, like many other ocular vascular occlusive disorders, is a multifactorial process and there is no single magic bullet that causes retinal vein occlusion. A comprehensive management of patients with retinal vascular occlusions is necessary to correct associated diseases or predisposing abnormalities that could lead to local recurrences or systemic event. Along with a review of the literature, a practical approach for the management of retinal vascular occlusions is required, which requires collaboration between the ophthalmologist and other physicians: general practitioner, cardiologist, internist etc. as appropriate according to each case.

Biomechanical Assessment of Radial Optic Neurotomy

PURPOSE

A biomechanical model was constructed to simulate the potential therapeutic effect that the surgical procedure radial optic neurotomy (RON) would have on an eye with a central retinal vein occlusion.

DESIGN

Experimental study.

CONTROLS

Model eyes undergoing RON were compared to control eyes under the same baseline conditions.

INTERVENTION

Radial optic neurotomy. We modeled the optic nerve, lamina cribrosa, and the sclera separately and then reassembled the components. Material properties of the sclera and lamina cribrosa were extracted from the literature and both stiff and more elastic values were used for the optic nerve. Intraocular and arterial pressures were varied across a wide range in the analysis.

MAIN OUTCOME MEASURE

Change in central retinal vein lumen size.

RESULTS

Over a clinically relevant range of boundary conditions, the increase in the lumen area of the central retinal vein lumen after RON remained trivial, ranging from 1% to a maximum of 5%.

CONCLUSIONS

The biomechanical effect of RON is negligible, and is unlikely to be a procedure that could mechanically ameliorate the clinical sequelae of a central vein occlusion.

[Radial optic neurotomy: efficacy monitoring using venous ophthalmodynamometry]

BACKGROUND

Retinal central venous outflow pressure (VOP) can be measured with a new ophthalmodynamometer (Meditron, Völklingen, Germany). Radial optic neurotomy (RON) is a new surgical approach for central retinal vein occlusion (CRVO) which is still controversially discussed. Particularly the early formation of retinochoroidal collaterals is intended to achieve normalization of the preoperatively increased pressure in the central retinal vein. We investigated the VOP after RON.

PATIENTS AND METHODS

In total, 21 eyes of 21 patients (9 male, 12 female) suffering from CRVO were treated by RON. Pars plana vitrectomy with nasal radial optic neurotomy and peeling of the internal limiting membrane were performed. The mean follow-up time was 10.8 months (6-24 months). Central venous outflow pressure was measured using ophthalmodynamometry.

RESULTS

The most frequent concomitant ophthalmic disease was glaucoma (52%), and the predominantly associated systemic disease was hypertension (81%). After RON in 16 eyes (76%) visual acuity improved by at least 2 lines; in 3 eyes (14%) visual acuity was unchanged (+/-1 line) and in 2 patients (10%) visual acuity decreased by 2 or more lines. Eyes with visual improvement and formation of chorioretinal anastomosis postoperatively showed a significantly lower venous outflow pressure assessed with ophthalmodynamometry.

Laser-induced chorioretinal venous anastomosis using combined lasers with different wavelengths

AIM

To evaluate the effectiveness of combined lasers with different wavelengths in creating chorioretinal venous anastomosis (CRVA) in nonischaemic central retinal vein occlusion (CRVO).

METHODS

In this retrospective, noncomparative, consecutive case series, records of all patients with a diagnosis of nonischaemic CRVO who underwent combined laser treatment to induce CRVA and who were followed-up for 6 months or longer were reviewed.

RESULTS

Records of 85 patients (85 eyes) were analysed. These patients were divided into two groups. In group 1 (24 cases, 24 eyes), combined lasers with two different wavelengths (argon blue-green laser combined with Nd-YAG laser were used. In group 2 (61 cases, 61 eyes), combined lasers with three different wavelengths (argon blue-green laser combined with krypton red laser and Nd-YAG laser) were used. Functional anastomosis formed in 13 out of 24 eyes (54%) in group 1 and 47 out of 61 eyes (77%) in group 2. In patients with successful anastomosis, visual acuity improved for two or more lines in 49 out of 60 eyes (82%), with the remaining eyes undergoing no change. There were no serious complications.

CONCLUSION

The use of three laser wavelengths results in the creation of laser anastomosis and the success rate may be higher than when using two wavelengths alone.

The management of retinal vein occlusion: is interventional ophthalmology the way forward?

Retinal vein occlusions (RVO) are the second commonest sight threatening vascular disorder. Despite its frequency treatments for RVO are unsatisfactory and include several that have not been tested by large, well designed, prospective, randomised controlled trials. There is also the lack of long term follow up in many of the available small uncontrolled studies, and the timings of interventions are haphazard. This review aims to evaluate the current knowledge relating to the pathogenesis, suggested treatments for the different types of RVO, and their complications. Isovolaemic haemodilution is of limited benefit and should be avoided in patients with concurrent cardiovascular, renal, or pulmonary morbidity. Evidence to date does not support any therapeutic benefit from radial optic neurotomy, optic nerve decompression, or arteriovenous crossing sheathotomy on its own. Vitrectomy combined with intravenous thrombolysis may offer promise for central RVO. Similarly, vitrectomy combined with arteriovenous sheathotomy intravenous tissue plasminogen activator may offer benefits for branch RVO. RVOs occur at significantly high frequency to allow future prospective randomised controlled studies to be conducted to evaluate the role of different therapeutic modalities singly or in combination.

Arterio-venous dissection after isovolaemic haemodilution in branch retinal vein occlusion: a non-randomised prospective study

PURPOSE

The rationale for this pilot study was to add arterio-venous dissection (AVD) after unsuccessful medical treatment in a well-defined group of patients with branch retinal vein occlusion (BRVO).

METHODS

In this prospective, interventional case series 35 consecutive patients with a visual acuity (VA) of 0.4 (logMar) or worse were scheduled for surgery within the first 3 months of the onset of BRVO. The study endpoint was VA 1 year after AVD. Secondary study endpoints were: correlation of VA and successful vessel dissection; complication rate; and number of additional surgical procedures within the first year of AVD.

RESULTS

Preoperative VA (logMar) was 0.82+/-0.05 (range 0.2-1.6). VA 6 weeks postoperatively was 0.54+/-0.06 (range 0-1.6), 3 months postoperatively 0.61+/-0.07 (0-1.56), 6 months postoperatively 0.74+/-0.08 (range 0-2) and 12 months postoperatively 0.55+/-0.07 (range 0.1-1.5). VA improved 1 year after AVD (p=0.0004). An improvement in VA did not depend on successful separation of the artery and the vein. Four patients had a retinal detachment, 19 patients needed cataract surgery within the first year of AVD. A total of 24 additional surgical procedures were needed.

CONCLUSIONS

Patients with BRVO may profit from AVD compared with a historical control group. Visual improvement was found irrespective of the successful dissection of vessels. The cataract formation rate and additional surgery was a shortcoming of the AVD procedure.

Quantitative grading of preretinal neovascularization in adult rats

PURPOSE

To quantify photodynamic venous occlusion-induced preretinal neovascularization with fluorescein isothiocyanate-dextran (FITC-dextran) angiography in adult Sprague-Dawley rats.

METHODS

Argon green laser was used to ablate retinal veins in the experimental group (24 rats), and applied between the vessels in the control group (10 rats) after systemic injection of rose bengal. Animals were systemically infused with FITC-dextran and killed 14 days after laser treatment. Retinal flat-mounts were observed under a fluorescence microscope. The number and area of neovascular tufts were measured. Confocal microscopy and histological study were performed to rule out possible artifacts, and to confirm FITC-dextran angiography findings.

RESULTS

Out of the entire group of 34 albino rats, no preretinal neovascularization was found in the control group (total 20 eyes, 10 rats). In the experimental group (total 48 eyes, 24 rats) 43 eyes (90%) developed well demarcated neovascular tufts revealed by FITC-dextran angiography. This well demarcated boundary of neovascular tufts was reconfirmed by confocal microscopy and histological study. There were no significant differences in the number or area of neovascular tufts between the right and left eyes.

CONCLUSION

FITC-dextran angiography provides a time- and labour-efficient basis for quantifying both the number and area of preretinal neovascularization induced by photodynamic venous occlusion in adult rats. This model is suitable for angiostatic study in the adult animals.

Problems with attempted chorioretinal venous anastomosis by laser for nonischemic CRVO and BRVO

PURPOSE

To report the complications and long-term results of laser-induced chorioretinal venous anastomosis in vein occlusions.

PATIENTS AND METHODS

Eight consecutive eyes, 3 with central retinal vein (CRVO) and 5 with branch retinal vein occlusion (BRVO), were observed for up to 5 years after attempted laser-induced chorioretinal venous anastomosis.

RESULTS

Successful chorioretinal venous anastomoses were created in 2 (25%) eyes. Patients had severe complications, including vitreous hemorrhage, choroidal neovascular membrane, choriovitreal neovascularization, rubeosis iridis and neovascular glaucoma.

CONCLUSION

The utilization of a chorioretinal venous anastomosis by laser with proposed laser settings as a therapeutic modality should be further analyzed, and a careful long-term follow-up must be done to avoid vision-threatening complications.

RETINAL ENDOVASCULAR SURGERY FOR CENTRAL RETINAL VEIN OCCLUSION

PURPOSE

The rate and magnitude of spontaneous visual recovery are very poor in central retinal vein occlusion (CRVO). In the first follow-up year, the Central Vein Occlusion Study Group reported that only 6% of eyes recovered > or = 3 lines of vision and none recovered > or = 8 lines of vision. Retinal endovascular surgery (REVS) is vitrectomy followed by cannulation of retinal vessels with injection of tissue plasminogen activator. After reports of one surgeon's experience suggested that the procedure promotes recovery of vision, other surgeons began to offer REVS to their patients. This report discusses the initial experience of four surgeons using REVS to treat CRVO.

METHODS

In this prospective, consecutive case series, patients with CRVO for > 1 week and visual acuity of < 20/50 were offered REVS and were followed by the authors. The main outcome measure was recovery of visual acuity.

RESULTS

This series represents the initial 25 consecutive REVS cases of the 4 authors (5-7 cases per author). The median CRVO duration was 2 months (mean 2.9, months), and the average preoperative visual acuity was 20/400 (< or = 20/200 in 80% of cases). Intravitreal triamcinolone acetonide (IVTA) was administered intraoperatively in three cases and at some time postoperatively in six cases. Overall, 18 eyes (72%) recovered > or = 3 lines of visual acuity, and 9 (36%) recovered > or = 8 lines of vision. Among the surgeons, the rates of > or = 3-line visual recovery ranged from 57% to 100%, and the rates of > or = 8-line visual recovery ranged from 14% to 71%. Of the 22 eyes that initially underwent REVS without intraoperative IVTA injection, 13 (59%) recovered > or = 3 lines of vision and 5 (23%) recovered > or = 8 lines of vision. Complications included macular edema (28%), anterior segment or retinal neovascularization (24%), and subsequent cataract surgery (5 [23%] of the 22 preoperatively phakic eyes). One eye had an intraoperative retinal detachment that was treated but recurred 4 months after REVS, and two of the eyes with anterior segment neovascularization developed late-onset traction retinal detachments (at 8 and 13 months after REVS).

CONCLUSION

Although the authors were on the "learning curve" of experience during this series, REVS appears to promote visual recovery far in excess of what would be expected to occur spontaneously, and IVTA injection greatly improved outcomes. We believe that mastery of REVS techniques and the inclusion of IVTA injection may lead to better visual results and lower complication rates.

[Surgical approach to retinal vein occlusion]

Retinal vein occlusions are the second most common vision threatening retinal vascular disorders. Our therapeutic armamentarium for functional improvement was very limited in the past for all types of retinal vein occlusions (branch, central and hemi-central retinal vein occlusion). Also pathomechanism and risk factors are not completely understood yet. Argon-laser-photocoagulation can prevent the development and treat neovascularizations successfully, but is unable to improve visual function in most cases. Thrombolytic therapy applied systemically is limited due to serious side effects but may be helpful when injected intraocularly. Isovolemic hemodilution may be efficacious in central retinal vein occlusion (CRVO). The creation of a laser-induced chorioretinal venous anastomosis showed serious complications. Since 1999 numerous reports on successful surgical techniques were published. It could be shown that the dissection of the adventitial sheath with separation of the artery from the vein at the arteriovenous crossing where branch retinal vein occlusion occurs can re-establish the retinal blood flow with reduction of macular edema. But it is still unclear which step of the surgery (vitrectomy, ILM-peeling, sheathotomy) is causative for the results. A new surgical approach in CRVO is the radial optic neurotomy (RON). This technique was primarily performed under the hypothesis of decompression of the central vein by cutting the scleral ring. Meanwhile there is some evidence that the formation of chorioretinal shunts may be the decisive factor in cases of successfully performed RON. Due to inconsistent and rare data this surgical procedure needs further evaluation. Another surgical option is the cannulation of the occluded vein. This technique seems to be feasible but the clinical results still have to be proved. Despite several uncertainties and open questions, surgical techniques are likely to overcome the desolate therapeutic situation for retinal vein occlusion of the past.

[Optic neurotomy for central retinal vein occlusion]

OBJECTIVE

To investigate the surgical effect and complication of optic neurotomy for ischemic central retinal vein occlusion (CRVO).

METHODS

Eight patients elected to undergo optic neurotomy, The age range was 32 - 67 years, Five of the 8 were women and three were men. The duration of the CRVO were 3 - 8 months. Systemic hypertension was present in 3 patients and severe cystoid macular edema was present in 3 patient. No diabetes mellitus was noted in all 8 patients. A standard three-port vitrectomy was performed on 8 patients with severe ischemic CRVO, A microvitreoretinal (MVR) blade was used to relax the scleral ring and adjacent sclera of the optic disk, The depth of the incision into the optic nerve placed the MVR blade just beyond the widest portion of the diamond-shaped tip. The depth of the incision was 2.2 mm approximately.

RESULTS

Optic neurotomy was performed in all 8 patients successfully, The small hemorrhage was noted during the surgical procedure in 2 patients limited to the incision site. The follow-up was 3 - 5 months range, All patients had improvement in the retina and macular edema and the appearance of the fundus as documented by photography, fluorescein angiography. And optic coherence tomography (OCT). Postoperative visual acuities were improved in 62.5% of patients and the visual acuities no changes were in 2 patients. Postoperative neovascular glaucoma was in 1 patient and vitreous hemorrhage in 2 patients.

CONCLUSIONS

Optic neurotomy may improve the intraretinal hemorrhage, macular edema and the visual acuity prognosis in patients with ischemic CRVO.

Chorioretinal Anastomosis After Radial Optic Neurotomy for Central Retinal Vein Occlusion

OBJECTIVES

To evaluate the incidence of chorioretinal anastomosis after radial optic neurotomy and to determine its effect on visual acuity and foveal thickness in patients with central retinal vein occlusion.

METHODS

We conducted a prospective, uncontrolled, interventional study of 14 patients with preoperative visual acuities below 20/125. Pars plana vitrectomy and radial optic neurotomy were performed. Fluorescein angiography and optical coherence tomography were used to monitor the evolution of macular edema.

RESULTS

All patients underwent radial optic neurotomy with no major complications. Eight patients (57.1%) gained 1 or more lines of visual acuity while the visual acuity of 6 patients (42.9%) improved by 2 or more lines (mean visual acuity, 20/80; P<.001) (mean visual acuity gain, 3 lines). The decrease in macular thickness was shown to be statistically significant (P<.001) (median, 282 microm). Retinochoroidal shunts developed in 6 eyes (42.9%) at the site of the radial optic neurotomy.

MAIN OUTCOME MEASURES

Improvement in visual acuity and a decrease in foveal thickness seen on optical coherence tomography.

CONCLUSIONS

Surgical decompression of central retinal vein occlusion via radial optic neurotomy seems to be a promising technique that improves or at least stabilizes the course of severe central retinal vein occlusion. Improvement may occur because of optic nerve decompression, vitrectomy, and by inducing new chorioretinal shunts that drain retinal circulation to the choroid and accelerate resolution of retinal edema.

Long-term follow-up of a modified technique for laser-induced chorioretinal venous anastomosis in nonischemic central retinal vein occlusion

PURPOSE

To evaluate the long-term outcomes of a modified technique for laser chorioretinal venous anastomosis in nonischemic central vein occlusion (CVO).

DESIGN

Prospective, noncomparative, consecutive case series.

PARTICIPANTS

Nineteen eyes of 19 patients.

METHODS

Nineteen consecutive eyes with nonischemic CVO were observed for a mean period of 48 months after attempted laser-induced chorioretinal venous anastomosis therapy using a technique modified intentionally to avoid vein wall rupture.

MAIN OUTCOME MEASURES

Anastomosis patency, visual acuity, maintenance of nonischemic status, and complications were measured.

RESULTS

At least one patent anastomosis developed eventually in 19 of 19 eyes (100%). Two anastomoses developed in 5 of 19 eyes (26%). There were one or two nonfunctioning sites in 8 of 19 eyes (42%). The maximum number of treatment attempts in a single eye was four. Snellen visual acuity was unchanged in 3 of 19 eyes (16%) and improved from 1 to 11 lines (mean improvement, 5 lines) in 16 of 19 eyes (84%) during the mean follow-up period of 48 months. Nineteen of 19 eyes (100%) maintained nonischemic status. Treatment complications were limited to localized preretinal fibrosis.

CONCLUSIONS

Rupture of the vein wall is not required to form a functioning laser-induced chorioretinal venous anastomosis in eyes with nonischemic CVO. A technique modified intentionally to avoid vein wall rupture seems to be safer and more predicable.

Optimal laser power to rupture Bruch's membrane and the retinal vein in the pig

BACKGROUND AND OBJECTIVE

For laser-induced chorioretinal venous anastomosis to become a viable treatment option for perfused central retinal vein occlusion, laser parameters must be refined to more reliably create venous anastomoses while minimizing complications. The aim of this study was to determine the lowest argon laser power at which Bruch's membrane and the retinal vein are ruptured in 100% of attempts in the porcine eye.

MATERIALS AND METHODS

Testing was performed on 6 eyes of 3 Yorkshire Cross pigs, using an argon green laser. The spot size was 50 microm and the duration was 0.2 seconds for all applications. Twelve laser powers were tested, from 0.5 to 6 W, increasing by increments of 0.5 W. Light microscopy was used to determine the frequency of rupture of Bruch's membrane and the retinal vein for each power.

RESULTS

The rupture rate of Bruch's membrane was 0% at 0.5 W, 5% at 1.0 W, 20% at 1.5 W, 70% at 2.0 W, and 100% for all powers from 2.5 to 6.0 W. The rupture rate of the retinal vein was 0% at 0.5 W, 5% at 1.0 W, 30% at 1.5 W, 60% at 2.0 W, 80% at 2.5 W, and 100% for all powers from 3.0 to 6.0 W.

CONCLUSION

Argon green laser powers of at least 2.5 and 3.0 W were necessary to rupture Bruch's membrane and the retinal vein, respectively, with a 100% success rate in the porcine eye. Because patients with central retinal vein occlusion have secondary retinal edema and may have lenticular opacity, higher laser powers may be required to achieve a 100% rupture rate of these structures.

Retinal endovascular surgery and intravitreal triamcinolone acetonide for central vein occlusion in young adults

PURPOSE

To report the results of retinal endovascular surgery and intravitreal triamcinolone acetonide on two eyes of two patients younger than 40 years of age with central vein occlusion.

DESIGN

Interventional case reports from a study approved by the Institutional Review Board of North Broward Medical Center, Pompano Beach, Florida.

METHODS

Two men, ages 37 and 39, with unilateral central vein occlusion were treated with retinal endovascular surgery and intravitreal triamcinolone acetonide. The main outcome measure was recovery of visual acuity.

RESULTS

One patient recovered 8 lines of visual acuity, the other recovered 11 lines. There was rapid clearance of intraretinal hemorrhage and edema in both cases.

CONCLUSIONS

Retinal endovascular surgery and intravitreal triamcinolone acetonide may promote recovery of visual acuity in eyes of young adults with central vein occlusion.

Preliminary clinical observation of arteriovenous sheathotomy for treatment of branch retinal vein occlusion

PURPOSE

To document the anatomic and functional improvement of six patients with branch retinal vein occlusion (BRVO) following successful arteriovenous adventitial sheathotomy (AAS).

METHODS

Retrospective study of 6 patients (6 eyes) with BRVO treated with AAS. All patients were not eligible for laser photocoagulation and had both macular edema and intraretinal hemorrhage. The visual acuity was in the range of 0.4 to 0.02. All patients underwent pars plana vitrectomy and AAS. The clinical improvement was determined by fundus photograph, fluorescein angiography (FAG), optical coherence tomography (OCT) and multifocal electroretinography (ERG). All patients were followed postoperatively for an average of 20 months ranging from 12 to 24 months.

RESULTS

Sheathotomy and decompression of the arteriole/venule (A/V) crossing were achieved in all 6 patients. 5 patients have improved their best-corrected visual acuity 4 lines or more. The best one could reach to 1.0. One month after the operation, fundus photograph and FAG demonstrated the resolution of intraretinal hemorrhage, reduction of non-perfusion area and apparent resolution of retinal venous dilation and tortuosity. OCT confirmed remarkable reduction of retinal thickness. The microcysts at the fovea diminished. Multifocal ERG showed the recovery of the central peak at the macular and the peripheral response density. However, capillary nonperfusion area and microaneurysm were found out by FAG in four patients at the points distal to the sheathotomy three months after the operation.

CONCLUSIONS

Anatomic and functional improvement of retina can be achieved in patients with BRVO through AAS. However, the capillary nonperfusion and microaneurysm may follow this surgical procedure in some cases that need further treatment with laser photocoagulation. The better visual improvement may be expected in the patients with earlier surgical intervention.

Vitrectomy with arteriovenous decompression and internal limiting membrane dissection in branch retinal vein occlusion

PURPOSE

The therapeutic armamentarium for functional improvement after branch retinal vein occlusion (BRVO) is limited with uncertain efficacy. Some surgeons have proposed surgical decompression of the vein at the arteriovenous (AV) crossing.

METHODS

Forty-three patients with BRVO were treated in the authors' department from August 1999 to April 2001 with AV decompression. Twenty-five patients with comparable BRVO who refused this surgical intervention served as a control group. All 68 patients received an isovolemic hemodilution therapy for 10 days. The surgical procedure consisted of a standard pars plana vitrectomy and separation of the overlying artery from the vein using microscissors. In 16 cases dissection of the internal limiting membrane (ILM) in the macular area and around the AV crossing was also performed. Assessment of visual acuity, fluorescein angiography, and multifocal electroretinography were performed preoperatively and 6 weeks after surgery in seven patients.

RESULTS

Surgical procedure and postoperative course were uneventful. In most of the treated eyes visual acuity improved and fluorescein angiography revealed capillary reperfusion. Functional results in patients with AV decompression were highly significantly better than in the control group. Furthermore, removal of the ILM seems to have an additional beneficial effect on the functional outcome.

CONCLUSION

These results demonstrate the therapeutic effect of surgical AV decompression in BRVO. Additional removal of the ILM seems to improve the functional results. Further experience may answer some open questions.

Effect of squalamine on iris neovascularization in monkeys

PURPOSE

To investigate the effect of squalamine, an antiangiogenic aminosterol, in an experimental model of iris neovascularization.

METHODS

Iris neovascularization was created in cynomolgus monkeys by occluding retinal veins with an argon laser and inducing persistent hypotony with a central corneal suture. Twenty-four eyes were treated in three groups. In Group 1, four eyes were injected intravitreally with 3 microg/0.1 mL squalamine and four eyes with balanced saline solution (controls) immediately after vein occlusion (day 1); injections were repeated every 3 days for 3 weeks. In Group 2, 1 mg/kg squalamine was administered with intravenous infusion in dextrose 5% in four animals; four control animals received only dextrose. Infusions began on day 1 and were repeated every 3 days for 3 weeks. In Group 3, after development of iris neovascularization on day 7, 1 mg/kg squalamine was injected systemically in four animals; four control animals received dextrose 5%. Monkeys were examined by slit-lamp biomicroscopy and underwent color photography and fluorescein angiography.

RESULTS

Group 1: All eyes, treated and control, developed intense and persistent rubeosis iridis. Group 2: Two of the four treated eyes in this group developed minimal iris neovascularization; the other two had no iris neovascularization. All four control eyes developed intense, persistent iris neovascularization. Group 3: All eyes developed extensive rubeosis iridis; iris neovascularization regressed in all four treated eyes after squalamine injections. Two of four treated eyes retained minimal iris neovascularization; two showed complete regression of rubeosis iridis. Rubeosis iridis completely regressed in two of the four control eyes; the remaining two control eyes had intense, persistent iris neovascularization.

CONCLUSIONS

Intravitreally injected squalamine did not affect the development of iris neovascularization; however, systemic squalamine injection inhibited the development of iris neovascularization and caused partial regression of new vessels in a primate model.

Intentional complete interruption of a retinal vein after vitrectomy might improve the rate of successful chorioretinal venous anastomosis formation in central retinal vein occlusion

BACKGROUND

Laser or surgical chorioretinal venous anastomosis has not become widespread as suitable treatment for central retinal vein occlusion (CRVO). We report here the effectiveness of cutting off a retinal vein with vitrectomy in making a chorioretinal venous anastomosis in CRVO.

METHODS

We performed a vitrectomy accompanied by a chorioretinal venous anastomosis procedure for seven consecutive patients with CRVO. These patients had shown no improvement in their visual acuity in the month following their first visit to our hospital and had a visual acuity of less than 20/200. Their preoperative visual acuity ranged from counting fingers to 20/300. The procedure included the complete cutting of the affected retinal vein, and the making of a small incision at both sides of the vein interruption through the full thickness of the retina, the retinal pigment epithelium and Bruch's membrane.

RESULTS

In five of the seven patients, successful chorioretinal venous anastomosis was observed. All five patients showed an improvement of two or more lines in visual acuity 6 months postoperatively. In three of the five, visual acuity was 20/100 or better. A postoperative complication of recurrent vitreous hemorrhage and fibrous proliferation was observed in one patient, and a second operation was necessary.

CONCLUSIONS

Surgical interruption of an affected vein was a feasible procedure and could raise the rate of successful chorioretinal venous anastomosis in CRVO.

[VEGF expression in dog retina after chorioretinal venous anastomosis]

OBJECTIVE

To identify changes in vascular endothelial growth factor (VEGF) expression in the dog retina after laser-induced chorioretinal venous anastomosis (CRVA), in order to find out the relationship between CRVA treatment and the related neovascular complications.

METHODS

Immediately after branch retinal vein occlusion (BRVO) model was made in 5 eyes of 5 normal dogs, CRVA treatment was done over a small tributary vein in the drainage distribution of the occluded vein. In each eye, there were 2 - 3 treatment sites. Four to six weeks later, a repeated treatment was given if the first treatment failed to show the anastomosis. The treatment sites with successful CRVA were divided into two groups: the small laser spot group, which received one treatment and the big laser spot group, which received more than one treatment. The expression of VEGF was investigated immunohistochemically in the treatment sites with successful anastomoses and in the 5 normal fellow eyes (control).

RESULTS

There were totally 10 successful anastomoses in the 5 experimental eyes, among which, five received one treatment and the other 5 received more than one treatment. On fundus examination, the small laser spots were round and small, and the big laser spots were large with local proliferation. VEGF immunoreactivity was absent/weak in the normal dog retina, and remained unchanged in the small laser spot group, but somewhat increased in the big laser spot group. No neovascular complications occurred. All immunostaining experiments were accompanied by proper controls and none of the negative controls showed any immunoreactivity.

CONCLUSIONS

Proper laser treatment can induce CRVA quite safely in nonischemic dog retina, which does not cause changes in the expression of VEGF, but severe laser damage in the treatment site can cause increased VEGF expression which may be related to neovascular complications.

Experimental macular edema induced by macular venule occlusion in monkey

PURPOSE

Visual prognosis after retinal vein occlusion varies, because it may be affected by macular edema or an avascular area. The mechanism describing how macular edema and avascular areas occur, however, has not been clearly understood. We induced macular edema in cynomolgus monkeys by occluding macular venules to evaluate the retinal microcirculation.

METHODS

We produced venous occlusion by applying dye laser in three cynomolgus monkeys. Macular edema was examined by slit lamp biomicroscopy and optical coherence tomography. Acridine orange leukocyte fluorography (AOLF) and fluorescein angiography were performed to study blood flow and vascular leakage before and after laser application.

RESULTS

We observed three types of retinal changes in the macular area: (1) macular edema did not develop; (2) macular edema developed, but improved with avascular area formation; (3) macular edema developed, but disappeared without avascular area formation. Under physiological conditions, observation revealed that leukocytes flowed from arterioles into either superior or inferior venules. When macular edema did not develop, most leukocytes from arterioles escaped into the adjacent non-occluded venules. In contrast, when macular edema occurred, leukocyte flow became stagnated. Macular edema developed when capillary leakage was observed from venules and subsequently arterioles, but disappeared when an avascular area was formed by arteriole occlusion.

CONCLUSIONS

We demonstrated that experimental macular edema could be induced by macular venule occlusion in monkeys. According to our observation by AOLF, whether macular edema is induced or not depends on the function of collateral routes of the remaining non-occluded venules. We could consider that a gradual increase in intravascular pressure was associated with the avascular area formation.

Spontaneous remodelling of retinal veins accidentally severed during vitreous surgery

BACKGROUND

To report the spontaneous remodelling of retinal veins inadvertently severed during vitreous surgery.

METHODS

Four diabetic patients who underwent vitrectomy during which retinal veins were damaged were followed for at least 6 months. Haemorrhages from severed veins were controlled by raising intraocular pressure and by endodiathermy of the distal ends of the veins. This was followed by fluid/gas exchange.

RESULTS

Remodelling of venous channels in the damaged areas was observed in all eyes. In three of the four eyes we found evidence of collateral veins. In the other eye we noted the connection of two ends of an interrupted vein. No signs of retinal vein occlusion (e.g. superficial retinal haemorrhages and retinal oedema) were observed.

CONCLUSION

These findings suggest that a spontaneous remodelling mechanism to repair damaged venous channels may exist in retina.

[A case of choroidovitreal neovascularization after unsuccessful laser chorioretinal venous anastomosis for central retinal vein occlusion]

BACKGROUND

A case of nonischemic central retinal vein occlusion, which developed severe neovascular complication after unsuccessful laser chorioretinal venous anastomosis is reported.

CASE

The patient was a 50-year-old man with nonischemic central retinal vein occlusion of the right eye. Two weeks after laser chorioretinal venous anastomosis attempt, closure of the venous segment distal to the anastomotic sites occurred and a choroidovitreal neovascularization developed, so that vitreous surgery was needed 2 months after the laser attempt.

CONCLUSION

Laser chorioretinal venous anastomosis should be used only on carefully selected patients, and close follow-up is needed after this treatment.

Successful erbium: YAG laser-induced chorioretinal venous anastomosis for the management of ischemic central retinal vein occlusion. A report of two cases

BACKGROUND

Central retinal vein occlusion (CRVO) is a disorder with potentially blinding complications, particularly when associated with retinal ischemia. There is no reliable treatment for ischemic CRVO.

METHODS

We developed a new approach for ischemic cases of CRVO consisting of vitrectomy, posterior hyaloid detachment, and four erbium:YAG laser-induced chorioretinal anastomoses, one in each quadrant.

RESULTS

We report two cases of ischemic CRVO treated with this approach, with initial visual acuity of count fingers at 30 cm and hand movements respectively. After the surgery, there was resolution of hemorrhages and macular edema and visual improvement to 20/400 in the first case and to 20/180 in the second case. In both cases, there was successful creation of chorioretinal anastomoses, and there was no anterior segment neovascularization or other complications related to the surgery.

CONCLUSION

This treatment shows promise in the management of the ischemic cases of CRVO, and further evaluation is justified.

[Experimental research of laser-induced collaterals in retinal vein occlusion]

OBJECTIVE

To evaluate the feasibility and safety of establishing chorioretinal venous anastomosis in rabbit eyes with a model of branch retinal vein occlusion

METHODS

By using laser photocoagulation, a chorioretinal venous anastomosis was created in rabbit eyes in which a branch retinal vein occlusion had previously been established photochemically. A similar attempt to create an anastomosis was made in the control eyes in which no branch vein occlusion was present.

RESULTS

In the 21 eyes with the model of branch retinal vein occlusion, a chorioretinal venous anastomosis formed in 4 eyes within 3 to 5 weeks. In the control eyes, an anastomosis in one eye presented by 5 weeks, during follow-up of 2 to 5 months. The hemorrhage in choroid, retina and vitreous associated with laser photocoagulation were absorbed within 3 weeks, and no other severe complications were found.

CONCLUSIONS

Chorioretinal venous anastomosis can be created by using laser photocoagulation. This technique is relatively safe. However, to improve the rate of successfully creating an anastomosis, more research work needs to be performed.

Antithrombotic effect of ticlopidine in an experimental model of retinal vein occlusion

PURPOSE

Ticlopidine inhibits adenosine diphosphate (ADP)-induced platelet aggregation and may be effective in patients with retinal vein occlusions (RVO). This study tests the efficacy of ticlopidine in an animal model of RVO.

METHODS

Rose bengal-mediated argon laser photothrombosis of retinal veins was created in rabbits pretreated with oral ticlopidine, aspirin, or saline. The number of laser spots necessary to produce a partial or complete RVO was recorded and tabulated.

RESULTS

Pretreatment with ticlopidine significantly increased the number of laser spots needed to produce a partial (P =.02), or a complete (P =.002) RVO as compared to the control group. Pretreatment with ticlopidine significantly increased the number of laser spots needed to produce a partial RVO (P =.02). Pretreatment with aspirin significantly increased the number of laser spots needed to produce a complete RVO (P =.002).

CONCLUSION

Ticlopidine may be a useful antiplatelet agent for the treatment of patients with RVO. Patients treated with ticlopidine should be monitored for the possible development of hematologic disorders.

Problems of chorioretinal venous anastomosis by laser for treatment of nonischemic central retinal vein occlusion

OBJECTIVES

Evaluate the efficacy of chorioretinal venous anastomosis in patients with nonischemic retinal vein occlusions with progressive visual loss and to concentrate on complications.

DESIGN

Case series of 6 patients, retrospective study. Six patients with nonischemic central retinal vein occlusions and progressive visual loss. Laser photocoagulation was performed to create a chorioretinal venous anastomosis to be able to supply venous blood to the choroid, bypassing the occlusion. Visual acuity, funduscopic appearance and fluorescein angiographic appearance were determined.

RESULTS

Two patients showed a chorioretinal anastomosis (33%), whereas in the other 4 patients the anastomosis could not be created. Yet 1 patient consequently had a neovascular tuft under the laser site. These new vessels caused minor vitreous hemorrhage and a tractional membrane which regressed after 10 months.

CONCLUSION

The utilization of a chorioretinal venous anastomosis by laser as a therapeutic modality should be further questioned and thoroughly evaluated and caution must be exercised to avoid vision-threatening complications.

Retinal surgery for treatment of central retinal vein occlusion

Vitreous surgery with retinal vein cannulation and injection of tissue plasminogen activator was performed in 8 eyes of 8 patients with longstanding visual loss secondary to central retinal vein occlusion. A modest improvement in visual acuity was demonstrated in 4 of the 8 eyes, and 3 of the 8 eyes maintained the preoperative vision. Retinal vein cannulation may offer a new treatment option for patients with central retinal vein occlusion.

Laser-induced chorioretinal venous anastomosis for non-ischaemic hemi-central vein occlusion

PURPOSE

To assess the effectiveness and complications of laser-induced chorioretinal venous anastomosis performed on eyes with non-ischaemic hemi-central retinal vein occlusions (hemi-CRVO).

METHODS

Fourteen eyes with a hemi-CRVO which reduced the visual acuity to 6/24 or less were treated with argon laser photocoagulation in an attempt to create a chorioretinal venous anastomosis between a retinal vein and the choroidal circulation.

RESULTS

Laser anastomoses were successfully created in six eyes (43%) and required a mean of 1.8 attempts in each eye. Of the eyes that developed an anastomosis, four had significant visual improvement. The distal retinal venous segment closed off in five eyes and these had prophylactic segmental argon pan-retinal photocoagulation performed. Two eyes had localized fibrovascular proliferation. No permanent vision-threatening complications were observed in any of the 14 eyes over the follow-up period.

CONCLUSIONS

Successful anastomosis between the retinal and choroidal circulation in eyes with hemi-vein occlusions may reduce macular oedema and improve vision. Complications of the technique are significant and a randomized clinical trial is due to commence which may clarify the suitability of this treatment.

[An update on the treatment of central retinal vein thrombosis (retinal vein occlusion)]

The paper reviews the actual therapeutical means in a severe invalid eye disease. The treatment is not able to improve the retinal blood flow, being more effective on the main symptoms and complications. The isovolumetric hemodilution method as an up-to-date method in the treatment of central retinal vein occlusion, appears to bring better recuperation hopes, by a higher improvement of the local anatomical and hemodynamical factors. That is the reason why we shall expose it widely in our paper. Unfortunately, despite its complexity, the treatment of central retinal vein occlusion is not satisfactory from the point of view of the high number of patients that remain with a low visual acuity. The main goal of the therapy is the recovery of visual function, but a few aspects and especially the late presentation for ophthalmological examination, reduce the objective of treatment to prevent complications.

Experimental preretinal neovascularization by laser-induced thrombosis in albino rats

The primary objective of this study was to develop a simple experimental model of angiogenesis by photodynamic thrombosis of the retinal veins in Sprague-Dawley rats. After a tail vein injection of rose bengal (40 mg/kg), all major retinal veins adjacent to the optic nerve head were photocoagulated with an argon green laser. The eyes were examined regularly for the following eight weeks. A grading system was devised using fluorescein angiograms and ADPase staining to describe the progression of the new vessels. Nine out of ten eyes showed development of the preretinal new vessels by day 14. Seven weeks after laser coagulation, 2 of 5 eyes developed localized tractional retinal detachment. Regression of the neovascularization was not noted in any of the animals during the follow-up period. The authors were able to establish an experimental model for preretinal neovascularization by vein occlusion. This model may be applied in study of the pathogenesis and treatment of retinal neovascularization.