Induced chorioretinal venous anastomosis in experimental retinal branch vein occlusion

Multimodal Imaging of Laser-Induced Retinal-Choroidal Anastomosis Masquerading as Type 3 Macular Neovascularization

The use of laser to induce a retinal-choroidal anastomosis (RCA) through photomechanical and photothermal rupture of the retinal pigment epithelium/Bruch's membrane beneath a retinal vein has been performed in eyes with retinal vein occlusion to create an alternate pathway for retinal venous outflow. The authors document the multimodal imaging findings of a 64-year-old female with type 2 diabetes presenting with a parafoveal vascular lesion simulating type 3 macular neovascularization. A review of the medical history and the benign course of the lesion suggested its inadvertent origin from prior focal/grid laser to treat diabetic macular edema. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:244-248.].

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.

High-resolution multimodal photoacoustic microscopy and optical coherence tomography image-guided laser induced branch retinal vein occlusion in living rabbits

Joint high-resolution multimodal photoacoustic microscopy (PAM) and optical coherence tomography (OCT) was developed to improve the efficiency for visualizing newly developed retinal neovascularization (RNV) and to monitor the dynamic changes of retinal vein occlusion (RVO) in living rabbits. The RNV and RVO models were created in New Zealand rabbits by Rose Bengal laser-induced RVO. Dual modalities imaging equipment, including color fundus photography, fluorescein angiography (FA), OCT, and PAM, was used to image and assess the changes of retinal vasculature. In vivo experimental results exhibited that not only the treatment boundaries and the position of the occluded vasculature but also the structure of individual RNV were markedly observed using PAM platform with great resolution and high image contrast. The laser light energy of 80 nJ was used to induce photoacoustic signal, which is approximately half the energy of the American National Standards Institute safety limit. A cross-sectional structure of RNV was identified with the OCT modality. Furthermore, vibrant transformations in the RNV and the retinal morphology were examined at different times after laser occlusion: days 4, 28, 35, 49, and 90. PAM revealed high contrast and high resolution vascular imaging of the retina and choroid with amplified penetration depth. Through the present custom-built imaging system, both RNV and RVO can be reconstructed and observed in two and three dimensions. A unique dual modality A unique dual modality PAM and OCT can help precisely visualize and distinguish individual microvessels, microvessel depth, and the surrounding anatomy. Thus, the proposed multimodal ocular imaging platform may offer a potential equipment to enhance classification of microvasculature in a reliable and proficient manner in larger rabbit eyes.

Photoacoustic Ophthalmoscopy: Principle, Application, and Future Directions

Photoacoustic ophthalmoscopy (PAOM) is a novel, hybrid, non-ionizing, and non-invasive imaging technology that has been used to assess the retina. PAOM can provide both anatomic and functional retinal characterizations with high resolution, high sensitivity, high contrast, and a high depth of penetration. Thus, ocular diseases can be precisely detected and visualized at earlier stages, resulting in an improved understanding of pathophysiology, improved management, and the improved monitoring of retinal treatment to prevent vision loss. To better visualize ocular components such as retinal vessels, choroidal vessels, choroidal neovascularization, retinal neovascularization, and the retinal pigment epithelium, an advanced multimodal ocular imaging platform has been developed by a combination of PAOM with other optical imaging techniques such as optical coherence tomography (OCT), scanning laser ophthalmoscopy (SLO), and fluorescence microscopy. The multimodal images can be acquired from a single imaging system and co-registered on the same image plane, enabling an improved evaluation of disease. In this review, the potential application of photoacoustic ophthalmoscopy in both research and clinical diagnosis are discussed as a medical screening technique for the visualization of various ocular diseases. The basic principle and requirements of photoacoustic ocular imaging are introduced. Then, various photoacoustic microscopy imaging systems of the retina in animals are presented. Finally, the future development of PAOM and multimodal imaging is discussed.

In Vivo 3D Imaging of Retinal Neovascularization Using Multimodal Photoacoustic Microscopy and Optical Coherence Tomography Imaging

The pathological process of neovascularization of the retina plays a critical role in causing vision loss in several diseases, including diabetes, retinal vein occlusion, and sickle cell disease. Retinal neovascularization can lead to vitreous hemorrhage and retinal detachment, yet the pathological process of neovascularization is a complex phenomenon under active investigation. Understanding and monitoring retinal neovascularization is critically important in clinical ophthalmology. This study describes a novel multimodal ocular imaging system which combines photoacoustic microscopy (PAM) and a spectral domain optical coherence tomography (SD-OCT) to improve the visualization of retinal neovascularization (RNV), their depth, and the surrounding anatomy in living rabbits. RNV was induced in New Zealand rabbits by intravitreal injection of vascular endothelial growth factor (VEGF). The retinal vasculature before and after injection at various times was monitored and evaluated using multimodal imaging including color fundus photography, fluorescein angiography (FA), OCT, and PAM. In vivo experiments demonstrate that PAM imaging distinctly characterized the location as well as the morphology of individual RNV with high contrast at a safe laser energy of 80 nJ. SD-OCT was used to identify a cross-sectional structure of RNV. In addition, dynamic changes in the retinal morphology and retinal neovascularization were observed at day 4, 5, 6, 7, 9, 11, 14, 28, and day 35 after VEGF injection. PAM demonstrated high-resolution optical absorption of hemoglobin and vascular imaging of the retina and choroid with increased depth of penetration. With the current multimodal imaging system, RNV can be easily visualized in both 2D and 3D angiography. This multimodal ocular imaging system provides improved characterization of the microvasculature in a safe manner in larger rabbit eyes.

Multi-wavelength, en-face photoacoustic microscopy and optical coherence tomography imaging for early and selective detection of laser induced retinal vein occlusion

Multi-wavelength en face photoacoustic microscopy (PAM) was integrated with a spectral domain optical coherence tomography (SD-OCT) to evaluate optical properties of retinal vein occlusion (RVO) and retinal neovascularization (RNV) in living rabbits. The multi-wavelength PAM of the RVO and RNV were performed at several wavelengths ranging from 510 to 600 nm. Rose Bengal-induced RVO and RNV were performed and evaluated on eight rabbits using color fundus photography, fluorescein angiography, OCT, and spectroscopic en face PAM. In vivo experiment demonstrates that the spectral variation of photoacoustic response was achieved. The location and the treatment margins of the occluded vasculature as well as the morphology of individual RNV were obtained with high contrast at a laser energy of 80 nJ, which was only half of the American National Standards Institute safety limit. In addition, dynamic changes in the retinal morphology and retinal neovascularization were administered using PA spectroscopy at numerous time points: 0, 3, 7, 14, 21, 28, and 35 days after photocoagulation. The proposed multi-wavelength spectroscopic PAM imaging may provide a potential imaging platform to differentiate occluded retinal vasculature and to improve characterization of microvasculature in a safe and efficient manner.

Effect of triamcinolone acetonide on vascular endothelial growth factor and occludin levels in branch retinal vein occlusion

PURPOSE

To investigate the molecular mechanism by which triamcinolone acetonide (TA) may reduce edema in a porcine model of branch retinal vein occlusion (BRVO).

DESIGN

Animal study.

METHOD

After baseline ophthalmoscopic examination and fundus photography, a BRVO was created photothrombotically in each eye of 6 pigs, using argon green photocoagulation and intravenous Rose Bengal. Following this, the left eye was injected intravitreally with 4 mg/0.1 ml TA. After 11 weeks, the eyes were re-examined. Fluorescein angiography, in addition to ophthalmoscopy and fundus photography, was performed. Following sacrifice of the animals, the eyes were enucleated and processed. The distribution of vascular endothelial growth factor (VEGF), occludin, and glial fibrillary acidic protein (GFAP) were localized by immunofluorescence cytochemistry on 10 microm frozen retinal sections of TA-treated and untreated eyes.

RESULTS

Retinal VEGF levels were significantly lower in the TA-treated eyes as compared with the untreated eye (P = .002). Conversely occludin levels were significantly higher in the treated eye (P = .026). There was also a significant reduction in GFAP immunoreactivity in the Muller cells of the treated eyes (P = .015) with no statistical significance in the astrocytes (P = .065).

CONCLUSION

Intravitreal TA down regulates VEGF, which may prevent a decrease in occludin and also inhibits an increase in GFAP expression in Muller cells. These events may contribute to a reduction in the blood retinal barrier breakdown that occurs in BRVO and promote resolution of the associated retinal edema.

Comparison of two doses of intravitreal bevacizumab (Avastin) for treatment of macular edema secondary to branch retinal vein occlusion: results from the Pan-American Collaborative Retina Study Group at 6 months of follow-up

PURPOSE

To report the 6-month anatomical and visual outcomes after injecting two different doses of intravitreal bevacizumab in patients with macular edema secondary to branch retinal vein occlusion (BRVO).

METHODS

An interventional, retrospective multicenter study of 45 eyes that were treated with at least one intravitreal injection (24 eyes, 1.25 mg; 21 eyes, 2.5 mg) of bevacizumab is reported. The main outcome measures were the central 1-mm macular thickness (CMT) and the change in ETDRS lines of best-corrected visual acuity (BCVA) at 6 months.

RESULTS

Forty-five eyes were injected on average 26.1 months (range, 3-86 months) after the diagnosis. The average follow-up was 35.2 weeks (range, 24-52 weeks). All patients completed at least 6 months of follow-up. In the 1.25-mg dose group, at 1 month, there was an average gain of 4.5 lines of BCVA; at 3 months, 5.1 lines of BCVA; and at 6 months, 5.1 lines of BCVA (P < 0.005). In the 2.5-mg dose group, at 1 month, there was an average gain of 2.3 lines of BCVA; at 3 months, 3.8 lines of BCVA; and at 6 months, 4.8 lines of BCVA (P = 0.05). In the 1.25-mg dose group, the mean CMT +/- SD decreased from 461 +/- 211 microm at baseline to 321 +/- 152 microm at 1 month, 273 +/- 99 microm at 3 months, and 277 +/- 114 microm at 6 months (P = 0.0002). In the 2.5-mg group, the mean CMT +/- SD decreased from 385 +/- 168 microm at baseline to 279 +/- 111 microm at 1 month, 249 +/- 97 microm at 3 months, and 240 +/- 93 microm at 6 months (P = 0.011).

CONCLUSION

There were no statistically significant differences between the two dose groups with regard to the number of injections and anatomical and functional outcomes. Intravitreal injection of bevacizumab at doses up to 2.5 mg appears to be effective in improving BCVA and reducing CMT in BRVO in the short term. Multiple injections are needed in a large number of eyes for continued control of macular edema and preservation of visual acuity in the short term. Longer studies are needed to determine what role if any intravitreal injection of bevacizumab may play in the long-term treatment of this condition.

Intravitreous bevacizumab in the treatment of macular edema from branch retinal vein occlusion and hemisphere retinal vein occlusion (an AOS thesis)

PURPOSE

To compare intravitreous bevacizumab to other current treatments of branch retinal vein occlusion (BRVO) and hemisphere retinal vein occlusion (HRVO) with consideration to visual outcome, cost, convenience, and risk of treatment.

METHODS

This is a retrospective chart review from a large referral retina practice. The data comprise 56 patients with BRVO and HRVO treated by intravitreous bevacizumab, with and without intravitreous triamcinolone acetonide. Initial visual acuities at the time of first bevacizumab injection, best acuities through the follow-up time, final acuity at last visit before review, initial macular thickness, and final macular thickness were measured. Changes in vision and thickness were calculated, as were the percentage of eyes improving, stabilizing, and worsening.

RESULTS

The data were compared to composite data derived from several current treatments of BRVO. The subgroup of 39 eyes that received only bevacizumab without triamcinolone acetonide had the most improvement in vision. The median change in visual acuity was 1.5 lines (P = .012) over a mean follow-up of 8.8 months. Twenty-three eyes (59%) improved visually, with 20 eyes (51%) improving 2 or more lines. These results are similar to those for eyes that received argon grid laser and chorioretinal anastomosis, but are worse than in eyes that received arteriovenous adventitial sheathotomy, macular decompression surgery, and intravitreous triamcinolone acetonide.

CONCLUSIONS

Visual benefit from intravitreous bevacizumab compares well against laser treatments for BRVO and HRVO but not as well opposed to surgical techniques and intravitreous triamcinolone acetonide. Intravitreous bevacizumab injection has a risk, cost, and convenience profile that is favorable.

Retinal vein cannulation with prolonged infusion of tissue plasminogen activator (t-PA) for the treatment of experimental retinal vein occlusion in dogs

PURPOSE

To evaluate the feasibility, safety, and efficacy of local thrombolytic agents directly injected into occluded retinal veins in an experimental animal model.

DESIGN

Experimental animal study.

METHODS

This experimental study was performed in two phases. In phase 1, 15 enucleated porcine eyes and 8 in vivo canine eyes were used for the development of the instrumentation and surgical technique required for retinal vein cannulation with prolonged intravascular infusion. In phase 2 of this study, experimental branch retinal vein occlusion was photo-chemically created using an intravenous injection of rose bengal followed by diode laser photocoagulation in eight eyes of eight dogs. Four eyes were treated by retinal vein cannulation and an injection of tissue plasminogen activator (t-PA) using a specifically designed microcatheter, while the remaining four eyes were untreated (control group). The total amount of t-PA injected intravenously ranged from 400 to 1000 mug, infused over a period ranging from 25 to 45 minutes with a mean pressure of 40 psi, resulting in a mean injection flow rate of 0.05 ml/min. The dogs underwent clinical examination, fluorescein angiography, and histologic examination. Main outcome measures were: Achievement of prolonged intravascular infusion of t-PA, changes in fundus appearance, fluorescein angiography, and histology.

RESULTS

A microcatheter instrument and a surgical technique for retinal vein cannulation with prolonged intravascular infusion were developed. Cannulation and t-PA infusion for a period of at least 30 minutes was achieved in all four treated eyes with experimental branch retinal vein occlusion. No complications were recorded in all treated eyes. One week and 1 month postoperatively, treated eyes exhibited marked decreases in retinal hemorrhages, retinal vein dilation, and tortuosity, whereas nontreated eyes exhibited persistence of these findings. Fluorescein angiography demonstrated improved circulatory flow in treated relative to nontreated eyes. Histologic analysis confirmed the presence of thrombi in nontreated eyes only.

CONCLUSIONS

Retinal vein cannulation with prolonged intravascular injection of t-PA is feasible and safe, and this may offer a new treatment option for retinal vein occlusion.

Evaluation of functional defects in branch retinal vein occlusion before and after laser treatment with scanning laser perimetry

OBJECTIVE

This study was aimed at localizing and quantifying retinal defects in patients with branch retinal vein occlusion by means of scanning laser perimetry and analyzing the mechanism involved in the functional recovery after laser therapy.

DESIGN

Prospective nonrandomized clinical trial with concurrent comparison group.

PARTICIPANTS

Fifty-eight patients with isolated branch retinal vein occlusion. Thirty-nine eyes received laser treatment; 19 eyes were observed without treatment.

INTERVENTION

Argon laser photocoagulation was performed according to the Branch Vein Occlusion Study recommendations.

MAIN OUTCOME MEASURES

Retinal functional deficits were evaluated with scanning laser perimetry and fluorescein angiography first at baseline, at 3-month follow-up visits and 3 months after laser treatment.

RESULTS

After laser treatment, the scotoma encroached on foveal fixation in 31% of eyes, remained stable in 36%, and regressed from the foveal avascular zone in 33%. Improvement in vision was correlated with increasing scotoma distance from fixation. Total scotoma size increased in 50% of eyes after treatment. Depth of scotoma and degree of angiographic leakage showed no direct correlation.

CONCLUSIONS

Stabilization and increase in visual acuity after laser treatment did not correlate with an overall decrease in scotoma size. Improved central visual function seen in 25% of treated eyes appeared to be due to withdrawal of scotoma from the fovea.

Central retinal vein occlusion: review of management

Central retinal vein occlusion is usually a disease of the elderly and is often associated with systemic vascular disease, e.g., hypertension, diabetes mellitus, arteriosclerotic vascular disease. Younger patients, especially those less than 45 years of age, with retinal vein occlusion should be evaluated carefully for the possibility of an underlying thrombotic tendency. The authors describe the ocular manifestations, pathogenesis, associated conditions, patient evaluation, and treatment of patients with central retinal vein occlusion.

Laser-induced chorioretinal venous anastomosis for nonischemic central retinal vein occlusion: evaluation of the complications and their risk factors

PURPOSE

To evaluate the complications of laser-induced chorioretinal venous anastomosis in nonischemic central retinal vein occlusion (CRVO) and to identify the associated risks.

METHODS

A retrospective consecutive series of 91 eyes (91 patients) with nonischemic CRVO with a mean +/- SD duration of 15.0 +/- 15.2 weeks (range, 3 to 72 weeks )and corrected visual acuity reduced to 20/100 or less because of perfused macular edema were reviewed. All eyes had one or more anastomotic attempts using argon laser (combined with Nd-YAG laser in 46 eyes) and a minimum of 12 months of follow-up.

RESULTS

Successful chorioretinal venous anastomoses were created in 49 eyes (54%). Eighteen eyes (20%) had neovascular complications. These consisted of intravitreal, intraretinal, and subretinal neovascular membranes and were significantly associated with retinal ischemia (P < .001). There was avascular fibrous tissue proliferation at the anastomotic site in eight eyes (9%), and it was not associated with retinal ischemia (P = .727). No eye developed further capillary nonperfusion once an anastomosis became functional. A chorioretinal venous anastomosis was associated with improved vision (P < .001); 84% of eyes had an average +/- SD improvement of 4.3 +/- 3.8 lines (range, 2 to 20 lines), with the remaining 16% having no improvement or reduced vision.

CONCLUSION

The major vision-threatening complication of laser-induced chorioretinal venous anastomosis for nonischemic CRVO is neovascular membranes occurring at the anastomotic site; these are associated with retinal ischemia. Prompt laser photocoagulation to areas of retinal ischemia that develop after the anastomotic attempt has been made may reduce the risk and severity of this complication.

Laser chorioretinal venous anastomosis for nonischemic central retinal vein occlusion

OBJECTIVE

This study aimed to test the efficacy and safety of laser chorioretinal anastomosis for central retinal vein occlusion (CRVO).

DESIGN

The study design was a consecutive case series.

PARTICIPANTS

Eight eyes of eight patients were treated.

INTERVENTION

The argon laser was used in the method of McAllister and Constable to attempt to form an anastomosis. The patients were observed for 1 to 19 months (median, 11 months).

MAIN OUTCOME MEASURES

Visual acuity, anastomosis success, and complications were measured.

RESULTS

Twenty attempts to create anastomoses were made with 2 successful anastomoses but not of a therapeutic type. Three patients developed rubeosis, retinal neovascularization at the laser site, and vitreous hemorrhage. Traction retinal detachment occurred twice and neovascular glaucoma occurred once. Secondary panretinal photocoagulation, pars plana vitrectomy, and glaucoma seton were required in three patients, one patient, and one patient, respectively. Visual acuity improved in two patients independent of failed attempts at anastomosis creation and did not improve or worsened in six patients, including the two patients with the successfully created anastomoses.

CONCLUSION

Laser chorioretinal anastomosis for nonischemic CRVO has greater risks and less success than the initial report suggested. Further refinement of the technique is needed before it is adopted extensively. Even when successful, macular pigment epithelial scarring can limit vision, implying a relatively short time window for its effective application in the face of severe macular edema. Successful laser chorioretinal anastomosis does not preclude development of anterior segment neovascularization.

Optimal conditions required for the creation of an iatrogenic chorioretinal venous anastomosis in the dog using argon green laser photocoagulation

We have previously reported iatrogenic retinal to choroidal vein anastomosis, developed as a potential method of by-passing the site of obstruction to venous outflow in retinal venous occlusion in dogs (1), and in rats (2). In order to minimise tissue damage to the retina and choroid and increase the rate of success in these experiments, we investigated in the dog model the factors that would promote an anastomosis and compare the effects of three different power levels. A small spot size (50 microns) argon green laser beam of 514 nm at power levels of 0.5w, 1.5w and 2.5w were used. Spaced serial sections from each lesion were examined by light and by transmission electron microscopy. Morphometric measurements of the corresponding retinal pigment epithelium (RPE)/glial scar was computed using IBMPC digitising pad and sigma scan software and the extent of tissue damage at the different power levels assessed. At the lowest power level of 0.5w the damage to the retina was mild and there was an absence of anastomosis formation. At the 1.5w power level an anastomosis formed in 40% of the lesions. At the highest power level of 2.5w a 71% rate of success was obtained however, the damage to the retina tended to be severe. The results of this study also indicate that disruption of Bruch's membrane and vein rupture at the time of irradiation are essential for anastomosis formation, which may be further enhanced by necrotic tissue, retinal pigment epithelial and glial scar formation and inflammation. These findings are useful in establishing optimal conditions for the creation of a chorioretinal venous anastomosis, for consideration in human trials.

Significance of Bruch's membrane in the creation of iatrogenic chorioretinal venous anastomosis

Iatrogenic retinal to choroidal vein anastomoses, as a method of bypassing retinal venous occlusions has been reported in dogs in which Bruch's membrane is poorly formed. In order to determine whether chorioretinal venous anastomoses can be induced in an animal with a Bruch's membrane that is well developed as in humans, pigmented rats were chosen. A high intensity, small spot size argon green laser beam of 514 nm was used to induce the anastomosis. Three out of 5 rat eyes developed a retinal vein to choroidal vein anastomosis. The success rate of iatrogenic retinal to choroidal vein anastomoses in the rat was comparable to that obtained in the dog. This study suggests that Bruch's membrane was not significant in the creation of an iatrogenic chorioretinal venous anastomosis.