Cellular mechanisms of iris neovascularization secondary to retinal vein occlusion

Puncture-Induced Iris Neovascularization as a Mouse Model of Rubeosis Iridis

We describe a model of puncture-induced iris neovascularization as a general model for noninvasive evaluation of angiogenesis. The model is also relevant for targeting neovascular glaucoma, a sight-threatening complication of diabetic retinopathy. This method is based on the induction of iris vascular response by a series of self-sealing uveal punctures on BALB/c mice and takes advantage of the postpartum maturation of mouse ocular vasculature. Mouse pups undergo uveal punctures from postnatal day 12.5, when the pups naturally open their eyes, until postnatal day 24.5. Due to the transparency of the cornea, iris vasculature can be analyzed easily through time by noninvasive in vivo methods. Furthermore, the semitransparent iris of BALB/c mice can be flatmounted for detailed immunohistologic analysis with minimal non-specific background staining. In this model, angiogenesis is mainly driven by the inflammatory and plasminogen activating systems. The puncture-induced model is the first to induce iris neovascularization in small rodents, and has the advantage of allowing direct noninvasive in vivo analysis of the angiogenic process. Moreover, the model can be combined with angiogenic modulating substances, which highlights its potential in the study of angiogenesis with an in vivo perspective.

[Prophylactic pan-coagulation from ischemic central vein occlusions? Practicability of the results from the Central Vein Occlusion Study Group]

PURPOSE

Central vein occlusions (CVO) with an avascular area of more than 10 optic-disc areas are classified as ischemic by the Central Vein Occlusion Study Group (CVOSG). For patients without neovascularizations (NV) clinical controls every 4 weeks during the first 6 months are recommended instead of prophylactic pancoagulation (PC). In this study we examined the practicability of this recommendation.

PATIENTS AND METHODS

We analysed the records of 15 patients with ischemic CVO and no clinical signs of NV and no prophylactic PC retrospectively. All these patients developed a neovascular glaucoma (NVG) despite using the criteria of the CVOSG and were then treated with cyclophotocoagulation (CPC).

RESULTS

The time between first presentation and CPC was 4.4+/-2.9 months. Of these patients 7 developed a NVG within 4 weeks after initial presentation.

CONCLUSIONS

This study shows that NV and NVG may develop much faster than 4 weeks and can already be irreversible. Therefore it seems advisable to follow-up patients with increased risk factors even more frequently especially during the initial phase after CVO.

Iris fluorescein angiography in clinical practice

Iris fluorescein angiography is a valuable technique for elucidating a wide range of eye pathologies, among them developmental anomalies, degenerative disease, retinal vascular occlusions, diabetic microangiopathy, uveitis of various etiologies, glaucoma, tumor, and surgical or accidental trauma. In fact, IFA is more sensitive than biomicroscopy in the evaluation of iris abnormalities. Moreover, it provides indirect but reliable information on the retinal circulation when this cannot be examined directly. Some of the most important clinical applications involve the early detection of iris new vessels, cataract management in diabetic patients, and monitoring of iris tumors. Equipment, procedures, and fluorescein angiography patterns in normal and disease states are described and extensively illustrated. More widespread use of this valuable technique is encouraged.

Experimental preretinal neovascularization by laser-induced venous thrombosis in rats

PURPOSE

Retinal ischemia and neovascularization (NV) are important components of many retinal disorders. To facilitate further investigation of retinal ischemia and neovascularization, we sought to develop a reproducible in vivo experimental model of venous occlusion by photodynamic thrombosis in rats.

METHODS

After anesthesia, 27 eyes of pigmented rats received an intraperitoneal injection of 0.2 ml of, 10% sodium fluorescein 15 minutes prior to laser treatment. With a blue-green argon laser, selected venous sites next to the optic nerve head were photocoagulated indirectly with a 78 diopter lens. Venous occlusion was accomplished using laser parameters of 1.0 second, 50 microns, and 50-100 mW. For a control group, 10 eyes were coagulated on the retina between major vessels using the same parameters after fluorescein injection. For a second control group, 1% sodium hyaluronate was injected into the subretinal space to make a long-standing retinal detachment in 5 eyes.

RESULTS

With 1-8 laser impulses, each venous occlusion was obtained and was associated with extreme venous constriction and tortuousity. Retinal edema became evident 10-30 minutes after treatment in the sectors associated with the occluded veins. This edema became a bullous retinal detachment (RD) within 12 hours and intra-retinal hemorrhage was observed. The retinal edema continued for 3-10 days and the retinas reattached spontaneously. Prior to or after retinal reattachment 70% (19/27) of eyes developed retinal NV and tractional RD. Of these, 11 developed NV of the optic disc (NVD), 6 developed NV elsewhere (NVE), and 2 developed NVD and NVE. In 30% (8/27) of the eyes, retinal edema resolved without evidence of NV. In control groups no eyes showed either circulatory disorders or evidence of NV.

CONCLUSIONS

This is a new model of retinal ischemia and associated neovascularization established by venous thrombosis that is easily reproducible. Many aspects of rat retinal physiology are known and this model has promise as an avenue for further investigation.

Regression of experimental iris neovascularization with systemic alpha-interferon

BACKGROUND

Intraocular neovascularization leads to visual loss in many eye diseases, including diabetic retinopathy, age-related macular degeneration, and neovascular glaucoma. Current treatment relies on laser photocoagulation, involving the destruction of functional retinal tissue. A pharmacologic treatment directed at the newly growing vessels would represent a major advance.

METHODS

The authors investigated the effect of systemic alpha-interferon in an experimental model of iris neovascularization in cynomolgus monkeys. Alpha-interferon was administered systemically to animals with angiographically documented iris neovascularization.

RESULTS

Animals in the treatment group showed regression of neovascularization angiographically and histologically in eight of eight eyes. Control animals with documented iris neovascularization, followed without drug treatment, showed progression of the neovascularization in three of three eyes.

CONCLUSION

Systemic alpha-interferon led to inhibition of neovascularization and regression of new vessels in an experimental model of iris neovascularization. This represents the first successful, controlled treatment of experimental neovascularization in the eye using a systemic drug directed specifically at the neovascular tissue.