Retinal toxicity of commercial intravitreal tissue plasminogen activator solution in cat eyes

BACKGROUND

We previously reported retinal toxic reactions in rabbit eyes receiving intravitreal injections of commercial tissue plasminogen activator (tPA) in concentrations greater than or equal to 50 microg/0.1 mL, and recent clinical experience suggests that intravitreal tPA solution may produce toxic effects in human eyes. We therefore investigated the dose-dependent retinal toxicity of intravitreal commercial recombinant tPA solution in cat eyes, which have a vascularized inner retina and vitreous volume similar to that of human eyes.

METHODS

Commercial tPA in L-arginine solution was injected into the mid vitreous cavity of normal cat eyes in doses of 25, 50, 75, and 100 microg/0.1 mL and 200 microg/0.2 mL. Control (fellow) eyes received an equal volume of sterile saline solution. After injection, eyes were evaluated by ophthalmoscopy and electroretinography for 14 days and then enucleated for histopathological evaluation.

RESULTS

Fundus pigmentary alterations were observed in eyes receiving doses greater than or equal to 50 microg/0.1 mL. Changes were centered in the area around the injection site, and the area's size increased in proportion to the dosage. Mean electroretinography B-wave amplitude measured at 14 days was significantly reduced in eyes receiving greater than or equal to 50 microg of tPA in a dose-dependent fashion. Light microscopy of the involved areas showed loss of photoreceptor elements with necrosis and proliferation of the retinal pigment epithelium.

CONCLUSION

Intravitreal injection of commercial tPA solution results in dose-dependent retinal toxicity in cat eyes.

CLINICAL RELEVANCE

Because cat eyes are similar to human eyes regarding retinal vascularity and vitreous volume, intravitreal injections of commercial tPA (with L-arginine vehicle) in concentrations greater than 25 microg/0.1 mL are potentially unsafe in human eyes.

Globe tenting as a result of head trauma

Ocular tenting in the setting of acute trauma, inflammatory processes, or carotid cavernous fistulas is reported to be associated with a poor outcome with respect to visual acuity. Therefore, acute decompressive intervention is recommended for these patients. We report a case of acute posttraumatic ocular tenting with acute visual compromise that resolved over 4 days with conservative management and intravenous corticosteroid therapy.

Variations in the vascular pedicle of the rat gracilis muscle flap

The rat gracilis muscle is a reliable model for microsurgical research. Exploration of 364 inguinal regions and preparation of 80 free gracilis muscle flaps in Sprague-Dawley and Lewis rats revealed six distinct origins of the dominant arterial pedicle and four variations of the venous pedicle. Popliteal, external iliac, and truncus pudendoepigastricus associations are described for the first time in this study. The total incidence of atypical variation of arterial pedicle origin is 20.7 percent. The most common origin of muscular branch arteries are the superficial epigastric artery (53.3 percent), femoral artery (22.0 percent), popliteal artery (14.6 percent), and the external iliac arteries (5.5 percent). Muscular branch veins drain most frequently into the femoral vein (79.1 percent). Gracilis muscle flaps prepared from rats weighing 329 +/- 45 g weighed an average of 0.64 +/- 0.13 g, and their volume averaged 0.87 +/- 0.12 ml. Muscular branch artery and vein diameters (external) averaged 0.21 +/- 0.05 mm and 0.54 +/- 0.06 mm, respectively. This new anatomic information is essential for reproducible microsurgery research using the rat gracilis muscle.