A Pilot Study of Peribulbar Triamcinolone Acetonide for Diabetic Macular Edema

Diabetic Macular Edema

diabetic, macular, edema, peribulbar, triamcinolone, acetonide, laser, photocoagulation, intraocular, DME

The study involves the enrollment of patients over 18 years of age with diabetic macular edema involving the center of the macula who have not already been given maximal laser treatment. Patients with one study eye will be randomly assigned (stratified by prior laser) with equal probability to one of five treatment groups: 1. Focal laser photocoagulation (modified ETDRS technique) 2. Posterior peribulbar injection of 40 mg triamcinolone (Kenalog) 3. Anterior peribulbar injection of 20 mg triamcinolone 4. Posterior peribulbar injection of 40 mg triamcinolone followed after one month by laser 5. Anterior peribulbar injection of 20 mg triamcinolone followed after one month by laser For patients with two study eyes (both eyes eligible at the time of randomization), the right eye (stratified by prior laser) will be randomly assigned with equal probabilities to one of the five treatment groups listed above. If the right eye was assigned to laser only, then the left eye will be assigned to one of the four triamcinolone groups above with equal probability (stratified by prior laser). If the right eye was assigned to receive triamcinolone, then the left eye will receive laser only. Triamcinolone acetonide will be the corticosteroid utilized in this study. The triamcinolone acetonide preparation to be used is Kenalog. Kenalog is manufactured by Bristol Myers Squibb and is approved by the Food and Drug Administration for intramuscular use for a variety of indications. Peribulbar injections of Kenalog have been used for a wide variety of ocular conditions, particularly uveitis and post-cataract extraction cystoid macular edema, for many years. Two different triamcinolone regimens will be assessed in the study: 40 mg injected posteriorly and 20 mg injected anteriorly. There is no indication of which treatment regimen will be better. Although the injection behind the eye is more common than the injection near the front of the eye, the injection near the front of the eye has less risk of injuring the eye. However, it is possible that the injection near the front of the eye may increase eye pressure more frequently. Little is known about which of the two injections decreases macular edema and improves vision more often. Patients enrolled into the study will be followed for three years and will have study visits 1 month, 2 months, 4 months, 8 months and annually after receiving their assigned study treatment. For the first 8 months of the study, patients should only be retreated with their randomized treatment. However, if the patient's visual acuity has decreased by 15 letters or more, then any treatment may be given at the investigator's discretion. After completion of the 8-month visit, treatment is at investigator discretion. The primary objective of this study is to obtain estimates of efficacy and safety outcomes for each of the treatment groups. These estimates will provide a basis for the sample size estimation and hypothesis generation in a phase III trial.

Diabetic retinopathy is a major cause of visual impairment in the United States. Diabetic macular edema (DME) is a manifestation of diabetic retinopathy that produces loss of central vision. Data from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) estimate that after 15 years of known diabetes, the prevalence of diabetic macular edema is approximately 20% in patients with type 1 diabetes mellitus (DM), 25% in patients with type 2 DM who are taking insulin, and 14% in patients with type 2 DM who do not take insulin. Diabetic macular edema results from abnormal leakage of macromolecules, such as lipoproteins, from retinal capillaries into the extravascular space followed by an oncotic influx of water into the extravascular space. Abnormalities in the retinal pigment epithelium may also cause or contribute to diabetic macular edema. These abnormalities may allow increased fluid from the choriocapillaries to enter the retina or they may decrease the normal efflux of fluid from the retina to the choriocapillaris. The mechanism of breakdown of the blood retina barrier at the level of the retinal capillaries and the retinal pigment epithelium may be due to changes to tight junction proteins such as occludin. The increase in retinal capillary permeability and subsequent retinal edema may be the result of a breakdown of the blood retina barrier mediated in part by vascular endothelial growth factor (VEGF), a 45 kD glycoprotein. Aiello et al, demonstrated in an in vivo model that VEGF can increase vascular permeability. Fifteen eyes of 15 albino Sprague-Dawley rats received an intravitreal injection of VEGF. The effect of intravitreal administration of VEGF on retinal vascular permeability was assessed by vitreous fluorophotometry. In all 15 eyes receiving an intravitreal injection of VEGF, a statistically significant increase in vitreous fluorescein leakage was recorded. In contrast, control eyes, which were fellow eyes injected with vehicle alone, did not demonstrate a statistically significant increase in vitreous fluorescein leakage. Vitreous fluorescein leakage in eyes injected with VEGF attained a maximum of 227% of control levels. Antonetti et al, demonstrated that VEGF may regulate vessel permeability by increasing phosphorylation of tight junction proteins such as occludin and zonula occluden 1. Sprague-Dawley rats were given intravitreal injections of VEGF and changes in tight junction proteins were observed through Western blot analysis. Treatment with alkaline phosphatase revealed that these changes were caused by a change in phosphorylation of tight junction proteins. This model provides, at the molecular level, a potential mechanism for VEGF-mediated vascular permeability in the eye. Similarly, in human non-ocular disease states such as ascites, VEGF has been characterized as a potent vascular permeability factor (VPF). The normal human retina contains little or no VEGF; however, hypoxia causes upregulation of VEGF production. Vinores et al, using immunohistochemical staining for VEGF, demonstrated that increased VEGF staining was found in retinal neurons and retinal pigment epithelium in human eyes with diabetic retinopathy. As the above discussion suggests, attenuation of the effects of VEGF provides a rationale for treatment of macular edema associated with diabetic retinopathy. Corticosteroids, a class of substances with anti-inflammatory properties, have been demonstrated to inhibit the expression of the VEGF gene. In a study by Nauck et al, the platelet-derived growth-factor (PDGF) induced expression of the VEGF gene in cultures of human aortic vascular smooth muscle cells was abolished by corticosteroids in a dose-dependent manner. A separate study by Nauck et al demonstrated that corticosteroids abolished the induction of VEGF by the pro-inflammatory mediators PDGF and platelet-activating factor (PAF) in a time and dose-dependent manner. This study was performed using primary cultures of human pulmonary fibroblasts and pulmonary vascular smooth muscle cells. As discussed above, corticosteroids have been experimentally shown to down regulate VEGF production and possibly reduce breakdown of the blood-retinal barrier. Similarly, steroids have anti-angiogenic properties possibly due to attenuation of the effects of VEGF. Both of these steroid effects have been utilized. For example, triamcinolone acetonide is often used clinically as a periocular injection for the treatment of cystoid macular edema (CME) secondary to uveitis or as a result of intraocular surgery. In animal studies, intravitreal triamcinolone acetonide has been used in the prevention of proliferative vitreoretinopathy and retinal neovascularization. Intravitreal triamcinolone acetonide has been used clinically in the treatment of proliferative vitreoretinopathy and choroidal neovascularization.

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