A Randomized Trial Comparing Intravitreal Triamcinolone Acetonide and Laser Photocoagulation for Diabetic Macular Edema

• To determine whether intravitreal triamcinolone acetonide injections at doses of 1mg or 4mg produce greater benefit, with an acceptable safety profile, than macular laser photocoagulation in the treatment of diabetic macular edema.
• To compare the efficacy and safety of the 1mg and 4mg triamcinolone acetonide doses.

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.

In a review of three early studies concerning the natural history of diabetic macular edema, Ferris and Patz found that 53% of 135 eyes with diabetic macular edema, presumably all involving the center of the macula, lost two or more lines of visual acuity over a two year period. In the Early Treatment Diabetic Retinopathy Study (ETDRS), 33% of 221 untreated eyes available for follow-up at the 3-year visit, all with edema involving the center of the macula at baseline, had experienced a 15 or more letter decrease in visual acuity score (equivalent to a doubling of the visual angle, e.g., 20/25 to 20/50, and termed “moderate visual acuity loss”).

In the ETDRS, focal/grid photocoagulation of eyes with clinically significant macular edema (CSME) reduced the risk of moderate visual loss by approximately 50% (from 24% to 12%, three years after initiation of treatment). Therefore, 12% of treated eyes developed moderate visual loss in spite of treatment. Furthermore, approximately 40% of treated eyes that had retinal thickening involving the center of the macula at baseline still had thickening involving the center at 12 months, as did 25% of treated eyes at 36 months.

Although several treatment modalities are currently under investigation, the only demonstrated means to reduce the risk of vision loss from diabetic macular edema are laser photocoagulation, as demonstrated by the ETDRS, and intensive glycemic control, as demonstrated by the Diabetes Control and Complications Trial (DCCT) and the United Kingdom Prospective Diabetes Study (UKPDS). In the DCCT, intensive glucose control reduced the risk of onset of diabetic macular edema by 23% compared with conventional treatment. Long-term follow-up of patients in the DCCT show a sustained effect of intensive glucose control, with a 58% risk reduction in the development of diabetic macular edema for the DCCT patients followed in the Epidemiology of Diabetes Interventions and Complications Study.

The frequency of an unsatisfactory outcome following laser photocoagulation in some eyes with diabetic macular edema has prompted interest in other treatment modalities. One such treatment is pars plana vitrectomy. These studies suggest that vitreomacular traction, or the vitreous itself, may play a role in increased retinal vascular permeability. Removal of the vitreous or relief of mechanical traction with vitrectomy and membrane stripping may be followed by substantial resolution of macular edema and corresponding improvement in visual acuity. However, this treatment may be applicable only to a specific subset of eyes with diabetic macular edema. It also requires a complex surgical intervention with its inherent risks, recovery time, and expense. Other treatment modalities such as pharmacologic therapy with oral protein kinase C inhibitors and antibodies targeted at vascular endothelial growth factor (VEGF) are under investigation. The use of intravitreal corticosteroids is another treatment modality that has generated recent interest.

The optimal dose of corticosteroid to maximize efficacy with minimum side effects is not known. A 4mg dose of Kenalog is principally being used in clinical practice. However, this dose has been used based on feasibility rather than scientific principles.

There is also experience using Kenalog doses of 1mg and 2mg. These doses anecdotally have been reported to reduce the macular edema. There is a rationale for using a dose lower than 4mg. Glucocorticoids bind to glucocorticoid receptors in the cell cytoplasm, and the steroid-receptor complex moves to the nucleus where it regulates gene expression. The steroid-receptor binding occurs with high affinity (low dissociation constant (Kd) which is on the order of 5 to 9 nanomolar). Complete saturation of all the receptors occurs about 20-fold higher levels, i.e., about 100-200 nanomolar. A 4mg dose of triamcinolone yields a final concentration of 7.5 millimolar, or nearly 10,000-fold more than the saturation dose. Thus, the effect of a 1mg dose may be equivalent to that of a 4mg dose, because compared to the 10,000-fold saturation, a 4-fold difference in dose is inconsequential. It is also possible that higher doses of corticosteroid could be less effective than lower doses due to down-regulation of the receptor. The steroid implant studies provide additional justification for evaluating a lower dose, a 0.5mg device which delivers only 0.5 micrograms per day has been observed to have a rapid effect in reducing macular edema.

In the trial, 4mg and 1mg doses will be evaluated. The former will be used because it is the dose that is currently most commonly used in clinical practice and the latter because there is reasonable evidence for efficacy and the potential for lower risk. Although there is good reason to believe that a 1mg dose will reduce the macular edema, it is possible that the retreatment rate will be higher with this dose compared with 4mg since the latter will remain active in the eye for a longer duration than the former. Insufficient data are available to warrant evaluating a dose higher than 4mg at this time.

The study involves the enrollment of patients over 18 years of age with diabetic macular edema. Patients with one study eye will be randomly assigned (stratified by visual acuity and prior laser) with equal probability to one of the three treatment groups:

For patients with two study eyes (both eyes eligible at the time of randomization), the right eye (stratified by visual acuity and prior laser) will be randomly assigned with equal probabilities to one of the three treatment groups listed above. The left eye will be assigned to the alternative treatment (laser or triamcinolone). If the left eye is assigned to triamcinolone, then the dose (1mg or 4 mg) will be randomly assigned to the left eye with equal probability (stratified by visual acuity and prior laser).

The study drug, triamcinolone acetonide, has been manufactured as a sterile intravitreal injectable by Allergan. Study eyes assigned to an intravitreal triamcinolone injection will receive a dose of either 1mg or 4mg. There is no indication of which treatment regimen will be better.

Patients enrolled into the study will be followed for three years and will have study visits every 4 months after receiving their assigned study treatment. In addition, standard of care post-treatment visits will be performed at 4 weeks after each intravitreal injection.

Subject-level Criteria

Exclusion Criteria

A patient is not eligible if any of the following exclusion criteria (7-13) are present:

Study Eye Eligibility

Inclusion

a. Best corrected E-ETDRS visual acuity score of ≥ 24 letters (i.e., 20/320 or better) and ≤73 letters (i.e., 20/40 or worse).
b. Definite retinal thickening due to diabetic macular edema based on clinical exam involving the center of the macula.
c. Mean retinal thickness on two OCT measurements ≥250 microns in the central subfield.
d. Media clarity, pupillary dilation, and patient cooperation sufficient for adequate fundus photographs.

Exclusion

e. Macular edema is considered to be due to a cause other than diabetic macular edema.
f. An ocular condition is present such that, in the opinion of the investigator, visual acuity would not improve from resolution of macular edema (e.g., foveal atrophy, pigmentary changes, dense subfoveal hard exudates, nonretinal condition).
g. An ocular condition is present (other than diabetes) that, in the opinion of the investigator, might affect macular edema or alter visual acuity during the course of the study (e.g., vein occlusion, uveitis or other ocular inflammatory disease, neovascular glaucoma, Irvine-Gass Syndrome, etc.)
h. Substantial cataract that, in the opinion of the investigator, is likely to be decreasing visual acuity by 3 lines or more (i.e., cataract would be reducing acuity to 20/40 or worse if eye was otherwise normal).
i. History of prior treatment with intravitreal corticosteroids.
j. History of peribulbar steroid injection within 6 months prior to randomization.
k. History of focal/grid macular photocoagulation within 15 weeks (3.5 months) prior to randomization.Note: Patients are not required to have had prior macular photocoagulation to be enrolled. If prior macular photocoagulation has been performed, the investigator should believe that the patient may possibly benefit from additional photocoagulation.
l. History of panretinal scatter photocoagulation (PRP) within 4 months prior to randomization.
m. Anticipated need for PRP in the 4 months following randomization.
n. History of prior pars plana vitrectomy.
o. History of major ocular surgery (including cataract extraction, scleral buckle, any intraocular surgery, etc.) within prior 6 months or anticipated within the next 6 months following randomization.
p. History of YAG capsulotomy performed within 2 months prior to randomization.
q. Intraocular pressure ≥25 mmHg.
r. History of open-angle glaucoma (either primary open-angle glaucoma or other cause of open-angle glaucoma.) Note: Angle-closure glaucoma is not an exclusion. A history of ocular hypertension is not an exclusion as long as (1) intraocular pressure is <25 mm Hg, (2) the patient is using no more than one topical glaucoma medication, (3) the most recent visual field, performed within the last 12 months, is normal (if abnormalities are present on the visual field they must be attributable to the patient's diabetic retinopathy), and (4) the optic disc does not appear glaucomatous. If the intraocular pressure is 22 to <25 mm Hg, then the above criteria for ocular hypertension eligibility must be met.
s. History of steroid-induced intraocular pressure elevation that required IOP-lowering treatment.
t. History of prior herpetic ocular infection.
u. Exam evidence of ocular toxoplasmosis.
v. Aphakia.
w. Exam evidence of pseudoexfoliation.
x. Exam evidence of external ocular infection, including conjunctivitis, chalazion, or significant blepharitis.

In patients with only one eye meeting criteria to be a study eye at the time of randomization, the fellow eye must meet the following criteria:

No longer recruiting. Comments: Recruitment has ended.

Completed, with results published. Comments: The Diabetic Retinopathy Clinical Research Network: A Randomized Trial Comparing Intravitreal Triamcinolone Acetonide and Focal/Grid Photocoagulation for Diabetic Macular Edema. Am J Ophthalmol 115 : 1447-9 , 2008

At 4 months, mean visual acuity was better in the 4-mg triamcinolone group than in either the laser group (P<0.001) or the 1-mg triamcinolone group (P = 0.001). By 1 year, there were no significant differences among groups in mean visual acuity. At the 16-month visit and extending through the primary outcome visit at 2 years, mean visual acuity was better in the laser group than in the other 2 groups (at 2 years, P = 0.02 comparing the laser and 1-mg groups, P = 0.002 comparing the laser and 4-mg groups, and P = 0.49 comparing the 1-mg and 4-mg groups). Treatment group differences in the visual acuity outcome could not be attributed solely to cataract formation. Optical coherence tomography results generally paralleled the visual acuity results. Intraocular pressure increased from baseline by 10 mmHg or more at any visit in 4%, 16%, and 33% of eyes in the 3 treatment groups, respectively, and cataract surgery was performed in 13%, 23%, and 51% of eyes in the 3 treatment groups, respectively. Over a 2-year period, focal/grid photocoagulation is more effective and has fewer side effects than 1-mg or 4-mg doses of preservative-free intravitreal triamcinolone for most patients with DME who have characteristics similar to the cohort in this clinical trial. The results of this study also support that focal/grid photocoagulation currently should be the benchmark against which other treatments are compared in clinical trials of DME.