Diabetes Mellitus Clinical Trial
To evaluate whether red krypton laser treatment is as effective at causing regression of
diabetic disc neovascularization as treatment with the blue-green argon laser, when both
lasers are used with identical panretinal photocoagulation patterns.
To assess the vision of study patients.
To test the feasibility of a prototype NEI-sponsored multicenter clinical trial in which
participating clinics are not financially reimbursed and in which both the Coordinating and
Fundus Photograph Reading Center functions are carried out by staff of the NEI Biometry and
Epidemiology Program.
The KARNS was a randomized clinical trial designed to compare the effectiveness of argon and
krypton laser photocoagulation in causing the regression of preexisting neovascularization
on the disc (NVD) in diabetic retinopathy. The main theoretical advantage for the krypton
laser in the treatment of diabetic retinopathy is that the red laser beam penetrates blood
and may be more effective in making burns in the pigment epithelium in eyes with vitreous
hemorrhage.
The burns produced by the krypton laser in the retina are different from those produced by
the argon laser. Specifically, the burns from the krypton laser do not involve the inner
retina. Also, the krypton laser spares the nerve fiber layer near the macula. In contrast,
nerve fiber layer burns are common with the argon laser. Pigment epithelium and outer
segments are usually destroyed by both krypton and argon photocoagulation, but there is no
uptake of energy by the vascular tissues within the retina when krypton photocoagulation is
used. Further, krypton treatment is more effective in penetrating nuclear sclerosis of the
lens and can be used to treat some diabetic eyes with this condition that cannot be treated
with the argon laser.
In the KARNS, patients with diabetic retinopathy and NVD of one-third disc area or greater
in extent were assigned at random to either argon or krypton laser scatter photocoagulation
(panretinal photocoagulation). The null hypothesis was that each treatment would result in a
similar proportion of eyes having regression of the NVD by 3 months. The KARNS pilot study
affirmed the benefits of argon laser photocoagulation in the treatment of proliferative
diabetic retinopathy, as demonstrated in the NEI-supported Diabetic Retinopathy Study
conducted a decade ago. (See publication list.) The KARNS study sought to determine whether
use of the krypton laser could be as effective as the argon laser in causing regression of
diabetic neovascularization, but with fewer side effects (such as smaller loss of central
visual acuity).
Thirty-two nationwide clinical centers participated initially in this multicenter clinical
trial. Following the initial study examination, the baseline examination and fundus
photographs were obtained within 1 week before application of photocoagulation. Study
followup visits occurred at 3 months and 1 year after entry in the study. Additional visits
were scheduled as clinically necessary.
The specific techniques for photocoagulation were similar for both argon and krypton scatter
photocoagulation. Scatter (panretinal) photocoagulation consisted of 1,600 to 2,000 burns
placed 0.5 to 1 burn width apart. Burns of moderate intensity (whiteness) and 500 ??m in
size at the retina were required. The burns were applied to the retinal periphery no closer
than 2 disc diameters from the center of the fovea and 500 ??m from the margin of the optic
disc.
In December 1985, the Early Treatment Diabetic Retinopathy Study groups reported that focal
photocoagulation was effective in reducing the rates of moderate visual loss in patients
with clinically significant diabetic macular edema. The KARNS protocol was then changed to
allow focal treatment for clinically significant macular edema in all study participants and
to allow an eye that had previous focal photocoagulation for macular edema to become
eligible for study.
The study primary end point was regression of NVD, as assessed on the 3-month visit stereo
fundus photographs of the disc, to less than one-third disc area in extent. Secondary end
points included change in extent of NVD, change in visual acuity after photocoagulation,
development of fibrous tissue proliferation, and change or development of macular traction
lines.
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Allocation: Randomized, Primary Purpose: Treatment
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