Comparison of Photocoagulation with the Argon, Krypton, and Diode Laser Indirect Ophthalmoscopes in Rabbit Eyes Jeffrey D. Benner, MD, Morgan Huang, MD, Lawrence S. Morse, MD, PhD, Leonard M. Hjelmeland, PhD, Maurice B. Landers III, MD Purpose: The purpose of this study is to compare photocoagulation with the argon green, krypton red, and diode infrared laser indirect ophthalmoscopes in an experimental setting. Methods: Photocoagulation was performed with each of the laser indirect ophthalmoscopes in a grid pattern within one sector of the same eye of 14 Dutch-belted rabbits. Treatment was performed either with or without scleral depression. Measurements of the retinal burn diameters were performed after hemisecting the globes, and the burns were examined with light microscopy. Results: Variation in burn intensity and diameter (10% to 28%) was common with all 3 laser indirect ophthalmoscopes. Five times more output energy was required to make equivalent burns with the diode laser indirect ophthalmoscope than with the argon or krypton laser indirect ophthalmoscopes. Choriovitreal hemorrhages only occurred during scleral depression. Histopathologically, the argon green laser indirect ophthalmoscope burns spared the choroid and inner sclera, while the intense krypton and diode burns had full-thickness choroidal involvement and even thermal injury to the inner sclera. Scleral depression reduced the mean energy required to create equivalent burns with all three laser indirect ophthalmoscopes. There was a 10% to 40% reduction in the mean retinal burn diameter with scleral depression (argon green, P < 0.0005; krypton red, P < 0.0005; and diode, P < 0.025). Conclusion: Photocoagulation with the argon green, krypton red, or diode infrared laser indirect ophthalmoscopes is a safe and effective method of retinal ablation. Decreasing the posterior nodal distance of the eye with scleral depression will produce a smaller spot on the retina with the laser indirect ophthalmoscope. Ophthalmology 1992;99: 1554-1563

Since its introduction in 1981,1 the laser indirect ophthalmoscope has been assimilated quickly into mainstream use in clinical vitreoretinal practice. Because of its wide field view and versatility, it offers a number of advantages

Originally received: February 27, 1992. Revision accepted: May 18, 1992. From the Retina Service, Department of Ophthalmology, University of California, Davis, Sacramento. Presented in part at the Association for Research in Vision and Ophthalmology Annual Meeting, Sarasota, May 1992. Supported in part by a grant from IRIS Medical, Inc, Mountain View, California.

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over the traditional slit-lamp and endoprobe delivery sys~ terns. It has been used to photocoagulate the extreme peripheral retina, to facilitate laser treatment in eyes with intraocular gas bubbles, to perform panretina! photocoagulation with the patient in a supine position,2.3 and to treat stage 3+ retinopathy ofprematurity.4-6 Disadvantages of the laser indirect ophthalmoscope include the inherent instability of its optical delivery system and a 5- to 7-fold decrease in magnification compared with slit-lamp delivery. None of the authors has a proprietary interest in the development or marketing of any of the lasers or other equipment used in this study. Reprint requests to Maurice B. Landers III, MD, The Center for Retina Vitreous Surgery, 6401 Poplar Ave, Suite 190, Memphis, TN 38119.

Benner et al . Comparison of Laser Indirect Ophthalmoscopes At present, there are laser indirect ophthalmoscopes available that deliver argon green and blue-green, krypton red, and diode near infrared laser irradiation. The argon and krypton gas ion lasers have been evaluated extensively.7-9 The diode laser, which only recently has been introduced to ophthalmologic practice, \0 has a high energy conversion efficiency because of the properties inherent to its semiconductor technology. It converts up to 50% of the input electrical energy into laser output energy I I compared with