Fiber optics is known to constitute a highly desirable transmission medium for a flexible, versatile laser retinal photocoagulator system. However, it had not been possible to deliver the high average power and high radi-ance required for photocoagulation through fibers due to their inability to sustain high transmittance under intense laser radiation. The development of a special core glass for fiber optics has now made it possible to reli-ably transmit CW power densities of 5 x 104 W/cm2 and maintain output radiance of 106 W/cm2/sr in the blue-green region of the spectrum. This performance has made it possible to design a compact argon laser retinal photocoagulator system which can be coupled to a direct or indirect ophthalmoscope delivery system, or be provided with a light-weight slit lamp adaptor for use with standard slit lamp instruments. Two incidental advantages of fiber optics transmission are increased uniformity of irradiance over the exposed area in the eye, and a convergence cone angle within the eye which is virtually independent of spot size.