The excimer laser offers entirely new corneal surgery procedures. In this paper, we describe conditions for one such procedure, photorefractive keratectomy, the direct reshaping of the cornea's central optical zone using tissue ablation with far ultraviolet radiation. We present equations for the required tissue ablation to achieve required refractive corrections. Conditions for beam uniformity are presented and a method of achieving better beam uniformity using beam integration by rotation is demonstrated. The healing of rabbit corneas after area ablation was observed. Five days after treatment, the surface quality of deep cuts was very irregular; the shallow cuts produced more regular results, as predicted by our calculations of beam characteristics.

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. Using an antibody specific for creatine phosphokinase (CPK), we have discovered an association between that enzyme and the cytoskeleton . Immunofluorescence observations show that CPK is associated with intermediate filaments in PTK cells and BALB/3T3 cells . The CPK distribution also follows intermediate filaments when cells are treated with colchicine .Intermediate (10-nm) filaments, microtubules, and actin filaments in the cytoplasm of cells contribute to a fibrous network known as the cytoskeleton. The role of microtubules in maintaining cell shape (10) and in organizing components of the cytoplasm (3, 7, 23) has been demonstrated in many systems (see also reference 28 for review). Intermediate filaments have been receiving increasing attention recently and are considered to be an integral part of the cytoskeleton as well . The distribution of these filaments has been determined in cultured cells by immunocytochemical methods (19) as well as in cytoskeleton models prepared by extraction with Triton X-100 (2, 25). The configuration of these filaments throughout the cytoplasm of many cells suggests a structural or supporting role (9). Desmin, a structural protein in skeletal muscle (15), is found as a component of intermediate filaments in embryonic chick cells (14), suggesting a structural role for these filaments.Although the configuration of these structural elements, as well as the characterization of their proteins, is well documented, less is known about the source of energy that may be used by contractile activities requiring cytoskeletal support. In muscle, it is well known that ATP is supplied by mitochondria . In addition, creatine phosphokinase (CPK) catalyzes the generation of ATP from creatine phosphate and ADP, maintaining an equilibrium . Thus, creatine phosphate serves as a energy source, readily converted into ATP. CPK has long been known as a mitochondrial constituent (24) where it likely catalyzes the formation of creatine phosphate from ATP and creatine . Much of the CPK is soluble, and recent evidence has shown that CPK may be found in the M-line of striated muscle (31, 33) as well as in mitochondria (24) . Immunological analysis has shown that antibodies specific for CPK will react with purified M-line protein, verifying the presence of CPK on the M-line (30) .

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