Fluoroquinolone therapy in Mycobacterium chelonae keratitis after lamellar keratectomy.

PURPOSE: To characterize a rabbit model of Mycobacterium chelonae keratitis after lamellar keratectomy and assess the effectiveness of fluoroquinolone therapy. SETTING: University Laboratory, University of California, Irvine, California, USA. METHODS: Twenty-eight New Zealand white rabbits had unilateral lamellar keratectomy with placement of 2.5 x 10(5) colony-forming units of log-phase M chelonae under each flap. Eyes (7 per group) were randomized and treated with sterile balanced salt solution, gatifloxacin 0.3%, ciprofloxacin 0.3%, or levofloxacin 0.5% 4 times daily. Two masked observers examined all eyes on days 2, 5, and 7 and weekly for 4 weeks. Severity of disease and bacterial culture results were the main outcomes measured. The means and standard deviations were calculated, and differences between the groups were statistically analyzed. RESULTS: All eyes developed clinical disease. At the time the rabbits were killed, eyes treated with balanced salt solution, ciprofloxacin, levofloxacin, and gatifloxacin were culture positive in 6 (85.7%), 7 (100%), 6 (85.7%), and 3 (42.9%) of 7 eyes per group, respectively. Frequency of positive culture and the severity of clinical disease in gatifloxacin-treated eyes were significantly less (P < .05) than in the other groups combined. CONCLUSIONS: The rabbit model of M chelonae keratitis was successfully developed in our study. A fourth-generation quinolone (gatifloxacin) showed the best performance among the fluoroquinolones tested in our experimental approach. The fourth-generation fluoroquinolone, gatifloxacin, could be effectively used for the treatment of mycobacterial keratitis.

Intelligent tutoring systems.

Cognitive psychology, artificial intelligence, and computer technology have advanced to the point where it is feasible to build computer systems that are as effective as intelligent human tutors. Computer tutors based on a set of pedagogical principles derived from the ACT theory of cognition have been developed for teaching students to do proofs in geometry and to write computer programs in the language LISP.

Generating visual images: units and relations.

Three major conclusions were drawn from the results of the experiments reported in this article: First, mental images may be constructed by amalgamating images of individual parts, and an increment of time is required to add each additional part to an image. This was true when "parts" were defined by the Gestalt laws of proximity, continuity, or similarity, when parts of objects were presented on separate pages initially and the subject mentally "glued" them together into a single image, and when the number of parts was varied by altering the way an ambiguous geometric form was described. Second, descriptive information can be used in constructing images. Subjects were able to image scenes in accordance with descriptions that specified the relative distances between component objects of the scene. More time was required to form images of scenes containing more objects, and more time was later required to scan between two imaged objects if they were mentally pictured at greater distances. Third, the ease of imaging a unit depends on how much material is included in each unit and on how difficult it is to locate where the unit should be placed relative to the existing portions of an image. This conclusion was supported by the finding that subjects require less time to image arrays composed of units containing fewer letters and require less time if arrays are composed of relatively discriminable letters than if arrays are composed of relatively indiscriminable letters. Finally, in two of the experiments nonimagery control groups were tested to demonstrate that generating an image is not the same as simply retrieving memorized verbal information or reviewing information in some more abstract format.

Relationship of plasma amino acids to nitrogen balance and portal-systemic encephalopathy in alcoholic liver disease.

Plasma amino acids were compared in three groups of patients with alcoholic liver disease including stable cirrhosis, acute alcoholic hepatitis without portal-systemic encephalopathy, and cirrhosis with encephalopathy. In addition, plasma amino acids were correlated with nitrogen balance in patients with acute alcoholic hepatitis and with clinical improvement in patients with encephalopathy. Significant differences in plasma amino acids within these groups were present. Plasma amino acids did not change with improvement in portal-systemic encephalopathy, and abnormalities of plasma amino acids did not prevent maintenance or attainment of positive nitrogen balance in patients with acute alcoholic hepatitis.

Reversible hepatotoxicity associated with hepatic vitamin A accumulation in a protein-deficient patient.

A 62-yr-old white male presented with edema, protein malnutrition, and abnormal liver function. He had ingested from 40,000-50,000 IU of vitamin A per day for 7 yr. Examination of liver tissue by light and electron microscopy revealed findings characteristic of an excessive accumulation of vitamin A. Liver tissue contained massive amounts of vitamin A (19,000 IU/g); however, both the serum concentration of vitamin A and retinol-binding protein were below normal, and serum RBP was not saturated. On a normal diet the patient was able to mobilize hepatic vitamin A, as indicated 71 days later by a repeat biopsy of the liver, which then contained 9000 IU of vitamin A/g. During this time his nutrition improved, serum vitamin A rose, and serum RBP became transiently saturated. The amount of vitamin A ingested by this patient was less than that usually producing recognizable hepatotoxicity, and he had no extra hepatic manifestations of vitamin toxicity, consistent with a low serum vitamin A concentration and a low vitamin A to retinol-binding protein ratio. At presentation he was apparently unable to normally mobilize vitamin A from his liver, which may have been due to an accompanying protein deficiency.

Visual images preserve metric spatial information: evidence from studies of image scanning.

Four experiments demonstrated that more time is required to scan further distances across visual images, even when the same amount of material falls between the initial focus point and the target. Not only did times systematically increase with distance but subjectively larger images required more time to scan than did subjectively smaller ones. Finally, when subjects were not asked to base all judgments on examination of their images, the distance between an initial focus point and a target did not affect reaction times.