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Biomedical subjects

H W Kwak

Publications and source records attributed to H W Kwak.

7 recordsLinked to original sources
PubMed1992

Evaluation of the retinal toxicity and pharmacokinetics of dexamethasone after intravitreal injection.

The intravitreal injection of steroids may be potentially useful in the treatment of endophthalmitis and other ocular inflammatory diseases. The retinal toxicity and intraocular turnover of aqueous solutions of dexamethasone sodium phosphate in doses ranging from 440 to 4000 micrograms were evaluated in the rabbit; evaluation was also performed for a 0.1-mL injection of a commercially available preparation (dexamethasone phosphate [Decadron] injection, 4 mg/mL). After the 440-micrograms dose, a transient increase in staining of the Müller cells was observed, which normalized after 2 days. Progressively higher doses resulted in an increasing spectrum of disorganization in Müller and other retinal cells. The half-life of the intravitreally injected drug was 3.48 hours. These findings suggest a primary interference in Müller cell function, possibly through dexamethasone-induced alterations in retinal glutamate or glucose metabolism.

Animals↗
PubMed1992

Intravitreal antibiotic therapy with vancomycin and aminoglycoside: examination of the retinal toxicity of repetitive injections after vitreous and lens surgery.

The combination of vancomycin and an aminoglycoside antibiotic is frequently injected into aphakic/vitrectomized eyes for the treatment of endophthalmitis. At 2 weeks after lens and vitreous removal, rabbit eyes received an injection of a combination of 1 mg vancomycin and either 400 micrograms amikacin or 100 micrograms gentamicin. Furthermore, the effects of repeating the same combination a second and third time at intervals of 48 h were examined by light and transmission electron microscopy at 7 days to 4 months after the last injection. A single injection of either combination produced no toxicity. After 2 or 3 sets of injections of either combination, 13 of 16 eyes displayed retinal toxicity manifested by macrophages in the subretinal space, disorganization of the outer segments and retinal pigment epithelium, and discontinuities in Bruch's membrane. These results indicate that whereas a single injection of these combinations is not toxic to aphakic/vitrectomized eyes, repetitive injections may result in increasing toxicity.

Amikacin↗
PubMed1992

Consequences of allocating attention to locations and to other attributes.

Simple reaction time to a light target may be lengthened when the light is preceded by a noninformative stimulus at the same location. This is known as inhibition of return. Does inhibition of return result if the relation between successive stimuli is defined in terms of color or orientation? Subjects pressed a key when a small square was displayed. In Experiments 1-3, location and color of the square were manipulated; there was inhibition of return based on location, but not on color. In Experiments 4-5, a confounding of color and luminance was eliminated, with no change in results. In Experiments 6-7, the background was composed of vertical stripes and the squares were composed of left- or right-oriented diagonal stripes. There was evidence of inhibition of return based on location, but not on orientation. These data support the idea that location is processed differently from other features.

Adult↗
PubMed1991

Further evidence for a time-independent shift of the focus of attention.

The separation between stimuli was manipulated in a same-different matching task. In Experiment 1, stimuli were upright Ts and/or Ls, whereas in Experiment 2, they were rotated Ts and/or Ls. In both experiments, mean reaction time (RT) for the same-different judgment did not increase as a function of interletter separation, suggesting either that the time needed to relocate attention was independent of distance, or that the stimuli were processed in parallel. These alternatives were tested in a third experiment, with a diagnostic for parallel processing proposed by Egeth and Dagenbach (1991). The diagnostic indicated that the rotated Ts and Ls in Experiment 2 were processed serially. If serial processing implies the utilization of attention, then the results of Experiment 2 suggest that relocation of attention is time-invariant with respect to distance.

Adult↗
PubMed1990

Stimulus repetition effects and the dimension-feature distinction in alternative targets.

The negative repetition effect (NRE) refers to a poorer perception of the target in noise-same-as-target than in noise-alternative-target displays. Using the parenthesis as target and noise that are either identical or different in orientation, we tested predictions derived from a feature-specific inhibition model (Bjork & Murray, 1977) that explains the NRE as arising from inhibitory interactions among channels handling identical inputs. Contrary to our expectation of evidence for orientation-specific inhibition, a positive repetition effect (PRE) was observed. We also found a PRE for the dimension target sets whose stimuli differ only in orientation and an NRE for the feature target sets whose stimuli differ in the number of elements. Further experiments that systematically varied relationships between alternative targets indicate that these basic findings, termed the stimulus attributes effects, do not arise from pattern masking, perceptual strategies, or response bias.

Adult↗