Biomedical subjects

S L Buck

Publications and source records attributed to S L Buck.

At least 19 recordsLinked to original sources

PubMed2000

Opponent-color models and the influence of rod signals on the loci of unique hues.

To investigate how rod signals influence hue perception and how this influence can be incorporated into opponent-color models, we measured the shift of unique-hue loci under dark-adapted conditions compared with cone-plateau conditions. Rod signals produced shifts of all spectral unique hues (blue, green, yellow) but in a pattern that was inconsistent with simple additive combinations of rod and cone inputs in opponent-color models. The shifts are consistent with non-linear models in which rod influence requires non-zero cone signals. Cone-signal strength may modulate or gate rod influence, or rod signals may change the gain of cone pathways.

Adaptation, Ocular↗

PubMed2000

Methods used to evaluate the effectiveness of contact lens care solutions and other compounds against Acanthamoeba: a review of the literature.

PURPOSE: The purpose of this paper is to review the literature concerning the methods used to evaluate contact lens care solutions against Acanthamoeba. Acanthamoeba keratitis is a potential threat, with 85% of the cases being reported in contact lens wearers. METHODS: Several studies from the published literature that evaluated contact lens disinfectants were reviewed. The variables included test organism, strain and morphology, growth conditions, inoculum preparation, inoculation method, test solutions and concentration, contact time, neutralization, recovery, quantitation method, and viability determination of survivors. The methods used to test Acanthamoeba against the disinfectants were compared and contrasted. RESULTS: After a thorough review of methods used to test Acanthamoeba, it was found that there is great variability in the methods used to evaluate contact lens disinfectants. The majority of the studies used A.castellanii and A.polyphaga cysts grown axenically in PYG medium containing cations at about 30 degrees C and the inoculum contained about 1.0 x 10(5) cells/mL. Inactivation media or centrifugation of cells was used to neutralize test samples. Quantitation was performed in most studies and viability was checked in all studies. The disinfectants tested most often were PHMB, hydrogen peroxide, thimerosal, and chlorhexidine. CONCLUSIONS: After reviewing the studies presented here it can be concluded that an effective method for testing Acanthamoeba against contact lens disinfectants would include A.castellanii or A.polyphaga grown axenically in PYG containing cations and a concentration of organisms high enough to adequately measure kill, a neutralization step, recovery and quantitation of organisms followed by a viability check of survivors.

Acanthamoeba↗

PubMed2000

Broad spectrum antimicrobial activity of a new multi-purpose disinfecting solution.

PURPOSE: There has been increasing awareness of the need for more powerful contact lens disinfectants, ideally having low toxicity and allergenicity to ocular tissue. Opti-Free Express with ALDOX Multi-Purpose Disinfecting Solution (MPDS) was recently marketed as a new multi-purpose disinfecting solution for soft contact lenses. MPDS contains two antimicrobial agents, polyquaternium-1 and myristamidopropyl dimethylamine, to broaden the range of antimicrobial activity. The purpose of this study was to evaluate the antimicrobial activity of MPDS against microorganisms that have been reported as contact lens and lens case contaminants and causative agents of microbial keratitis. METHODS: MPDS was challenged with high numbers of gram-positive and gram-negative bacteria, yeast, mold, and Acanthamoeba. Several lots of product were challenged with at least three separate inocula of each isolate. After exposure to the disinfecting solution, a sample was removed from the product and plated for survivors by suitable recovery methods. The plates were incubated and the number of survivors was enumerated. RESULTS: The results showed that MPDS was bactericidal, fungicidal and amoebicidal against an extensive variety of environmental contaminants of lens care accessories and ocular pathogens. MPDS was capable of killing a broad spectrum of microorganisms. The log reduction exceeded the primary criteria for disinfecting products and produced a notable reduction of other clinical and environmental isolates as well. CONCLUSIONS: Opti-Free Express MPDS contains antimicrobial agents that can kill an extensive spectrum of many different types of microorganisms that may contaminate contact lenses and solutions.

Acanthamoeba↗

PubMed1999

Sensitivity and dynamics of rod signals in H1 horizontal cells of the macaque monkey retina.

We measured the sensitivity, temporal frequency response, latency, and receptive field diameter of rod input to the H1 horizontal cell type in an in vitro preparation of the macaque retina. The H1 cell has both a cone-connected dendritic tree and a long axon-like process that terminates in a rod-connected arbor. We recorded from the H1 cell body where rod signals were distinguished by sensitivity to short wavelength light after dark adaptation. Receptive fields of rod vs. cone mediated responses were coextensive, indicating that the rod signal is transmitted via rod-cone gap junctions. Sensitivity of the H1 cell rod signal was approximately 1 log unit higher than that of the cone signal. Below cone threshold rod signals were temporally low-pass, with a cutoff frequency below 10 Hz. Rod signals became faster and more transient with increasing light levels. We conclude that the H1 cell rod signal is not sensitive in the low scotopic range and, by comparison with the rod signal recorded directly in cones (Schneeweis & Schnapf (1995) Science, 268, 1053-1056), signal transmission across the cone-H1 synapse does not significantly filter the temporal properties of the rod signal.

Adaptation, Ocular↗

PubMed1998

Rods affect S-cone discrimination on the Farnsworth-Munsell 100-hue test.

Rod influence on hue discrimination was assessed by the Farnsworth-Munsell 100-hue test. Rod influence was taken as the difference in error scores obtained after complete dark adaptation and during the cone plateau at three mesopic (23, 9, 3 td) and one standard (158 td) light level. On the FM 100, rods produced a differential discrimination loss along a tritan axis as compared with a red-green axis without any bias toward a rod confusion axis. Rods appear to impair discrimination mediated by S-cone pathways, which at moderate levels of illumination can differentially elevate tritan errors on the FM 100.

Adult↗

PubMed1998

Rod influence on hue-scaling functions.

Rod influence on hue appearance of spectral lights was characterized by comparing the scaling of red, green, yellow, and blue hue sensations for an 8 degrees-diameter, 7 degrees-eccentric test spot under conditions that minimized (cone plateau) and maximized (dark adapted) rod influence at two mesopic light levels (1.5 and 3.0 log scoptic trolands). At the lower light level, the hue-scaling functions showed that rod signals influenced the spectral range and magnitude of all four primary hues. The rod influence could not be characterized as a ubiquitous augmentation or diminution of any hue over the entire spectrum. This constrains models of rod influence on color vision.

Adult↗

PubMed1998

Amoebicidal activity of a preserved contact lens multipurpose disinfecting solution compared to a disinfection/neutralisation peroxide system.

The amoebicidal activity of a contact lens multipurpose disinfecting solution (MPDS) containing polyquaternium-1 and myristamidopropyl dimethylamine was compared to a disinfection/neutralisation peroxide system against Acanthamoeba castellanii and Acanthamoeba polyphaga trophozoites and cysts. A quantitative microtitre method was used to evaluate the solutions. The MPDS showed similar amoebicidal activity to the disinfection/neutralisation peroxide system against the trophozoites of both species and equal or more rapid activity against the cysts of both species.

Journal Article↗

PubMed1997

Influence of rod signals on hue perception: evidence from successive scotopic contrast.

In successive scotopic color contrast, a colored adapting field induces a hue into a successively presented, purely rod-detected test field. To determine the rod influence on hue perception, a comparison was made, for both spectral matches and hue names, between photopic and scotopic color contrast hues produced by the same adapting fields adjusted to each of the four unique hues. Rod signals evoked hues reflecting each direction of both red/green and blue/yellow hue dimensions. Rod signals differentially strengthened blue relative to red or green hue components under some conditions but not under others. No other differential rod influences on hue were found.

Color Perception↗

PubMed1996

A quantitative method to evaluate neutralizer toxicity against Acanthamoeba castellanii.

A standard methodology for quantitatively evaluating neutralizer toxicity against Acanthamoeba castellanii does not exist. The objective of this study was to provide a quantitative method for evaluating neutralizer toxicity against A. castellanii. Two methods were evaluated. A quantitative microtiter method for enumerating A. castellanii was evaluated by a 50% lethal dose endpoint method. The microtiter method was compared with the hemacytometer count method. A method for determining the toxicity of neutralizers for antimicrobial agents to A. castellanii was also evaluated. The toxicity to A. castellanii of Dey-Engley neutralizing broth was compared with Page's saline. The microtiter viable cell counts were lower than predicted by the hemacytometer counts. However, the microtiter method gives more reliable counts of viable cells. Dey-Engley neutralizing medium was not toxic to A. castellanii. The method presented gives consistent, reliable results and is simple compared with previous methods.

Acanthamoeba↗

PubMed1994

Partial additivity of rod signals with M- and L-cone signals in increment detection.

Test additivity experiments revealed the combination rules for increment detection by rods and either M- or L-cone-dominated mechanisms isolated by means of chromatic adaptation (Stiles' pi 4 and pi 5, respectively). Increment thresholds were measured for single test wavelengths detected by each mechanism. Pairs of test wavelengths were then superimposed, and increment thresholds were measured for simultaneous detection by both rod and cone mechanisms. The observed degree of additivity was corrected (reduced) to compensate for the partial detection by each mechanism of both test wavelengths in the combined stimuli. We find that subthreshold rod signals are partially additive with subthreshold signals from both M- and L-cones. The degree of additivity is high and similar for both M- and L-cones: less than the ideal prediction of linear addition, but greater than that predicted by either probability summation of independent mechanisms or orthogonal vector addition.

Color Perception↗

PubMed1993

Cone pathways and the pi 0 and pi 0' rod mechanisms.

The field-adaptation properties of two scotopic (rod) mechanisms, pi 0 and pi 0', were measured to test a two-pathway model that associates the fast temporal properties of pi 0' with the processing of rod signals by early cone pathways, possibly including cone photoreceptors, and the sluggish temporal properties of pi 0 with processing of rod signals by classical rod pathways. This model predicts that cone stimulation will differentially affect the flicker sensitivity of pi 0' compared to pi 0. Both rod mechanisms are seen in double-branched flicker-threshold-vs-intensity (FTVI) curves measured with a 15-Hz, square-wave-modulated, rod-detected test stimulus. We show that the position of the upper branch (pi 0') shifts relative to the lower branch in response to changes of background wavelength, indicating that different receptor types regulate sensitivity of pi 0 and pi 0'. Field spectral sensitivity (FSS) functions for pi 0 closely match the scotopic spectral sensitivity function, indicating that only rods adapt pi 0 under these conditions. In contrast, fitting of FSS functions for pi 0' required a combination of cone and rod spectral sensitivity functions. The relative adaptational effect of cone stimulation compared to rod stimulation increases with background light level: at highest levels, cone stimulation has more influence than rod stimulation. Test additivity experiments assessed the degree of additivity between cones and rods to ensure that the pi 0' branch did not result from sub-threshold summation between receptor mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗

PubMed1993

Quantification of monocular optokinetic nystagmus asymmetries and motion perception with motion-nulling techniques.

When tested monocularly, strabismic and amblyopic subjects often show asymmetries of optokinetic nystagmus (OKN), with OKN being more readily elicited by temporal-to-nasal than by nasal-to-temporal stimulus motion. We tested five visually normal subjects and ten strabismic and/or amblyopic subjects by use of motion-nulling stimuli, which consisted of superimposed temporal-to-nasal and nasal-to-temporal sinusoidal-grating components with a summed contrast of 100%. Both the direction of OKN and the subject's perceived direction of motion (PDM) were tested. Most normal subjects showed symmetrical OKN and PDM, but a rightward OKN bias was observed in one of the visually normal subjects. Temporal-to-nasal eye-movement biases were seen in most strabismic and amblyopic subjects, whereas PDM biases were smaller and less frequent. The primary purpose of this study was to demonstrate the feasibility of quantifying OKN and PDM asymmetries in a diverse group of visually abnormal adults by use of the motion-nulling technique. Application of this technique to larger and more homogeneous clinical populations may contribute to the continued differentiation and characterization of variants of the visual disorders associated with strabismus and amblyopia and with other defects of binocular vision.

Adolescent↗

PubMed1991

Test-additivity experiments: different procedures, different results.

Test-additivity experiments reveal the combination rules for separate contributions to visual detection. The measured degree of additivity and the shape and symmetry of the additivity function have been used to design or evaluate theories about the underlying visual pathways. However, all these characteristics can be distorted if measured by means of a variable-proportion procedure, in which the amount of one primary is held constant while the amount of the other is varied in order to measure threshold. A fixed-proportion procedure, in which the amounts of each primary are varied together in constant proportion in order to measure threshold, is preferable. These differences in results were found by using the method of adjustment but may also apply to the method of limits and other psychophysical procedures.

Color Perception↗

PubMed1987

Rod-cone interaction in monocular but not binocular pathways.

Photopic background stimulation elevates scotopic increment thresholds (rod-cone interaction) at moderate background levels when both test and concentric disk-background stimuli enter the same eye (monocular condition) but not when they enter different eyes (dichoptic condition). Only when background levels are made extremely high is there any measurable dichoptic interaction, and this interaction does not resemble that observed monocularly. Rod-cone interaction, as usually studied, is a property of monocular pathways in human vision.

Cell Communication↗

PubMed1985

Determinants of the spatial properties of cone-rod interaction.

Photopic increment thresholds can be elevated by 0.2-1.9 log units, depending on the diameter of a concentric scotopic background. This cone-rod interaction displays spatial properties that resemble the spatial sensitization (Westheimer effect) observed in the isolated scotopic and photopic systems. This raises the possibility that the spatial properties of the interaction are determined by the same mechanisms or pathways that determine the spatial properties of either scotopic or photopic vision. When annulus backgrounds are used, the spatial properties of interaction match those of the scotopic system but not the photopic system. When disk backgrounds are used, the spatial properties of interaction match those of neither photopic nor scotopic systems. Thus, under some conditions, the scotopic visual system alone is sufficient to determine the spatial properties of cone-rod interaction. Under other conditions, additional complications arise. The results are discussed in terms of the center-surround model that has previously been applied to cone-rod interaction.

Adaptation, Ocular↗

PubMed1985

Cone-rod interaction over time and space.

Scotopic background stimulation can elevate photopic increment thresholds by more than 2 log units. This cone-rod interaction is greatest on small backgrounds (less than 1 degree diameter), but is found consistently on large backgrounds as well. Interaction develops and disappears quickly as backgrounds are turned on or off, respectively. The onset, and in some cases the offset, of a background stimulus can produce an additional, transitory interaction that augments the interaction that is maintained by continued presentation of the same background. The majority of the present findings lend support to a simple center-surround model of cone-rod interaction: nearby scotopic excitation raises photopic thresholds and more distant scotopic stimulation primarily antagonizes this interaction.

Cell Communication↗

PubMed1984

The time-course of rod-cone interaction.

The time-course of rod-cone interaction (change of scotopic sensitivity caused by photopic background stimulation) was measured in the presence of briskly exchanged, scotopically matched, 490- and 630-nm background disks. In all conditions, interaction rose and fell quickly with changes of photopic stimulation. When the background was a small 0.6 degree-diameter disk, photopic stimulation produced relatively constant maintained interaction of about 0.6 log units. When the background was a large 7.8 degree-dia disk, photopic stimulation produced larger initial (0.6-1.0 log unit) than maintained (0.2 log unit) interaction. When a 0.6 degree by 7.8 degree annulus was used instead of a background, photopic stimulation produced substantial interaction only at offset, a transitory interaction. Thus, the spatial dependence of transitory interactions differs from that of maintained interaction: transitory interactions can be large even when maintained interaction is small or absent. The results are discussed in terms of a simple center-surround model of rod-cone interaction that unifies both maintained and transient interaction.

Dark Adaptation↗

PubMed1983

Background visibility and increment thresholds.

Increment thresholds for small test flashes measured on superimposed backgrounds sometimes differed depending on whether an observer was instructed to keep the background subjectively visible or (Troxler) faded. The magnitude and direction of the threshold change varied among observers. For some observers, the magnitude of the effect of such instructions also varied with background size, psychophysical method, and displacement of test from background. How the instructions and their presumed association with different phenomenological states affect thresholds is not known. However, these results show that the magnitude of effects and the shapes of psychophysically measured functions can be affected by the instructions followed by the observer, whether self-imposed or imposed by the experimenter.

Dark Adaptation↗