Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CHROMATES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,783 records · Page 99Linked to original sources
PubMed2002

Chromatic light adaptation measured using functional magnetic resonance imaging.

Sensitivity changes, beginning at the first stages of visual transduction, permit neurons with modest dynamic range to respond to contrast variations across an enormous range of mean illumination. We have used functional magnetic resonance imaging (fMRI) to investigate how these sensitivity changes are controlled within the visual pathways. We measured responses in human visual area V1 to a constant-amplitude, contrast-reversing probe presented on a range of mean backgrounds. We found that signals from probes initiated in the L and M cones were affected by backgrounds that changed the mean absorption rates in the L and M cones, but not by background changes seen only by the S cones. Similarly, signals from S cone-initiated probes were altered by background changes in the S cones, but not by background changes in the L and M cones. Performance in psychophysical tests under similar conditions closely mirrored the changes in V1 fMRI signals. We compare our data with simulations of the visual pathway from photon catch rates to cortical blood-oxygen level-dependent signals and show that the quantitative fMRI signals are consistent with a simple model of mean-field adaptation based on Naka-Rushton (Naka and Rushton, 1966) adaptation mechanisms within cone photoreceptor classes.

Adaptation, Ocular↗
PubMed2003

[Diagnostic value of the chromatic contents of fundus photography].

The optical properties of the human lens change with age and are affected by both ocular and systemic diseases. A usual change is a gradual diffuse browning or sclerosis of the lens nucleus. This nuclear sclerosis leads to selective absorption of short wave (blue) light when broad band (white) light is sent into the eye. During fundus photography a light is flashed in front of the eye which enters the pupil and is reflected from the retina to be recorded on film. The light from the flash will pass twice through the optics of the eye where the short wave lengths will be absorbed. A new method has succeeded in describing the correlation between age and the selective absorption of blue light in the ocular lens. Preliminary studies using this method have shown that the ocular lens displays increased "ageing" in diabetic patients which is probably related to the cumulative exposition to hyperglycemia. The advantages of the method are that it uses clinical data already available in patients with retinal diseases and that it is fast, inexpensive, and non-invasive to carry out. The method is another example of the eye as a significant viewer to the study of generalized diseases and their systemic complications.

Age Factors↗
PubMed1992

Relationship between axial length and chromatic refraction of the eye.

A new mathematical expression is derived to provide an estimate, alpha x, of the axial length of the human schematic eye. Approximations in the expression are made after considering effects in the Gullstrand-Emsley schematic eye. Parameters required to solve the expression are, for two wavelengths, the refractive indices of the humours, the focal power of the cornea and refractive errors in two states of accommodation. Unlike recognized optical methods, additional intraocular parameters are not required. For emmetropic variants of the Gullstrand-Emsley schematic eye with axial lengths between 19 and 27 mm, alpha x is within 0.06 to 0.26 mm of the actual value. Furthermore, alpha x is essentially independent of variations in the refractive indices of the crystalline lens. However, the estimate of alpha x is critically dependent on the accuracy of values assigned to the parameters. For that reason, the model is considered impractical for clinical application.

Accommodation, Ocular↗