Search PubMed⌕ Search

Biomedical subjects

C M Kemp

Publications and source records attributed to C M Kemp.

At least 37 records · Page 2Linked to original sources
PubMed1988

The distribution and kinetics of visual pigments in the cat retina.

An imaging fundus reflectometer has been used to study the distribution and regeneration of visual pigments in the retina of the adult living cat. Measurements were made over an area of tapetal retina extending 25 degrees nasal and 40 degrees temporal to the area centralis on the horizontal meridian and 5 degrees inferior to 40 degrees superior on the vertical meridian. The measured density differences show large variations with retinal location, with values in the central retina up to 60% higher than those in the superior region. The area of high density differences forms a horizontal streak. There are two peaks of density difference values, one centered on the area centralis and the second in the nasal section of the streak. Spectral measurements indicate that the contribution of cone pigments is negligible everywhere except at the area centralis, where it is about 5%. The distribution of density differences is shown to correlate well with anatomical data if the effects of fundal stray light are taken into account and if it is assumed that the cross section of light capture by the rods is determined by the dimensions of the inner segments. The time required for essentially complete regeneration of rhodopsin depends on retinal location, varying from about 80 min in the superior retina to more than 90 min in the regions of peak densities.

Animals↗
PubMed1988

Two types of visual dysfunction in autosomal dominant retinitis pigmentosa.

Visual thresholds and rhodopsin levels were determined in nine subjects with autosomal dominant retinitis pigmentosa. The subjects fell into two groups, corresponding to two subtypes of the disease revealed by two-color, dark-adapted static perimetry. In the first of these subtypes, rod-mediated function was variably reduced and was accompanied by a corresponding reduction in cone function in the same retinal region. Dark-adapted threshold elevations varied in a way consistent with decreased quantal absorption by the rods as a result of reduced rhodopsin levels. In the second subtype, rod function was greatly reduced or absent throughout the retina, while cone function was much less severely affected. Although the levels of rhodopsin were only about half of normal, they were much too great to account for the visual threshold elevations on the basis of decreased probabilities of absorption by the visual pigment. Rhodopsin regeneration appeared to follow normal kinetics in patients from both groups. The results indicate that the examples of the two psychophysical subtypes of AD RP investigated here have very different disease manifestations.

Adult↗
PubMed1987

Rhodopsin topography and rod-mediated function in cats with the retinal degeneration of taurine deficiency.

Cats on a taurine-deficient diet were studied with imaging fundus reflectometry and full-field electroretinography. The pattern of rhodopsin loss and the natural history of the disease were determined from maps of the rhodopsin distribution in the central and nasal retina of cats with different degrees of severity of the retinopathy. Rhodopsin loss is first detectable in a focal region of the central retina. Subsequently, there are decreases in rhodopsin in the paracentral and nasal midperipheral retina. The horizontal streak of high rhodopsin levels is preferentially reduced in this retinopathy. The b-wave amplitude of the rod-dominated ERG is markedly reduced in cats with only mildly decreased levels of rhodopsin in the peripheral retina. In an affected cat with moderate rhodopsin loss in the central retina but minimal loss nasally, a light-microscopic study of the retina showed that there was disorganization and shortening of rod outer segments and loss of rod photoreceptor cells in the areas of reduced rhodopsin levels.

Animals↗
PubMed1987

Retinal dysfunction in central serous retinopathy.

Patients with acute and chronic central serous retinopathy (CSR) were studied by psychophysical and photochemical means to establish the extent of visual depression and to investigate the basis of rod dysfunction in this disorder. In acute disease with serous detachment of the retina, the loss of sensitivity attains 3 log units and parallels the height of retinal elevation as does its recovery with resolution of the episode. Immediately after resolution, there is a residual 0.5 log unit threshold elevation. In chronic disease, marked loss of function exists over areas of abnormal retinal pigment epithelium in the absence of clinically detectable serous detachment. Although rhodopsin levels are low in both acute and chronic CSR, this relative lack of visual pigment does not totally account for the functional deficits in either situation.

Fluorescein Angiography↗
PubMed1984

Vitamin A treatment for night blindness in primary biliary cirrhosis.

Three patients with late stage primary biliary cirrhosis were found to have appreciable night blindness. Serum vitamin A concentrations were low in all three patients despite regular intramuscular supplementation in two. All patients responded dramatically to high dose oral supplementation, with full recovery of adaptation to dark and visual fields. Oral rather than intramuscular vitamin A supplementation seems appropriate in the prevention of ocular complications of vitamin A deficiency in biliary cirrhosis.

Administration, Oral↗
PubMed1984

Human rhodopsin measurement using a T.V.-based imaging fundus reflectometer.

An imaging fundus reflectometer for in vivo mapping of rhodopsin levels is described. The instrument is based on a high-sensitivity television camera attached to a Zeiss fundus camera, which enables areas of retina of angular subtense 25 degrees to be examined at a resolution of about 1 degree. Digital processing techniques are used to average the video signal spatially and temporally and to analyse the spatial information. Measurements with an artificial eye indicate that performance is comparable to that of photomultiplier-based systems. Rhodopsin levels and regeneration data for a normal human subject are presented; these are consistent with published values. The map of visual pigment levels derived from these normal data is contrasted with that for a subject with a patchy retinal dysfunction (autosomal dominant retinitis pigmentosa).

Adult↗
PubMed1983

The products of photoreversing rhodopsin bleaching by microsecond flashes in the isolated vertebrate retina.

Bleaching experiments were carried out at room temperature on rhodopsin in isolated rat, frog and rat retinas with blue and orange laser flashes of very high energy and duration less than 3 microseconds. Blue flashes bleached a maximum of about 50% at the highest energies; orange ones bleached about 30% at intermediate energies but the value decreased to below 20% as the energy increased. This bleaching behaviour can be explained in terms of a kinetic model which assumes that bleaching is photoreversed during the flashes and which incorporates the relevant properties of rhodopsin, isorhodopsin, bathorhodopsin and lumirhodopsin.

Animals↗
PubMed1983

Visual pigment levels in retinitis pigmentosa.

A broad-field imaging fundus reflectometer was used to determine the levels of visual pigment and their relationship to rod-mediated sensitivity in 3 patients with autosomal dominantly inherited retinitis pigmentosa. In each case the loss of sensitivity could be accounted for wholly by the decreased probability of light absorption by the rod photoreceptors resulting from the decreased levels of rhodopsin they contained. In contrast, in a subject whose night blindness was due to vitamin A deficiency, the large sensitivity loss was accompanied by a relatively small reduction in the rhodopsin level.

Female↗
PubMed1981

Flash photolysis of rhodopsin in the cat retina.

The bleaching of rhodopsin by short-duration flashes of a xenon discharge lamp was studied in vivo in the cat retina with the aid of a rapid, spectral-scan fundus reflectometer. Difference spectra recorded over a broad range of intensities showed that the bleaching efficacy of high-intensity flashes was less than that of longer duration, steady lights delivering the same amount of energy. Both the empirical results and those derived from a theoretical analysis of flash photolysis indicate that, under the conditions of these experiments, the upper limit of the flash bleaching of rhodopsin in cat is approximately 90%. Although the fact that a full bleach could not be attained is attributable to photoreversal, i.e., the photic regeneration of rhodopsin from its light-sensitive intermediates, the 90% limit is considerably higher than the 50% (or lower) value obtained under other experimental circumstances. Thus, it appears that the duration (approximately 1 ms) and spectral composition of the flash, coupled with the kinetic parameters of the thermal and photic reactions in the cat retina, reduce the light-induced regeneration of rhodopsin to approximately 10%.

Animals↗