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Biomedical subjects

R F Fisher

Publications and source records attributed to R F Fisher.

At least 55 records · Page 3Linked to original sources
PubMed1977

The force of contraction of the human ciliary muscle during accommodation.

1. Apparatus has been designed to alter the shape of the human lens by tensile forces applied to the zonular fibres indirectly through the ciliary body. The changes in dioptric power of the lens for monochromatic sodium light were measured at the same time. Simultaneous serial photography, and direct measurement enabled one to relate a change in shape of the lens to the change in dioptric power. Subsequently, the same lens was isolated and spun around its antero-posterior polar axis and high speed photography recorded its changing profile.2. By comparing the changes in lens profile due to zonular tension and centrifugal force respectively, the force developed in the zonule for a given change in the shape of the lens could be calculated. Changes in dioptric power associated with those of shape can thus be related directly to the force of contraction of the ciliary muscle necessary to reduce the initial tension of the zonule in the unaccommodated state.3. The force of contraction of the ciliary muscle as measured by radial force exerted through the zonule and the change in dioptric power of the lens were not linearly related. The relationship is more exactly expressed by the equation [Formula: see text] where D = amplitude of accommodation in dioptres (m(-1)), F(CB) = force of contraction of the ciliary muscle as measured by changes in tension of the zonule (N), K(df) = dioptric force coefficient and is constant for a given age (m(-1)N(-(1/2)) x 10(2.5)). This coefficient is 0.41 at 15 yr and 0.07 at 45 yr of age.4. In youth for maximum accommodation (10-12 D) the force is approximately 1.0 x 10(-2) N while to produce sufficient accommodation for near vision (3.5 D) the force is less than 0.05 x 10(-2) N.5. After the age of 30 yr the force of contraction of the ciliary muscle necessary to produce maximum accommodation rises steadily to about 50 yr of age and thereafter probably falls slightly. At about 50 yr of age the ciliary muscle is some 50% more powerful than in youth.6. Even if hypertrophy of the muscle did not occur the amplitude of accommodation would be reduced at the most by only 0.8 D of that observed at the onset of presbyopia.

Accommodation, Ocular↗
PubMed1977

Changes in the permeability of the lens capsule in senile cataract.

When the water permeability of the lens capsule of a group containing all types of cataractous lenses is compared with a group of transparent lenses matched for age, there is no significant difference in permeability between the groups. If however, only those cataracts are selected which show changes in the cortex, namely, cuneiform opacities or 'water clefts', then the correlation between the water content of the cortex of these lenses and the permeability of their capsules is significant.

Cataract↗
PubMed1976

Utilization of 14C-labelled Escherichia coli by rats.

1. Escherichia coli was grown on 14C-labelled glucose and fractions representing "whole cells", "cell contents" and "cell walls" were administered orally to rats. 2. 14C appearing as 14CO2 in the expired air and as unidentified radioactive products in urine and faeces was measured until the cumulative recovery showed little change with time. 3. All fractions were digested. The digestibility of cell walls was less than that of the other fractions. 4. There was considerable variation among individual rats.

Animals↗
PubMed1975

Effect of platinum and palladium salts on thymidine incorporation into DNA of rat tissues.

The intraperitoneal administration of PtCl4 or Pd(NO3)2 at levels of 28 or 56 mumole/kg body weight decreased the thymidine incorporation into DNA of spleen, liver, kidney, and testis. Spleen was most sensitive to both the platinum and the palladium salt. In liver, DNA syntheses in parenchymal cells and stromal cells were about equally sensitive to PtCl4. In control rats, only 20-30% of the 3H in the acid-soluble fraction of liver or spleen was in the form of thymidine and its phosphate esters 2 hr after the intraperitoneal injection of 3H-thymidine; prior injection of PtCl4 (56 mumol/kg body weight) did not change the pattern.

Animals↗
PubMed1973

Presbyopia and the changes with age in the human crystalline lens.

1. A method of determining the distribution of capsular moulding pressure is described. This includes:(a) measuring the decrease in polar depth of the lens from photographed lens profiles before and after the capsule has been cut around the entire equator of the lens,(b) measuring the elastic properties of the lens substance by subjecting the lens to known centrifugal forces and photographing the polar strain so produced.2. A method of determining the relationship between capsular and lenticular strain is described. This includes (a) measuring the elastic properties of the capsule (b) measuring the elastic properties of the lens substance and (c) measuring the profiles of the photographed lens. The ratio of the strain of lens substance to capsule is expressed as a dimensionless parameter, the lens number.3. The decrease in the amplitude of accommodation with increasing age is proportional to the lens number divided by the square of the radius of the accommodated lens, assuming that the movement of the capsulozonular attachments of the lens remains unimpaired in the ageing eye.4. Ageing changes in the human crystalline lens are sufficient to account for a total loss of accommodation by the age of 61 years.

Accommodation, Ocular↗
PubMed1973

Presbyopia and the water content of the human crystalline lens.

1. The water content of the human crystallaline lens nucleus is 63.4% S.D. +/- 2.9%, and cortex 68.6% S.D. +/- 4.3%.2. Neither the total water content of the cortex, nor that of the nucleus show any significant changes with age, so ;sclerosis' of the lens due to loss of water is not a cause of presbyopia.3. The initial loss of water from the nucleus of the lens substance obtained by drying in vacuo at 20 degrees C for 2 hr is related to age (P = 0.05) and deformability (0.02 > P > 0.01).4. The lens fibres of the ageing nucleus have an increased resistance to deformation associated with a decrease in initial water loss. These characteristics can be explained by a common physical property of the fibres, namely increased adhesion to each other as the lens nucleus ages. The newly formed cortical fibres do not appear to show these changes.

Adolescent↗
PubMed1971

The elastic constants of the human lens.

1. When the lens is spun around its antero-posterior polar axis in an apparatus designed for the purpose, high speed photography can be used to record its changing profile. By this method a variable radial centrifugal force can be applied to the lens which mimics the pull of the zonule.2. If the lens is not stressed at its centre beyond 100 Nm(-2) it behaves as a truly elastic body. When stressed beyond this limit visco-elastic strain is produced at its poles.3. The human lens has isotropic elastic properties at the extremes of life, but at the other times Young's Modulus of Elasticity varies with the direction in which it is measured.4. Young's Modulus of Elasticity of the lens varies with age, polar elasticity and equatorial elasticity, at birth being 0.75 x 10(3) and 0.85 x 10(3) Nm(-2) respectively, while at 63 years of age both are equal to 3 x 10(3) Nm(-2).5. A comparison of Young's Modulus of the young human lens with that of the rabbit and cat shows that the polar elasticity of the lenses of these animals was 5 times greater in the young rabbit, and 21 times greater in the adult cat. Equatorial elasticities of the rabbit and human lens were equal, while in the cat the equatorial elasticity was four times greater.6. A mathematical model showing the lens substance possessing a nucleus of lower isotropic elasticity than that of the isotropic elastic cortex surrounding it, accounts for the difference between polar and equatorial elasticity of the intact adult lens.7. The implications of these findings are discussed in relation to:(i) accommodation and the rheological properties of the lens;(ii) possible differences in the physical state of the lenticular proteins in the cortex and nucleus which may account for the senile variations in Young's Modulus of Elasticity in these regions of the lens;(iii) the loss of accommodation due solely to an increase in Young's Modulus of Elasticity of the lens between the ages of 15 and 60. This would amount to 44% of the total observed in vivo.

Adolescent↗