Presbyopia and the water content of the human crystalline lens

Fisher, R. F.; Pettet, Barbara E.

doi:10.1113/jphysiol.1973.sp010353

Cited by 100 publications

(55 citation statements)

References 2 publications

(3 reference statements)

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“…With age, the lens changes in size and in elastic properties [34, 35, 62, 63, 64, 65, 66], the choroid changes in elastic properties [66, 67], the ciliary muscle shows hypertrophic changes [68]and loss of elastic tissue at its choroidal attachment [69]while the elastic properties of the zonules do not change [65, 66]. …”

Section: Presbyopiamentioning

confidence: 99%

The Ageing Lens

et al. 2000

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The human lens grows by a process of epithelial cell division at its equator and the formation of generations of differentiated fibre cells. Despite the process of continuous remodelling necessary to achieve growth within a closed system, the lens can retain a high level of light transmission throughout the lifetime of the individual, with the ability to form sharp images on the retina. Continuous growth of the lens solves the problem imposed by terminal differentiation within a closed, avascular system, from which cells cannot be shed. The lens fibre tips arch over the equator to meet anteriorly and posteriorly and form branching sutures of increasing complexity. The stages of branching may create the optical zones of discontinuity seen on biomicroscopy. The lens is exposed to the cumulative effects of radiation, oxidation and postranslational modification. These later proteins and other lens molecules in such a way as to impair membrane functions and perturb protein (particularly crystallin) organisation, so that light transmission and image formation may be compromised. Damage is minimised by the presence of powerful scavenger and chaperone molecules. Progressive insolublisation of the crystallins of the lens nucleus in the first five decades of life, and the formation of higher molecular weight aggregates, may account for the decreased deformability of the lens nucleus which characterises presbyopia. Additional factors include: the progressive increase in lens mass with age, changes in the point of insertion of the lens zonules, and a shortening of the radius of curvature of the anterior surface of the lens. Also with age, there is a fall in light transmission by the lens, associated with increased light scatter, increased spectral absorption, particularly at the blue end of the spectrum, and increased lens fluorescence. A major factor responsible for the increased yellowing of the lens is the accumulation of a novel fluorogen, glutathione-3-hydroxy kynurenine glycoside, which makes a major contribution to the increasing fluorescence of the lens nucleus which occurs with age. Since this compound may also cross-link with the lens crystallins, it may contribute to the formation of high-molecular-weight aggregates and the increases in light scattering which occur with age. Focal changes of microscopic size are observed in apparently transparent, aged lenses and may be regarded as precursors of cortical cataract formation.

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Section: Presbyopiamentioning

confidence: 99%

The Ageing Lens

et al. 2000

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“…Fisher & Pettet (1973) showed that there is no loss of water in the presbyopic lens, but only a closer packing of fibres within the ageing lens nucleus which may cause a rise in its Young's modulus of elasticity.…”

Section: Introductionmentioning

confidence: 99%

The force of contraction of the human ciliary muscle during accommodation

Fisher¹

1977

The Journal of Physiology

Self Cite

210

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SUMMARY1. 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 equationwhere D = amplitude of accommodation in dioptres (m-l), FCB = force of contraction of the ciliary muscle as measured by changes in tension of the zonule (N), Kdf = dioptric force coefficient and is constant for a given age (m'-N-A x 102.5). 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 10 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.

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“…Alguns autores relataram frações relativamente fixas quanto ao peso líquido do cristalino, em amostras cujas idades oscilaram de 2,5 a 89 anos (4,11,13) ; outros estudos, porém, sugerem evidências de um aumento contínuo e gradativo na gravidade específica após o nascimento, indicando desidratação pequena, mas estável, de todo o cristalino, levando à afirmação de que, da vida fetal à vida adulta, há redução do volume ocupado pelo cristalino no globo ocular (1,9,(14)(15) .…”

Section: N T R O D U ç ã Ounclassified

Variações nas dimensões do cristalino humano de acordo com a idade

Waiswol¹,

Cursino²,

Cohen³

2001

Arq. Bras. Oftalmol.

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Variações nas dimensões do cristalino humano de acordo com a idadeObjetivo: Demonstrar eventual relação entre a idade e o aumento da espessura e diâmetro do cristalino humano. Métodos: Diâmetro e espessura de 108 cristalinos removidos de olhos doados para transplante de córnea foram medidos com uso de paquímetro e microscopia estereoscópica. Resultados: As medidas médias obtidas com os cristalinos avaliados foram de 3,73 mm de espessura com desviopadrão de 0,73 mm e de 8,96 mm de diâmetro com desvio-padrão de 0,41 mm. Sessenta e três cristalinos (58,3%) provinham de indivíduos do sexo feminino e 45 (41,7%), do sexo masculino, não havendo diferenças significativas entre os sexos relativamente à sua idade e à espessura e diâmetro dos cristalinos. Foi encontrada correlação significativa e diretamente proporcional entre a idade dos indivíduos e a espessura dos cristalinos, que mostrou aumento médio de 54,86% entre os dez e os 90 anos de idade. Esta correlação não foi observada com relação ao diâmetro dos cristalinos. Conclusões: Ocorre aumento da espessura do cristalino em ambos os sexos e em todos os grupos etários estudados. I N T R O D U Ç Ã OO desenvolvimento pós-natal do cristalino humano não segue o mesmo padrão de desenvolvimento de outras estruturas do sistema nervoso central ou a ele associadas. Enquanto nos primeiros anos de vida o crescimento do cristalino parece seguir um padrão que é comum à maior parte das estruturas tanto do sistema nervoso central como do periférico, com o correr dos anos este crescimento continua em taxas estáveis e progressivas, ao passo que as demais estruturas chegam às suas dimensões finais ou muito próximas às finais pelo final da segunda década de vida (1) .Curiosamente, o padrão de crescimento do cristalino humano também difere do de outras espécies animais, como ocorre com a vaca, o coelho e o rato, que apresentam um platô no crescimento do cristalino muito antes do curso da vida estar completo (2) .Os primeiros estudos sobre o crescimento do cristalino humano datam já de três séculos atrás (3)(4) , e parece que a preocupação destes pesquisadores era entender as implicações do crescimento contínuo do cristalino sobre a ocorrência de glaucoma de ângulo fechado bem como os seus efeitos sobre a sua posição e sobre as constantes ópticas do olho (5)(6) .Diversos autores estudaram as dimensões do cristalino em condições

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Presbyopia and the water content of the human crystalline lens

Cited by 100 publications

References 2 publications

The Ageing Lens

The Ageing Lens

The force of contraction of the human ciliary muscle during accommodation

Variações nas dimensões do cristalino humano de acordo com a idade

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