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.

Hayflick L, Moorhead PS: The serial cultivation of human diploid cell strains. Exp Cell Res 1961;25:585–621.
Hayflick L: The cellular basis for biological ageing; in Finch CE, Hayflick L (eds): Handbook of the Biology of Ageing. New York, Van Nostrand Reinhold, 1977.
van Heyningen R: Experimental studies on cataract. Proctor lecture. Invest Ophthalmol 1976;15:685–697.
Willekens B, Kappelhof J, Vrensen G: Morphology of the aging human lens. I. Biomicroscopy and biometrics. Lens Res 1987;4:207–230.
Bours J, Födisch HJ: Human fetal lens: Wet and dry weight with increasing gestational age. Ophthalmic Res 1986;18:363–368.
van Heyningen R: The human lens. III. Some observations on the post-mortem lens. Exp Eye Res 1972;13:155–160.
Brown NP, Bron AJ: Lens Disorders. A Clinical Manual of Cataract Diagnosis. Oxford, Butterworth-Heinemann, 1996.
Manzitti E, Damel A, Gamio S, Benozzi J: Eye length in congenital cataracts; in Cotlier E, Lambert S, Taylor D (eds): Congenital Cataracts. Medical Intelligence Unit Series. Austin, Landes, 1994, pp 251–259.
Weale RA: A Biography of the Eye: Development, Growth, Age. London, Lewis, 1982.
Brown NAP: Dating the onset of cataract. Trans Ophthalmol Soc UK 1976;96:18–23.
Brown NAP, Sparrow JM, Bron AJ: Central compaction in the process of lens growth as indicated by lamellar cataract. Br J Ophthalmol 1988;72:538–544.
Koretz JF, Cook CA, Kuszak JR: The zones of discontinuity in the human lens: Development and distribution with age. Vision Res 1994;34:2955–2962.
Strenk SA, Semmlow JL, Strenk LM, Munoz P, Gronlund-Jacob J, DeMarco JK: Age-related changes in human ciliary muscle and lens: A magnetic resonance imaging study. Invest Ophthalmol Vis Sci 1999;40:1162–1169.
Koretz J, Handelman GH: The ‘lens paradox’ and image formation in accommodating human eyes; in Duncan G (ed): The Lens: Transparency and Cataract. Rijswijk, Eurage, 1986, pp 57–64.
Pierscionek BK, Chan DYC, Ennis JP, Smith G, Augusteyn RC: Nondestructive method of constructing three dimensional gradient index models for crystalline lenses. 1. Theory and experiment. Am J Optom Physiol Opt 1988;65:481–491.
Siebinga I, Vrensen GFJM, de Mul FFM, Greve J: Age-related changes in local water and protein content of human eye lenses measured by Raman microspectroscopy. Exp Eye Res 1991;53:233–239.
Smith GTH, Smith RC, Brown NAP, Bron AJ, Harris ML: Changes in light scatter and width measurements from the human lens cortex with age. Eye 1992;6:55–59.
Kuszak JR, Bertram BA, Rae JL: The ordered structure of the crystalline lens; in Hilfer SR, Sheffield JB (eds): Cell and Developmental Biology of the Eye. Development of Order in the Visual System. New York, Springer-Verlag, 1986, pp 35–60.
Kuszak JR, Peterson KL, Brown HG: Electron microscopic observations of the crystalline lens. Electron microscopy of the visual system: The anterior segment of the eye (special issue). J Electron Microsc 1992;1:1.
Kuszak JR, Sivak JG, Weerheim JA: Lens optical quality is a direct function of lens sutural architecture (published erratum appears in Invest Ophthalmol Vis Sci 1992;32(6):2076–2077) Invest Ophthalmol Vis Sci 1991;32(7):2119–2129.
Bron AJ, Lambert SR: Specular microscopy of the lens (abstract). Ophthalmic Res 1984;16:209.
Bron AJ, Tripathi RC, Tripathi BJ: Wolff’s Anatomy of the Eye and Orbit. London, Chapman & Hall Medical, 1997.
Salzmann M: The Anatomy and Histology of the Human Eyeball in the Normal State. Its Development and Senescence. Chicago, University Chicago Press, 1912.
Fisher RF, Pettet BE: The postnatal growth of the capsule of the human crystalline lens. J Anal 1972;112:207–214.
Seland JH: Ultrastructural changes in the normal human lens capsule form birth to old age. Acta Ophthalmol 1974;52:688–706.
Krag S, Olsen T, Andreassen T: Biomechanical characteristics of the human anterior lens capsule in relation to age. Invest Ophthalmol Vis Sci 1997;38:357–363.
Guggenmoos-Holzmann I, Engel B, Henke V, Naumann GOH: Cell density of human lens epithelium in women higher than in men. Invest Ophthalmol Vis Sci 1989;30:330–332.
Li WC, Spector A: Lens epithelial cell apoptosis is an early event in the development of UVB-induced cataract. Free Radic Biol Med 1996;20:301–311.
Li DWC: The lens epithelium, apoptosis and cataract formation. Nova Acta Leopoldina 1997;75:81–108.
Harocopos GJ, Alvares KM, Kolker AE, Beebe DC: Human age-related cataract and lens epithelial cell death. Invest Ophthalmol Vis Sci 1998;39:2696–2706.
Farnsworth PN, Burke PA: Three-dimensional architecture of the suspensory apparatus of the lens of the Rhesus monkey. Exp Eye Res 1977;25:563–576.
Farnsworth PH, Shyne SE: Anterior zonular shifts with age. Exp Eye Res 1979;28:291–297.
Sakabe I, Oshika T, Lim SJ, Apple DJ: Anterior shift of zonular insertion onto the anterior surface of human crystalline lens with age. Ophthalmology 1998;105:295-299.
Fisher RF: The elastic constants of the human lens capsule. J Physiol 1969;201:1–19.
Fisher RF: The significance and shape of the lens and capsular energy changes in accommodation. J Physiol 1969;201:21–47.
Peczon BD, Peczon JD, Cintron C, Hudson BG: Changes in chemical composition of anterior lens capsules of cataractous human eyes as a function of age. Exp Eye Res 1980;30:155–165.
Dark AJ, Streeten BW, Jones DB: Accumulation of fibrillar protein in the aging human lens capsule. Arch Ophthalmol 1969;82:815–821.
Perry MM, Tassin J, Courtois YA: A comparison of human lens epithelial cells in situ and in vitro in relation to aging: An ultrastructural study. Exp Eye Res 1979;28:327–341.
Cohen MP, Yu-Vu V: Age-related changes in non-enzymatic glycosylation of human basement membranes. Exp Gerontol 1983;18:461–469.
Bailey AJ, Sims TJ, Avery NC, Miles CA: Chemistry of collagen cross-links: Glucose-mediated covalent cross-linking of type-IV collagen in lens capsules. Biochem J 1993;296:489–496.
Niesel P: Visible changes of the lens with age. Trans Ophthalmol Soc UK 1982;102:327–330.
Goldmann H: Studien über die Alterskernstreifen der Linse. Arch Augenheilk 1937;110:405–414.
Huggert A: Are the discontinuity zones of the crystalline lens iso-indicial surfaces? Acta Ophthalmol 1946;24:417–421.
Fagerholm PP, Phillipson BT, Lindstrom B: Normal human lens – The distribution of protein. Exp Eye Res 1981;33:615–620.
Fagerholm P, Phillipson BT, Lydahl E: Subcapsular zones of discontinuity in the human lens. Ophthalmic Res Suppl 1990;22:51–55.
Yaroslavsky IV, Yaroslavsky AN, Otto C, Puppels GJ, Vrensen GFJM, Duindam H, Greve J: Combined elastic and raman light scattering of human eye lenses. Exp Eye Res 1994;59:393–400.
Siebinga I, Vrensen GFJM, Otto K, Puppels GJ, de Mul FFM, Greve J: Ageing and changes in protein conformation in the human lens: A raman microspectroscopic study. Exp Eye Res 1992;54:759–767.
Bassnett S: Mitochondrial dynamics in differentiating fiber cells of the mammalian lens. Curr Eye Res 1992;11:1227–1232.
Bassnett S: Fiber cell denucleation in the primate lens. Invest Ophthalmol Vis Sci 1997;38(9):1678–1687.
Bassnett S, Beebe DC: Coincident loss of mitochondria and nuclei during lens fiber differentiation. Dev Dyn 1992;194:85–93.
Bassnett S, Mataic D: Chromatin degradation in differentiating fiber cells of the eye lens. J Cell Biol 1997;137:37–49.
Vrensen GFJM, de Wolf A: Calcium distribution in the human eye lens. Ophthalmic Res 1996;28(suppl 2):78–85.
Forbes JE, Holden R, Harris M, et al: Growth of the human crystalline lens in childhood. Proceedings of the Xth ISER Meeting, Stresa, Italy. Exp Eye Res 1992;55:172.
Cook CA, Koretz JF, Pfahnl A, Hyun J, Kaufman PL: Aging of the human crystalline lens and anterior segment. Vis Res 1994;34:2945–2954.
Smith G, Atchison DA, Pierscionek BK: Modelling the ageing human eye. J Opt Soc Am 1992;9:2111–2117.
Rohen JW: Der Ziliarkörper als funktionelles System. Morph Jahrb 1952;92:415–440.
Patnaik B: A photographic study of accommodative mechanims: Changes in the lens nucleus during accommodation. Invest Ophthalmol 1967;6:601–611.
Brown NAP: The change in shape and internal form of the lens of the eye on accommodation. Exp Eye Res 1973;15:441–459.
Koretz J, Handelman G, Brown N: Analysis of human crystalline lens curvature as a function of accommodative state and age. Vision Res 1984;24:1141–1151.
Koretz JF, Kaufman PL, Neider MW, Goeckner PA: Accommodation and presbyopia in the human eye – Aging of the anterior segment. Vision Res 1989;29:1685–1692.
Beers APA, van der Heijde GL: Age-related changes in the accomodation mechanism. Optom Vis Sci 1996;74:235–242.
Fisher RF: The elastic constant of the human lens. J Physiol 1971;212:147–180.
Fisher RF: Presbyopia and the changes with age in the human crystalline lens. J Physiol 1973;228:765–779.
Fisher RF, Pettet BE: Presbyopia and the water content of the human crystalline lens. J Physiol (Lond) 1973;234:443–447.
Fisher RF: The force of contraction of the human ciliary muscle during accommodation. J Physiol 1977;270:51–74.
van Alphen GWHM, Graebel WP: Elasticity of tissues involved in accomodation. Vision Res 1991;31:1417–1438.
Graebel WP, van Alphen GWHM: The elasticity of sclera and choroid of the human eye, and its implications on scleral rigidity and accommodation. J Biomech Eng 1977;99:203–208.
Stiev E: The structure of the human ciliary muscle, its changes during life and its influence on accommodation. Anat Anz 1949;97:69–79.
Tamm S, Tamm E, Rohen JW: Age-related changes of the human ciliary muscle. A quantitative morphometric study. Mech Ageing Dev 1992;62:209–221.
Alcala J, Maisel H: Biochemistry of lens plasma membranes and cytoskeleton; in Maisel H (ed): The Ocular Lens: Strucutre, Function and Pathology. New York, Dekker, 1985, pp 169–222.
Duindam JJ, Vrensen GFJM, Otto C, Greve J: Aging affects the conformation of cholesterol in the human eye lens. Ophthalmic Res 1996;28(suppl 1):86–91.
Maraini G, Fasella P: Reversible binding of soluble lens proteins to lens fibre ghosts. Exp Eye Res 1970;10:133–139.
Bracchi PG, Carta F, Fasella P, Maraini G: Selective binding of aged α-crystallin to lens fibre ghosts. Exp Eye Res 1971;12:151–154.
Broekhuyse RM, Kuhlmann ED: Lens membranes. IV. Preparative isolation and characterization of membranes and various membrane proteins from calf lens. Exp Eye Res 1978;26:305–320.
Rafferty NS, Scholz DL, Goldberg M, Lewyckyj M: Immuno-cytochemical evidence for an actin-myosin system in lens epithelial cells. Exp Eye Res 1990;51:591–600.
Rafferty NS, Scholz DL: Comparative study of actin filament patterns in lens epithelial cells. Are these determined by the mechanism of lens accommodation? Curr Eye Res 1989;8:569–579.
McFall-Ngai MJ, Ding LL, Takemoto LJ, Horowitz J: Spatial and temporal mapping of the age-related changes in human lens crystallins. Exp Eye Res 1985;41:745–758.
Harding JJ: Free and protein bound glutathione in normal and cataractous human lenses. Biochem J 1970;117:957–960.
Ahrend MHJ, Bours J, Födisch HJ: Watersoluble and -insoluble crystallins of the developing human fetal lens, analyzed by agarose/polyacrylamide thin-layer isoelectric focusing. Ophthalmic Res 1987;19:150–156.
Thomson JA, Augusteyn RC: Ontogeny of human lens crystallins. Exp Eye Res 1985;40:393–410.
Bours J: Species specificity of the crystallins and the albuminoid of the ageing lens. Comp Biochem Physiol 1980;65:215–222.
Duncan G, Hightower KR, Gandolfi SA, Tomlinson J, Maraini G: Human lens membrane cation permeabiltiy increases with age. Invest Ophthalmol Vis Sci 1989;30:1855–1859.
Gooden M, Rintoul D, Takehana M, Takemoto L: Major intrinsic polypeptide (MIP26K) from lens membrane: Reconstitution into vesicles and inhibition of channel forming activity by peptide antiserum. Biochem Biophys Res Commun 1985;128:993–999.
Cenedella RJ: Apparent coordination of plasma membrane component synthesis in the lens. Invest Ophthalmol Vis Sci 1993;34(7):2186–2195.
Duindam JJ, Vrensen GFJM, Otto C, Greve J: Cholesterol, phospholipid, and protein changes in focal opacities in the human eye lens. Invest Ophthalmol Vis Sci 1998;39:94–103.
Derham BK, Harding JJ: Effect of aging on the chaperone-like function of human α-crystallin assessed by three methods. Biochem J 1997;328:763–768.
Derham BK, Harding JJ: The effects of ageing on the chaperone-like function of rabbit α-crystallin, comparing three methods of assays. Biochim Biophys Acta 1997;1336:187–194.
McFall-Ngai M, Horowitz J, Ding LL, Lacey L: Age-dependent changes in the heat-stable crystallin βBp, of the human lens. Curr Eye Res 1986;5:387–394.
Takemoto L, Takemoto D, Brown G, Takehana M, Smith J, Horwitz J: Cleavage from the N-terminal region of βBp crystallin during aging of the human lens. Exp Eye Res 1987;45:385–392.
Zigler JS Jr, Russell P, Takemoto LJ, Schwab SL, Hansen JS, Horwitz J, Kinoshita JH: Partial characterization of three distinct populations of human gamma-crystallins. Invest Ophthalmol Vis Sci 1985;26:525–531.
Dilley KJ, Harding JJ: Changes in proteins of the human lens in development and aging. Biochim Biophys Acta 1975;386:391–408.
Lampi KJ, Ma Z, Hanson SRA, Azuma M, Shih M, Shearer TR, Smith DL, Smith JB, David LL: Age-related changes in human lens crystallins identified by two-dimensional electrophoresis and mass spectrometry. Exp Eye Res 1998;67:31–43.
Ma Z, Hanson SRA, Lampi K, David LL, Smith DL, Smith JB: Age-related changes in human lens crystallins identified by HPLC and mass spectrometry. Exp Eye Res 1998;67:21–30.
Boyle D, Takemoto L: Characterization of the α-γ and α-β complex: Evidence for an ‘in vivo’ functional role of α-crystallin as a molecular chaperone. Exp Eye Res 1994;58:9–16.
(a) Spector A, Garner WH: Hydrogen peroxide and human cataract. Exp Eye Res 1981;33:673–681. 95 (b) Garner B, Vazquez S, Griffith R, Lindner RA, Carver JA, Truscott RJW: Identification of glutathionyl-3-hydroxykynurenine glucoside as a novel fluorophore associated with aging of the human lens. J Biol Chem 1999;274:20847–20854.
Rathbun WB, Bovis MG: Activity of glutathione peroxidase and glutathione reductase in the human lens related to age. Curr Eye Res 1986;5:381–385.
Eckerskorn U, Kokkas K, Hockwin O, Laser H, Janke M: Physiologic changes of lens transparency during ageing: A Scheimpflug photography study. Dev Ophthalmol 1989;17:72–74.
Benedek GB: Theory of transparency of the eye. Appl Opt 1971:10:459–473.
Spector A, Freund T, Li L-K, Augusteyn RC: Age-dependent changes in the structure of alpha crystallin. Invest Ophthalmol 1971;10:677–686.
Jedziniak JA, Kinoshita JH, Yates EM, Hocker LO, Benedek GB: On the presence and mechanism of formation of heavy molecular weight aggregates in human normal and cataractous lenses. Exp Eye Res 1973;15:185–192.
Harding JJ: Disulphide cross-linked protein of high molecular weight in human cataractous lens. Exp Eye Res 1973;17:377–383.
Yu NT, DeNagel DC, Pruett PL, Kuck JFR: Disulfide bond formation in the eye lens. Proc Natl Acad Sci USA 1985;82:7965–7968.
Thurston GM, Hayden DL, Burrows P, Clark JI, Taret VG, Kandel J, Courogen M, Peetermans JA, Bown MS, Miller D, Sullivan KM, Storb R, Stern H, Benedek GB: Quasielastic light scattering study of the living human lens as a function of age. Curr Eye Res 1997;16:197–207.
Patrick JS, Thorpe SR, Baynes JW: Nonenzymatic glycosylation of protein does not increase with age in normal human lenses. J Gerontol 1990;45:B18–B23.
Dunn JA, Patrick JS, Thorpe SR, Baynes JW: Oxidation of glycated proteins: Age-dependent accumulation of NE-(carboxymethyl)lysine in lens protein. Biochemistry 1989;28:9464–9468.
van Heyningen R: Fluorescent glucoside in the human lens. Nature 1971;230:393–394.
Truscott RJW, Wood AM, Carver JA, Sheil MM, Stutchbury GM, Zhu J, Kilby GW: A new UV-filter compound in human lenses. FEBS Lett 1994;348:173-176.
Bando M, Nakajima A, Satoh K: Spectrophotometric estimation of 3-OH L-kynurenine O-beta-glucoside in the human lens. J Biochem 1981;89:103–109.
Wood AM, Truscott RJW: UV filters in human lenses: Tryptophan catabolism. Exp Eye Res 1993;56:317–325.
Wood AM, Truscott RJW: Ultraviolet filter compounds in human lenses: 3-yhdroxykynurenine glucoside formation. Vision Res 1994;34:1369–1374.
Malina HZ, Martin XD: 3-Hydroxykynurenine transamination leads to the formation of the fluorescent substances in human lenses. Eur J Ophthalmol 1996;6:250–256.
Weale RA: Age and the transmittance of the human crystalline lens. J Physiol 1988;395:577–587.
Said FS, Weale RA: The variation with age of the spectral transmissivity of the living human crystalline lens. Gerontologia 1959;3:213–231.
Zeimer RC, Noth RM: A new method of measuring in vivo the lens transmittance, and study of lens scatter, fluorescence and transmittance. Ophthalmic Res 1984;16:246–255.
van Best JA, Vrij L, Oosterhuis JA: Lens transmission of blue-green light in diabetic patients as measured by autofluorophotometry. Invest Ophthalmol Vis Sci 1985;26:532-536.
Dillon J, Atherton ST: Time resolved spectroscopic studies on the intact human lens. Photochem Photobiol 1990;51:465–468.
Mellerio J: Yellowing of the human lens: Nuclear and cortical contributions. Vision Res 1987;27:1581–1587.
Weale RA: The lenticular nucleus, light and the retina. Exp Eye Res 1991;53:213–218.
van Heyningen R: The glucoside of 3-hydroxykynurenine and other fluorescent compounds in the human lens; in Elliott K, Fitzsimmons DW (eds): The Human Lens – in Relation to Cataract. Amsterdam, Elsevier, 1973.
Satoh K: Age related changes in the structural proteins of the human lens. Exp Eye Res 1972;14:53–57.
Jacobs R, Krohn DL: Variations in fluorescence characteristics of intact human crystalline lens segments as a function of age. J Gerontol 1976;31:641.
Yu NT, Kuck JFR, Askren CC: Red fluorescence in older and brunescent human lenses. Invest Ophthalmol Vis Sci 1979;18:1278–1280.
Bando M, Mikuni I, Obazawa H: Calcium-induced lens protein aggregation accelerated by reactive oxygen species photosensitized in the presence of hydroxykynurenines. Exp Eye Res 1985;40:813–818.
Stutchbury GM, Truscott RJW: The modification of proteins by 3-hydroxykynurenine. Exp Eye Res 1993;57:149–155.
Ellozy AR, Wang RH, Dillon J: Model studies on the photochemical production of lenticular fluorophores. Photochem Photobiol 1994;59:479–484.
Vrensen G, Kappelhof J, Willekens B: Morphology of the aging human lens. II. Ultrastructure of clear lens. Lens Eye Toxic Res 1990;7:1–30.
Bron AJ, Brown NAP: Lens structure and forms of cataract; in Duncan G (ed): The Lens: Transparency and Cataract. EURAGE Publications, Netherlands, 3–11, 1986.
Sparrow JM, Bron AJ, Brown NAP, Aliffe W, Hill AR: The oxford clinical cataract classification and grading system. Int Ophthalmol 1986;9:207–225.
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