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|Light from a single point of a distant object and light from a single point of a near object being brought to a focus by changing the curvature of the lens.|
|Gray's||subject #226 1019|
|Schematic diagram of the human eye.|
The lens is a transparent, biconvex (lentil-shaped) structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. Its function is thus similar to a human-made optical lens. The lens is also known as the aquula (Latin, a little stream, dim. of aqua, water) or crystalline lens.
The main function of the lens is to change the focal distance of the eye to allow focusing on objects at various distances. This adjustment of the lens is known as accommodation (see also Curvature and Thickness, below). It is similar to the focusing of a photographic camera via movement of its lenses. Adjustment of the lens is controlled by the nervous system and executed by a system of muscles around the lens to allow a sharp image of the object of interest to be formed and detected on by retina.
The average adult human lens is about 5 mm thick and has a diameter of about 9 mm. Its thickness can be adjusted by surrounding muscles, and crystallins are its main protein building blocks.
Curvature and thickness
The lens is flexible and its curvature is controlled by ciliary muscles through the zonules. By changing the curvature of the lens, one can focus the eye on objects at different distances from it. This process is called accommodation. At short focal distance the ciliary muscles contract, zonule fibers loosen, and the lens is thick resulting in a high refractive index. Changing focus to an object at a distance requires the stretching of the lens by the ciliary muscles which reduces the refractive index and increases the focal distance.
The lens continually grows throughout life, laying new cells over the old cells resulting in a stiffer lens. The lens gradually loses its accommodation ability as the individual ages, the loss of the individual's focusing ability is termed Presbyopia.
The lens is mostly made of transparent proteins called crystallins at an average concentration of about twice that of other intracellular proteins. Crystallins are thought to be key to the refractive properties of the lens while at the same time allowing most light to pass through.
The proteins are arranged in approximately 20,000 thin concentric layers, with a refractive index (for visible wavelengths) varying from approximately 1.406 in the central layers down to 1.386 in less dense cortex of the lens. This index gradient enhances the optical power of the lens. The lens is included into the capsular bag, maintained by the zonules of Zinn.
- A cataract is an opacification of the normally transparent crystalline lens that leads to blurred vision.
- Ectopia lentis is a displacement or malposition of the lens from its normal location.
- Nuclear sclerosis is a normal age-related change of the center of the lens; in veterinary medicine, most commonly seen in dogs.
- Aphakia, the absence of the natural crystalline lens of the eye.
The common disease diabetes affects the lens causing blurred vision. The underlying molecular cause is probably non-enzymatic addition of glucose (glycation) to lens proteins, mainly crystallins. This causes them to form aggregates that obstruct the passage of light through the lens .
The late diabetic symptom of blindness is probably due to effects on hyperglycemia (elevated blood glucose) on the retina not the lens (see diabetic retinopathy).
- Hecht, Eugene. Optics, 2nd ed. (1987), Addison Wesley, ISBN 0-201-11609-X. p. 178.
- Perry RE, Swamy MS, Abraham EC (1987). Progressive changes in lens crystallin glycation and high-molecular-weight aggregate formation leading to cataract development in streptozotocin-diabetic rats. Exp. Eye Res. 44 (2): 269-82.
- Intraocular lens
- Lens capsule
- Light refraction
- Ocular accomodation
- Visual perception
- Zonules of Zinn
- Beers, A. P. A., & van der Heijde, G. L. (1994). In vivo determination of the biomechanical properties of the component elements of the accommodation mechanism: Vision Research Vol 34(21) Nov 1994, 2897-2905.
- Benel, R. A. (1980). Visual accommodation, the Mandelbaum effect, and apparent size: Dissertation Abstracts International.
- Blaker, J. W. (1980). Toward an adaptive model of the human eye: Journal of the Optical Society of America Vol 70(2) Feb 1980, 220-223.
- Bour, L. J. (1981). The influence of the spatial distribution of a target on the dynamic response and fluctuations of the accommodation of the human eye: Vision Research Vol 21(8) 1981, 1287-1296.
- Campbell, M. C., & Hughes, A. (1981). An analytic, gradient index schematic lens and eye for the rat which predicts aberrations for finite pupils: Vision Research Vol 21(7) 1981, 1129-1148.
- Chen, Q., Liang, D., Yang, T., Leone, G., & Overbeek, P. A. (2004). Distinct Capacities of Individual E2Fs to Induce Cell Cycle Re-Entry in Postmitotic Lens Fiber Cells of Transgenic Mice: Developmental Neuroscience Vol 26(5-6) 2004, 435-445.
- Ciuffreda, K. J., Selenow, A., Wang, B., Vasudevan, B., Zikos, G., & Ali, S. R. (2006). "Bothersome blur": A functional unit of blur perception: Vision Research Vol 46(6-7) Mar 2006, 895-901.
- Crewther, D. P., & Grewther, S. G. (2002). Refractive compensation to optical defocus depends on the temporal profile of luminance modulation of the environment: Neuroreport: For Rapid Communication of Neuroscience Research Vol 13(8) Jun 2002, 1029-1032.
- de Graauw, J. G., & Van Hof, M. W. (1978). Relation between behavior and eye-refraction in the rabbit: Physiology & Behavior Vol 21(2) Aug 1978, 257-259.
- Delahunt, P. B., Webster, M. A., Ma, L., & Werner, J. S. (2004). Long-term renormalization of chromatic mechanisms following cataract surgery: Visual Neuroscience Vol 21(3) May-Jun 2004, 301-307.
- Denieul, P. (1982). Effects of stimulus vergence on mean accommodation response, microfluctuations of accommodation and optical quality of the human eye: Vision Research Vol 22(5) 1982, 561-569.
- Deubel, H., & Bridgeman, B. (1995). Fourth Purkinje image signals reveal eye-lens deviations and retinal image distortions during saccades: Vision Research Vol 35(4) Feb 1995, 529-538.
- Ellis, S. R., Wong, J. H., & Stark, L. (1979). Absence of accommodation during perceptual reversal of Necker cubes: Vision Research Vol 19(8) 1979, 953-955.
- Freeman, R. D., & Lai, C. E. (1978). Development of the optical surfaces of the kitten eye: Vision Research Vol 18(4) 1978, 399-407.
- Gawron, V. J. (1980). Eye accommodation, personality, and autonomic balance: Dissertation Abstracts International.
- Goldstein, L. E., Muffat, J. A., Cherny, R. A., Moir, R. D., Ericsson, M. H., Huang, X., et al. (2003). Cystolic beta -amyloid deposition and supranuclear cataracts in lenses from people with Alzheimer's disease: Lancet Vol 361(9365) Apr 2003, 1258-1265.
- Hammond, B. R., Jr., Nanez, J. E., Fair, C., & Snodderly, D. M. (2000). Iris color and age-related changes in lens optical density: Ophthalmic and Physiological Optics Vol 20(5) Sep 2000, 381-386.
- Harkness, L. (1977). Chameleons use accommodation cues to judge distance: Nature Vol 267(5609) May 1977, 346-349.
- Harkness, L., & Benet-Clark, H. C. (1978). The deep fovea as a focus indicator: Nature Vol 272(5656) Apr 1978, 814-816.
- Heron, G., McQuaid, M., & Morrice, E. (1995). The Pulfrich effect in optometric practice: Ophthalmic and Physiological Optics Vol 15(5) Sep 1995, 425-429.
- Hine, T. (1992). Compensatory eye movements during near fixation after fast adaptation to lenses: Ophthalmic and Physiological Optics Vol 12(3) Jul 1992, 335-339.
- Howells, T. H., & Cutler, T. H. (1933). The experimental control of visual factors: Journal of Experimental Psychology Vol 16(6) Dec 1933, 865-872.
- Jackson, G. R. (1999). Aging and dark adaptation. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Jagger, W. S. (1990). The refractive structure and optical properties of the isolated crystalline lens of the cat: Vision Research Vol 30(5) 1990, 723-738.
- Kelly, J. E., Mihashi, T., & Howland, H. C. (2004). Compensation of corneal horizontal/vertical astigmatism, lateral coma, and spherical aberration by internal optics of the eye: Journal of Vision Vol 4(4) 2004, 262-271.
- klein Brink, H. B. (1991). Birefringence of the human crystalline lens in vivo: Journal of the Optical Society of America, A, Optics, Image & Science Vol 8(11) Nov 1991, 1788-1793.
- Koretz, J. F., & Handelman, G. H. (1985). Internal crystalline lens dynamics during accommodation: Age-related changes: Atti della Fondazione Giorgio Ronchi Vol 40(4) Jul-Aug 1985, 409-416.
- Kotulak, J. C., & Schor, C. M. (1986). Temporal variations in accommodation during steady-state conditions: Journal of the Optical Society of America, A, Optics, Image & Science Vol 3(2) Feb 1986, 223-227.
- Kroliczak, G., Goodale, M. A., & Humphrey, G. K. (2003). The effects of different aperture-viewing conditions on the recognition of novel objects: Perception Vol 32(10) 2003, 1169-1179.
- Kruger, P. (1977). The role of accommodation in increasing the luminance of the fundus reflex during cognitive processing: Journal of the American Optometric Association Vol 48(12) Dec 1977, 1493-1496.
- Land, M. F. (1980). Compound eyes: Old and new optical mechanisms: Nature Vol 287(5784) Oct 1980, 681-686.
- Levett, J., & Karras, L. (1977). Effects of alcohol on human accommodation: Aviation, Space, and Environmental Medicine Vol 48 May 1977, 434-437.
- Loerzel, R., Tran, L., & Goss, D. A. (2003). Effect of Lens Power on Binocular Lens Flipper Accommodative Facility Rates: Journal of Behavioral Optometry Vol 14(1) Feb 2003, 7-9.
- Lovicu, F. J., Ang, S., Chorazyczewska, M., & McAvoy, J. W. (2004). Deregulation of Lens Epithelial Cell Proliferation and Differentiation during the Development of TGFfbeta -Induced Anterior Subcapsular Cataract: Developmental Neuroscience Vol 26(5-6) 2004, 446-455.
- Mader, T. H., Carey, W. G., Friedl, K. E., & Wilson, W. R. (1987). Intraocular lenses in aviators: A review of the U.S. Army experience: Aviation, Space, and Environmental Medicine Vol 58(7) Jul 1987, 690-694.
- Malmstrom, F. V., & Randle, R. J. (1976). Effects of visual imagery on the accommodation response: Perception & Psychophysics Vol 19(5) May 1976, 450-453.
- Martin, H., Guthoff, R., Terwee, T., & Schmitz, K.-P. (2005). Comparison of the accommodation theories of Coleman and of Helmholtz by finite element simulations: Vision Research Vol 45(22) Oct 2005, 2910-2915.
- Miller, R. J. (1978). Mood changes and the dark focus of accommodation: Perception & Psychophysics Vol 24(5) Nov 1978, 437-443.
- Mordi, J. A., & Ciuffreda, K. J. (2004). Dynamic aspects of accommodation: Age and presbyopia: Vision Research Vol 44(6) Mar 2004, 591-601.
- Mordi, J. A., & Ciuffreda, K. J. (2004). "Dynamic aspects of accommodation: Age and presbyopia": Reply: Vision Research Vol 44(19) Sep 2004, 2315-2316.
- Murphy, M. R., Randle, R. J., & Williams, B. A. (1977). Diurnal rhythms of visual accommodation and blink responses: Implication for flight-deck visual standards: Aviation, Space, and Environmental Medicine Vol 48 Jun 1977, 524-526.
- Navarro, R., Mendez-Morales, J. A., & Santamaria, J. (1986). Optical quality of the eye lense surfaces from roughness and diffusion measurements: Journal of the Optical Society of America, A, Optics, Image & Science Vol 3(2) Feb 1986, 228-234.
- Nolander, C. R. (1999). The effect of expectation and tinted overlays on reading ability in dyslexic adults. (scotopic sensitivity). Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Owens, D. A. (1979). The Mandelbaum effect: Evidence for an accommodative bias toward intermediate viewing distances: Journal of the Optical Society of America Vol 69(5) May 1979, 646-652.
- Owens, D. A. (1980). A comparison of accommodative responsiveness and contrast sensitivity for sinusoidal gratings: Vision Research Vol 20(2) 1980, 159-167.
- Pedrigi, R. M., David, G., Dziezyc, J., & Humphrey, J. D. (2007). Regional mechanical properties and stress analysis of the human anterior lens capsule: Vision Research Vol 47(13) Jun 2007, 1781-1789.
- Peli, E., & Lang, A. (2001). Appearance of images through a multifocal intraocular lens: Journal of the Optical Society of America, A, Optics, Image Science & Vision Vol 18(2) Feb 2001, 302-309.
- Petersik, J. T. (1979). Optical defocusing reverses perceptual organization: Perception Vol 8(2) 1979, 225-228.
- Pierscionek, B., Green, R. J., & Dolgobrodov, S. G. (2002). Retinal images seen through a cataractous lens modeled as a phase-aberrating screen: Journal of the Optical Society of America, A, Optics, Image Science & Vision Vol 19(8) Aug 2002, 1491-1500.
- Post, R. B., Owens, R. L., Owens, D. A., & Leibowitz, H. W. (1979). Correction of empty-field myopia on the basis of the dark-focus of accommodation: Journal of the Optical Society of America Vol 69(1) Jan 1979, 89-92.
- Provine, R. R., & Enoch, J. M. (1975). On voluntary ocular accommodation: Perception & Psychophysics Vol 17(2) Feb 1975, 209-212.
- Radhakrishnan, H., Pardhan, S., Calver, R. I., & O'Leary, D. J. (2004). Effect of positive and negative defocus on contrast sensitivity in myopes and non-myopes: Vision Research Vol 44(16) Jul 2004, 1869-1878.
- Ramos, F., & Smith, A. C. (1975). Protein differences in the lens nucleus from the desert woodrat (Neotoma lepida): Psychological Reports Vol 37(1) Aug 1975, 219-222.
- Reza, H. M., & Yasuda, K. (2004). The Involvement of Neural Retina Pax6 in Lens Fiber Differentiation: Developmental Neuroscience Vol 26(5-6) 2004, 318-327.
- Rhodes, S. K., Nugent, K. A., & Roberts, A. (2002). Precision measurement of the electromagnetic fields in the focal region of a high-numerical-aperture lens using a tapered fiber probe: Journal of the Optical Society of America, A, Optics, Image Science & Vision Vol 19(8) Aug 2002, 1689-1693.
- Roorda, A., & Glasser, A. (2004). Wave aberrations of the isolated crystalline lens: Journal of Vision Vol 4(4) 2004, 250-261.
- Ruggieri, V., & Alfieri, G. (1992). The eyes in imagery and perceptual processes: First remarks: Perceptual and Motor Skills Vol 75(1) Aug 1992, 287-290.
- Schachar, R. A. (2004). "Dynamic aspects of accommodation: Age and presbyopia": Comment: Vision Research Vol 44(19) Sep 2004, 2313.
- Schmucker, C., & Schaeffel, F. (2004). A paraxial schematic eye model for the growing C57BL/6 mouse: Vision Research Vol 44(16) Jul 2004, 1857-1867.
- Semmlow, J., & Wetzel, P. (1979). Dynamic contributions of the components of binocular vergence: Journal of the Optical Society of America Vol 69(5) May 1979, 639-645.
- Sivak, J. G., Hildebrand, T. E., Lebert, C. G., Myshak, L. M., & et al. (1986). Ocular accommodation in chickens: Corneal vs lenticular accommodation and effect of age: Vision Research Vol 26(11) 1986, 1865-1872.
- Sivak, J. G., & Kreuzer, R. O. (1983). Spherical aberration of the crystalline lens: Vision Research Vol 23(1) 1983, 59-70.
- Stark, W. S., Wagner, R. H., & Gillespie, C. M. (1994). Ultraviolet sensitivity of three cone types in the aphakic observer determined by chromatic adaptation: Vision Research Vol 34(11) Jun 1994, 1457-1459.
- Stolper, J. H. (1977). Color induced physiological response: Man-Environment Systems Vol 7(2) Mar 1977, 101-108.
- Stringham, J. M., & Hammond, B. R., Jr. (2007). Compensation for light loss due to filtering by macular pigment: Relation to hue cancellation: Ophthalmic and Physiological Optics Vol 27(3) May 2007, 232-237.
- Suzuki, T., Yi, Q., Sakuragawa, S., Tamura, H., & Okajima, K. (2005). Comparing the Visibility of Low-Contrast Color Landolt-Cs: Effect of Aging Human Lens: Color Research and Application Vol 30(1) Feb 2005, 5-12.
- Toh, Y., & Okamura, J.-y. (2007). Morphological and optical properties of the corneal lens and retinal structure in the posterior large stemma of the tiger beetle larva: Vision Research Vol 47(13) Jun 2007, 1756-1768.
- Tovee, M. J., Bowmaker, J. K., & Mollon, J. D. (1992). The relationship between cone pigments and behavioural sensitivity in a New World monkey (Callithrix jacchus jacchus): Vision Research Vol 32(5) May 1992, 867-878.
- Trachtman, J. N. (1978). Biofeedback of accommodation to reduce functional myopia: Dissertation Abstracts International.
- Troelstra, A. (1972). Intraocular noise: Origin and characteristics: Vision Research Vol 12(8) Aug 1972, 1313-1326.
- Turuwhenua, J. (2005). A theoretical study of intraocular lens tilt and decentration on perceptual image quality: Ophthalmic and Physiological Optics Vol 25(6) Nov 2005, 556-567.
- Varga, P. (2002). Focusing of electromagnetic radiation by hyperboloidal and ellipsoidal lenses: Journal of the Optical Society of America, A, Optics, Image Science & Vision Vol 19(8) Aug 2002, 1658-1667.
- Vincent, S. B. (1916). The refractive power of lens and fluid media of the mammalian eye: Journal of Animal Behavior Vol 6(4) Jul-Aug 1916, 334.
- von Noorden, G. K., & Crawford, M. L. (1977). Form deprivation without light deprivation produces the visual deprivation syndrome in Macaca mulatta: Brain Research Vol 129(1) 1977, 37-44.
- Williams, T. D. (1976). Effect of meridional disparity on depth perception: Dissertation Abstracts International.
- Winawer, J., & Wallman, J. (2002). Temporal constraints on lens compensation in chicks: Vision Research Vol 42(24) Nov 2002, 2651-2668.
- Winn, B., Pugh, J. R., Gilmartin, B., & Owens, H. (1990). The frequency characteristics of accommodative microfluctuations for central and peripheral zones of the human crystalline lens: Vision Research Vol 30(7) 1990, 1093-1099.
- Zlatkova, M. B., Coulter, E. E., & Anderson, R. S. (2006). The effect of simulated lens yellowing and opacification on blue-on-yellow acuity and contrast sensitivity: Vision Research Vol 46(15) Jul 2006, 2432-2442.
- Histology at Boston University 08001loa
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