Aging of the human lens: changes in lens shape upon accommodation and with accommodative loss

Abstract

Accommodation in the human eye occurs through controlled changes in crystalline lens shape, thickness, and refractive surface placement relative to the cornea. The changes in lens curvatures, whether surface or internal, have been characterized as a function of accommodation and subject age by use of quantitative analysis of Scheimpflug slit-lamp photographic images. Radii of curvature of the major lens refractive surfaces--the external and nuclear boundaries--decrease linearly with increasing accommodation in all eyes that are capable of accommodation. The rates at which they change with accommodation are age dependent, decreasing steadily toward zero with increased age. For the curves visible in each lens half, arising from boundaries between adjacent zones of discontinuity, radius of curvature and location are linearly related over the entire accommodative range for a given lens and over the age range for the population. The slope of this relationship changes with both accommodation and age, decreasing linearly in both cases. The relationship between these geometric changes and the loss of accommodative amplitude is discussed.

Age-dependence of the optomechanical responses of ex vivo human lenses from India and the USA, and the force required to produce these in a lens stretcher: The similarity to in vivo disaccommodation

“…The age-related in vivo decline has been variously attributed to changes in lens surface curvature and refractive index distributions as well as, but less likely, alterations in other ocular components ([Atchison, 1995], [Fincham, 1937], [Glasser and Kaufman, 2003] and [Strenk et al ., 2005]). Recent studies on isolated lenses ([Borja et al ., 2008] and [Jones et al ., 2005]) indicate that the surfaces contribute only 20-40% of accommodated power change, most from the anterior surface ([Dubbleman et al ., 2005], [Fincham, 1937], [Garner and Yap, 1997] and [Koretz et al ., 2002]) and this changes little with age. Thus, alterations in the refractive index distribution, such as the development of the nuclear refractive index plateau (Augusteyn et al ., 2008), would be major factors responsible for the loss of power.…”

Pentacam Scheimpflug Quantitative Imaging of the Crystalline Lens and Intraocular Lens

“…Although a Scheimpfl ug system could not compete in resolution with anterior segment optical coherence tomography (OCT), 15 which otherwise should also be corrected from optical distortion, 16,17 the large depth of focus in Scheimpfl ug images allows full cross-sections of the anterior segment, from the anterior cornea to the posterior lens, in a single snapshot generally not possible with OCT. Applications of corrected Scheimpfl ug crystalline lens/IOL in vivo imaging include customized eye modeling, 18,19 studies of quantitative changes of crystalline lens morphology with accommodation, 11,[20][21][22] aging, 6,23 or disease, 24 and assessment of new intraocular implants and surgical approaches for the correction of presbyopia. 25 …”

The lens capsule

“…This reshaping results from a reorganization of the lens cortical fibers and nucleus (Koretz and Handelman, 1982). Coordinated sliding of the fiber cell basal and apical tips (Kuszak et al, 2006) gives the lens the ability to mold around the shape of the lens nucleus (Brown, 1973; Koretz et al, 2002). …”