X-Message-Number: 25780
Date: Fri, 11 Mar 2005 20:29:42 -0800 (PST)
From: Doug Skrecky <>
Subject: The cause of presbyopia is not aging

[Instead it is lifelong growth in the thickness of the eye
lens. Greater force is then required to deform the lens
to refocus at short distances. Eventually increases in
muscle strength can no longer keep pace with this increased
load and presbyopia results. There are currently no
eye-drops or similar non-invasive procedures for correcting
this age-associated defect.(sigh)]


Prog Retin Eye Res. 2005 May;24(3):379-93. Epub 2004 Dec 19
The mechanism of presbyopia.
  Accommodation in humans refers to the ability of the lens
to change shape in order to bring near objects into focus.
Accommodative loss begins during
childhood, with symptomatic presbyopia, or presbyopia that
affects one's day to day activities, striking during midlife.
While symptomatic presbyopia has traditionally been treated
with reading glasses or contact lenses, a number of surgical
interventions and devices are being actively developed in an
attempt to restore at least some level of accommodation. This
is occurring at a time when the underlying cause of presbyopia
remains unknown, and even the mechanism of accommodation is
occasionally debated. While Helmholtz' theory regarding the
mechanism of accommodation is generally accepted with regard
to broad issues, additional details continue to emerge.
Age-related changes in anterior segment structures associated
with accommodation have been documented, often through in
vitro and/or rhesus monkey studies. A review of these findings
suggests that presbyopia develops very differently in humans
compared to non-human primates. Focusing on non-invasive in
vivo human imaging technologies, including Scheimpflug
photography and high-resolution magnetic resonance imaging
(MRI), the data suggest that the human uveal tract acts as
a unit in response to age-related increasing lens thickness
and strongly implicates lifelong lens growth as the causal
factor in the development of presbyopia.

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