• DOI:10.1097/00004397-200604630-00003
• Corpus ID: 45247729

Scleral Expansion Procedure for the Correction of Presbyopia

@article{Kleinmann2006ScleralEP,
  title={Scleral Expansion Procedure for the Correction of Presbyopia},
  author={Guy Kleinmann and Hee Joon Kim and Richard W. Yee},
  journal={International Ophthalmology Clinics},
  year={2006},
  volume={46},
  pages={1-12}
}

• G. Kleinmann, H. Kim, R. Yee
• Published 1 August 2006
• Medicine
• International Ophthalmology Clinics

Since 1855, the dominant theory for accommodation is that of Hermann von Helmholtz. The Helmholtz mechanism of accommodation states that contraction of the ciliary muscle results in a release of the tension on the zonular fibers allowing the lens to round up and become more convex during accommodation to allow near objects to be brought into focus. Thus, according to Helmholtz, accommodation results in the movement of the equatorial edge of the lens away from the sclera and disaccommodation results in the lens movement toward the sclera. Extensive studies by Fincham, Fisher, Pau and Kranz provided supplemental evidence that presbyopia resulted because of hardening of the crystalline lens and the inability of the lens capsule to mold the hardened lens substance into the accommodated form. Despite its wide acceptance, fundamental elements of the Helmholtz mechanism of accommodation remain controversial. First, the theory lacks the ability to adequately explain planar stability of the lens diaphragm despite zonular relaxation. When prone, gravity should pull the lens away from the retina thereby increasing its optical power and when supine, the opposite should occur. However, studies of subjects in supine versus prone positions by Schachar and Cudmore and studies of astronauts by Vanderploeg, have failed to show a gravitational effect on the amplitude of accommodation. Also, from the Helmholtz theory arises the ‘‘lens paradox.’’ According to this theory,