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Optomechanical Response of Human and Monkey Lenses in a Lens Stretcher

¹From the Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida; the ²Biomedical Optics and Laser Laboratory, Department of Biomedical Engineering, University of Miami College of Engineering, Coral Gables, Florida; ³Service d’Ophtalmologie, Centre Hospitalier Universitaire de Caen, France; the ⁴Vision Cooperative Research Centre, Sydney, Australia; the ⁵Institute for Eye Research, Sydney, Australia; and the ⁶School of Optometry and Vision Sciences, University of New South Wales, Sydney, Australia.

PURPOSE. To quantify the forces necessary to change the shape and optical power of human and monkey lenses.

METHODS. Cynomolgus monkey (n = 48; age: 3.8–11 years), rhesus monkey (n = 35; age: 0.7–17 years) and human (n = 20, age 8–70 years) eyes obtained postmortem, including the lens, capsule, zonules, ciliary body, and sclera were mounted in an optomechanical lens-stretching system. Starting at zero load, the lenses were symmetrically stretched in a stepwise fashion in 0.25- or 0.5-mm steps. The load, lens diameter, inner ciliary body diameter, and lens power were measured at each step and the diameter- and power-load responses were quantified.

RESULTS. The diameter- and power-load responses were found to be linear in the physiologically relevant range of stretching. The average change in cynomolgus, rhesus, and human lens diameter, respectively, was 0.094, 0.109, and 0.069 mm/g in young lenses, and 0.069, 0.067, and 0.036, mm/g in older lenses. For the same lenses, the average change in lens power was –3.73, –2.83, and –1.22 D/g in young lenses and –2.46, –2.16, and –0.49 D/g in older lenses.

CONCLUSIONS. The force necessary to change the lens diameter and lens power increases with age in human and monkey lenses. The results agree with the Helmholtz theory of accommodation and with presbyopia theories that predict that the force required to disaccommodate the lens increases with age.

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