Anterior Lens Curvature and the Catenary Suspension Model of Accommodation: A High Frequency Ultrasound Study

Abstract

Abstract: : Purpose: To determine if changes in the shape of the anterior lens surface during accommodation, as measured by very high frequency ultrasound, are consistent with the catenary diaphragm model of accommodation in relation to both accommodation and presbyopia. Methods: The anterior segment of young adult subjects was scanned with a very high frequency (50 MHz) ultrasound digital arc scanner before and during accommodative challenge to the fellow eye. The curvature of the anterior lens surface was fit with direct least–square polynomials and b–splines. The changing spatial relationship to the ciliary body and anterior chamber depth during accommodation was also measured. Results: Anterior translation of the front surface of the lens and anterior curvature change were found to be consistent with the catenary model, since a high order polynomial shape provided optimal fit to the anterior lens surface. They were also consistent in shape with Scheimpflug–based measurements by Koretz et al of adult human eyes. Conclusions: The specific high order polynomial anterior shape of the lens in accommodation accounts for depth of field and difficulties in routine evaluation of accommodative range. The unique aspherical, i.e. high order polynomial shape, of the anterior lens and its rapid reproducibility are inconsistent with a capsular mechanism for accommodation, but are easily explained by and consistent with a catenary diaphragm model.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optical properties