Syneretic Response to Incremental Pressures in Calf Lenses

Abstract

Purpose: Syneretic response to pressure variation of 1 atm or more has been demonstrated previously in bovine and human lenses with nuclear magnetic resonance (NMR) relaxation measurements. This study is designed to prove that a similar response is observable in smaller pressure increments closer to the normal physiological range.Methods: Excised calf eyes were enucleated, the lenses dissected out, and immersed in medium. The lenses were exposed to incremental pressures ranging from 1 to 3 atm. At each pressure increment, a series of T1-weighted and spin echo images were acquired. Each image was segmented into seven regions of interest and tabulated. Longitudinal (T1) and transverse (T2) relaxation times were calculated from numerical fits of the experimental values to a one-term exponential expression.Results: The relaxation parameters were obtained from fitting the image intensities to exponential equations, which yielded a relaxation time T and a pre-exponential factor M. The relaxation times and the pre-exponential terms of both parameters displayed linear dependence on pressure. There was no evidence of a threshold for syneretic response. Both T1 and T2 relaxation times decreased with increasing pressure. The pre-exponential term M2 increased with pressure, whereas M1 decreased with pressure; however, the slope of the latter was statistically not significantly different from zero.Conclusions: Syneretic response to pressure in calf lenses as determined by NMR relaxation measurements proved to be linearly dependent on pressure over a wide range of hydrostatic pressures. There was no range where the syneretic response was absent. These two findings allow the conclusion that the phenomenon observed hitherto at large pressure changes in vitro could be operative in vivo under physiological pressure changes during accommodation.