title: Syneretic response to incremental pressures in calf lenses.
abstract: OBJECTIVE
  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.
authors.affiliation: NMR Imaging Research Facility, National Institute of Neurological Disorder and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA. lizakm@ninds.nih.gov
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Lizak
authors.forename: J Samuel
authors.initials: JS
authors.lastname: Zigler
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Bettelheim
mesh_terms: D000818:Animals; D002417:Cattle; D006874:Hydrostatic Pressure; D007908:Lens, Crystalline / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy