Hydration (water binding) of the mammalian corneal stroma ex vivo and vitro: sample mass and error considerations.

The corneal stroma is well-known for its capacity to absorb water from experimental solutions but there are considerable differences in how this is actually assessed and described. Measurements on rabbit, sheep, and cow samples ex vivo are presented along with examples of the progressive changes in the stroma in vitro in saline solutions. These are used as the basis for theoretically assessing the impact of systematic and unintentional errors (related to excesses of water or water vapor on the samples) on the estimates of water content, as are the effects of unintentional loss of water from wet samples. Substantial differences in data can easily arise from such errors and/or differences in sample mass. Standardization of the methods for stromal hydration and swelling is required. As a minimum, sample origin (including species), sample dimensions and mass, and the resolution of the weighing protocols are needed, along with details of dry and wet sample handling. With the likelihood of modest errors for the commonly used samples and procedures, reporting hydration data to more than one decimal place is not justified.