Abstract
Purpose :
To investigate how inhibition of the lens microcirculation system differentially affects water transport, water content, lens geometry, GRIN, and power of the bovine lens.
Methods :
Bovine lenses were incubated in either artificial aqueous humour (AAH), high extracellular K+ (AAH-High K+), or ouabain (AAH+ouabain) for 4 hours. A microelectrode/pico-injector based pressure measurement system was utilised to measure the intracellular hydrostatic pressure gradient that drives water efflux. MRI was used to measure free and total water content. A custom-built Laser Ray Tracing (LRT) system that scanned lenses with 151 parallel rays delivered at 4 different angles was used to extract changes in lens geometry, gradient refractive index (GRIN) and power over time. Lens geometry and GRIN were inputted into ZEMAX optical modelling software to assess changes in overall vision quality.
Results :
Like smaller rodent lenses, the larger bovine lens exhibited an intracellular hydrostatic pressure gradient that varied from approximately 0 mmHg at the lens surface to 326 mmHg in the core. Inhibiting the microcirculation system by depolarization of the lens membrane potential with AAH-High K+, reduced the lens central hydrostatic pressure by 16%, increased the water content across the whole lens, caused a slight rounding of the lens geometry and a decrease in GRIN, which manifested as a slight increase in power in the lens core over time. Inhibiting the microcirculation by blockade of the Na+/K+-ATPase with AAH+ouabain, reduced the lens central hydrostatic pressure by 24%, increased the water content specifically in the lens core, caused a substantial rounding up of the lens geometry, but increased the central GRIN. Taken together these changes induced a significant increase in lens power and resulted in a marked myopic shift in overall vision quality.
Conclusions :
While inhibition of the microcirculation system by depolarizing the lens, or blocking the Na+/K+-ATPase both decreased lens pressure, increased lens water content and increased power, ouabain counter-intuitively increased central GRIN. This suggests that blockade of Na+/K+-ATPase has altered the refractive index increment (dn/dc) of crystallins in the lens core, presumably by changing the ionic environment in this lens region.
This is a 2021 ARVO Annual Meeting abstract.