Cross-linked actin networks (CLANs) in bovine trabecular meshwork cells.

A cytoskeletal feature of human trabecular meshwork (HTM) cells in vitro and ex vivo is the presence of cross-linked actin networks (CLANs) that are abundant in a proportion of TM cells exposed to dexamethasone (DEX) and also in cells from glaucoma patients. We wished to determine whether CLANs were present in the bovine trabecular meshwork (BTM), whether they were similarly induced by dexamethasone and whether the structures were comparable to CLANs in HTM cells. Cultures of HTM and BTM cells and ex vivo dissections of BTM tissue were stained with phalloidin (F-actin) and propidium iodide (nuclei) and imaged by confocal microscopy, thereafter being subjected to image analysis. Some CLAN-like structures were identified in ex vivo BTM tissue cultured with and without DEX. However we found that BTM cells in culture produced abundant CLANs when exposed to DEX; comparable to the best response from HTM cells. The CLANs were of similar dimensions and morphology to those found in human cells and they had a similar half life of 2 or 3 days following the removal of DEX. This work demonstrates that BTM cells provide a suitable model for future investigations of CLAN formation and function. BTM cultures are sufficiently hardy to thrive in low serum and serum-free conditions so we were able to show that aqueous humor stimulates CLAN formation in the target cells. Future research is directed at identifying the aqueous component(s) responsible for CLAN production.

Monte Carlo simulation of latanoprost induced iris darkening.

The aim of this study was to provide numerical evidence that latanoprost induced iris darkening (LIID) can be caused by changes to the melanin granule size distribution in the anterior segment of the iris. Iridectomies from two patients were used, where both had undergone unilateral treatment with latanoprost and had exhibited LIID. The untreated eye provided the comparative control. Micrographs from the iris samples were analysed to determine the number and size of the mature melanin granules. Monte Carlo (MC) simulation of light propagation in the iris was performed to examine the changes in reflectance and absorption with varying particle size and density. The reflected intensity of light was obtained as a function of wavelength. CIE colour theory was employed in order to estimate a perceived colour from the reflectance data. MC simulations showed that the reflectance was reduced for the LIID irises compared to the control irises for both subjects and for all wavelengths of light. The MC simulated colours were in good agreement with the in vivo photography of the eye colour. Hence, we have demonstrated that increases in melanin granule size causes iris darkening, and can explain LIID.