Optical Analysis of Subcapsular Cataracts in TGF–ß Transgenic Mice and TGF–ß–Treated Rat Lenses

Abstract

Abstract: : Purpose: Cataract research often involves qualitative evaluation of lens optics by simply photographing the appearance of a grid target through the lens. The approach used here involves the quantification of the primary function of the lens, the focusing of light. This study analyzes the optical effects of TGF–ß induced subcapsular cataracts in TGF–ß transgenic mice and TGF–ß–treated rat lenses, as well as the potential role of MMPs in TGF–ß–induced subcapsular cataract. Methods: Lenses were dissected from wild–type mice (n=7) and TGF–ß transgenic mice (5–7 months), in which TGF–ß is expressed in the lens under control of the αA crystallin promoter (n=10). Lenses were also obtained from 2–6 months–old Wistar rats either left untreated (control) (n=4)or treated with TGF–ß1 (1ng/ml, n=5) or TGF–ß1 plus Ilomostat (MMP inhibitor 25µM, n=4). The mouse and rat lenses were transferred into a glass chamber with Medium 199 and optical analyses were performed using a scanning laser instrument. The image of a scanning HeNe laser beam was collected by digital cameras and the refracted direction for each of the beam positions is recorded with respect to the optical center. Back vertex distance variability (BVD variability) is used as an indicator for changes in the sharpness of focus. Results: The results show a significant increase in BVD variability (decreased sharpness of focus) in TGF–ß1 mice (0.157±0.016 mm) when compared to the lenses from the wild–type group (0.020±0.010 mm). Each TGF–ß1 mouse lens exhibited a consistent disruption in the quality of focus, while control lenses maintained optimal focal measurements. TGF–ß1– treated rat lenses show a significant increase in BVD variability (0.225±0.036 mm) when compared to the control (0.134±0.004mm) and TGF–ß1 + Ilomostat treated lenses (0.121±0.007mm). The optical analysis of TGF–ß1–treated lenses detected the presence of distinct subcapsular opacities which were not apparent in the TGF–ß1 +Ilomostat–treated lenses. Conclusions: These findings indicate that the scanning laser measurement of lens focal characteristics is an effective means of quantifying lens optical function in transgenic mice and in vitro rat lens models of subcapsular cataract. This method will provide the optical sensitivity required for further investigation of the temporal induction of TGF–ß cataract formation and the apparent inhibition by Ilomostat.

Keywords: cataract • growth factors/growth factor receptors • optical properties