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K.P. Cracknell, I. Grierson, P. Hogg; Morphological Effects of Long-Term Exposure of Iris Tissue to Latanoprost (Xalatan®) . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4399.
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Purpose: This is an ongoing study, investigating the latanoprost-induced iris darkening (LIID) side effect, in patients after long-term drug treatment. Its aim is to characterise at an electron microscopic (EM) level any morphological changes in affected iris tissue, particularly emphasising changes in melanogenesis. Method: The peripheral iridectomes were sent to us for evaluation. LIID samples were only accepted into the study if accompanied by photographic evidence of color change. We have completed the analysis on 11 treated and 8 control iridectomies at the present time. The exposure to latanoprost in our study ranges from 3 months to 3 years 5 months. Tissue cellularity was assessed by light microscopy and the ultra-structure was investigated by EM. A series of micrographs were obtained for each sample (mag 5,200x) and analysed using image analysis software. The tissue area occupied by melanocytes and other cells was determined. Melanin granules within the melanocyte cytoplasm were analysed to determine their, number, maximum diameter and the area they occupied. Results: No pathological changes were seen in any of the iris tissue samples. The ultra-structural analysis revealed that the controls of blue and brown/hazel eye colors have vastly differing quantities of melanin within their cytoplasm. In blue irides the area occupied by melanin per 100µm2(granularity) was 1.1 ± 0.4 whereas in the brown group the granularity was 14.7 ± 4.8, with the LIID group the granularity was found to be 14.8 ± 6.0. The number of melanin granules per 100µm2 of melanin cytoplasm was 35 ± 8 for blue 279 ± 60 for browns and 254 ± 73 for LIID groups. The mean melanin granule diameters were 0.25 ± 0.02µm in blue irises, 0.31± 0.04µm for browns and 0.33 ± 0.03µm in the LIID group. Conclusion: Results to date revealed that LIID irises with short or prolonged exposure to latanoprost were structurally similar to irises from our control groups. There were no significant differences in size, numbers of melanin granules or granularity in the melanocytes of LIID specimens when compared to the peripheral iris of untreated hazel/brown patients.
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