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G. Qing, N. Wang, Q. Lu, S. Zhang; Why Are Iris Transillumination Defects Uncommon in Chinese Pigment Dispersion Syndrome Patients. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2488.
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In previous studies of pigment dispersion syndrome (PDS) of Chinese patients, we have found that iris transillumination defects (ITDs) are rare in this patient population. This study was carried out to investigate why striking radial spoke-like ITDs are not as common in Chinese PDS patients as that in whites.
In the first part, patch and fan-shaped posterior iris pigment epithelium (IPE) was scratched on a Caucasian and a Chinese donor iris, in order to investigate the impact of posterior IPE scratch on the color of the iris. The transillumination status at the IPE-absent area before and after the scratch was also documented. In the second part, eleven radial posterior IPE scratches were made on the posterior aspect of six donor Chinese irides mimicking the condition of the iris of PDS patients. Least light densities of direct illumination required to elicit ITD in at least one of the scratches from the posterior aspect of the iris were determined with a digital light meter of all these Chinese irides. In the third part, histological study was carried out to investigate the distribution of pigment granules in the Chinese iris.
In the first part, the color of the Caucasian iris changed markedly from light blue into white-grey after IPE scratch, where iris transillumination was also noted. But in the Chinese iris, neither recognizable change of the color of the iris nor iris transillumination was visualized after IPE scratch. In the second part, the average least light density to elicit ITD of six IPE-scratched Chinese irides was calculated to be 1,372 Lux (ranging from 424 to 3040 Lux). The light density of a 3mm-in-diameter slit-lamp beam which is usually used in ITD test in clinical practice was 2040, 1367, and 2167 Lux, respectively for Haag-streit BQ 900, QD 900, and BM 900 slit-lamp. In the third part, dense pigment granules were noticed in both the IPE layer and melanocytes of the iris stroma and anterior surface of the Chinese iris.
Posterior IPE plays a more important role in determining the color of the iris in Caucasian than that in Chinese. Absence of IPE leads to iris transillumination in Caucasian iris, but not in Chinese iris. The average least light density of direct illumination required to elicit ITD in IPE-scratched Chinese iris is 1372 Lux. It is hard to elicit ITDs in Chinese pigment dispersion syndrome patients with a 3mm-in-diameter slit light beam of which the light density will greatly attenuate after being reflexed and scattered by the ocular media and retina.
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