Introduction Latanoprost, a prostaglandin (PG)-related ophthalmic solution, is widely used because, unlike -blockers, it has few systemic adverse effects on the cardiovascular or respiratory system; however, this ophthalmic solution has been found to cause local ocular adverse effects specific to it. The main ocular adverse effects reported in Japan and attributed to ophthalmic treatment with latanoprost, which has been in clinical use in the U.S. since 1997, are conjunc- tival hyperemia, iridial pigmentation, eyelid pigmentation, and eyelash change, with the eyelashes becoming denser, thicker, and longer. 1–6 Clinical studies of iridial pigmentation in the US and Europe revealed that the incidence of the adverse effects varies with the color of the iris and between different races. 3,7,8 Jpn J Ophthalmol 2004;48:141–147 DOI 10.1007/s10384-003-0039-6 © Japanese Ophthalmological Society 2004 CLINICAL INVESTIGATION A Prospective Study of Iridial Pigmentation and Eyelash Changes Due to Ophthalmic Treatment with Latanoprost Tatsuya Chiba, Kenji Kashiwagi, Kiyotaka Ishijima, Mieko Furuichi, Satoshi Kogure, Keitetsu Abe, Nami Chiba, and Shigeo Tsukahara Department of Ophthalmology, University of Yamanashi, Faculty of Medicine,Tamaho, Yamanashi, Japan Abstract Purpose: To conduct a 12-month prospective study on the occurrence of latanoprost-induced iridial pig- mentation and eyelash change in Japanese patients with glaucoma. Methods: Seventy-five patients (75 eyes) were enrolled in the study. Photographs of the iris and eye- lashes were taken under identical conditions before and after treatment. Three glaucoma specialists assessed the iridial pigmentation/eyelash change independently with no knowledge of patient data. The effects of age, sex, concomitant medication, and type of glaucoma on iridial pigmentation/eyelash change were investigated, and intraocular pressure (IOP) reduction and iridocorneal angle pigmentation before and after latanoprost treatment were compared between patients with iridial pigmentation/eyelash change and patients without these changes. Results: The incidence of iridial pigmentation was 6.3% at 1 month, 15.7% at 3 months, 37.8% at 6 months, and 56.5% at 12 months.The incidence of eyelash change was 0% at 1 month, 33.8% at 3 months, 44.4% at 6 months, and 46.2% at 12 months. Latanoprost did not affect IOP reduction or iridocorneal angle pigmentation. No significant relationship between iridial pigmentation and eyelash change was observed. None of the investigated parameters except age affected the iridial pigmentation/eyelash change. Conclusion: Iridial pigmentation and eyelash change occurred at a high frequency in long-term treat- ment with latanoprost in Japanese glaucoma patients. Jpn J Ophthalmol 2004;48:141–147 © Japanese Ophthalmological Society 2004 Key Words: eyelash change, glaucoma, iridial pigmentation, Japanese patients, latanoprost Received: February 10, 2003 / Accepted: August 15, 2003 Correspondence and reprint requests to: Kenji Kashiwagi, Depart- ment of Ophthalmology,University of Yamanashi,Faculty of Medicine, 1110 Shimokato, Tamaho, Yamanashi 409-3898, Japan e-mail: kenjik@yamanashi.ac.jp