The melanin changes of melasma are well known with both pregnancy and oral contraceptives. The observation of Krukenberg spindles shortly after delivery suggested a relationship of female hormones to melanin physiology in the eye. Of 100 pregnant patients examined for Krukenberg spindles, three had them. In one, spindles diminished under observation, and in another they disappeared. Ocular tension outflow studies were normal. No spindles were found in 120 similar, but nongravid female patients.
It is noted that Krukenberg spindles and the pathological condition of pigmentary glaucoma have strong sexual disparities in distribution. Progesterone and possibly estrogen have been implicated in melasma. Progesterone increases iris stromal melanin phagocytosis. Melanocyte-stimulating hormone and insulin may be additional etiological factors. Progesterone, relaxin, and estrogen may increase pigment clearance from the anterior chamber.
Duncan TE. Krukenberg Spindles in Pregnancy. Arch Ophthalmol. 1974;91(5):355-358. doi:10.1001/archopht.1974.03900060367003