Hudson8 in 1911 and Stahli12 in 1918 independently described a superficial horizontal brown line in otherwise normal corneas of predominantly elderly patients. The frequency with which the line was observed was not stated. The youngest patient having a line was 25 years of age. Hudson believed that the location of the line at the junction of the middle and the lower one third of the cornea was related to exposure and the trauma of lid closure which might be responsible for "a primary hyalinization of the cornea." He judged the location of the line to be, "a short distance beneath the corneal epithelium." He noted its similar appearance to Fleischer's pigment ring in keratoconus. Although Fleischer3 had attributed the ring to deposition of hematoidin in the region of breaks in Bowman's membrane, Hudson believed that there was no evidence that the senile line was derived from blood.
GASS JDM. The Iron Lines of the Superficial CorneaHudson-Stahli Line, Stocker's Line and Fleischer's Ring. Arch Ophthalmol. 1964;71(3):348-358. doi:10.1001/archopht.1964.00970010364010