Red (rust) spots in hydrogel contact lenses

The red spot phenomenon was investigated by examining sagittal sections of corroded ferrous particles embedded in the matrix of hydrogel contact lenses and also by analyzing the incidence of this contamination. The incidence of the red spot phenomenon was found to be 4.4% and was unrelated to the method of manufacture or whether the lens was new or used. The ferrous particles are of probable exogenous origin, introduced by environmental or aqueous debris, and the subsequent corrosion is accelerated by heat disinfection.