A long term follow up of ocular siderosis: quantitative assessment of the electroretinogram

Siderosis oculi is a severe sequel of retained, iron made, intraocular foreign body. Iron atoms or ions, dissolved from the foreign body, may diffuse to the retina and produce irreversible cellular damage. Therefore, early extraction of an iron foreign body is recommended. When the risks of surgical intervention outweigh the danger of siderosis, the patient is periodically examined in order to detect the initial signs of siderosis. The most commonly used test for quantitative and objective assessment of retinal function is the electroretinogram (ERG). We report here a long term ERG follow-up (about 8 years) of a patient suffering from a unilateral iron intraocular foreign body. The development of siderosis was detected by any of the ERG responses; cone-dominated, rod-dominated or mixed cone-rod responses. However, the degree of the assessed damage varied and strongly depended upon the flash intensity used to elicit the ERG response and upon the ERG wave chosen to assess retinal function. The relationship between the ERG b- and a-waves showed a profound deterioration reflecting a reduction in signal transmission from the photoreceptors to the inner nuclear layer. These findings suggested that iron toxicity produced more damage to the inner retina than to the outer retina.