Subconjunctival ocular argyrosis Following Treatment with Ruthenium 106 Brachytherapy for Choroidal Melanoma

Purpose Ruthenium-106 (Ru-106) brachytherapy is one of the commonest eye-sparing treatments for choroidal melanoma. New or progressive pigmented lesions in treated eyes are often regarded as suspicious - especially if there are concerns of extra-scleral extension. This short case series describes two patients, previously treated with Ru-106 brachytherapy for uveal melanoma, who developed subconjunctival pigmentation. This study aims to examine the cause for this presentation. Methods Retrospective case series presenting the histopathological features, electron microscopy and energy dispersive X-ray (EDAX) microanalysis results of subconjunctival pigmentation in patients treated with Ru-106 for uveal melanoma. Results The two patients were treated for posterior choroidal melanoma five and ten years previously, with Ru-106 brachytherapy. Both cases developed subconjunctival dark/black lesions on the anterior surface of the eye in the quadrant of the conjunctival peritomy during Ru-106 treatment. Both had similar findings on histopathology: black, non-organic, particulate foreign material of varying confluence, deposited on elastin and collagen fibres. Energy dispersive X-ray microanalysis confirmed the material predominantly contained silver. Conclusions The Ru-106 applicator consists of a radioactive core of Ru-106, encapsulated within pure silver as a radiation shield. During surgical insertion, stainless steel suture needles and forceps can occasionally scratch the applicator's silver eyelets and scatter microscopic particles of elemental silver into the operative field. We believe the observed silver in these cases was likely deposited within the subconjunctival tissues during brachytherapy administration, leading to localised ocular argyrosis. Iatrogenic ocular argyrosis should be considered in the differential diagnosis of new pigmented lesions in patients treated with Ru-106 brachytherapy. This study is the first to unequivocally identify the cause of some post-brachytherapy ocular surface pigmentation as caused by silver.