Microvascular changes after proton beam radiotherapy for iris melanoma: An optical coherence tomography angiography study

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Abstract
Purpose: To evaluate macular and peripapillary microvascular changes after proton beam radiotherapy for iris melanoma using optical coherence tomography angiography (OCT-A). Methods: Patients treated with proton beam radiotherapy for iris melanoma were included in the iris melanoma group. Fellow eyes were used as controls. Vessel density (VD) of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) of the macula, radial peripapillary capillary plexus (RPCP) and foveal avascular zone (FAZ) were evaluated using OCT-A. Central macular thickness (CMT) and nerve fiber layer thickness (RNFL) were also investigated. Results: A total of 11 patients were included. Vessel density in the whole SCP was comparable between treated eyes and untreated fellow eyes ( p = 0.32). Vessel density in the whole DCP was lower in the iris melanoma group compared with untreated fellow eyes: 39% [standard deviation (SD) 1.9] versus 49% (SD 4.1), respectively ( p < 0.001). Vessel density of the whole RPCP was lower in the iris melanoma group compared with untreated fellow eyes: 44% (SD 3.5) versus 48% (SD 2.2), respectively ( p = 0.02). No differences between treated eyes and untreated fellow eyes were noted when evaluating FAZ, CMT and RNFL thickness. Conclusion: Irradiation of the iris may determine vascular damage in the uveal tract, which, consequently, can affect the retinal vascular network. Changes in OCT-A parameters detected in DCP and RPCP may be early signs of microvascular impairment in these patients.

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