Assessment of Choroidal Nevi with Polarization-Diversity Optical Coherence Tomography

Authors: Hoyoung Jung  , Yusi Miao, Steven Bae, Myeong Jin Ju, Katherine Paton, Zaid Mammo.  University of British Columbia.

Author Disclosures: H. Jung:   None.  Y. Miao:   None.  S. Bae:   None.  M. Ju:   None.  K. Paton:   None.  Z. Mammo:   None.

Abstract Body: 

Purpose:   Polarization-diversity optical coherence tomography (PD-OCT) is a functional extension of OCT that measures the polarization state of light and can detect depolarization due to melanin pigment within the retinal pigment epithelium (RPE) and choroid. This is the first study to characterize choroidal nevi based on their melanin content and qualitative imaging features on PD-OCT in comparison to fundus photography and spectral-domain OCT (SD-OCT).   

Study Design:   Cross-sectional observational cohort study.   

Methods:   Research ethics board approval and written informed consent from all patients were obtained. Twenty-two eyes with at least one choroidal nevus were imaged using a custom-built 55-degree field-of-view PD-OCT system. Our PD-OCT is based on a 1060-nm swept-source OCT system combined with a polarization diversity detection unit that simultaneously detects two orthogonal polarization signals. It has an imaging range of 5 mm, theoretical axial resolution of 4.94 µm, a root mean square (RMS) lateral resolution of 15.8 µm, and delivers approximately 1.5 mW of power to the cornea. A bi-directional scanning pattern was employed for fast and efficient data acquisition, with volume sizes of 1000 A-scans by 1000 B-scans, corresponding to 2.5 seconds of total volume acquisition time. By measuring polarization signal randomness with a novel adaptive kernel, depolarizing melanin structures were exclusively highlighted as a degree of polarization uniformity (DOPU) metric. To produce layer-specific en-face melanin concentration maps, deep neural network segmentation of the RPE and choroid was employed. Images were compared with fundus photographs and SD-OCT images.   

Results:   Twelve melanotic nevi of twelve patients with average area of 9.95 mm² (range: 2.64-33.53 mm²) and average longest basal diameter of 3.72 mm (range: 2.01-7.48 mm) were imaged with the entire margin captured in a single acquisition. The PD-OCT B-scan and en-face projections of melanotic nevi showed well-circumscribed axial and en-face nevus margins, thus providing three-dimensional margin visualization. The PD-OCT projections also visualized RPE changes normally detected on SD-OCT, including subretinal fluid, retinal layer elevation, and drusen.   

Conclusions:   PD-OCT provides non-invasive, cross-sectional in-vivo visualization of choroidal nevi by harnessing the light-polarization properties of melanin pigment granules. Our PD-OCT system demonstrated improved delineation of nevus margins compared to fundus photography and SD-OCT, which may improve monitoring of growth and potential malignant transformation. Characterization of melanin features of choroidal nevi with PD-OCT may also be a useful means to differentiate and monitor choroidal lesions.