Choroidal vascularity index in hereditary optic neuropathies

Abstract

Purpose: To assess the choroidal vascularity index (CVI) in patients affected by Leber hereditary optic neuropathy (LHON) compared to patients affected by dominant optic atrophy (DOA) and healthy subjects.

Methods: In this retrospective study, we considered three cohorts: LHON eyes (48), DOA eyes (48) and healthy subjects' eyes (48). All patients underwent a complete ophthalmologic examination, including best-corrected visual acuity (BCVA) and optical coherence tomography (OCT) acquisition. OCT parameters as subfoveal choroidal thickness (Sub-F ChT), mean choroidal thickness (ChT), total choroidal area (TCA), luminal choroidal area (LCA) were calculated. CVI was obtained as the ratio of LCA and TCA.

Results: Subfoveal ChT in LHON patients did not show statistically significant differences compared to controls, while in DOA a reduction in choroidal thickness was observed (p = 0.344 and p = 0.045, respectively). Mean ChT was reduced in both LHON and DOA subjects, although this difference reached statistical significance only in DOA (p = 0.365 and p = 0.044, respectively). TCA showed no significant differences among the 3 cohorts (p = 0.832). No changes were detected in LCA among the cohorts (p = 0.389), as well as in the stromal choroidal area (SCA, p = 0.279). The CVI showed no differences among groups (p = 0.898): LHON group was characterized by a similar CVI in comparison to controls (p = 0.911) and DOA group (p = 0.818); the DOA group was characterized by a similar CVI in comparison to controls (p = 1.0).

Conclusion: CVI is preserved in DOA and LHON patients, suggesting that even in the chronic phase of the neuropathy the choroidal structure is not irreversibly compromised.

Fig. 1. Retinal nerve fiber layer and ganglion cell layer thickness diagrams and optic nerve head appearance comparison.

a Severe retinal nerve fiber layer (RNFL) and ganglion cells layer (GCL) thickness reduction in the LE of a patient affected by Leber hereditary optic neuropathy (LHON). b Fundus photograph of the same eye revealing a diffuse pallor of the optic disc and angiopathy. Severe GCC impairment with almost preserved RNFL thickness in a case of dominant optic atrophy (DOA, c). d The optic disc of the same eye demonstrates a temporal pallor. RNFL, GCC thickness and clinical appearance of the optic nerve in a healthy subject, as comparison (e, f).

Fig. 2. Choroidal vascularity index (CVI) calculation procedure.

a Structural horizontal b-scan OCT in a case of Leber hereditary optic neuropathy (LHON) passing through the fovea. A region of interest (ROI) of 1000 µm centered on the fovea was delineated (b) and binarized (c) using Niblack’s auto-local threshold to calculate the CVI. The luminal area is represented by dark pixels, instead the stromal area by the white pixel. CVI was obtained as the ratio between the luminal area and the total choroidal area.