Unusual choroidal vessels in neurofibromatosis type 1 observed with near-infrared reflectance and spectral domain optical coherence tomography.

Abstract

In ophthalmology, the cardinal diagnostic signs of neurofibromatosis type 1 (NF1) are Lisch nodules of the iris occurring in over 90% of cases and optic pathway gliomas in 15% of cases. Retinal microvascular alterations have been described in 35–37.5% of patients (Muci-Mendoza et al. 2002; Abdolrahimzadeh et al. 2014) but the significance of these is still unclear. Choroidal nodules are present in 82–100% of cases (Abdolrahimzadeh et al. 2015), and with the advent of near-infrared reflectance (NIR) imaging, these alterations have been proposed as a new diagnostic criterion. We carried out a retrospective review of the NIR and enhanced depth imaging spectral domain optical coherence tomography (EDI-SDOCT) records of 34 eyes of 17 consecutive patients with diagnosis of NF1 and typical choroidal nodules and 34 eyes of 17 healthy, age-matched subjects (data published in a previous report, Abdolrahimzadeh et al. 2015). All patients were of Caucasian/Mediterranean origin and had similar fundus pigmentation. Best-corrected visual acuity (BCVA) was 20/20 (Snellen charts), and the patients did not have refractive errors above the spherical equivalent of 3 dioptres. Bilateral anomalous choroidal vessels were observed with NIR imaging in four patients and EDI-SDOCT scans were positioned on the alterations observed with NIR and revealed unusually dilated choroidal vessels. The distinct vessels had a diameter, which extended from the choroid–scleral junction to the outer border of the hyper-reflective band corresponding to the retinal pigment epithelium/Bruch's layer. There was an absence of the choriocapillaris or Sattler's layer above the dilated vessels (Fig. 1). No such alterations were observed in age-matched healthy control subjects. Near-infrared light has a deeper penetrance into ocular structures because of the long wavelength that penetrates through melanin and lipofuscin and therefore enables visualization of the choroid. Therefore, NIR and EDI-SDOCT show the choroidal alterations in NF1 and can provide information on choroidal morphology and the depth of choroidal vessels, which cannot be shown with indocyanine green angiography. Yan et al. (2015), in a large population-based study, reported that prominent choroidal vessels are correlated with subfoveal choroidal thinning and speculated that alteration of the choriocapillaris or reduced choriocapillaris filling can be a contributing factor. Pang et al. (2015) recently reported on extreme choroidal thinning in high myopia and reported on the presence of prominent choroidal vessels observed with fundus photography and near-infrared reflectance. These authors hypothesized that the preservation of vision in these patients with extreme choroidal thinning was due to the large choroidal vessels, which maintain the perfusion of the choroid, in turn fundamental to the trophism of the outer retina. Generalized choroidal and retinal thinning has been reported in NF1, and the choriocapillaris has been shown to be thinner and compressed above choroidal nodules (Rao & Choudhry 2014; Abdolrahimzadeh et al. 2015, 2016). Choroidal thinning in NF1 may be due to the presence of choroidal nodules which compromise choroidal blood flow (Abdolrahimzadeh et al. 2014). The choroid is a multifunctional structure with a dynamic vascular nature, and it can be hypothesized that the presence of choroidal nodules and generalized choroidal thinning in NF1, which is an age-related chronic disease, may induce compensatory mechanisms of the choroid in order to provide nutrients and oxygen to the overlying retina similar to the mechanism hypothesized in extreme choroidal thinning in myopia. However, our results should be interpreted with caution as the number of cases reported is small and the abnormal vessels could not necessarily be specific to NF1 as these could possibly be found in other diseases and a larger population of healthy subjects. Figure S1. Near infrared reflectance (NIR) image and cross sectional enhanced depth imaging spectral domain optical coherence tomography (EDI-SDOCT) scan of the right fundus in a 61-year old male patient with neurofibromatosis type 1 (NF1). Figure S2. Near infrared reflectance image (NIR) and cross sectional enhanced depth imaging spectral domain optical coherence tomography (EDI-SDOCT) scan of the right fundus in a 43-year old female patient with neurofibromatosis type 1 (NF1). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.