Distinct retinal oxygenation patterns in acute zonal occult outer retinopathy assessed by multimodal imaging

Acute zonal occult outer retinopathy (AZOOR) is a rare outer retinal disorder that may mimic inherited retinal dystrophy. This study revises a retrospective AZOOR case series by integrating retinal oximetry as a metabolic imaging biomarker and comparing the oximetry findings with retinitis pigmentosa (RP) and healthy control data.

Seven consecutive patients diagnosed with AZOOR at HOCH Health Ostschweiz in St. Gallen, Switzerland were retrospectively reviewed. Multimodal assessment included best-corrected visual acuity, fundus examination, spectral-domain optical coherence tomography (SD-OCT), fundus autofluorescence (FAF), near-infrared reflectance (NIR-R), fluorescein angiography, visual field testing, multifocal electroretinography (mfERG), full-field electroretinography (ffERG), laboratory work-up, and magnetic resonance imaging. Retinal vessel oxygen saturation data (arteriolar: A-SO₂, venular: V-SO₂ and their difference: A-V SO₂) were available in four AZOOR patients and compared with an existing institutional retinal oximetry dataset containing RP patients and healthy controls. Retinal oxygen saturation and vessel diameter were assessed using Oxymap T1 dual-wavelength retinal oximetry in a predefined peripapillary measurement area. Because of the limited AZOOR sample, all comparative analyses were exploratory.

The AZOOR cohort comprised seven patients (5 female, 2 male; median age 28 years, range 20-53). Six patients presented unilaterally; one patient had congenital aniridia bilaterally but AZOOR was clinically assigned to one presenting eye. Ellipsoid-zone disruption on SD-OCT was present in all affected eyes. MfERG demonstrated macular dysfunction in six of seven patients, whereas ffERG was abnormal in five of seven patients or showed normal full-field responses. Complete retinal oximetry data were available for eight eye/image measurements from four patients. Kruskal-Wallis testing across controls, RP, and AZOOR showed significant intergroup differences for A-SO₂ (H = 10.406, df = 2, p = 0.005) and A-V SO₂ (H = 9.538, df = 2, p = 0.008), but not for V-SO₂ (H = 1.002, df = 2, p = 0.606). Exploratory pairwise Mann-Whitney U tests showed lower A-SO₂ and lower A-V SO₂ in AZOOR compared with controls and RP, whereas V-SO₂ did not differ significantly.

Retinal oximetry added a metabolic dimension to multimodal AZOOR assessment. In this small exploratory cohort, AZOOR showed reduced arterial saturation and reduced arteriovenous oxygen difference compared with controls and RP, whereas venous saturation was not altered. This distinct metabolic AZOOR profile indicates reduced oxygen delivery resulting in altered oxygen use contrary to the known RP pattern of increased oxygen saturation and reduced oxygen use associated with photoreceptor degeneration. These findings should be interpreted cautiously but support further prospective evaluation of retinal oximetry as a complementary imaging biomarker in AZOOR and other outer retinal disorders.