Sir,

Type 1 primary hyperoxaluria1 is an autosomal recessive disorder caused by a deficiency of a liver enzyme (alanine-glyoxylate aminotransferase).2 Eye involvement in primary hyperoxaluria consists of calcium oxalate deposits at the level of the retinal pigment epithelium (RPE) with surrounding areas of hypertrophic and hyperplastic RPE.1, 3 Some authors reported on unusual intraretinal distribution of oxalate deposits, apparently sparing the RPE (studies carried out on ocular tissues obtained at autopsy).4, 5

Here, we describe the in vivo spectral-domain optical coherence tomography (Spectralis SD-OCT, Heidelberg Engineering, Heidelberg, Germany) findings in a patient with retinal oxalate deposits (retinal oxalosis) due to primary hyperoxaluria.

Case report

A 19-year-old man diagnosed with type 1 primary hyperoxaluria was referred to our Department. He underwent combined cadaveric liver and kidney transplantation 15 years before. The patient signed a comprehensive consent form according to good clinical practice guidelines, before proceeding with any examinations. His best-corrected visual acuity was 6/24 in the right eye and 20/38 in the left eye. On fundus biomicroscopy, both the eyes showed a fibro-atrophic lesion within the macular area, as well as retinal crystalline deposits, most of which appeared centred by patches of pigment (Figure 1); these deposits were widely distributed in the fundus, and appeared interposed between the RPE and the neurosensory retina. Fundus autofluorescence (AF) showed hyper-autofluorescent dots and ring-shaped areas of hyper-autofluorescence with central hypo-autofluorescence associated with crystal deposition (Figure 1). Interestingly, both fluorescein angiography (FA) (Figure 1) and indocyanine green angiography (Figure 1) revealed almost the same fluorescence features associated with crystal deposition, as the one seen on AF frames (hyper-fluorescent dots and ring-shaped areas of hyper-fluorescence with central hypo-fluorescence). Spectralis SD-OCT clearly showed the oxalate deposits as tiny hyper-reflective lesions localised within areas of dome-shaped elevated RPE (Figure 2).

Figure 1
figure 1

Colour fundus photographs of both right eye (RE) (a1) and left eye (LE) (B) show fibro-atrophic lesions within the macular area, as well as retinal crystalline deposits, most of which appear centred by patches of pigment. Fundus autofluorescence (AF) frame of the RE shows hyper-autofluorescent dots (a2, enlarged view, right side) and ring-shaped areas of hyper-autofluorescence with central hypo-autofluorescence associated with crystal deposition (a2, enlarged view, left side). Both fluorescein angiography (FA) (a3) and indocyanine green angiography (a4) frames reveal almost the same fluorescence features, associated with crystal deposition, as the one seen on AF frames (hyper-fluorescent dots and ring-shaped areas of hyper-fluorescence with central hypo-fluorescence).

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Figure 2
figure 2

Infrared and spectral-domain optical coherence tomography (Spectralis SD-OCT) frames showing the exact correspondence between the oxalate deposits and the tiny hyper-reflective SD-OCT lesions (a–c), which appear localised within areas of dome-shaped elevated RPE (enlarged views), as well as the presence of a fibro-atrophic lesion within the macular area (b).

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Discussion

Spectralis SD-OCT, using confocal scanning laser ophthalmoscopy technology to track the eye and guide OCT to the selected location, gives a real-time reference for locating the SD-OCT scan. Hence, in vivo visualisation of intraretinal structures is possible.

In our patient, Spectralis SD-OCT clearly showed tiny hyper-reflective lesions localised within the areas of dome-shaped elevated RPE (probably representing calcium oxalate deposits, seen on tissues obtained at autopsy, surrounded by area of hyperplasia/hypertrophy of the RPE), associated with retinal oxalate deposits. Interestingly, no crystals deposits were detected, in vivo, within the neurosensory retina.

The tiny hyper-reflective SD-OCT lesions appeared on FAF either as ring-shaped areas of hyper-fluorescence with central hypo-fluorescence, either as hyper-fluorescent dots, probably depending on the pattern of RPE changes associated with crystalline deposits (centred or not by patches of pigment, respectively).

To the best of our knowledge, this is the first description by SD-OCT (in vivo) of the retinal distribution of oxalate deposits in primary hyperoxaluria.