Acute macular neuroretinopathy (AMN) is a rare, macular disorder of unknown aetiology. Patients with AMN are typically young women who present with paracentral scotomata in one or both eyes corresponding to red wedge-shaped parafoveal lesions. The retinal location of the lesion in patients with AMN is not clear. High-speed, ultra-high-resolution optical coherence tomography (hsUHR-OCT) is an investigational research prototype instrument capable of producing cross-sectional images of the retina; it supports an axial resolution of about 3.5 μm compared with about 10 μm in Stratus OCT (Dublin, California, USA)¹ which enables enhanced imaging of intraretinal morphology including photoreceptor inner segments, outer segments and the external limiting membrane.² We report a patient with AMN who underwent imaging with hsUHR-OCT suggesting that the lesion in AMN is located in the outer retina.

Case report

A 51-year-old woman presented with a 10-day history of a sudden onset of a grey, oval paracentral scotoma in her right eye. Her medical history was notable for systemic hypertension; her drugs included trivoral and ramipril. Best-corrected visual acuity was 20/25 in both eyes. She was able to precisely demarcate the paracentral scotoma on an Amsler grid. Funduscopy of the right eye showed a focal, reddish petaloid lesion superior to fixation. Fluorescein angiography and images on the Stratus OCT were unremarkable. hs UHR-OCT images showed focal depression of the external limiting membrane, inner/outer photoreceptor segment (IS/OS) junction, photoreceptors and retinal pigment epithelium. Changes in the photoreceptor outer segments (fig 1A) in the region of the petaloid lesion were also noted. The inner retina appeared normal.

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Figure 1

 Three-dimensional, high-speed ultra-high-resolution optical coherence tomography scan of the macula. A 180-image raster scan (512 axial scans per image) provides a 6×6-mm pattern. The cross-sectional images are precisely registered to a fundus image created from an anterior view of all 180 images. (A) Perimacular petaloid lesion (arrowheads), corresponding to a focal reduction in the photoreceptor outer segments (arrow). (B) Marked resolution of both the petaloid lesion and outer segment morphology at 3-month follow-up. ELM, external limiting membrane; IS/OS, inner/outer segment photoreceptor junction; PR IS, photoreceptor inner segments; PR OS, photoreceptor outer segments; RPE, retinal pigment epithelium.

After 3 months, visual acuity was 20/25 in the right eye, and the patient reported a slight reduction of the scotoma. Funduscopy showed resolution of the petaloid lesion. hsUHR-OCT showed realignment of the outer photoreceptor layer and the IS/OS junction (fig 1B).

Comments

The pathogenesis of AMN remains unknown, although an acute inflammatory process or vascular disease associated with hypertension have both been proposed as mechanisms.^3,4 Acute macular neuroretinopathy has also been associated with oral contraceptive use,⁵ eclampsia⁶ and heavy caffeine consumption.⁷ The resulting scotomata can persist for several years.⁵ Proven treatment is not available.

An early report suggested that the AMN lesion was located in the superficial layers of the retina.³ A later report using OCT suggested that the lesion was located in the outer retina.⁸ Studies using early receptor potential⁹ and a multifocal electroretinogram¹⁰ pointed to photoreceptor involvement.

hsUHR-OCT showed that the focal lesion in patients with AMN occurs in the outer retina, possibly at the level of the photoreceptor outer segments with distortion of the IS/OS junction. The lesion may also represent a disturbance at the outer nuclear layer, resulting in the downward depression and disruption of the underlying external limiting membrane, photoreceptors and rentinal pigment epithelium.hs UHR-OCT shows that the structural changes in the outer retina in this patient with AMN may be reversible despite the persistence of visual symptoms.