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Editor,—Patients with acute zonal occult outer retinopathy (AZOOR) may present with a normal fundus examination and almost normal fluorescein angiography (FA), despite severe loss of visual field and electroretinogram (ERG) abnormalities.1 2 The lesion defined zones of the retinal receptor cells; however, the cause of the disease remain unclear.3 There is also no established conclusion about progression of visual field loss.1
With a multifocal ERG (m-ERG), a large number of retinal locations can be stimulated simultaneously and local responses can be extracted independently in a single recording session. High resolution topographic mapping of retinal function also is possible.4A previous report indicates its efficiency in the diagnosis of AZOOR.5 There are no reports about the clinical course. Thus, using m-ERG and static perimetry (Humphrey 30-2), the alteration of retinal function in a clinical course of a patient with AZOOR was investigated.
A healthy 26 year old woman presented to our outpatient clinic complaining of acute onset of visual disturbance in her left eye. Her corrected visual acuity was 20/20 in her right eye, and 20/100 in her left. The pupils were equal and reactive normally. Slit lamp and fundus examination, computed tomography, magnetic resonance imaging scan, and general examination were normal. HVF 30-2 demonstrated blind spot enlargement breaking out to the inferotemporal periphery in the left eye (Fig 1, top). Full field ERG showed grossly reduced A and B waves in the left eye. The FA showed slight leakage from peripapillary capillaries. Indocyanine green (ICG) angiography showed slight hypofluorescence of the macular area at a late phase.
Analysis of the mean deviation in HVF over the clinical course corresponded with the visual acuity (Fig 1, bottom). In addition, m-ERG (Veris III, Tomey, Nagoya, Japan) was analysed during the clinical course. In this examination, the fundus was divided into four foci and the sum of amplitudes in each group was measured (Fig 2, top). In the left eye, the sum of amplitudes was altered individually but all of them were affected during the clinical course. Only in the inferotemporal area did it correspond with HVF. The values in the right eye were about 5000 μV in each focus. This is almost the same as normal volunteers in our clinic (data not shown).
AZOOR may be precipitated by various retinal disorders and is characterised by rapid visual field loss which cannot be explained by the ophthalmoscopic changes resulting from the initiating disease. The ERG is abnormal, indicating that the field loss is due to retinal dysfunction.6 The cause of the acute damage to sharply defined zones of the retinal receptor cells in the absence of visible fundus changes in patients with AZOOR is unknown.7 In some previous reports, an apparent response to corticosteroid therapy suggested that an inflammatory and perhaps an immune reaction may play a part in the disease; however, there is no specific evidence for an immune abnormality.6 8 An infectious aetiology could also be the cause of AZOOR.8
The findings of AZOOR that we observed in our patient suggest that the retinal recovery assessed by m-ERG was different for the lesion (main focus was related to the inferotemporal retina) and was delayed compared with visual acuity and HVF. Perhaps this delayed retinal recovery reflects a subtle microcirculatory disturbance that can not be clearly detected by FA or ICG. Slight leakage in FA and slight hypofluorescence on the late phase in ICG would suggest such a microcirculation disorder.
When better understanding of the aetiology and pathophysiology of AZOOR is available, the clinical response to appropriate therapy may perhaps best be followed by m-ERG.
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