Multifocal electroretinographic and angiographic changes in pre-eclampsia

CASE REPORT

A 28 year old Chinese woman, gravida II, para I, was hospitalised at 31 weeks' gestation with blood pressure of 178/98 mm Hg, 4+ proteinuria and pretibial oedema. At 34 weeks' gestation, emergency caesarean section was performed because of uncontrolled pre-eclampsia. Two days post partum, she complained of blurring of vision in the right eye. On examination, her visual acuity was right eye: 20/30, left eye: 20/15. There was no afferent pupillary defect. Anterior segment and intraocular pressure was normal. Fundal examination revealed bilateral greyish-yellow lesions at the level of retinal pigment epithelium (RPE), distributed mainly in peripapillary area and posterior pole. There was shallow inferior serous retinal detachment in the right eye. FA and ICGA of both eyes showed early patchy hypofluorescence with delayed filling of choroid around the discs and nasal maculae, suggestive of choroidal ischaemia. Late phase showed leakage with stippled staining (Fig 1).

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Figure 1

Right eye at 2 weeks post partum. (Top) Fluorescein angiogram shows delayed filling of choriocapillaries in the early phase and leakage with staining in the late phase. (Bottom) Similar changes in indocyanine green angiogram.

MERG was performed 2 weeks post partum. Stimulation used was the 103 hexagons at rate of 75 Hz using pseudorandom binary m-sequence withveris system (Electro Diagnostic Imaging, Inc, San Mateo, CA, USA). Three dimensional topography and trace array of the MERG showed decreased response amplitudes in both nasal maculae and the right fovea. There was also delayed N1 and P1 implicit times and diminished response density of the nasal macula compared with the temporal macula in both eyes (Fig 2). Five weeks post partum, her visual acuity improved to 20/15 in both eyes. RPE changes corresponding to areas of delayed filling and leakage were found. FA and ICGA performed 3 months post partum were unremarkable. However, MERG showed persistent bilateral mild decrease in amplitude of the nasal macula compared with the temporal macula, despite full recovery of the right foveal peak. Visual field assessment was not performed.

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Figure 2

Multifocal electroretinogram (MERG) of right eye. (Left) At 2 weeks post partum, trace array and three dimensional MERG topography showing decreased retinal response density in the fovea and nasal part of the macula. Average MERG responses of the temporal and nasal maculae showing prolonged N1 and P1 latencies as well as diminished response amplitude of the nasal macula compared with the temporal macula. Mean N1 and P1 latencies were 16.7 ms and 30.0 ms for the nasal macula, and 14.2 and 27.5 ms for the temporal macula, respectively. Mean P1 response amplitude for the nasal right macula is 70% of the temporal response (18.0 nV/deg² v 26.3 nV/deg²). (Right) At 3 months post partum, trace array and three dimensional MERG topography show recovery of the foveal response. However, average MERG response shows persistent mild decrease in response amplitude in the nasal macula, which is 83% of the temporal macula (19.2 nV/deg² v 23.4 nV/deg²).

COMMENT

In our patient, the area of decreased response amplitude and delayed latencies in MERG corresponded with the area of choroidal ischaemia detected by FA and ICGA. Additionally, it detected abnormal area in the right fovea that did not show up with FA or ICGA. When repeat FA and ICGA were unremarkable 3 months later, MERG still showed persistent abnormality in both nasal maculae. The partial recovery of MERG in our case supports the current concept of transient vasospasm in choroidal circulation in pre-eclampsia. However, the damage may not be completely reversible as previously reported. The signals of MERG are thought to be derived from the outer retinal layers of cones and also the inner retinal layer including the bipolar and Muller cells. The retinal response may be impaired secondary to RPE dysfunction and choroidal ischaemia. Similar MERG findings in central serous chorioretinopathy were reported, in which the RPE abnormality is thought to be secondary to the underlying choroidal vascular disease. MERG has the advantage of being non-invasive and risk of breastfeeding after angiography can be avoided. It is more sensitive than FA and ICG in the evaluation of macular choroidal ischaemia in pre-eclampsia.