Unilateral electronegative ERG in a presumed central retinal artery occlusion

Abstract

A unilateral electronegative electroretinogram (ERG) was seen in a 94-year-old man with presumed central retinal artery occlusion. Goldmann perimetry revealed central scotoma in the right eye and no abnormalities in the left eye. Full-field ERG in the right eye described a reduction of the b-wave with a relative preservation of the a-wave which is characteristic of electronegative ERG. Hence, our case illustrates that ERG testing is essential for the work-up of individuals with suspected retinal vascular disorders.

Keywords: central retinal artery occlusion; electronegative ERG; inner retina; spectral domain optical coherence tomography.

Figure 1

Color fundus photographs shows few drusen on the posterior pole in both eyes, and retinal pigment epithelium (RPE) atrophy with pigmentary clumps on the macular area of left eye. Minimal retinal artery narrowing can be observed in both eyes. Fundus fluorescein angiography depicts window defect in the posterior pole compatible with RPE atrophy in the left eye in the venous phase. There was no apparent delayed fluorescein filling in both eyes.

Figure 2

Spectral domain optical coherence tomography (SD-OCT) revealed reduced retinal thickness in the right eye (A) and left eye (B). Note the decreased thickness of the inner retina in right eye is more advanced than the left eye.

Figure 3

The thickness of the inner retina was established as the distance between retinal nerve fiber layer and inner nuclear layer and was measured using the 1,000 μm caliper available in the OCT-SLO Spectralis. Ten age-matched normal eyes were used as controls. Observe the decrease in the nasal and temporal inner retinal thickness in the right eye in comparison to the left and normal control eyes.

Figure 4

Full-field electroretinogram (ERG) showing electronegative ERG in the right eye and minimal generalized dysfunction in the left eye. Scotopic rod specific ERG has b-wave amplitude of 27 μV and in the right and 71 μV in the left. Maximal ERG a- and b-wave amplitudes were 59 and 9 μV in the right eye and 83 and 130 μV in the left eye. Maximal ERG a-wave implicit times were 22 milliseconds in the right and 19 milliseconds in the left. Transient photopic ERG b-wave amplitudes were extinguished in the right and 68 μV in the left. Photopic 30 Hz flicker ERG were extinguished in the right but had implicit times and amplitudes of 50 μV and 30 milliseconds in the left.