PMC5643501_01
Fundus photographs. Top:fundus examination reveals a whitish striated appearance of the peripapillary retina. Note that the disk margin is clear, without dilation of the optic disk capillaries or hemorrhages, and that the retinal abnormality begins distant from the optic disk margin. Bottom:red free photographs show better the appearance of the peripapillary retinal nerve fiber layer.
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Fundus examination revealed a striated whitish peripapillary appearance with a normal optic disk in both eyes (Figure 1).
Optical coherence tomography (OCT). Top:OCT (Cirrus, Carl Zeiss Meditec, Inc., Germany). Peripapillary retinal nerve fiber layer (RNFL) was regularly thickened in both eyes (190 microm RE, 198 microm LE; norm 85-110 microm), in all clock hours, with the preservation of the "double hump" appearance (i.e., thicker RNFL superiorly and inferiorly). Bottom:OCT (Spectralis, Heidelberg Engineering GmbH, Germany). A high definition horizontal line through the fovea shows the absence of the normal physiological foveal depression in both eyes (arrow), despite the outer retinal ellipsoid layer exhibiting normal thickening at the fovea (arrowhead).
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Macular OCT showed absence of the normal foveal depression in both eyes (Figure 2).
Electrophysiology. Full-field electroretinography (ERG) was performed using gold foil electrodes. The labeling is conventional and reflects the adaptive state of the eye [dark-adapted (DA) and light-adapted (LA)] and the flash strength (in cd s/m2). The data from a representative normal subject are shown in the lower row for comparison. Dim flash DA ERGs (DA 0.01) show no definite abnormality; the bright flash DA ERGs (DA 10.0) have a negative (electronegative) waveform with a normal a-wave, confirming normal photoreceptor function, but a lower amplitude b-wave in keeping with inner retinal dysfunction. The 30 Hz flicker ERG is bilaterally delayed, and although the single flash LA ERG (LA 3.0) shows no definite abnormality, photopic long duration stimulation, to separate the function of the cone On- and Off- pathways, shows a markedly negative On- response (reduced b:a ratio). The findings overall indicate generalized inner retinal dysfunction in both rod and cone systems, probably predominantly involving the On- pathways. The pattern electroretinogram (PERG) is bilaterally subnormal in keeping with the optical degradation introduced by keratoconus.
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Bright flash dark-adapted ERG had an electronegative waveform (i.e., the b-wave amplitude was lower than the a-wave amplitude), in keeping with inner retinal rod system dysfunction (Figure 3).
Magnetic resonance imaging (3 T). Left:sagittal cut, T1-weighted sequence revealing cerebellar vermis atrophy (arrow). Right:axial cut, T2-weighted sequence revealing bilateral and symmetrical hypointense linear lesions in the pons (small arrows in insert).
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T1-weighted sequences (Figure 4). The combination of an atrophy of the superior cerebellar vermis with the presence of linear hypointense striated lesions in the pons on T2 or Flair sequences has been reported by several authors in ARSACS patients.