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Heather Moss, Jason C Park, J Jason McAnany; Inner and outer retinal dysfunction in idiopathic intracranial hypertension. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3540.
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© ARVO (1962-2015); The Authors (2016-present)
To define patterns of inner and outer retina dysfunction in idiopathic intracranial hypertension (IIH).
5 subjects (4 female, 25-52 years old) meeting Dandy criteria for IIH with moderate vision loss (mean deviation(MD) -4.4 - -25.9 dB, Humphrey 24-2 SITA fast) were prospectively recruited and studied in undertreated (n=3), treated (n=1) and both undertreated and treated states (n=1). Pupil light responses (PLR) to full field blue and red light stimuli optimized to stimulate cone, rod and melanopsin ganglion cell pathways were recorded with an infra-red based eye tracking system. The photopic negative response (PhNR), a marker of retinal ganglion cell function, was extracted from the electroretinogram (ERG), recorded with DTL electrodes during full field stimulation designed to optimize the PhNR. PLR and PhNR in IIH subjects were compared with lab norms. Full field ERGs (ISCEV protocol) were obtained in 4 subjects and compared with age adjusted norms.
Measures of rod pathway function and ganglion cell function showed greater abnormalities than measures of cone pathway function. Specifically, the rod ERG and the peak response of the rod-mediated PLR were affected (borderline or abnormal) in 3/4 and 3/5(figure) of IIH subjects, respectively. Similarly, the PhNR and sustained response of the melanopsin-mediated PLR were affected in 3/5 and 2/5(figure) of IIH subjects, respectively. In contrast, 2/4 of IIH patients had a borderline-abnormal cone ERG and the cone-mediated PLR was normal in all 5 subjects. For the subject in whom repeated PLR measures were obtained, there was a systematic improvement in baseline dilation (i.e. pupil size in the dark) following treatment that was concurrent with visual field improvement.
Vision loss in IIH has previously been attributed to retinal ganglion cell dysfunction in the setting of papilledema. Our findings of PhNR and melanopsin PLR abnormalities provide evidence of such ganglion cell dysfunction. We also find evidence of concurrent outer retinal dysfunction with rod pathways being more frequently affected than cone pathways. These observations align with reports of outer retinal dysfunction in other optic neuropathies. Further study is needed to assess the time course of outer retinal dysfunction in IIH and to determine if the etiology is due to primary outer retinal injury or secondary to trans-synaptic effects following ganglion cell injury.
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