Sir,
Case report
A 22-year-old man was referred with decreased visual acuity of 4 years duration and bilateral ‘positive’ scotomata. Past medical and ocular history was unremarkable. Visual acuity (VA) was 0.30 logMAR in the right eye (OD) and 0.60 in the left (OS). Slit lamp and fundus examination were normal. Automated perimetry (Humphrey 24–2) showed small bilateral central scotomata. Electrophysiologic tests, including full field and pattern electroretinography (PERG), were normal, but modified dark adaptometry was consistent with enhanced rod–cone interaction (E-RCI) (Figure 1). After 6 years, he was complaining of poor central vision and constant flickering, especially when going from a dark to an illuminated environment and VA had dropped to 0.79 OD and 0.83 OS. Fundus exam remained normal. PERG elicited significantly reduced activity from both eyes, and a multifocal ERG (mfERG) showed central macular dysfunction. Full-field ERGs remained normal showing the dysfunction to be confined to the maculae. Three dimensional Optical Coherence Tomography (3D-OCT) showed bilateral disruption of the photoreceptor inner segment/outer segment (IS/OS) layer (Figure 2).
Comment
E-RCI, first described by Arden1, 2 in 1985, is a rarely reported disorder in which the normal elevation of dark adapted cone thresholds by dark adapting rods is greatly enhanced. A modified dark adaptometer is needed to make the diagnosis, as conventional Goldman-Weekers dark adaptometer cannot adequately differentiate rod and cone thresholds and cannot evaluate dark adapted cone sensitivity/thresholds. In this case, modified dark adaptometry1 demonstrated enhanced elevation of cone thresholds by dark adapting rods and established the diagnosis of E-RCI. The condition is usually benign and previous reports have not shown progression.3, 4, 5 The continuing reduction in VA in the present case and the markedly reduced PERG and mfERG suggested progressive macular dysfunction, which was confirmed by 3D-OCT demonstration of bilateral disruption of the photoreceptor IS/OS layer. To our knowledge, this is the first case of progressive macular dysfunction in association with E-RCI. It demonstrates the value of electrophysiology, psychophysics, and OCT in revealing functional and structural abnormalities despite the presence of a normal fundus exam.
References
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The authors have no proprietary interest in the subject or materials discussed in this manuscript. GEH is supported by National Institute of Health Research funding to the Biomedical Research Centre at Moorfields Eye Hospital/Institute of Ophthalmology
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De Salvo, G., Hogg, C., Holder, G. et al. Enhanced rod–cone interaction with progressive macular dysfunction. Eye 25, 823–825 (2011). https://doi.org/10.1038/eye.2011.27
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DOI: https://doi.org/10.1038/eye.2011.27