L E T T E R S :

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P U B L I S H E D

A R T I C L E S

Thomas Theelen, MD, PhD1 RadboudUMC, Ophthalmology, Nijmegen, The Netherlands

References 1.

Roth NM, Saidha S, Zimmermann H, et al. Photoreceptor layer thinning in idiopathic Parkinson’s disease. Mov Disord 2014.

2.

Lee JY, Ahn J, Kim TW, Jeon BS. Optical coherence tomography in Parkinson’s disease: is the retina a biomarker? J Parkinson Dis 2014.

3.

Schuman SG, Koreishi AF, Farsiu S, Jung SH, Izatt JA, Toth CA. Photoreceptor layer thinning over drusen in eyes with agerelated macular degeneration imaged in vivo with spectraldomain optical coherence tomography. Ophthalmology 2009; 116:488-496.

Reply: Photoreceptor Layer Thinning Is Not Specific for Parkinson’s Disease Reply letter Dear Editor We wish to thank Dr. Theelen for his letter regarding our recent paper on photoreceptor layer thinning in Parkinson’s disease (PD).1 We agree that the investigation of retinal pathological conditions in PD, and other neurological disorders, both within the scope of clinical care and research, should be a concerted and collaborative approach by ophthalmologists and neurologists. Given the comparably older age of PD patients, primary ophthalmologic disorders may be more common in such patients, although their detection may be somewhat hampered by the disability and immobility commonly seen in PD. Although primary retinal disorders are more common in the elderly, the overall prevalence of conditions such as age-related macular degeneration and macular dystrophy remains low. Therefore, from a statistical perspective, average thickness of the photoreceptor layer in a cohort of PD patients would be unlikely to be significantly reduced relative to controls, unless most of the included PD patients were afflicted by co-incidental and previously undetected concomitant retinal diseases. This of course is most unlikely. Moreover, our collective group is highly experienced in the investigation and interpretation of optical coherence tomography scans, from both quantitative and qualitative perspectives, and would be most unlikely to overlook such obvious retinal pathological conditions as those illustrated by Dr. Theelen. All optical coherence tomography scans were carefully examined to exclude any confounding measurements that

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*Correspondence to: Alexander U. Brandt, NeuroCure Clinical Research  - Universita €tsmedizin Berlin, Germany, E-mail: Center, Charite [email protected] Relevant conflicts of interest/financial disclosures: Nothing to report. Full financial disclosures and author roles may be found in the online version of this article. Received: 27 May 2014; Accepted: 2 June 2014 Published online 1 July 2014 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/mds.25957

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could be construed for PD-unrelated retinal pathological conditions. This led to the exclusion of a large number of scans. Nonetheless, the possibility that our results may be confounded to a degree by ophthalmologic disorders is acknowledged and discussed as a potential weakness in our original publication. Because we did not detect significant retinal nerve fiber layer (RNFL) thinning in this cohort of PD patients, as has been previously described in glaucoma2 as well as in PD itself,3 a glaucomatous confound is as unlikely as that from primarily retinal disorders. To clarify, our study findings do not contradict those of previous studies with regard to photoreceptor changes in PD. This is the first study to investigate the photoreceptor layer in PD using a reliable method.4 In fact, an immediate reply to our paper by an independent group further supports our findings, making it unlikely that our findings are either coincidental or attributable to a PD-unrelated process.5 Our study’s results do contradict previous studies with regard to RNFL thinning, which others found3 and we did not.1 This discrepancy and its potential causes were discussed in detail in our main publication and the reply to M€ uller et al.1,5 Please refer to these for further detail. We were not implying that photoreceptor thinning is by any means specific to PD. Important ophthalmological diseases, such as age-related macular degeneration, may produce photoreceptor loss. Naturally, these diseases should be diagnosed and treated by an ophthalmologist. However, amongst neurological diseases, and especially neurodegenerative diseases, photoreceptor layer thinning has rarely been reported, with RNFL thinning representing the most frequently reported finding. For the neurologist, therefore, investigating the photoreceptor in PD, after ruling out potential unrelated retinal or macular diseases in collaboration with an ophthalmologist, might prove to be a potentially important addition in primary or secondary diagnostics. Alexander U. Brandt, MD,1 Peter A. Calabresi, MD2, and Shiv Saidha, MD2 1 NeuroCure Clinical Research Center, Charite Universit€atsmedizin Berlin, Germany 2 Department of Neurology, Johns Hopkins School of Medicine, Baltimore, USA

References 1.

Roth NM, Saidha S, Zimmermann H, et al. Photoreceptor layer thinning in idiopathic Parkinson’s disease. Mov Disord 2014; [Epub ahead of print]

2.

Bock M, Brandt AU, D€ orr J, et al. Patterns of retinal nerve fiber layer loss in multiple sclerosis patients with or without optic neuritis and glaucoma patients. Clin Neurol Neurosurg 2010;112:647652.

3.

Yu J-G, Feng Y-F, Xiang Y, et al. Retinal nerve fiber layer thickness changes in Parkinson disease: a meta-analysis. PLoS ONE 2014;9:e85718.

4.

Seigo MA, Sotirchos ES, Newsome S, et al. In vivo assessment of retinal neuronal layers in multiple sclerosis with manual and automated optical coherence tomography segmentation techniques. J Neurol 2012;259:2119-2130.

5.

M€ uller A-K, Blasberg C, S€ udmeyer M, et al. Photoreceptor layer thinning in parkinsonian syndromes. Mov Dis 2014; [Epub ahead of print]

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