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Original Investigation |

The Relationship of Central Foveal Thickness to Urinary Iodine Concentration in Retinitis Pigmentosa With or Without Cystoid Macular Edema

Michael A. Sandberg, PhD1; Elizabeth N. Pearce, MD2; Shyana Harper, MSc1; Carol Weigel-DiFranco, MA1; Lois Hart, RDMS3; Bernard Rosner, PhD1; Eliot L. Berson, MD1
[+] Author Affiliations
1Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston
2Section of Endocrinology, Diabetes and Nutrition, Boston University School of Medicine, Boston, Massachusetts
3Retina Service, Massachusetts Eye and Ear Infirmary, Boston
JAMA Ophthalmol. 2014;132(10):1209-1214. doi:10.1001/jamaophthalmol.2014.1726.
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Importance  Current treatments for cystoid macular edema (CME) in retinitis pigmentosa (RP) are not always effective, may lead to adverse effects, and may not restore visual acuity. The present research lays the rationale for evaluating whether an iodine supplement could reduce CME in RP.

Objective  To determine whether central foveal thickness (CFT) in the presence of CME is related to dietary iodine intake inferred from urinary iodine concentration (UIC) in nonsmoking adults with RP.

Design, Setting, and Participants  We performed a cross-sectional observational study of 212 nonsmoking patients aged 18 to 69 years referred to our institution for RP with visual acuity of no worse than 20/200 in at least 1 eye.

Exposure  Retinitis pigmentosa with or without CME.

Main Outcomes and Measures  With the eye as the unit of analysis, the relationship of log CFT measured by optical coherence tomography to UIC measured from multiple spot samples and represented as a 3-level classification variable (<100, 100-199, and ≥200 µg/L), assigning greater weight to patients with more reliable UIC estimates.

Results  Analyses were limited to 199 patients after excluding 11 who failed to return urine samples for measuring UIC and 2 outliers for UIC. Of the 199 patients, 36.2% had CME in 1 or both eyes. Although log CFT was inversely related to UIC based on findings from all eyes (P = .02), regression of log CFT on UIC separately for eyes with and without CME showed a strong inverse significant relationship for the former group (P < .001) and no significant relationship for the latter group (P = .66) as tested. For the eyes with CME, CFT ranged from a geometric mean of 267 µm for a median UIC of less than 100 µg/L to a geometric mean of 172 µm for a median UIC of 200 µg/L or greater. In contrast, we found no significant association between CME prevalence and UIC based on the entire sample as tested (odds ratio, 1.01 [95% CI, 0.38-2.67]; P = .99).

Conclusions and Relevance  A higher UIC in nonsmoking adults with RP was significantly associated with less central foveal swelling in eyes with CME. Additional study is required to determine whether an iodine supplement can limit or reduce the extent of CME in patients with RP.

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Figure 1.
Distribution of the Within-Subject Coefficient of Variation for Urinary Iodine Concentration

Analysis is based on multiple spot samples from 199 patients with retinitis pigmentosa.

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Figure 2.
Central Foveal Thickness (CFT) by Urinary Iodine Concentration (UIC)

Among patients with retinitis pigmentosa, 120 eyes had cystoid macular edema (CME) (model 3) and 255 eyes had no CME (model 4). Error bars designate SEM. See the Methods section for details of the analyses.

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