The Relationship of Cystoid Macular Edema to Urinary Iodine Concentration in Retinitis Pigmentosa

Abstract

Purpose: To determine whether central foveal thickness in the presence of cystoid macular edema is related to dietary iodine intake inferred from urinary iodine concentration in non-smoking adults with retinitis pigmentosa.

Methods: In a cross-sectional study by an institutional referral center, non-smoking adult patients with retinitis pigmentosa (n = 212, ages 18 to 69 years) with a visual acuity ≥ 20/200 in at least one eye were studied. The main outcome measure was the relationship of log central foveal thickness measured by optical coherence tomography to urinary iodine concentration measured from multiple spot samples and represented as a 3-level classification variable (< 100 µg/L, 100 µg/L - 199 µg/L, and ≥ 200 µg/L), assigning greater weight to patients with more reliable urinary iodine concentration estimates.

Results: Analyses were limited to 199 patients after excluding 11 patients who failed to return urine samples for measuring urinary iodine concentration and 2 outliers for urinary iodine concentration. Thirty-seven percent of these patients had cystoid macular edema in one or both eyes. Log central foveal thickness was inversely related to urinary iodine concentration (p = 0.02) based on all patients. However, regression of log central foveal thickness on urinary iodine concentration separately for patients with and without cystoid macular edema showed a strong inverse relationship for the former group (p < 0.001) and no relationship for the latter group (p = 0.55).

Conclusions: A higher urinary iodine concentration in non-smoking adults with retinitis pigmentosa was significantly associated with less central foveal swelling in eyes with cystoid macular edema. Additional study is required to determine whether an iodine supplement can limit or reduce the extent of cystoid macular edema in patients with retinitis pigmentosa.

Keywords: 696 retinal degenerations: hereditary • 505 edema • 550 imaging/image analysis: clinical