World Journal of Nuclear Medicine · 3 authors, 3 centres
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This prospective study found no significant changes in macular thickness or retinal nerve fiber layer thickness (RNFLT) in patients with hyperthyroidism or thyroid cancer up to six months after radioactive iodine (RAI) treatment. These findings suggest that RAI therapy does not cause measurable retinal damage, supporting its ocular safety. The study provides reassurance for clinicians regarding the posterior segment effects of RAI.
**Background:** Radioactive iodine (RAI) is a standard treatment for hyperthyroidism and differentiated thyroid carcinoma. While RAI can accumulate in extrathyroidal tissues such as the choroid plexus, its effects on the retina have not been systematically studied. This study aimed to quantitatively assess macular and retinal nerve fiber layer thickness (RNFLT) before and after RAI treatment using optical coherence tomography (OCT).
**Methods:** This prospective study included 80 eyes of 40 patients (7 men, 33 women) divided into two groups: Group 1 (25 hyperthyroid patients, mean age 43.76±11.85 years) and Group 2 (15 thyroid cancer patients, mean age 39.87±9.13 years). Exclusion criteria included significant ocular surface disease, thyroid eye disease, diabetes mellitus, and recent ocular surgery. All patients received Iodine-131: Group 1 received low-dose (mean 603.1 MBq, range 481–740 MBq) and Group 2 received high-dose (3,700 MBq). A low-iodine diet was prescribed 10 days before therapy, and antithyroid medications were withdrawn 7 days before. All cancer patients and 5 hyperthyroid patients had prior thyroid surgery. Complete ophthalmologic examination and OCT (Nidek RS-3000) measurements of macular center thickness, macular 6-mm ring area thickness, and peripapillary RNFLT were performed before RAI and at 1 month, 6 months, and 1 year post-treatment. Statistical analysis used repeated measures ANOVA and Newman–Keuls tests.
**Key Results:** In both groups, no significant differences were observed in any OCT parameter over time. In Group 1, pretreatment macular center thickness was 223.84±16.8 µm, macular 6-mm ring thickness was 252.72±14.77 µm, and RNFLT was 107.52±7.47 µm. At 6 months, these values were 223.42±13.18 µm, 250.66±12.93 µm, and 105.48±15.25 µm, respectively (all p>0.05). In Group 2, pretreatment values were 230.53±14.72 µm, 250.4±14.09 µm, and 109.27±5.19 µm; at 6 months they were 229.4±16.67 µm, 249.7±12.28 µm, and 109.1±4.51 µm (all p>0.05). No significant differences were found between groups at any time point.
**Clinical Implications:** This study provides the first quantitative OCT evidence that RAI treatment does not cause measurable retinal damage in the short term (up to 6 months). These findings are reassuring for patients and clinicians, as they suggest that RAI therapy is safe for the posterior segment of the eye. However, the study did not measure actual RAI accumulation in ocular tissues, and longer follow-up may be needed to detect subtle or delayed effects. The authors recommend further large-scale studies to confirm these results.