Effect of Hyperthyroidism on Electroretinogram Photopic Responses

Introduction. It has been shown that thyroid hormone levels regulate cone photoreceptors development and modulate opsin production in mature cones. A limited number of cases have been reported where the flash electroretinogram (fERG), a global retinal response, have shown enhanced responses in patients with adult-onset thyroid dysfunction. It is unknown how retinal photoreceptor functions are affected topographically, and how this might impact multifocal ERG (mfERG) responses. Case Presentation. We report on a patient with hyperthyroidism caused by recently diagnosed Graves disease who presented with enhanced ERG cone responses. A 27-year-old white female was diagnosed with Graves disease two months prior and started on Methimazole and Propranolol. Her past ocular history was significant for strabismic amblyopia treated at age of six years with patching. Her best-corrected visual acuity was 20/25 in the right and 20/20 in the left eye. Flash ERG showed enhanced amplitude in the photopic responses. Further mfERG testing showed amplitude enhancement with normal implicit time from foveal to perifoveal areas topographically in both eyes. Deviation From the Expected. This case first demonstrates enhanced cone responses in both fERG and mfERG testing in a patient with hyperthyroidism. Discussion. It provides evidence that thyroid hormone levels continue to affect adult retinal cone function. Conclusion. It shows the potential application of mfERG testing in mapping retinal function and diagnosis of ocular involvement in patients with early hyperthyroid dysfunction.