Case Report: Changes in Spatial Summation for Chromatic Stimuli in a Patient with Hypothyroidism Due to Autoimmune Thyroiditis Before and After Treatment with Levothyroxine.

Introduction: Acquired hypothyroidism is associated with a wide range of deficits including visual effects. Investigating colour vision mediated by S-cones has shown potential to detect diseases such as glaucoma or diabetes, however, studies of colour vision in hypothyroidism are scarce. Case presentation: In the present study we report spatial summation data of a patient with hypothyroidism due to autoimmune thyroiditis tested with S-cone specific stimuli. The area of complete spatial summation (Ricco’s area) is believed to reflect neural convergence and has been widely used to study structural changes to compensate for cell loss. We measured Ricco’s area before and after treatment with levothyroxine. Colour contrast thresholds were measured as a function of stimulus area in the retinal periphery, under S-cone isolating conditions. Ricco’s area was determined from the Threshold vs Area curve for either blue (S-cone increments) or yellow (S-cone decrements) stimuli. The patient’s data before treatment showed enlarged Ricco’s area (3 to 10 times larger) only for yellow stimuli compared to participants without hypothyroidism. After a treatment with levothyroxine and having reached euthyroidism, Ricco’s area decreased significantly (p < 0.05) for yellow stimuli, but remained unchanged for blue stimuli (p = 0.177). A second subject without hypothyroidism, who participated in both experiments did not show any significant differences for either blue (p = 0.081) or yellow stimuli (p = 0.78). Conclusion: The observed increase in Ricco’s area in hypothyroidism may be related to increased convergence to compensate for ganglion cell dysfunction. The results suggest that this process can be reversible after treatment. Examination of the S-cone system provides the potential to monitor this condition.