Reversible increase of intraocular pressure in subclinical hypothyroid patients

Objective: The aim of the study was to analyse the relationship between the ocular parameters, namely intraocular pressure (IOP), and the early forms of subclinical hypothyroidism. Design: Fifty-three subjects (9 male and 44 female) aged from 18 to 45 years (mean 32+/-7 years) were selected for this study. Twenty-nine met the criteria of subclinical hypothyroidism and 24 euthyroid subjects, age- and sex-matched, were used as controls. Methods: All individuals underwent a complete ocular examination, including visual field examination and serial measurement of IOP by means of a Goldmann tonometer. A tonographic examination was also performed. Results: The hypothyroid patients showed a substantially higher pressure in both eyes compared with control subjects (right eye=17.52+/-4.74 vs 13.42+/-1.95 mmHg, P<0.0001; left eye=17.55+/-3.99 vs 13.71+/-1.55 mmHg, P<0.0001). Indeed, the tonometric pressure exceeded 18 mmHg in 11 out of the 29 (38%) patients in the right eye and in 8 out of 29 (27%) patients in the left eye. The outflow index was normal in all subjects except in two hypothyroid patients. After two months of L-thyroxine (L-T-4) replacement therapy, only one patient continued to show tonometric values above 18 mmHg and the hypothyroid patients showed a significant reduction in mean IOP in both eyes compared with pretreatment values (right eye=14.96+/-1.32 mmHg, P<0.0097; left eye=15.03+/-1.38 mmHg, P<0.0018). Treatment did not lead to any change in the outflow indices; however, the C value (outflow coefficient at the sclerocorneal corner) returned to normal in the two patients with increased pre-treatment tonographlc values. Conclusions: These findings indicate that the intraocular pressure is increased even in subclinical. hypothyroid patients and that, at this early stage, the impairment is fully reversible with L-T-4 therapy.