Low intraocular pressure resulting from ciliary body detachment in patients with myotonic dystrophy

PURPOSE: To investigate why myotonic dystrophy type 1 (DM1) patients have low intraocular pressure (IOP). DESIGN: Prospective, comparative case series. PARTICIPANTS: One hundred two eyes of 51 patients with DM1 (age range, 21-64 years) and 44 eyes of 22 healthy subjects of similar age (21-64 years). METHODS: All participants underwent IOP measurement with Goldmann applanation tonometry and an in vivo examination of the ciliary body with a 35-MHz high-resolution B-scan. The findings were compared between the 2 groups. In both groups, only patients with no history of ocular trauma or surgery were included. The differences were evaluated using the unpaired Student t test. MAIN OUTCOME MEASUREMENTS: Intraocular pressure, central corneal thickness (CCT), and echographic evidence of ciliary body detachment. RESULTS: The mean ± standard deviation (SD) IOP in patients with DM1 was 10.9 ± 3.1 mmHg and that in the control patients was 15.4 ± 2.2 mmHg, a difference that reached significance (P<0.01). The mean ± SD CCT (measured at the pupillary center) was 574.4 ± 37.9 μm in the patients with DM1 and 557.8 ± 39.2 μm in the controls (P = 0.02). Detachment of the ciliary body was identified in all DM1 subjects. Size was variable and the detachment involved 1 or more quadrants. The number of quadrants affected by the detachment was not correlated with the IOP (R(2) = 0.088) or the size of the CTG expansion. No detachments were found in the healthy controls. CONCLUSIONS: Detachment of the ciliary body may explain the low IOP values in patients with DM1. The finding of a ciliary body detachment in an individual who has not had recent eye surgery or trauma raises the possibility of a DM1 diagnosis.