Hypotony and aqueous humor dynamics in myotonic dystrophy

A group of 26 subjects with myotonic dystrophy were studied with fluorophotometry to evaluate the relationship between aqueous humor dynamics and the hypotony found in this disorder. All 26 received topical fluorescein to determine the anterior chamber elimination coefficient; five received systemic fluorescein to evaluate the integrity of the blood-aqueous barrier. The group has a mean intraocular pressure of 7.1 mm Hg. The rate of clearance of fluorescein from the anterior chamber and the cornea-to-anterior chamber transfer coefficient for fluorescein were normal. An abnormally high level of fluorescence, three times normal, was observed in the anterior chambers of the myotonic subjects after oral administration of fluorescein. This finding could not be attributed to abnormal absorption and elimination of fluorescein or to abnormal plasma binding. This finding indicates that there is a defect in the blood-ocular barrier to fluorescein in myotonic subjects. Thus conclusions regarding aqueous humor flow cannot be made from the rate of clearance of topically applied fluorescein in myotonic subjects, since the clearance due to diffusion may represent a significantly large fraction of the total clearance.