Abstract
We report two cases of myotonic dystrophy in one family; both diagnosed from genetic analysis following ophthalmic indications, but before the manifestation of systemic symptoms. A 39-year-old female visited our clinic for routine examination. Mild ptosis, sluggish pupillary response, and bilateral snowflake cataracts were found. Fundus examination revealed an increased cup-to-disc ratio (CDR) in both eyes and a defect in the retinal nerve fiber layer in the right eye. Intraocular pressure was low, but within the normal range in both eyes. Because cataracts are characteristic of myotonic dystrophy, we suggested that her 14-year-old daughter, who did not have any systemic complaints, undergo ophthalmic examination. She also had mild ptosis and snowflake cataracts. Both patients underwent genetic evaluation and were diagnosed with myotonic dystrophy caused by unstable expansion of cytosine-thymine-guanine trinucleotide repeats in the dystrophia myotonica-protein kinase gene. Ophthalmologists can diagnose myotonic dystrophy based on clinical and genetic findings, before the manifestation of systemic abnormalities.