Progressive myelination of the retinal nerve fibre layer associated with a lamina cribrosa cleft

Myelination of the retinal nerve fibre layer (MNFL) is generally an incidental asymptomatic finding on fundus exam. While MNFL is thought to be a congenital and stationary finding, there have been cases of acquired and progressive MNFL reported. Here, we discuss a case where a girl in middle childhood presented with reading difficulties and was found to have normal vision and MNFL superior to the left optic disc. Over 5 years, the MNFL was observed to grow, and a new patch appeared inferior to the left disc. A Y-shaped cleft was detected in lamina cribrosa. The shape of the cleft suggested incomplete embryological closure of the optic cup and optic stalk. This case offers support for the concept that defects in lamina cribrosa allow oligodendrocyte precursor cells to enter the retina, where they may later proliferate and differentiate to form MNFL.