Bietti crystalline dystrophy: a morpho-functional evaluation

We report the clinical findings and macular function of a patient with Bietti crystalline dystrophy. A 39-year-old woman reported visual loss in both eyes and nyctalopia. A complete ophthalmological evaluation, retromode imaging, SD-OCT acquisition, MP1 microperimetry, and multifocal electroretinogram (mfERG) were performed. Microcrystalline deposits in the cornea and the retina with retinal pigment epithelial atrophy were observed. Retromode imaging revealed visualization of normal large choroidal vessels, cystoid macular edema, and small defined glistening lesions. SD-OCT showed changes in the outer retina with numerous microcrystalline deposits. Microperimetry showed an absolute scotoma involving the perimacular area but sparing of the fovea. In both eyes, mfERG analysis suggests a dysfunction of pre-ganglionic retinal elements detectable in the 20 central retinal degrees. The genetic characterization showed an homozygous mutation c.772C > T[p.Leu258Phe] in exon 6. Retromode imaging and SD-OCT were useful tools to determine the extent and the localization of the crystals. Microperimetry should allow evaluation of the progression of the macular changes.