Amino Acid Disorders
In cystinosis, intralysosomal cystine accumulates because of a deficiency in the carrier protein cystinosin that typically transports it out of lysosomes. Three types are recognized, all autosomal recessive: (1) nephropathic, (2) late-onset (or intermediate), and (3) benign. Cystine crystals accumulate in the cornea and conjunctiva in all 3 types, but retinopathy develops only in patients with the nephropathic type who present early (8 to 15 months of age) with progressive renal failure, growth delays, renal rickets, and hypothyroidism. The retinopathy is characterized by areas of patchy depigmentation of the RPE alternating with irregularly distributed pigment clumps and associated fine retinal crystals, but no significant visual disturbance. Treatment with cysteamine may be beneficial. Bietti crystalline dystrophy may also cause crystalline keratopathy and retinopathy associated with patchy loss of the choriocapillaris and RPE and with associated photoreceptor loss.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.