Cystinosis is a rare autosomal recessive lysosomal storage disorder, characterised by the intra-lysosomal accumulation of cystine. Cystinosis results from a defect in the CTNS protein, a lysosomal transport protein for cystine. There are three subtypes of cystinosis: infantile nephropathic cystinosis, juvenile nephropathic cystinosis and ocular non-nephropathic cystinosis. Corneal cystine crystal accumulation is pathognomonic for ocular cystinosis. Ocular cystinosis also occurs as a consequence of nephropathic cystinosis. Patients can suffer from ocular symptoms such as photophobia, blepharospasm and visual impairment. Diagnosis is currently primarily made using slit lamp examination. The mainstay of cystinosis treatment is cysteamine, a cystine depleting drug. The treatment of ocular cystinosis is challenging due to the avascular nature of the cornea, and the requirement for frequent administration of topical treatment. There are currently only two topical cysteamine treatment options on the market – ‘Cystaran’ and ‘Cystadrops’. Many studies are ongoing using modern technologies such as nano wafers, gold nanoparticles and stimuli responsive ‘smart’ hydrogels and ‘smart’ contact lenses to improve treatment options for patients. The majority of research is focused on increasing the residence time of the drug on the ocular surface, aiming to reduce the need for frequent reapplication, improving compliance and quality of life. There is a great need for modern treatment options to alleviate symptomatology and improve disease pathophysiology. This review examines ocular cystinosis and ocular involvement as a complication of nephropathic cystinosis, with an added focus on the diagnosis, current and future treatment options.

Ocular cystinosis, Cornea, Cystine, Cysteamine