<p>Cystinosis is a rare disease caused by mutations in the CTNS gene that encodes for cystinosin, a protein responsible for transporting cystine out of the cell lysosome. A defect in cystinosin function is followed by cystine accumulation throughout the body, especially the eyes and kidneys.<sup class="text-reference-group"><a class="reference-popover-link" data-content="Elmonem MA, Veys KR, Soliman NA, van Dyck M, van den Heuvel LP, Levtchenko E: Cystinosis: a review. Orphanet J Rare Dis. 2016 Apr 22;11:47. doi: 10.1186/s13023-016-0426-y. (PubMed ID 27102039)" href="#reference-A218721">2</a></sup></p><p>Several preparations of cysteamine exist for the treatment of cystinosis manifestations, some in capsule form, and others in ophthalmic solution form.<sup class="text-reference-group"><a class="reference-popover-link" data-content="FDA Approved Products: Cystadrops (cysteamine solution 0.37%) for ophthalmic use" href="#reference-L15606">10</a>,<a class="reference-popover-link" data-content="FDA approved products: PROCYSBI (cysteamine bitartrate) delayed-release oral capsules" href="#reference-L15616">12</a></sup> In particular, cystine deposits on the eye can cause significant discomfort throughout the day and require frequent treatment with eye drops, typically every waking hour.<sup class="text-reference-group"><a class="reference-popover-link" data-content="FDA approved products: CYSTARAN (cysteamine 0.44%) for ophthalmic use" href="#reference-L15611">11</a></sup></p><p>On August 25th 2020, the first ophthalmic solution for cystinosis requiring only 4 daily treatments was granted FDA approval.<sup class="text-reference-group"><a class="reference-popover-link" data-content="FDA Approved Products: Cystadrops (cysteamine solution 0.37%) for ophthalmic use" href="#reference-L15606">10</a></sup> Cysteamine eye drops are a practical and effective option for those affected by ocular cystinosis. Marketed by Recordati Rare Diseases Inc., CYSTADROPS® reduce the burden of multiple frequent medications normally administered to those with cystinosis.<sup class="text-reference-group"><a class="reference-popover-link" data-content="PRN News Wire: U.S. FDA Approves CYSTADROPS® (Cysteamine Ophthalmic Solution) 0.37%, A New Practical Treatment Option for the Ocular Manifestations of Cystinosis" href="#reference-L15601">9</a></sup></p>