Cystinosis is a rare, childhood lysosomal storage disorder caused by mutations in cystinosin, the transporter responsible for cystine from the lysosome to the cytosol. In cystinosis, mutated cystinosin causes cystine crystal accumulation and cell death. Photophobia, or abnormal sensitivity to light, is an early symptom of the disease and can be debilitating for patients. Historically, this photophobia has been attributed to ocular corneal cystine crystal accumulation, but eyedrops prescribed to disrupt these crystals do not fully alleviate symptoms. Furthermore, photophobia is known to have a neurobiological basis that extends beyond eye injury alone. Interestingly, when individuals with cystinosis were presented with a series of visual stimuli, they had increased early, cortical visual evoked responses. Given these data, we hypothesize that photophobia in cystinosis could be due to a central nervous system (CNS) hyperexcitability that results from prolonged corneal cystine accumulation. To explore this, we have developed a cystinosin knockout (Ctns -/-) mouse model using CRISPR/Cas9. This model has been confirmed to produce a truncated, nonfunctional protein product. Phenotypically, our model recapitulates the human disease and demonstrates corneal eye crystal accumulation. Our model will be used to conduct similar visual electrophysiology studies to those conducted in patients, as well as probe for a mechanism of cortical hyperexcitability using various neuromarkers. By recording similar neurophysiologic signatures across species and correlating them with changes in molecular signatures, we aim to deepen our understanding of the pathophysiology of photophobia in cystinosis and develop new therapeutics for individuals.