Neuroretinal structure changes in infantile nephropathic cystinosis

The aim of this study was to investigate the neuroretinal structure of patients with the lysosomal storage disease cystinosis.

In this retrospective cross-sectional analysis, optical coherence tomography (OCT) was used to measure the peripapillary retinal nerve fiber layer (pRNFL), the optic disc volumes, the prelaminar depth and the macular ganglion cell layer volumes (mGCL) in patients with genetically confirmed infantile nephropathic cystinosis. The same measurements were repeated in an age -and spherical equivalent (SE) matched, healthy control group.

The cystinosis group included 40 patients (40 eyes) with a mean age of 20.6 ± 8.6 years and a SE of 0.47 ± 1.85. The healthy control group consisted of 30 patients (30 eyes) with a mean age of 20.7 ± 12.5 years and a SE of 0.47 ± 1.29. A pronounced deposition of crystals in the optic disc was observed in all cystinosis cases. Cystine crystals follow the nerve fibers in a dense, pearl-string pattern. A significantly thicker pRNFL and a higher rate of positive prelaminar depth was evident in the cystinosis group (839.7 ± 151.0 μm vs. 775.7 ± 79.6 μm, p = 0.004). A significantly smaller mGCL volume was found in the cystinosis group as compared to normal controls (0.25 ± 0.03 mm³ vs. 0.35 ± 0.03 mm³, p = 0.036).

Cystinosis leads to pronounced crystal accumulation in the optic disc in early stages of the disease. This accumulation occurs in concomitance with the well-described cystine crystal deposits in the cornea, which have previously been considered the foremost ocular sign of cystinosis. The pearl-string appearance of crystal deposition suggests a primarily glial localization. A significantly thicker pRNFL and a higher rate of positive prelaminar depth was observed in the OCT scans of cystinosis patients, explaining the clinical impression of a crowded optic disc. Additionally, retinal neurodegeneration was significant in patients with cystinosis if compared to healthy controls. The optic disc crowding may result from the dense deposition of cystine crystals in the optic nerve head and the GCL thinning could be due to metabolically induced ganglion cell atrophy. However, the exact reason for these changes remains to be elucidated.