A 15 month follow‐up study characterizing the progression of retinal pathology and visual loss in CLN3 ex7/8 mice

Aims/Purpose: Juvenile form of neuronal ceroid lipofuscinosis is a is a rare neurological disease that manifests in childhood, by progressive visual dysfunction. The progression and timeline of the retinal degeneration in the eye has not been comprehensively characterized. We performed a 15‐month follow‐up study aiming to reveal the progression of retinal pathology in CLN3 ex7/8 mice modelling juvenile neuronal ceroid lipofuscinosis. Methods: ERG, OCT, and fundus imaging was performed in CLN3 ex7/8 mice every three months at 3, 6, 9, 12 and 15 months. Scotopic electroretinography was performed with Espion ERG using silver electrodes. Mice were kept overnight in dark room before testing. Eyes were exposed to flashes of light periodically increasing in intensity (0,0001–1 Cd × s/m2). Responses to multiple flashes were averaged to obtain a single waveform at each intensity. OCT and fundus images were captured with the Phoenix MICRON® Image‐Guided OCT. Results: In scotopic ERG responses lower amplitudes of a‐ and b‐wave were observed CLN3 ex7/8 mice compared to WT mice at all time points. A progressive, almost 2‐fold decrease of b‐wave amplitude (at 0.03 Cd × s/m2) was seen in CLN3 ex7/8 mice between 3 and 15 months, compared to WT. Most notable decline of b‐wave amplitude (~70% of the decrease, at 0.03 Cd × s/m2) was seen from age of 6 to 12 months. A‐wave amplitudes in CLN3 ex7/8 mice were consistently lower but not progressively reduced when compared to WT mice. The accumulation of drusen was observed in the fundus images of CLN3 ex7/8 mice. In OCT images we observed signs of retinal outer segment atrophy. These effects were not observed in WT animals to the same degree. Conclusions: We observed age‐dependent retinal outer segment atrophy with drusen‐like deposit accumulation visually with OCT and fundus imaging in CLN3 ex7/8 mice, and the results correlate well with ERG results. According to the progressive decline of b‐wave amplitude, the decrease of vision seems to be most prominent between the ages of 6 and 12 months. This result indicates progressive loss of function in inner retinal neurons. The present results reveal the progression of the pathology in CLN3 ex7/8 mice as well as the time window for testing novel disease‐modifying interventions in CLN3 ex7/8 mice.