Abstract
Purpose :
To develop a high-throughput method for objective assessment of retinal spatial resolution in the eyes of mice using the pattern electroretinogram (PERG).
Methods :
PERG were simultaneously recorded from each eye of Ketamine/Xylazine anesthetized C57BL/6J mice (n=10, 20 eyes) in response to a black-white gratings of 100% contrast and of different spatial frequencies (0.04 – 0.4 cycles/deg in five steps, repeated twice) generated on two LED displays presented to each eye and reversing at slight different rates (OD, 0.984 Hz; OS, 0.992 Hz). Retinal signals were derived from a common subcutaneous snout electrode, and independent PERGs from each eye were retrieved using one channel continuous acquisition and phase-locking average (IOVS 2014, 55:2469-75). For each spatial frequency, the RMS amplitude of PERG waveforms was automatically assessed, together with the RMS amplitude of corresponding noise waveforms obtained with an even/odd sweep difference method. PERG acuity was defined as the highest spatial frequency at which amplitude exceeded the median noise amplitude by a factor of √2. The recording process had duration of about 30 minutes.
Results :
Eighteen out of 20 eyes had reproducible PERG acuity of 0.4 cycles/deg. Two eyes had reproducible acuity of 0.1 cycles/deg, which was due to the presence of cataract.
Conclusions :
Previous PERG estimates of retinal acuity in C57BL/6J mice (PNAS 1996, 93:14955-9; PNAS 2001, 98:6453-8; IOVS 2012, 53:1211-8) have yielded values of 0.5-0.6 cycles/deg by linear regressing PERG amplitude vs. log spatial frequency to the noise level. This method is suitable for assessing the acuity of mouse populations, as it requires large dataset to average variability of individual estimates and hence considerable time effort. The lower retinal acuity of 0.4 cycles/deg obtained with the present method is expected, as the PERG amplitude is not extrapolated to noise but rather defined as 1.4 times higher than noise. This appears to be a robust method for rapid assessment of acuity in individual eyes of mice that minimizes variability of estimates.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.