Optic nerve crush mice followed longitudinally with spectral domain optical coherence tomography

Abstract

Purpose: To investigate the longitudinal effect of optic nerve crush injury in mice by measuring retinal thickness with spectral-domain optical coherence tomography (SD-OCT).

Methods: Optic nerves of one eye from each C57Bl/6 mouse were crushed under direct visualization for 3 seconds, 1 mm posterior to the globe. The optic nerve head (ONH) was imaged with SD-OCT (1.5 × 1.5 × 2.0 mm scan) before the surgical intervention and repeated subsequently for up to 32 days postinjury. A cohort of mice not exposed to the nerve crush procedure served as control. En face SD-OCT images were used to manually align subsequent scans to the baseline en face image. Total retinal thickness (TRT) (along a sampling band with radii 0.33-0.42 mm centered on the ONH) from each follow-up day was automatically quantified for global and sectoral measurements using custom software. Linear mixed-effects models with quadratic terms were fitted to compare TRT of nerve-crushed and control eyes over time.

Results: Eleven eyes from 11 nerve crush mice (baseline age 76 ± 11.8 days) and eight eyes from four healthy mice (baseline age 64 ± 0 days) were included. The control eyes showed a small, gradual, and consistent TRT increase throughout follow-up. Nerve-crushed eyes showed an initial period of thickening, followed by thinning and slight rebound after day 21. The decrease in thickness observed after the early thickening resolved was statistically significantly different from the control eyes (P < 0.05 for global and sectoral measurements).

Conclusions: SD-OCT can be used to quantitatively monitor changes in retinal thickness in mice over time.

Figure 1.

SD-OCT en face image from 23 days post–nerve crush, manually aligned to baseline by rotating and translating

Figure 2.

TRT map from baseline and 23 days post-nerve crush, with the post-crush thickness map aligned to baseline using the coordinates obtained from en face image alignment. The red concentric circles indicate the boundaries of the measurement sampling region. An overall thinning can be discerned on day 23 by observing the broadening of the yellow region on the TRT map compared with baseline.

Figure 3.

Top: Individual total retinal thickness (TRT) measurements, each eye represented by a different color; bottom: mean global TRT over time for control and nerve-crushed eyes. The solid line represents mean thickness, and dashed lines represent the SD.