Purpose:
To investigate Spectral Domain Optical Coherence Tomography (SD OCT) for quantitative high resolution measurement of retinal thinning in a longitudinal study of two rat models of retinal damage.
Methods:
Microsurgeries were performed to induce an acute injury (optic nerve transection) or chronic elevated intra-ocular pressure (episcleral vein cauterization) in the right eye of 12 rats. The contralateral eye of each animal was maintained as a control. Half of the rats (3 from each group) received a neurotrophic neuroprotection treatment to slow the progression of axonal degeneration. SD OCT volume images, as shown in Fig 1 (a), were acquired from both eyes every second day over 14 days for the acute injury group, and every week over 6 weeks for the elevated IOP group. The thickness of the combined Nerve Fiber Layer, Ganglion Cell Layer, and Inner Plexiform Layer (abbreviated NGI) was measured 1.5mm from the ONH at 4 locations on each of 6 frames selected throughout the volume. Data from 3 volume acquisitions from each day for each eye (a total of 72 measurements per eye) were averaged and recorded. The NGI thickness as observed with SD OCT of a control and an acute injury eye after 14 days is presented in Fig 1 (b) and (c).
Results:
The combined thickness of the NGI layers as measured by SD OCT in normal retinas was 71±0.6µm. The SD OCT measurements of NGI gradually decreased to a final thickness 54.7±1.15µm 14 days after ON transection, while in the treated group it was 60.8±0.33µm (significant versus untreated, P≤0.001). In the elevated IOP group, the SD OCT measurements of NGI thickness gradually decreased to 51.2±2.6µm, while in the treated group it was 60.4±0.13µm (significant versus untreated, p≤0.02).
Conclusions:
SD OCT was successfully demonstrated as a repeatable technique for quantitative measurements of retinal thinning in time course studies of acute and chronic injury to the optic nerve.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • imaging/image analysis: non-clinical • neuroprotection