Purpose:
To investigate the impact of involuntary eye movements on ultrawide-field retinal OCT images, which were acquired with a multi-MHz Fourier-domain mode-locked (FDML) laser OCT system.
Methods:
A 1050nm FDML OCT device was constructed with an axial line rate of 1.68MHz, and imaging of 5 normal subjects was performed with a total acquisition time of only 0.8s for 1100*1100 axial scans. Ultra-wide field en-face fundus projections spanning ~60° field of view were reconstructed from those datasets and investigated for motion artifacts. We compared the results with 54 fundus projections consisting of 1900x1900 axial scans from 11 normal subjects, which were acquired in 6.1s and 3.0s, at 684kHz and 1.37MHz axial scan rate, respectively.
Results:
For the longer acquisition times, we found that a significant number of datasets was distorted by fixational instabilities. At 684kHz, 63% of datasets showed motion artifacts by (micro-) saccades, compared to 42% at 1.37MHz. We observed a maximum displacement of ~2° and a positive correlation between saccade duration and amplitude. Saccades were usually composed of a short displacement period, followed by stable gaze and another fast displacement to the original position (see Fig. 1). At 1.68MHz and reduced scan time of 0.8s, no motion artifacts were apparent so far.
Conclusions:
Even for MHz axial line rates, densely sampled ultrawide-field OCT imaging can be severely affected by microsaccades. To reduce the impact of motion artifacts, two strategies are feasible: (1) Higher axial scan rates and (2) reduced sampling density. Since both strategies reduce image quality, a scan protocol at 1.68MHz and 0.8s acquisition time may be a reasonable choice for ultra wide-field ophthalmic imaging today.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • eye movements • imaging/image analysis: non-clinical