Abstract
Purpose: :
Adaptive optics scanning laser ophthalmoscopy (AOSLO) provides a unique opportunity for the objective and noninvasive study of hemodynamics in patients. In this study, we quantified the blood flow velocity in the parafoveal capillaries of patients with diabetic retinopathy (DR) by using our prototype of the AOSLO system developed by Canon Inc.
Methods: :
We developed a novel AOSLO system with high-efficiency wavefront correction using a dual liquid-crystal phase modulator. The imaging light wavelength was 840 nm and the frame rate was 32 or 64 Hz. The imaging light exposure level was set to lower than the maximum permissible exposure indicated by the American National Standards Institute. The scan area at the retina was either 1.2 × 1.2° or 1.4 × 2.8°, and was sampled at 400 × 400 pixels or 200 x 400 pixels, respectively. The AOSLO videos were recorded for 2-4 seconds per scan area, and 10-25 scan areas were obtained per subject in order to cover the parafoveal areas of 5 DR patients. The capillary images were constructed as projections of the sequential division images, and velocities of the moving particles were measured as blood flow velocities by using the spatiotemporal images of the target capillary obtained by reslicing the sequential frames. Five individual randomly selected capillaries per subject were measured. For each capillary, the velocities of 3 individual successive moving particles were measured, yielding 75 measurements. All digital image processing procedures, including image warping, for correcting image distortion were performed by using the public domain software ImageJ.
Results: :
We successfully constructed high-contrast images of capillaries. The velocities of all moving particles ranged from 0.48 to 3.45 mm/s and the mean value was 1.39 mm/s (SD = ±0.71 mm/s). No significant differences were observed between the velocities of patients with DR and the velocities of healthy subjects without a history of prior ocular or systemic diseases, which we previously reported as 1.34 ± 0.42 mm/s (range, 0.73-2.36 mm/s) (P = 0.700).
Conclusions: :
The velocity of moving particles in DR had a wider range than that of normal subjects, suggesting that the decrease in blood flow due to microvascular damage may result in a compensatory increase in blood flow in other vessels in DR patients.
Keywords: diabetic retinopathy • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • blood supply