Abstract
Purpose::
In the living human eye, photoreceptors were imaged with the adaptive optic (AO) ophthalmoscope (Roorda and Williams, 1999). Several reports showed AO images of diseased retina (Wolfing, 2006, Choi, 2006), however the origins of pathological changes observed in AO image have not clearly been described. For this purpose, a comparison between AO images and histological data is necessary. In this study, we examine a dutch-belted rabbit retina using a high resolution AO ophthalmoscope and compared with histological data.
Methods::
Eyes of Dutch-belted rabbits were examined using AO opthalmoscope under general anesthesia. The pupil was dilated by tropicamide and a hard contact lens was attached on the cornea. AO fundus camera (Topcon Co.) equipped with a 635nm luminescence diode illuminator and 768 x 768 pixel refractive liquid crystal light modulator (Hamamatsu Photonics) was used. The liquid crystal device corrected wavefront aberration at 3Hz response rate and the wavefront aberration was reduced up to 8th order. Fundus image was taken when RMS error was reduced below 0.1um ( ϕ = 5.0mm). After AO examination, rabbits were sacrificed by deep anesthesia and the retina was examined histologically. The retinal structures were examined by changing the focal plane with a light microscope and were compared with the images of AO ophthalmoscope. The retina was also examined by immunohistochemistry to visualize cones (PNA) and rods (WGA).The magnification of the AO image was calibrated by comparing the histology.
Results::
Two characteristic retinal images were obtained by changing the focal plane of AO camera. In the superficial layer, striped structures with 25 µm width were observed, which corresponded to the myelinated nerve fibers in histology. In the deeper layer, a 2 µm-wide rectangular mosaic structures were observed. By comparing the histology, the rectangular mosaic corresponded to the outer segment of rods. Distance between the two layers was 90 µm by AO, which was equal to the value obtained by histological examination.
Conclusions::
Although the size was close to the resolution limit of AO ophthalmoscope, the rectangular structure observed in deeper layers of the retina by AO ophthalmoscope may be rod outer segment as compared with histology.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina: distal (photoreceptors, horizontal cells, bipolar cells) • imaging/image analysis: non-clinical