Ongoing Projects

In-vivo Imaging of the Human Rod Mosaic
Although cone photoreceptor images have been imaged in the living human eye for several years, imaging the rod receptors has been more challenging. In 2011 and in collaboration with the University of Arizona and the University of Rochester we reported the first in-vivo rod images (Doble et al., Optics Letters 2011).




Figure 4. In-vivo rod images (a) 5° temporal retina - the rods are the small structures in between the much larger cones (b) equivalent images at 10° temporal retina - as expected, the cone spacing increases and the number of the rods increases. (c) Power spectrum analysis - the cones show a decrease in spatial frequency with increasing eccentricity giving peak spatial frequencies of 30 and 24 c/deg at 5° and 10° temporal retina respectively. The rods showed a similar spatial frequency peak of around 92 c/deg at each retinal location.

This is an ongoing NEI/NIH funded research project within the lab, looking at further ways of enhancing the rod contrast and determining their mosaic properties within normal and diseased eyes.


Correlation of Cone Density with Visual Function in Patients with Retina Dystrophy (collaboration with UC Davis)
This was one of the first studies that quantified AO images of thecone photoreceptor mosaic in terms of cone density and correlated it to visual function in patients. (Choi et al. IOVS 2006)

Figure 5: AO retinal images obtained from a RP patient at different locations of the retina. The retinal locations tested were selected based on the visual field results (HVF 24-2 SITA Standard). Retinal location is denoted in terms of visual field in degrees from the fovea. The AO images showed that the cone mosaic is not regular (unlike that of normal eyes) at the retinal locations where sensitivity is reduced (i.e., there were areas of dark spaces between groups of cones, where no cones were visible). Cone density was calculated for each retinal image and compared with the extrapolated cone densities from histologic data at corresponding locations. The variation in cone density from the least to the most affected areas was 96% to 49% in this patient (RCD1). These numbers provide a quantitative index of cone loss. (Choi et al., IOVS 2006)


AO-OCT Imaging of Optic Neuropathy (collaboration with UC Davis)

Figure 6 shows AO-OCT images obtained from a non-arteritic anterior ischemic optic neuropathy (NAION) patient. The AO-OCT images were taken at 2 retinal locations, 2° temporal 2° superior retina and 4° nasal 4° superior retina. The 4° nasal 4° superior retina had better visual function than 2° temporal 2° superior retina, hence, the layer labeled 3 (the junction between the cone outer segment tip and RPE) was better defined and distinct at that location, while it was not visible at the 2° temporal 2° superior retina.


Figure 6. AO-OCT images at two retinal locations in the right eye of the patient with NAION. (a) 2° temporal 2° superior retina and (b) 4° nasal 4° superior retina. 1: external limiting membrane (ELM), 2: Inner and outer segment junction (IS/OS), 3: junction between cone outer segment tip and RPE (OS/RPE). (Choi et al., IOVS 2008)








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