Purchase this article with an account.
Leonardo Blanco, Johanan L. Codona, Nathan Doble; Rapid Measurement of Cone Photoreceptor Pointing using Focus Diversity. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5202.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
We present a method to rapidly measure the pointing direction of individual cone photoreceptors with adaptive optics (AO). Roorda and Williams (JOV, 2002) adjusted the entrance pupil to alter the direction of the light incident on the cones and showed that in normal eyes cones point towards the same pupil location. Choi et al. (IOVS 2008) used the same technique in a diseased eye showing a higher degree of variability. Here, for a fixed entrance pupil we rapidly change the focus to image the waveguided light in various axial planes. This defocus causes, in successive images, a relative shift in the apparent position of cones with different pointing directions. The relative shift with known defocus allows the relative tilt to be measured.
The AO flood illuminated fundus camera at The Ohio State University was used to acquire AO retinal images on normal subjects at 2 and 4° in the temporal retina (680nm light, 0.75° field of view, 6 mm pupil). Once the best focus was achieved, focus plane was rapidly changed both anterior and posterior to this position and the corresponding images recorded. Defocus was introduced using the AO DM, in sweeps of up to 0.5D in 0.025D steps lasting 1 second. Images were registered and cone positions measured in each image.
The pointing variability of cones can be clearly seen, the majority of cones appearing essentially parallel. We explored using open and closed-loop images, seeing the effect in both. We collected data on subjects using both this technique and the method of Roorda and Williams, 2002. Tilt measurements can be compared on a per-cone basis.
Focus diversity allows the relative tilt of cones to be measured in less than a second. The degree of uniformity in the cone pointing may be an indicator of retinal health. The coming months will see the imaging of further normal subjects and refinement of the analysis procedure.
This PDF is available to Subscribers Only