June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
Cellular morphometry of the outer retina using adaptive optics OCT
Author Affiliations & Notes
  • Ravi Sankar Jonnal
    Ophthalmology, UC Davis, Sacramento, CA
  • Justin Migacz
    Ophthalmology, UC Davis, Sacramento, CA
  • Iwona Gorczynska
    Ophthalmology, UC Davis, Sacramento, CA
  • Robert J Zawadzki
    Ophthalmology, UC Davis, Sacramento, CA
  • John S Werner
    Ophthalmology, UC Davis, Sacramento, CA
  • Footnotes
    Commercial Relationships Ravi Jonnal, US Patent No. 7,364,296; unlicensed; (P); Justin Migacz, None; Iwona Gorczynska, None; Robert Zawadzki, None; John Werner, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2015, Vol.56, 4097. doi:https://doi.org/
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      Ravi Sankar Jonnal, Justin Migacz, Iwona Gorczynska, Robert J Zawadzki, John S Werner; Cellular morphometry of the outer retina using adaptive optics OCT. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4097. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Diseases and disorders which impact the outer retina, such as AMD, diabetic retinopathy, macular hole, and retinal detachment are routinely evaluated using optical coherence tomography (OCT). As such, correct interpretation of clinical OCT images is of great importance. Interpretation of these images, though, is clouded by optical properties of the eye, the complexity of light-tissue interactions, and image post-processing. We have designed and built a custom OCT system equipped with adaptive optics that provides greatly improved 3D resolution and permits precise instrument calibration and characterization. We investigated the OCT outer retinal band 3, thought to originate from either the cone outer segment tips or zone of interdigitation between cone outer segments (OS) and apical processes of the RPE.

 
Methods
 

Five subjects were imaged between 1.5 and 4.25°. Cones were segmented and aligned by their band 3 peaks. The resulting aligned B-scan was averaged and the thickness of band 3 was measured. Next, after bulk motion correction, the phase of the band 3 reflection was extracted and variance of this phase, which is a measure of the surface's roughness, was computed.

 
Results
 

After subtracting measured axial blur, average thickness of band 3, measured in single cones, was 2.1 μm. Typical variance of bulk-motion-corrected phase measurements was 0.09 rad, which corresponds to a surface roughness of 4 nm RMS.

 
Conclusions
 

Cellular measurements of band 3 suggest strongly that the reflection comes from a thin, optically smooth origin, such as a reflective surface, and not from an axially extended zone of scattering material. This surface must be located distal to the cone OS lumen and proximal to the RPE body. The most likely origin is the distal plasma membrane of the cone outer segment.  

 
AO-OCT B-scan taken at 1.5° temporal to the fovea. In (a), band 3 reflections from single cones are marked. Axial shifts of reflections are evident. In (b), the cones are shown without axial alignment. In (c), the cones are aligned by band 3.
 
AO-OCT B-scan taken at 1.5° temporal to the fovea. In (a), band 3 reflections from single cones are marked. Axial shifts of reflections are evident. In (b), the cones are shown without axial alignment. In (c), the cones are aligned by band 3.
 
 
(a) Bulk-corrected phase of band 3 of the cones in Fig. 1. Average longitudinal reflectance profiles of the (b) unaligned cones and (c) the band 3-aligned cones. Unaligned band 3 FWHM is 10.8 μm and aligned FWHM is 4.1 μm, which includes the 2.8 μm (measured) axial PSF. This suggests that the bulk of band 3's thickness in commercial OCT images is due to axial displacements of the reflections.
 
(a) Bulk-corrected phase of band 3 of the cones in Fig. 1. Average longitudinal reflectance profiles of the (b) unaligned cones and (c) the band 3-aligned cones. Unaligned band 3 FWHM is 10.8 μm and aligned FWHM is 4.1 μm, which includes the 2.8 μm (measured) axial PSF. This suggests that the bulk of band 3's thickness in commercial OCT images is due to axial displacements of the reflections.

 
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