title: DIRECTIONAL OPTICAL COHERENCE TOMOGRAPHY PROVIDES ACCURATE OUTER NUCLEAR LAYER AND HENLE FIBER LAYER MEASUREMENTS.
abstract: OBJECTIVE
  The outer nuclear layer (ONL) contains photoreceptor nuclei, and its thickness is an important biomarker for retinal degenerations. Accurate ONL thickness measurements are obscured in standard optical coherence tomography (OCT) images because of Henle fiber layer (HFL). Improved differentiation of the ONL and HFL boundary is made possible by using directional OCT, a method that purposefully varies the pupil entrance position of the OCT beam.
  
  
  METHODS
  Fifty-seven normal eyes were imaged using multiple pupil entry positions with a commercial spectral domain OCT system. Cross-sectional image sets were registered to each other and segmented at the top of HFL, the border of HFL and the ONL and at the external limiting membrane. Thicknesses of the ONL and HFL were measured and analyzed.
  
  
  RESULTS
  The true ONL and HFL thicknesses varied substantially by eccentricity and between individuals. The true macular ONL thickness comprised an average of 54.6% of measurements that also included HFL. The ONL and HFL thicknesses at specific retinal eccentricities were poorly correlated.
  
  
  CONCLUSIONS
  Accurate ONL and HFL thickness measurements are made possible by the optical contrast of directional OCT. Distinguishing these individual layers can improve clinical trial endpoints and assessment of disease progression.
authors.affiliation: *Vision Science Graduate Group, School of Optometry, University of California, Berkeley, Berkeley, California; †West Coast Retina Medical Group, San Francisco, California; ‡Department of Ophthalmology, Medical College of Wisconsin, Milwaukee, Wisconsin; §Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, Wisconsin; ¶Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin; and **Department of Ophthalmology, University of California, San Francisco, California.
authors.forename: Brandon J
authors.initials: BJ
authors.lastname: Lujan
authors.forename: Austin
authors.initials: A
authors.lastname: Roorda
authors.forename: Jason A
authors.initials: JA
authors.lastname: Croskrey
authors.forename: Adam M
authors.initials: AM
authors.lastname: Dubis
authors.forename: Robert F
authors.initials: RF
authors.lastname: Cooper
authors.forename: Jan-Kristine
authors.initials: JK
authors.lastname: Bayabo
authors.forename: Jacque L
authors.initials: JL
authors.lastname: Duncan
authors.forename: Bhavna J
authors.initials: BJ
authors.lastname: Antony
authors.forename: Joseph
authors.initials: J
authors.lastname: Carroll
mesh_terms: D000293:Adolescent; D000328:Adult; D002467:Cell Nucleus; D063928:Ependymoglial Cells / Q000166:cytology*; D005260:Female; D005583:Fourier Analysis; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009412:Nerve Fibers; D011446:Prospective Studies; D055351:Retinal Neurons / Q000166:cytology*; D041623:Tomography, Optical Coherence / Q000379:methods*; D055815:Young Adult
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