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Monica Chen, Toco Yuen Ping Chui, Paula Alhadeff, Robert Ritch, Richard B Rosen, Donald C Hood, Alfredo Dubra; Imaging Retinal Nerve Fiber Bundles in Glaucoma Patients with Deep Local Visual Field Damage of the Macular Region. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4778.
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© ARVO (1962-2015); The Authors (2016-present)
To better understand the structural changes from relatively healthy to severely affected regions as seen on visual fields (VF) in glaucoma patients using an adaptive optics scanning light ophthalmoscope (AO SLO) and frequency domain optical coherence tomography (fdOCT).
Nine eyes of 9 glaucoma patients with arcuate defects within the macula region as seen on 10-2 VF were tested as well as 4 eyes of 4 controls. Using a prototype AO SLO system, the retinal nerve fiber (RNF) bundles in a 20° vertical by 1° horizontal region centered at the fovea were imaged. High-resolution images, 1° by 1°, were montaged. RNF layer (RNFL) thickness was obtained from fdOCT vertical line scans after segmentation [1,2]. Using the fdOCT images, the RNFL was divided into 3 regions based upon a comparison to the RNFL thickness of 54 controls: 1. within normal limits (WNL), 2. severely affected (SA: little or no RNFL), and 3. transition zone (TZ), the region between the WNL and SA regions. To compare corresponding regions, the scale of the AO SLO and fdOCT images were corrected based upon axial length.
The average 10-2 VF total deviation values for the 3 OCT defined regions were: better than -3 dB (WNL); ≤-3 dB, but ≥-15 dB (TZ); and worse than -15 dB (SA). The RNF bundles in the WNL region were highly reflective and densely packed on the AO images; they appeared similar to controls (Fig 1A). In the TZ, RNF bundles were clearly present, but were less densely packed and less reflective (Fig 1B). In the SA region, RNF bundles, if present, were sparse and of low contrast (Fig 2A). In 2 eyes with deep VF loss, no RNF bundles were present, but circular structures about 14-28 µm in dia. were present (Fig 2B) and in 2 eyes, reflective membrane structures previously reported  were seen (Fig 2C). In general, the transition zone marked on the fdOCT scans agreed with the AO SLO images.
Both structural tests, as well as the 10-2 VF, support the existence of a transition zone, where the sensitivity is reduced, the RNFL is thinned, and the RNF bundles appear abnormal. This region should be followed for progression as well as for neuro-protective changes. 1. Raza et al. AO 2011; 2. Yang et al. Opt Exp 2010; 3. Scoles et al. ARVO 2012
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