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Brett King, Lucie Sawides, Stephen A Burns; Quantifying Peripapillary Capillaries in Patients with Glaucoma Compared to Age-Similar Controls Using AOSLO. Invest. Ophthalmol. Vis. Sci. 2016;57(12):63.
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© ARVO (1962-2015); The Authors (2016-present)
Open angle glaucoma (OAG) is disease that causes characteristic changes in the retinal nerve fiber layer (RNFL) and optic nerve head. Vascular abnormalities have been reported in patients with OAG yet it has been difficult to quantify the apparent change in capillary beds. We investigate the use of adaptive optics scanning laser ophthalmoscopy (AOSLO) to develop capillary maps in patients with glaucoma and age-similar controls quantifying capillary density.
In this prospective, pilot study, we enrolled 9 subjects, 5 with OAG and 4 age-similar controls from an ongoing study that is collecting spectral domain ocular coherence tomography (SD-OCT) images and perimetric sensitivities. Each subject was imaged by AOSLO at the depth of the RNFL. Aligned and averaged images were montaged using I2K retina image program and custom software developed with Matlab.Images were processed with a custom Matlab tool using a derivative-of-Gaussian edge detection. The aspect ratio of the filter was set at 2. Filters were systematically varied in spatial scale and orientation. The maximum filter response at each pixel was used as an estimate of the vascular map. The spatial standard deviation of the vascular map was computed in 251x251 micron regions, and pixel values greater than the local standard deviation were set to 1, the others were set to 0. Next, in an 11x11 micron region the percent of pixels set to 1 was used as a capillary density map (Figure 1). Density maps were divided and analyzed according to superior-temporal (ST), temporal (T), and inferior-temporal (IT) regions and mean values calculated.
Density maps were generated in all subjects. All 5 subjects with OAG had maps where the area of observed RNFL loss corresponded with a decrease in capillary density. Mean sector values for controls were ST= 0.13, T = 0.13 and IT = 0.07 and for OAG were ST = 0.09, T = 0.08, and IT = 0.06 with the most notable difference between controls and OAG in ST and T sectors. In OAG subjects with asymmetric RNFL and associated field defects, larger capillary density was found in the less affected sector mean Δ=0.05.
The positive findings from this pilot study warrant further investigation of using AOSLO to investigate the relationship between capillary blood flow and RNFL loss in OAG.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1. An example of capillary density mapping in a subject with OAG and superior RNFL loss.
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