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Brett J King, William Howard Swanson, Bright Senyo Ashimatey; Comparing RNFL defects to depth of defect across perimetric stimuli. Invest. Ophthalmol. Vis. Sci. 2017;58(8):704.
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© ARVO (1962-2015); The Authors (2016-present)
Current clinical thought is to use larger stimuli for visual field testing in patients with advanced glaucoma. Several studies have found visual field defects can be deeper for larger stimuli compared to size III, which contradicts the current clinical approach. Therefore, we performed a prospective, observational study to characterize visual field defects in relation to categories of retinal nerve fiber layer (RNFL) damage across different stimuli. Specifically, we hypothesize depth of defect may vary depending on stimulus and according to type of RNFL damage.
Twenty subjects with glaucoma (56-84 yr. ave 69 yr.) and 20 age-similar controls (49-89 yr. ave 68 yr.) were enrolled from our clinic population. All subjects were imaged with Heidelberg Spectralis to allow for en face imaging and were tested on a custom testing station allowing for presentation of different stimuli in 18 locations across the nasal field. Stimuli presented were standard size III and size V as well as flickering sinusoidal grating (FS), non-flickering sinusoidal (NFS) grating stimuli and a Gaussian blob. En face RNFL images were reviewed with the 18 visual field locations overlaid allowing for Henle fiber displacement. Each location over the RNFL was independently labeled as either normal or defects listed as wedge, slit, edge, or diffuse, allowing for comparison of perimetric defect to RNFL defect type. The controls were tested to develop normative data to define depth of defect per stimulus on the custom station. An ANOVA was run to identify interactions.
Mean depth of defect was similar for all stimuli. Areas graded as wedge had deeper perimetric defects for all stimuli compared to other types of RNFL loss (See Figure). There was a significant interaction between the type of stimulus used and the defect type; F (13,60) = 4.21;p<0.01. Wedge defects demonstrated the largest differences between stimuli with sinusoidal gratings having shallower defects compared to other stimuli (III to NFS p=0.01, V to NFS p=<0.01 and FS p=0.03, Blob to NFS p=<0.01 and FS p=0.03).
All stimuli produced similar results comparing across type of RNFL damage. Type of RNFL damage related to severity of defect which was deepest for diffuse and wedge. Sinusoidal gratings may not demonstrate as deep of defect as other types of stimulus in areas of wedge damage.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Depth of defect and stimulus type related to RNFL damage. Error bars show SEMs.
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