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E.S. Storey, C.F. Burgoyne, J.C. Downs; Canine Optic Nerve Head (ONH) Surface Compliance Following Intraocular Pressure (IOP) Elevation from 10 to 30 mm HG . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1233.
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© ARVO (1962-2015); The Authors (2016-present)
To implement ONH surface compliance testing in normal dogs so as to characterize normal ONH and peripapillary retinal position and compliance prior to the institution of a laser–induced intraocular (IOP) elevations in one eye.
Both eyes of 4 normal beagle dogs have been compliance tested on 3 separate occasions. For each test, under general inhalant anesthesia a 27–gauge needle connected to a BSS manometer was placed into the anterior chamber of both eyes and six 15 degree HRT (Heidelberg Retinal Tomograph II, Heidelberg Engineering) images were obtained 10 min and 30 min following adjustment of the IOP to 10 then 30 mm Hg. For each eye, HRT images were aligned to a reference image in which the borders of the myelinated ONH were chosen as the area of interest (AOI). At each observation point, the mean elevation of all pixels within the area of interest was calculated, and then averaged for all 6 images (Mean Position of the Disc –MPD). Baseline ONH surface position (MPDBaseline) was calculated from the 6 images at the second (30 min) IOP 10 observation point. Baseline ONH surface compliance (Change from MPDBaseline) was separately calculated from the 6 images at the 10 and 30 minute IOP 30 observation points.
Change from MPDBaseline data demonstrated a mean posterior deformation of –62 µm (range: +20 to –183.2 µm) in the eight eyes 10 minutes after IOP elevation to 30 mm Hg, increasing minimally to –65 µm (range: +16 to –118 µm) of deformation 20 minutes later. A positive (counterintuitive) Change from MPDBaseline following acute IOP elevation was recorded for at least one time point in 7 of 15 compliance tests however these were sporadic and inconsistent within individual eyes.
In four dogs, normal ONH surface position (MPDBaseline) and compliance (Change from MPDBaselin) are reproducible and should allow sensitive HRT detection of early glaucomatous damage. ONH surface compliance in these four dogs is substantially greater than in normal monkeys and may indicate differences in the underlying connective tissue architecture of the canine ONH.
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