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Christianne A Wa, Kenneth M Yee, Jonathan Mamou, Ronald H Silverman, Jesse Gale, Amitha K Ganti, Jeffrey A. Ketterling, Alfredo A Sadun, J Sebag; Quantitative Ultrasonography of Vitreous Correlates with Contrast Sensitivity in Patients with Floaters. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5857. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies demonstrated that patients complaining of floaters have reduced contrast sensitivity (CS) [Sebag et al.; Retina Nov 27, 2013, e-pub]. We sought a structural correlate of this functional deficit and hypothesized that quantitative ultrasound (QUS) of vitreous would correlate with CS.
Twenty-three eyes in 16 subjects (11 males; mean age 46 years, range 19-72) with very mild to severe floaters underwent ultrasonography (Aviso, Quantel, France) with a 15 MHz probe (focal length = 20mm) to obtain two-dimensional B-scans in three positions (nasal longitudinal, inferotemporal longitudinal and inferotemporal transverse) using standardized settings. The exam was performed with a contact technique on the globe, at the limbus to avoid attenuation by the eyelid and lens. Within each cross-section, two regions of interest were analyzed: whole-central vitreous and pre-macular posterior vitreous. One hundred video frames from each position were screened for artifact and processed to generate 6 averaged QUS parameters; e.g. total energy, mean echo amplitude, and cluster analysis for groups of adjacent echogenic points. The CS at a spatial frequency of 5 cpd was measured with the Freiburg acuity contrast test (FrACT, expressed as threshold contrast: %Weber = Imax - Imin / Imax).
The CS threshold ranged from 1.4 %W (normal) to 5.4 %W (worst). Multiple QUS parameters correlated strongly with CS for all three scanning positions (most R > 0.6 and P < 0.05). In sub-group analysis, parameters for the whole-central vitreous region and the nasal longitudinal position had greatest correlations to CS. Of all QUS parameters generated, the reflected ultrasound energy in the whole-central vitreous region imaged with the nasal longitudinal scan had the highest R-value, 0.823; P < 0.001 (see figure). The coefficient of variation was 41%.
Quantitative ultrasound parameters correlate with contrast sensitivity providing a structural correlate to the functional deficit associated with vitreous floaters. Both indices could thus be measures of floater-induced visual disability and useful for the evaluation of surgery, YAG laser, or pharmacologic therapy of floaters.
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