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E. Schmidt, L.E. Arnold, L.E. Pillunat; GDxVCC: Effects of Plastic vs. Glass Spectacles . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3647.
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© ARVO (1962-2015); The Authors (2016-present)
For refractional compensation measurement with the GDxVCC can alternatively be performed with glasses. Especially in case of severe astigmatism this leads to an improved sharpness of the intensity image. In the present study we compared the effects of plastic vs. glass spectacles on GDxVCC measurements.
40 healthy subjects, 20 with glass and 20 with plastic spectacles were enrolled in this study. Either the right or left eye was randomly selected for examination. First the refraction was entered in the software and three scansets of macula and optic nerve head were performed without glasses. Thereafter, measurements were repeated with glasses, setting the refraction in the software at zero. Means of the three single measurements were taken and descriptive statistic was performed using the Bland–Altman–Analysis and Intraclass correlation coefficients (ICC).
Bland–Altman–Analysis of the differences of means show: 1) glass spectacles: magnitude 3 ± 3 nm, polarization axis 2 ± 1°, TSNIT average 3 ± 2 µm, superior average 4 ± 3 µm, inferior average 4 ± 3 µm, TSNIT SD 2 ± 2 and NFI 3 ± 2. 2) plastic spectacles: magnitude 31 ± 23 nm, polarization axis 28 ± 27°, TSNIT average 13 ± 11 µm, superior average 8 ± 10 µm, inferior average 14 ± 10 µm, TSNIT SD 7 ± 6 and NFI 5 ± 4. ICC show: 1) glass spectacles: magnitude 0.93, polarization axis 0.98, TSNIT average 0.83, superior average 0.84, inferior average 0.88, TSNIT SD 0.66 and NFI 0.78. 2) plastic spectacles: magnitude –0.04, polarization axis 0.17, TSNIT average 0.12, superior average 0.47, inferior average 0.46, TSNIT SD 0.46 and NFI 0.59.
Our results suggest that the use of plastic glasses was associated with larger variation of measured values with the GDxVCC as compared to glass spectacles. This may lead to miscalculation in glaucoma diagnostics. These variations are most likely attributable to polarizing properties of the polymeric medium. We conclude that wearing plastic spectacles for measurements with the GDxVCC is not recommendable.
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