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Claude Giasson, Corinne Deschênes, Vasile Diaconu; Is the Use of an Integrating Sphere Really Desirable When Measuring Contact Lens Transmittance?. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5454.
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© ARVO (1962-2015); The Authors (2016-present)
The standard indicates that contact lens transmittance should be measured with an integrating sphere (IS) in order to include the scatter (or indirect transmittance). To compare contact lens transmittance obtained with and without an integrating sphere and to evaluate how much light is lost in measurements done with an IS.
After a baseline percent transmittance measurement of a quartz chamber filled with saline, the total and direct percent transmittance of the chamber with a contact lens (Encore 100) were respectively measured 4 times with and without an integrating sphere with a scanning spectrophotometer (Cary 5000, Varian) in the range of 200 to 800 nm. In other experiments, relative light levels were measured with and without the measuring chamber with and without the IS in order to estimate how much of the signal was lost upon the addition of the measuring chamber. Differences between total and direct transmittance for contact lenses were tested for significance at 550nm with an independent t test using the SPSS 17.0 software for Windows.
There were no significant differences at 550 nm between the total (100.8 ± 8.5%) and direct transmittance (98.3 ± 0.2%) when tested with an independent t test. The standard deviations of total transmittance measurement were consistently larger than the ones obtained without the integrating sphere. At 550 nm, the ratio of light intensities measured in the absence of the chamber filled with saline to the one measured with the chamber with saline represented 46% of the signal when the IS was in position and 92% when it was not.
The use of an integrating sphere when measuring the transmittance of a contact lens allows to include the diffusion of the contact lens in the measurement. However, in our system, the light intensity is drastically decreased by the simple addition of a wet cell in front of an integrating sphere that reduce the signal and may increase the noise.
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