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T.J. T. P. van den Berg, L. Franssen, J.E. Coppens; Performance of the C–Quant Instrument for Retinal Straylight Assessment . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1220.
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© ARVO (1962-2015); The Authors (2016-present)
In 2005 the commercial C–Quant instrument was introduced for routine clinical assessment of retinal straylight. Retinal straylight is the cause of important patient complaints such as glare hindrance and contrast loss. It results from disturbances in the optical media, increasing light scattering over 1 to 90 degrees. Its assessment would help to decide on surgery of (early) cataract, or to evaluate corneal or vitreal problems.
The instrument is based on the psychophysical technique of "Compensation Comparison" (ARVO 2005 #4315). Retinal straylight is assessed in a functional way, i.e. as sensed by the retina. It is an individual characteristic of the eye, quantified using the physically well–defined straylight parameter s. Added value in comparison to visual acuity was assessed in 2400 active drivers of the European GLARE study. Repeatability of the straylight value using the C–Quant was tested for 17 naive subjects and several groups of patients. Absolute measurement precision of the C–Quant was tested using a scattering sample with known straylight value in front of the eyes of the 17 naive subjects.
An important finding in the population study was that many individuals suffer from increased straylight that is undetected in visual acuity. In 6% of cases with decimal visual acuity > 0.5 straylight was increased more than 4 times compared to normal. The figure shows performance with respect to repeatability ( x = y line ), and with respect to absolute calibration (dashed line) of the C–Quant. The straylight value of the scattering sample estimated with the C–Quant data of the figure corresponds to log(s)=1.14, close to the true value of 1.15. For the patient populations repeatability was comparable to that of the figure, but for decimal visual acuities down to 0.1 repeatablility was less.
Absolute precision and repeated measures standard deviation is very good compared with differences in the population. Straylight measurement promises important extra diagnostic power over visual acuity. The C–Quant by Oculus is a well suited instrument for clinical assessment of retinal straylight.
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