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P. Rodriguez, R. Navarro, J. Aporta; Double–Pass Versus Aberrometric MTF in Green Light . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1216.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the Modulation Transfer Function (MTF) obtained with double–pass and a laser ray tracing (LRT) wavefront sensor, in green light, and to study the relative influence of intraocular scattering on the MTF as a function of age.
A dual experimental system was built to obtain the MTF in two different ways. One measurement system consists of a LRT to measure the wave aberration, and the other is a system to record the double–pass aerial point–spread function. The two subsystems share the same optical path (including Badal lenses, beam splitters, etc.), and use the same green laser light source (532 nm). By using green light we avoid the retinal scattering from the choroid, which can potentially bias the double–pass measurements when working under red or infrared illumination. For each eye, two MTFs, LRT and double–pass, were obtained and compared. The aberrometric MTF only accounts for the effect of aberrations (up to 7th order), whereas the double–pass method yields a more direct measurement of the MTF, which now includes the combined effect of all factors, namely scattering and aberrations. Measurements were done on 3 groups of subjects with normal, healthy eyes of different ages (twenties, forties and sixties). The MTF was obtained for a 6 mm pupil diameter (pupil was dilated with tropicamide) and for a partial refractive compensation through a Badal lens system.
No statistically significant difference could be found between the MTFs obtained with both methods. Furthermore, in most cases, the agreement between both types of measurement was excellent, no matter the age group. Small differences were observed only in a few eyes from both younger and older age groups.
In normal eyes, double–pass and LRT techniques were totally equivalent, as they provided equal measurements of the retinal image quality, regardless of age. When working in green light, the dynamic range of the double–pass device was insufficient to capture any scattering halo, even in older subjects. These results might be different in pathological eyes with medium to high levels of intraocular scattering.
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