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Stefan Schramm, Patrick Schikowski, Monika Reder, Kathleen Kunert, Bernd U. Seifert; Plausibility of Stray Light Measurement with a modified Wavefront Analyzer. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6217.
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© ARVO (1962-2015); The Authors (2016-present)
A number of publications and patents suggest the adoption of a modified wavefront analyzer to measure forward light scatter in the human eye. In this work Hartman-Shack (HS) images acquired with a modified wavefront analyzer (WASCA) from 267 eyes from 143 people (age 43±16) were investigated. Additional stray light simulations with a numerical Gulstrand eye model focus on device parameter influence.
To support stray light measurement the confocal pinhole of the wavefront analyzer was removed. HS image analysis includes the separation of each point spread function (PSF) and extraction of local characteristics like most frequent value (MFV). Each parameter was averaged over the whole pupil (MEAN), the periphery of the pupil (P_MEAN) and over the image center (C_MEAN) where the laser enters the eye. Correlations of these parameters with age and stray light parameters of Pentacam Scheimpflug camera were analyzed. To evaluate the plausibility of the results stray light simulations were performed in FRED 9.10. The imaging path of the wavefront aberrometer with relay system and HS sensor was modeled. HS lenslet focal length was 3 and 6mm respectively. A light source on the retina simulating the emission pattern of a volume scattered laser beam on the retina was introduced. To model stray light scattering bodies were implemented in cornea and lens with various densities. Simulated HS images were analyzed like described above.
The MEAN-MFV has no correlation with age. The difference of C_MEAN-MFV and P_MEAN-MFV correlates significant (p<<0.01) with age (r=0.43) and stray light parameters of Pentacam (r=0.4). All other parameters have weak or no correlation. To remove the influence of pupil diameter a partial correlation was performed which yielded only a weak correlation of C_MEAN-MFV minus P_MEAN-MFV with age (r=0.262) and non with Pentacam. In the simulations increasing density of scattering bodies lead to increasing MEAN-MFV at 3mm focal length of the HS-sensor and nearly no change at 6mm.
In vivo measurement results indicate that a regular wavefront analyzer may not be applicable for stray light measurement. However depending on device configuration light scatter in the human eye could be measured with HS-sensors under consideration to pupil size. The simulations suggest a longer focal length of the HS sensor to be the cause of the weak correlation of the MEAN-MFV with age in vivo.
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