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P. Rodriguez, R. Navarro; MTF and Pupil Transmittance of Cataractous Eyes From Aberrometric and Double-Pass Measurements. Invest. Ophthalmol. Vis. Sci. 2007;48(13):6005.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the Modulation Transfer Function (MTF) and pupil transmittance of cataractous eyes, by means of a Laser Ray Tracing (LRT) wavefront sensor and a double-pass (DP) device and to compare them with a control group of normal healthy eyes.
A dual system comprising a LRT wavefront sensor and a double-pass device was used to measure the ocular MTF in two different ways. The LRT sensor provides both the wavefront aberration and the effective pupil transmittance (i.e. the complex pupil function). Consequently, the resulting MTF includes the effect of aberrations and that of the pupil transmittance as well. A second MTF is obtained from the double-pass aerial point-spread function, which includes the effect of intraocular scattering. Both subsystems, LRT and DP, work under green illumination (532 nm), thus minimizing scattering from blood vessels. A set of 25 cataractous eyes (average LOCS III grade 2) was measured under pharmacological dilation and a partial refractive compensation through a common Badal lens system. The pupil diameter (6.0 mm) and alignment were carefully controlled. Aberrometric and double-pass MTFs were obtained for each eye and compared to estimate ocular scattering.
The group of normal eyes showed a normal Gaussian pupil transmittance (Stiles-Crawford effect), and the LRT and DP MTFs were similar. On the contrary, most of the 25 cataractous eyes showed an altered pupil transmittance, opposite to that found in healthy eyes: i.e. more light was transmitted through the periphery than through the centre of the pupil. In addition, a statistically significant difference between the aberrometric and double-pass MTFs was found in 23 out of 25 eyes (p = 0.009). This difference was higher than that previously found in old, normal eyes.
Overall optical quality diminishes in cataractous eyes. An increase in ocular forward-scattering was observed in cataractous eyes compared with a control group of old, healthy eyes. The scattering due to the cataract was patent in both double-pass MTF and LRT pupil transmittance. In addition, the latter allowed us to quantify the spatial distribution of the cataract optical density. Thus, this method provides a double way to detect cataracts which could be useful for early diagnosis.
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