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R. Michael, O. Guevara, R. Arcari de Araujo, R. I. Barraquer; Calculation of the Neural Contrast Sensitivity From Measured Total Contrast Sensitivity and Modulation Transfer Function. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2783.
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© ARVO (1962-2015); The Authors (2016-present)
To test the feasibility of calculating neural contrast sensitivity function (neural CSF) from conventionally measured total contrast sensitivity function (total CSF) and estimated modulation transfer function (MTF). Neural CSF considers the retina and the brain, whereas total CSF considers the optical eye media, the retina and the brain together.
Three groups of 9 subjects each, one with normal ocular optics but with retinal alterations (diabetes mellitus with moderate diabetic retinopathy, mean age 49), another with altered ocular optics and normal retina (keratoconus, mean age 33) and a normal control group (mean age 30) were investigated. Total CSF was measured with best spectacle correction for 5 spatial frequencies (1.5 to 18 cyc/deg) with the CST 1800 and a FACT Near Chart. MTF and Strehl ratio (SR) for higher order aberrations and 3 mm pupil were calculated from Zernike coefficients obtained from optical aberration measurements (Tracey-iTrace). Neural CSF was calculated knowing that the MTF is the ratio of total CSF to neural CSF.
Total CSF in the keratoconus and diabetes mellitus group was significantly lower for 6 and 18 cycl/deg (0.5 and 0.7 log units respectively) as compared with the control group. MTF for keratoconus (SR 0.30) was lower and in diabetes mellitus group (SR 0.78) was similar to the control group (SR 0.80). Calculated neural CSF in the diabetes mellitus group was lower than in the control group whereas in the keratoconus group it was similar to the control group, with some overestimation for severe keratoconus cases.
It is possible to calculate a meaningful neural CSF from measured total CSF and MTF data. The neural CSF represents a CSF adjusted for optical aberrations. This would allow comparing the neural component of visual function in eyes with different optical aberrations.
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