Letter contrast sensitivity function of the eye

To provide empirical data of letter CSF for various levels of defocus under controlled conditions of luminance and age.Corrected distance visual acuities were tested at different levels of contrast and defocus. An experiment was conducted using the Medmont visual acuity tester on 10 young subjects and under normal room lighting.Empirical data of visual acuity were obtained for 7 levels of contrast (5, 10, 15, 25, 40, 60, 80%) and defocus levels of 0, +1 and +2D. A mathematical model was derived (R2=0.995) and this can be used to estimate visual acuity at various contrast levels for defocus of < or =+2D.This information is useful for the clinician as normative data and for further development of optical models to predict visual performance of the eye.