Contrast sensitivity measurements with the Echelon diffractive bifocal contact lens as compared to bifocal spectacles

We examined the contrast sensitivity function of presbyopic subjects wearing the Hydron Echelon diffractive bifocal contact lens. Contrast sensitivity with the Echelon lens was compared to contrast sensitivity with bifocal spectacle correction. Each eye was tested for near and distance vision with the Echelon contact lens and with spectacle correction. Most subjects achieved a visual acuity of 20/20 with the Echelon lens; however, on average, contrast sensitivity was found to be significantly decreased with the contact lens as compared to spectacles for both distance and near vision. The largest decrease in contrast sensitivity was seen for mid-range spatial frequencies (4 to 16 cycles/degree). Although most subjects experienced a significant decrease in contrast sensitivity, two experienced only small decreases with the Echelon lens. Only one subject who met entry criteria reported that vision was as good with the Echelon lens as with spectacles. The decreased contrast sensitivity may result from contact lens decentration as well as inherent optical characteristics of the Echelon lens.