Methods: We used a binocular adaptive optics visual analyzer (Fernández, Prieto & Artal, Opt. Lett. 34, 2628, 2009) to measure both monocular and binocular VA as a function of object vergence. Four subjects were tested under the following visual conditions: one eye had a fixed amount of vertical coma induced (0.22 µm), while the other eye had the same magnitude of coma but 8 different orientations ( 0, 45, 90, 135, 180, 225, 270 and 315 degrees). While artificial pupils were set to 3.5 mm in diameter, aberrations were induced over a 4.8mm pupil. Astigmatism was corrected if it exceeded 1D. Through focus VA was measured with a tumbling E from 1.5 to -1.5 D of defocus in 0.5 D steps. DOF was estimated as the dioptric range where VA was higher than 0.8.
Results: Monocular DOF increased when coma was induced. On average, we observed a maximum increase of 0.5 D from the baseline case of natural aberrations (1.5 D). The average DOF ranged from 1.4 to 2 D depending on the particular coma orientation, with the vertical and horizontal cases providing the largest values of DOF. A correlation was not found between the pre-existing orientation of coma for each subject and the angles providing the largest DOF, nor did ocular dominance play a role. It should be considered that other aberrations, notably trefoil, may interact with the induced coma in a distinct way in each subject. DOF measured binocularly was larger than the monocular estimates, and showed a minor dependence on orientation. Binocular interaction seems to equalize the impact of coma orientation on DOF.
Conclusions: The addition of a controlled amount of coma increases DOF. The orientation of coma seems to have a significant effect monocularly but less of an effect when DOF is measured for binocular conditions.