Purpose: : Increasing the aberrations of the eye extends depth of focus (DOF) at the cost of reducing contrast at best focus. It is possible that by combining some specific patterns in each eye, in particular coma, a compromise for optimal vision at all distances may be achieved. In this study we investigate both monocular and binocular visual acuity (VA) and DOF when one eye has a fixed amount of vertical coma and the other eye has the same magnitude of coma, but varied orientations.
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.