This study investigated the change in corneal curvature and corneal wave-front aberrations with accommodation. The corneal curvature of the right eyes of 12 young adults was measured using a corneal topography system, while subjects fixated far (4.0 m) and near (0.2 m) targets with their left eyes. Convergence was controlled. Both the mean corneal radius at the vertex and the shape parameter significantly increased from the far to the near viewing condition. No significant change in root mean square of wave-front aberrations with accommodation was observed for the group, but there was individual variation in the change of wave-front aberration. A significant mean change for the group in both x-axis coma and spherical aberration was found. The change in corneal surface with accommodation suggests an increase in peripheral curvature with flattening at the vertex.

^{2}. The infrared illumination provides greater comfort for the subject. A red spot inside the system was used as the fixation point for the right eye.

*Rc*for the aberration-free surface was approximated with the average radius derived from corneal curvature for the first inner ring in the corneal measurement. The shape parameter (

*p*) for an aberration-free conic surface is determined by: where

*n*is the refractive index of the cornea (

*n*= 1.376), and thus is a constant equal to 0.47184.

*Hc*(

*x,y*) and

*Hr*(

*x,y*), respectively, the anterior corneal wave-front aberration would be determined as following:

*t*test yielded a significant mean increase in the radius from far to near (mean difference = 0.026 ± 0.041 mm; paired

*t*= 2.21,

*p*< .025).

*t*= 2.12,

*p*= .029).

*t*= 1.63,

*p*= .065). The change in shape parameter ranged from −0.080 to 0.278. Relative to the mean shape parameters for the 11-mm corneal area, the mean shape parameters for the 7-mm corneal area at both the far and the near viewing condition were significantly greater (mean difference = 0.053 ± 0.054; paired

*t*= 3.36,

*p*= .003 for far; and mean difference = 0.072 ± 0.077; paired

*t*= 3.25,

*p*= .004 for near). But, the change in shape parameter from far to near for the 7-mm corneal area was not significantly different from that for the 11-mm area (mean difference = 0.019 ± 0.058; paired

*t*= 1.15,

*ns*).

*t*= 3.77,

*p*< .01). The Zernike coefficients for Z3, Z5, and Z8 for the far condition were significantly different from those for the near condition (

*t*= 3.49,

*p*< .02 for Z3;

*t*= 2.84,

*p*< .025 for Z5 and

*t*= 2.63,

*p*< .05 for Z8, respectively).

*t*test showed no significant difference in the change in RMS values from far to near (mean difference = 0.03 ± 0.12 µm; paired

*t*= 0.85,

*ns*). However, 3 of the 12 subjects were found to have a significant difference in RMS values for total wave-front aberrations between the far and near viewing conditions (difference = 0.310 µm;

*t*= 3.77,

*p*< .01, for subject 4; difference = 0.179 µm;

*t*= 3.38,

*p*< .02, for subject 5; and difference = 0.115 µm;

*t*= 2.14,

*p*< .05, for subject 11). While the RMS value at far viewing was greater than that at near viewing for subject 11, subjects 4 and 5 had RMS values greater at near than at far.

*t*= 2.20,

*p*< .05). The mean RMS values for the 12 subjects for the far (0.69 ± 0.09 µm) and the near (0.71 ± 0.09 µm) viewing conditions were similar, and there was no significant change in the RMS values (mean difference = 0.02 ± 0.06; paired

*t*= 0.94,

*ns*), as shown in Figure 5b.

*t*test values for the change in Zernike coefficients with accommodation are also listed. For the 2nd order Zernike aberrations (Z3 and Z5 astigmatisms), there was no significant change in the coefficients from far to near. Among the four 3rd order aberrations (Z6-Z9), only one (Z8, x-axis coma) was found to have a significant change (

*p*< .007; the significant level was corrected from the level of

*p*= .05 for multiple comparisons using the Bonferroni correction). In addition, corneal spherical aberration (Z12) was significantly changed when the eye’s fixation changed from far to near (

*p*< .007).

Z3 | Z5 | Z6 | Z7 | Z8 | Z9 | Z12 | |
---|---|---|---|---|---|---|---|

Far | −0.009 ± 0.469 | −0.616 ± 0.523 | −0.003 ± 0.178 | −0.133 ± 0.227 | −0.152 ± 0.260 | 0.024 ± 0.136 | 0.482 ± 0.103 |

Near | −0.008 ± 0.481 | −0.632 ± 0.520 | 0.007 ± 0.155 | −0.155 ± 0.215 | −0.066 ± 0.251 | 0.013 ± 0.134 | 0.512 ± 0.098 |

Near-Far | 0.001 ± 0.088 | −0.016 ± 0.141 | 0.010 ± 0.081 | −0.022 ± 0.070 | 0.086 ± 0.100 | −0.011 ± 0.046 | 0.030 ± 0.029 |

Paired t | 0.02 | −0.40 | 0.44 | −1.08 | 2.96* | −0.83 | 3.55* |