Defocus and relative defocus for a 4 mm pupil diameter. (
A) The relative locations of the hypothetical optical image shells (
a,
c,
e) and retinal shapes (
b,
d) determine relative peripheral defocus. Image shell (
c) is foveally emmetropic for both retinas (
b) and (
d), but is peripherally hyperopic relative to retina (
b) and peripherally myopic relative to retina (
d). Relative peripheral myopia between (
c) and (
d) first increases, then decreases, with field angle primarily owing to the oblate profile of retina (
d). This is the reason for the recoiling patterns in the far periphery of the cohort curves in (
B) and (
C). (
B and
C) Relative peripheral defocus along the horizontal field meridian calculated using either second-order or second-, fourth-, and sixth-order Zernikes (
Appendix D); (
E and
F) use the latter calculation. (
D and
E) Relative peripheral defocus is essentially the same as actual defocus for the
ideal emmetropic and
typical emmetropic models because foveal dioptric defocus is +0.005 D and −0.023 D, respectively. (
F) Relative (upper) and actual (lower) defocus surfaces for the −
2.75 D myopic eye model are offset from each other by 2.761 D of foveal myopic defocus. Like total root mean square wavefront error in
Figure 3, the relative change in defocus with field angle is greater (steeper plots and surfaces) for emmetropic eye models than for the myopic model.