Purpose: We provide an account of the relationships between eye shape, retinal shape and peripheral refraction. Recent findings: We discuss how eye and retinal shapes may be described as conicoids, and we describe an axis and section reference system for determining shapes. Explanations are given of how patterns of retinal expansion during the development of myopia may contribute to changing patterns of peripheral refraction, and how pre-existing retinal shape might contribute to the development of myopia. Direct and indirect techniques for determining eye and retinal shape are described, and results are discussed. There is reasonable consistency in the literature of eye length increasing at a greater rate than height and width as the degree of myopia increases, so that eyes may be described as changing from oblate/spherical shapes to prolate shapes. However, one study indicates that the retina itself, while showing the same trend, remains oblate in shape for most eyes (discounting high myopia). Eye shape and retinal shape are not the same and merely describing an eye shape as being prolate or oblate is insufficient without some understanding of the parameters contributing to this; in myopia a prolate eye shape is likely to involve both a steepening retina near the posterior pole combined with a flattening (or a reduction in steepening compared with an emmetrope) away from the pole. Summary: In the recent literature, eye and/or retinal shape have often been inferred from peripheral refraction, and, to a lesser extent, vice versa. Because both the eye's optics and the retinal shape contribute to the peripheral refraction, and there is large variation in the latter, this inference should be made cautiously. Recently retinal shape has been measured independent of optical methods using magnetic resonance imaging. For further work on retinal shape, determining the validity of cheaper alternatives to magnetic resonance techniques is required.

Changes in pupil size and shape are relevant for peripheral imagery by affecting aberrations and how much light enters and/or exits the eye. The purpose of this study is to model the pattern of pupil shape across the complete horizontal visual field and to show how the pattern is influenced by refractive error. Right eyes of 30 participants were dilated with 1% cyclopentolate, and images were captured using a modified COAS-HD aberrometer alignment camera along the horizontal visual field to ±90°. A two-lens relay system enabled fixation at targets mounted on the wall 3 m from the eye. Participants placed their heads on a rotatable chin rest, and eye rotations were kept to less than 30°. Best-fit elliptical dimensions of pupils were determined. Ratios of minimum to maximum axis diameters were plotted against visual field angle. Participants' data were well fitted by cosine functions with maxima at (-)1° to (-)9° in the temporal visual field and widths 9% to 15% greater than predicted by the cosine of the field angle . Mean functions were 0.99 cos([ + 5.3]/1.121), R(2) 0.99 for the whole group and 0.99 cos([ + 6.2]/1.126), R(2) 0.99 for the 13 emmetropes. The function peak became less temporal and the width became smaller with increase in myopia. Off-axis pupil shape changes are well described by a cosine function that is both decentered by a few degrees and flatter by about 12% than the cosine of the viewing angle, with minor influences of refraction.

We measured wave aberrations over the central 42 degrees x 32 degrees visual field for a 5-mm pupil for groups of 10 emmetropic (mean spherical equivalent = 0.11 +/- 0.50 D) and 9 myopic (MSE = -3.67 +/- 1.91 D) young adults. Relative peripheral refractive errors over the measured field were generally myopic in both groups. Mean values of C(4)(0) were almost constant across the measured field and were more positive in emmetropes (+0.023 +/- 0.043 microm) than in myopes (-0.007 +/- 0.045 microm). Coma varied more rapidly with field angle in myopes: modeling suggested that this difference reflected the differences in mean anterior corneal shape and axial length in the two groups. In general, however, overall levels of RMS aberration differed only modestly between the two groups, implying that it is unlikely that high levels of aberration contribute to myopia development.

Small levels of crossed cylinder blur (≤0.75 D) produces losses in visual acuity that are dependent on the cylinder axis. Crossed cylinders of 0.75 D produce losses in visual acuity that are twice those produced by defocus of the same blur strength.

Variations in luminance and accommodation influence pupil size, but only the former affects pupil center location significantly. Pupil center shifts are too small to be of concern in fitting progressive addition lenses.