Abstract: The change in asphericity recorded by the Tscherning aberrometer in the author’s left eye during accommodation represents a shift toward negative asphericity (decrease in spherical aberration) from a position of positive asphericity (greater than normal spherical aberration).1Krueger R.R Mrochen M Kaemmerer M Seiler T Understanding refraction and accommodation through “retinal imaging” aberrometry a case report.Ophthalmology. 2001; 108: 674-678Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar Although the author’s age, manifest, and cycloplegic refractions are not indicated in the article, the aberrometer-recorded refraction without accommodation is listed in Table 1 of the article as +0.60–0.70 × 166 for the central 3 mm; and +0.30–0.47 × 164 for the full pupil diameter of 6.5 mm.1Krueger R.R Mrochen M Kaemmerer M Seiler T Understanding refraction and accommodation through “retinal imaging” aberrometry a case report.Ophthalmology. 2001; 108: 674-678Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar “Near maximal accommodation” was attempted by the author (age 39) while maintaining a central view of a defocused fixation light during the accommodative mechanism. The author’s near point of accommodation and whether further accommodative amplitude could be achieved is not recorded and is irrelevant for the discussion of asphericity in association with the change in spherical equivalent refraction. The spherical magnitude of accommodation recorded in the central 3 mm is 2.15 diopters (D) and this is even less, 1.38 D, when considering the full 6.5 mm pupillary diameter. The fact that the magnitude at 3 mm did not meet the expected accommodative amplitude of a normal 40-year-old may, in part, be explained by the even smaller pupil diameter (miosis) that is typically achieved during accommodation, which would increase the author’s depth of field. Measuring the near point of accommodation as suggested by Dr. Lothringer is not a true measure of the magnitude of accommodation, but is a functional value aided by the increased depth of field of miosis.Table 1Lens Measurements of Accommodation Using High-resolution Magnetic Resonance ImagingLens EquatorLens PoleAnterior Radius of CurvaturePosterior Radius of Curvature0 D stimulus8.970 mm3.580 mm12.204 mm5.060 mm3 D stimulus8.563 mm3.882 mm8.429 mm4.794 mm3 D minus 0 D0.307 mm0.302−3.775 mm0.266P = 0.05P < 0.00001P < 0.00001P > 0.05D = diopter. Open table in a new tab D = diopter. The greatest significance of these data in relation to the mechanism of accommodation can be seen by the decrease in spherical aberration (negative asphericity) associated with accommodation viewed through a larger pupil size. The Schachar theory of accommodation assumes a “steepening of the central surfaces with a simultaneous flattening of the peripheral surfaces of the crystalline lens, resulting in a decrease in spherical aberration.”2Schachar R.A Cause and treatment of presbyopia with a method for increasing the amplitude of accommodation.Ann Ophthalmol. 1992; 24: 445-452PubMed Google Scholar If this is to be achieved by equatorial zonular tension (stretching), then the anterior/posterior (polar) dimensions of the lens would also be of decreased magnitude, resulting in an overall negative or zero accommodative amplitude when considering the refractive effect over the full area of a 6.5-mm pupil. To state this more simply, the magnitude of change in asphericity of .77 D is too small to account for the full spherical equivalent refractive change of 2.15 D if the Schachar theory of accommodation were correct in this example. Nevertheless, the change toward decreased spherical aberration brings question to the Helmholtz mechanism of accommodation as to what asphericity changes could be expected by a lens that increased its curvature and anterior/posterior (polar) thickness with the zonular relaxation. Glasser and Campbell3Glasser A Campbell M.C.W Presbyopia and the optical changes in human crystalline lens with age.Vision Res. 1998; 38: 209-229Crossref PubMed Scopus (461) Google Scholar answer this asphericity question, in association with accommodation, by demonstrating a shift toward negative asphericity (decrease in spherical aberration) in prepresbyopic lenses measured with a cadaver experimental scanning laser wavefront system, which stretches and then relaxes the ciliary body/zonule/lens complex to simulate accommodation. This verifies that the spherical aberration pattern observed in the author’s left eye is consistent with the Helmholtz theory of accommodation from an optical and physiologic standpoint. A further illustration of this point can be visualized anatomically by the use of high-resolution magnetic resonance imaging (MRI).4Strenk S.A Semmlow J.L Strenk L.M et al.Age-related changes in human ciliary muscle and lens a magnetic resonance imaging study.Invest Ophthalmol Vis Sci. 1999; 40: 1162-1169PubMed Google Scholar Diagnostic MRI was performed on the author’s left eye using a GE 1.5 Tesla imager with a custom radiofrequency receiver coil dedicated to eye imaging. T1-weighted images with a 4-cm field of view were acquired by the expertise of Susan and Larry Strenk, PhD, to visualize axial images of the author’s crystalline lens orthogonal to the lens equator, both during distance viewing and while focusing on a 4 D target. Figure 1 demonstrates the author’s crystalline lens with 0 D and 4 D of accommodation. Note the decrease in equatorial diameter and increase in polar dimension of the lens in accommodation. Also note that accommodation produces an anterior displacement of the lens with a shallower anterior chamber depth (4.38–3.28 mm) and anterior change in iris orientation. Table 1 lists the lens polar and equatorial dimensions, as well as the radius of curvature calculated by second-order polynomials for the anterior and posterior lens surfaces. Statistical analysis for each measurement was based on the difference between the mean values for each accommodative state divided by the pooled standard error. A statistically significant P value implies a distinct difference between the values at 0 D and 4 D. This differentiation is statistically significant and most pronounced for the lens polar dimensions and anterior radius of curvature. In summary, although the direction of change in spherical aberration associated with accommodation may favor Schachar’s theory, the magnitude of change using “retinal imaging” aberrometry, and the anatomic change in shape of the lens during accommodation, using high-resolution MRI, clearly fails to confirm Schachar’s theory, while supporting the Helmholtz’s theory of accommodation.