Peripheral Defocus of the Monkey Crystalline Lens With Accommodation in a Lens Stretcher

Peripheral refraction of myopic eyes with spectacle lenses correction and lens free emmetropes during accommodation

PURPOSE

To measure axial and off-axis refraction patterns in myopic eyes with spectacle lenses correction and lens free emmetropes in young healthy subjects at different target distances from 2.00 m (0.50 D) to 0.20 m (5.00 D) in terms of sphere, astigmatism, and spherical equivalent refraction.

METHODS

Refraction was measured at the center, 20 and 40 degrees from the line of sight both nasally and temporally in 15 emmetropic and 25 myopic young healthy subjects with an open field, binocular, infrared autorefractor (Grand Seiko WAM-5500, Hiroshima, Japan). Fixation target was a Maltese cross set at 2.00, 0.50, 0.33 and 0.20 m from the corneal plane. Changes in off-axis refraction with accommodation level were normalized with respect to distance axial values and compared between myopic eyes with spectacle lenses correction and lens free emmetropes.

RESULTS

Off-axis refraction in myopic eyes with spectacle lenses correction was significantly more myopic in the temporal retina compared to lens free emmetropes except for the closest target distance. Relative off-axis refractive error changed significantly with accommodation when compared to axial refraction particularly in the myopic group. This change in the negative direction was due to changes in the spherical component of refraction that became more myopic relative to the center at the 0.20 m distance as the J0 component of astigmatism was significantly reduced in both emmetropes and myopes for the closest target.

CONCLUSION

Accommodation to very near targets (up to 0.20 m) makes the off-axis refraction of myopes wearing their spectacle correction similar to that of lens free emmetropes. A significant reduction in off-axis astigmatism was also observed for the 0.20 m distance.

Age-Dependence of the Peripheral Defocus of the Isolated Human Crystalline Lens

Purpose

To characterize the peripheral defocus of isolated human crystalline lenses and its age dependence.

Methods

Data were acquired on 116 isolated lenses from 99 human eyes (age range, 0.03–61 years; postmortem time, 40.1 ± 21.4 hours). Lenses were placed in a custom-built combined laser ray tracing and optical coherence tomography system that measures the slopes of rays refracted through the lens for on-axis and off-axis incidence angles. Ray slopes were measured by recording spot patterns as a function of axial position with an imaging sensor mounted on a positioning stage below the tissue chamber. Delivery angles ranged from –30° to +30° in 5° increments using a 6 mm × 6 mm raster scan with 0.5-mm spacing. Lens power at each angle was calculated by finding the axial position that minimizes the root-mean-square size of the spot pattern formed by the 49 central rays, corresponding to a 3-mm zone on-axis. The age dependence of the on-axis and off-axis optical power and the relative peripheral defocus (difference between off-axis and on-axis power) of lenses were quantified.

Results

At all angles, lens power decreased significantly with age. Lens power increased with increasing delivery angle for all lenses, corresponding to a shift toward myopic peripheral defocus. There was a statistically significant decrease in the lens peripheral defocus with age.

Conclusions

The isolated human lens power increases with increasing field angle. The lens relative peripheral defocus decreases with age, which may contribute to the age-related changes of ocular peripheral defocus during refractive development.

System for on- and off-axis volumetric OCT imaging and ray tracing aberrometry of the crystalline lens

We present a new in vitro instrument for measuring shape and wavefront aberrations of the primate crystalline lens, both on- and off-axis, while simulating accommodation with a motorized lens stretching system. The instrument merges spectral domain optical coherence tomography (SD-OCT) imaging and ray tracing aberrometry using an approach that senses wavefront aberrations of the lens with the OCT probing beam. Accuracy and repeatability of aberration measurements were quantified. Preliminary experiments on two human and four cynomolgus monkey lenses demonstrate the ability of the system to measure the lens shape, spherical aberration and peripheral defocus, and their changes during simulated accommodation.