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A Sokolowska, F Thorn; Does Accommodation Alter Crystalline Lens Position? . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2015.
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Purpose: Glasser et al used Scheimpflug microscopy to show that the crystalline lens in iridectimized monkeys drops significantly during accommodation in infancy and to a lesser extent in juveniles. But it remains stable in adults. The accommodative lens subluxation in infants and juveniles should induce serious wavefront aberrations and image degradation. Since wavefront aberrations have been hypothesized to be a source of image degradation promoting myopia in human children, a simple procedure to monitor lens position changes during accommodation would be useful. Methods: The Canon R-1 Autoref, a standard instrument used in accommodation research, provides two infrared light sources 20° to either side of pupillary center. This allows us to the record Purkinje images, accommodation, and pupil size almost simultaneously. Three computer image samples showing the size of the pupil and the position of the Ist, 3rd, and 4th Purkinje were recorded for each eye for each condition. Corneal radius, lens radius, and lens position and tilt were calculated from these positions (Barry et al, 1997). Subjects were nine optometry students age 23.1±0.9 years. They viewed targets 25 cm, 33 cm and 4 m away in the straight ahead position and 5° up, down, right, and left of straight ahead. Results: The positions of the Purkinje images indicate that the lens was tilted 2° to 6° and usually displaced slightly down and nasally. The Purkinje images remained in the same position during accommodation to all distances for all subjects indicating that the lens remains rigidly stable in the same position during accommodation. Conclusion: As in adult monkeys, the crystalline lens remains rigidly in place during accommodation. This promotes relative stability in wavefront aberration profiles (especially in astigmatism and coma) during accommodation in adults who are relatively unsusceptible to myopogenic factors. However, young children who are susceptible to myopia may yet be shown to have an unsteady lens position during accommodation similar to that in young monkeys.
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