Схема. Показатели рефракции преломляющих сред глаза. Перевести на русский язык = Translate into Russian Модификация: Levin L.A., Nilsson Siv F.E., Ver Hoeve J., Wu S., Kaufman P.L., Alm A., Eds. Adler's Physiology of the Eye, 11th ed., Elsevier, 2011, 820 p. см.: Физиология человека: Литература. Иллюстрации.

Примечание:

A. Diagram of the schematic eye with representative average dimensions in millimeters and refractive indices of the relaxed, non-accommodating eye. The starred values change with accommodation. These dimensions are average values used to construct a representative or schematic eye – in real life, all dimensions of the eye can vary greatly between individuals and from these average values. Upper-right diagram shows that the principle of corneal contact lens wear is to make the anterior corneal surface ineffective as it is now bathed with aqueous tears and the new anterior refractive surface is the air–anterior contact lens interface. Middle-right diagram shows that the principle of myopic correction using the excimer laser is based on a graded removal of central anterior corneal tissue to decrease the central anterior corneal curvature, analogous to the removal of a biologic contact lens that is thicker in the center. Lower-right diagram shows that the principle of hyperopic correction using the excimer laser is based on a graded removal of a peripheral and paracentral concave lenticule of tissue to increase the central anterior corneal curvature (i.e. a donut-shaped trough) analogous to the removal of a biologic contact that is thicker in the periphery and of no or minimal thickness in the center. B. Variations in conicoid shape for different asphericities, or Q-factors, with the same radius of curvature. C. Schematic diagrams showing the three possible anterior corneal surface contours with ray tracings from a distant fixation point being refracted onto the retina. Upper left diagram is of a prolate cornea (Q factor < 0), which has a larger peripheral radius of curvature than at the apex (Rp > Ra). Lower middle diagram is of a spherical cornea (Q factor = 0), which has equal peripheral and apical radii of curvature (Ra = Rp). Upper right diagram is of an oblate cornea (Q factor > 0), which has a smaller peripheral radius of curvature than at the apex (Ra > Rp). As a prolate cornea reduces spherical aberrations, its image is more tightly or precisely focused than spherical or lastly oblate corneas. The mean value of the Q factor for normal healthy adult corneas is -0.2, which reduces natural spherical aberration by about half; a Q factor of -0.50 eliminates all spherical aberration. Thus, the human cornea typically is not designed to induce zero spherical aberrations. In fact, the human lens is optically coupled to cornea in such a way that spherical aberrations are reduced close to zero in youth since during childhood and young adulthood the lens has negative asphericity. Lens asphericity dynamically changes with aging, usually resulting in a Q of zero around age 40 and then has positive asphericity after age 40. The overall effect on the optical properties of the human eye is that it gains progressively more spherical and other optical aberrations with increasing age, which perhaps best explains the direct association of deterioration of visual performance and quality with aging. Most degradation of image quality is due to age-related changes in the lens