Purchase this article with an account.
D.M. Silver, A. Csutak; Ray Trace Analysis of Visual Aberrations After Laser Vision Correction Surgery . Invest. Ophthalmol. Vis. Sci. 2005;46(13):846.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine the dependence of visual aberrations on the relation between ablation diameter, pupil diameter, other ocular geometry, and light scattering emanating from disrupted collagen fibrils in the peripheral region of the ablated corneal stroma following laser refractive surgery. Methods: Computer calculations are used for ray trace analysis of light passing through the cornea, aqueous, pupil, lens, and vitreous to the retina. Light rays are affected by the transition from the curvature of the cornea in the ablated zone to the curvature of the untreated regions of the cornea. Laser ablation also damages the structure of collagen fibrils in the ablation region of the stroma by terminating fibrils along the rim of the ablation circle. From the physical dimensions of the fibrils, this change in fibril continuity is assumed to give rise to Mie scattering, which is predominantly in the forward direction. The computational problem is parameterized with respect to physiological and anatomical properties of the ocular path (radii of curvature, thicknesses, indexes of refraction, pupil diameter, and relative positions of structures within the globe) as well as forward scattering angles from damaged stromal fibrils. Results: Graphs of the paths of parallel and oblique incident light rays illustrate the effect of refraction and scattering and their dependence on the relation between the ocular parameters, changes in corneal curvature and scattering angles. Mie scattering from the perimeter of an ablation zone significantly affects the effectiveness of the iris to block aberrant light rays from entering the pupil. Conclusions: The uniformity and ordered arrangement of collagen fibrils in stromal lamellae is important for the transparency of the cornea. Normally, the fibrils run parallel to the surface of the cornea, extending limbus to limbus, within alternating layers of lamellae. Light rays diffracted by the fibrils tend to cancel each other by destructive interference, leaving the normal undiffracted rays unaffected. In addition to changing the curvature of the cornea, laser ablation of stromal layers gives rise to sources of light scattering along the circumference of the ablation zone. The present calculations have implications for the quantitative understanding of concepts such as the effective corneal refractive diameter, the entrance pupil and the physical pupil relative to visual aberrations that are not blocked by the iris.
This PDF is available to Subscribers Only