2020–2021 BCSC Basic and Clinical Science Course™
3 Clinical Optics
Chapter 1: Geometric Optics
Flat Refracting Surfaces—Snell’s Law
The optics of a flat refracting interface, such as the surface of a still pool of water or a flat slab of glass, are easy to describe. As light passes from a “less dense” medium (lower refractive index, greater speed of light) to a denser medium (higher refractive index, lesser speed of light), light rays bend toward the line perpendicular to the interface at the point of entry (the surface normal, or just the “normal line”), according to Snell’s law (Figure 1-1):
n
1 sin θ1 = n2 sin θ2
If light travels from a denser medium to a less dense medium, light rays bend away from the surface normal.
This redirection of light at a flat interface produces an apparent object displacement, such as that seen when you look into a body of water (Figure 1-2) or that provided by an ophthalmic prism.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.