Introduction to Optical Eye Modeling with Zemax

Explore the law of reflection, including the plane of incident, the equality of the incident and reflected angles, and the formation of virtual images from real objects on reflective surfaces.

Explore Snell's law and the law of refraction, linking refractive indices to light bending, the plane of incidence, and total internal reflection, with examples from cornea and common materials.

Explore the thin lens equation and focal length, revealing how sphere surfaces form a lens and how radii of curvature r1 and r2, thickness d, and index n determine focusing.

Explore focal length and optical power, the inverse relation P = 1/f, and how lens shapes yield positive, negative, or zero diopter power.

Examine image formation with Snell's law at air-glass interfaces, showing how nonperpendicular rays bend toward focal points under paraxial approximation. Learn focal length, magnification, and sign conventions for object and image distances.

Explore how dispersion causes refractive index to vary with wavelength, so blue light refracts more than red, enabling color separation through a prism and phenomena like chromatic aberrations and rainbows.

Explore Abbe number and dispersion, showing how v relates n_d, n_f, and n_C across the eye's visible wavelengths, with crown and flint glasses in Zemax.

Explore aberration theory by examining how paraxial, first-order Gaussian optics approximate image formation, and how neglecting higher-order terms causes aberrations in optical systems.

Define aberrations by contrasting chromatic and monochromatic types, explain wavelength dependence, and introduce paraxial and third-order Seidel aberrations, including spherical aberration, coma, astigmatism, curvature of field, and distortion.

Explore defocus aberration in optical systems, showing how misplaced focus blurs images on the retina and highlighting myopia and hyperopia as shifts of focus along the optical axis.

Show how spherical aberration causes light rays through a spherical lens or curved mirror to focus at different points away from the optical axis, producing circles on the image plane.

Explore coma aberration, where beams not parallel to the optical axis fail to focus to a single point, producing comet-shaped images and tail-like star appearances on CCDs.

Explore astigmatism, a non-symmetric aberration from differences in curvature or refractive index between x and y directions, producing vertical and horizontal focus and blur, with glasses as a remedy.

Identify field curvature, an aberration causing the image plane to be curved rather than flat as beams from infinity and angled rays focus at different points.

Explore distortion in optical systems, including barrel, pincushion, and moustache aberrations. Understand how magnification changes with distance from the optical axis for each type.

Axial, or longitudinal, chromatic aberration occurs when the refractive index varies with wavelength, causing blue light to refract more and focus at different points along the optical axis.

Explore lateral (transverse) chromatic aberration arising from wavelength-dependent refraction, showing how off-axis light causes red, green, and blue rays to focus at different transverse points.

Explore the eye's optical system, detailing the cornea, anterior chamber, pupil, crystalline lens with gradient refractive index, vitreous chamber, and retina to understand light refraction and imaging.

Explore the cornea’s refractive index, its layered structure and tear film that minimizes scattering, and why the index is about 1.376 with collagen lattice and sub-200 nm spacing driving transparency.

Explore toric lenses built from torus geometry to explain cornea astigmatism, showing how two perpendicular radii of curvature produce two optical powers and distinct focal lengths.

Explore corneal astigmatism concepts, contrasting with-the-rule and against-the-rule patterns, based on radius-of-curvature differences and axial optical power in x and y directions, including oblique astigmatism.

Defines corneal asphericity and aspheric surfaces, and introduces the q parameter as surface asphericity that governs radius of curvature and classifies shapes like hyperboloid, paraboloid, ellipsoid, and sphere.

Measure central corneal thickness for Zemax eye modeling to support risk assessment and indicate health; distance between the anterior and posterior surfaces defines the zmax thickness, 0.536 ± 30 microns.

Analyze cornea anterior surface toricity, where two radii of curvature create direction-dependent optical power and astigmatism, with roughly 75% of people showing about 0.5 diopter or more.

Examine the cornea’s anatomical structure, focusing on tear film and stroma, to understand how hydration, surface smoothing, and refractive index drive optical clarity in Zemax.

Explore the crystalline lens of the eye, its accommodation via ciliary muscles and zonules, its capsule and the growth of nucleus and cortex, and how curvature changes optical power.

Explore how the crystalline lens refractive index distribution varies from nucleus to cortex and is modeled with Gaussian 9009, enabling in vivo MRI spin-spin relaxation time mapping.

Learn how to use the equivalent refractive index, or effective refractive index, to represent a gradient lens with uniform index, preserving lens power with 1.2 and 1.41 at the center.

Learn how to estimate crystalline lens power in vivo using Purkinje imaging, leveraging radii of curvature and an equivalent refractive index to determine adult lens power near 25 diopters.

Examine how the iris forms the pupil aperture and controls pupil size via antagonistic sphincter pupil and dilator pupil muscles under autonomic reflexes.

Identify aperture stop as the diaphragm that limits light in optical systems. Explain entrance pupil and exit pupil as the image of the aperture stop through the lens.

Examine pupil centration in rotationally symmetric optics, noting decentered eye pupils and a typical 0.4 mm offset from the optical axis. Model this movement in Zemax as pupil diameter changes.

Examine how illumination drives pupil size from 2 mm in bright rooms to 8 mm in dark rooms, noting ~16× area change, Zemax stop implications, and Moon and Spencer equations.

Explore how depth of field shapes image quality in optical systems, comparing sharp and blurred views and showing how aperture, f-number, focal length, and pupil size govern depth of field.

Define the optical axis as the best-fit line through the centers of optical elements. Note that the eye lacks full rotational symmetry, so this axis serves as its approximation.

Examine the line of sight, the axis from a fixation point to the pupil center, its role in visual function, and how pupil size causes center fluctuation that challenges modeling.