Eye model in Zemax involves simulating the optical properties of the human eye. The model typically includes various components that represent the cornea, lens, aqueous humor, vitreous humor, and retina.
An ametropic eye is one that has a refractive error, meaning it does not focus light correctly on the retina, leading to blurred vision. Ametropia is a state where refractive error is present, or when distant points are no longer focused properly to the retina. Myopia or near-sightedness (short-sightedness) is one form of ametropia where the eye is effectively too long or has too high a power. Consequently, a point at infinity focuses in front of the retina. In myopia, a point lying between infinity and the eye is conjugate to the retina. Hyperopia or far-sightedness is a form of ametropia where the eye’s power is too weak or the eyeball too short.
Modeling an ametropic eye in Zemax requires adjustments to the parameters of the eye model. Wavelength typically used for eye modeling between 486 nm and 656 nm. Angular field of view. The human eye typically has a FOV of around 160 degrees horizontally and 120 degrees vertically. Pupil size varies with lighting conditions, usually set to 4 mm in diameter.
Figure below shows a layered eye model set in Zemax with various surfaces and materials. Cornea is modeled as a single or double surface with an aspherical shape. Use typical refractive index (n ≈ 1.376) and thickness. Aqueous humor region is between the cornea and lens. Assign a refractive index (n ≈ 1.336). Natural lens is modeled with multiple surfaces (anterior and posterior), possibly aspherical. an average index (n ≈ 1.406) is used for lens. The region of vitreous humor between the lens and retina. Use a refractive index (n ≈ 1.336). Retina is the image plane, set at the back of the eye model, often represented as a flat or curved surface.
Ametropic eye can be corrected with intraocular correction lens. Such correction lens is placed in between IRIS and natural lens, with the thickness of about 500 microns. The lens is with negative diopter to push focus towards the retina, as the figure shown above. The intraocular lens with complex geometric description can be inserted with a CAD file in Non-sequential mode of Zemax, as below:
Intraocular lens made with CAD file can be placed in a nonsequential object through mixed mode of Zemax based on sequential mode. The entry port and exit port are set properly and closely to the CAD model of the intraocular lens, with about 0.1 mm distance. Material of the man-made intraocular lens is defined as 1.44 in refractive index and 56 in Abbe number. The rest region of the Nonsequential object is set with material of vitreous.
From Merit function, the effective focal length of the intraocular lens is -58 mm. The overall optical focal length is 24 mm.
Geometrical MTF below suggests best correction in field of 0 degree, among the three fields defined in the model.
Enclosed energy below reflects the light distribution in a circular shape distribution at the retina as image plane.
The CAD model above utilizes a pure spherical surface to correct the defocus in ametropic eye. Although this is not perfect correction, it shows the way of building intraocular focus correction methodology. More intraocular lenses with various functional surface can be integrated in such model.