There have been literally dozens of eye models published over more than 150 years, from very simple “reduced” eyes consisting of a single refracting surface to very complex models with more than 4,000 refracting surfaces. Some models have a gradient index crystalline lens, some represent the gradient index with two or more homogeneous shells, and some have a homogeneous lens.

It is important to realise that there is no perfect optical model of the eye that is best for every purpose. An appropriate model is one that gives valid results for a particular project, and a more sophisticated model is not necessarily better. There is no point, for example, in using a model that includes a gradient index crystalline lens if that gives no more valid information than a homogeneous lens but slows the computing time significantly during optimisation or during calculations on an NSC model with a large number of rays. Often paraxial calculations at a single wavelength are all that are needed, and these can be carried out using a very simple model with spherical surfaces. A common “reduced” eye used for paraxial calculations has a single refracting surface of radius 5.55mm, a refractive index of 1.333 and an axial length of 22.22mm.

Users of the models included here should feel free to change the parameters or modify the models in any way if it seems to be appropriate for a particular purpose.