Posted by: Roger King
3D animation, 3D modeling
People with limited vision.
One of the things I teach is 3D animation (using Autodesk Maya). I also happen to have had cornea transplant surgery in both of my eyes, as a result of a degenerative disease that caused my corneas to thin gradually, thereby losing their structural integrity. The corneas, by the way, are the clear outer surface of the eye.
This is the third blog posting in a series relating to the use of modeling and animation software to develop technology to assist folks with limited vision caused by deformed corneas.
Today, we look at using animation software to simulate the treatment of eyes diseased by keratoconus, the disease that affected my eyes. Keratoconus causes the corneas to thin and lose their structural integrity. Folds and bulges develop. Eventually, all you can see are multiple distorted, fragmented, and overlapping versions of everything you look at.
A simple treatment.
As it turns out, a short or medium term treatment for the condition, which works until the corneas become so thin that they absolutely must be replaced, is very simple: scleral contact lenses can be placed on the eyes, forming a sort of false corneas. I’ve been told that the same treatment can be applied to folks with astigmatism or cornea damage from a botched Lasik surgery.
As near as I can tell, this is why it works: As ambient light passes into the eye, it of course goes through the transparent outer surface of the eye, the cornea. If the slope of the cornea varies, the angle of refraction of light as it passes through the cornea will vary. But if a large contacts lens, one that covers the sclera or white part of the eye, is sitting on top of the cornea, it holds a layer of fluid over the cornea. This means that light passes through the contact lens, through the fluid, and then through the contact. Since the layer of fluid is close in density of the cornea, the angle of refraction remains more consistent over the cornea as a whole. Thus, a smoothing effect takes over. The light is refracted more uniformly before it passes into the eyeball.
Modeling the disease and the treatment with 3D modeling.
What does this have to do with 3D animation? If you have keratoconus or an astigmatism or a cornea damaged by bad laser surgery, this is a very cheap, non-surgical, and effective treatment. (An astigmatism is not a caused by a cornea defect, however, and I don’t fully understand why the scleral lens treatment works.) And, as it turns out, the optics of the treatment can be easily simulated with a 3D animation application, and this presents the possibility for refining the treatment using simulation.
How would this be done? The effects of an irregular cornea can be modeled by a sphere whose surface has been altered using deformation primitives. The effects of keratoconus lead to a distinctive shape of the cornea. Since the eye puts more pressure on the center of the eye, the middle of the cornea is pushed out into a cone shape – thus the name of the disease, which means “cone shaped cornea”. The lack of structural integrity also causes irregularities in the slope of the cornea in general. Ophthalmologists routinely take topographical maps of corneas and these maps could be used to create a simulated cornea within an animation application. (I use Maya in my research.)
The effects of a scleral lens laid over the cornea can also be simulated. Animators routinely model transparent surfaces and fluids, and can very carefully control the effects of lights going through surfaces and fluids. This means a program like Maya can model both the disease and the treatment. This is very exciting.
More on this next time…