In my last post I decided on the parts that were necessary in building the eye in 3d,
now I've approached the modelling of each part.

In the diagrams below I show the different parts.





To model each element I traced off a sliced section of the eyeball, that was distortion corrected and published in a scientific journal as an accurate eye cross section. What I did note was that the top of the eye was slightly different than the bottom. This was something I chose to bypass until later as it had little effect on the actual outward appearance of the eye in render.

I used the spline tools to draw out the cross section, deleting the lower half and using a lathe modifier to revolve the curve 360 degrees. Once that was complete I made sure the vertices at the core were welded and applied a turbosmooth. Using an FFD modifier I reshaped the turbosmoothed version to make sure it still matched the cross section exactly.




Shaderss
Now for the tricky part, the shaders.
After much deliberation I chose to use mental ray and a mix between older mental ray and the new architectural shaders. The important thing was to get accurate refraction through the eye.
The cornea shader was going to be the one on the surface and that should have the highest reflection. The sclera I chose to merge directly into the cornea as one object rather than before I considered two, the reason being was that fading two transparent objects into each other simply created too many problems with internal reflections.

Shadows
Shadows should not be too strong on the eye, and the way to ensure this was to either turn them off on all eye objects or to create the eye shaders in a way that ensured the correct level of transparency in the shadows. The sclera then should already be using an SSS shader to handle it's look when in shadow, and the cornea should be using the architectural shader options - refract light and generate caustics. This ensures a good shadow. Shadow casting was turned off for other objects. This also ensures the inside of the eye is dark when rendering, as opposed to turning shadows off ( this I did during test renders for speed ) and through the pupil it is as expected ..dark.

Texturing
I textured each section with a mixture of gradient ramps and painted textures. The iris texture and sclera being the most important. You can see the iris texture here. The iris is unwrapped into segments and laid out flat so painting the texture involved only painting vertically and the challenge of painting radially is removed. I created a bump, diffuse and specular map for the Iris.
I also gave the iris morph targets as you can see in the image. I rigged this morph target up using the wire parameters to a slider to control the Iris pupil contraction.



More to come on the texturing process, materials and render setup.

Eyes are the window to the soul.
It's something you hear a lot, but never really think about with much depth. There are hundreds of images out there in 3d that 'almost get it', but there are a few things that you can't pinpoint that make it not quite there. When an image has good eyes and eyelashes, the face can be off by quite a way, and people just won't notice. The reason ? Personally I think it's because we as humans have such varied faces, characteristic expressions and range from extreme ugly to serene beauty. The thing that links them all together is the eyes. That's to say, the eyeballs. The eye shapes vary between people, but the functionality in design of the eye remains the same to all of us. For that reason, if you nail the eye(ball)s then you nail the face.

The first thing for me was to research the topic in depth. Find out how the eye works, the anatomy and construction. Bear in mind I am far from an anatomy major, so if there are minor errors please forgive me, or correct me. I'll do my best to be accurate nonetheless.

At a very simple explanation.The eye is constructed of multiple parts, the cornea and the lens being two of the most important. When light enters the eye through the cornea, is is refracted, or bent. It then passes through the pupil into the lens. The lens bends the light again,essentially flipping the image and projecting it onto the retina. From there,the light sensitive layerof the retina ( consisting of rod and cone cells ) converts the image into electrical impulses which are in turn delivered to our brain through the optical nerve. Our brain interprets these signals and we see the image.



As I am trying to simulate the eye to the extent the software allows me, I plan on building the key areas of the eye, and using mental ray shaders toinput the correct IOR ( Index of refraction ) Values.

After deliberation, I've narrowed the object list down to.

Sclera ( What shows up to us as the white of the eye. The sclera is a fibrous, protective layer that covers the eye)

Cornea( The cornea is the transparent covering of the iris pupil and anterior chamber, it also refracts light and helps focus )

Aqueous Humor ( A watery substance that fills the anterior chamber behind the cornea )

Lens ( Sits behind the iris, it is also responsible for the refraction of light.A process called accomodation alters the shape of the lens to focus )

Conjunctiva ( A clear membrane that lines the inside of the eyelids and covers the white part of the eye )

Iris ( The part of the eye we all recognize, it's unique to the individual and consists of fibrovascular tissue called stroma. The stroma connects a sphincter and dilator muscle which contract and open the pupil to allow more light in)

Creating these pieces in 3d was trickier than I imagined, simply due to the complexity. In 3d when we create an object with thickness, the shader handles the object as if it were a solid object, as opposed to two pieces of geometry with inversed normals.But the problems arise when we put a transparent material on a section of this geometry. Unless we model that cut out section and cap off the holes, two pieces of geometry will now be visible. This makes creating an object like the eye harder than it may appear. The cornea centrally, consists of 5 layers of which merge into the sclera.The sclera connects to the cornea in a very organic manner, one that's extremely hard if not near impossible to replicate accurately in 3d. Perhaps some sort of point cloud based visualization could simulate it, but I'm far from doing that in 3d studio max. We're fakers after all, so I need to find a way to simulate it on a simple scale.Texturing, SSS and fading throgh alpha mapping will be my weapons here.

In my next post i'll discuss the creation of the objects, and update with more renders.