Merging two spheres with different radii I see many posts here on how to merge cubes, but I think my problem is a little more complex.

I'm very new to blender and am trying to create a model of the human lens. The front and rear surfaces have different radii of curvatures. This is no problem and I used to sphere meshes with the correct radii, and then cut them using the bisect tool the model shown here is a reasonably accurate staring point:



I am now trying to merge the two models. Because the spheres are not bisected along their equator, you can see that both "halves" end with a sharp edge. In the human lens there is, of course no such sharp demarcation between the two parts of the lens - it is a smooth curve.

That is my question - how do I smoothly merge the two parts of the lens model while making it look "organic"?
Bridging two sections with  a different number of vertices will yield untidy topology ... perhaps an approach like this would be more flexible?




Start with some sort of sphere for the lens (here I've used a rounded cube). It helps to set its display property to X-Ray.
Create 2 vertex groups in the lens: one of all the vertices above the equator ('top'), and one of all the vertices below the equator('bottom').
Create 2 high-resolution spheres 'top' (the lower one in the illustration) and 'bottom' (the higher one) to represent the curvatures of your lens. (It helps to set their maximum display to 'wire')
Assign 2 Shrink-Wrap modifiers to the lens. One is set to affect the 'top' vertex group with the target sphere set to 'top'.. the other, vice-versa. Perhaps pop in a Subdivision Surface modifier at the bottom of the stack.
Uniformly scale your target spheres and move them along Z until you are happy. 


Variations might include leaving a wider unaffected margin between the vertex groups, and/or scaling that margin in XY to get the transition you'd like between the spherical sections.