light deflection in a glass sphere

I was asking myself what would be happen to the parallel light beams after passing a spherical glass. Do they pass through one point, exactly? I was interested in observing the result mathematically but solving the equations was difficult and time consuming for me. But afterwards I found it easy and interesting to perform an experiment with Matlab and this is the result. Any suggestion for completeness of this program or further works is really appreciated.

I have a Pentium III processor(500 MHz)and it take about 45 seconds to complete the task.