Computer simulation of thin film growth has been used extensively to gain insight into the origin and nature of the microstructure of vapor-deposited thin films. Usually, however, no attempts are made to predict film properties other than column angle and film density from such simulations. The aim of our work is to derive quantitative data from computer simulations in order to be able to predict relevant properties of optical coatings. The deposition of 2500 to 25,000 particles has been simulated on different computers by random deposition of two-dimensional hard disks, using a simple relaxation scheme. Statistical analysis of the results yields quantitative data for the density, column angle, and column period. On the basis of these results, a simple model has been developed for the microstructure of a three-dimensional film. The birefringence and the shape of water-penetration fronts in evaporated optical coatings, predicted from this model, are confirmed by experiment.