According to collaborative research conducted by Swedish, Tunisian, and American researchers, it is a mutation in the gene PRSS56, which is a serine protease, that causes the eye disease glaucoma.
The most common form of glaucoma is open-angle glaucoma. It affects more than 16 million people in the world. The nerve fiber layer of the optic nerve is slowly damaged, leading to a deterioration of wide-angle vision and ultimately to serious vision impairment.
The scientists studied Tunisian families who have been afflicted with both glaucoma and microphthalmia (diminished eyeballs) and managed to identify the gene that is mutated and causes the disease. The American researchers identified an altered version of the gene in a mutagenesis screen in mice, selected for glaucoma.
Source: Clinical & Refractive Optometry, Volume 22, Number 5/6, 2011