Serine protease required during eye development. Expressed in the eye: present in the retina and in the optic nerve. First detected in the eye at 17 dpc and maintained into adulthood. Mice display the glaucoma-relevant mutant 4 (Grm4) phenotype, with angle-closure glaucoma and eyes having short axial length. High intraocular pressure (IOP) in mutant eyes increases with age and the anterior chambers become enlarged in some eyes at around 3 months of age. Eye's angles are not occluded with abnormal tissue (synechia) and have detectable trabecular meshwork and Schlemm's canal (2 important drainage structures). However, compromised aqueous humor drainage (outflow) contributes to the IOP elevation. After IOP elevation, mutants develop glaucomatous neurodegeneration, which is characterized by retinal ganglion cell death and optic nerve atrophy. Belongs to the peptidase S1 family.