Key enzyme in the cholesterol biosynthesis pathway. Catalyzes the cyclization of (S)-2,3 oxidosqualene to lanosterol, a reaction that forms the sterol nucleus (PubMed:7568116). Through the production of lanosterol may regulate lens protein aggregation and increase transparency (By similarity). (S)-2,3-epoxysqualene = lanosterol Terpene metabolism; lanosterol biosynthesis; lanosterol from farnesyl diphosphate: step 3/3. Monomer. Hypomorphic mutations in this gene and the Fdft1 gene were identified, as well as a null mutation in this gene. Cataract onset is associated with the specific combination of Lss and Fdft1 mutant alleles that decrease cholesterol levels in cataractous lenses to about 57% of normal. Cholesterol insufficiency may cause the deficient proliferation of lens epithelial cells in Shumiya cataract rats, resulting in the loss of homeostatic epithelial cell control of the underlying fiber cells and ultimately cataractogenesis. Belongs to the terpene cyclase/mutase family.