PIP and keratoconus: Some of the proteins have been detected as potential biomarkers for KC or associated with tumor growth and proliferation in previous studies, such as Multimerin-2 [47, 48], transmembrane protein 106A [49, 50], apolipoprotein D [51], vasorin [52], ras-related protein Rab-14 [53], retinol-binding proteins 5 [54], neuronal growth regulator 1 [55] and prolactin-inducible protein [56, 57].