Author’s Disclosure Block: Alicia Liu, none; Oi Ying Wong, none; Man Hin Leung, none; Connie Lai, none; Thomas Lam, none; Wai-Ching Lam, none

Abstract Body
Retinopathy of prematurity (ROP) is the leading cause of preventable childhood blindness. Tear protein biomarkers identified from next-generation label-free proteomics may offer an accessible, non-invasive option for ROP screening.A cross-sectional study was conducted. Infants whose birth weight ≤1500g or gestational age ≤30 weeks were recruited. Examination began at 4 weeks chronologic age or 31 weeks postmenstrual age. ROP was diagnosed according to the International Classification for Retinopathy of Prematurity, Third Edition. ROP (n=13) and non-ROP (n=21) tear samples were collected with Schirmer’s strips. Tear proteins were identified and quantified using data-independent acquisition mass spectrometry and analyzed with Spectronaut. Further gene ontology functional and enrichment analyses were completed on the resulting differential proteins.2279 unique proteins (1% FDR) were quantified, with 362 significantly differentiated proteins (Log2FC≥1.5 or ≤0.5, p<0.05). Gene ontology pathway analysis revealed that the most significantly suppressed canonical pathway was the LXR/RXR activation pathway (p<0.01, |z|≥2). This is mainly contributed by significant differential protein markers from the apolipoprotein family, which are consistently down-regulated. This includes APOA1 (Log2FC=-1.3, p=3.55E-15), APOA4 (Log2FC=-1.7; p=3.55E-15), and APOD (Log2FC=-1.3, p=1.24E-03).The LXR/RXR activation pathway is reported to regulate gene expression in the retina. LXRα/β is suggested to regulate angiogenesis and contribute to ocular neovascularization by increasing the expression of ATP-binding cassette transporters (ABCA1 and ABCG1) by interfering with the signalling of vascular endothelial growth factor receptor 2 (VEGFR2). Suppressed LXR/RXR activation pathway can therefore result in disrupted lipid rafts that could interfere with neovascularization in ROP.Further validation and development ofthe reference range of the key ROP tear biomarkers we discovered may facilitate the development of a non-invasive ROP screening kit for clinical application, which is accessible and convenient. As little as 1mm of tear fluid collected with Schirmer’s strips is sufficient to identify the significantly differential ROP biomarkers. Additionally, tear proteins on Schirmer's strips can be preserved at room temperature if dry-heated upon sample collection. Therefore, such innovation can facilitate early ROP screening to identify high-risk cases and potentially reduce the rate of vision loss in ROP, especially in rural areas.