title: Antioxidant content and ultraviolet absorption characteristics of human tears.
abstract: OBJECTIVE
  Dry eye syndrome is a common age-related disorder, and decreased antioxidant/ultraviolet (UV) radiation protection in tears may be part of the cause. This study aimed to compare the tear antioxidant content and flow rate in young and older adults. The total antioxidant content and UV absorbing properties of various commercially available ophthalmic solutions used to alleviate dry eye symptoms were also examined.
  
  
  METHODS
  Minimally stimulated tears were collected from 120 healthy Chinese adults with no ocular pathology. Two age groups were studied: 19 to 29 years (n = 58) and 50 to 75 years (n = 62). Tear samples from each subject and 13 ophthalmic solutions were analyzed for total antioxidant content (as the Ferric Reducing/Antioxidant Power value). Tear flow rates were estimated from time taken to collect a fixed volume of tear fluid. UV absorbance spectra of pooled fresh reflex tear fluid and the ophthalmic solutions were determined.
  
  
  RESULTS
  Results showed that the antioxidant content of minimally stimulated tears from older subjects (398 ± 160 μmol/l) was not significantly lower than that of younger subjects (348 ± 159 μmol/l; p = 0.0915). However, there was a significant difference in the tear flow rates between the two groups (p < 0.0001), with the younger group having three to four fold higher flow rate. None of the commercial preparations tested had detectable antioxidant content, and none showed the UV absorption characteristics of natural reflex tears.
  
  
  CONCLUSIONS
  The effect of low flow rate on the dynamic antioxidant supply to the corneal surface indicates that older subjects have poorer overall defense against photooxidative and other oxidative processes. This could predispose older persons to corneal stress and development of dry eye syndrome. The commercially available artificial tears tested lack both the antioxidant content and UV absorbing characteristics of natural tears. Artificial tears formulations that help restore natural antioxidant and UV absorbing properties to the tear film of the aging eye may help prevent or improve dry eye symptoms and promote ocular health.
authors.affiliation: Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong SAR, China. socamus@inet.polyu.edu.hk
authors.forename: Camus Kar Man
authors.initials: CK
authors.lastname: Choy
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
authors.forename: Iris F F
authors.initials: IF
authors.lastname: Benzie
mesh_terms: D000042:Absorption; D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism; D000975:Antioxidants / Q000032:analysis*; D003315:Cornea / Q000378:metabolism; D015352:Dry Eye Syndromes / Q000188:drug therapy / Q000209:etiology; D006801:Humans; D008875:Middle Aged; D009883:Ophthalmic Solutions / Q000737:chemistry; D013666:Tears / Q000737:chemistry* / Q000502:physiology / Q000528:radiation effects*; D014466:Ultraviolet Rays; D055815:Young Adult
chemical_list: D000975:Antioxidants; D009883:Ophthalmic Solutions