Tear Flow, Not Aox Content, Affects Ocular Health

HONG KONGOlder adults have a lower flow rate of tears, which may impair their ability to adequately refresh the eye and deliver key antioxidants, according to a new study (Optom Vis Sci. ePub 17 Feb 2011. DOI: 10.1097/OPX.0b013e31820e9fe2). Researchers from Hong Kong Polytechnic University compared tear antioxidant content and flow rate in young and older adults to determine whether decreased antioxidant/ultraviolet (UV) radiation protection in tears may be part of the cause of dry eye syndromea disorder commonly seen in older adults. The team also looked at the antioxidant content and UV absorbing properties of several commercially available ophthalmic solutions used to alleviate dry eye symptoms.

Researchers recruited 120 healthy Chinese adults in two age groups: 19 to 29 years (n=58) and 50 to 75 years (n=62). Minimally stimulated tear samples were collected and analyzed for total antioxidant content and UV absorbance spectra; tear flow rates were estimated from time taken to collect a fixed volume of tear fluid.

There was no significant difference in the antioxidant content of the tears between the older and younger subjects; however, there was a significant difference in tear flow rates, with younger subjects having three- to four-fold higher flow rates. The researchers speculate the low flow rate in older adults impacts the dynamic antioxidant supply to the corneal surface, reducing defenses against antioxidant stressors. This could increase corneal stress and contribute to dry eye syndrome.

While none of the commercial ophthalmic solutions contained detectable antioxidant content or UV absorption characteristics of natural tears, the researchers suggested formulations that help restore antioxidant and UV absorbing properties to the corneal surface could promote ocular health and prevent or improve dry eye symptoms.