Effect of contact lens wear on the tears of Hong Kong-Chinese

Chinese subjects living in Hong Kong (HK-Chinese) were recruited in order to investigate the effect of soft contact lens wear on tear stability and quantity. All subjects were asymptomatic and non-contact lens wearers. The tests used for tear stability were the tear break-up time (TBUT) test and a non-invasive tear break-up time (NITBUT) test; for tear quantity, the Schirmer test (ST) and a modified cotton thread test (CTT) were used. Measurements were taken before and after various periods of contact lens wear. Inconsistent changes in the pre-lens tear film (PLTF) stability were observed. There was no association between corneal staining and low PLTF stability. Soft contact lens wear caused a significant initial transient decrease in the tear stability but no changes in tear quantity. The median NITBUT and TBUT before soft contact lens wear were 9.7s and 4.0s respectively. After 28 weeks of daily soft contact lens wear, the median NITBUT was 5.6s and TBUT was 6.2s. The mean (± SD) CTT value was 23.2 (±11.2) mm/min before soft contact lens wear and 19.4 (±14.0) mm/min after 28 weeks of daily soft contact lens wear. NITBUT and TBUT tests do not appear to identify which patients would have potential problems with contact lens wear whereas CTT values appear to predict subjects most likely to be successful soft contact lens wearers.