Potential risk of coloured contact lenses

Researchers of The Hong Kong Polytechnic University (PolyU)’s School of Optometry (SO) have recently conducted a study on 15 brands of coloured contact lenses available from various sources including Internet, cabinet stores and optical shops. Results showed that most of these cosmetic contact lenses have surface coloured pigments which can easily come off when using a standardised lab-based rub-off test.

When challenged with micro-organisms, lenses with surface pigments have significantly more attachment of microorganisms. Users purchasing coloured contact lenses casually from unauthorised or street vendors without prescription are exposing themselves to high risk of contact lens-associated complications. “All contact lenses, coloured or otherwise, should be prescribed by registered contact lens practitioners after proper eye examination and lens fitting, and with proper advice and aftercare,” said Professor Pauline Cho of PolyU SO

In Hong Kong, coloured contact lenses have become trendy fashion accessories. Many people wear these lenses at parties and on festivals such as Halloween and Christmas. As there is no regulation that restricts the sales of contact lenses in Hong Kong, the public can easily purchase these lenses via internet sellers, retailers or consignment counters. However, information about the countries of origin, materials, pigments used, and manufacturing processes of these contact lenses are not readily available. Improper use of these contact lenses will impose risks to the users’ ocular health.

Professor Pauline Cho, Professor of SO, led her research team in this study on 15 brands of coloured contact lenses available in the market. “This is the first ever study in the world comparing the levels of microbial adhesion to coloured contact lenses which have surface, embedded or sandwiched pigments. All other published reports on microbial adhesion only focussed on clear hydrogel and silicone hydrogel lenses,” said Professor Cho.

In this study, Professor Cho and her team conducted two experiments on coloured contact lenses. The first experiment was to compare the level of microbial adhesion among 15 brands of coloured contact lenses. As materials and water content levels of the contact lenses can affect the level of microbial adherence, the second experiment compared three brands of coloured contact lenses with their clear counterparts (i.e. clear contact lenses with the same material and water content).

A total of 15 brands of coloured contact lenses (5 lenses per brand), purchased from optical shops, consignment counters and internet sellers were tested. All lenses, except those of 2 brands, failed the standardised rub-off test (i.e. pigments came off in the rub-off test), indicating that the coloured pigments were neither embedded nor sandwiched in the contact lenses. When challenged with micro-organisms (new sets of lenses, 5 lenses per brand), the levels of microbial adherence to the lenses of the 13 brands of contact lenses which failed the rub-off test were at least six times higher than the lenses of the other two brands which passed the test.

Results of the second experiment showed that coloured contact lenses which failed the rub-off test have higher levels of microbial adherences when compared to their clear counterparts. Coloured contact lenses which passed the rub-off tests (pigments embedded or sandwiched) showed no significant difference in microbial adhesion when compared to their clear counterparts. These results confirmed that surface pigment on coloured contact lenses which were not employing embedded or sandwiched design, was most likely to be the factor leading to higher microbial adherence in these lenses.

Professor Cho reminded consumers that consultation with their contact lens practitioners before wearing contact lenses is of paramount importance. “Coloured contact lenses are increasing in popularity as fashion accessories. However, it is important that they are prescribed by professional contact lens practitioners, not only to ensure the quality and reliability of the contact lenses, but also to ensure proper eye examination, fitting and instructions on usage and care, and regular check-ups to minimize complications that can be associated with contact lens wear. Consumers are therefore reminded not to patronise hawkers, consignment counters or internet sellers,” said Professor Cho.

“This is not to say that coloured contact lenses with surface pigments are not safe but that lenses with surface pigments allow more adhesion of microorganisms. It is therefore very important that such lenses should be cared for appropriately or discarded accordingly according to the modality,” said Professor Cho.

(Source: The Hong Kong Polytechnic University)