Contact lenses with cornea-like comfort

Contact lenses are increasingly important to many people, no matter their age. School children are prescribed contact lenses because of a rise in myopia in young people, whereas an aging population require effective correction for myopia and presbyopia. As life expectency continues to improve, there is growth in the contact lens market in the aging population from continued and first time contact lens wear.

Comfort is a crucial selection criterion for contact lenses, and poor comfort is often the main reason for discontinuation of lens wear. Discomfort could be in the form of initial lens insertion, irritation during wear, or end of day tiredness and dry-eye symptoms. These problems are linked to the contact lens surface and its interaction with the ocular environment. The hydrogel material that makes-up the contact lens, does not provide a satisfactory compatibility with the eye for long-term wear. Even though conventional hydrogel materials, that mimic soft tissues, are successful in other applications, they are unable to completely reflect the natural tissue in the eye.

The cornea is an extradordinary example of a natural tissue, that when exposed to air is able to effectively retain water and maintain a fluid layer over its surface.  This fluid layer, or tear film, covers the cornea and keeps it hydrated. Although the tear film has a tendency to break-up at regular intervals, the hydration of the cornea allows the eyelids to glide smoothly over the eye, to create a new tear film. In comparison to the cornea, hydrogels are prone to dehydration and lose water quickly. During contact lens insertion and wear the tear film is split in two, creating a thin layer over the front surface of the contact lens. This thin layer is less stable than the original tear film and breaks up more readily. An unstable tear film exposes the contact lens surface to air, making it more difficult for a new tear-film to spread over it during blinking. This can cause irritation to the upper eye-lid and is a factor for dry-eye symptoms.

Contact lens manufacturers aim to promote better interaction between the contact lens and the eye, through improvement of the contact lens surface. In this project I am developing molecular engineering techniques to build a “biomimetic” structure, similiar to the corneal surface, onto conventional hydrogel contact lenses. Successful alteration of the contact lens is assessed using contact angle and coefficient of friction techniques, to measure surface wettability and lubricity. A reduction in contact angle and coefficient of friction indicates an improved surface. If successful modification is achieved, then clinical trials will be established to monitor if the modified contact lenses are truely compatible during wear.  Clinical trials would consist of patient contact lens wear and an individual review where patients can grade their wear experience. If the clinical assessments are positive, the modified contact lens could potentially be introduced as a new commercial lens material.

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Sessile Drop Instrument
The sessile drop instrument (GBX Digidrop) used for measuring contact angles on contact lens surfaces.
Sessile Drop Analysis
An image of the sessile drop contact angle method, showing points of analysis at the liquid drop interfaces (with air and the contact lens).