Once again ZEISS CONTACT DAY 30 COMPATIC demonstrates excellent compatibility and wearing comfort due to its balanced material properties Nowadays great emphasis is placed on health, and almost every product is characterised by its "wellness factor". In product information on contact lenses, the focus has been increasingly directed at the easily comprehensible concept of oxygen permeability. In recent years this has led to the quality of a contact lens being defined more and more through a high DK/t (lens specific value for oxygen permeability). This article will show that other properties are also of great importance for the compatibility of a contact lens. Increased oxygen permeability is indisputably a very important criterion for extended wear with special contact lenses. However, above a certain Dk/t value in a specific lens any additional uptake of oxygen by the cornea is so minimal that increasing this parameter has an insignificant effect on daily wear. Thus the assertion ?the more not necessarily the merrier? proves true in this case too.
The following questions must be posed in order to get nearer to fathoming the secret of optimal compatibility: ? Is there only one essential characteristic? ? Is it sufficient to focus solely on one of the properties of the material? ? Is silicone hydrogel the key or just one key to optimal compatibility?
Contrary to the general trend prevailing at the time, these considerations led to the development of a material with balanced material properties at Wöhlk, enabling us to choose the best material combination for best wearing comfort. Wöhlk considers balanced material characteristics as the combination of good oxygen permeability, a minimum modulus of elasticity (stiffness of the material) and good wettability with consequent good lubricity values (slippage). In addition, above all the lens design with a well thought out edge shaping is responsible for a good fit and maximal tear exchange. All these factors are crucial for wearing comfort and the long term compatibility of a contact lens. Bearing all the above in mind, would not a material whose composition emulates that of the human cornea be a realistic alternative which would also be comfortable? As a result of the bionic, patented material structure of the Vitafilcon-A material, the ZEISS CONTACT DAY 30 COMPATIC lens has considerably improved water binding properties and a higher water content than other silicone hydrogels. Consequently this contact lens reveals its strengths regarding dehydratisation and dryness symptoms, its subjective comfort advantages particularly towards the end of the day. This also applies with dry and sensitive eyes, and has been proven in a comparative study with other contact lenses. The other lenses dehydrated more in a given time than the ZEISS CONTACT DAY 30 COMPATIC
The most important characteristic for subjective compatibility, the high water binding capability, positively influences the wettability, and thus not only wearing comfort; it also ensures that the lens retains its shape stability. This means that visual acuity remains constantly good with ZEISS CONTACT DAY 30 COMPATIC throughout the whole day (Vision Control).
Lubricity is increasingly recognised as an important property in contact lenses. This is the ability of a hydratised material to withstand friction. In contact lenses this refers to the friction experienced by the eyelid when it glides over the surface of the contact lens. Here, too, the ZEISS CONTACT DAY 30 COMPATIC lens showed the lowest coefficients of friction in a comparison of silicone hydrogel lenses. This means that the contact lens feels very soft and, above all, that the minimum friction force means that there is hardly any lid irritation.
The modulus of elasticity is also closely connected to compatibility. This describes the ability of the material to fit itself to the shape of the surface of the eye. A too stiff material can result in the lens being too mobile on the eye or cause increased irritation. The increased coefficient of friction in silicone hydrogels will also have a negative effect on this problem. Overall ZEISS CONTACT DAY 30 COMPATIC is a perfect balance of a palpably pleasing material which, thanks to clever lens design, is also easy to handle. ZEISS CONTACT DAY 30 COMPATIC is a Wöhlk lens produced in a patented process from Vitafilcon A. Based on the ingenious example of nature Vitafilcon A provides a perfect mixture of material properties, thus guaranteeing excellent comfort. It is no surprise that ZEISS CONTACT DAY 30 COMPATIC and the Vitafilcon A material were awarded the Sicca Research Prize of the BVA Working Group "Dry Eyes" immediately after its introduction in 2004.
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