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The development of the material has not been without challenges. The first generation of SiH lenses had a high modulus of rigidity. This meant that many patients found the transition from conventional hydrogels to SiH less than comfortable. Furthermore, the increased wearing times allowable with good oxygen characteristics also saw the renaissance of lesions such as superior epithelial arcuate lesions (SEALs) (Figure 1) and contact lens-induced papillary conjunctivitis associated with the increased stiffness of the lenses.
A second generation of lens designs aimed to address these concerns by reducing the modulus and employing various methods of surface modification and incorporation of wetting agents to improve comfort and reduce deposition. Developers are continually looking to improve surface biocompatibility, interactions with care systems and surface wettability. The fact that comfort concerns are the major reason for patients ceasing to wear lenses means manufacturers are continually striving to improve in these areas and now third-generation SiH lenses are being introduced.
First for Sauflon
UK contact lens company Sauflon has just launched its first silicone hydrogel lens. Familiar to all as a supplier of 'optician only' care systems, Sauflon introduced contact lenses to its portfolio relatively recently and just last month launched the Clariti lens (Figure 2), consolidating Sauflon's position as the fifth largest contact lens company in the world and making it one of only three companies manufacturing both lenses and solutions. This is a monthly replacement lens designed for daily wear. The lens launch occurs at a time when the company is expanding its production facilities. With the manufacturing plant in Hungary working to maximum capacity to produce daily disposables, Clariti is being produced at Sauflon's Southampton facility.
The lens, which has taken five years to develop, is being sold in conjunction with Synergi solution which, Sauflon maintains, will ease any concerns by practitioners over which care systems to use with SiH lenses. The brief to developers, according to Sauflon's UK sales director Bradley Wells, was to make a lens 'with a lower modulus but better oxygen and ocular health properties'. The transmissibility (Dk/t units) of the material is 86, based on a -3.00DS lens. This compares favourably with all other available SiH lenses and is easily in excess of the values suggested as a minimum requirement for healthy daily wear.
The water content of the lens is 58 per cent, a level more like that of conventional hydrogel lenses and higher than rival SiH lenses (Table 1). This higher water content makes the lens more wettable and less likely to deposit heavily, so improving biocompatibility.
To maximise comfort, Clariti has a lower modulus than rival lenses (Table 2), with a value of 0.5MPa. This should show benefits for the user in terms of greater comfort.
Other SiH lenses - to overcome the problem of silicon being so hydrophobic - have surface alterations to improve comfort for the wearer based on either treatment of the actual surface or the incorporation into the lens material of a wetting agent. Sauflon has patented a new process, AquaGen, which, according to Wells, 'produces a unique silicone hydrogel lens material with enhanced oxygen permeability and superior levels of wettability and biocompatibility'.
'This is achieved by controlling how the novel silicone and hydrophilic materials are combined at the molecular level to produce a surface with unparalleled biocompatibility and wettability without the need for surface modification, while retaining excellent clarity and low modulus to achieve the uncompromised visual and comfort standards required by third generation silicone hydrogel lens products,' Wells added.
The lens is available in powers from -10.00DS to +8.00DS, has a base curve of 8.4mm and diameter of 14.1mm. It boasts an aspheric back surface and a blended edge design. In a clever move to protect practitioners from losing patients to the internet, Sauflon has linked the lens to its patient protector plan, ensuring that patients return to their original practitioner for future lenses rather than relying on internet suppliers and supermarkets. Clinical data with any brand new project is likely to be less than plentiful. However, one study (held on file by Sauflon) shows that the pre-lens tear break-up time with a conventional lens is eight seconds while this value rises to 30 seconds and still rising when the Clariti is used.
Optician aims to publish in detail some of the clinical performance trials later in the next year. In the meantime, look out for the latest SiH to appear in the UK.
? For more details contact Sauflon on 020 8322 4200.