Contamac developed the Definitive Silicone Hydrogel material as a benchmark for the new generation of lathe cut materials and has utilised the latest technology in its advanced polymer matrix. With unique surface qualities, outstanding levels of on eye comfort and a high level of Dk that promotes corneal health, the contact lens wearer will need to ask for nothing more than Definitive.
Definitive is a new generation of Silicone Hydrogel materials developed specifically to be lathe cut by manufacturers of speciality soft contact lenses. The oxygen permeability of Definitive is the highest available to manufacturers of lathe cut hydrogel lenses and is achieved with an exclusive blend of Fluorosilicone and hydrophilic monomers. Its Dk is significantly higher than conventional hydrogels and promotes improved corneal health. The polymer composition has been optimised to ensure that the Definitive material can be machined in the same manner as any other high water content contact lens material. However unlike other high water content materials, Definitive exhibits exceptional on eye water retention combined with excellent stability. Definitive also provides an inherently wettable lens surface, that does not require surface treatment. It has the same stiffness as a conventional mid water content contact lens material, so does not suffer from the mechanical complications associated with other silicone hydrogels. Lenses of excellent visual acuity and outstanding on eye comfort can be produced using Definitive and its combined properties make Definitive suitable for producing a wide range of lens designs.
For further information on the Definitive Silicone Hydrogel please email sales@contamac.com.
Definitive technical information
Material Characteristics:
| Property | Definitive |
|---|
| Classification | filcon V3 |
| FDA Approved | Yes |
| USAN | Efrofilcon A |
| Ionic or non-ionic | Non-Ionic |
Oxygen Permeability at 35°C (ISO)
X10-11 (cm2/sec)[mlO2/(mlxmmHg)]
| 60 |
Oxygen Transmissibility at 35°C (ISO) 0.08ct
X10-9 (cm2/sec)[mlO2/(mlxmmHg)]
| 75 |
| Swell Factor | 1.63 at 20°C |
| Water Content | 75% at 20°C by refractometer
74% at 20°C by weight |
| Refractive Index | 1.3750 at 20°C
1.3730 at 35°C |
| Dry Refractive Index | 1.5100 at 20°C |
| Light Transmission | >99% |
| Tensile Strength (MPa) | 0.39 |
| Elongation to Break (%) | 180 |
| Modulus (MPa) | 0.35 |
| Hardness (Shore D) | 84 |
| Handling Tint | Blue |
| Diameter | 12.70mm |
| Thickness | Standard |
Please note: These are typical values. Always check the certificate of compliance supplied with the goods for the actual values of the batch.
Diamond Tooling:
| Tooling | Radius (mm) |
|---|
| Rough | 0.30 – 0.50mm |
| Fine | 0.30 – 0.50mm |
Machining Recommendations:
| Spindle Speeds: | 7000 – 10,000 rpm |
|---|
| Rate of Cut: |
| Roughing | 0.40 – 0.80 mm @ 1.4mm / second |
| Fine | 0.03 – 0.05mm @ 0.70mm / second |
|
| Radius of Diamond Tool: |
| 0.50mm or less (0.25 mm recommended) |
| 2.5º negative top rake |
|
Environment Control:
For best manufacturing conditions Contamac recommends 19-23°C with a relative humidity of 45%-60%.
Polishing:
The recommended polishing compound is Contapol 2 with a spindle speed of 3500rpm and minimal weight. With the above machining recommendations polishing should require a maximum of 30 seconds.
Blocking:
Use low temperature blocking wax with an operational temperature of less than 60°C such as Contamac Low Melt Wax.
De-Blocking:
Recommend the use of Isopar E, Petroleum Ether or equivalent in an ultrasonic bath for dissolving blocking wax and cleaning the lens.
Hydration, Sterilisation and Storage of Definitive Lenses:
The choice of saline for the hydration, sterilisation and storage of lenses can have an impact on the stability of the finished lens parameters. We recommend a commercially available, non-buffered saline solution, such as those used for irrigation during surgical procedures. The pH of the saline can be adjusted to the range of 7.0-7.4 if required by the addition of analytical grade anhydrous sodium carbonate. Such adjustment should be closely monitored and this can be achieved through use of a calibrated pH meter at a controlled temperature.
Experience has shown that performing initial hydration in saline at 2-5°C can be advantageous. To enable wet checking of lenses prior to autoclave it is recommended that they are then held at 45±5°C overnight to ensure complete hydration. Either the glass vial containing the lens can be put into an appropriate incubator or the lens can be placed in a basket and put in a heated saline bath.
Once the lens is fully hydrated and has reached ambient temperature, digitally clean with a standard soft lens cleaning solution and inspect wet parameters at room temperature 19-21°C.
Alternatively if the wet parameters do not require checking then the 45°C hydration step is not essential, as autoclaving will complete the hydration process. For autoclaving, the lens should be placed in fresh non-buffered saline solution as described above and it should be ensured that no alcohol based cleaners are used throughout the process.
It is recommended that manufacturers should keep the heat treatment of the Definitive material to a minimum. For best results, exposure at the internationally recommended temperature of 121°C for sterilisation should not exceed 30 minutes. Ramp up and cool down cycles should be kept to a minimum. Validation of the autoclave using Definitive and in the recommended parameters suggested above is required by the FDA and ISO requirements.