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Hydrophilic Materials Facts

Hydroxyethyl methacrylate/Vinyl pyrrolidone

KEY DATES - HEMA/VP

  • 1961 - First soft contact lens patented - polyHEMA - Wichterle
  • 1966 - First recorded work on HEMA/VP polymers in US

KEY PRODUCTS - HEMA/VP

  • 1968 - Permalens - Materials and Lathe cut lenses

Current  situation - HEMA/VP

In 1991 the British Standard BS 7208: Part 2 was published. This is a generic classification for the materials used to manufacture contact lenses.  The group filcon 3 is reserved for materials made from HEMA/VP and their chemically related species. An additional notation a or b is specified to indicate whether the material is non-ionic or ionic.  An examination of the Contact Lens Yearbook for 1993, shows that some of the most widely dispensed lenses fall into the filcon 3 group, including:

  • Nissel 45 - Lathed, Incanto 78 - Moulded
  • PBH CV - Classic & Soft Mate I/II/B - Lathed & moulded  Hydrocurve II 45/55 - Lathed/moulded
  • Permalens 71/XL - Lathed/moulded
  • Hydron - Ultra T - Spun cast
  • B&L - Optima Toric - Lathed
  • Aspect  - Formula/Frequency 55 VH - Moulded
  • Eyetech - Eurosoft 52/55 - Lathed

In addition many of these suppliers and others will supply prescription specials, torics, bifocals, tinted and UV blocked versions. Some of these have been approved by the FDA in the US and include - Permalens, Hydrocurve, & Soft Mate. There are also many US only products which are approved and which are based on HEMA/VP polymers. The history of the HEMA/VP lenses spans more than 20 years and spans the world. The market for low water content lenses continues to decline in favour of high water. High water lenses are made from MMA/VP or from modified HEMA and HEMA/VP.

With regards numbers of HEMA/VP lenses, one can only guess in the order of ten million over the last 20 years. Currently, PBH and New Focus are cast moulding in excess of one million lenses per year of HEMA/VP lenses into the frequent replacement market, and each claims to be increasing their production.

Since 1995 Award B&L have been using HEMA/VP to produce a daily disposable lens, being the first 'daily' in the UK. Production is in excess of a million lenses per month.

2007 Andrews Wright Ltd.

Examples of hydrophilic types:

AEP 40
Low water absorption and swell with maximum mechanical stability and dessicant action.

AEP 50
Most used for encapsulation of other chemical materials for preservation and controlled release.

AEP 60
Most used for moulding and mechanical devices with best combination of mechanical stability and volume expansion.

AEP 80
High volume expansion and water absorption used for wound care and similar applications

Biogel
Contact lens and implant materials are available in a range of water contents from 61% to 78% and with linear expansions from 1.39 to 1.67.

AEP blends
Blended formulations are made using a combination of proprietry and/or commercial materials for the manufacture of a range of products.