The authoritative publication in this field is the In Touch Handbook, an offshoot of the BBC Radio 4 programme. Until now, the book has come in three hard formats, each of which has its own limitations.
The printed version runs to 530 pages of standard type, which presents partially sighted readers with difficulties; the tape version is now much easier to get round but this has meant expanding it to 27 cassettes; and the Braille version, in seven volumes, occupies well over a cubic foot (the storage space for approximately 75 LPs) and weighs 16lb.
But this year, for the first time, each hard copy comes with two free computer disks containing all the text and, for an extra pounds 4.95, another six discs can be supplied which enormously expand the potential of the book. The whole package takes up 5MB and will run on a 286.
Pia, the Cardiff-based producers of the multi-media disk version were faced with some severe technical tests.
As Mike Joseph, its managing partner, said: 'We could have gone for CD-rom and Windows, which would have given us a superb product, but most of our potential market runs modest computers and Windows presents visually impaired computer users with problems. 'We just had to stretch Dos to the limits, and beyond, in order to produce the results we wanted.'
The basic text is easy to load and its most pleasing feature is the use of a 'link' mechanism to deal with cross referencing. The problem with ordinary searching tools is that you can only look for something if you strongly suspect it is there; you have to know your subject.
But with this system each sub-section signposts cross-references so that people suffering from a particular eye condition might be pointed towards special areas, for example in the self-administration of insulin or cricket clubs that cater for visually impaired people. These handy stepping-stones in the data lake are as easy to use with a voice synthesiser as they are on screen.
The simultaneous launch of four formats is a UK first but there are other ways in which this publication breaks new ground.
One of the additional disks contains Ferret software which allows clients and carers to calculate their state benefits rights. Another disk contains the stills from the book with sound picture captions for visually impaired people which use the ordinary PC speaker facility; yet another contains animations of the onset of various blinding conditions and another contains a video of a blind person tackling independent mobility problems. 'We could have done a lot more,' Mr Joseph explained, 'if we had not been limited to Dos.'
Perhaps the really important feature of the publication is the licence which allows users to print off sections of the book in Braille or large 14-point print. 'We recognise that there has always been informal photocopying by fully sighted people,' Mr Joseph said. 'We just wanted to put visually impaired people on an equal and legitimate footing.'
What started as the 'fourth force' may soon be primary. The handbook data is being continuously updated so disk versions soon supersede hard copies.
The day is not long off when the publishers will have to consider turning the publication into an updated information service paid for by subscription with hard copies published in Braille, large print or standard print to order.
These developments raise other issues, too. When is a book not a book but a broadcast? How important are sales compared with circulation when backers like the Royal National Institute for the Blind and the Guide Dogs Association might be more interested in circulation than sales? In this world the intricacies of copyright and profit take on a new aspect.
Mr Joseph, who put the multi-media version together as an experiment, thinks that CD-rom could be just round the corner but he may not even reach the end of the street.
The idea needs long-term commitments from major backers but for all the rhetoric about the entrepreneurial spirit and the need to experiment, this project might be just too adventurous to attract support.