In reply to lost1977:
Re VAT specifically, I don't know.
From an employer's perspective I am (not unreasonably) required to fund biennial eye tests and provide 'suitable' glasses for those who need them if they are using display screen equipment.
Where I have had peiople with an existing disability or a progressive medical condition I have had to make 'reasonable' adjustments to the workplace (accessible offices, big screens, allowing flexible working) - none of which I have a problem with.
If the provision of better quality aids would make it easier for you to perform your job, and therefore make you more effective or productive, I would hope any reasonable employer would consider funding or partly funding the necessary equipment.
Could you pose the question to Action on Hearing Loss, or one of the other national bodies?