from revenue.ie:
"Relief can be claimed for health expenses paid in each tax year, or for the year in which the expenses were incurred. Claims can be in respect of subscription year or tax year but must be consistent every year. Relief is given by way of repayment at the end of the year.
In cases of hardship relief may be granted during the tax year. All such cases will, of course, be subject to lodgement of form Med1 in the normal way, and to review after the end of the year in question."