Is this the system by which you obtained a prescription for respirator lenses that was then sent through the system to have the lenses manufactured (and if you sneakily ticked a box on the form, also obtained a pair of defence (or aviator) glasses?).
I don't know what has changed in the last 10 years or so but the F Med form* could be used at any optician. You paid for the test then claimed the cost back when you submitted the form through the Chief Clerk.
*Can't remember the number but there have been a few threads where the number was quoted.
Remember to photocopy the prescription before giving it to the Chief Clerk.
If you mean the provision of glasses for DSE use (through DE&S etc) then it's managed at Team level. Your unit/dept's Business team (or perhaps IHub) should be able to sort it out but there's also some bits on Defnet regards the guidance iaw the JSP.