Fitting the lens...

With the eyeball fixed in place, it's time to add the 'lens'.
This photo gives you a better insight into the "Perspex sandwitch" used to make the iris unit.
This fits snugly into the front of the eyeball.
A few tiny dabs of PVA glue have been used to ensure that it is secure.

If it ever needs to be removed to change the bulb, this will be a straightforward task.
A small suction cup, like those used on a child's toy, will be used to pull the two sections apart.

My fingernails are clean on this occasion - they'd had time to recover after I'd built the shoulders!