Both can be done, more cheaply but probably not as well as in SIN or KUL.

Tailoring business shirts: there are plenty of tailors here in PNH. Some are OK - I've had suits made (the going rate seems to be around $150-180 including fabric) and they are fine if not fantastic; they're also cheaper than the equivalent would be in BKK and, I assume, SIN/KUL. However, there is also much more of a language barrier - some tailors do not speak much English - and the selection of available fabrics is generally not as good. The work also tends to take longer - they're not used to the tourist trade ("I'm here for 24 hours and want 5 shirts and 2 suits delivered to my hotel by 3 pm tomorrow..."). That said, I've always been wary of 24-hour suits.

Eyeglasses: there are a number of shops in PNH that will test your eyes and produce glasses at a cost lower than in the US or Europe. Again, quality varies; costs can be as low as $40 a pair, but those will be pretty basic frames that may not last. The more you pay, the better the quality. Again, I find the value for money to be OK but not the best in Asia (which, for glasses, is Beijing IMO). Eyeglasses will probably have a fast turnaround (1 day or so).

I hope this helps.

- Michael