glasses

I need a new glasses.
I need new glasses.
I need a new pair of glasses.

When glasses means ‘spectacles’, it is plural, so we cannot say a glasses. We use a plural verb: ‘My glasses are new.’

To talk about one set, use a pair of glasses: ‘This pair of glasses is new.’

The same pattern is used with words such as trousers, shorts, jeans, pyjamas, binoculars and scissors.