You read whole words rather than individual letters. Sometimes you read familiar groups of words. Psychologists call this 'chunking' and reading would be very laborious without it.
Similarly, when you read music you need to get into the habit of chunking common rhythm patterns and significant pitch collections; segments of scale, broken chords, chains of thirds and so on.
The ability to recognise these chunks has to be linked to your ability to play them, of course. It will be pointless doing the exercise below, for instance, if your fingers don't already know their way around the scales of C, F and G majors or at least the segments of them between C & F.