For pilot or nav you need 3 GCSE A-C plus A-C in English and Maths. For WSOp you also need Physics.
At A-level you need 2 passes at grade E and above.
Experience shows that low, acceptable grades tend to indicate poor aptitude scores.
Short-sightedness will prevent acceptance as a pilot. Mild short-sightedness may be acceptable for navigator but you would need to be able to read a car number plate at 25 metres.