Employers can set standards for physical (or mental) ability as a pre-condition of obtaining a job without the risk of thereby bestowing disability status on all those who fail the test.
To qualify as disabled an employee must show that their impairment has a substantial and long-term adverse effect on their ability to carry out normal day-to-day activities.
An employee's minor visual impairment caused her to fail an eyesight test set by the employer for promotion to a new role. Her inability to obtain this new role was insufficient by itself to establish the necessary adverse effect. An employee's status as disabled cannot turn on how the employer chooses to react to the employee's condition. (Lothian v Cumming, EAT)