Зрение у него стало ухудшаться, и в

Зрение у него стало ухудшаться, и вскоре он с трудом различал, что написано на доске.

Результаты (английский) 1:

The vision he was deteriorating, and soon he found it difficult to distinguish between what is written on the Board.

Результаты (английский) 2:

His vision began to deteriorate, and soon he could hardly distinguish what is written on the blackboard.

Результаты (английский) 3:

Vision he has taken a turn for the worse, and soon he was difficult to excess, that is written on the blackboard.