amblyopia

Dimness of vision without apparent eye disorder. The centre of the field of vision is most affected, and there are blind spots for both red and green. The condition is progressive and may ultimately, though rarely, lead to total blindness.

The condition may be congenital or acquired. In the latter case, it is sometimes due to psychological trauma, but more often to the excessive use of tobacco or alcohol, and in some cases to poisons such as lead, arsenic, quinine, and ergot. Undetected astigmatism or a squint early in life can also be responsible. A less frequent cause is inflammation of the optic nerve.