In some cases the eye is congenitally absent (_Anophthalmos_). In others
it is abnormally small. One such case came under the notice of the
author in which the eyeball was represented by a small black sphere
about half an inch in diameter moved by the ocular muscles. The dam of
the filly, born with this defect, had, during the pregnancy, a burdock
entangled in the forelock and causing a violent ophthalmia which was
supposed to have lasted for months. In other cases there is a fistula
opening from the vitreous behind.
Cases of wasting and atrophy of the eye follow on exudates into the
vitreous and their subsequent contraction, or on suppuration and
granulation as noted under _internal ophthalmia_, _recurrent
ophthalmia_, and _panophthalmia_. The condition may also result from
atrophy or degeneration of the optic nerve or of its cerebral ganglia
(thalamus, corpora quadrigemini, geniculata, etc.). These conditions are
irremediable.