We are given that the distances from the pupil to the top and bottom of the object is congruent, and the distances from the pupil to the top and bottom of the image on the retina is congruent.
AB=EB and CB=DB
This means that the ratio of the corresponding sides will be constant.
AB/CB=EB/DB
The lengths of two sides of one triangle are proportional to the lengths of two corresponding sides of another triangle, and the included angles are congruent. Therefore, by the Side-Angle-Side Similarity Theorem, these triangles are similar.
