HISTORICAL PERSPECTIVE ON HYPERMETROPIA HEREDITARY

It is not an infrequent occurrence to find many members of the same family affected with hypermetropia. This is so commonly the case that when the diagnosis of hypermetropia is reached in the examination of a patient, the question naturally presents itself in the examiner's mind as to whether some other members of the family are not similarly affected; and when this question is put to the patient, the answer generally corroborates the assumption, at least to the extent of admitting that one or both parents commenced to wear convex glasses for reading at a very early age. (Hypermetropia in some cases first shows itself as an early presbyopia)

Cases will sometimes be met with in which one eye is emmetropic and the other eye hypermetropic; and in such cases there may be a very marked difference in the form of the bones on the two sides of the face, thus illustrating the shallowness of the orbits and the flatness of the face with the diminished prominence of the nose, which so often accompanies and indicates hypermetropia. A writer relates a case of this kind, the patient being a young lady who presented herself for treatment of stricture of the nasal duct. The lack of symmetry between the two sides of the face and in the size of the eyeballs was strikingly noticeable, and on examination showed the presence of hypermetropia in one eye.

It will be remembered that the normal or emmetropic eye, when the accommodation is at rest, is accurately adapted for parallel rays, which come to a focus on the retina, forming on this membrane sharply defined images of distant objects, from which these rays emanate. This is accomplished without any action of the accommodation, which is left unrestricted for its normal purpose of adjusting the dioptric apparatus of the eye for the divergent rays issuing from objects close at hand.

In hypermetropia, on the contrary, we find the dioptric system of the eye, when the accommodation is suspended (this is a supposed condition, however, and one that seldom occurs.  Because in this defect the accommodation is in active and continuous use), on account of the shallowness of the ball, arranged for the refraction of convergent rays, as no other form of rays can be united on the retina in the production of a clearly defined image. Now it is a well-known fact that in nature all rays of light are either parallel or divergent, and hence the hypermetropic eye, being conformed for convergent rays, is adapted for a condition which does not naturally exist.

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