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When in a hypermetropic eye the accomodative capacity is insufficient to focus the radiations on the retina, eyesight is subnormal and the part of the defect that cannot be corrected by accomodation is called “absolute hypermetropia”.

As a rule, with high levels of hypermetropia a part of it is nearly always absolute.

Lower levels which in youth were facultative become partially or entirely absolute between 55-60 years of age when the accomodative range is reduced by a diopter.

Abolute hypermetropy is also manifest, at an advanced age the hypermetropia is entirely absolute and, obviously, manifest.

With absolute hypermetropia one can have a binocular vision: single, not always single and monocular vision.

Related article: Facultative Hypermetropia

The part of hypermetropia that can be compensated by accomodation is called “facultative”. If the eyesight is normal a part may be manifest and the other part latent.

The latent part is certainly facultative, the manifest part may be facultative or not.

Usually low degrees of hypermetropia are entirely facultative because it is easy for an individual with a good range of accomodation to neutralize the refractive defect of vision at a distance and, generally, to have a single binocular view.

Related article: Total Hypermetropia

If we exclude the age of senility, total hypermetropia is usually in part manifest and in part latent; the proportions vary significantly between different eyes and between the same eyes during the life span. The latent part depends very much on the eye’s accomodation capability which in turn depends on the individual’s age.

In very young individuals and also those slightly older than 30, a small degree of hypermetropia is probably latent and the eye, if checked, is emmetropic. Much later, at 50-55 years, the accomodation becomes that little that it cannot correct the defect, i.e., the hypermetropia becomes manifest.

Usually, the higher the degree of hypermetropia the smaller is the latent part. Thus, if at a given age, total hypermetropia is 1.5 D, it can be totally latent while at 3.5 D the latent part will be half, at 6.0 D instead one can expect that the latent part is not higher than ¼ of the total hypermetropia.

Thus, with a certain approximation, in a total hypermetropia of 3.0 D the half is latent at 20 years of age, ¼ a 30 years, and at 40 will be totally manifest. Frequently this trend changes and we find individuals at 40 with a latent hypermetropia which is ca. ¼ of the total.

Related article: Latent Hypermetropia

All hypermetropics, provided they are not elderly with poor accomodation capacity, excercise this accomodation constantly when viewing at a distance.

This part of hypermetropia is practically hidden and called “latent”.
Obviously it can also be optional.

A part of latent hypermetropia can transform itself in clear hypetropia putting a positive lens, with a power superior to the hypermetropia, in front of the eye.
The presence of latent hypermetropia, and its approximate value, can be determined with the measurement of the closest point to the eye.

Related article: Clear Hypermetropia

In real shortsightedness, the general rule is that for young people the correction prescription must be complete even when the eyesight flaw is slight and the correction must be worn permanently to fight myopia. For slightly hypermetropic children (not more than 1,00 D), having a high accomodation capacity,
there is no reason to correct the flaw with lenses, even though they may be useful at school. Considering the prescription of lenses in the case of strabismus and of severe heterophoria, we can see that there are many exceptions given that in this case the rule consist in influencing the binocular anomaly.

Art. 3/3 Related article: The Prescription of Corrective Lenses (Part 2)

If a subject has in one eye a medium to high refraction flaw, while the other is (almost) normal, we have a problem that cannot be resolved easily because fixing the “nearby” problem without balancing the refraction of the eyes for “far away” vision can cause a problem for the near sight. The problem to resolve is whether to ignore the medium to high refraction flaw and concentrate only on the other eye or both should be treated for the binocular vision. Some times we can use bifocal lenses, especially if the prismatic effect introduced for nearsightness by the different lens strengths can be resolved through bifocals with a compensated prismatic effect. But also here success depends on the patient’s degree of binocular vision. Sometimes we encounter patients that say to feel well; the reason being that the vision of the “bad” eye is suppressed. In that case it is not necessary to prescribe compensating bifocals because it wouldn’t benefit the patient.

Art. 2/3 Related article: The Prescription of Corrective Lenses (Part 1)