Hypermetropia

Hypermetropia (far-sightedness)

One of the refractive conditions of the eye in which light rays fails to focus on the retina. Hypermetropia or hyperopia is the condition of the eye in which rays of light converge to focus behind the retina. This causes close objects to be blurry while far objects may appear normal. If we assume that there is a “normal” axial length and a “normal” focal length for the optical system. Hyperopia can occur in two forms, the axial length of the optical system can be normal and the focal length of the optical system longer than normal, or the axial length can be shorter than normal and the focal length of the optical system normal.

Studies have shown that hyperopia of small amount are normally due of a combination of both axial and focal lengths within the normal ranges for the emmetropic eye. However, hyperopia of moderate to large amounts (about 4.00 D and more) is usually due to axial length being shorter than normal.

Signs and symptoms

Signs and symptoms of hyperopia include small eye ball, small cornea, anterior chamber is shallow and the angle is narrow, blurry vision, headaches, and eyestrain. There is also difficulty maintaining binocular vision and with depth perception.

As already mentioned, in hyperopia the light rays focus behind the retina. With correct amount of accommodation in play, the image formed behind the retina will coincide with the retina, and normal (6/6 or better) visual acuity is obtained.

The extent to which a hyperope’s distance visual acuity can be improved by accommodation is limited by the amplitude of accommodation while near visual acuity in hyperopia is dependent on the amount of hyperopia, the amplitude of accommodation, and the distance at which reading is attempted.

Correction of hypermetropia

Correction of hypermetropia is usually achieved by the use of spectacle or contact convex corrective lenses or positive lenses. The correcting lens must be of such a power that makes the secondary focal point of the lens coincide with the ar point of the eye.

Other methods include; PRK, LASEK, LASIK (Laser eye surgery in which the cornea is reshaped)

Manifest and Latent Hyperopia

Most hyperopes especially the young are pretty good compensating for their defect by accommodating. A condition in which all of the patient’s hyperopia is compensated for by tonicity of the ciliary muscle, is known as latent hyperopia.

With time latent hyperopia may cause severe asthenopia until the hyperopia is found and corrected with appropriate lenses. As people age and their amplitude of accommodation decreases, latent hyperopia tends to become manifest: For this reason, some low hyperopes not requiring glasses (and not having enough latent hyperopia to cause symptoms of eyestrain) find that, as the amplitude of accommodation gradually decreases with age, glasses are eventually required for clear and comfortable vision. The hyperopia was there all the time but became manifest when the amplitude of accommodation decreased significantly.

The strongest convex lens with which the patient can still maintain full distance vision 6/6, indicates manifest hypermetropia.

Absolute and Facultative Hyperopia

Facultative hyperopia is normally confused with latent hyperopia. Facultative hyperopia can (at will) be compensated for by accommodation, latent hyperopia the individual cannot help but accommodate for it. For example, if a person has 3.50 D of hyperopia and 1.00D of accommodation, the 2.50 D of hyperopia that cannot be compensated or overcome by accommodation represents absolute hyperopia. The additional diopter of hyperopia that can be overcome by accommodation is facultative hyperopia. Facultative hyperopia= manifest-absolute hyperopia.

Absolute hyperopia is that hyperopia that cannot be compensated for by accommodation. If a patient can not normally see 6/6 without a lens then the weakest convex lens that will allow him to read this line indicates absolute hyperopia.