Hyperopia is a common optical defect, characterized by the existence of a too short look. The image formed on the retina by a farsighted eye at rest is blurred, because from the observed target light rays converge in a plane located behind the retina. If the distance between the cornea and the retina is too short compared to the focus distance of the cornea-crystalline couple, Visual symptoms of hyperopia are variable and depend on the age of the farsighted subject, on its degree of farsightedness, and the existence of an associated with presbyopia. In all case, the farsighted sees even more unclear that the objects he sees are close together.
Distance vision (10 meters and in the past) is sometimes preserved, and some hypermetropes are happy with their long-range vision, while objects located a few meters, as in an office room, seem more or less blurred.
On the optical plan hyperopia is mainly related to a insufficient axial length of the eye, which is that the image of a distant object is de-focused spontaneously behind the retina. The image projected in the plan of the retina is blurred.
Hyperopia is corrected by lenses of glasses or convex lenses: these features make rays converge retinal plan. The degree of farsightedness in diopter (ex: + 2 D) corresponds to the power of the glass required to refocus the image on the retina.
In some case, much rarer, hyperopia is mainly related to corneal power (vergence) insufficient. The cornea is not curved enough, not quite fast after refraction by the corneal diopter incident rays converge.
Signs associated with hyperopia
There are two types of hyperopia: farsightedness low and moderatewhich is often well tolerated (hyperopia latent) and does not require the patient to correct permanently (at least until the installation of presbyopia to 40 years), and hyperopia strongwhich requires a fixed permanent, generally appears in early childhood, and is often associated with disorders of binocular vision (strabismus) or amblyopia. The border between these two types of hyperopia is located around 2 to 3 dioptres.
If hyperopia is moderate, theaccommodation (normally reserved for near vision) may be jeopardized in order to re - focus the image of the object away on the retina. Distance vision is corrected, but at the cost of an effort signals more or less permanent. However, this effort is well tolerated in young subjects (see the) page dedicated to the hyperopia and presbyopia). Vision away from the weak hypermetropia is paradoxically excellent, because a focus on the retina is perfect and can be adjusted to an optimal perception ("principle of the" auto focus"). The moderate hypermetropia more often judge their far excellent vision, especially for 'very remote' targets: road signs, etc. The notion of 'distance' differ substantially among the farsighted with respect to the short-sighted; a farsighted considers remote targets tens of meters, while for the myopic, an array of Visual acuity 5 meters is part of the domain of the distant.
If the vision of "far away" is good, to be clear, near vision requires farsighted patients an extra effort which can, especially if it is extended (reading, nearly painstaking work, ect.), induce a various symptoms "Visual fatigue": light-sensitive and easily irritated eyes, headache, vision is blurring by intermittent, intermittent eye redness, ect.
The "moderate" hypermetropes have often received in childhood or adolescence of a so-called eyeglass prescription "to rest", they wore for homework or watch TV. A large proportion of the moderate hypermetropies unnoticed and not to unmask that around the age of presbyopia.
Thus, moderate hyperopia is often very well tolerated (because of the accommodative compensation), appears relatively late, in is "décompensant" sometimes during installation of presbyopia. The power of the compensatory accommodative effort decreases, allowing more patients to see net far without correction in a comfortable way. Patients, who have never worn glasses, must, to the quarantine, to equip themselves not only for vision closely, but also sometimes for the vision by far. except for undemanding activities and targets very far away (because of the optical defect involved,) and clinical factors as the diameter of the pupil, the moderate hypermetropes see their vision of far relatively satisfactory for distant objects, to several tens of meters, while the measure of their Visual acuity uncorrected 5 metres is less than 10/10.
Hyperopia medium to high
If hyperopia is more important (or already well installed at a medium hypermetropic presbyopia), it will induce an important gene in vision closely from afar, accommodation no longer sufficient in total compensation.
Unlike the 'weak' hypermetropia in which Visual disorders begin after 40 years, the 'strong' hypermetropia are usually corrected as a child and often present a history of strabismus was sometimes the subject of surgery.
Strongly farsighted eyes setting usually involves external rotation marked with respect to the optical axis of the eye, and an increase of theKappa angle. These considerations are important in refractive surgery to perfect centering of the laser corrections.
This type of farsightedness is observed after surgery of myopia by the technique of radiaire keratotomii; in some patients, there is a prolonged effect of surgery, which leads to a correction and a secondary hyperopia. One correction by PKR for hyperopia post radial keratotomy is possible in most of the case.
A strong farsightedness is also result of a cataract surgery where it has not been placed implant)aphakia). The removal of the lens corresponds to the withdrawal of a biconvex lens, whose power in the eyewear plan is equivalent to 12-to-15 D (20 D about in terms of the lens). The placement of an implant of artificial lens is intended to so to compensate for this loss of optical power and correct a farsightedness which would not reduce vision and force the patient to wear thick convex glasses in case of non-pose of implant.
A secondary hyperopia can be observed in a patient operated on cataract who received an implant of power lower than that which would have been necessary to obtain the emmetropia (from afar clear vision without glasses).
Correction of hyperopia
Hyperopia is corrected by the use of glasses or lenses glasses convex to refocus the image of an object far closer to the retina. The power of these glasses, expressed in Diopter, is positive (ex: + 3 D).
More farsightedness is important, more corrective glass will be curved and so thick in the Center (like a magnifying glass). In addition to the unsightly side, such glasses can induce a magnification of images and a narrowing of the peripheral Visual field.
Contact lenses will avoid these problems subject to their tolerance and acceptance.
The most effective refractive corneal surgery for the correction of Hyperopic is LASIK, which uses the excimer Laser to induce a bulge of the central part of the anterior face of the cornea. After LASIK, the vision becomes clear without any effort of accommodation, and visual fatigue can disappear. In case of early cataract, or high hyperopia in the subject of quarantine and more (> + 6 D), the removal of Crystalline lens with the installation of an artificial Crystalline lens implant can be Indicated.
The correction of hyperopia low and medium is made elective way by the technique of the LASIK. It has some features that are discussed in the following pages:
Learn more about: hyperopia surgery – the hypermetropique LASIK – hypermetropiques photoablations
The hyperopic eye biometrics
The hyperopic eye is an eye on average shorter than the Emmetropic eye, and of course the myopic eye.
The Visual setting of the hyperopic eye usually results in a slight external rotation of the eyeball towards its optical axis (centerline). THEVisual axis an angle relatively more great with thepupillary axis the Emmetropic and the myopic: increase of thekappa angle. The reflection of a light target set by the patient is thus formed in a nasal portion of the entry pupil.
The anterior segment (cornea, room earlier, crystalline) is statistically shorter, but the proportion of shortening is usually smaller and relatively little commensurate with that of the posterior segment. This can cause some problems with respect to the calculation of cataract surgery implant. Formulas adapted to short eyes are Holladay 2 formulas, and Hoffer Q Haigis.
Following biometrics has been obtained for a nanophtalme look. The nanophthalmia is an impairment of ocular development, is a rare congenital malformation. The growth of the eyeball is hampered, but the volume of the lens remains significant with respect to that of the entire eye. The wall of the eye (sclera) is usually thickened. This reduction in the volume of the anterior and posterior segment exposes to various complications, such as by angle closure glaucoma, uveale effusion syndrome, etc.