Hyperopia and presbyopia
Hyperopia and presbyopia are two common optical defects, which can be added and penalize the vision of far and near, making it necessary to port a lens correction (glasses, lenses) for all activities of daily living. This page is dedicated to the explanations to understand the commonalities and differences between hypermetropia and presbyopia. and surgical techniques for correcting them.
Light Hyperopia is often ignored until the age of 40, when the presbyopia is settled. While the near vision decreases rapidly, and involves wearing corrective lenses for reading closely, the vision from afar decreases in turn, while it was excellent before. While he was independent with glasses, the hyperopic became longsighted must equip itself with an optical correction not only to see closely, but also from afar...
"Neither close nor far, you will see yesterday," "You won't see anything near or far." (Excerpt from "The Flower of the Age", by Albin de La Simone)
We will begin by addressing the explanations for the visual disturbances of the farsighted presbyopic, and then the surgical solutions used to correct these patients.
Differences between presbyopia and hyperopia
The presbyopia is related to the gradual loss of accommodation resulting from the loss of elasticity of the Crystalline lens whose ability to deform and allow the objects or texts observed to form a sharp image on the retina decreases over time.
The reduction in the flexibility of Crystalline lens is a phenomenon that begins early in life, but since the capacity of accommodation is very important at birth, it takes 4 decades for the residual accommodation to become insufficient to Meet visual needs closely like reading. The range of net vision distance is reduced: from infinity (FAR) to 10 cm in a young subject, from infinity to 20 cm in a pre-longsighted, and when the nearest point where the vision is still sharp is pushed back beyond 30 to 40 cm , the symptoms of presbyopia appear: The longsighted instinctively tends the arms to read, and must increase the illumination of his work.
Presbyopia thus begins at 43 years in patients with no optical defect in distant vision (Emmétropes), and is characterized by a difficulty in reading small characters closely.
THEhyperopia (or hyperopia) st a common optical defect which concerns the distance vision, but can also interfere with near vision: farsightedness is caused by the fact that the eye is "too short" (insufficient axial length, the light received by the eye is focused in a plane located behind the retinal plan: it receives an image blurred because de-focused). One of the peculiarities of hyperopia is that in light of its forms, and in non-presbytes patients, it can be 'auto-corrigée' by the eye makes a tune-up in accommodating: this accommodation effort is being done to improve vision by far, while this mechanism is normally used to see up close.
To see net off, the Hyperopic therefore accommodates constantly, and to see net closely, it must accommodate even more. The hyperopic is therefore very sensitive to the effects of presbyopia, as the gradual loss of accommodation makes it increasingly difficult to compensate for this optical defect. This is why the close vision can be difficult early in life among the farsighted: all the sooner the hyperopia is important. A 35-year-old patient who feels the need for a correction to read is not an early longsighted, but a hyperopic who can no longer accommodate enough to see net the close, as it already accommodates to see net from afar. Hyperopia and presbyopia combine to alter the vision closely!
As underlined in introduction, moderate and undetected hyperopia is not a visual handicap, at least to quarantine. Previously, it is associated with a TRES good distance vision! Even after the onset of presbyopia, a low farsightedness is a Visual annoyance for intermediate vision or close range (2 to 3 meters), but not for the distances further away (beyond a few tens of meters). Of many hypermetropes become presbyopic arrive to drive without feeling discomfort, because they can see traffic information located at great distance.
Amplitude of accommodation
The range of accommodation is expressed in diopters and is related to the distance between the Punctum point (The furthest seen net point without accommodation) and the Punctum proximum (The nearest net point in accommodating to the maximum). The presbyopia can be defined as a residual accommodation amplitude less than 5 D: the focus cannot be carried out at a distance of less than 1/5 or 20 cm, and it is generally considered that it is necessary to have double the capacity Accommodation required to comfortably read at a given distance (the accommodation required for reading being 2.50 D, an accommodation power of at least 5 D appears as necessary).
On average, most adults experience difficulties in reading closely between 35 and 45 years; The age at which the first difficulties in close vision are felt varies in fact not only according to individual factors, but also according to the potential refractive defect for vision from afar. Patients with moderate hyperopia generally feel the effects of nascent presbyopia earlier (just before 40 years) than patients who do not wear eyeglasses from afar and do not compensate for any optical defects (these Patients are the "real" emmétropes).
In other words, patients with suggestive manifestations of presbyopia around 35 or 40 years are often low farsighted: some are unaware of the existence of this optical defect, that they tolerated well so far. In fact, these patients,. that younger often enjoyed excellent vision, are those for which not only the presbyopia reduces the near uncorrected vision, but also the distance vision ! These weak farsighted, with a form of "latent" hyperopia, have to equip themselves with a correction in progressive glasses, which are often all the more poorly tolerated and accepted that the subjects concerned had never worn glasses before. Indeed, in the past, they used their accommodation to perform permanently and "unconsciously" a precise "focus" for vision from afar, while retaining sufficient reserve accommodative to continue this effort in xxx_xxx 51633470 close focus on a close target.
Low or latent hyperopia
The hyperopia is defined as a state where the refractive eye is such that the light rays from a distant source that are refracted by the cornea and the Crystalline lens form the sharpest image behind the plane of the retina (the Rays do Not converge in the plane of the retina but in the back of it).
Hyperopia is related to insufficient axial length towards the optical power)vergence) combined the cornea and the crystalline lens: the hyperopic eye is usually shorter than the Emmetropic eye, and of course the myopic eye. We correct hyperopia by convex glasses glasses, whose optical power (vergence) is a positive convention. The degree of hyperopia is expressed as the power of the corrector glass required to correct: a farsightedness from + 1.50 D can be corrected by a convex glass the vergence is + 1.50 diopters. As we have reported before, the weak hypermetropia can "auto correct" their farsightedness by increasing the power of their crystalline, IE in accommodating (short-sighted do not have this possibility: instead, accommodating, they improve the blur of the retinal image). The Visual acuity of a farsighted patient who adapted to "correct" this defect can reach or exceed 10/10! The focus of the image on the retina is "modulated" by accommodation, and can in fact be performed fine. The hypermetropic is 'latent', because she can to slip if it paralyzes the accommodation - some techniques of measure for refraction, as well as some eye drops, let make a latent, hyperopia becomes manifest.
Accommodation and latent hyperopia
It is important to specify that the hyperopia is defined for an eye is "at rest", i.e. an eye that does not accommodate. Indeed, the accommodation of the Crystalline lens consists of an increase of the power of the Crystalline lens via the bombing of it. The accommodation allows a emmetropic eye to see net closely, but can also be solicited to further the vision by far from a hyperopic eye.
A light hyperopia (e.g. + 1 D to + 2 D) can be compensated by an accommodation, whose power is expressed in diopters, equal to that of the hyperopia.
A low hyperopia can be compensated by a slight accommodative effort, enough to keep from light rays from a distant source converge in terms of the retina, through the increase of the optical power of the lens. This mechanism is "unconsciously": it provides a very good vision, because it allows to adjust the accommodation so that the development in the plan of the retina is optimally. At the age of 25, a low hypermetropic boasts an excellent distance vision, his uncorrected Visual acuity can reach 12 or even 16 tenths. However, her near vision (example: reading) requires extra accommodative effort. Without correction. the hypermetropic must accommodate twice : for long distance, then to see up close. This poses no problem as long as the amplitude of accommodation exceeds the maximum accommodative effort.
Accommodation and eyestrain
Accommodation can increase the optical lens power, so that the rays emitted by nearby objects are focused in terms of the retina. If the lens (young) was not stretched permanently by ligaments (which forms what is called the zonule), its form was that of a very convex lens, and its maximum optical power. The lens in one eye at rest is in tension, and his front and his back are less curved than the released State. Accommodation requires the game to a complex mechanism, which associated a muscular contraction (ciliary muscle), a relaxation of the ligaments of the zonule, causing a bulge of the lens... as long as it retains its elastic properties, which unfortunately wither over time, which in return causes a decrease in the amplitude of accommodation over time (the crystalline bomb less and less).
To be comfortable and allow a vision extended nearly effortless, estimated as pointed out above that all of the accommodation set game to correct hyperopia and allow to see net close must not exceed half of the total amplitude of accommodation of the patient (approximately). This amplitude is high at birth, but steadily declining then, because the lens of the eye loses its flexibility during the existence. On average, she is 8 dioptres at age 30, but is more than 4 dioptres at age 40. If Visual needs (far and near) require a maximum accommodation of 2.50 to 3 diopters in farsighted patients presbyopia pre including the amplitude of accommodation is more than + 4 diopters, eyestrain symptoms may appear: blurred vision by intermittent, headaches, red eyes, etc.
For example, a + 2 D (latent) light farsighted. This farsighted may request its accommodation to see net by far: it accommodates so close + 2 D. To read 40 cm (0.4 meter), must make an extra effort of 1/0.4 = 2.5 diopters. Altogether, necessary to see accommodation is close to 4.5 diopters for this farsighted (she would only 2.5 diopters at an Emmetropic that does not need to accommodate for net long distance).
Asymptomatic so far, a farsighted + 2 diopters exceeding 30 may feel a fatigue increased in near vision ; However, it isn't yet farsighted, because its amplitude of accommodation is far greater than + 5 diopters.
However, at midlife, when the amplitude of residual accommodation becomes lower than 4 diopters, the accommodative effort needed to see net by far (+ 2 D) exceeds half of the amplitude of residual accommodation: by far the vision blurs late in the day, and near vision becomes very difficult if not impossible without correction in glasses.
A prescription of glasses far then progressive (far and near) should be performed. This patient, who saw from far and near without effort or eyestrain to the 30 or 40 quickly became Depending on the optical correction. If he can dispense with distance vision glasses, near his poor vision forced him to put on glasses for Visual tasks close to everyday life. Reading, DIY, viewing screen of tablets and smartphones, labels, maps, restaurant menus... are impossible without glasses.
Thus, latent hyperopia is a State where the distinction between Beginner presbyopia and hyperopia with a pre-presbyte is sometimes difficult. When we measure the refraction of a low hypermetropic, is needed to use so-called "interference" techniques that are designed to minimize the accommodation.
Can also be used for so-called "cycloplegics" eyedrops to paralyze the accommodation (cycloplegia). Besides using these drops in children, which accommodates very easily and sometimes in very important... which can conceal strong hypermetropies.
Effects of glasses
One can show that for a same correction absolute value (ex: + 3 D vs - 3 D) hypermetropia corrected vision at a distance by convex lenses have to equal residual accommodation amplitude, an accommodative effort to see closely compared to short-sighted corrected vision at a distance by concave lenses. This factor explains that the young presbyopic hypermetropes need a slightly stronger than the young myopic presbyopic correction for vision (adding) closely.
Thus, after a period or the view was often excellent, the weak hypermetropes need a distance vision correction between 35 and 40 years, then a correction close to correct presbyopia in midlife.
Surgical correction of hyperopia, presbyopia
The Hypermetropique LASIK is the most suitable surgical technique for the correction of low to moderate hyperopia (up to + 3.50 D) in Young longsighted (40-55 years). Not only is LASIK effective on vision from afar, But this technique promotes the recovery of a near uncorrected visual acuity because it naturally induces a certain degree of multifocal corneal. This multifocal can be modulated using some of the so-called "aspherical" laser ablation profiles.
Thus,. the presbyopic hypermetropia, whose farsightedness is between + 1.50 D and 3 D are good potential candidates for LASIK refractive surgery, because the synergistic effect of the vision by far on the near vision correction allows maximize their independence to the corrective lenses in post operative. This effect can be potentialized by some adjustments during surgery: for example, the size of the optical zone programmed can be modulated to accentuate the multifocal effect of the correction, and a little more on the non-dominant eye correction allows to increase vision closely on this side.
Thus, the depth of field of the hyperopic eye surgery LASIK increases significantly in the postoperative period. Adjustments to increase the natural multifocalite corrections in hyperopia LASIK-induced are sometimes combined and presented as a technique of "presbyLASIK. The contours of this term are rather vague, as the correction of hyperopia (far vision) is a source of multifocalite, and there are sometimes subtle differences between multifocalite and monovision: a certain degree of "over-correction" is always done on the side of the eye non-dominant with these techniques... "PresbyLASIK' as the Supracor techniques are mainly proposed and issued at farsighted presbyopes. The Supracor is an algorithm providing a profile of aspheric ablation to induce a multifocalite at the presbyopic farsighted.
Some laser platforms (ex: Alcon/Wavelight) allow to aim a particularly negative Asphericity for postoperative corneal profile, by an adjustment of the corneal Asphericity factor (commonly referred to as 'Q factor'). A nomogram (check) of treatment can be developed from this feature the Alcon/Wavelight company called "custom q", for the correction of presbyopia and hyperopia. The author of this site has developed a non-empirical technique that allows a multifocal aspheric correction for the eye no dominant presbyopic hypermetropia (here in English). Other laser platforms (Zeiss / "Laser blended vision" renamed "Presbyond") also offer some modalities of treatment for presbyopia correction, and are more particularly suited to the presbyopic hypermetropia, but the mechanisms involved are not revealed.
In the vast majority of the case, to remember that the multifocalite induced by hypermetropique LASIK is mainly related to an increase in the rate of negative spherical aberration, itself is secondary to the induction of a profile hyper-prolate aspherical after surgery.
The installation of a corneal implant KAMRA is also a particularly interesting technique in weakly farsighted presbyopes: it allows to increase the depth of field of the eye where the implant is placed (non-dominant eye).
Some farsighted patients have been sighted in the past, and made radial keratotomy, which was a technique for correction of myopia based on corneal incisions. A common complication of this technique is the appearance of a progressive over-correction (over-correction of a correction for myopia, inducing a farsightedness). Today, these patients, operated during the late 1980s and early 1990s, have reached or passed the age of presbyopia. They may be subject a correction by PKRwhich is effective to reduce their dependence on glasses in far and near vision.
In conclusion, hyperopia is presbyopia potentiate their negative effects on the vision from far and close to midlife. However, when it is feasible, surgical correction in LASIK induced a synergistic beneficial to restore independence to the optical correction in these patients.