Refractive implants are ophthalmic lenses surgically positioned inside an eye, in front of the crystalline lens. They are indicated in patients who cannot have their visual abnormality corrected using a laser technique. They are reserved to persons under 40 years of age who have retained a sufficient degree of accommodation (the crystalline lens has remained in its place). Indications for implants represent less than 5% of all indications for refractive surgery; they are given in cases of severe ametropia (myopia up to 25 diopters or hypermetropia up to 9 diopters) or of atypical corneas (too fine, or irregular).
The optical correction achieved is identical to that obtained by contact lenses, and in terms of visual quality, the results are excellent. The rate of operative complications is very low, identical to the rate recorded for any intraocular surgery (less than 1%), but this type of intervention necessitates regular, lifelong monitoring to screen belated signs of long-term intolerance (appearance of cataract, hypertonia or lowering of endethelial cell density), signs that would necessitate their being changed or ablated.
There exist several models, grouped into two main categories: anterior chamber implants positioned in front of the iris, and posterior chamber implants positioned between the iris and the crystalline lens. Choice of one or the other depends on the anatomic configuration of the eye, particularly the depth of its anterior chamber, as well as the experience of a given surgeon; neither one of the models has been shown to be superior the other.
Prelex ou Presbyopic Exchange Lens
In this case, modification of the overall optical power of the eye is no longer achieved by the addition of a lens inside the eye (refractive implants), but rather by change in the power of the crystalline lens: a natural crystalline lens is replaced by a lens of which the power is adapted to the visual disorder (technique identical to the one used in cataract surgery). Ablation of the natural crystalline lens puts an end to accommodation and immediately renders the eye presbyopic; that is why it is reserved for persons over 50 years of age. Indications are the same as those for refractive implants (severe ametropia or atypical corneas). Correction of induced presbyopia can be contemplated in two different ways, according to the initial ametropia: “swing” for myopic patients (master or dominant eye corrected for distance vision, and non-dominant eye for near vision), multifocal implants for hypermetropic patients. This technique is particularly recommended when there is a cataract, even at the beginning stage, or when the patient is aged (proximity of the age of the person to the age of the cataract).