The lens is the natural lens of the eye that allows focusing light rays on the retina. In particular, the crystalline lens changes its shape to vary the focal distance and adapt it to the distance of the object to be focused, by a process called accommodation.
The natural lens contributes approximately + 15/+20 diopters (D) to the refractive power of the human eye, while 43 diopters are provided by the cornea.
In the presence of cataract, the lens becomes opaque and must be removed, and the normal refractive power of a transparent lens must be restored. Removal of the opacified lens from the anterior capsule is performed by phacoemulsification and irrigation/aspiration. The modern cataract surgeryallows the capsular bag to remain virtually intact (in fact, a tiny incision is made), so inside it can be placed an artificial intraocular lens (IOL: IntraOcular Lens) to restore refractive power of a natural lens.
Cataract surgery with IOL implantation is the most common eye surgery today, and surgeons have a varied range of IOLs, designed with different designs and materials.
Intraocular lens: all types
IOLs, depending on the material from which they are made, can be subdivided into:
-Acrylics
-Folding (flexible)
-Hydrophobic acrylics
-Hydrophilic acrylics
-Non-folding (polymethyl methacrylate-PMMA)
-Silicon
The use of flexible materials make the lenses easy to insert (with forceps or injection systems) into the eye through very small incisions. Modern IOLs have in fact a optical diameter of approximately 5 mm and are soft and flexible, so that they can be folded and introduced into the eye through a 2-2.5 mm incision that often does not require stitches.
As far as IOL design is concerned, several new technologies have emerged in recent years; the main categories are shown in the table below.
|
IOL |
Features
|
Near | Intermediate |
Far |
|
MONOFOCAL |
Designed to provide clear vision in a single distant focal point.
Required to wear glasses or contact lenses for near vision e.g. reading) |
V |
||
|
MULTIFOCAL |
Designed to be able to see objects at all distances without glasses or contact lenses.
High probability of glare or slightly blurred distance vision |
V |
V |
V |
|
ACCOMODATING |
Designed to correct de-focussing at near and intermediate distances. The lens changes the optical power of the eye by axial, forward-backward movement, or flexibility in lens thickness or shape | V | V | V |
| EDOF
(extended depth of focus) |
Designed to increase depth of focus in order to generate progressive multifocality (continuous fires). Absence of halos and glare |
V |
V |
V |
The choice of the most suitable intraocular lens to be implanted is important for the success of the procedure of cataracts and the resulting patient satisfaction. For this reason, the specialist, after a thorough consultation and preoperative examination, will decide whether the patient is a good candidate for surgery and which IOLs are best for optimal success that can, in cases with the appropriate optical conditions, even lead to the elimination of the need for glasses.
Sources
–Intraocular Lens Materials and Design. Oliver Findl. Achieving excellent in cataract surgery-chapter 12.
Dr. Carmelo Chines
Direttore responsabile
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