9. What are the different types of intraocular lenses? Do they give the same visual result?

Advances in technology have led to the creation of numerous new types of intraocular lenses, suitable for the different needs of our patients.

(1) Monofocal lenses are the traditional intraocular lenses and they have been used for decades.
They have the same refractive power throughout all the regions of the eye and therefore are in sharpest focus, at only one distance. The general rule is that the power of monofocal lenses is such, that it facilitates sharpest vision at all distances without the need to wear glasses. Patients who have had monofocal intraocular lenses implanted, usually require reading glasses.

(2) Toric lenses are also monofocal lenses, adjusted to facilitate distance vision and are suitable for patients who, apart from myopia or hypermetropia, also suffer from astigmatism (more than 1.5 degrees).

The difference from monofocal lenses lies in the fact that they need extra care that the lens be positioned in a very specific configuration.

In contrast to monofocal lenses, which have the same power in all eye regions, toric lenses have different power in some regions, aiming to correct current astigmatism in the patients.
This results in the need to accurately position the toric lens inside the capsule, because even a slight divergence can lead to blurry sight.

(3) Aspheric intraocular lenses are an advancement in monofocal lenses with a lot of advantages. While the traditional monofocal lens is uniformly spherical across the surface, aspherical lenses have a more flattened body on the periphery. This special design results in better contrast sensitivity and reduces aberrations which in real terms means better vision especially at night.

In Athens Eye Hospital almost all intraocular lenses used are aspheric.

(4) Bifocal intraocular lenses  have been designed to focus on objects both at close range and in the distance. The upper part of a bifocal lens is designed to focus on objects in the distance while the lower part has increased power to focus on a book, at reading range (30-35 cm).

Nowadays that computers have become an integral part of our lives, they have given rise to the need for acute sigh in an intermediate distance (50-60 cm) that is not covered by bifocal intraocular lenses.

(5) Multifocal intraocular lenses were created with the aim of satisfying focal demands of a wider range of distances ( long distance, medium and short). The surface of multifocal lenses is divided into circular zones (like a target) using different focal power to facilitate the patient in focusing in different distances.

The main disadvantage of these lenses is the reduction in contrast sensitivity. In real terms this means, a greater difficulty in distinguishing more distant objects in conditions where lighting is intense or, on the contrary, dim, for example, during night driving, when one needs to see the pedestrians walking at the side of a poorly lit road.

Most patients report a very satisfactory vision in short or intermediate distances, although a small number of patients may eventually require reading glasses.

(6) Adjustable intraocular lenses is an effort to make artificial intraocular lenses imitate the functions of a natural eye lens. While all the other lenses, either monofocal or multifocal, remain immobile in their position, adjustable lenses move forward to increase the eye’s focal power during the muscle’s contraction, which is normally responsible for the focusing of the eye in various distances. (radial muscle) Despite the advantages of these intraocular types ,in theory, the results are not always those which are expected.

(7) The Tassignon intraocular lenses for child cataracts are a special category, with a lot of advanatages, yet, they require a remarkably difficult and delicate technique to position them.
Apart from the anterior vitrectomy of the capsule, which is anyway performed to suck the natural opaque lense, we also perform capsulorhexis ( a second opening) to the posterior capsule.

While all aforementioned intraocular lenses are positioned inside the open lining that had accommodated the natural eye lens, Tassignon intraocular lenses, owing to their special design, hermetically seal the lining trapping its edges to a special flange running around the perimeter. From one point of view, instead of the lens being placed into the lining, the lining is placed into the flanges of the lens and that is why this technique is also called bag-in-the-lens.

The placement of a Tassignon ocular lens constitutes the ideal solution for complicated cataracts, after inflammations in young children.

This operation is considered to be remarkably difficult, therefore most ophthalmology centres, despite its advantages, avoid it.

Athens Eye Hospital, with its highly experienced surgeons who perform more than 10,000 cataract operations  in Greece and in other countries annually, is the only ophthalmology clinic that can and does perform this operation with accuracy and complete safety.

(8) Experimental intraocular lens designs

8.a.  Light adjustable intraocular lens. This is an intraocular lens design that allows adjustment of the lens at a later stage, after the operation, using ultraviolet light. This is a very sophisticated material, made from a light sensitive silicon and a special microchip. After having achieved the best optical acuity for the patient (even with a multifocal result), another light beam ‘locks’ the shape and the power of the lens.

8.b. Lens refilling.
In reality, this is not a manufactured artificial lens but a special transparent gel that is injected into the sac that contained the opaque natural lens. This method aspires to use the natural focal system the human eye possesses, but it is still far from a clinical application.

8.c. Dual optical lens.
Yet another realisation of an intraocular manufacture that tries to utilize the natural focal system of the eye.

8.d. Μulticomponent IOL.
This lens consists of three optical elements. Its spherical optical element closely resembles an ordinary intraocular lens and it is placed into the capsule, just as in most cataract operations, but it is also connected to two more optical elements ( a toric lens and a spherical or multifocal one), which can be adjusted through a second optional surgery in order to achieve optimal visual result.

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