Intraocular lens

A posterior chamber lens

An intraocular lens (from Latin intra 'inside' and Latin oculus 'eye' ), IOL for short, is an artificial lens in the eye . It is usually implanted after removal of the natural lens ( aphakia ) as part of cataract surgery , but it can also be used in addition to the natural lens ( phakic intraocular lens ). The presence of an artificial lens in the eye is called pseudophakia in ophthalmology .

A new development in intraocular lenses is the light-adjustable lens (LAL), in which the refractive power can be changed and readjusted after the operation by irradiating with UV light.

Aphakic intraocular lenses

The replacement of the body's own lens with an implant is usually due to a clouding of the lens ( cataract ). In certain cases, a refractive lens exchange can also be carried out in order to correct a very high visual defect.

As early as the 18th century, Felice Tadini formulated the idea of artificial lens implantation to Giacomo Casanova . In 1795 Giovanni Virgilio Casaamata carried out an attempt at realization in Dresden. Harold Ridley implanted the first intraocular lens in 1949. Under his leadership, eye surgeons from all over Europe organized the International Intraocular Implant Club (IIIC) in 1966 with the primary aim of compensating for the loss of refractive power in the eye during cataract surgery by implanting an artificial lens. Today it is possible to make such precise predictions of the postoperative refractive power through previous measurements of the eye that the implantation of an artificial lens - which was previously viewed with suspicion - has become the standard. As part of cataract operations, around 650,000 intraocular lenses are implanted annually in Germany (as of 2005).

Structure and variants

MICS-IOL made of acrylic in a holder

An intraocular lens is built up from the central optical lens and the peripherally adjoining haptic , which fixes the optical lens in the eye. The diameter of the optical zone is 5 mm to 7 mm, usually around 6 mm. The haptics can have different shapes, mostly C-haptics or plate haptics are used.

Based on the material, the lenses can be divided into hard IOL and soft, foldable IOL. Foldable lenses are made of acrylic , silicone or hydrogel . The hard lenses are made of polymethyl methacrylate . One-piece intraocular lenses are completely formed from a single material, while multi-part intraocular lenses are composed of different materials. The advantage of foldable lenses is the much smaller incision that is required for implantation. Conventional foldable lenses can be implanted through an incision approximately 3 mm in size. Modern MICS intraocular lenses (MICS = Micro Incision Cataract Surgery ) only require an incision of less than 2 mm.

The intraocular lenses are differentiated based on their optical properties .

Positive refractive intraocular lens: The most common implanted lens, usually around 20 diopters in the originally normal-sighted ( emmetropic ) eye. Aspherical intraocular lenses have particularly good optical properties .
negative refractive intraocular lens: When implanted when the original eye extremely nearsighted ( myopic is).
Toric intraocular lens: Occasionally implanted in eyes with moderate to severe astigmatism .
Multifocal lens: has two or more focal lengths and is intended to enable the patient to live without reading glasses.
Accomodating intraocular lens: Should mimic the accommodation of the natural lens and thereby also make reading glasses superfluous.

Preliminary examinations and treatment process

Implanting an intraocular lens requires a number of preliminary examinations. Precise measurement of the eye is particularly important in order to select the right refractive power for the IOL. Special devices can carry out these measurements quickly and conveniently with the help of ultrasound or light beams.

In most cases, the operation is performed on an outpatient basis and under local anesthesia. The pupil is dilated with medication and, depending on the technique, the required access incisions are made. The body's own lens is smashed with the help of an ultrasound probe and suctioned off. This process is known as phacoemulsification . The covering of the lens, the capsular bag, is retained and the procedure is carried out through a central opening in the anterior capsular bag. Alternatively, the lens can be completely removed with the capsular bag, which has various disadvantages. The IOL is inserted and positioned in the empty capsular bag. It is not necessary to sew up the incisions.

Risks and Side Effects

As with any surgical procedure, there are a number of risks associated with IOL implantation. The type and frequency of occurrence depend on the experience of the surgeon, the technique used and individual factors.

In general, IOL implantation during cataract surgery has a very low complication rate of less than 1%. Possible complications are bleeding, injuries to the cornea (mechanical or thermal), pressure drop in the eye (hypotension), tearing of the capsular bag and others. The most common postoperative complication is the "after cataract". This is a clouding of the posterior side of the capsular bag due to cells caught in the removed body's own lens. This cloudiness can easily be removed by a laser capsulotomy with an Nd: YAG laser . A comparatively rare complication (around 1.5%) affects the retina and is called cystic macular edema . In the first one to three months after the operation, cysts form in the retina, which usually disappear after about six months, but in rare cases leave holes in the retina. Endophthalmitis (infection in the eye) is a very serious risk . With the use of modern surgical techniques, the rate is very low at 0.05%. There is also a risk of lens dislocation with a corresponding drop in visual acuity.

Special features of accommodating intraocular lenses

By changing its refractive power, the body's own lens ensures sharp vision from near to far. By replacing it with an intraocular lens, this function is lost and the eye can only see clearly from a certain distance. The refractive power of the IOL is usually calculated so that the eye has a sharp distance vision. This means that nearby objects cannot be seen clearly and reading glasses are required. Modern multifocal or accommodative IOLs can compensate for this effect to a certain extent. Since the ability to accommodate decreases with increasing age (presbyopia), and cataract patients are mostly at the age at which the eye hardly accommodates, the implantation of such lenses can represent an improvement in near vision.

It is reported, however, that the actually achievable accommodation effect is small.

Further research approaches for accommodating intraocular lenses are liquid-based intraocular lenses (FluidVision from PowerVision, Juvene from LensGen) and electronically controlled intraocular lenses (Sapphire AutoFocal IOL from Elenza).

Phakic intraocular lenses

Phakic intraocular lens

A phakic intraocular lens (PIOL) is an artificial lens which in addition to the natural lens ( ancient Greek φακός phakos ) into the eye is implanted. Phakic intraocular lenses can be implanted as part of the correction of ametropia . This method is an alternative for people with severe ametropia, even if laser surgery is not possible due to opposing indications.

Phakic intraocular lenses were first used in 1953 by Benedetto Strampelli; serious complications occurred with the first implants. Advances in lens design, in particular haptics, and the use of biocompatible materials have made it possible to improve phakic intraocular lenses so that they are now used to correct high refractive visual defects. As refractive operations on the cornea became more and more successful in the mid-1980s , the trend towards implanting phakic lenses revived - mostly among ophthalmic surgeons who did not have an excimer laser . A large number of different phakic lens models have been launched and propagated internationally. Its developers include a. Swjatoslaw N. Fjodorow , Paul U. Fechner , Peter Choyce , Binkhorst and Jan GF Worst .

Structure and variants

A PIOL is made up of the central optical lens and the peripheral haptic that fixes the optical lens in the eye. The optically effective zone of the PIOL has a diameter of 4.5 mm to 6 mm, depending on the type of lens and the dimensions of the eye. Depending on the location of the PIOL in the eye, a distinction is made between anterior and posterior chamber lenses. The anterior chamber lens is implanted between the cornea and the iris and the posterior chamber lens between the iris and the eye lens . There are different ways of attaching the anterior chamber lenses. They can either be fixed to the iris or supported at the angle of the chamber . The feel of the lens is designed differently accordingly.

Phakic intraocular lenses are made from different materials. Anterior chamber lenses are made of either hard PMMA or soft materials such as silicone or acrylic compounds. There are multi-part PIOLs that are composed of different materials. The feel is made of hard material and the actual lens is made of soft. Posterior chamber lenses are always made of soft materials such as silicone compounds or collamer (a product made from a collagen polymer from Visian ICL). Soft lenses can be folded and can therefore be implanted through a smaller incision than hard ones.

The optical properties differ

spherical or aspherical, positive refractive PIOL: is implanted when the eye is extremely farsighted ( hyperopic ).
spherical or aspherical negative refractive phakic IOL: When implanted when the eye extremely nearsighted ( myopic is).
Toric PIOL: Occasionally implanted in eyes with moderate to severe astigmatism .
Multifocal lens: Has two or more focal lengths and is intended to compensate for the effect of presbyopia

Aspherical lenses offer a better image quality than conventional spherical models.

Treatment area and contraindications

The implantation of PIOLs is indicated for the correction of:

Myopia from at least −0.5 diopters (depending on the type of lens up to over -20 diopters)
Clarity from at least +3 diopters (depending on the lens type up to over +15 diopters)
Astigmatism up to about 7 diopters (depending on the lens type)

Contraindications are circumstances that prohibit treatment or allow treatment only after careful consideration of the particular risks. If the patient's refraction is not stable, that is, if the measured refraction values deviate significantly from one another in relatively short time intervals, a PIOL should not be implanted. Anterior chamber lenses require sufficient space. If the depth of the anterior chamber is too small, implantation of such a lens is not indicated. Likewise, the density of the endothelial cells on the posterior corneal surface should not be less than 2000 mm ⁻² . Finally, patients eligible for PIOL implantation should be over 18 years of age and not be pregnant.

Preliminary examinations

The expectations of the treatment result vary greatly from patient to patient and should be discussed extensively with the attending physician in advance. The preliminary examinations serve to record the correct treatment data in order to rule out contraindications and to compare the patient's expectations with the outcome prognosis.

An essential part of the preliminary examinations is the determination of the patient's exact subjective refraction by a qualified optometrist or ophthalmologist. The refraction should be determined at least twice with an interval of at least two weeks. The measurement of only the objective refraction values, for example by means of an automatic refractometer , is in any case insufficient. In addition, the measurement of the exact biometric data of the eye (axial length, keratometry, anterior chamber depth) is very important in order to select the appropriate intraocular lens.

Other important preliminary examinations are:

Measurement of the endothelial cell density.
A general ophthalmological examination of the anterior, middle, and posterior segments using a slit lamp examination
Measurement of intraocular pressure ( tonometry )
A detailed medical history

Treatment process

The procedure is carried out on an outpatient basis and under local anesthesia. The modern foldable PIOL are inserted into the eye through a small incision about 3 mm in size. Non-foldable types require a wider incision of up to 6 mm. The location of the incision depends on the position and type of the intraocular lens. The small incision heals relatively quickly and no suturing is necessary.

Advantages and disadvantages

Advantages of intraocular lenses compared to refractive laser treatments:

High refractive corrections are possible, regardless of the corneal thickness.
The cornea is not destabilized by removing tissue.
It is a reversible procedure, so the lens can be removed again.

Disadvantages compared to laser treatments:

There is a higher risk of infection.
Damage to the corneal endothelium is possible.
The implant is sensitive to mechanical influences on the eye (heavy rubbing, accidents).
The lens can shift and this may require reoperation.
Lifelong check-ups with an ophthalmologist are necessary.

Risks

As with any surgical procedure, there are a number of risks associated with PIOL implantation. The type and frequency of occurrence depend on the experience of the surgeon, the technology used and individual influencing factors. General risks associated with any type of refractive surgery are limitations in twilight and night vision due to reduced contrast sensitivity, glare (glossy effects) and halogons (halos). Short-term to long-term over- or undercorrections as well as a reduction in visual acuity with optimal eyeglass correction ("best corrected visual acuity") can also occur. Infections of the eye are possible with any type of treatment, especially with implants.

When implanting phakic intraocular lenses, there is a risk of damage to the corneal endothelium. Regular postoperative control of the endothelium is therefore absolutely advisable. Particularly with posterior chamber lenses, the body's own lens (cataract) can become cloudy. An increase in intraocular pressure and, in the worst case, a pupillary block with seizure glaucoma (a sudden sharp rise in intraocular pressure due to pupil blockage) can occur after PIOL implantation. With larger incisions (6 mm), the shape of the cornea can change in such a way that there is significant post-operative astigmatism. Angle-assisted lenses can also influence the shape of the pupil. Under certain circumstances this can take on an oval shape.

literature

Bruno Zuberbühler, E. Haefliger, Rupert Menapace, Thomas Neuhann: Cataract surgery . Springer, Berlin 2008, ISBN 978-3-540-79943-6 .
JL Allo, JJ Perez-Santonja: Refractive Surgery With Phakic Iols: Fundamentals And Clinical Practice. Highlights of Ophthalmology, 2003, ISBN 9962-613-21-3 .
Thomas Kohnen: Refractive Surgery. Springer, Berlin 2010, ISBN 978-3-642-05405-1 .
T. Oshika, G. Sugita, K. Hayashi, S. Eguchi, K. Miyata, T. Kozawa, K. Oki: Influence of cataract and intraocular lens surgery on health-related quality of life. In: Nippon Ganka Gakkai Zasshi. 109, 2005, pp. 753-760.

Web links

Commons : intraocular lens - collection of images, videos and audio files

Patient information on cataract surgery and intraocular lenses from BVA and DOG as PDF
Overview of different refractive procedures (University Hospital Salzburg)
Information from the Refractive Surgery Commission
www.iol-test.org - Information from the ITIV on the imaging quality (quality) of intraocular lenses
www.iol-info.de - database of intraocular lenses

Individual evidence

^ Aloys Henning: On the paradigm shift in cataract surgery, especially in Berlin from 1755 . In: Würzburg medical history reports . tape 18 , 1999, p. 271 , PMID 11624384 .
↑ Cataract surgery: Risk of bleeding reduced with oral anticoagulation. In: Deutsches Ärzteblatt 102 (1-2), 2005, pp. A-58 / B-49 / C-46.
↑ ^a ^b T. Kohnen, M. Baumeister, D. Kook, OK Klaproth, C. Ohrloff: Cataract surgery with implantation of an artificial lens . In: Dtsch Arztebl Int . tape 106 , November 2009, p. 695–702 , doi : 10.3238 / arztebl.2009.0695 .
Jump up ↑ Cataracts & Cataracts. Hospital St. Joseph-Stift Bremen, archived from the original on August 17, 2016 ; accessed on August 23, 2016 .
↑ Nadine Eckert: Cloudy view of miracle lenses. In: www.wissenschaft.de. May 17, 2011, accessed November 2, 2019 .
^ David Evans: Accommodating the Demand for IOLs. In: www.bettervisionguide.com. April 23, 2019, accessed November 2, 2019 .
↑ Benedetto Strampelli: Anterior chamber lenses . In: Arch Ophthalmol . tape 66 , 1961, pp. 1-17 .
↑ Myopia, Phakic IOL. Retrieved November 4, 2010 .
↑ ^a ^b Phakic Intraocular Lenses (PIOL) - a current overview. (PDF; 834 kB) Retrieved on August 23, 2016 .
↑ Anterior versus Posterior Phakic IOLs: What is the best lens? Retrieved February 23, 2010 .
↑ Thomas Kohnen, Anja Strenger, Oliver K. Klaproth: Basic knowledge of refractive surgery. Correction of refractive errors with modern surgical procedures. In: Deutsches Ärzteblatt. Vol. 1051, No. 9129, 2008, pp. 163–177 (PDF)
↑ necessary examinations before the ametropia can be corrected. Archived from the original on October 3, 2014 ; accessed on February 11, 2016 .

[1] Aloys Henning: On the paradigm shift in cataract surgery, especially in Berlin from 1755 . In: Würzburg medical history reports . tape 18 , 1999, p. 271 , PMID 11624384 .

[2] Cataract surgery: Risk of bleeding reduced with oral anticoagulation. In: Deutsches Ärzteblatt 102 (1-2), 2005, pp. A-58 / B-49 / C-46.

[Kohnen:_Kataraktchirurgie_S_695-702-3] T. Kohnen, M. Baumeister, D. Kook, OK Klaproth, C. Ohrloff: Cataract surgery with implantation of an artificial lens . In: Dtsch Arztebl Int . tape 106 , November 2009, p. 695–702 , doi : 10.3238 / arztebl.2009.0695 .

[4] Jump up ↑ Cataracts & Cataracts. Hospital St. Joseph-Stift Bremen, archived from the original on August 17, 2016 ; accessed on August 23, 2016 .

[5] Nadine Eckert: Cloudy view of miracle lenses. In: www.wissenschaft.de. May 17, 2011, accessed November 2, 2019 .

[6] David Evans: Accommodating the Demand for IOLs. In: www.bettervisionguide.com. April 23, 2019, accessed November 2, 2019 .

[7] Benedetto Strampelli: Anterior chamber lenses . In: Arch Ophthalmol . tape 66 , 1961, pp. 1-17 .

[8] Myopia, Phakic IOL. Retrieved November 4, 2010 .

[Phake_Intraokularlinsen_(PIOL)-9] Phakic Intraocular Lenses (PIOL) - a current overview. (PDF; 834 kB) Retrieved on August 23, 2016 .

[10] Anterior versus Posterior Phakic IOLs: What is the best lens? Retrieved February 23, 2010 .

[11] Thomas Kohnen, Anja Strenger, Oliver K. Klaproth: Basic knowledge of refractive surgery. Correction of refractive errors with modern surgical procedures. In: Deutsches Ärzteblatt. Vol. 1051, No. 9129, 2008, pp. 163–177 (PDF)

[12] necessary examinations before the ametropia can be corrected. Archived from the original on October 3, 2014 ; accessed on February 11, 2016 .