Ординатура / Офтальмология / Английские материалы / Mastering theTechniques of Lens Based Refractive Surgery (Phakic IOLs)_Garg, Alio, Dementiev_2005

Figure 3.13: Implantable contact lens – ICL (Staar©-Monrovia, CA, USA)

This is a one-piece lens made purely of silicon, a soft, elastic, hydrophobic material. Its refraction index is 1.46. The lens was designed to float in the posterior chamber but studies performed with the UBM indicate the lens is generally placed on the sulcus, zonula or ciliary body.9 For the implant of the PRL, an anterior chamber depth equal to or greater than 3.0 mm is recommended (excluding corneal thickness), as well as two Yag laser iridotomies or a surgical iridectomy before lens implant.10

There are three different models available (Fig. 3.15): one to correct hyperopia (model PRL-200) and two for the treatment of myopia (models PRL-100 and PRL-

Figure 3.14: Toric-ICL (Staar©-Monrovia, CA, USA)

Figure 3.15: Phakic refractive lens – PRL (IOLtech©-La Rochelle, France). A): PRL 200 for hyperopia. B): PRL 100 for myopia

101). Model PRL-200 is 10.6 mm long, 6.0 mm wide, has an optical zone of 4.5 mm and comes in powers of +3.00 to +15.00 D in 0.50 D increments, allowing a maximum correction of +11.00 D of hyperopia. The properties of the PRL-100 and PRL-101 models respectively for myopia are: length 10.8 mm and 11.3 mm, optical zone 4.5 to 5.0 mm for both depending on lens power, width 6.0 mm for both, dioptric power –3.00 to –20.00 D in 1.00 D (PRL-100) and 0.50 D (PRL-101) increments and maximum correction for both of –23.00 diopters of myopia. The main difference between the two models is the length of the lens and the choice of model is based on the white-to-white distance of the eye.9 The manufacturers suggest the measurements provided in Table 3.2 to select the most suitable model.

Table 3.2: Selecting the best PRL model for myopia according to the white-to-white (W-W) distance

Although some injector models have been used to implant this lens, at present the company recommends

their placement using forceps through a self-sealing corneal incision 3.5 to 4.0 mm long.

Precrystalline Lens

In 1995, Joaquín Barraquer in collaboration with Corneal WK© (Paris, France) developed a rigid posterior chamber lens fixed on the sulcus, which is now in its third generation.

The lens is composed of PMMA and has a rigid 6.0 mm optical zone with flexible haptics that rest on the sulcus. Its anterior surface is slightly convex and the posterior side is concave. Its overall diameter is 14.0 mm, with a lens body 9.0 mm long and 6.0 mm wide, and two platforms in the optic that rest above the anterior crystalline lens capsule, which help the excursion of the iris and avoid pupillary capture of the lens. The body of the second generation lens is 8.0 mm long and pupillary capture has been observed during spontaneous pupil dilation.11 Attempts to avoid this complication by lengthening the platforms by 0.5 mm to give a final length of 9 mm have led to the third generation lens (Fig. 3.16).

The main complication of the first generation of this lens was the adhesion of the lens to the crystalline through a vacuum effect. This gave rise to myopization as the anterior crystalline surface bellowed and to an increased incidence of cataract, since the space between the lens

Figure 3.16: Second and third generation models of the precrystalline lens (Corneal WK©-Paris, France)

and the anterior surface of the crystalline lens was lost.9 This problem was resolved in the second generation by creating drainage ducts on the posterior lens surface such that the aqueous humor could freely circulate between the lens and the anterior surface of the crystalline lens.

Since this lens is rigid, its implant in the posterior chamber requires a wide incision. Two iridotomies using the Yag laser are recommended prior to surgery to avoid pupillary block and secondary glaucoma due to angular closure. This lens allows the correction of severe myopia from –10.00 to –30.00 D.

REFERENCES

1.Strampelli B. Lentilles camerulaires après années d’expériences. Acta Cong Ophthal Belgica (Brussels) 1958; 11:1692-98.

2.Rodríguez A, Cardoner A. Lente intraocular fáquica ZSAL-4 para la correcci©n de la alta miopía. In: Menezo JL, Guell JL, eds. Correcci©n quirúrgica de la alta miopía. Barcelona: Espaxs 2001; 296-303.

3.Menezo JL, et al. Lente de sujeci©n iridiana tipo Artisán. En: Menezo JL, Guell JL, eds. Correcci©n quirúrgica de la alta miopía. Barcelona: Espaxs 2001; 19:305-23.

4.Fyodorov SN, Zuev VK, Azanabayev BM. Intraocular correction of high myopia with negative posterior chamber lens. Ophthalmosurgery 1991;3:57-58.

5.Merlin F, Caramello G. Lenti intraoculari per la correzione della miopia in occhi fachici: premessa e cenni storici. In Merlin F, Caramello G (Eds): Chirurgia refrattiva. Principi e tecniche. Italia: Fabiano Editore, 2000;491-95.

6.Trindade F, Pereira F. Cataract formation after posterior chamber phakic intraocular lens implantation. J Cataract Refract Surg 1998; 24:1661-63.

7.Fink AM, Gore C, Rosen E. Cataract development after implantation of the Staar Collamer posterior chamber phakic lens. J Cataract Refract Surg 1999;25:278-82.

8.Dementiev D, Hoffer KJ, Sborgia G, et al. Phakic Refractive Lens for correction of myopia and hyperopia. In: Agarwal S, Agarwal A, Pallikaris IG, Neuhann TH, Knorz MC, Agarwal A, Eds. Refractive Surgery. New Delhi: Jaypee Brothers 2000; 440-61.

9.Hoyos J, Cigales M, Castanera F, et al. Ultrasound biomicroscopy evaluation of the PRL. New Technologies in Phakic Refractive Lenses. Ocular Surgery News. Europe/ Asia-Pacific Edition. Marzo 2002; 11-13.

10.Hoyos JE, Dementiev DD, Cigales M, et al. Phakic refractive lens experience in Spain. J Cataract Refract Surg 2002; 28:1939-46.

11.Barraquer J, Uxó M. Corrección quirúrgica de la alta miopía. Indicaciones, técnica, complicaciones y resultados. Arch Soc Canar Oftal 2000; 11:109-15.

Antonio Marinho

Maria Ceu Pinto

Fernando Vaz (Portugal)

CORNEAL SURGERY FOR MYOPIA AND

HYPEROPIA: AN OVERVIEW

The cornea is the most powerful refractive surface of the human eye. Its convex power ranges generally from 39 to 46 diopters. So it is quite understandable that the first attempts to change the refraction of the human eye were focused on that structure. In addition to its refractive power the cornea offered other several advantages to that purpose, such as the fact that it allows the surgery to be extraocular, with easiness of access and manipulation.

As a matter of fact corneal surgery for astigmatism dates from the late 19 century when Lans1 described relaxing incisions in the cornea. However, modern refractive surgery is considered to be born in 1949, when Jose Ignacio Barraquer described a surgical technique named keratomileusis.2-6 In this technique a disc with two-thirds of the thickness of the cornea was cut using a microkeratome; then it was frozen and its curvature was modified according to the refraction (myopia or hyperopia) by means of a rotating device. In the last step of the operation the disc was sutured back (Fig. 4.1).

Although historically this type of keratomileusis was a giant step to the advancement of corneal refractive surgery, because it established the principles of changing the central corneal curvature to correct myopia (flattening) and hyperopia (steepening), it was never a popular procedure due to the following:

a.Complicated surgical technique needing costly and difficult devices

Figure 4.1: Keratomileusis

b.Long recovery of visual acuity (1 year) due to the freezing of the keratocytes

c.Poor predictability of the refractive results

d.Use of small optical zones (max 4.2 mm)

e.Sometimes induced irregular astigmatism leading to important losses of lines of Best Corrected Visual Acuity

(BCVA)

Keratomileusis was performed in any degree of myopia and hyperopia but mostly in important ametropias.

Keratomileusis was simplified in the 80s by Barraquer, Krumeich and Swinger7 who replaced the freezing technique by a set of moulds and using an artificial anterior chamber. This nonfreezing keratomileusis, as it was called, presented two advantages over its predecessor: the recovering time was much shorter (4 to 6 weeks) and the surgery was somewhat simpler although it remained difficult and in need of costly equipment.

The last version of keratomileusis was introduced in 1990 by Luis Ruiz and was known as keratomileusis “in situ”. This technique available only for myopia introduced the concept of removing a 160 micra corneal disc of parallel faces (no refractive power) and then performing a second cut (refractive) with diameter and thickness according to the intended correction. Then the first disc was replaced with (Ruiz)or without(Guimaraes) suture. This technique with a rationale so similar to present day Lasik was short lived. As a matter of fact although the surgical procedure was now easy and accessible to the average ophthalmic surgeon and the recovery was now a matter of days, all the accuracy and predictability problems associated with the mechanical (blade) aspects of the refractive cut remained as well

as the often reported poor quality of vision due to small optical zones and induced astigmatism.8

In the last part of this chapter a personal study (1993) comparing keratomileusis in situ and phakic IOLs will show striking differences between the two procedures.

A different approach to refactive corneal surgery for myopia was introduced by Sato in Japan in 1951.9,10 In Sato’s radial keratotomy the needed flattening in central cornea to correct myopia was achieved not, as in keratomileusis, by taking tissue out of the central cornea (direct effect) but by means of radial peripheral incisions, both on the anterior and posterior surface of the cornea causing the central flattening (indirect effect). The original Sato technique turned in disaster in many cases, because the incisions on the posterior surface of the cornea caused important damage to the corneal endothelium.

However this idea of correcting myopia by means of radial incisions was revived by Fyodorov in Russia in 1974.11 In modern Radial Keratotomy (RK)12 incisions were only performed on the anterior surface of the cornea in different numbers (4 – 16) and lengths (optical zones 3.0 – 4.0 mm) according to the desired refractive correction.

Radial keratotomy was a very simple surgery, not needing special surgical skills or costly equipment.(Fig. 4.2) It was very effective in low myopia (up to –3.00) and moderately effective up to –6.00. It was relatively safe (although progressive hyperopia is reported in 10 to 30 percent of cases in different series),12 so became the refractive procedure of choice before the advent of Excimer Lasers.

An incisional surgery for hyperopia (Hexagonal Keratotomy) introduced by Mendez) was never performed in a large basis due to poor predictability and important corneal complications.

The advent of Excimer Laser caused a revolution in refractive surgery. Excimer Laser photoablation surgery is based in the principles of the “old” keratomileusis described by Barraquer. The difference was, that not only any type of tissue ablation was possible (central, peripheral, round, annular, elliptical, etc.), but the precision of this ablation was dramatically increased from the mechanical devices of the past.16

Figure 4.2: Radial keratotomy

The first surgery performed with Excimer Laser was Photo Refractive Keratotomy (PRK). In PRK the epithelium was manually removed and the photoablation was performed.

First reports and publications presented PRK as nothing short of a miracle. An extremely simple and easy surgery that was suggested to the correction of myopia up to –20.00.17,18 However, the reality proved to be quite different. First as the Bowman membrane of the cornea was not respected (it was ablated by the Excimer Laser),some eyes developed a reticular scar (known as “haze”)19 with induced myopia and losses of lines of BCVA (Fig. 4.3). Although this haze was more common in important ablations (more than 6 diopters) it could be present with any amount of ablation. Some hazes would disappear spontaneously or with steroid treatments in a few months, but in other cases severe hazes can persist for many years.

Although severe haze was the most frightening complication of PRK, there was also very important regression in some cases due to important epithelial hyperplasia and possible corneal ectasia.

In Laser in situ Keratomileusis (LASIK) first described by Ioannis Pallikaris in Greece20 a corneal flap with a

Figure 4.3: Haze after PRK

hinge (mostly superior or temporal) is created (Figs 4.4 and 4.5) and then the laser ablation is performed in the stroma. The flap thickness ranges from 130 to 180 micra.

As the Bowman membrane is not ablated the problem of haze disappeared, and as the epithelium is not disturbed, the sometimes severe pain associated with the first postoperative days in PRK does not occur in LASIK. Also the time of recovery of PRK that was measured in weeks (due to corneal healing) is now with LASIK measured in hours. As a matter of fact most LASIK patients have recovered their visual acuity in 24 hours.

Figure 4.4: Lasik: Creating a corneal flap with a microkeratome

Figure 4.5: Lasik: Lifting the flap before laser ablation

LASIK became the most popular form of refractive surgery until now, both for ophthalmologists and the general public mostly for the following reasons:

a.Easy surgery

b.Associated with few complications during surgery and the immediate post-op

c.Almost no pain

d.Extremely rapid recovery of vision

LASIK is now the standard of care in corneal refractive surgery, and in some centres the only refractive procedure performed. But is LASIK a possible option for almost all the refractive errors? As with PRK, LASIK has been suggested to treat an important range of myopia (–1.00 to –20.00) and of hyperopia (+1.00 to +6.00).

However important complications have led most surgeons to lower dramatically the limits of LASIK.

In the following parts of this chapter we will try to establish the rationale for the limits of LASIK, pointing to the important complications that can occur when these limits are not respected, and finally showing some comparative studies with alternative methods, when LASIK is not the procedure of choice.

LIMITS OF LASIK

To understand the limits of LASIK, we must take in consideration some anatomical data of the cornea, that are modified by the laser ablation.

The cornea is a convex avascular and transparent structure made of five different layers: the epithelium, the Bowman membrane, the stroma, the Descemet membrane and the endothelium. The total thickness of the cornea in normal subjects has important interindividual differences, but very small intraindividual variation, ranges from 500 to 600 micra. However corneas between 450 and 500 micra are present through life without any clinical problems. Another important issue in corneal anatomy is the corneal curvature. The usual corneal curvature is between 39 and 46 diopters.Corneas with a higher curvature are considered a sign of subtle keratoconus.

To achieve a change in refraction, the laser ablates the cornea in such a way that the above mentioned properties of the cornea are modified.

So, in myopia the laser ablates tissue from the central cornea creating the following changes:

a.The central cornea becomes thinner (reduces thickness)

b.The cornea becomes flatter (reduces the curvature). In hyperopia, the laser ablates tissue in an annular

form, leaving the center undisturbed, inducing the following changes:

a.The central cornea becomes steeper (increases curvature)

b.No change in thickness in central cornea.

Another important point in the mathematical concept of changing the refraction of the cornea by means of a laser ablation is the fact that it is possible to obtain the same change in curvature (so the same refractive modification) with different amounts of tissue ablated (different changes in corneal thickness). This leads us to the notion of Optical Zone. In fact all corneal refractive procedures (LASIK included) do not change the refraction of the entire surface of the cornea but only the power of the central part. The optical zone is defined as the area of the cornea where the maximal correction of the refractive error is achieved.

As stated before it is possible to obtain the same refractive correction ablating different amounts of tissue. This fact is dependant of the optical zone, i.e. the smaller the optical zone, less amount of ablated tissue is needed

to obtain the same refractive change. So, reducing the optical zone it is possible to correct very high degrees of ametropia, without compromising too much the corneal thickness. In fact this was the basis of all the keratomileusis procedures.

The importance of the size of the corneal optical zone arises from the fact that the cornea, although being the most important ocular diopter is not the only one. The refracted light in the cornea travels through the pupil (acting like a diaphragm) to be refracted again by the lens and finally reach the retina. The pupil being a dynamic structure changes its diameter according to the light intensity, having a smaller diameter as light intensity increases. So, when after a refractive procedure the optical zone it is smaller than the pupil, the central rays are correctly focused in the fovea, allowing the patient to see a sharp image, but the peripheral rays refracted outside the optical zone will be not correctly focused, giving the patient a blurred image encircling the sharper central image. This can occur in all light conditions,(very small optical zone or too large pupil) but is more often experienced in low light, because the physiological mydriasis enhances the problem. This the anatomical basis for the so common night vision problems and halos often referred by patients after refractive surgery.

The previous considerations lay the basis to establish the limits of LASIK. When considering doing a LASIK we must be aware of three factors:

a.The depth of ablation and the consequent final corneal thickness

b.The final corneal curvature

c.The optical zone related to the pupil size.

As it was stated before, the normal cornea has in

most individuals a thickness between 500 and 600 micra. The flap thickness in LASIK is in most cases 160 micra (130 to 180). As the flap does not contribute for the corneal stability as demonstrated by the relative success of the ALK-H (automated lamellar keratoplastyhyperopia, where the hyperopia was corrected by just cutting a two-third thickness corneal disc and putting it back creating a “controlled corneal ectasia”) and a few complicated LASIK cases where the flap was removed without developing ectasia, the available cornea before

ablation is between 340 and 440 micra. It has been widely accepted (although not scientifically demonstrated) that a stromal residual bed of 250 micra is needed to avoid ectasia. This leaves us with a maximum ablation from 90 to 190 micra. This shows that the pre-op thickness of the cornea sets different limits of correction. This ablation values are the total ablation than a cornea can endure (enhacements included). Another important point we must be sure before performing a laser ablation, is that the flap is indeed 160 micra. Thicker flaps can lead to dangerous consequences, and we know that the flaps created by most microkeratomes are not exactly as intended (thinner or thicker); so,the flap thickness must be measured intraoperatively.

Some considerations must be done on the subject of the so-called “thin” corneas. There are apparently healthy corneas with a thinner than 500 micra. Although anterior corneal surface topography is generally normal and these corneas may remain stable though life, some of them can represent subtle forms of keratoconus (as shown in some cases by posterior corneal surface topography) and ablating these corneas can be dangerous. We advise that no laser ablation is to be performed in any circumstances in a virgin cornea with a thickness less of 500 micra.

As we have seen above in very thick corneas the theoretical ablation could be very important. However, it is not advisable to perform an ablation greater than 130 micra in one session.

Regarding the issue of corneal thickness the guidelines for a safe LASIK are as follows:

a.Do not perform LASIK in corneas thinner than 500 micra.

b.Measure the thickness of your flap intraoperatively.

c.Leave a stromal bed at least 250 micra after ablation (including enhancements).

d.Do not perform ablations more than 130 micra (even in very thick cornea).

Laser ablation, not only changes the corneal thickness, but also changes corneal shape. It flattens the cornea in myopia and steepens it in hyperopia. Moreover, it changes the normal aspheric form of the cornea, creating new edges (transition zones of the present day lasers

minimize this effect, but do not annul it). The normal cornea has a curvature between 39 and 46 diopters. A cornea with a curvature of more than 47 diopters is considered a suspect of keratoconus and shall not be ablated. The physical properties of the cornea allows us to flatten it to a minimum of 34 diopters and to steepen it to a maximum of 48 diopters. Going outside this range leads to important regression (due to “biological memory” of the corneal tissue) and important visual aberrations (due to dramatic change in corneal shape).

The practical conclusion of these considerations is that it is possible to correct more myopia in steeper corneas and more hyperopia in flatter ones.

As for corneal thickness, we also present some guidelines regarding corneal curvature:

a.Do not ablate corneas steeper than 47 diopters.

b.Do not flatten a cornea below 34 diopters (myopia).

c.Do not steepen a cornea above 48 diopters (hyperopia).

Pupil size is another important issue when performing a laser ablation. As we saw before when the pupil is larger than the fully corrected optical zone, the peripheral rays of light are refracted outside the optical zone causing a blurred annular image around a central sharper one. But if the pupil has not a fixed diameter how can we solve the problem? Pupillometry, a long neglected examination has become important with the development of refractive surgery. The different pupillometers measure the pupil diameter in different light conditions. For purposes of laser ablation we measure the mesopic pupil, that must at least be equal to the fully corrected optical zone.

After these considerations we see that trying to establish the limits of LASIK based solely in refraction (like: my limit for myopia is –10.00 !!!) is an over simplification with potential dangerous complications as we will see later.

For the time being we will show five examples where these important parameters come into play, determining

Conclusion: Although ablation was possible in a convenient optical zone, the corneal thickness and curvature do not ALLOW LASIK

Conclusion: Although corneal thickness is O.K., the final corneal curvature would be theoretically around –31.00 !! Contra-indication for LASIK

Conclusion: Good candidate for LASIK

Conclusion: If LASIK is performed severe night vision problems will be present, including impairment in night driving. Better not to perform surgery

Conclusion: Good candidate for Lasik

These are the real criteria to establish the limits of LASIK. Although we do not establish the limits of LASIK in terms of refraction it is obvious that, for example it is impossible to advise a LASIK in a –15.00 myope. Even if the cornea was very steep(46 diopters) and thick (600 micra) such an ablation would flatten the cornea beyond

reasonable limits and would need a very small optical zone with all its problems.The same criteria would apply to high hyperopia.

For practical reasons myopias above –12.00 and hyperopias above +4.00 are out of the LASIK range.25 However refractions below that range can qualify or not as candidates for LASIK according to the three main criteria:

a.Corneal thickness.

b.Corneal curvature.

c.Pupil size.

COMPLICATIONS OF LASIK

In this section, only the complications of Lasik, related to the disregard of the principles enunciated above will be described. Those complications can arise because the ablation was too deep in a normal cornea (not respecting the 250 micra rule of the stromal bed) or because an ablation was performed in a nondetected subtle keratoconus (attention to thin and steep corneas !). In these both situations a terrible complication of LASIK may occur

—Corneal ectasia.

Corneal ectasia is the most important complication

of LASIK related to bad selection of patients and to too aggressive surgery.

Corneal ectasia has been described after Lasik mostly following deep ablations needed to correct high degrees of myopia.26-29 However in a recent publication a case was described after Lasik for correction of only –6.50.30 The cause of these ectasias can be subclinical keratoconus overlooked before Lasik, but in most cases a normal cornea was present before surgery, but a too deep ablation was performed. Although it is not clearly established the amount of stromal tissue needed to avoid ectasias, most authors agree that a minimum of 250 micra (excluding the flap) is necessary to stay out of trouble.31-33

We will review the literature on this subject as well as our personal experience (4 eyes) and present our present approach to manage these cases.

Corneal ectasia consecutive to LASIK usually (not always) appears after ablations of more than –10.00 in

thin corneas. In our personal experience we have seen four cases after ablations of –12.00,–13.50,–19.00 and –22.00. Two of these cases have been subjected to two laser treatments. The timing of the onset of the ectasia is different in each case, but reports point from 6 to 12 months.30 In our cases the complaining of the patients began after 12 to 18 months.

The ectasia can present itself in two ways. Most commonly (our 4 cases) the ectasia is central, not inducing irregular astigmatism and with fairly good best corrected visual acuity. Figure 4.6 (Scheimpflug photography) and Figure 4.7 (topography) show a typical case of this type of ectasia. In these eyes the ectasia developed over a period of 2 years and then remained stable.

In other cases the ectasia is not central, induces irregular astigmatism and provides a poor best corrected visual acuity. This type is more similar to noniatrogenic keratoconus.

Corneal ectasia after Lasik is always a very adverse effect of the surgery and has to be avoided at all costs. The most important guidelines to stay out of this problem are:

1.Do not perform Lasik (regardless of refraction) in any cornea suspect of subclinical keratoconus (central K readings higher than 46.5 must be considered suspects).

2.Do not perform Lasik (regardless of refraction) in any cornea, where after the ablation you do not leave at least 250 micra of corneal stroma (excluding the flap).

3.To stay on the safe side avoid doing Lasik above –12.00.

The management of this complication of Lasik is in

our view dependant on the type of ectasia and its stability. In most published cases a penetrating corneal graft was performed. However as we all know this kind of procedure is highly unpredictable regarding unaided visual acuity and can turn in a clinical failure for the patient, despite a good surgical technique.

We present our current approach to this problem, with more consevative and reversible surgery using the corneal graft only when other procedures fail (what has no happened yet in our hands).

Figure 4.6: Corneal ectasia after Lasik (Scheimpflug photograph)

Figure 4.7: Corneal ectasia after Lasik (Topography)

In the first type of ectasia, when the apex is central, with no irregular astigmatism and a fairly good best corrected visual acuity, we do not touch the cornea. We only must wait enough to have a stable refraction (usually after 2 years). In three of our cases we used the PISP method (Phakic IOL as a Secondary Procedure), that means we implanted an Artisan IOL to correct the myopia.The Artisan IOL was chosen because is associated with less complications than other phakic IOLS.

When the corneal ectasia is similar to noniatrogenic keratoconus we suggest as first approach the intracorneal rings.34 Intracorneal rings have been used successfully

in residual myopia after Lasik,35 as well in noniatrogenic keratoconus.

In keratoconus (with no apex dystrophy) we are using the intracorneal rings (INTACS Keravision) of 0.40 mm putting the pair of rings in the flattest meridian of the cornea. The rationale of this approach is to add tissue to the flattest meridian and “recenter” the apex.The results are very good and stable for at least 6 months with important gains in uncorrected and best corrected visual acuity. As the corneal ectasia consecutive to Lasik is generally more stable than keratoconus, this method is probably very useful in these situations. A slightly different approach with INTACS has been proposed by Colin.36 In his method two rings of different thickness are used, the thicker being placed “below” the apex and the thinner opposite. Longer follow-up will show which placement of rings is more effective. An alternative type of ring (Ferrara Ring), that is closer to the central cornea may also be used, if the ectasia is central (Fig. 4.8).

The goal of the rings is (as in Keratoconus) not to achieve emmetropia, but to turn optical correction (glasses, contact lenses) possible. So, after the implantation of the rings, if a significative myopia persists the PISP method can be used as a second step.

Only when all this fails (what have not happened in our hands) the penetrating keratoplasty must be performed.

Corneal ectasia after Lasik is always a serious complication that should be avoided at all costs. The present better knowledge of the mechanisms and limits of Lasik will certainly turn these cases in a rarity, but now we keep seeing them as a result of the early enthusiasm with Lasik.

To manage these cases we must not run immediately to penetrating keratoplasty. First rule is to wait (usually 2 years) until the refraction is stable. Second is to study the type of ectasia. If it is central with no induced astigmatism, implant a phakic IOL and do not touch the cornea. If it is a keratoconus-like ectasia insert the rings, wait 6 months and if needed implant the phakic IOL.

We think that using this approach will enable us to obtain a reasonable uncorrected visual acuity, without the need of corneal graft. However, the validity of these guidelines need the test of time, but early results are