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

Figure 7.28: PRL hyperopic lens

procedures in eyes with higher refractive errors. There is also a considerable improvement in BCVA with these lenses because of the magnification factor.

•Highly skilled procedure: Prevents misuse of the procedure.

Bioptics

Bioptics is a combination of phakic IOL and Lasik. Bioptics is done under following situations.

CONCLUSION

Phakic IOLs have evolved considerably over a period of time like any other surgical procedure. There has been a tremendous improvement in design and material which have enhanced the safety and efficacy of the procedure with better clinical outcomes. Phakic IOLs should be present in the armamentarium of every refractive surgeon to cover the entire range of correctable refractive errors so that the refractive outcomes are good, stable and safe.

Dimitrii Dementiev

Kurenkov Vetchiaslav

Milano (Italy)

INTRODUCTION

The last years more and more refractive surgeons are looking to use not only the corneal refractive procedures (RK, KM, LASIK, PRK, LASEK) for myopia and hyperopia correction, but also the phakic implants. It was just approved that the quality of vision after the refractive implants is much better that after corneal procedures, especially in high refractive error eyes .The evidence of reversibility, stability (no regression was noticed) and high predictability of the final refractive effect of the implants make this kind of surgery to become more popular among the refractive surgeons all over the globe.

In this chapter we want to describe our experience with Phakic Refractive Lense (PRL Medennium-Ciba Vision) implantation and to show the evolution of the phakic refractive lenses we have worked with, to compare the different models of the lenses we used in the past and we use today, to analyze the follow-up and complications we had, to present the instrumentation we developed for this surgery.

HISTORY OF PRLS BACKGROUND AND

DEVELOPMENT

Pupil-Fixated Lens (Mushroom) (Figs 8.1A to C)

In 1986, in Moscow Research Eye Institute Drs V Zuev and S Fyodorov proposed a new phakic silicone IOL, named the Mushroom lens, which was implanted from 1986 until 1990 in Russia. The lens was fixated in the pupil. The main idea was to avoid contact between the lens and the endothelium. We implanted more than

A

B

C

Figs 8.1A to C: Mushroom lens

Figure 8.2

120 lenses with good refractive results. A new era of phakic correction using a lens in the posterior chamber was started. The diameter of the optic zone of this lens was 3.2 mm and the total length of the PRL was 8.0 mm. The haptic was placed in the PC and the optic part remained in the AC; the lens being fixated by the pupil (Fig. 8.2).

Despite of the good refractive results many complications were manifested. The complications such as iridocyclitis (the material was toxic), night glare, night vision acuity loss, pupillary block, endothelial cell loss, cataracts in several cases, and inflammation reaction in long term follow up were the serious reason to stop the study of this implant design.

Posterior Chamber Phakic Lens Made in Russia (Fig. 8.3)

Based on the work with the Mushroom lens the concept of a purely posterior chamber PRL was proposed at MERI in Russia and was made from a completely new silicone material, which was not toxic but biocompatible and had a higher refractive index than previous silicon.

Its configuration, parameters and the mechanism of fixation of this PRL were completely different from the previous Mushroom model. It was intended for implantation entirely in the posterior chamber with fixation on the zonular fibers. The OZ diameter was 4.5 mm and the total length was 10.6 mm. The lens was

A

B

Figs 8.3A and B: Posterior chamber phakic IOL (Russian)

created for surgical high myopia correction starting from –10.0 D. This lens was the first prototype of all other posterior chamber PRLs available on the market today.

The problems with endothelium cells loss, cataract formation, severe glare were resolved. But a new complication like an implant decentration occurred in many cases (Fig. 8.4).

Posterior Chamber Phakic Lens (PRL TM) by IVI-Medennium (Fig. 8.5)

International Vision, Inc

This Company was set up in Cincinnati, Ohio to produce the PC PRL that we have been using for the past 6 years. The idea of PRL design was moved from Russia to USA, modified and improved according to the complications we had in the past. The size and the curvature of the implant were changed, and FDA study started. The

Figure 8.4: Decentration of the PC phakic IOL

Phakic Refractive Lens (PRL) is made from silicon with a 1.46 refractive index. The diameter of the optic zone is from 4.5 to 5.5 mm depending upon the dioptric power of the lens. They produce PRLs for myopia and hyperopia (range from +3.5 to+13.5 and from –5.0 to –20.0), which permits a maximum correction of 27.0 D of myopia and 11.0 D of hyperopia. The material is soft, elastic, and hydrophobic. It is easy to perform the implantation through a 3.0 to 3.5 mm clear cornea incision. The lens doesn’t contact the anterior capsule of the crystalline lens. Beeing done from hydrophobic material and having the curvature that repeats the curvature of the crystalline lens the edges of the PRL are lying on the zonulars and all the body floats in the

Figure 8.5: The last modifications of phakic refractive lens PRLTM

Figure 8.6: UBM picture shows floating of PRL in PC. No contact with the anterior capsule, contact with the iris

posterior chamber keeping the space between the implant and anterior capsule of the lens. This floating phenomena let the aqueous easy to pass under the PRL keeping the lens metabolism unchanged (Fig. 8.6). No synechiae have been noted in long-term follow-up. It is easy to remove if it should become necessary. After changing the size parameters of the PRL, decentration has not been observed. Other possible complications are cataract formation and pigmentary glaucoma.

PRL Medennium/Ciba Vision Surgical (Fig. 8.7)

Today the PRL has received the CEE mark and available on the markets of Europe and South America. In the USA it is under the phase III FDA study. Manufactured by IVI/Medennium Inc. Irvine, CA , USA and distributed by Ciba Vision Corp. (Surgical), Dulith, GA USA.

When implanted PRL functions as an optical element to correct refractive error and avoids contact with the natural lens of the eye. PRL does not have the contact with the anterior capsule of the crystalline lens. PRL Myopic and hyperopic implants are available. PRL is done from high refractive index (1.46) highly purified, optically clear silicone elastomer that has undergone biocompatibility testing in Russia and USA. The specific Gravity of the PRL is 0.99. PRL has spherical, thin, flexible and elastic haptic for ease of insertion and conformance to the natural shape and dynamic changes of the eye. The PRL is not fixed in the ciliary sulcus,

B Figures 8.7A and B: (A) Myopic PRL and (B) Hyperopic PRL

but floats in the posterior chamber touching the natural lens zonulars with its edge. The implant’s width is 6.0 mm. Myopic implant (MI) is 11.3 mm length (one size fits all) and hyperopic implant (HI) is 10.6 mm length (one size fits all).

The optic diameter of MI is varying from 5.0 mm to 4.5 mm.

HI has 4.5 mm diameter in all the implants. The power of MI is from –3.0 D to –20.0 D The power of HI is from +3.0 D to + 15.0 D With 0.5 D increment both MI and HI.

From here we shall describe our study of the PRLs and our experience of its implantation.

Beginning in 1987 we implanted 483 lenses of three generations.

In this study, we analyze the clinical data of 122 implants in 72 patients. The patients age ranged between

9 and 53 years. The dioptric power of the implanted lenses ranged between +3.5 and +16.0 D (hyperopic implants) and between –5.0 and –18.5 D (myopic implants) performed in our Day-Hospitals in Milano and Bari, Italy from 1992 to the present time. We used the II and III generation implants in this study.

PATIENT SELECTION

Myopic Range

From –3.00 D to –27.00 D

Hyperopic Range

From +3.00 to +16.00 D.

A +16.0 D hyperope is the maximum we have corrected. Because the anterior chamber of the hyperopic patients is usually shallow, it is safer to limit the hyperopic correction for PRL implantation to a maximum of +11.00 D unless there is a deep AC (Table 8.1).

Unilateral High Myopia with Amblyopia in Children

So far we have performed seven implantations for correction of unilateral high myopia in children with

amblyopia. In cases of progressive myopia, scleral reinforcement surgery is recommended.

Combined Astigmatism

In cases with astigmatism greater than 1.0 D we performed PRL implantation with additional AK surgery.

Keratoconus Correction and Correction of the Refractive Error of the Previous Surgery

PRL implantations can be performed for keratoconus correction with a high myopia component and for overcorrection of a previous refractive procedure such as RK, PRK, or LASIK.

Exchange of a previous model of PRL.

Poor Candidates

1.Clouded or nontransparent cornea

2.Cataract

3.Lens subluxation

4.Glaucoma or ocular hypertension

5.Shallow anterior chamber (less then 2.5 mm)

6.Vitreo-retinal problems that would preclude good vision or require posterior segment intervention.

7.Previous ocular surgery: vitreo-retinal surgery, glaucoma filtration, etc.

8.Age limited to age 60.

PREOPERATIVE PREPARATION

PRL Power Calculation

It is important to obtain a precise refraction of the eye (with accurate vertex distance measurement) as well as an accurate axial length and corneal power readings to use the various methods (Table 8.2).

The spherical equivalent of the most accurate refraction of the eye is used to interpolate the power of the posterior chamber PRL. These powers are based on a simple vertex correction from 12 mm to the corneal plane. This does not seem to make sense optically, but so far has resulted in excellent accuracy in our experience.

CLINICAL RULES

1.Cycloplegic Rx must be less minus than Manifest Rx in Myopes.

2.Cycloplegic Rx must be more plus than Manifest Rx in Hyperopes.

3.If cycloplegic Rx is different, see if patient can accept full cycloplegic correction.

4.Best to attempt correction of cycloplegic Rx in Hyperopes and Manifest Rx in Myopes.

5.Hyperopic patients 18-35 can accommodate a small undercorrection (up to +1.00).

6.Myopic patients 18-35 should not be overcorrected but left emmetropioc or small myopia.

7.All patients 36 to 50 must obtain emmetropia or slight overcorrection (up to –1.00).

8.If cylinder is not to be corrected, using the S.E. plans for PO mixed astigmatism.

9.If correcting cylinder prior to PRL, use the S.E. of the resultant healed refraction.

10.If correcting cylinder after the PRL:

a.If your astigmatic surgical correction will not change the average K, use the S.E.

b.If your astigmatic surgical correction will change the average K (flatten), use the Sphere only.

Iridectomy

Surgical

Usually we recommend performing a surgical iridectomy at the time of PRL implantation. We feel it should be a basal iridectomy made at 12:00 and we prefer to perform it after the PRL is inserted. It is of the utmost importance to make sure that it is a complete iridectomy by checking to be sure the pigment layer has been cut through. This must be done carefully so as not to damage the crystalline lens.

Laser

Those surgeons who prefer not to make it surgically must do it by YAG-Laser. It is recommended that two YAG iridectomies always be performed at around two weeks before the surgery and that they be made at 10:00 and 2:00. To avoid light and additional images passing through the iridectomies, it is very important not to make them too large and to make them as peripheral as possible. We had one patient with severe complaints of night glare. The iridectomy was found to be too large and located nearer to the pupil. We decided to suture it and after it became smaller, the patient complained much less. We have concluded that the iridectomy’s size and placement is very important.

INSTRUMENTATION (Fig. 8.10)

A.Incision: Incision trapezoid diamond Dementiev Blade for Clear cornea incision 3.0-3.2-3.5 mm (Rumex Int., USA).

Figure 8.8

B.Paracentesis: Dementiev diamond paracentesis 1.0 mm blade (Rumex Int.)

C.Implant loading: PRL titanium loading block (DK, UK)

Figure 8.9

D.Insertion: Titanium Dementiev Forceps for PRL implantation (DK, UK)

Titanium diamond dust covered Dementiev PRL forceps (Rumex int, USA)

A

B

Figures 8.10A and B: Forceps

E.Manipulation: Dementiev PRL Titanium double ended haptic spatula (DK,UK)

Dementiev PRL Titanium diamond dust covered manipulator (Rumex Int, USA)

F. Iridectomy: PRL set for manual iridectomy (iris scissors + iris forceps) [Rumex Int, USA]

G.Other: Standard blepharostat and eye fixation forceps (Rumex Int, USA).

Handling the Implant

The PRL implant is supplied in a plastic sterile container. After the container is opened, the implant has to be picked up using PRL Dementiev forceps. It is important to be careful to be sure that the lens does not come into contact with the skin, conjunctiva, lids, lashes or epithelium of the cornea because some microelements can be attracted to and become deposited on the lens surface. It is necessary to be sure that the implant is grasped with the forceps in the correct position. The anterior surface of the lens should be up and posterior surface should be down. This can be seen by observing the fact that the PRL has a similar convexity (curvature) paralleling that of the natural lens. While grasping the lens with the forceps, don’t squeeze too hard it’s optics since it can be easy damaged. Implant is put on the PRL loading block, after that is grasped by the forceps in length.The edge of the implant has to correspond to the end of the forceps. We don’t fold the lens; it is selffolding during its insertion. After the implant has been grasped in the correct manner and orientated in the forceps, we irrigate it profusely using BSS from a syringe. It is important to inspect it carefully and with fine forceps gently remove any foreign particulate matter or fibers that may have become attached to its surface. The lens is now ready for insertion (Figs 8.11A and B).

SURGICAL STEPS

Do not start the surgery if the pupil is not wider than 5.0 mm.

Incision

Usually the incision is placed at the temporal cornea. Our experience recommends performing a clear corneal, self-sealing incision of 3.0 to 3.2 mm in width. The incision can be made with either a diamond or stainless steel blade.

Figures 8.11A and B: Handling the PRL

Any method of fixation may be used to ensure that there is no possibility of the blade contacting the anterior lens capsule since the pupil is widely dilated. The incision architecture should be one the surgeon is familiar with for self-sealing cataract surgery. Nonsuture closure is the intended aim (Fig. 8.12).

Viscoelastic Insertion (Fig. 8.13)

Next the anterior chamber should be filled with viscoelastic to achieve a chamber of not less than 3.0 mm in depth. It is also helpful to place some viscoelastic under the iris to make more room to facilitate lens insertion in the posterior chamber.

Figure 8.12: 3.0 mm clear cornea incision

Paracentesis (Fig. 8.14)

This incision is needed to perform the iridectomy and to create an additional entry point for the lens manipulator that will be needed in the next step to position the PRL in the posterior chamber.

We make it no larger than 0.5 mm and it should be placed at the 12:00 position. It can be made with a stainless steel or diamond knife. The position of the knife has to be perpendicular to the cornea surface and the cut has to be made at the limbus so that the iridectomy will be more basal. This will avoid:

1.Light passing through the iridectomy and the upper lid will cover it (less halos),

2.The possibility of the iridectomy being blocked by the edge of the PRL (pupillary block).

Figure 8.13: Viscoelastic insertion