Ординатура / Офтальмология / Английские материалы / Hyperopia and Presbyopia_Tsubota, Boxer Wachler, Azar_2003

are made at approximately two-thirds of the corneal depth, otherwise the segments are placed too superficially; this may lead to extrusion of the segments or undercorrection.

Each segment is then manually inserted into each tunnel with the use of specially designed forceps (Kera Vision, Fremont, CA). All ICS were supplied sterile. The ICS were sterilized with ethylene oxide (EtO) and subjected to aeration to remove residual EtO. The segments should be introduced far enough that they are left at the 6.0-mm optical zone. Leaving them too close to the limbus increases the possibility of neovascularization. The 1.8-mm segments are easier to insert, as they are shorter. There is generally no need to suture the incisions. In our hands the surgical procedure takes 15 to 17 min in all.

E. POSTOPERATIVE CARE

After the procedure is completed, topical gentamicin 0.3% eyedrops and topical diclofenac 0.1% are instilled into the eye before removal of the speculum. The patient is then discharged wearing a protective eye shield. No patch is necessary. The postoperative management for ICS placement is similar to that for Intacs (3).

Patients are instructed to apply 0.3% tobramycin and 0.1% dexamethasone four times daily for 1 week. Artificial tears are used as needed. Patients should be examined the day after the procedure for wound revision. The incision sites will show a linear fluorescein staining for 3 to 5 days. By the first postoperative week most of the staining, is resolved. Each subsequent postoperative visit should include a manifest and a cycloplegic refraction with and without correction visual acuity testing, slit-lamp examination, tonometry, keratometry, and topography examination.

After 3 months of follow-up on the operative eye and if refractive stability is achieved, the patient’s contralateral eye can be surgically corrected.

F. VISUAL OUTCOMES

We have performed over 50 ICS implantations in men and women under 58 years of age. We have implanted all the types of segments manufactured to date: the 2.0-, 1.8- and 1.5- mm segments and a variety of thinner segments. The hyperopias we have treated have not exceeded the manifest refraction spherical equivalent (SE) of 2.75 and cycloplegic refraction SE of 4.5 D.

Visual recovery after the ICS procedure was not as rapid as after Intacs (4). Patients experienced blurry vision for distance but were able to read without glasses after a week. Near (uncorrected visual acuity) (UCVA) was better than distance UCVA because there was an initial overcorrection.

Improvement in UCVA occurred earlier with the 1.8-mm segments than with the others. Some 71% of the patients achieved 20/20 or better UCVA 2 weeks after the surgery compared with 27% in the 2.0-mm segment group. Ghost images and halos were a frequent complaint in this first postoperative period. Visual acuities continued to improve over the following weeks; by the first month, 76% of the patients were 20/20 or better in the 1.8- mm segments and 64% in the 2.0-mm group. The visual acuity and visual recovery were similar to those reported for other keratorefractive procedures, and the results remained constant at 18 months (5,6).

The procedure has not been associated with loss of best spectacle-corrected visual acuity (BSCVA), demonstrating the safety of the procedure. Moreover, no patient had a BSCVA less than 20/20. This can be attributed to the fact that the central cornea is not

Figure 3 Corneal topographies of the right and left corneas showing the central steepening of the cornea produced by the ICS.

touched during the procedure. Some 25% of the patients in the 2.0-mm group and 35% of the patients in the 1.8-mm group experienced a gain of one line of BSCVA at 18 months. This advantage is due to the preservation of the corneal positive asphericity with this procedure.

Refractive stability was achieved later than in the Intacs for myopia (4). After the initial overcorrection, stability is obtained by the third month postoperatively. Corneal topographies showed the central steepening of the cornea with an optical zone between 5 and 6 mm in diameter (Fig. 3). Continuing follow-up however, has demonstrated that there is no long-term stability of the correction and visual outcome achieved. We followed these patients for over 3 years and found that there is progressive hyperopic drift with time, which is observed after the second year. This finding is similar to that observed with laser thermokeratoplasty, where one sees a good initial correction but loss of effect with time (7). With the ICS, only 60% of the initial manifest refraction correction and 46% of the cycloplegic refraction is maintained after 3 years. Eyes with higher corrections (hyperopias greater than 2.0 D) show a greater tendency to lose correction with time. The average amount of hyperopic drift is 0.9 D, ranging from 0.5 to 1.75 D. Although the amount of loss of correction has been small, considering that the attempted correction was 2.0 D, this change is significant for these patients. Similarly, by 3 years, only 9% of the patients have an UCVA of 20/15 or better.

G. COMPLICATIONS

Most of the complications we encountered were related to the fact that the surgical technique is mostly manual. Among the single segment complications we encountered, the presence of neovascularization was the most common. Segments placed too peripherally and close to the limbus will predispose for growth of neovessels surrounding the segments. These neovessels can grow deeply in the stromal tunnel and will eventually surround the segment. We encountered this complication in 19% of the patients. In our experience,

one eye are varied. Undercorrection and patient dissatisfaction with the refractive result, usually due to induced irregular astigmatism, are among the most common causes.

Removal of the intracorneal segments is performed under topical anesthesia (tetracaine 0.5%) after sterilization of the eye with topical povidone-iodine solution. The patient is prepared and draped in the same fashion as in the original surgery. A speculum is inserted to hold the eyelids apart. The incision is reopened with a diamond blade, as this allows minimally traumatic reopening of the incision. In our experience, attempts at blunt dissection with instruments like a Sinskey hook are more traumatic than reopening with a sharp blade. After the incision is opened, the tunnel is approached with a corneal spreader spatula designed for this purpose. The spatula is used to reopen the tunnel and loosen each segment within the tunnel. Subsequently, two small hooks are used to slide the segments into the corneal tunnel and bring them through the incision. There is no positioning hole at the tip of the segments to engage each segment and facilitate its removal. Care is taken to do this in a minimally traumatic manner.

The explantation of the ICS for hyperopia is not an easy procedure, unlike the explantation of the Intacs for myopia (4,11). The exceptions are when single segments are explanted in the presence of neovascularization. These segments are usually loose, close to the limbus, and easy to remove. When the segments are inserted close to the 6.0- mm optical zone, they are harder to loosen, and no instruments are available to grasp the segment and pull it out through the tunnel and out of the incision. Potential problems can also be encountered when there have been difficulties with wound healing.

Postoperative care after total explantation of the ICS for hyperopia is moderately painful; patients usually require systemic analgesia and topical anti-inflammatory drops. Reversibility of the refractive effect, as demonstrated with the return of BSCVA and manifest refraction to preoperative levels, is on average achieved at 3 months after the explantation, rarely before. Removal of these segments can be followed, if desired, by a safe and effective Lasik or PRK for low to moderate myopia.

This procedure is not intended to produce astigmatism; however, we induced 1D or more of astigmatism in 23% of our cases. All segments should be placed symmetrically and at the same depth in order to avoid this complication.

Rarely, patients have reported occasional pain without apparent cause or an unexplained photophobia. We have not seen cases of glare or halos 6 months after the surgery and beyond.

H. SUMMARY

The ICS procedure reduces low hyperopic errors without astigmatism while sparing the visual axis. They work better for patients with hyperopias of less than 2.0 D. As opposed to laser thermokeratoplasty and conductive keratoplasty, the ICS procedure offers the benefit of reversibility and preservation of the positive corneal asphericity. The procedure is safe and there has been no loss of BSCVA in any treated patient so far. The effect of ICS implantation appears to stabilize after the first 3 months and is maintained for 18 to 24 months after the procedure. However, after the second year there is a progressive loss of correction, which leads us to question the benefit of performing this procedure. Complications with ICS implantation are mostly related to the surgical technique, which is manual.

In general, removal of these segments can be followed by a safe and effective segment reinsertion or, if preferred, LASIK or PRK for low to moderate myopia.

REFERENCES

1.Nose W, Neves RA, Burris TE. The intrastromal corneal ring: 12-month sighted myopic eyes. J Refract Surg 1996; 12:20–28.

2.Holmes-Higgin DK, Baker PC, Burris TE, Silvestrini TA. Characterization of the aspheric corneal surface with the intrastromal corneal ring segments. J Refract Surg 1999; 15:520–528.

3.Asbell PA. Intrastromal corneal ring. In: Kaufman HE, Barron BA, McDonald M, eds. Cornea, 2nd ed. Boston: Butterworth-Heinemann, 1997: 1037–1044.

4.Gomez L, Chayet A. Laser in situ Keratomileusis results after intrastromal corneal ring segments (intacs). 2001; 108:1738–1743.

5.Anschutz T. Laser correction of hyperopia and presbyopia. Int Ophthalmol Clin 1994; 34: 107–137.

6.Jackson WB, Casson E, Hodge WG, Mintsioulis G, Agapitos PJ. Laser vision correction for low hyperopia. Ophthalmology 1998; 105:1727–1737.

7.Koch DD, Berry MJ, Vassiliadis A. Noncontact holmium: YAG laser thermal keratoplasty. In: Salz JJ, ed. Corneal Laser Surgery. St Louis: Mosby, 1995:247–254.

8.McCarey B, Andrews D. Refractive keratoplasty with intrastromal hydrogel lenticular implants. Invest Ophthalmol Vis Sci 1981; 21:107–115.

9.Gomez ML, Barraquer JI. Permalens hydrogel intracorneal lenses for spherical ametropia. J Refract Surg 1997; 13:342–348.

10.Reinstein DZ, Srivannaboon S, Holland SP. Epithelial and stromal changes induced by Intacs examined by three-dimensional very high-frequency digital ultrasound. J Refract Surg 2001; 17(3):310–318.

11.Asbell PA, Ucakgan O, Odrich M. Photorefractive keratectomy after intrastromal corneal ring segment explantation. Am J Ophthalmol 1999; 128(suppl 6):755–756.

12.Koch DD, Kohnen T, McDonnell PJ, Menefee R, Berry M. Hyperopia correction by noncontact holmium: YAG laser thermal keratoplasty: US phase IIA clinical study with 2-year followup. Ophthalmology 1997; 104(suppl 11):1938–1947.

13.Brinkmann R, Radt B, Flamm C, Kampmeier J, Koop N, Birngruber R. Influence of temperature and time on thermally induced forces in corneal collagen and the effect on laser thermokeratoplasty. J Cataract Refract Surg 1995; 26:744–754.

14.Asbell PA, Maloney RK, Davidorf J, Hersh P., McDonald M, Manche E. Conductive Keratoplasty Study Group. Conductive keratoplasty for the correction of hyperopia. Trans Am Ophthalmol Soc 2001; 99:79–84, discussion 84–87.

We decided on foldable anterior chamber lens that may be inserted using a 3.2 mm incision. A 2 piece implant has been designed: the haptics with PMMA properties have a “2” shape that ends with three footplates fixated in the angle. A very soft optic, in hydrophilic acrylic, binds tangentially to the haptics. This design allows maintaining a stable anterior chamber as well as a gentle fixation in the angle (with the hydrophilic acrylic footplates).

The len’s profile is equivalent to that of the NUVITA. Indeed, prospective and retrospective studies demonstrated the short and long term safety of the ZB5M and the NUVITA on the endothelium. The only problem detected with these lenses was cosmetic: moderate pupil deformations (that may give a cat’s eye aspect) have been rarely reported (less than 5% of the cases).

In order to reduce the risk of pupil ovalization, a special interest has been held on a precise measurement of the anterior chamber. The measurement from sclera to sclera using a caliper is indeed inaccurate. It is the reason we developed an objective technique based on the retro-illumination of the anterior segment. This method allows precise and accurate assessment of the angle-to-angle inner diameter of the anterior chamber and therefore to exactly adjust the size of the implant. Additionally, a plastic stick has been designed to confirm this measurement preoperatively.

B. FOLDING OF THE OPTIC

The optic was initially folded in two; the aperture was then either anterior (with a risk of endothelial touch) or posterior (with a risk of iris contact). It was therefore necessary to expand significantly the anterior chamber with healon. A special folding device is now available to overcome this problem.

Indeed, an “N shaped” folding system has been designed to allow an aperture of the implant parallel to the iris plan. The first model of presbyopic implant favors far vision in the center of the optic, while the middle and the peripheral parts allow near and far vision respectively. Many other possibilities may be evaluated throughout the future clinical trials.

C. INDICATIONS AND CONTRAINDICATIONS

The current indication includes presbyopic patients with emmetropia and without astigmatism. It is known that pseudophakic emmetropic patients without astigmatism implanted with multifocal lenses have a success rate of 70%; which means that they do not wear glasses for either near or far vision. If either an ametropia or an astigmatism exists, this success rate falls down to 30%. Accordingly, in the first set of investigation, the implantation of presbyopic intraocular lenses is only proposed to emmetropic and stigmatic patients in order to obtain optimal results. However, it may be possible in the near future to develop implants with spherical power to treat low myopia or hyperopia. The only method currently available to treat an associated astigmatism is to perform LASIK.

CONTRAINDICATIONS

Contraindications are those of anterior chamber implant surgery, including the need to respect a 3 mm anterior chamber depth, an endothelial cell count over 2500 cells per mm2, and the absence of other disorders of the anterior chamber (cataract, uveitis, corneal dystrophy, glaucoma, etc.).

D. PREOPERATIVE MANAGEMENT

Preoperative management is generally easy. The eye to be treated, obviously lacking any signs of conjunctival or corneal infection, must be in therapeutic myosis.

E. SURGICAL TECHNIQUE

The first patients have been operated under general or loco-regional anesthesia. In the future topical anesthesia may be used. A 3.2 mm surgical incision, using a pre-calibrated phako knife is first performed.

The incision, performed in an auto-sealed fashion, may be placed at 12 o’clock while one or two lateral paracenthesis may be performed to help the manipulations. The anterior chamber is then deepened using viscous material to:

1.Protect the endothelium

2.Enhance the volume of the anterior chamber to facilitate the lens aperture without any danger for either endothelium or iris.

The implant removed from its container is then placed on the folder. Once folded in N, the implant is held with a special forceps that will allow the anterior chamber followed by the rest of the inferior handle. The haptic may be easily folded to pass through the 3.2 mm incision. Subsequently, the optic is introduced in the anterior chamber and the inferior footplates are directed towards the opposite angle. Once the optic is entirely introduced, the superior blocks the implant and the inserting forceps is removed. The optic gently opens in the anterior chamber parallel to the iris. The last manipulation of the insertion is to place the trailing haptic in the anterior segment using either a forceps or a Leister hook. Gonioscopy is performed to check the correct location of the handles, then viscous is removed.

F. VISUAL OUTCOMES/COMPARISON OF RESULTS

As of today, 6 eyes of 5 patients benefited the implantation with more than 1 year follow up (thanks to professor Eva VOLKOVA in BRNO, Czech Republic). As the first implanted lenses were prototypes, the correct sizes were not available for all the treated eyes. Two have been removed due to an oversizing, the 4 remnants are still in place. No anatomical complications have been detected on these eyes and visual outcome is excellent. Three eyes recovered 20/20 and the other 20/25 without additional correction in the 1st day postoperatively. No complications could be observed on this first series.

G. SUMMARY

Presbyopic phakic IOLs implantation is an emergent technique that will become more and more important in the future due to its simplicity. The benefit of a foldable implant is to be inserted with a small auto sealed incision without induced astigmatism. The technique has been simplified since the beginning and it will soon be feasible under topical anesthesia.

The major interest of this technique is to adjust the power of the addition to the patient’s presbyopia and to be reversible in case of unfavorable outcome. Multicentric studies must be performed to better assess the quality of the optic.