Journal of Refractive Surgery

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Reports 

INTACS Before or After Laser in situ Keratomileusis: Correction of Thin Corneas With Moderately High Myopia

Mitsutoshi Ito, MD, PhD; Hiroyuki Arai, MD; Teruki Fukumoto, MD; Ikuko Toda, MD, PhD; Kazuo Tsubota, MD

Abstract

ABSTRACT

PURPOSE: Intrastromal corneal ring segments (INTACS Micro-Thin Prescription Inserts by Addition Technologies, Fremont, Calif) were inserted as a combined surgery with laser in situ keratomileusis (LASIK) in six eyes with thin corneas to correct moderately high myopia.

METHODS: INTACS were implanted before LASIK (INTACS-LASIK) in three eyes and after LASIK (LASIK-INTACS) in three eyes. Mean preoperative manifest spherical equivalent refraction was -7.88 diopters. Mean follow-up was 306 days.

RESULTS: No intraoperative complications occurred. The LASIK-INTACS eyes were slightly more o ver corrected than the INTACS-LASIK eyes because of the enhanced performance of INTACS in the thinned corneal tissue. Induced astigmatism by INTACS per se was less in the LASIK-INTACS eyes than in the INTACS-LASIK eyes. At last examination, uncorrected visual acuity was better than 20/25 in all eyes. Best spectacle-corrected visual acuity was within 1 line of the preoperative value in all eyes.

CONCLUSION: Both methods resulted in significant improvement in visual acuity and refraction. Based on our limited experience, however, LASIK followed by INTACS is preferred for reasons of safety, convenience, and lower induced cylinder. [J Refract Surg 2004;20:818-822]

Abstract

ABSTRACT

PURPOSE: Intrastromal corneal ring segments (INTACS Micro-Thin Prescription Inserts by Addition Technologies, Fremont, Calif) were inserted as a combined surgery with laser in situ keratomileusis (LASIK) in six eyes with thin corneas to correct moderately high myopia.

METHODS: INTACS were implanted before LASIK (INTACS-LASIK) in three eyes and after LASIK (LASIK-INTACS) in three eyes. Mean preoperative manifest spherical equivalent refraction was -7.88 diopters. Mean follow-up was 306 days.

RESULTS: No intraoperative complications occurred. The LASIK-INTACS eyes were slightly more o ver corrected than the INTACS-LASIK eyes because of the enhanced performance of INTACS in the thinned corneal tissue. Induced astigmatism by INTACS per se was less in the LASIK-INTACS eyes than in the INTACS-LASIK eyes. At last examination, uncorrected visual acuity was better than 20/25 in all eyes. Best spectacle-corrected visual acuity was within 1 line of the preoperative value in all eyes.

CONCLUSION: Both methods resulted in significant improvement in visual acuity and refraction. Based on our limited experience, however, LASIK followed by INTACS is preferred for reasons of safety, convenience, and lower induced cylinder. [J Refract Surg 2004;20:818-822]

Laser in situ keratomileusis (LASIK) has been widely accepted as the principal modality of laser vision correction for treatment of low to moderate myopia. However, there is consensus among surgeons that LASIK should no longer be performed to treat high myopia because of compromised visual outcomes.1 Moreover, stromal bed thickness should be preserved at no less than 250 µm to avoid iatrogenic keratectasia.2 For patients who seek correction beyond this limit, some modifications to LASIK or alternative modalities of refractive surgery are required.

Implantation of intrastromal corneal ring segments (INTACS Micro-Thin Prescription Inserts, Addition Technologies, Fremont, Calif) is a technique that uses the insertion of two plastic half rings into the cornea to achieve central flattening, thus stromal tissue is preserved. It was originally intended to correct primary myopia between -1.00 and -3.00 diopters (D),3 but has also been used in a patient with previous LASIK,4 and patients with iatrogenic keratectasia after LASIK5,6 or after photorefractive keratectomy (PRK).7 However, there has been no report on the technique of implanting INTACS first, then performing LASIK to correct residual refractive error. We report a study of the two combined surgeries for correction of moderately high myopia with thin corneas: INTACS insertion before or after LASIK.

PATIENTS AND METHODS

Patient Selection

Six eyes of four myopic patients (three male and one female) underwent both LASIK and INTACS implantation in one eye on separate days. The age of the patients ranged between 35 and 49 years with a mean of 43.5 years. Mean follow-up from the initial procedure to the last examination was 306 days (range 74 to 510 days).

Of the six eyes, three were treated with INTACS for postoperative LASIK undercorrection (LASIK-INTACS) (Table). The right eye of patient #1, in particular, was initially treated with PRK at a clinic elsewhere, which resulted in undercorrection; then the patient visited our clinic for further remedy. In our facility, this patient had LASIK followed by INTACS implantation. For the remaining three eyes, INTACS were implanted as a planned surgery followed by LASIK CINTAC S-LASIK). The mean interval from LASIK to INTACS implantation was 344 days (range 234 to 441 days) and from INTACS implantation to LASIK, 72 days (range 49 to 101 days).

Surgical Procedure

Informed consent was obtained from all patients prior to each surgical procedure. Four different thicknesses of INTACS (0.25 mm, 1 eye; 0.30 mm, 2 eyes; 0.35 mm, 2 eyes; 0.45 mm, 1 eye) were used according to a nominal predicted correction for each thickness.3 The surgical technique for INTACS implantation was a standard one used for the correction of low myopia. Using topical anesthesia, a 1.2-mm superior radial incision was made with a calibrated diamond knife set to 68% of the incision site thickness. From the incision site, specially designed dissecting instruments were introduced and rotated in clockwise and counterclockwise directions to create two intrastromal channels of 190° each. INTACS, which are composed of two 150° polymethylmethacrylate segments, were inserted into each intrastromal channel.3 The edges of the incisions were approximated at the end of surgery but were not sutured, as the wound gape was not enough to require sutures.

To create the corneal flaps for LASIK, the LSK-One microkeratome (depth plate 130 µm, Moria, Antony, France) was used in all eyes that underwent LASIK-INTACS; the MK-2000 microkeratome (depth plate 130 µm, Nidek, Aichi, Japan) was used in all eyes that underwent INTACS-LASIK. According to manufacturers' definitions, a flap thickness of 130 µm or thicker was intended with the 130-µm depth plate of the LSK-One microkeratome; a flap thickness of 130 µm on average was intended wtih the 130-µp? depth plate of the MK-2000 microkeratome. The surgeon arbitrarily chose the microkeratome for the LASIK-INTACS eyes; however, for the INTACS-LASIK eyes, the MK-2000 microkeratome was selected because relatively thin flaps with high predictability were intended,8 to prevent the oscillating blade from interfering with INTACS. For corneal ablation in all eyes, the Nidek EC-5000 excimer laser (Nidek, Gamagori, Japan) was used.

RESULTS

No intraoperative complications occurred in either INTACS implantation or LASIK. Following INTACS implantation, two eyes experienced foreign body sensation during the early postoperative period, which self-resolved over time without particular medication. No INTACS were explanted. No consistent trend in induced astigmatism with regard to the surgical method, INTACS-LASIK or LASIKINTACS, was evident.

Mean preoperative baseline manifest spherical equivalent refraction was -7.88 D (range -3.25 to -13.00 D). After the first surgical intervention, the eyes that underwent INTACS implantation were more undercorrected than the eyes that underwent LASIK. Mean manifest spherical equivalent refraction at final examination demonstrated that two eyes treated with LASIK-INTACS were overcorrected, and one eye treated with INTACS-LASIK was undercorrected (Table).

The refractive correction achieved with 0.25-mm INTACS was 3.50 D, 0.30-mm INTACS was 2.69 D on average, 0.35-mm INTACS was 2.44 D on average, and 0.45-mm INTACS was 5.00 D on average. None of the 0.40-mm INTACS were used. The eye implanted with the 0.25-mm INTACS was previously treated with PRK and LASIK, in the aforementioned sequence. All eyes that underwent LASIKINTACS were overcorrected by INTACS per se compared to the performance predicted for each thickness of INTACS; the eyes that underwent INTACS-LASIK demonstrated some similarity with the predicted amount of correction (Fig).

Mean surgically induced astigmatism, comparing postoperative to pre-INTACS implantation status by means of Jaffe vector analysis, was 0.47 ± 0.81 D (mean ± SD) in the eyes that underwent LASIK-INTACS, 1.50 ± 1.12 D in the eyes that underwent INTACS-LASIK, and 0.99 ± 1.04 D in all eyes (Table).

Uncorrected visual acuity (UCVA) at baseline, after the first procedure, and after the second procedure are shown in the Table. In all eyes, preoperative UCVA was 20/200 or worse in Snellen visual acuity units (logarithm of minimum angle of resolution [logMAR], 1.00). After the first procedure, UCVA in the eyes that received LASIK was improved (logMAR range 0.52 to 0.82), but UCVA in eyes that received INTACS first was worse than 20/200 (logMAR range 1.15 to 1.40). After the second procedure, UCVA in all eyes that underwent LASIKINTACS was better than in any of the eyes that underwent INTACS-LASIK. However, UCVA was better than 20/25 in all eyes (Table).

Table

TableMeasurements at Baseline and After the First and Second Procedures in Six EyesFigure. INTACS thickness and correction achieved (manifest spherical equivalent refraction) in six eyes. The performance by INTACS per se is indicated.

Table

Measurements at Baseline and After the First and Second Procedures in Six Eyes

Figure. INTACS thickness and correction achieved (manifest spherical equivalent refraction) in six eyes. The performance by INTACS per se is indicated.

At baseline, best spectacle-corrected visual acuity (BSCVA) was better than 20/20 (logMAR 0) in all eyes. All eyes maintained BSCVA to within 1 line of the baseline level after the first procedure and after the second procedure (Table).

Mean keratometric power values of each eye at baseline and following each procedure are presented (Table). Baseline values ranged from 41.3 to 46.0 D. Following the first procedure, the values ranged from 39.9 to 40.9 D in the LASIK-INTACS eyes, and from 38.4 to 41.0 D in the INTACS-LASIK eyes. All the values were reduced with each surgical intervention in every eye and ranged from 33.6 to 38.1 D at the final examination (Table).

At baseline, the mean value for corneal thickness (pachymetry) in eyes that had LASIK-INTACS was 483 µm (range 450 to 516 µm). Following LASIK, it was 430 µm (range 424 to 441 µm) and the mean residual refractive error was -1.67 D, which was subsequently treated with INTACS as an enhancement procedure. The mean value for corneal thickness (pachymetry) in the eyes that had INTACSLASIK was 522 µm (range 495 to 575 µm) at baseline. In these eyes, mean preoperative baseline manifest spherical equivalent refraction was -9.67 D (Table). No sign of iatrogenic keratectasia was detected at the latest follow-up examination in any eye.

DISCUSSION

The flattening effect of INTACS was enhanced when inserted in the thin corneal tissue, as demonstrated in the Figure. Probably, it is this enhanced performance of INTACS that caused the slight overcorrection and better UCVA in eyes that underwent LASIK-INTACS. This observation is in line with the results of treating keratoconus by INTACS, in which greater flattening effect was demonstrated on the thinner corneal keratoconic tissue.9 Another potential reason for the enhanced effect in the LASIK-INTACS eyes may have been relatively closer placement of INTACS to the endothelial layer, since a diamond knife was uniformly set to 68% of the incision site thickness.

Yet another interesting finding was that induced astigmatism by INTACS per se was less in eyes that underwent LASIK. We assume this is because the relatively thinner INTACS was used in LASIK-INTACS to correct residual refractive error, whereas the thicker INTACS was used in INTACS-LASIK to initially treat higher refractive error. Therefore, the thinned stromal bed following LASIK did not affect cylindrical change as much as spherical change induced by INTACS. Davis et al10 described with-the-rule astigmatism induced by INTACS implantation, which is likely due to wound contracture. However, whether LASIK-INTACS or INTACS-LASIK was performed, no such trend in induced astigmatism was evident in our study. This is probably because we intended minimal wound manipulation and used no suture to close the wound in INTACS implantation.

To refine the predictability of refractive outcome of INTACS implantation following LASIK, or even in a primary case of INTACS placement, preoperative pachymetry readings or the depth of INTACS placement may need to be incorporated as a factor indicating the performance for each INTACS thickness. In the INTACS-LASIK eyes, the low keratometric power values after INTACS implantation may have affected the predictability of subsequent LASIK. Adjustment in the LASIK nomogram to treat the cornea in the low-keratometric range may further advance the predictability of INTACS-LASIK.

Although the small sample size of this preliminary study does not allow definitive conclusions, we found advantages and disadvantages in both LASIK-INTACS and INTACS-LASIK methods. If LASIK was performed first, patients did not experience severe undercorrection while awaiting INTACS placement and were provided with an option to withhold INTACS implantation once they were satisfied with the results of LASIK. Actually, we intentionally made a longer interval between LASIK and INTACS placement compared to INTACS-LASIK. This interval was necessary to carefully rule out iatrogenic keratectasia with regard to low pachymetry following LASIK. Also, we were concerned that creating stromal channels in the early postoperative LASIK eyes might interfere with the flap-bed interface, although, with the availability of the Intralase femtosecond laser (Intralase, Irvine, Calif) to create INTACS channels, the interval could be shorter. However, the surgical effect of INTACS would be less predictable, at least until the nomogram incorporating corneal pachymetry or the depth of INTACS placement is established.

If INTACS were implanted first, predictability was higher, since the surgeon can control LASIK to correct refractive errors remaining after INTACS placement. However, patients were left with severe undercorrection following INTACS implantation until LASIK was performed. Concerns remain that INTACS might interfere with a microkeratome blade when the corneal flaps are being created. In this study, we did not experience this complication, probably because INTACS are normally inserted into a much deeper layer in the corneal stroma than where the LASIK flap is created.

Theoretically, the combined techniques of INTACS implantation and LASIK provide a higher limit of myopic correction by no more than 3.00 D compared to the LASIK-only procedure. In this range of moderately high myopia, a phakic intraocular lens (PIOL) may be preferred by some surgeons.11 However, several complications have been reported with the use of modern-generation PIOLs: pupillary ovalization, endothelial cell loss, chronic inflammatory reaction, ocular hypertension,12,13 and cataract development14 for angle-supported PIOLs; pupillary block glaucoma, pigment dispersion, and cataract development15,16 for posterior chamber PIOLs.

By virtue of the tissue saving properties, reversibility,17 and adjustability18 in refractive effect of INTACS, we assume the combined surgeries of INTACS implantation and LASIK are viable options for the correction of moderately high myopia with thin corneas. INTACS can be implanted in eyes where the residual stromal bed in a LASIK-treated eye rules out re treatment by LASIK. It can also be performed as a planned surgery when preoperative corneal thickness predicts LASIK undercorrection by no more than 3.00 D.

Additional studies with more eyes are required to confirm the safety regarding the use of microkeratomes on corneas that have been implanted with INTACS. Also, predictability needs to be evaluated in a longer follow-up period in terms of which procedure should be performed first, INTACS implantation or LASIK. In the meantime, we assume LASIK, then INTACS, provides more benefit for patients because of safety, more convenience, and lower induced cylinder.

REFERENCES

1. Knorz MC, Wiesinger B, Liermann A, Seiberth V, Liesenhoff H. Laser in situ keratomileusis for moderate and high myopia and myopic astigmatism. Ophthalmology 1998; 105:932-940.

2. Seiler T, Koufal K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg 1998; 14: 312-317.

3. Schanzlin DJ, Abbott RL, Asbell PA, Assil KK, Burris TE, Durrie DS, Pouraker BD, Lindstrom RL, McDonald JE 2nd, Verity SM, Waring GO 3rd. Two-year outcomes of intrastromal corneal ring segments for the correction of myopia. Ophthalmology 2001;108:1688-1694.

4. Fleming JP, Lovisolo CF. Intrastromal corneal ring segments in a patient with previous laser in situ keratomileusis. J Refract Surg 2000;16:365-367.

5. Siganos CS, Kymionis GD, Astyrakakis N, Pallikaris IG. Management of corneal ectasia after laser in situ keratomileusis with INTACS. J Refract Surg 2002;18:43-46.

6. Alio J, Salem T, Artola A, Osman A. Intracorneal rings to correct corneal ectasia after laser in situ keratomileusis. J Cataract Refract Surg 2002;28:1568-1574.

7. Lovisolo CF, Fleming JF. Intracorneal ring segments for iatrogenic keratectasia after laser in situ keratomileusis or photorefractive keratectomy. J Refract Surg 2002; 18: 535-541.

8. Shemesh G, Dotan G, Lipshitz I. Predictability of corneal flap thickness in laser in situ keratomileusis using three different micro keratomes. J Refract Surg 2002;18(suppl): S347-S351.

9. Colin J, Cochener B, Savary G, Malet F, Holmes-Higgin D. INTACS inserts for treating keratoconus: one-year results. Ophthalmology 2001;108:1409-1414.

10. Davis EA, Hardten DR, Lindstrom RL. Laser in situ keratomileusis after intracorneal rings. Report of 5 cases. J Cataract Refract Surg 2000;26:1733-1741.

11. Malecaze FJ, Hulin H, Bierer P, Fournie P, Grandjean H, Thalamas C, Guell JL. A randomized paired eye comparison of two techniques for treating moderately high myopia: LASIK and artisan phakic lens. Ophthalmology 2002;109:1622-1630.

12. Allemann N, Chamon W, Tanaka HM, Mori ES, Campos M, Schor P, Baikoff G. Myopic angle- supported intraocular lenses: two-year follow-up. Ophthalmology 2000;107:1549-1554.

13. Perez-Santonja JJ, Alio JL, Jimenez -Alfaro I, Zato MA. Surgical correction of severe myopia with an angle-supported phakic intraocular lens. J Cataract Refract Surg 2000;26:1288-1302.

14. Alio JL, de la Hoz F, Ruiz-Moreno JM, Salem TF. Cataract surgery in highly myopic eyes corrected by phakic anterior chamber angle-supported lenses. J Cataract Refract Surg 2000;26:1303-1311.

15. Uusitalo RJ, Aine E, Sen NH, Laatikainen L. Implantable contact lens for high myopia. J Cataract Refract Surg 2002;28:29-36.

16. Menezo JL, Peris -Martinez C, Cisneros A, Martinez-Costa R. Posterior chamber phakic intraocular lenses to correct high myopia: a comparative study between St aar and Adatomed models. J Refract Surg 2001;17:32-42.

17. Asbell PA, Ucakhan 00, Abbott RL, Assil KA, Burris TE, Durrie DS, Lindstrom RL, Schanzlin DJ, Verity SM, Waring GO 3rd. Intrastromal corneal ring segments: reversibility of refractive effect. J Refract Surg 2001;17:25-31.

18. Asbell PA, Ucakhan 00, Durrie DS, Lindstrom RL. Adjustability of refractive effect for corneal ring segments. J Refract Surg 1999;15:627-631.

Table

Measurements at Baseline and After the First and Second Procedures in Six Eyes

Figure. INTACS thickness and correction achieved (manifest spherical equivalent refraction) in six eyes. The performance by INTACS per se is indicated.

10.3928/1081-597X-20041101-10

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