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Laser thermokeratoplasty after lamellar corneal cutting Mahmoud M. Ismail, MD, PhD, Juan J. Pdrez-Santonja, MD, PhD, Jorge L. All6, MD, PhD ABSTRACT Purpose- To evaluate the effect of laser thermokeratoplasty (LTK) in eyes that i previously had a lamellar corneal cut.
Setting; University of AI-Azhar, Cairo, Egypt, and Instituto Oftalmol6gico de Alicante, Spain.
Methods- In 15 eyes (10 patients), noncontact LTK was applied 6 to 8 weeks after a lamellar corneal cut had been made. Central pachymetry, keratometry,-and videokeratography were performed and uncorrected visual acuity, best spectaclecorrected visual acuity (BSCVA), and manifest and cycloplegic refractions measured before and 1, 6, 12, and 18 months after LTK.
Results; Mean follow-up was 19.13 months. Mean refraction was +5.93 diopters (D) _+ 1.9 (SD) before LTK and -0.43 +__1.5 D at 1 month, +1.63 +__1.6 D at 6 months, 1.91 _ 1.41 at 12 months, and +2.01 _.+ 1.5 D at the end of the study. Total regression did not occur in any case. Mean BSCVA before I_TKwas 0.66 +_ 0.2, and spontaneous visual acuity at the end of the study was 0.58 +_ 0.18. No patient lost any lines of preoperative BSCVA. There was no significant difference between the results at 12 months and at the end of the study.
Conclusion; Corneal lamellar cutting appeared to improve the magnitude of the refractive effect of noncontact /TK and to decrease the amount of regression.
JCataract Refract Surg 1999; 25:212-215 ---
urgical procedures to correct hyperopia are based on inducing peripheral corneal alteration to produce central steepening. This can be achieved by lamellar corneal cutting (hyperopic lamellar keratoplasty), hexagonal incisions (hexagonal keratotomy), peripheral photorefractive stromal ablation by excimer
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Accepted~ r publication November 30, 1998. From the Re,active Surgery Unit, Instituto Ofialmol6gico de Alicante (P~rez-Santonja), and Department of Ophthalmolog~ University of Alicante (Ali6), Spain; University of Al-Azhar, Cairo, Egypt (Ismail). Reprint requests to Mahmoud M. IsmaiL MD, PhD, 1 E1 Hussien Square, 11261 Cairo, Egypt. 212
laser, or collagen contraction by holmium laser thermokeratoplasty (LTK)) -6 Laser thermokeratoplasty induces a beneficial central steepening, but it is used to correct only low hyperopia, especially in middle-aged patients. Partial or complete regression of the obtained effect is the primary reported drawback of this technique. 4-6 The regression reaches its peak 3 to 6 months after surgery and gradually declines until approximately 1 year. The deposition of new collagen in the corneal stroma, together with the elasticity of Bowman's layer, helps the cornea restore its preoperative topography and thus causes regression of the obtained refractive effect. 5-7
J CATARACT REFRACT SURG---VOL 25, FEBRUARY 1999
LASER THERMOKERATOPLASTY AFTER LAMELLAR CORNEAL C U T T I N G
Corneal thickness and patient age are crucial factors in regression. 4'5'8'9 Moreover, LTK corrects a large amount of induced hyperopia following myopic photorefractive keratectomy (PRK) with significant stability. I° This might be due to the absence of Bowman's layer and to low central corneal pachymetry. In this study, we present the results of noncontact LTK after corneal lamellar cutting.
Patients and Methods This study comprised 15 eyes of 10 hyperopic patients. Five patients had bilateral surgery with at least 2 months between procedures. Mean age of the 6 men and 4 women was 29.9 years -+ 3.1 (SD) (range 17 to 46 years). Central pachymetry, keratometry, and videokeratography were performed prior to surgery and 1, 6, 12, and 18 months after LTK. Additional measurements were uncorrected visual acuity (UCVA), best spectaclecorrected visual acuity (BSCVA), manifest and cycloplegic refractions, and slitlamp evaluation. Mean followup was 19.13 months (range 18 to 24 months). Written informed consent was obtained from each patient. In the lamellar keratoplasty (LK) procedure, topical anesthesia (tetracaine chlorhydrate 0.1%) was instilled every 10 minutes for half an hour before the automated microkeratome (Automated Corneal Shaper, Chiron Vision) was applied. The cornea was marked with 2 pararadial gentian violet lines. The suction ring was centered around the limbus and the intraocular pressure verified as greater than 65 mm Hg with a Barraquer tonometer. The 5.5 mm applanation lens was inserted in the suction ring to check the disc diameter. The 160'plate was used to obtain a 160 gm thick corneal flap. The hinged flap was reposited using a 23 gauge cannula and the interface irrigated with balanced salt solution to remove all particles and epithelial cells. The flap was then centered for proper alignment using the pararadial marks. The keratectomy incision was dried with surgical sponges, and the flap was checked for adhesion by asking the patient to blink several times. The patient was sent home with antibiotic eyedrops (tobramycin [Tobrex®]) for 6 days without an eye patch. Six to 8 weeks after the lamellar cut, a previously described LTK procedure 5'8 was performed using the
noncontact hoimium laser (gLase 210 model, Sunrise Technologies). The holmium laser spots were pladed outside the previous lamellar cut (i.e., 6.0 mm or more of corneal diameter). After the procedure, the eye was rinsed with Tobrex eyedrops, and an ointment with the same antibiotic was applied. The same topical treatment was continued for 4 days. The patient was sent home with an eye patch for 24 hours. A simple analgesic agent (aydolid) was prescribed in case of eye discomfort. The Student t test was used for statistical analysis. Differences were considered statistically significant when the P value was less than .05.
Results No change in patient refraction or keratometry was found after the lamellar corneal cut. During the first 3 days after the LTK surgery, the patients experienced variable discomfort and photophobia, which generally disappeared within 2 weeks. No sight-threatening complications were recorded during the study. Immediately after LTK surgery, a significant myopic shift was observed (Figure 1). However, 4 to 6 months after surgery, most patients had a more stable emmetropic refraction due to partial regression of the LTK effect (Figures 2 to 4). Mean BSCVA before LTK was 0.66 -- 0.2 (range 0.3 to 0.9); mean UCVA at the end of the study was 0.58 -+ 0.17 (range 0.3 to 0.8). Ten patients (66.6%) had a UCVA of 0.6 or better. No patient lost 2 lines or more of BCVA. There was no statistically significant difference between the mean BSCVA before LTK and the mean postoperative UCVA. Mean cycl6plegic refraction and keratometry before and after LTK are shown in Table 1. There was a statistically significant difference between the preopera-
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Figure 1. (Ismail) Follow-up of mean and range of cycloplegic refraction.
j CATARACTREFRACTSURG--VOL 25, FEBRUARY1999
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F i g u r e 4. (ismail) Videokeratography 18 months after LTK, showing a change of almost 5,0 D in the central topography.
tive and final postoperative results (P < .005). No statistically significant differences were found between the cycloplegic refraction and the keratometry at 12 months and at the end of the study.
Discussion Noncontact thermokeratoplasty by holmium laser has been proposed to correct hyperopia up to +5.0 diopters (D). 4'5'~'9 Regression of the initial obtained effect has been the primary limitation of this technique. In the early postoperative period, a satisfactory correction
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(Ismail) Videokeratography 8 months after LTK.
up to +6.0 D can be achieved. However, during the first 3 months, regression occurs and the central corneal power may return to previous readings. 4'5 We demonstrated that corneas previously treated by myopic PRK l° and myopic laser in situ keratomileusis 11 behave differently when treated by LTK for hyperopic shift. 6 In these cases, lower central pachymetric values, in addition to the absence of Bowman's layer, explain the stability of the refractive outcome after LTK. Bowman's layer is considered the backbone of the cornea because its elasticity is different from that of the stroma) 2 Once cut, this structure never heals as before, leading to fibrous tissue accumulation in corneal wounds, lz Lamellar cutting before LTK might induce a beneficial partial loss of the corneal topographic memory due to discontinuity and alteration of the integrity of Bowman's layer. This might improve regression of the obtained effect when treating hyperopia by noncontact LTK. In the present study, we applied the LTK technique to 15 eyes of patients who wanted hyperopic correction. A significant improvement in mean UCVA, central keratometry, and cycloplegic refraction occurred in all eyes. No statistically significant difference was found between the 12th month and the final refractions.
Preoperative and postoperative cycloplegic refraction and keratometry.
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214
.I CATARACT REFRACT SURG--VOL 25, FEBRUARY 1999
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LASERTHERMOKERATOPLASTYAFTER LAMELLARCORNEAL CUTTING Koch et al. 4'5 obtained an average o f - 1 . 6 4 _+ 0.61 D of correction with stability of regression 1 year after LTK treatment using 2 rings. In our previous studies, 6'9 we obtained a mean correction of - 2 . 4 8 D after 15 months of treatment with 3 rings. However, in the present study, with Bowman's layer cut, a correction of - 3 . 9 1 D was obtained after a mean follow-up of 19.13 months. From these results, we conclude that corneal lamellar cutting (LK) improves the magnitude of the refractive correction for noncontact LTK, with evident improvement of the regression. Long-term follow-up may provide useful data for adjusting special treatment algorithms to improve the predictability of this new procedure (LK-LTK). Also, a special instrument is under trial to produce a homogenous 360 degree complete cut to Bowman's layer.
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References 1. Swinger CA, Barraquer JI. Keratophakia and keratomileusis--clinical results. Ophthalmology 1981; 88:709715 2. Grandon SC, Sanders DR. Clinical evaluation of hexagonal keratotomy for the treatment of primary hyperopia. J Cataract Refract Surg 1995; 21:140-149 3. Dausch D, Klein R, Schr6der E. Excimer laser photo-
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refractive keratectomy for hyperopia. Refract Corneal Surg 1993; 9:20-28 Koch DD, Abarca A, Villareal R, et al. Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty; clinical study with two-year follow-up. Ophthalmology 1996; 103:731-740 Koch DD, Kohnen T, McDonnell PJ, et al. Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty; United States phase IIA clinical study with a 1-year follow-up. Ophthalmology 1996; 103:1525-1536 Ismail MM, P6rez-Santonja. JJ, Ali6 JL. Correction of hyperopia and hyperopic astigmatism by laser thermokeratoplasty. In: Serdarevic ON, ed, Refractive Surgery: Current Techniques and Management. New York-Tokyo, Igaku-Shoin, 1997; 263-274 Er H, Menefee RF, Valderrama GL. Acute histological changes induced by laser thermal keratoplasty. ARVO abstract 3541. Invest Ophthalmol Vis Sci 1994; 35:2021 lsmail MM, Ali6 JL, Sanchez Castro P. Efectos histol6gicos de la termoqueratoplastla con l~ser de holmio. Estudio experimental. In press, Arch Soc Esp Oftalmol Ali6 JL, Ismail MM, Sanch~ Pego JL. Correction of hyperopia with non-contact Ho:YAG laser thermal keratoplast)~ J Refract Surg 1997; 13:17-22 All6 JL, Ismail MM, Artola A, P~rez Santonja JJ. Correction of hyperopia by photorefractive keratectomy using non-contact Ho:YAG laser thermal keratoplasty. J Refract Surg 1997; 13:13-16 Waring GO III. Refractive Keratotomy for Myopia and Astigmatism. St Louis, MO, Mosby Year-Book, Inc, 1992
j CATARACT REFRACT SURG--VOL 25, FEBRUARY 1999
215

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