Phacoemulsification and extracapsular cataract extraction are the most commonly employed techniques for cataract surgery.1 These techniques are constantly evolving in an attempt to decrease residual ametropia and postoperative astigmatism.
Residual myopia and regular astigmatism account for most of the decreased uncorrected visual acuity after cataract surgery, although intraocular lens (IOL) power is calculated for emmetropia.2 In some cases, the residual refractive defect is not tolerable due to anisometropia, or it is undesirable because the patient strongly desires not to require corrective lenses. The residual refractive error after cataract surgery may be due to biometrie errors3,4, inadequate calculation and selection of the IOL power2, and other reasons.5
Laser in situ keratomileusis (LASIK) is a technique for the correction of myopia.6 The procedure combines lifting a corneal flap made with a microkeratome and refractive photoablation on the stromal bed by means of a 193-nm argon fluoride excimer laser.6 Recent clinical studies report that LASIK offers good efficacy, predictability, and safety for the correction of low, moderate, and high myopia.7,8 However, no clinical data are available concerning LASIK for correcting residual myopia after cataract surgery.
The purpose of this study was to evaluate the refractive and clinical results of correction of residual myopia and myopic astigmatism after cataract surgery by means of LASIK.
PATIENTS AND METHODS
This retrospective study comprised 22 consecutive eyes (22 patients) that underwent LASIK for correcting symptomatic residual myopia or myopic astigmatism after cataract surgery. Eight of the patients were men (36.4%) and fourteen were women (63.6%). Mean patient age was 65 ± 10 years (range, 50 to 80 yr).
The surgical technique used for cataract surgery in all eyes was phacoemulsification with intraocular lens implantation in the posterior chamber. The types of lenses used were: Silens 2 in 12 eyes (corneal incision, Chiron Vision-Domilens, Lyon, France), AL3 in three eyes (scleral incision, Chiron Vision-Domilens, Lyon, France), Perlens 2 in two eyes (scleral incision, Chiron Vision-Domilens, Lyon, France), and SI30NB in five eyes (corneal incision, Allergan Medical Optics, Irvine, CA).
Patient selection criteria were: older than 45 years of age, myopia between -0.75 and -12.00 diopters (D), myopic astigmatism less than -3.50 D, stable refraction (change less than 0.50 D between two consecutive examinations), contact lens intolerance, inability to wear glasses because of anisometropia, undesirable residual refractive defect because the patient strongly desires not to wear corrective lenses, normal anterior segment, and no general health problems. Patients who had previous ocular surgery other than phacoemulsification, corneal diseases, severe dry eye syndrome, glaucoma, history of ocular trauma, or retinal diseases were excluded. In addition, the cornea had to be thick enough so that the total corneal thickness after LASIK was greater than 400 µm (>240 ?ta of stroma remaining under the flap). Informed consent was obtained from all patients after they received a detailed description of LASIK and a thorough review of its known risks.
Preoperative and postoperative examinations included visual acuity, manifest and cyclopegic refraction, videokeratography (EyeSys Corneal Analysis System, Houston, TX), slit-lamp microscopy, Goldmann applanation tonometry, indirect ophthalmoscopy, and corneal thickness measurement (DGH-500 pachymeter, DGH technology, Inc., Exton, PA). Postoperative examinations were conducted at 1 day, 1 week, and at 1, 3, 6, and 12 months. Results are reported for 1, 3, 6, and 12 months after LASIK
All LASIK procedures were performed using the Automated Corneal Shaper microkeratome (Chiron Vision, Irvine, CA), and the NIDEK EC-5000 193nm, argon fluoride excimer laser (Nidek Co Ltd, Tokyo, Japan). Patients received 5 mg of oral diazepam 30 minutes before surgery. The procedure was done using topical anesthesia of oxybuprocaine 0.4%, one drop every 10 minutes for 30 minutes before surgery.
The eyelids were retracted using a Barraquer speculum, and the eye was cleaned with normal saline. After placement of the suction ring, IOP was verified to be greater than 65 mmHg with a Barraquer tonometer. A nasally-based, 160-µm thick and 8.5-mm diameter corneal flap was then made using the automated microkeratome. The hinged flap was lifted using a 23-gauge cannula and placed against the nasal sclera. The exposed stromal bed was then ready for laser ablation.
Excimer laser ablation was performed on the stromal bed with the NIDEK EC-5000 excimer laser, with an energy fluence of 180 mJ/cmp 2 and a frequency of 5 to 50 Hz. A 5.5- to 6.0-mm diameter ablation zone along with an additional 1-mm transition zone was used. After ablation, the flap was replaced in its original position and the interface was irrigated copiously with balanced salt solution using a 23-gauge cannula. The flap was then centered for proper alignment, and no sutures were used.8
Eyes were not occluded after the procedure. Antibiotic (tobramycin 0.3%, Tbbrex, Alcon Iberhis S.A., Alcobendas, Madrid, Spain) and corticosteroid eye drops (fluorometholone 0.10%, FML, Allergan S.A., Tres Cantos, Madrid, Spain) were instilled four times a day for the first 10 days. Patients were advised to avoid direct pressure to their eyes for 12 weeks. All eyes were followed for a period of 1 year.
Differences for continuous variables were tested using two-way analyses of variance (two-way ANOVA) for normally distributed data. Differences were considered statistically significant when P-values were less than .05.
We present data on residual myopic refraction obtained in 22 eyes in which cataract surgery followed by LASIK was performed.
After cataract surgery (before LASIK), the mean residual spherical equivalent refraction was -2.90 ± 1.80 D (range, -0.80 to -8.50 D). Mean uncorrected visual acuity (UCVA) after cataract surgery was 0.11 ± 0.16 (range, 0.002 to 0.5), and mean best spectacle-corrected visual acuity (BSCVA) was 0.54 ± 0.17 (range, 0.2 to 0.8). Mean keratometric astigmatism was -1.70 ± 1.40 D (range, -0.25 to -6.50 D). The average corneal thickness after cataract surgery was 534 ± 39 µm (range, 481 to 614 µm), and the mean central corneal keratometric power was 44.00 ± 1.60 D (range, 40.00 to 47.00 D). The mean cylinder refraction after cataract surgery was -1.00 ± 1.00 D (range, 0 to -3.25 D).
The mean elapsed time between cataract surgery and LASIK was 10 ± 15 months (range, 3 to 72 mo). Mean UCVA after LASIK was 0.47 ± 0.22 (range, 0.05 to 0.8) at 1 month, 0.47 ± 0.22 (range, 0.1 to 0.9) at 3 months, 0.44 ± 0.16 (range, 0.1 to 0.7) at 6 months, and 0.44 ± 0.16 (range, 0/1 to 0.7) at 12 months (Fig 1). Differences in UCVA before and after LASIK were statistically significant at all follow-up intervals (P < .01, two-way ANOVA). There were no significant differences in UCVA after LASIK (P > .05, two-way ANOVA). In 9 eyes (40.9%) at 3 months, 10 eyes (45.4%) at 6 months, and 10 eyes (45.4%) at 12 months, UCVA was 0.5 (20/40) or better. No eyes achieved an UCVA of 20/20 or better.
Figure 1. Time course of uncorrected visual acuity (UCVA) (mean ± standard deviation) for 22 eyes with LASIK for residual myopia after cataract surgery.
Figure 2. Time course of best spectaclecorrected visual acuity (BSCVA) (mean ± standard deviation) for 22 eyes with LASIK for residual myopia after cataract surgery.
Mean BSCVA after LASIK was 0.55 ± 0.2 (range, 0.15 to 0.9) at 1 month, 0.59 ± 0.2 (range, 0.15 to 0.9) at 3 months, 0.59 ± 0.18 (range, 0.15 to 0.9) at 6 months, and 0.6 ± 0.18 (range, 0.15 to 0.9) at 12 months (Fig 2). Best spectacle-corrected visual acuity after LASIK was significantly better than before LASIK at 3, 6, and 12 months (P < .05, twoway ANOVA), although at 1 month after LASIK, BSCVA was not significantly different from before LASIK (P > .05, two-way ANOVA). Postoperative BSCVA improved significantly between 1 and 3 months, and between 1 and 12 months (P < .05, two-way ANOVA).
Mean postoperative spherical equivalent refraction in the first month after LASIK was +0.10 ± 0.50 D (range, -1.00 to +1.75 D); in the third month it was +0.20 ± 0.60 D (range, -1.00 to +1.25 D); in the sixth month, it was +0.30 ± 0.70 D (range, -1.00 to +1.50 D), and in the twelfth month it was +0.40 ± 0.60 D (range, -0.60 to +1.50 D) (Fig 3). The differences between preoperative and postoperative values were statistically significant at all follow-up intervals (P < .01, two-way ANOVA). No significant change occurred between postoperative follow-up intervals (P > .05, two-way ANOVA). In 19 eyes (86.3%) at 3 months, 19 eyes (86.3%) at 6 months, and 18 eyes (81.8%) at 12 months after LASIK, spherical equivalent refraction was within ?1.00 D. In 12 eyes (54.5%) at 3 months, 12 eyes (54.5%) at 6 months, and 11 eyes (50%) at 12 months, postoperative spherical equivalent refraction was within ±0.50 D of emmetropia.
Figure 3. Spherical equivalent refraction over 1 year after LASIK to correct residual myopia following cataract surgery (mean ± standard deviation) in 22 eyes.
The mean postoperative cylinder refraction was -0.10 ± 0.60 D (range, -1.50 to +1.75 D) at 1 month, -0.40 ± 0.90 D (range, -3.00 to +1.75 D) at 3 months, -0.90 ± 1.00 D (range, -3.00 to +1.75 D) at 6 months, and -0.80 ± 0.90 D (range, -2.75 to +1.75 D) at 12 months.
Mean keratometric astigmatism was -1.50 ± 0.80 D at 1 month, -1.50 ± 0.80 D at 3 months, -1.50 ± 0.80 ± at 6 months, and -1.80 ± 0.90 D at 12 months after LASIK. The differences between values before and after LASIK were not significant at any follow-up interval (P > .05; two-way ANOVA), nor were the differences between postoperative values (P > .05).
Mean postoperative central corneal keratometry was 41.20 ± 1.30 D at 1 month, 41.30 ± 1.20 D at 3 months, 41.40 ± 1.30 D at 6 months, and 41.40 ± 1.30 D at 12 months. The differences between values before and after LASIK were significant for all follow-up intervals (P < .01; two-way ANOVA). There were no significant differences among postoperative central keratometric values (P > .05; twoway ANOVA).
Mean IOP before LASIK was 14.8 ± 2.9 mmHg. It decreased postoperatively to 13.6 ± 2.1 mmHg at 1 month, 13.7 ± 1.8 mmHg at 3 months, 13.5 ± 2 mmHg at 6 months, and to 13.5 ± 3.1 mmHg at 12 months. No patient developed high IOP after surgery.
No patient developed haze, epithelial ingrowth, or flap melting. No changes in the IOL position or in the cataract incision were observed after LASIK in any eye.
Cataract surgery using extracapsular cataract extraction or phacoemulsification with IOL implantation is one of the most common opthalmic surgeries carried out in general clinical practice.9
Due to technological progress in cataract surgery, severe complications are rare; postoperative problems are related mainly to the control of surgically induced astigmatism10 and refractive errors.2 Myopia, with or without astigmatism, is the most frequent refractive error found after cataract surgery.2
At present, to correct residual myopia, we can perform radial keratotomy or photorefractive keratectomy (PRK). Radial keratotomy seems to be more unpredictable in patients over 40 years of age than in young patients.11 Photorefractive keratectomy offers good efficacy, predictability, and safety for myopia up to -6.00 D12; however, poor predictability, regression of effect, and corneal haze can occur in eyes with high myopia.13
Laser in situ keratomileusis combines the accuracy of the excimer laser to remove tissue and the ability of the microkeratome to access the inner stroma and preserve Bowman's membrane, reducing the effect of wound healing and leading to less scarring and regression of effect.6-8 Preliminary studies found that LASEK offers good results with fast visual rehabilitation for the correction of low, moderate, and high myopia.14
The advantages of LASIK make it the procedure of choice for correcting residual myopia after cataract surgery. However, no published information is available concerning LASIK after cataract surgery. Since LASIK involves placement of a suction ring which puts the eye under? high pressure (65 mmHg or more), some complications could arise related to the cataract incision or to stability of the intraocular lens.
The purpose of this study was to evaluate the effectiveness, predictability, and safety of LASIK to correct residual myopia and myopic astigmatism after cataract surgery. This study concerns an advanced age group, in contrast to younger age groups in published studies of primary LASIK (Piander DC, Tayfour F. Excimer laser in situ keratomileusis in 124 myopic eyes. J Refract Surg 1995;11(suppl):S234-S238; Kremer FB, Dufek M. Excimer laser in situ keratomileusis. J Refract Surg 1995;11(suppl):S244-S247).8,14-16
Uncorrected visual acuity is one of the main criteria used to assess the effectiveness of a refractive procedure.7,15 Our data show an improvement in mean UCVA after LASIK; 45.4% of eyes at 6 months and 45.4% at 12 months had a mean UCVA of 0.5 (20/40) or better. In addition, mean BSCVA improved half a line at 12 months after LASIK over preoperative values. Concerning predictability7, 86.3% of eyes had a spherical equivalent refraction within ±1.00 D of emmetropia 6 months after LASIK, and 81.8% at 12 months. The refraction was stable 1 month postoperatively, although some refractive changes have been reported beyond 1 month after primary LASIK for low and moderate myopia in young patients.14
No patient developed haze, epithelial ingrowth, flap melting, or other complications. No problems were observed related to the IOL position or to the cataract incision. Although LASIK was a safe procedure when performed beyond 3 months after cataract surgery, performing this procedure sooner could create potential complications related to the cataract incision or to the IOL stability, mainly when the patient is using medications (corticosteroids) that might affect wound healing after cataract surgery. In addition, LASIK may not be a safe procedure in patients with associated glaucoma or marked glaucomatous optic nerve damage.
We conclude that LASIK, performed on Pseudophakie, medium age patients, is an effective, predictable, stable, and safe technique for the correction of residual myopia after cataract surgery. No complications related to IOL or cataract incision were found when IASIK was performed beyond 3 months after cataract surgery.
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