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Jin et al. (2005) evaluated and compared the efficacy and safety of LASIK in the correction of primary and secondary mixed astigmatism after previous LASIK surgery in a retrospective, comparative case series that included 118 eyes. The eyes were divided into two groups: in group A (n = 64), LASIK was for primary mixed astigmatism and in group B (n = 54), LASIK was for secondary mixed astigmatism. Mean follow-up was 10.6 +/- 5.90 months. Overall, the postoperative uncorrected visual acuity (UCVA) was 20/20 in 51% of eyes and 20/40 or better in 97% of eyes at the last visit. The mean refractive cylinder was -2.18 +/- 0.94 D preoperatively and -0.56 +/- 0.56 D postoperatively. Sixty-one percent of eyes had a refractive cylinder of 0.50 D or less. The difference of preoperative cylinder was significant between group A and group B. However, there was no statistical difference of postoperative refraction and UCVA between these two groups. At 12 months, the mean vector magnitude achieved was 93% of intended cylinder correction with a mean angle of error of -3.0 +/- 16 degrees. The investigators concluded that LASIK is a safe, effective, and predictable procedure to treat both primary and secondary mixed astigmatism.
Several other uncontrolled studies (number of eyes=20-43) also resulted in the conclusion that LASIK was effective for treating surgically induced astigmatism or anisometropia (Lima et al., 2001;
Lindstrom et al., 1999; Buzard et al., 2004; Donnenfeld et al., 1999; Horackova et al., 2008; Norouzi et al., 2003).
Li et al. (2005) assessed the visual and refractive outcome of LASEK for the correction of residual myopia and astigmatism after laser in situ keratomileusis (LASIK) in a prospective study of 66 eyes in 34 patients who developed myopic regression after LASIK. Mean follow-up was 13.2 months after laser ablation. Postoperative results revealed a reduction in the residual myopia and astigmatism.
Higher order aberration was increased postoperatively. The investigators concluded that LASEK performed in eyes with myopic regression after LASIK result in an improvement in uncorrected visual acuity.
La Tegola et al. (2007) evaluated the use of a software ablation program (Corneal Interactive Programmed Topographic Ablation [CIPTA] that provides customized photorefractive keratectomy (PRK) to correct astigmatism after keratoplasty in a prospective, noncomparative, consecutive case series of 44 eyes. Eighteen eyes were treated for regular astigmatism and 26 eyes were treated for irregular astigmatism after penetrating keratoplasty. Orbscan II topography (Bausch & Lomb) and a flying-spot laser (LaserScan 2000; LaserSight) were used. Mean target-induced astigmatism was 8.19 +/- 2.68 diopters (D) and 7.68 +/- 4.50 D in the regular and irregular astigmatism groups,
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respectively. Mean follow-up was 25.4 +/- 13 months. At last postoperative follow-up, 13 (72.2%) and 18 (69.2%) eyes in the regular and irregular astigmatism groups, respectively, had uncorrected visual acuity (UCVA) better than 20/40. Four (22.2%) and 8 (30.7%) eyes in the regular and irregular astigmatism groups, respectively, had UCVA of 20/20. Fourteen (77.7%) and 18 (69.2%) eyes in the regular and irregular astigmatism groups, respectively, were within 1.00 D of attempted correction in spherical equivalent manifest refraction. Mean surgically induced astigmatism was 7.66 +/- 2.70 D and 6.99 +/- 3.80 D for the regular and irregular astigmatism groups, respectively. Index of success of astigmatic correction was 0.138 and 0.137 for the regular and irregular astigmatism groups, respectively. Haze developed in three eyes. The investigators concluded that topography-driven PRK using CIPTA software is a suitable solution for correcting regular and irregular astigmatism after penetrating keratoplasty.
Xie et al. (2007) evaluated the long-term safety and effectiveness of photorefractive keratectomy (PRK) in the treatment of refractive errors (n=14 eyes) after epikeratophakia (EP) for keratoconus.
Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refractive error, corneal astigmatism, pachymetry, corneal topography, and complications were monitored. Mean follow-up after PRK was 63.4 +/- 19.8 months. Mean spherical equivalent was -5.5 +/- 3.9 D before PRK, -0.9 +/- 0.5 D at 1 month after PRK, and -1.5 +/- 1.0 D at 3 years. Mean astigmatism was 4.2 +/- 2.1 D before PRK, 1.2 +/- 0.5 D at 1 month after PRK, and 1.5 +/- 0.6 D at 3 years. The investigators concluded that PRK appears to be reliable and safe for the correction of residual ametropia after EP for keratoconus, and the visual acuity can remain stable after PRK for a long time.
The National Institute for Health and Clinical Excellence has issued guidance for photorefractive (laser) surgery for the correction of refractive errors. The guidance report concludes that there are no significant differences between PRK, LASEK, or LASIK for achieving the predicted refractive outcome in eyes treated for myopia or astigmatism. Final uncorrected visual acuity is similar for all 3 techniques. According to the guidance, photorefractive laser surgery is safe and effective for use in appropriately selected patients. (National Institute for Health and Clinical Excellence, 2006) Computerized Corneal Topography-guided Customized Excimer Laser Ablation Several primarily prospective but uncontrolled and unblinded studies reported topographical and refractive outcomes, visual acuity, subjective symptoms, and patient satisfaction after CCT-guided customized ablation. Final topographical and refractive outcomes were good, although reoperation was sometimes necessary because of regression of effect. In the Knorz and Jendritza (2000) study of 10 patients (11 eyes), corneal topography at 1 year was the same as, or better than anticipated, in 91% of patients. Reoperation was required in 36% of patients. Alessio et al. (2001) studied 32 patients and reported that after a mean of 10 months, 69% of eyes were within 0.50 diopters (D) of intended correction and 88% were within 1 D; no reoperations were reported. Other studies (total patients, 21; total eyes, 23) reported good centration and only 2 reoperations (Kymionis et al., 2004, Lin and Manche, 2004, Wiesinger-Jendritza, Knorz et al., 1998, Dausch et al., 2000).
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The primary clinical benefit of customized ablation in these studies was the elimination or improvement of subjective symptoms. Among the 53 patients for whom this outcome was clearly reported, 43 patients had 100% elimination of symptoms, such as halos and glare, and the other 10 reported improvement (Kymionis GD et al., 2004, Lin and Manche, 2004, Knorz and Jendritza, 2000, Wiesinger-Jendritza, Knorz et al., 1998, Dausch et al., 2000). In the study by Alessio et al., the effect on monocular diplopia (double vision) was reported separately; prevalence was reduced from 88% to 14% (Alessio et al., 2001).
All studies reported general improvement in visual acuity at last follow-up. Postoperative mean uncorrected visual acuity (UCVA) was 20/20 to 20/50 in several studies, 0.76 as expressed by the decimal method in one study, and improved by greater than or equal to 1 Snellen line in 63% of eyes in another. Postoperative mean best corrected visual acuity (BCVA) was 20/20 to 20/37, 0.95, or improved by greater than or equal to 1 Snellen line in 75% of eyes. In the largest study (n=32), BCVA improved from 20/28 to 20/22 (Alessio et al., 2001).
There was one assessment of overall patient satisfaction (n=10). At 1 year, 18% of patients reported they were very satisfied, 46% were moderately satisfied, and 36% were not satisfied. The authors did not discuss reasons for dissatisfaction. Reported postoperative visual acuity in this study was lower than in other studies, and the specific effect on subjective symptoms was not reported (Knorz and Jendritza et al., 2000).
Wu et al., (2008) assessed the efficacy of topography-guided laser ablation for correction of previously decentered laser ablation using LaserSight's excimer laser in 18 patients who previously underwent LASIK surgery for myopia correction in both eyes. For each patient, only the decentered eye was re-treated while the other asymptomatic eye formed a control group. For the retreated 18 eyes, the mean decentration was significantly reduced from 1.32+/-0.28mm to 0.61+/-0.23mm postoperatively. Corneal higher-order aberrations, including the coma-like aberrations and spherical aberration, were decreased. In comparing the measurements for the retreated group to those for the control group, no significant difference was found either in decentration or in best spectaclecorrected visual acuity (BSCVA), but the contrast sensitivity at 0.70 was lower and the level of corneal aberrations was higher. The investigators concluded that topography-guided ablation with LaserSight excimer laser is effective to correct decentered ablation. However, the re-treated eye is still inferior to the eye with originally centered ablation in corneal optical quality or visual performance.
Conclusions regarding topography-guided laser ablation are limited by the small number of studies with very small sample sizes and the lack of objective methods for assessing patients' experience of higher order aberrations. Additional studies are needed to establish efficacy and safety, and to define patient selection criteria.
Professional Societies American Academy of Ophthalmology (AAO): According to technology assessments prepared by
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the AAO, LASIK provides effective, predictable treatment for patients with low to moderate myopia and hyperopia. These assessments also state that, although there is less data available concerning treatment of hyperopic astigmatism, LASIK seems to be effective for this indication, with the clinical results becoming less compelling for patients who have hyperopia exceeding 4.0 diopters. Likewise, the AAO has indicated that LASIK is a less reliable treatment for moderate to high myopia and mild to moderate myopic astigmatism. The AAO technology assessments indicate that adverse effects such as dry eye, starbursts at nighttime, and reduced contrast sensitivity occur relatively frequently after LASIK for myopia and hyperopia; however, complications including infection and ectasia that can cause significant permanent visual loss occur rarely. (AA0, 2002; Varley, 2004) A 2007 AAO Preferred Practice Pattern on Refractive Errors and Refractive Surgery states that the most frequently performed procedures for low to moderate myopia utilize the excimer laser. A surface ablation technique, photorefractive keratectomy (PRK), was the first procedure performed;
subsequently, LASIK has become the most commonly performed keratorefractive surgery. Other keratorefractive procedures to correct low to moderate myopia include variations of PRK called laser epithelial keratomileusis (LASEK) and epi-LASIK, insertion of intrastromal corneal ring segments and radial keratotomy. (AAO, 2007) American Society of Cataract and Refractive Surgery (ASCRS): The educational arm of the ASCRS, the Eye Surgery Education Council (ESEC), released guidelines to help patients decide if LASIK is right for them and to guide them as to what they should expect from their doctor and the procedure. According to the guidelines, all LASIK candidates will fall into one of three broad
categories (ASCRS, 2003):
- Category 1: Ideal candidates are over 18 years of age, have had a stable eyeglass or contact lens prescription for at least 2 years, have sufficient corneal thickness to allow the surgeon to safely create a clean corneal flap of appropriate depth, have common types of vision problems or refractive error (myopia, astigmatism, hyperopia, or a combination), do not have disease that may reduce the effectiveness of the surgery or their ability to heal properly or quickly, and understand the benefits as well as risks and limitations of the procedure.
- Category 2: Less-than-ideal candidates have a history of dry eyes, have scarring of the cornea, are being treated with medications such as steroids or immunosuppressants that can prevent healing, or are suffering from diseases such as autoimmune disorders that slow healing.
- Category 3: People who should postpone surgery are under age 18, have unstable vision, are pregnant or nursing, have a history of ocular herpes within 1 year prior to the surgery, or have refractive errors too severe for treatment with current technology. Non-LASIK candidates include individuals who have diseases such as cataracts, advanced glaucoma, corneal diseases, corneal thinning disorders (keratoconus or pellucid marginal degeneration), or certain other preexisting eye diseases that affect or threaten vision. In addition, individuals who do not give informed consent or who have unrealistic expectations are not candidates for LASIK surgery.
Additional Search Terms Excimer Laser- Commercial Medical Management Guideline Anisometropia, bifocals, pachymetry, corneal steepening, corneal topography, cycloplegic refraction, emmetropia, funduscopy, photoablation, presbyopia, pterygium, radial keratotomy, refractive error, Reis-Buckler dystrophy, retina, RK, slit-lamp biomicroscopy, Snellen testing, thermokeratoplasty, UCVA, videokeratography, visual acuity testing Additional Medical Products
Commercially available excimer lasers for eye surgery include but are not limited to the following:
Technolas™ 217A (Bausch & Lomb Surgical Inc, San Dimas, CA), Nidek® EC-5000 (Nidek Inc, Tokyo, Japan), and the VISX® Star X4 (VISX Inc, Santa Clara, CA).
Ablation planning software include but are not limited to the following: Corneal Interactive Programmed Topographic Ablation (CIPTA) (Ligi Technologie Medicali).
Computerized corneal topography software unit: Humphrey® Atlas (Carl Zeiss Meditec) (includes VisionPro Ablation Simulator) References and Resources Resources Alessio G, Boscia F, La Tegola MG, Sborgia C. Topography-driven excimer laser for the retreatment of deentralized myopic photorefractive keratectomy. Ophthalmology. 2001: 108(9):1695-1703.
American Academy of Ophthalmology (AAO) [Web site]. Laser in situ keratomileusis for myopia
and astigmatism: safety and efficacy. January 2002. Available at:
http://one.aao.org/CE/PracticeGuidelines/Ophthalmic_Content.aspx?cid=c19e38d8-264d-405e-bc4ae6ba12dc99bd. Accessed March 2009.