Laser in situ keratomileusis to treat myopia: early experience

Lasik enhancements: a comparison of lifting to recutting the flap

PURPOSE

To compare the visual outcomes and incidence of complications of lifting with recutting the lamellar flap in laser in situ keratomileusis (LASIK) enhancement surgery.

DESIGN

Retrospective case-control study.

PARTICIPANTS

Two hundred twelve consecutive eyes undergoing a LASIK enhancement procedure at a single surgery location during a 5-year period.

METHODS

Charts of participants were obtained and outcome measures obtained.

MAIN OUTCOME MEASURES

Uncorrected visual acuity, best-corrected visual acuity, refractive error, complications.

RESULTS

Relifting of flaps was performed in 164 of 212 eyes (77.4%), and recutting of flaps was performed in 48 of 212 eyes (22.6%). There were no significant differences in early visual outcomes between the two groups. At 1 year patients had significantly better uncorrected vision if the flap was lifted rather than recut (20/24.7 vs. 20/31.3, P < 0.008). In addition, the flap lift group had a significantly more stable refraction at 1 year than did the recut group (change in spherical equivalent: +0.05 diopters (D) vs. -0.57 D). The incidence of complications did not significantly differ between the two groups.

CONCLUSIONS

LASIK enhancement surgery can be performed safely and effectively by either lifting or recutting a flap. Lifting the flap may show better long-term stability of refractive error and uncorrected acuity.

Pathologic myopia: where are we now?

PURPOSE

To describe current concepts and available treatments for pathologic myopia.

DESIGN

Review of experimental and clinical studies.

METHODS

The demography, natural history, medical and surgical treatments for choroidal neovascular membrane, vitreoretinal interface disorders and future strategies for pathologic myopia are reviewed.

RESULTS

Several medical and surgical modalities are currently available to treat various complications of pathologic myopia. Macular translocation appears to stabilize or improve visual function in many eyes with choroidal neovascularization.

CONCLUSION

Newer strategies are emerging to better ameliorate or prevent the complications of pathologic myopia.

Bilateral Simultaneous Laser in situ Keratomileusis With the Aesculap Meditec MEL 60 Laser

PURPOSE

To report the outcome of bilateral simultaneous excimer laser in situ keratomileusis (LASIK) with the Aesculap Meditec MEL 60 laser for the correction of myopia and hyperopia.

METHODS

This retrospective study included 338 eyes of 169 patients who had bilateral simultaneous LASIK performed by one surgeon (D.L.V.).

RESULTS

Postoperatively, 20/20 or better visual acuity was achieved by 78.5% (186 eyes) in the <-6.00-D group, and 55.6% (54 eyes) in the > or = -6.00-D group. Postoperatively, the mean spherical equivalent refraction was within +/- 0.50 D for 78% (185 eyes) in the <-6.00-D group (range, -2.25 to +1.25 D), 55% (53 eyes) in the > or = -6.00-D group (range, -2.38 to +1.13 D), and one eye in the hyperopic group. Complications at 3 months included regression in five eyes (1.4%), infiltrates in six eyes (1.7%), primary undercorrection in two eyes (0.6%), superficial punctate keratitis in four eyes (1.1%), ten eyes (2.9%) underwent enhancement, two eyes (0.6%) underwent refractive lensectomy, and four eyes (1.1%) underwent astigmatic keratotomy 3 months postoperatively. Two eyes lost two lines of best spectacle-corrected visual acuity.

CONCLUSION

Bilateral simultaneous LASIK with the Aesculap Meditec MEL 60 laser was effective and predictable. It was more economical and convenient for the patient than unilateral LASIK and binocular visual rehabilitation was rapidly restored. No sight threatening complications occurred in this group of patients.

Subclinical inflammation after laser in situ keratomileusis in corneal grafts

PURPOSE

To evaluate postoperative inflammatory reaction in the eye after laser in situ keratomileusis (LASIK) in corneal grafts.

SETTING

Department of Ophthalmology, Helsinki University Central Hospital, Helsinki, Finland.

METHODS

Ten eyes of 9 patients with penetrating keratoplasty (PKP) and significant postoperative refractive errors and astigmatism had LASIK 22 months or more after the PKP. All patients were treated with the VISX Star excimer laser and the Bausch & Lomb Hansatome microkeratome. Preoperative and early postoperative inflammation was evaluated by quantifying the aqueous flare intensity with a laser flare photometer (Kowa FM-500). A full ophthalmic assessment was also performed before LASIK and up to 6 months postoperatively.

RESULTS

The inflammatory response was mild and limited to the first postoperative hour. The mean anterior chamber flare increased from 6.0 photons/millisecond (ph/ms) preoperatively to 14.0 ph/ms at 1 hour and then decreased to 6.7 ph/ms (hour 3), 6.8 ph/ms (day 1), and 8.2 ph/ms (day 7). The mean spherical equivalent (SE) refraction decreased from -3.81 diopters (D) (range -9.63 to -0.25 D) to -0.46 D (range -1.13 to +0.38 D), and the mean preoperative astigmatism decreased from 3.0 D (range 6.5 to 0.5 D) to 0.7 D (range 0.0 to 2.0 D). At the last examination, 9 eyes were within +/-1.0 D (6 within +/-0.5 D) and all were within +/-1.5 D of the intended SE refraction. Three eyes achieved full cylinder correction, and 7 were within +/-1.0 D of the intended correction. Eight eyes had a best corrected visual acuity of 20/40 or better (unchanged or gain of 1 to 4 lines [6], loss of 1 line [1], and loss of 3 lines [1]), and 8 had an uncorrected visual acuity of 20/50 or better.

CONCLUSIONS

Uneventful LASIK induced subtle, short-lasting anterior chamber flare when measured by the laser flare meter. In corneal grafts, LASIK appeared to be a safe and effective procedure for residual refractive errors.

LASIK complications: etiology, management, and prevention

Laser in situ keratomileusis (LASIK) is a rapidly evolving ophthalmic surgical procedure. Several anatomic and refractive complications have been identified. Anatomic complications include corneal flap abnormalities, epithelial ingrowth, and corneal ectasia. Refractive complications include unexpected refractive outcomes, irregular astigmatism, decentration, visual aberrations, and loss of vision. Infectious keratitis, dry eyes, and diffuse lamellar keratitis may also occur following LASIK. By examining the etiology, management, and prevention of these complications, the refractive surgeon may be able to improve visual outcomes and prevent vision-threatening problems. Reporting outcomes and mishaps of LASIK surgery will help refine our approach to the management of emerging complications.

Laser in situ Keratomileusis in Children 8 to 15 Years Old

PURPOSE

To determine the safety, efficacy, predictability, and stability of laser in situ keratomileusis (LASIK) to correct high myopia or high myopic astigmatism in patients with high anisometropia in whom conventional treatments have failed.

METHODS

Nine eyes of nine patients, three boys and six girls with high anisometropia (>3.50 D), were included in this study. Patient age was 8 to 15 years. Minimum follow-up was 12 months. All patients were treated with the Chiron Technolas 217 excimer laser.

RESULTS

Three months after LASIK, uncorrected visual acuity improved by at least five Snellen lines in all eyes. Three eyes (33.3%) were 20/40 or better without correction. Due to dense amblyopia, no eye had uncorrected visual acuity of 20/20 or better. The mean spherical equivalent refraction decreased from -7.66 to -0.22 D, and mean preoperative astigmatism decreased from -3.11 to -0.69 D. Eight eyes (88.8%) were within +/-1.00 D of emmetropia. Two eyes (22.2%) were within +/-0.50 D of the desired outcome. All patients were able to function binocularly.

CONCLUSION

In this study of selected older children, LASIK was a safe and effective option for the correction of high anisometropia and for improved binocularity, when conventional therapies had failed. Further study is necessary to determine the long-term refractive stability in these young patients.

Two-year Corneal Endothelial Cell Assessment Following INTACS Implantation

PURPOSE

To evaluate the 2-year effects of intrastromal corneal ring segments (INTACS) on the corneal endothelium.

METHODS

Non-contact specular microscopy was performed as a subgroup test in a Phase III clinical trial. Endothelial cell images were collected before surgery and at 6, 12, and 24 months after surgery at the central and peripheral (6 and 10 o'clock) regions. Images were recorded and analyzed later by a central reading center. Cell density, coefficient of variation, and percent hexagonal cells were determined.

RESULTS

There were no clinically significant changes in the endothelial cell structure at 6, 12, and 24 months (102 eyes). There was a gain of 5 cells/mm2 (6 months) and 3 cells/mm2 (12 months) at the central region of the cornea and a loss of 28 cells/mm2 at 24 months. At the 6 o'clock region of the cornea, there was a loss of 0, 24, and 92 cells/mm2 at 6, 12, and 24 months. At the 10 o'clock region of the cornea, there was a loss of 14, 30, and 94 cells/mm2 at 6, 12, and 24 months. INTACS did not statistically affect the central cell density at 6 and 12 months, however, there was a slight loss centrally at 24 months. At 24 months, all corneal regions had a slight decrease in cell density. In all eyes, mean central and peripheral endothelial cell counts remained above 2495 cells/mm2. Coefficient of variation improved and percent hexagonal cells remained unchanged.

CONCLUSION

Endothelial cell density changes at 2 years after INTACS implantation were not clinically significant and endothelial cell remodeling was present.

Morphology of the Stromal Surface and Endothelium Using Two Different Microkeratomes

PURPOSE

To compare stromal surface and endothelial morphology after keratectomies and after laser in situ keratomileusis (LASIK), using two different microkeratomes.

METHODS

Keratectomies (160-microm and 400-microm) were performed on 82 enucleated porcine eyes using the Chiron Automated Corneal Shaper (52 eyes) and the Microtech Turbokeratome (30 eyes). LASIK procedures of -9.00 D, -27.00 D, and -36.00 D were performed with a Schwind excimer laser. The corneas were immediately fixed in glutaraldehyde or stained with alizarin red and trypan. Scanning electron microscopy was then performed.

RESULTS

All keratectomies performed with the Chiron microkeratome displayed a relatively smooth surface. The quality of the keratectomies with the manually advanced Microtech microkeratome was variable, with a high incidence (4 of 9) of incomplete cuts and irregular surfaces. In the eyes in which the stromal laser ablation was performed, a thin layer of condensed stroma (pseudomembrane formation) was seen. Vital staining did not indicate endothelial damage.

CONCLUSIONS

The surface morphology was unacceptable for one of the microkeratomes tested. Keratectomies of 160 to 400 microm and LASIK up to -36.00 D did not acutely alter endothelial morphology in porcine eyes.

Stability after laser in situ keratomileusis in moderately and extremely myopic eyes

OBJECTIVE

To evaluate the stability, mechanism, and degree of regression following laser in situ keratomileusis (LASIK) in cases with moderate to extreme myopia after 2 years of follow-up.

SETTING

Single-center clinical trial.

METHODS

Fifty-two eyes of 38 patients were enrolled in the study. One year follow-up was available for 47 eyes of 35 patients and 2 year follow-up for 39 eyes of 27 patients. Eyes were divided into 2 groups based on the level of preoperative myopia: Group 1, moderate to high myopia > or =15.0 diopters (D) (range -7.0 to -15.0 D, n = 24); Group 2, extreme myopia >15.0 D (range -15.3 to -25.8 D, n = 15). Laser in situ keratomileusis was performed using the Chiron Automated Corneal Shaper(R) microkeratome and the Summit OmniMed excimer laser. Manifest spherical equivalent, mean central keratometry, and central corneal thickness (CCT) were measured preoperatively and 12 and 24 months postoperatively.

RESULTS

Group 1 exhibited a mild myopic shift (mean -0.07 +/- 0.28 D; P >.2) and a mild increase in keratometry (mean 0.05 +/- 0.46 D; P >.6), with an accompanying increase in CCT (mean 7.5 +/- 12.2 microm; (P =.006) at 24 months. Group 2 displayed a significant myopic shift (mean -0.7 +/- 0.7 D; P =.001) and a significant increase in keratometry (mean 0.4 +/- 0.5 D; P =.01), with a mild increase in CCT (mean 2.4 +/- 9.7 microm; P =.35) at 24 months. Corneal ectasia was evident in 1 eye in the extreme myopia group.

CONCLUSION

The refractive effect of myopic LASIK up to -15.0 D remained reasonably stable during the second postoperative year. Significant regression of the refractive effect occurred in eyes with higher levels of myopia (>15.0 D), with the risk of progressive ectasia. Extreme caution is recommended when myopic LASIK is performed in eyes with higher levels of myopia.

Color vision after laser in situ keratomileusis

PURPOSE

To evaluate the effect of laser in situ keratomileusis (LASIK) on color vision.

SETTING

Department of Ophthalmology, China Medical College Hospital, Taichung, Taiwan.

METHOD

This prospective study comprised consecutive patients having LASIK. Patients were eligible for inclusion if they had a best corrected visual acuity of 20/20 or better and a normal color vision test preoperatively and an uncorrected near visual acuity of 20/40 or better postoperatively. Color vision was tested using the Farnsworth-Munsell 100-hue test (FM 100 test) preoperatively and 1 day, 1 week, and 1 month postoperatively.

RESULTS

Twenty-nine eyes of 15 patients having LASIK were enrolled in the study. The mean patient age was 29.2 years +/- 2.9 (SD). The mean preoperative spherical equivalent refractive error was -5.6 +/- 1.8 diopters, and the mean preoperative error score of the FM 100 test was 3.79 +/- 1.55. After surgery, no significant change in the error score was observed at 1 day (4.30 +/- 1.07, P =.1039, paired t test), 1 week (3.72 +/- 1.25, P =.8125, paired t test), or 1 month (3.97 +/- 1.29, P =.6149, paired t test).

CONCLUSION

Laser in situ keratomileusis did not affect color vision evaluated by the FM 100 test.

Laser in situ Keratomileusis and Photorefractive Keratectomy for Residual Refractive Error After Phakic Intraocular Lens Implantation

PURPOSE

To determine the visual and refractive outcome of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in eyes with prior posterior chamber phakic intraocular lens implantation for high myopia.

METHODS

We studied a series of 37 consecutive eyes of 31 patients who underwent LASIK or PRK for residual refractive error following collamer posterior chamber intraocular lens (IOL) (Staar Surgical Implantable Contact Lens) implantation into a phakic eye. Twenty-eight eyes had LASIK and nine eyes had PRK. Mean follow-up was 8.1 +/- 4.7 months after laser ablation (range, 3 to 18 mo).

RESULTS

The preoperative mean spherical equivalent refraction prior to phakic posterior chamber IOL implantation was -17.74 +/- 4.89 D (range, -9.75 to -28.00 D). Following phakic IOL implantation and prior to LASIK or PRK, mean spherical equivalent refraction was -2.56 +/- 2.34 D (range, -0.25 to -8.75 D). One month following LASIK or PRK, mean spherical equivalent refraction was -0.24 +/- 0.52 D (range, -1.50 to +1.50 D), 3 months following LASIK or PRK, mean spherical equivalent refraction was -0.19 +/- 0.50 D (range, -1.50 to +1.00 D). The refraction was within +/-1.00 D of emmetropia in 36 eyes (97.2%) and within +/-0.50 D in 31 eyes (83.7%). Three eyes developed anterior subcapsular opacities several weeks after laser ablation, one eye developed macular hemorrhage 4 weeks after laser ablation, and one eye had corticosteroid induced ocular hypertension.

CONCLUSIONS

LASIK or PRK can be used to treat the residual refractive error following posterior chamber phakic IOL implantation.

Complications of Laser in situ Keratomileusis: Etiology, Prevention, and Treatment

PURPOSE

To review the etiology, prevention, and management of laser in situ keratomileusis (LASIK) complications.

METHODS

Review of literature and the experience of the authors.

RESULTS

Careful preoperative screening is critical to prevention of many potential complications of LASIK. Flap complications that occur during surgery are typically managed by replacement of the flap and repeating the surgery or applying special methods such as transepithelial photorefractive keratectomy weeks to months following the initial procedure. A common source of serious complications is the use of a microkeratome that functions after improper assembly. Timely treatment of postoperative complications such as diffuse lamellar keratitis, flap striae, and infection is critical to an optimal outcome.

CONCLUSION

Most complications of LASIK can be treated effectively and have minimal effect on the final outcome after surgery, if appropriate methods are used for management.

Safety and predictability of laser in situ keratomileusis enhancement by flap reelevation in high myopia

PURPOSE

To evaluate the safety and predictability of laser in situ keratomileusis (LASIK) retreatment following primary procedures for high myopia and astigmatism.

SETTING

Corneal Diseases and Excimer Laser Research Unit, Department of Ophthalmology, University of Dundee, Dundee, United Kingdom.

METHODS

This prospective observational study of retreatment comprised a cohort of 109 eyes having primary LASIK for high myopia and astigmatism with a spherical equivalent (SE) of -9.70 diopters (D) +/- 4.06 (SD). Twenty-four eyes (22%) with an initial myopic SE of -9.83 +/- 3.50 D, a comparable subset of the entire group (P < .05), had retreatment for residual myopia (-3.02 +/- 2.17 D) to improve uncorrected visual acuity (UCVA) by reelevating the corneal flap and ablating the stromal bed.

RESULTS

The mean follow-up after retreatment was 12.8 +/- 5.1 months (range 1.5 to 24 months; 19 eyes >/=6 months, 13 eyes > or = 12 months). The mean myopic SE was reduced to +0.53 +/- 0.62 D at 1 week, +0.05 +/- 0.50 D at 1 month, +0.30 +/- 0.50 D at 6 months, and +0.18 +/- 0.42 D at the latest follow-up, 12.8 months. At the latest review, 62% of eyes were within +/-0.50 D of emmetropia and 100% were within +/-1.00 D. The mean refraction did not alter statistically between 1 week and subsequent times. The mean UCVA improved from 6/30 prior to retreatment to 6/9 at the latest follow-up. Uncorrected visual acuity of 6/6 or better, 6/9 or better, and 6/12 or better was achieved by 33.0%, 75.0%, and 95.8% of eyes, respectively. No significant complications that led to a loss of best corrected visual acuity were encountered, although retreatment procedures were more uncomfortable than primary procedures and self-limiting; epithelial ingrowth that did not threaten vision was common, and 2 patients complained of nighttime visual symptoms.

CONCLUSIONS

Retreatment of residual myopia by reelevating the flap was relatively safe and predictable, with a low risk of sight-threatening complications. However, longer term studies may be required to detect late complications.

Unexpected Corneal Flattening After Laser in situ Keratomileusis

PURPOSE

To perform a statistical study of the variation (flattening) from the surgical radius (sculpted in the corneal stroma) to the final radius of the first surface of the cornea after laser in situ keratomileusis (LASIK) for correction of myopia.

METHODS

The study included 387 eyes with myopia or myopic astigmatism that underwent LASIK using the Nidek EC-5000 excimer laser. Mean age was 34 years (range, 19 to 75 yr). Mean myopia was -5.19 D (range, 0 to -19.00 D) and mean astigmatism was -1.22 D (range, 0 to -5.00 D). The flattening coefficient was defined as: (f) = (Rpost-Rs)/Rs where Rpost. was the corneal radius after surgery (topography performed 1 month after surgery) and Rs was the surgical radius sculpted in the stroma. Mean values and standard deviations of the flattening coefficient were calculated for the 387 eyes for four myopic ranges (0 to -3.00 D, -3.00 to -6.00 D, -6.00 to -9.00 D, and more than -9.00 D), and for three astigmatic ranges (0, -0.25 to -2.00 D, and more than -2.00 D). The correlations between the flattening coefficient and several preoperative ocular variables were obtained.

RESULTS

A linear combination of quasi-independent ocular variables (age, anterior corneal radius, corneal thickness, sphere and cylinder) was found in order to maximize the correlation with the flattening for every range. Values for the correlations between 0.4 to 0.5 were obtained.

CONCLUSION

The flattening phenomenon was characterized by a flattening coefficient (f).

Effects of laser in situ keratomileusis (LASIK) on the corneal endothelium 3 years postoperatively

PURPOSE

To investigate the effects of laser in situ keratomileusis (LASIK) on the corneal endothelium 3 years postoperatively.

METHODS

Patients who were subjects of a previous prospective study (Am J Ophthalmol 125:465-471, (April) 1998) were contacted for a follow-up analysis of the central corneal endothelium. Noncontact specular microscopy was performed 35 to 37 months after LASIK on 52 eyes of 27 patients of the original cohort of 98 eyes of 65 patients and six eyes of three patients who were previously lost to follow-up after their initial post-LASIK evaluation. Patient age ranged from 29 to 66 years at the time of the original LASIK procedure. Attempted corrections ranged from 2.25 to 14.5 diopters of myopia, giving theoretical ablation depths of 182 to 332 microm below the corneal surface. Forty-eight eyes (83%) had a history of preoperative contact lens use (3 to 33 years). Central endothelial cell density, coefficient of variation of cell size, and percent of hexagonal cells were analyzed using 72 to 152 cells from each image. Multivariate analysis was used to search for factors that might predict changes in cell density, coefficient of variation, and percent of hexagonal cells.

RESULTS

The mean +/- SD preoperative cell density was 2,498 +/- 354 cells per mm(2), the mean coefficient of variation was 0.36 +/- 0.07, and the percent of hexagonal cells was 58 +/- 6. Three years after surgery there was no statistically significant change in the mean endothelial cell density (2,489 +/- 335 cells per mm(2); P = 0.88, paired t test) or the percent of hexagonal cells (60 +/- 7; P = 0.14, paired t test). The mean coefficient of variation was significantly lower postoperatively (0.32 +/- 0.04; P = 0.0006, paired t test); a repeated measures analysis showed that this significant improvement could not be explained by cessation of contact lens wear after LASIK (P = 0.34). Multivariate analysis did not identify any factors that were predictive of change in cell density, coefficient of variation, and percent of hexagonal cells.

CONCLUSIONS

Laser in situ keratomileusis for the correction of 2.25 to 14.5 diopters of myopia had no significant effect on central corneal endothelial cell density or the percent of hexagonal cells 3 years after surgery. The coefficient of variation of cell size improved significantly 3 years after surgery.

Cut Edges and Surface Characteristics Produced by Different Microkeratomes

PURPOSE

To determine the cutting characteristics of seven different microkeratomes and to compare the cut edges and surface characteristics of the corneas with respect to different keratome parameters, ie, blade oscillation frequencies and keratome speed.

METHODS

Lamellar keratectomies were performed using each microkeratome on eight freshly enucleated porcine corneas. The freshly cut corneal bed was then examined using scanning electron microscopy. A scoring system was used to evaluate the serration of the cut edge and the regularity of the corneal wound bed.

RESULTS

Serrated cut edges were produced by the Microtech microkeratome, the Automatic Corneal Shaper, the Draeger rotor keratome, and the Schwind microkeratome. The other tested cutting devices generally yielded a smooth cut edge. Smooth and regular wound surfaces were obtained with the Schwind microkeratome, the Automatic Corneal Shaper, the Microtech microkeratome, and the MKM set. The specimens cut with the Schwind microkeratome showed particularly regular surface characteristics.

CONCLUSION

The relationship between keratome propulsion speed, blade oscillation frequency, and blade material appears crucial for the quality of the microkeratome cut. Our results favor a low advancement/oscillation ratio among automated microkeratomes.

Outcome of flap subluxation after laser in situ keratomileusis: results of 6 month follow-up

PURPOSE

To evaluate the long-term outcome in cases with flap subluxation after laser in situ keratomileusis (LASIK).

SETTING

Private clinic in Turkey.

METHODS

Data of all patients who had LASIK were documented and the follow-ups of those who had flap subluxation evaluated. The number of LASIK cases was 1481 and the number of flap subluxations, 21. Laser in situ keratomileusis was performed with the Moria microkeratome and the VISX Twenty/Twenty B excimer laser using a multizone profile and the sutureless hinged corneal flap technique.

RESULTS

The incidence of flap subluxation was 1.42%. Statistical analysis of uncorrected visual acuities, best corrected visual acuities, and mean spherical equivalents in eyes with and without flap subluxation was performed. No significant differences were found, although the results in eyes with flap subluxation were worse than those in eyes without flap subluxation. Additional complications were also higher in eyes with flap subluxation.

CONCLUSION

Flap subluxation is a serious but manageable complication of LASIK. If it is detected early, the visual prognosis is as good as that in eyes without flap subluxation.

Laser in situ Keratomileusis After Penetrating Keratoplasty

PURPOSE

To determine the safety, efficacy, predictability, and stability of laser in situ keratomileusis (LASIK) to correct myopia and myopic astigmatism in eyes with prior penetrating keratoplasty.

METHODS

Eight eyes of 8 patients with penetrating keratoplasty had significant postoperative refractive error. Each eye received LASIK 1 year or more after penetrating keratoplasty. All were followed for 6 months or more. All patients were treated with the Chiron Technolas 217 excimer laser and the Automated Corneal Shaper microkeratome.

RESULTS

Mean spherical equivalent refraction decreased from -4.50 D (range, -3.00 to -7.25 D) to -0.75 D (range, -1.50 to +0.50 D) and the mean preoperative astigmatism decreased from 3.50 D (range, 1.50 to 5.00 D) to 1.25 D (range, 0.75 to 2.00 D). Uncorrected visual acuity improved by at least two Snellen lines in all eyes. Best spectacle-corrected visual acuity did not change in four eyes (50%) and improved in three eyes (37.5%).

CONCLUSION

LASIK effectively reduced low and moderate myopia and myopic astigmatism following penetrating keratoplasty.

Macular hemorrhage after laser in situ keratomileusis for high myopia

We describe 2 women with high myopia of -12.0 and -18.0 diopters who presented with myopic macular hemorrhages 1 and 4 days, respectively, after being treated by laser in situ keratomileusis (LASIK). One hemorrhage was related to a pre-existing choroidal neovascularization and the other to the presence of lacquer cracks. The hemorrhages resolved but resulted in a permanent decrease in vision. A careful fundus examination should be conducted before performing LASIK in highly myopic patients. In cases of similar macular pathology, fluorescein angiography should be done before LASIK.

Prediction of letter contrast sensitivity using videokeratographic indices

PURPOSE

To analyze the relationship between corneal topography and letter contrast sensitivity.

METHOD

Experiments were conducted on 59 eyes of 51 patients who had best spectacle-corrected visual acuity of 20/20 or better and no ocular pathology except for the corneal shape. Thirty-nine eyes had an abnormal topographic pattern resulting from keratoconus, and the other 20 eyes showed a normal topographic pattern. Videokeratography was performed with the TMS-2 videokeratoscope, and the surface regularity index, surface asymmetry index, and coefficient of variation of power were obtained for each subject. Letter contrast sensitivity was measured with the CSV-1000LV with spectacle correction. The correlation between the number of correct letters and topographic indices was calculated.

RESULTS

The abnormal topography group had a significantly greater loss of letter contrast sensitivity (median = 20 letters) than the normal control (median = 23 letters; P =.0001). There were statistically significant correlations between number of correct letters and the coefficient of variation of power (r = -.77; P =. 001), number of correct letters and surface regularity index (r = -. 76, P =.001), and the number of correct letters and surface asymmetry index (r = -.64; P =.001). The linear regression equation between number of correct letters and the coefficient of variation of power was the number of correct letters = -0.05 x the coefficient of variation of power + 23.2.

CONCLUSIONS

Our results suggest that subtle visual deteriorations, which are barely detected by contrast sensitivity testing, can be predicted objectively by the corneal topographic indices.

Premacular Subhyaloid Hemorrhage Following Laser in situ Keratomileusis

PURPOSE

To report a case of premacular subhyaloid hemorrhage following laser in situ keratomileusis (LASIK).

METHODS

Case report.

RESULTS

The subhyaloid hemorrhage did not resolve over 1 month of observation, necessitating Nd:YAG posterior hyaloidotomy.

CONCLUSION

The LASIK procedure can be associated with postoperative subhyaloid hemorrhage, presumably from rapid release of the microkeratome vacuum pressure.

Microkeratome complications of laser in situ keratomileusis

PURPOSE

To evaluate the incidence, types, and outcome of microkeratome complications that occur during laser in situ keratomileusis (LASIK).

DESIGN

Retrospective, noncomparative, case series.

PARTICIPANTS

Three thousand nine hundred ninety-eight eyes that underwent primary LASIK by four surgeons between November 1996 and August 1998 at a university-based refractive center.

METHODS

All cases with significant microkeratome complications leading to abandonment of the LASIK procedure were identified and reviewed.

MAIN OUTCOME MEASURES

Incidence of complications, change in best corrected visual acuity (BCVA), change in refractive error, and types of complication.

RESULTS

There were 27 complications leading to abandonment of the LASIK procedure of 3998 eyes. The overall rate of microkeratome complication was 1 in 150 (0.68%), but it was 1 in 77 (1.3%) in the surgeons' first 1000 eyes, decreasing to 1 in 250 (0.4%) in the last 1000 eyes. Of the 24 planned bilateral cases, 15 complications (63%) happened on the first operated eye. Twenty-six of 27 eyes (96%) recovered to within one line of preoperative BCVA, and one eye lost two lines. At last examination before any repeat refractive procedures, spherical equivalent manifest refraction returned to within 1 diopter (D) of its preoperative value in 18 of 19 eyes (95%), and astigmatism in 16 of 19 eyes (84%) returned to within 1 D of its preoperative value. Sixteen of 27 eyes (59%) had repeat LASIK. Two eyes had complications at repeat LASIK, one of which led to abandonment of the LASIK procedure for a second time.

CONCLUSIONS

There is a significant learning curve in the use of the microkeratome. If ablation is not performed, flap complications rarely lead to significant visual loss and generally do not result in a change in refractive error.

Laser in situ keratomileusis for high myopia with the VISX star laser

PURPOSE

To evaluate the results of laser in situ keratomileusis (LASIK) for spherical and spherocylindrical myopia (range, 9-22 diopters [D]) with the VISX Star laser, (VISX Inc., Santa Clara, CA).

DESIGN

Non-comparative, single-surgeon interventional case series.

PARTICIPANTS

Two hundred ninety eyes of 175 patients.

METHODS

Consecutive patients who underwent LASIK in the study range with the VISX Star laser were evaluated for early (approximately 1 month) and late (after 9 months) outcomes. Both single procedure outcomes and results after reoperation for refractive enhancement were included.

MAIN OUTCOME MEASURES

Outcome measures included uncorrected visual acuity, manifest refraction, refractive predictability, refractive stability, best spectacle-corrected visual acuity (BSCVA), results of reoperations, and complications.

RESULTS

At the early postoperative examination, approximately 1 month after surgery, 285 of 290 eyes (98.3%) were examined. Uncorrected visual acuity of 20/40 or better occurred in 209 of 285 (73.3%) eyes, and 198 of 285 (69.5%) eyes had a manifest spheroequivalent between +/-1.00 D. Subsequently, 60 eyes (20.7%) underwent reoperation for refractive enhancement. Late results, beyond 8 months from the initial surgery and including reoperations, were available in 195 of 290 eyes (67.2%). Uncorrected visual acuity results of 20/40 or better were found in 166 of 195 eyes (85.1%) and of 20/25 or better in 99 of 195 eyes (50.8%). Manifest spheroequivalent results were +/-2.00 D in 187 of 195 eyes (95.9%) and +/-1.00 D in 148 of 195 eyes (75.9%). In a paired-cohort analysis of 131 single-procedure eyes seen at both intervals, refractive stability (change in manifest refractive spheroequivalent of less than 1.00 D) was present in 101 of 131 eyes (77.1%) between the two observation intervals. Overall, approximately 3.6% eyes lost 2 lines or more of BSCVA, and other complications (flap wrinkling and epithelial ingrowth) were reported in 2% of eyes. Improvement in BSCVA of 1 line or more occurred in 5.6% eyes.

CONCLUSIONS

Laser in situ keratomileusis for high myopia with the VISX Star laser provided satisfactory refractive and visual results that compare well with other reports in the literature. Subjective results and other measures of visual function need further evaluation.

Laser in situ Keratomileusis for Anisometropic Amblyopia

PURPOSE

To evaluate the efficacy and benefit of laser in situ keratomileusis (LASIK) for correction of anisometropic amblyopia.

METHODS

LASER was performed in 21 eyes of 21 anisometropic amblyopes with a mean age of 27.71 ± 12.24 years. Three patients were less than 18 years of age. LASIK was performed in the more myopic and amblyopic eye using the Chiron Automated Corneal Shaper microkeratome and the Nidek EC-5000 excimer laser system.

RESULTS

Results of 3-month follow-up are presented. Preoperative mean manifest spherical equivalent refraction was -13.20 ± 3.84 D (range, -5.25 to -20.00 D). Mean attempted correction was -12.28 ± 3.47 D. Mean postoperative refraction at 3 months was -0.78 ± 1.63 D. Postoperative uncorrected visual acuity improved by 2 or more lines in all patients and was the same or better than preoperative best spectacle-corrected visual acuity in 95.2% of eyes. Best spectacle-corrected visual acuity improved by 1 or more lines in 61.9% of eyes. The 12-year-old child had a gain of more than 4 lines of uncorrected visual acuity.

CONCLUSION

LASIK was a good alternative to contact lenses in adults for anisometropia and resulted in a gain of best spectacle-corrected visual acuity. In children it may be an alternative method of treatment for amblyopia. [J Refract Surg 2000;16(suppl):S264-S267].

Laser in situ Keratomileusis Retreatment for Residual Myopia and Astigmatism

PURPOSE

To evaluate the visual and refractive results of laser in situ keratomileusis (LASIK) retreatment on eyes with residual myopia with or without astigmatism.

METHODS

LASIK retreatment was performed on 35 eyes of 23 patients for correction of residual myopia, with or without astigmatism, with a mean manifest spherical equivalent refraction of -2.17+/-0.82 D (range, -1.00 to -3.87 D) and mean refractive astigmatism of -0.55+/-0.61 D (range, 0 to -1.75 D). Retreatment was performed 3 to 18 months after primary LASIK (mean, 5.1+/-2.6 mo). The corneal flap of the previous LASIK was lifted and laser ablation was performed using the Chiron-Technolas Keracor 116 excimer laser. Follow-up was 12 months for all eyes.

RESULTS

At 1 year after retreatment, manifest spherical equivalent refraction was reduced to a mean -0.23+/-0.28 D (range, 0 to -0.87 D), and refractive astigmatism was reduced to a mean -0.16+/-0.25 D (range, 0 to -0.75 D). Thirty-two eyes (91.5%) had a manifest spherical equivalent refraction within +/-0.50 D of emmetropia, and 33 eyes (94.3%) had 0 to 0.50 D of refractive astigmatism. Uncorrected visual acuity was 20/20 or better in 11 eyes (31.4%). Spectacle-corrected visual acuity was not reduced in any eye after retreatment. There were no significant complications.

CONCLUSION

LASIK retreatment was effective for correction of residual myopia or astigmatism after primary LASIK. Refractive results were predictable with good stability after 3 months. Lifting the flap during LASIK retreatment was relatively easy to perform and did not result in visual morbidity in eyes treated from 3 up to 18 months after primary LASIK.

Epithelial ingrowth in a corneal graft treated by laser in situ keratomileusis: light and electron microscopy

PURPOSE

To demonstrate progressive epithelial ingrowth histopathologically in a human cornea after laser in situ keratomileusis (LASIK) and review its pathophysiology.

SETTING

Department of Ophthalmology, Medical College of Virginia Campus, Virginia Commonwealth University, and the Veterans Affairs Medical Center, Richmond, Virginia, USA.

METHODS

Tissue from a corneal transplant specimen was examined 6 weeks after LASIK by light and transmission electron microscopy.

RESULTS

Epithelial ingrowth in the flap interface with connection to the surface corneal epithelium was evident on light microscopy. In areas without epithelial ingrowth, the flap interface was imperceptible. Electron microscopy revealed minimal disruption of the stromal collagenous lamellae.

CONCLUSION

Progressive epithelial ingrowth occurred with a continuous sheet of epithelium to the flap edge. Location of epithelial ingrowth and cytokine epithelial-stromal interaction appear to be important factors in this complication. Histopathological changes in the cornea after LASIK are difficult to detect in areas with normal wound healing.

Management of severe flap wrinkling or dislodgment after laser in situ keratomileusis

PURPOSE

To review the management and results of cases with severe flap wrinkling or dislodgment after laser in situ keratomileusis (LASIK).

SETTING

University Eye Center, Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, The Chinese University of Hong Kong.

METHODS

Four patients with severe flap wrinkling or dislodgment after LASIK are described. Surgical repositioning of the flap was performed in all cases. Flap status, refractive changes, and final uncorrected and best corrected visual acuities were used to evaluate the outcome of flap repositioning.

RESULTS

Flap repositioning required suturing in 2 patients, 1 of whom developed severe epithelial ingrowth with melting of the corneal flap and stromal bed and eventually required flap removal. The stromal inflammation resolved, and the corneal surface re-epithelialized after flap excision. In 2 other patients, wedge-shaped tissue excision (1.0 x 1.5 mm) from the superior portion of the corneal flap was necessary to allow better flap realignment. In 1 of these patients, the corneal flap was eventually converted to a free cap to correct residual wrinkling. At a mean follow-up of 15 months, the postoperative uncorrected visual acuity ranged from 20/20 to 20/60, and the best spectacle-corrected visual acuity (BSCVA) was 20/30 or better in all patients. In 1 patient, BSCVA decreased by 1 line.

CONCLUSIONS

Flap dislodgment and wrinkling are serious postoperative complications of LASIK. Early recognition of these complications and prompt surgical management are crucial to achieve a successful surgical and visual outcome.

Contact lens management of patients who have had unsuccessful refractive surgery

The advent of corneal refractive surgery has, inevitably, resulted in the occasional need for contact lens fitting after surgery. For each new, developing procedure, new contact lens fitting challenges arise. The literature on contact lens use after radial keratotomy is rich and well known, but reports on the use of contact lenses after photorefractive keratectomy or laser-assisted in situ keratomileusis are few and far between. This review summarizes the prevailing clinical opinions on the contact lenses and contact lens fitting methods that are most effective after refractive surgery that results in high refractive error, irregular astigmatism, or anisometropia.

The status of hyperopic laser-assisted in situ keratomileusis

The development of excimer laser technology, coupled with advances in lamellar corneal surgery, has heralded a new era in the treatment of refractive errors. This paper discusses the current status of hyperopic laser-assisted in situ keratomileusis. This surgical modality is at a relatively early stage of investigation but appears to offer promise for the surgical correction of hyperopia. This paper considers the evolution of the technique, analyzes the current literature, and discusses the current indications, limitations, and possible future developments.

Refractive lensectomy to correct ametropia

PURPOSE

To assess the postoperative outcome of refractive lensectomy for ametropia.

SETTING

Pacific Eye Center, Brisbane, Australia.

METHODS

One hundred thirty-eight cases of refractive lensectomy performed from September 1994 to September 1997 by 1 surgeon were analyzed retrospectively. Preoperative refractive spherical equivalent (SE) ranged from -0.25 to -23.75 diopters (D) in the myopic group and from +0.25 to +11.62 D in the hyperopic group. In all cases with a low SE, the astigmatism was greater than -2.00 D. Eyes were divided into 6 groups by the preoperative SE.

RESULTS

Overall, 90.0% of eyes achieved an uncorrected visual acuity of 20/40 or better; 81.2% achieved 20/30 or better. Postoperative SE was within +/- 2.0 D of emmetropia in 93.5% of eyes and within +/- 1.0 D in 78.3%. The postoperative incidence of retinal detachment was 0.7%; intraocular lens (IOL) exchange, 2.8%; late uveitis, 0.7%; piggyback IOL, 2.1%; and neodymium: YAG capsulotomy, 8.0%. No cystoid macular edema, capsule tear, or endophthalmitis was seen.

CONCLUSION

Refractive lensectomy can achieve excellent visual acuity and refractive outcomes with few complications. The surgery can be considered in selected patients with myopia, hyperopia, and astigmatism and to correct residual ametropia after refractive surgery.

Laser in situ keratomileusis to correct refractive errors after keratoplasty

PURPOSE

To assess the safety and effectiveness of excimer laser in situ keratomileusis (LASIK) to correct refractive myopia, astigmatism, or both after keratoplasty.

SETTING

Eye Clinic Day Hospital, São Paulo, Brazil.

METHODS

Twenty-two eyes that had previously had corneal transplantation were studied. Laser in situ keratomileusis was performed using the Chiron automated microkeratome and the VISX Twenty-Twenty B excimer laser.

RESULTS

Mean follow-up after LASIK was 10.09 months +/- 3.87 (SD). The spherical equivalent refraction dropped from -4.55 +/- 3.66 D before LASIK to -0.67 +/- 1.24 D after surgery. At the last examination, 72.7% of patients had a refractive error within +/- 1.00 D of emmetropia and 54.5% had uncorrected visual acuity of 20/40 or better. Vector analysis of astigmatic correction showed an index of success of 54.0%. Best spectacle-corrected visual acuity was unchanged in 8 cases, improved in 9, and decreased in 5. Significant endothelial cell loss, keratoplasty wound dehiscence, and other serious complications did not develop in any eye.

CONCLUSION

The correction of refractive error with LASIK in postkeratoplasty patients proved to be safe, effective, and predictable. Further studies with longer follow-up are needed to determine the method's clinical value.

Laser in situ keratomileusis versus arcuate keratotomy to treat astigmatism

PURPOSE

To analyze the effectiveness of laser in situ keratomileusis (LASIK) and arcuate keratotomy (AK) to treat simple myopic, compound myopic, and mixed astigmatism.

SETTING

Instituto de la Visión, Buenos Aires, Argentina.

METHODS

This retrospective nonrandomized study comprised 821 cases treated with LASIK and 46 cases treated with AK. Patients were divided into 4 groups, which had the following preoperative cylinder corrections: simple myopic astigmatism (Group 1) (LASIK: n = 76, -3.91 diopters [D] +/- 1.29 [SD]; AK: n = 5, -3.85 +/- 0.65 D); compound myopic astigmatism up to 2.00 D (Group 2) (LASIK: n = 401, -1.69 +/- 0.76 D; AK: n = 14, -1.48 +/- 0.41 D); compound myopic astigmatism over 2.00 D (Group 3) (LASIK: n = 253, -3.61 +/- 0.89 D; AK: n = 16, -3.09 +/- 0.84 D); mixed astigmatism (Group 4) (LASIK: n = 91, +3.65 +/- 1.62 D; AK: n = 11, 4.39 +/- 0.92 D).

RESULTS

Six months postoperatively, the cylinder's vector-corrected change was as follows: Group 1, LASIK 3.75 +/- 1.08 D, AK 3.16 +/- 0.84 D; Group 2, LASIK 1.55 +/- 1.12 D, AK 1.34 +/- 0.44 D; Group 3, LASIK 3.39 +/- 0.98 D, AK 2.70 +/- 1.21 D; Group 4, LASIK 3.77 +/- 1.43 D, AK 3.75 +/- 0.89 D. Respective mean uncorrected visual acuities in each group were as follows: Group 1, 0.71 +/- 0.12 and 0.60 +/- 0.12; Group 2, 0.83 +/- 0.12 and 0.78 +/- 0.24; Group 3, 0.78 +/- 0.18 and 0.48 +/- 0.24; Group 4, 0.69 +/- 0.21 and 0.55 +/- 0.18.

CONCLUSIONS

The vector-corrected change and visual acuity achieved with LASIK were better, although not significantly, than those attained with AK except for the UCVA obtained with LASIK in eyes with compound myopic astigmatism over 2.00 D. Both methods proved to be safe.

Complications of laser in situ keratomileusis for the correction of myopia

OBJECTIVE

To determine the incidence and severity of complications from laser in situ keratomileusis (LASIK) for the correction of myopia by experienced and inexperienced surgeons.

DESIGN

Prospective, observational clinical study.

PARTICIPANTS

Fourteen surgeons and 1062 eyes of 574 myopic patients who desired surgical correction of myopia ranging from -2.00 to -22.50 diopters (D; mean, -7.57 D) and astigmatism no greater than 4.00 D participated in this study.

INTERVENTION

Myopia was corrected with LASIK. Astigmatism was corrected with arcuate keratotomy at the same time as the initial procedure or subsequently.

MAIN OUTCOME MEASURES

Primary outcome measures were change in best spectacle-corrected visual acuity (BSCVA) and the incidence of complications.

RESULTS

Eyes were followed for a mean of 9.5 months after their last surgical procedure (range, 2 weeks-21 months). Three hundred eighty-one eyes (36%) underwent 468 enhancement procedures 3 months or more after the initial treatment. There were 27 (2.1%) intraoperative and 40 (3.1%) postoperative complications. Laser ablation was not performed during the initial treatment of 17 (1.6%) eyes because of intraoperative complications. Seventy-four eyes gained 2 or more lines of BSCVA, while 50 eyes lost 2 or more lines of BSCVA. Only three eyes lost two or more lines of BSCVA to a level worse than 20/40. One eye with a flap buttonhole (BSCVA 20/50) also had an epiretinal membrane. The second eye (BSCVA 20/60) had a flap buttonhole that may have been related to a previous corneal transplant. The third eye (-22.50 D before surgery) had a rhegmatogenous retinal detachment develop, reducing BSCVA from 20/60 to 20/200. The incidence of intraoperative complications decreased from 3.1% during the first 3 months to 0.7% during the last 9 months of the study (P = 0.02).

CONCLUSIONS

LASIK is acceptably safe for the correction of myopia. Although complications occur in approximately 5% of cases, these rarely lead to visual loss of more than two Snellen lines and postoperative acuity below 20/40. Flap buttonholes were more likely to cause loss of BSCVA than free or incomplete flaps (P = 0.02); flap buttonholes may be more likely in eyes that have undergone previous surgery. Complication rates can be reduced as the surgical team gains experience.

Retreatment after laser in situ keratomileusis

OBJECTIVE

To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) retreatment for correcting residual myopia.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS AND INTERVENTION

Fifty-nine consecutive eyes (43 patients) underwent LASIK retreatment at 3 or 6 months after the primary LASIK procedure. Lifting the corneal flap and reablating the stromal bed with a VISX 20/20 excimer laser was the procedure used for LASIK enhancement.

MAIN OUTCOME MEASURES

The following parameters were studied before and after retreatment: visual acuity, refraction, videokeratography, applanation tonometry, and corneal thickness. Complications after LASIK enhancement also were evaluated. Follow-up was 12 months.

RESULTS

Before retreatment, only 3.38% of eyes (2 of 59) had an uncorrected visual acuity of 0.5 (20/40) or better, and after retreatment, this percentage increased to 60% (30 of 50) at 6 months and 61.8% (34 of 55) at 12 months. After reoperation, mean best-corrected visual acuity improved by half a line over the values before retreatment. The preretreatment refraction of -2.92 +/- 1.22 diopters (D) (mean +/- standard deviation) decreased significantly to -0.44 +/- 0.80 D at 6 months and to -0.61 +/- 0.82 D at 12 months (P < 0.001). In 82% of eyes (41 of 50) at 6 months and 81.8% (45 of 55) at 12 months, the spherical equivalent was within 1.00 D of emmetropia. There was a significant regression of effect (0.38 D) between 3 and 12 months (P < 0.01). Postretreatment refraction was related to the original refraction before the primary LASIK, the preretreatment refraction, and the ablation diameter used. Although no vision-threatening complications were found, epithelial ingrowth and flap melting were more common after than before LASIK retreatment, with 31% of eyes at 12 months with epithelial ingrowth and 10.9% with flap melting. However, LASIK enhancement improved decentration and night-vision problems.

CONCLUSIONS

LASIK retreatment was an effective and predictable procedure for correcting residual myopia. Epithelial ingrowth and flap melting were more frequent after than before LASIK retreatment, whereas decentration and night-vision symptoms improved.

Prospective comparison of single-zone and multizone laser in situ keratomileusis for the correction of low myopia

OBJECTIVE

This study aimed to determine whether there is a true difference in predictability between single-zone and multizone laser in situ keratomileusis (LASIK) for the correction of low myopia or whether any difference in predictability is because of a need for separate clinical nomograms for the two treatments.

DESIGN

A prospective, randomized, clinical trial.

PARTICIPANTS

Fourteen surgeons and 190 eyes of 95 patients with myopia who desired surgical correction of myopia ranging from -2.00 to -7.00 diopters (D) participated.

INTERVENTION

Fellow eyes of patients with myopia undergoing bilateral simultaneous LASIK were randomized to single-zone and multizone ablation. Astigmatism was not corrected at the time of LASIK.

MAIN OUTCOME MEASURES

Predictability, postoperative videokeratography, and contrast sensitivity were assessed at 3 months after surgery.

RESULTS

At 3 months, r2 values relating laser setting to change in spherical equivalent refraction were 0.78 for single-zone and 0.76 for multizone ablation; mean outcome with respect to intended was -0.84 D (0.65 standard deviation [SD]) for single-zone and -0.62 D (0.78 SD) for multizone eyes (P = 0.035). There was no relationship between single-zone and multizone ablation and the likelihood of asymmetric postoperative videokeratography (P = 0.83). The only difference in contrast sensitivity was a significantly greater decrease in log contrast for multizone eyes at 12 cyc/deg under undilated conditions.

CONCLUSIONS

There is no true difference in predictability between single-zone and multizone LASIK for the correction of low myopia. Separate clinical nomograms for single-zone and multizone LASIK should eliminate the difference in predictability that was observed in this clinical trial.

Laser in situ keratomileusis: literature review of a developing technique

We reviewed papers published in peer-reviewed journals describing techniques and results of laser in situ keratomileusis (LASIK) and summarized the instruments used, nomograms, preoperative and postoperative refractions, predictability, outcome, safety, and complications. We performed a similar review of abstracts published in the abstract books of the 1996 meeting of the International Society of Refractive Surgery, the 1997 meeting of the Association for Research in Vision and Ophthalmology, and the 1997 meeting of the American Society of Cataract and Refractive Surgery. The number of LASIK and photorefractive keratectomy (PRK) patients described in the abstracts were sorted by city. Mean weighted latitudes were calculated and compared for each procedure. The mean preoperative refraction in the papers was -12.59 diopters (D), which was statistically higher than that in the abstracts, -8.71 D (P < .001), and the mean postoperative refraction, -1.10 and + 0.93 D, respectively. The mean percentage of cases within +/- 1.00 D was 67.0% in the papers and 82.5% in the abstracts. Uncorrected visual acuity (UCVA) of 20/40 or better was achieved in 49.2% of eyes in the papers and 83.2% of those in the abstracts; a UCVA of 20/20 or better was achieved in 22.0 and 56.6%, respectively. The portion of eyes that lost two or more lines of best corrected visual was 8.0% in the papers and 0.9% in the abstracts. Complications in the papers included irregular flap (4.0%), incomplete cut (2.5%), free cap (4.9%), perforated lenticule (2.6%), short flap (3.0%), sliding flap (1.4%), interface debris (6.8%), central island (5.3%), decentration (4.7%), epithelial ingrowth (4.3%), induced astigmatism (5.1%), wrinkles (5.9%), haze (8.7%), night vision problems (14.0%), and reoperation (8.2%), Mean latitude for LASIK cases (27.00 degrees +/- 13.73 [SD] was significantly lower than that for PRK cases (42.85 +/- 11.7 degrees). Visual outcomes of LASIK surgery show significant improvements when recent abstracts are compared with published papers. This may reflect continued improvement in the surgical techniques, surgeons' skills, and visual outcomes.

Effect of surface photorefractive keratectomy and laser in situ keratomileusis on the corneal endothelium

PURPOSE

To investigate endothelial cell loss in pairs of fresh human autopsy globes following high-diopter myopic photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK).

SETTING

Center for Research on Ocular Therapeutics and Biodevices and Magill Laser Center for Vision Correction, Storm Eye Institute, Charleston, South Carolina, USA.

METHODS

In the first part of the study, 12 globes had either -10 diopters (D) multizone surface PRK or -10 D single-zone LASIK. In the second part, three groups of 5 globes each had -15 D, -20 D, or -25 D multizone-blend LASIK procedures. Fellow globes in both groups were used as untreated controls. Corneoscleral buttons were excised from all globes. Following 7 days in corneal organ culture, the endothelial surface was stained with two vital dyes: calcein-AM and ethidium homodimer. Fluorescence microscopy was used to obtain endothelial cell counts.

RESULTS

The mean dead cells per square millimeter (cells/mm2) were 0.94 in the -10 D PRK treated corneas compared with 0.91 in the fellow untreated eyes (P = 0.06(. The mean dead cells/mm2 in the -10 D single-zone LASIK-treated corneas and in the fellow untreated eyes were 0.61 (P = 0.88). The mean dead cells/mm2 in the -15 D, -20 D, and -25 D multizone-blend LASIK-treated corneas were 3.08, 2.33, and 5.55, respectively, compared with 3.49, 1.92, and 5.01 in the fellow untreated eyes (P = 0.276, P = 0.339, and P = 0.427, respectively). Dead cell counts for treated and control paired corneas were highly correlated in all treatment groups.

CONCLUSIONS

No significant endothelial cell loss occurred after -10 D PRK or LASIK corrections up to -25 D. Although this study has limitations that prevent direct extrapolation to the clinical situation, it does afford a comparable clinical correlate for endothelial cell toxicity following a typical excimer laser ablations.