BACKGROUND:The possibility of using an argon fluoride excimer laser to perform the refractive incision in keratomileusis spurred us to develop the present surgical technique of using a microkeratome to make a primary corneal incision that yields a corneal disc, then making the refractive excision of stroma with excimer laser ablation, and finally suturing the corneal disc in place.METHODS:We describe the procedures and a prospective study of 30 consecutive eyes from 22 consecutive patients with high myopia (range, -11.20 D to -24.50 D) who underwent excimer laser myopic keratomileusis. A plano corneal disc was cut with a BKS 1000 microkeratome, followed by argon fluoride excimer laser ablation of the stroma with the Summit Eximed UV 200LA laser (Summit Technology, Inc, Waltham, Mass), either of the resected disc (28 eyes) or in situ on the stromal bed (two eyes).RESULTS:By 3 weeks after surgery, 83% of the corneas were considered clear. In 17 eyes (57%), the difference between the intended and achieved refraction was < 1.00 D; in 9 eyes (30%), the difference was 1.00 to 3.00 D; in 4 eyes (13%), the difference was 3.00 to 6.00 D. At 12 months after surgery, uncorrected visual acuity was 20/40 or better in 3 (10%) eyes, and 20/50 to 20/100 in the remaining 27 (90%) eyes, in contrast to 100% of eyes that saw worse than 20/200 before surgery. Two eyes had a very deep ablation of the lenticule that led to irregularities in Bowman's layer.CONCLUSIONS:Excimer laser myopic keratomileusis is an effective way to correct high myopia and may be more accurate than other methods of keratomileusis. A new nomogram for the procedure is presented.
This paper reports a new approach for performing photorefractive keratectomy (PRK) that uses an erodible mask to control shape transfer processes. The advantages of this technique, when compared to conventional PRK performed with mechanical diaphragm, are 1) the possibility of transferring almost any shape onto corneal surface; 2) a smoother corneal surface following photoablation; 3) easier eye fixation; and 4) a controlled humidified environment over ablation zone. We report our experimental study on scanning electron microscopy of polymethylmethacrylate (PMMA) plates ablated using conventional technique versus erodible mask technique; the results showed a smoother surface in the PMMA plate ablated using the erodible mask. We also report our preliminary clinical results of four eyes treated for the correction of myopia combined with astigmatism. Myopia ranged from -2.00 to -10.00 D, and astigmatism ranged from -1.50 to -2.50 D. Three months after surgery, all four eyes were within +/- 1.00 D of myopic attempted correction, but astigmatism was completely corrected only in one eye. No complications or scarring have been reported. We believe the erodible mask could be effective in the correction of myopia and myopic astigmatism, but further improvements are necessary to allow easier alignment of the mask over the eye. All commonly available excimer laser devices produce photorefractive keratectomy as a concentric ablation of the corneal stroma, deeper in the center than in the peripheral part; this is produced by means of an iris or diaphragm which, depending on the type of laser, progressively opens or closes, allowing a greater laser beam delivery in the center.(ABSTRACT TRUNCATED AT 250 WORDS)
An ophthalmic laser unit with a Lambda-Physik LPX excimer emitting 193 nm and a unique beam shaping system was designed at the Complex "Eye Microsurgery." An absorbing cell, used as the main element of the delivery system, allowed us to obtain a precise profile of the laser energy density on the patient's cornea, smoothly changing the corneal refraction with each shot in the whole ablation area. The absorbing cell also allowed for varying the shape of distribution of radiation energy density depending on the patient's corneal shape. We performed more than 7000 photorefractive keratectomy laser operations in myopic patients, and report results in 3251 myopic eyes (approximately 46%) from -4.00 to -26.00 D, up to 4 years after surgery. In eyes with myopia greater than 6.00 D, emmetropia was obtained in 48% of cases; 42% had a residual mild myopia within 5.00 D; and 12% had a residual myopia more than 3.00 D. The corneal haze disappeared in 48.8% of cases; haze not affecting the visual acuity remained in 39%; and clinically significant haze remained in 12.2%. These eyes required a powerful medication or repeated PRK. After surgery, 87.7% of patients needed no spectacle correction. Excimer laser PRK with the use of the forming system efficiently corrects high myopia.
The holmium:YAG laser can be used to perform corneal collagen shrinkage and treat refractive errors. Studies are underway for the treatment of hyperopia by shrinking collagen in the peripheral cornea, which produces central and paracentral steepening. There is initial overcorrection followed by a regression of effect postoperatively, which appears to stabilize 4 to 6 months postoperatively. Refinement of current nomograms and definition of the amount of expected regression will enhance its accuracy. The holmium:YAG laser may be superior to radial thermokeratoplasty with a hot needle. Nearly 100 years ago, Lans was the first to report that heating of the cornea could induce collagen shrinkage with resultant corneal curvature changes. Various collagen shrinkage procedures have evolved since then. To date, the most well-known form of collagen shrinkage involves the hot needle and a technique developed by Fyodorov to do radial thermokeratoplasty for hyperopia. This article will review the current state of holmium:YAG laser technology and the advantages it may provide over radial thermokeratoplasty.
Between July 1990 and July 1992, 472 eyes were treated with photorefractive keratectomy (PRK) using the ExciMed UV200 193-nanometer excimer laser (Summit Technology, Inc, Waltham, Mass). The sphere equivalent refractions ranged between -1.25 and -9.60 D, with less than 1.25 D of astigmatism. Eyes with refractive error up to -6.00 D were treated with a spherical ablation, as determined by the surgeon's decision and the algorithm built into the laser software. In this group, 92% had a refraction within 1.00 D of intended correction. Eyes with more than -6.00 D of myopia were treated with a dual-zone procedure, using a nomogram developed by the author. After 6 months, 45% of eyes had a refraction within +/- 1.00 D, and 84% were within +/- 2.00 D of emmetropia. Excimer PRK up to -6.00 D is safe and predictable; above -6.00 D it is less predictable.
BACKGROUND:Following excimer laser photorefractive keratectomy, patients experience significant ocular pain until corneal reepithelialization. Despite the use of cold compresses, bandage soft contact lenses, cycloplegics, narcotics, and topical corticosteroids, the pain has not been adequately controlled in many patients.METHODS:A randomized, double-masked, parallel-group study of diclofenac sodium 0.1% ophthalmic solution and its placebo vehicle was evaluated. Patients undergoing excimer myopic photorefractive keratectomy on their second eye were admitted overnight. Postoperative procedures included two drops of diclofenac or placebo immediately after surgery and then qid until reepithelialization, topical tobramycin (qid), 0.1% fluorometholone (q2h), cycloplegics, and a disposable soft contact lens. Thirty-two patients (diclofenac = 16, placebo = 16) were evaluated from +30 minutes to +96 hours by several types of questionnaires.RESULTS:Most patients who received placebo experienced pain, starting within 1 hour, peaking at 4 to 6 hours and lasting 36 to 48 hours. The diclofenac-treated patients rarely experienced the early peak in pain, had less pain overall until 72 hours postoperatively, and experienced significantly less photophobia and burning/stinging. Significantly fewer patients on diclofenac required oral narcotics. Three patients (diclofenac = 2, placebo = 1) developed corneal infiltrates, the etiology of which is not known. In a separate study we conducted, there was no difference in epithelial healing times between the diclofenac-treated eyes and those not receiving the drug.CONCLUSIONS:Diclofenac appears to significantly reduce the ocular pain following excimer photorefractive keratectomy.
BACKGROUND:Current excimer laser photorefractive procedures use empiric etch rates to determine specific changes in corneal shape. A real-time analytic method for monitoring the tissue ablation process may be useful in tailoring energy delivery to a specific patient and in detecting detrimental phenomena such as corneal desiccation.METHODS:We monitored excimer laser ablation by studying the amplitude and temporal characteristics of ArF laser pulses reflected from the ablation site. Two target materials were used: polymethylmethacrylate (PMMA, a synthetic polymer that undergoes an incubation phase where no ablation occurs for an initial finite number of laser pulses), and bovine cornea. Observed reflectivity changes during irradiation of PMMA were compared to profilometric ablation depth measurements. Corneal ablation was performed both with and without nitrogen gas flow at the ablation site to study the effect of tissue desiccation.RESULTS:For ablation of PMMA at 160 mJ/cm2, the incubation phase included the initial eight laser pulses. For corneal tissue ablation at a fluence of 125 mJ/cm2, flowing nitrogen gas caused significant shortening and amplitude reduction in the reflected laser signals.CONCLUSIONS:Noninvasive time-resolved reflectometry provided real-time information about target ablation. This technique may have diagnostic utility during laser corneal surgical procedures.
BACKGROUND: Recent reports have suggested that a secondary effect of radial keratotomy may be a reduction in intraocular pressure (IOP) levels.METHODS: In an effort to study the relationship of radial keratotomy to IOP, we compared the mean IOP from the baseline and follow-up visits during year after surgery of operated versus nonoperated eyes of patients enrolled in the Prospective Evaluation of Radial Keratotomy (PERK) study. To investigate if radial keratotomy had more of an effect on eyes with higher baseline IOPs, the same analysis was performed on a subset (134 patients) who had a baseline IOP of 15 mm Hg or greater,RESULTS: The average baseline IOP for both operated eyes and nonoperated eyes was 14.6 mm Hg. There was no significant difference in mean IOP between operated and nonoperated eyes across all time points (p=.18). Although mean IOP changed over time, it did not clinically differ in operated versus nonoperated eyes at any time point. These findings were similar in the analysis of eyes with higher baseline IOP (15 mm Hg or greater). CONCLUSION: We conclude that the radial keratotomy performed in the PERK study had no effect on IOP within 1 year after surgery.
As part of a multicenter study of excimer laser procedures, we performed phototherapeutic keratectomy (PTK) on 12 eyes in 11 patients. Three eyes had superficial corneal scarring, two Salzmann's degeneration, two Reis-Bückler's dystrophy; and one each with recurrent lattice dystrophy in a corneal graft, band keratopathy, recurrent erosion syndrome, after pterygium scarring, and contact-lens related keratopathy. Indications for treatment included poor visual acuity, severe glare symptoms, ocular surface discomfort, recurrent erosions, and monocular diplopia. Follow up ranged from 1 to 4 months. Best spectacle corrected visual acuity improved in ten eyes with no eyes suffering loss of best spectacle corrected visual acuity. A hyperopic refractive shift was found in eight of 12 treated eyes. Corneal surface regularity improved in six of 12 eyes and worsened in one eye as measured by computerized corneal topographic analysis. Ten patients (11 eyes) noted improvement in their visual perception and subjective symptoms. We review various strategies of phototherapeutic keratectomy designed to treat particular corneal disorders: patient selection criteria to optimize clinical outcome are reviewed as well.
Excimer lasers are now used for corneal surgery; however, the physical processes occurring during photoablation of the cornea are incompletely understood. High speed laser-based photographic arrangement was constructed. The temporal resolution was better than 1 ns. The setup could work as a Schlieren arrangement, which is sensitive to the refractive index change caused by the shock wave propagating in the air above the eye. With minor changes the setup was converted into a shadowgraph, which could detect the ablation plume and the waves propagating on the surface of the eye. Due to the impact of the excimer laser pulse onto the surface of the cornea, a shock wave was generated in the air. The shadowgraph clearly showed the ejection of the ablated cornea. The ejection velocity of the plume was found to be over 600 m/s. It was shown for the first time that the recoil forces of the plume are generating a wave on the surface of the eye. The laser-based high speed photographic arrangement is a powerful arrangement in the study of physical effects occurring during photoablation of the cornea.
BACKGROUND:During the last decade, new refractive surgery procedures have been introduced; older techniques have been modified or even abandoned. Cryolathe myopic keratomileusis has been in clinical use for approximately 30 years. In this retrospective study, we present our experience in applying this technique for the correction of 4.00 to 8.00 diopters of myopia.METHODS:Autoplastic cryolathe keratomileusis was performed on 61 eyes of 44 patients who were at least 18 years of age, with a preoperative myopia of 8.00 D or less, and 4.00 D or less of astigmatism. The surgical technique used the Barraquer microkeratome and cryolathe. The mean postoperative observation period was 28 months (range, 12 to 73 months).RESULTS:The mean preoperative spherical equivalent refraction was -5.95 +/- 1.14 D (range, -4.25 to -8.00 D). After a mean follow up of 28 months, the mean postoperative spherical equivalent refraction was -0.91 +/- 1.49 D (range, +2.00 to -7.75 D). At the end of follow up, 37 eyes (60.7%) were within +/- 1.00 D of emmetropia and 44 eyes (72.1%) achieved 20/40 or better uncorrected visual acuity. Complications included corneal ectasia in one eye (1.6%) and epithelial inclusions of the interface in another eye (1.6%). Irregular astigmatism was not a major problem, occurring in only two eyes (3.3%).CONCLUSIONS:Cryolathe keratomileusis is a proven and feasible technique for correcting moderate to high amounts of myopia in properly selected patients; there is a low incidence of vision-threatening complications.
PURPOSE: This study sought to determine whether pre- and posttreatment with topical diclofenac sodium 0.1% eye drops suppresses corneal inflammation after 193-nanometer excimer laser corneal ablation more effectively than does posttreatment alone.METHODS: Eight rabbits were divided into four groups. Animals in group I were treated with topical diclofenac every half hour for 2 hours prior to photorefractive keratectomy; treatment was continued every hour for 3 hours after the ablation. Group II animals, used as controls, were treated with the diclofenac vehicle according to the same schedule. The third group (III) received diclofenac topically only after the excimer laser ablation. The fourth group (IV) consisted of normal corneas from these same animals. At 3 hours after ablation, prostaglandin E2 (PGE2) levels were measured in the corneas and leukocytes were quantified.RESULTS: Treatment with topical diclofenac significantly reduced levels of PGE2 compared to treatment with the vehicle (p = .024). Presurgical treatment with topical diclofenac did not result in greater suppression of PGE2 than did posttreatment alone (5.72 +/- 0.91 pg/mL versus 5.79 +/- 1.29 pg/mL). Similarly, there was a significant inhibition of leukocyte invasion in the diclofenac treated corneas (I vs II: p = .019, III vs II: p = .024), but no statistically significant difference between pretreatment and posttreatment alone groups (I vs III: p = .72).CONCLUSIONS: Topical administration of diclofenac reduces the release of PGE2 and the migration of polymorphonuclear leukocytes in the rabbit cornea 3 hours after 193-nanometer excimer laser ablation. However, pretreatment of the cornea, starting 2 hours prior to laser surgery, does not seem to offer advantages over postablation treatment in this animal model.
