Excimer Laser Surface Ablation Research Articles

Topography-guided customized laser-assisted subepithelial keratectomy for the treatment of postkeratoplasty astigmatism

To assess topography-assisted corneal wavefront excimer laser surface ablation for the correction of ametropia and irregular astigmatism after keratoplasty. Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. In this pilot study, 15 patients (16 eyes) who were intolerant of spectacle and contact lens correction due to astigmatic anisometropia after keratoplasty (15 penetrating and 1 lamellar) had topography-assisted customized excimer laser treatments. Corneal topographic data using a Keratron Scout, Placido disk system allowed for preoperative analysis of wavefront anomalies of the anterior corneal surface from which a customized excimer laser correction of both lower-order aberrations (LOAs) and higher-order aberrations (HOAs) was prepared (ORK software) for treatment with a Schwind Esiris flying-spot laser. All eyes had laser-assisted subepithelial keratectomy (LASEK) using 15% alcohol with a 20-second to 30-second application. Four eyes received an application of mitomycin-C (MMC) 0.2 mg/mL for 1 minute after stromal ablation. The mean preoperative spherical equivalent (SE) was -3.50 diopters (D) +/- 3.97 (SD) (range +1.625 to -9.25 D). The preoperative cylindrical error was -7.2 D (range -2.75 to -13.5 D). The programmed laser correction was -3.14 D (range +1.62 to -9 D) with a maximum attempted cylindrical correction of -7 D. Adherent LASEK epithelial flaps along suture lines and the graft-host junction were noted in 9 eyes (56%), although it was possible to obtain and replace a partial flap. A follow-up of 18 months was achieved in all eyes. At the final follow-up visit, the mean postoperative SE was -1.08 +/- 1.85 D (range +3 to -4.78 D) (P<.01, F<.01). Ten eyes (62.5%) were within +/-1 D of the intended correction. The mean postoperative cylindrical error was -2.72 D (range -0.5 to -6.5 D) (P<.001), with vector analysis demonstrating a mean 6.23 D correction. Analysis of HOAs using a 6.0 mm pupil size demonstrated a significant reduction of higher-order root mean square (RMS) (P<.002), trefoil (P<.005), and 4th-order spherical aberration (P<.02) at 18 months compared with preoperative values. Uncorrected visual acuity improved in all eyes (P<.0001). Best spectacle-corrected visual acuity was unchanged or improved in 13 eyes (81%) and worse in 2 eyes by 1 line; 1 eye lost 3 lines due to an increase in preexisting cataract. In eyes that did not receive MMC, corneal haze (grade II to IV) was encountered in 3 eyes (27%). One eye required phototherapeutic keratectomy with MMC application at 12 months. Of the 4 eyes treated with MMC, 1 had trace haze and 3 had no detectable haze. There were no reported cases of epithelial instability, ectasia, or graft rejection. Topography-assisted customized LASEK was effective in the correction of postkeratoplasty astigmatism. A significant improvement of both LOAs and HOAs was obtained with good refractive stability for over 18 months. Iatrogenic haze typically occurred but appeared to be minimized with adjunctive use of intraoperative MMC.

Indications for Excimer Laser Surface Ablation

Indications for Excimer Laser Surface Ablation

Mitomycin-C assisted photorefractive keratectomy in the treatment of buttonholed laser in situ keratomileusis flaps associated with epithelial ingrowth

The prophylactic intraoperative use of mitomycin-C (MMC) to prevent haze and scarring after excimer laser surface ablation (phototherapeutic/photorefractive keratectomy [PTK/PRK]) in an eye with a previous laser in situ keratomileusis (LASIK) flap buttonhole with epithelial ingrowth is described. A well-centered buttonhole measuring 2.0 mm in diameter was cut within a thin LASIK flap in an amblyopic eye. Over the next 8 weeks, corneal haze and progressive epithelial ingrowth formed centrally. An early transepithelial PTK/PRK approach was chosen to manage the buttonhole together with the epithelial ingrowth and to treat ametropia before the onset of scarring. The approach included epithelial removal with PTK, application of MMC 0.02% for 1 minute, irrigation, a short waiting period to allow for diffusion, PRK correction of -4.0 diopters without nomogram adjustment, and bandage contact lens. A regimen of prednisolone acetate 1% and ofloxacin 0.03% 5 times a day for 1 week (steroid tapered) was prescribed. Epithelial ingrowth was removed successfully. Minimal haze formation was visible 2 weeks after the retreatment but did not reduce best spectacle-corrected visual acuity (BSCVA) and resolved within the next few weeks. After 6 weeks, uncorrected visual acuity was equal to BSCVA preoperatively (20/50). There was no evidence of recurrent epithelial ingrowth or central scarring after 24 months. Transepithelial PTK/PRK was effective in managing central epithelial ingrowth in a buttonholed LASIK flap. Prophylactic intraoperative use of MMC may reduce haze formation and corneal scarring in early treatments and may also prevent recurrent epithelial ingrowth. This approach may offer faster visual recovery and no risk for a repeated buttonhole creation compared with the widespread recutting a new flap after a couple of months. The optimal application time and concentration of MMC need to be established.

Automatic Control and Real-Time Monitoring of Laser Cleaning and Laser Ablation

AbstractClosed-loop control and real-time monitoring of pulsed excimer laser cleaning and ablation have been realised by software and hardware design and development. The audible acoustic wave generated during excimer laser surface cleaning and ablation has been used as the feedback signal for the automatic control system of laser-surface interaction. Man–machine interface for laser operation and acoustic monitoring has been developed with LabVIEW 4.1 under Windows 95 environment. This system has been used to control and monitor laser cleaning and ablation processes in real-time and proven to successfully meet the requirements in our study. By database exchange, this automatic control system can also be applied to control drilling and materials removing.

Tear Hepatocyte Growth Factor (HGF) Availability Increases Markedly after Excimer Laser Surface Ablation

Tear cytokines and growth factors are likely to modulate the wound healing process following corneal epithelial injury. Hepatocyte growth factor (HGF) is a paracrine mediator of epithelial proliferation, motility, and differentiation that is produced by keratocytes and the lacrimal gland. Tear samples were collected preoperatively and one, two, and seven days postoperatively in eyes undergoing excimer laser surface ablation [photorefractive keratoplasty (PRK) or phototherapeutic keratoplasty (PTK)]. Tear HGF concentration was measured with a sensitive ELISA assay, Tear HGF production was calculated using the tear flow rate in the collection capillary and HGF concentration. Although the instantaneous concentration of HGF in tears decreased significantly in the days following PRK, a large increase in tear flow resulted in a marked increase in HGF bioavailability. The heparin-binding characteristics of HGF would result in increased binding to glycosaminoglycans and other heparin-like matrix components and, therefore, increased growth factor availability to the cognate receptor. This is the first report documenting changes in tear film HGF production. HGF may have an important function in maintenance and wound healing of the ocular surface epithelium since HGF is present in the normal tear film and the HGF secretion rate increases markedly in parallel with aqueous tear production following corneal surgical injury.

Tribological properties of smooth diamond films

The friction and wear properties of smooth diamond coatings sliding against a monocrystalline ruby ball were studied using a pin-on-disk tribometer. The smooth diamond film surface was prepared either by (i) deposition of ultrathin nanocrystalline films in the thickness range from 0.2 to 2 μm or by (ii) postgrowth polishing. Excimer laser surface ablation, microwave plasma etching and mechanical lapping with diamond grit were used for postgrowth polishing. A correlation of film surface properties examined with different techniques (atomic force microscopy, Auger electron spectroscopy, Raman spectroscopy, stylus profilometry) and the tribological properties of the diamond films tested was established. The influence of laser-induced surface graphitization on the friction coefficient of laser-polished films was investigated.

Tribological behaviour of smooth diamond films

The tribological properties of smooth diamond coatings sliding against ruby were studied using a pin-on-disk tribometer. Smooth diamond film surface was prepared by (i) deposition of thin nanocrystalline films in the thickness range from 0.2 to 2 μm and by (ii) post growth polishing. Excimer laser surface ablation, microwave plasma etching and mechanical lapping with diamond grit were applied for post growth polishing. A correlation of film surface properties examined with atomic force microscopy, Auger electron spectroscopy, Raman spectroscopy and stylus profilometry has been established with the tribological performance of the tested diamond films.

Excimer laser in situ keratomileusis.

We have been using a 193-nm excimer laser under protocol to ablate the corneal stromal bed after creating a hinged corneal flap with a microkeratome in order to reduce or eliminate refractive error. Thirty-one consecutive eyes are reviewed with a preoperative mean spherical equivalent refraction of -6.25 diopters (D) (range -3.50 to -11.75 D). Preoperative mean astigmatism was +0.87 D (range +0.25 to +2.75 D). At 6 months postoperatively, the mean spherical equivalent refraction was -0.50 D (range -3.50 to +2.00 D). Mean postoperative astigmatism was 0.64 D (range 0.25 to 3.50 D). A result within 1.00 D of attempted correction was achieved in 74.2% of eyes. Uncorrected visual acuity after a single procedure was 20/40 or better in 81% of eyes. Spectacle corrected visual acuity was unchanged in 26 (84%), decreased 1/2 line in 2 (6%), and increased 2 lines in 1 (3%). The incidence of postoperative complications was minimal. Excimer laser ablation in the stromal bed in combination with a hinged corneal flap seems to offer many advantages over excimer laser surface ablation with fewer complications.