Excimer Laser Keratectomy Research Articles

Excimer laser keratectomy and phakic intraocular lens implantation surgery for children with autism: improvements in visual function and behavior

Excimer laser keratectomy and phakic intraocular lens implantation surgery for children with autism: improvements in visual function and behavior

Excimer laser keratectomy for hyperopia in special needs children: longer-term outcomes

We report the results of excimer laser photorefractive keratectomy (PRK) for hyperopia in special needs children who are intolerant of spectacle wear or contact lenses.

Whether does the granular corneal dystrophy indicate for the excimer laser ablation surgery or not

With the development of excimer laser technologies, the corneal refractive surgical procedures are improved constantly and the indication of excimer laser keratectomy is expanded. In clinic, PRK or LASEK or PTK or LASIK were performed on the eyes of granular corneal dystrophy with refractive error and the early results were satisfied, but the reoccurrence and server opacity of cornea are worried. Is this corneal disease the indication of excimer laser keratectomy? Nowadays, the exact indication for the disease should be declared in clinic. In this article, the customized treatment nomogram for three types of granular corneal dystrophy is explicated according to the clear classification and exact diagnosis on this disease, in order to apply the excimer laser keratectomy reasonably and correctly for the patient approaching the safe, effective and long term satisfactory result.

Effects of topical corticosteroids on subepithelial haze after excimer laser corneal surgery: Objective and quantitative method for evaluating haze

To examine the effectiveness of topical corticosteroids in decreasing subepithelial haze induced by excimer laser keratectomy, we performed excimer laser keratectomy on 24 eyes of 12 albino rabbits using a scanning excimer laser system (EC-5000, NIDEK, Japan). Topical dexamethasone 0.1% was applied topically to 8 corneas after surgery (steroid group), but not to the others (control group). Slit-lamp biomicroscopic examination and objective measurement of scattered light from subepithelial haze were performed before and 2, 4, 8 and 12 weeks after surgery, the rabbits were killed after 2 or 12 weeks and the eyes were examined histologically. In both groups, densitometric values of scattered light intensity increased up to 4 weeks after surgery, and then decreased gradually. However, the values of the steroid group were larger than those of the control group at all stages, and the values of the steroid group at 12 weeks after surgery were similar to preoperative values. There was statistically significant difference in scattered light intensity between the two groups (p < 0.005). Two weeks after surgery, the corneas of the control group showed epithelial hyperplasia and a remarkable increase in activated keratocytes and subepithelial fibrous tissues. However, in the steroid group these light microscopic findings could not be observed. At 12 weeks after surgery, the corneas of the control group retained a small amount of activated keratocytes and fibrous tissues, and those of the steroid group were normal. This study suggests that a short course of topical corticosteroids may be very effective in decreasing subepithelial haze after excimer laser corneal surgery.

Increased gene expression of the apoptosis‐related molecule Fas and the inducible nitric oxide synthase (iNOS) after excimer laser ablation in rat corneas

Abstract Purpose The aim of this study was to analyse the gene expression of the apoptosis‐related molecule Fas in relation to the production and accumulation of nitric oxides 1, 12 and 24h after excimer laser keratectomy in rat corneas. Methods Wistar rats with excimer corneal ablations (Chiron laser, 66‐68 µm/pulse, 1606 pulses, diameter 4‐7.6 mm, and depth in cornea 50µm) were killed 1, 12 and 24h after treatment. Fas mRNA in situ hybridizations were performed in the analysed corneas by using a rat‐Fas specific gene probe. The generation and further accumulation of reactive nitrogen intermediates (RNI) due to the activity of the inducible nitric oxide synthase (iNOS) in corneal cells were further evaluated by systematic mRNA in situ hybridizations with a specific gene probe for iNOS. Results One hour after treament, the Fas gene expression was higher than in untreated controls, but clearly lower than 12h after treatment. Whereas 24h after treatment, the expression remained higher than in the controls, slight decreases were observed when compared to the corresponding levels 12h after treatment. A similar expression pattern was observed for the accumulation of RNI in plasma. This effect was further confirmed in corneal cells by the detection of similar iNOS hybridization patterns in the corresponding corneas. Conclusion After excimer laser keratectomy, the Fas gene expression was increased, especially 12h after treatment. These increases were found to be related to the accumulation of RNI in plasma and to the expression of iNOS in corneal cells. The expression of all these three considered markers together may play a relevant role in wound healing after laser treatment.

The clinical experience in the treatment of myopia with surface excimer laser keratectomy

目的 探讨准分子激光表面切削手术治疗近视的临床效果和不同手术方法的优点.方法 近视980例1906眼分别采用PRK、LASEK和Epi-LASIK手术,观察3种手术方法的效果和主要并发症.结果 3种准分子激光表面切削手术方式中LASEK术后反应最轻.术后6个月PRK 249眼中217眼(87.15%)达到术前最佳矫正视力,haze和皮质类固醇性高眼压的发生率分别为2.81%和12.23%;LASEK 1406眼中1265眼(89.97%)达到术前最佳矫正视力,haze和皮质类固醇性高眼压的发生率分别为2.20%和10.86%;Epi-LASIK 251眼中228眼(90.84%)达到术前最佳矫正视力,haze和皮质类同醇性高眼压的发生率分别为1.59%和9.65%.结论 准分子激光表面切削技术由于其并发症少且操作方便,是安全、有效、可预测性强的届光手术。

O impacto da cirurgia de ceratectomia fotorrefrativa (PRK) e ceratomileuse assistida por excimer laser in situ (LASIK) na qualidade visual e de vida em pacientes com ametropias

To evaluate the quality of life, vision and stress before and after refractive surgery. This is a longitudinal, observational study, where 100 patients were evaluated; 54 espectacles wearers, 21 contact lens users before surgery and 25 controls wearers spectacles or contact lenses, who did not want to undergo refractive surgery during one year despite refractive error. The applied questionnaires were Self Reporting Questionnaires SRQ-20 of quality of life and vision and National Eye Institute Visual Function Questionnaire NEI VFQ-25 for the assessment of mental health. The intervention group answered the questionnaires before surgery, three, six and twelve months after follow-up and the control group answered the questionnaires at six and twelve months after the baseline. The questionnaires of the intervention group were applied by an independent person. In the intervention group (54 spectacle wearers), 39 were treated by photorefractive excimer laserkeratectomy (PRK) and 15 by laser in situ keratomileusis (LASIK), of the 21 contact lens users: 12 received photorefractive excimer laser keratectomy and nine were treated by laser in situ keratomileusis (LASIK). The control group remained stable during the study. After three months of follow-up the intervention group showed improvement in quality of life, vision and reduction of stress. After one year of follow-up the assessments of quality of life and mental health were similar to the control group. After three months there was a significant reduction of psychiatric symptomatology in the intervention group. Patients operated for correction of ametropia showed a significant improvement in quality of life and mental health assessments.

Transplantation of Tissue-Engineered Epithelial Cell Sheets after Excimer Laser Photoablation Reduces Postoperative Corneal Haze

To apply tissue-engineered cell sheet transplantation after excimer laser keratectomy as a novel approach for the reduction of postoperative corneal haze. Limbal biopsy specimens were obtained, and epithelial cells were cultured on temperature-responsive culture inserts without the use of feeder cells. Laser keratectomy (7.0-mm ablation zone and 160-microm depth) was performed in the contralateral eye, and autologous epithelial cell sheets were transplanted to the ablated corneal stroma. Transplant and control group eyes were assessed by slit lamp biomicroscopy, and corneal haze was scored in a masked fashion, according to the Fantes grading scale. For further examination histologic and immunohistochemical analyses were performed. Tissue-engineered cell sheets produced stable attachment to the laser-ablated sites, resulting in epithelialization, 5 minutes after transplantation. Conversely, control corneas required 3 to 5 days for complete re-epithelialization. At both 1 and 2 months after surgery, corneal haze was significantly inhibited in the transplant group. Histologic analyses showed that the number of keratocytes undergoing apoptosis was decreased in the transplant group at 3 days after surgery. Similarly, the expression of both collagen III and alpha-smooth muscle actin, which may enhance corneal haze, were diminished in the transplant group at 2 months. The transplantation of tissue-engineered epithelial cell sheets can successfully prevent the development of corneal haze after excimer laser keratectomy.

Anti-angiogenic role of angiostatin during corneal wound healing

The purpose of this study is to determine whether angiostatin is involved in maintaining corneal avascularity after wounding. We generated polyclonal rabbit anti-mouse angiostatin antibodies directed against each of the five kringle domains, (K1-5) and anti-mouse plasmin B chain antibodies. Mouse corneas were immunostained with anti-K1 angiostatin antibody after excimer laser keratectomy. Corneal epithelial cell lysate was harvested and angiostatin was isolated using lysine sepharose. Purified plasminogen was incubated with lysate of mouse corneal epithelial cells from wild type mice in the presence or absence of MMP inhibitors. Angiostatin activity was determined using calf pulmonary artery endothelial (CPAE) cell proliferation assay with and without angiostatin immunoprecipitation; and corneal neovascularization was assayed by intrastromal injection of anti-plasminogen, anti-K1-3 or anti-B chain antibodies after corneal wounding. Using the anti-mouse angiostatin antibodies that we generated, we confirmed that angiostatin-like molecules were expressed in the corneal epithelium and in cultured corneal epithelial cells. Western blotting after incubation of scraped corneal epithelial cell lysate with purified plasminogen showed reduction of the plasminogen bands at 6, 12, and 24 hr, respectively. Complete cleavage of plasminogen occurred by 48 hr. Functional assays in which corneal epithelial cell extracts were incubated with CPAE cells resulted in inhibition of vascular endothelial cell proliferation. Depletion experiments using anti-angiostatin (K1) antibodies resulted in a 25±1·2% increase in vascular endothelial cell proliferation as compared to 12±1·8% using the protein A control ( p<0·05). Corneal neovascularization was observed after excimer laser keratectomy when anti-angiostatin antibodies were injected into the cornea (65±13%) which was significantly higher than when plasmin B chain antibodies were injected (10±2·6%; p<0·05). Plasminogen and angiostatin are produced in the cornea. They may play a role in preventing vascularization and may contribute to the maintenance of corneal avascularity after excimer laser keratectomy.

Corneal wound healing after excimer laser keratectomy

Excimer laser keratectomy is widely used to correct refractive errors. Several complications of excimer laser keratectomy are reported including corneal infection, regression, corneal haze formation, glare and halo. Most of the complications are closely related to the corneal stromal wound healing process. In order to perform the excimer laser keratectomy with minimum complications, we should understand the mechanism of the corneal stroma wound healing process. In addition, such knowledge will help us to regulate the corneal stromal wound healing process in the future. In the present article, we discuss the molecular mechanism of the corneal stromal wound healing process after excimer laser keratectomy and its regulation by anti-inflammatory agents.

On the structural origin of refractive instability and corneal haze after excimer laser keratectomy for myopia

On the structural origin of refractive instability and corneal haze after excimer laser keratectomy for myopia

Corneal wound healing after excimer laser keratectomy

Excimer laser keratectomy is widely used to correct refractive errors. Several complications of excimer laser keratectomy are reported including corneal infection, regression, corneal haze formation, glare and halo. Most of the complications are closely related to the corneal stromal wound healing process. In order to perform the excimer laser keratectomy with minimum complications, we should understand the mechanism of the corneal stroma wound healing process. In addition, such knowledge will help us to regulate the corneal stromal wound healing process in the future. In the present article, we discuss the molecular mechanism of the corneal stromal wound healing process after excimer laser keratectomy and its regulation by anti-inflammatory agents.

Expression of type XVIII collagen during healing of corneal incisions and keratectomy wounds.

To determine the distribution of type XVIII collagen in mouse ocular tissues and to investigate the expression of type XVIII collagen during healing of corneal incisions and keratectomy wounds. Immunohistochemical analysis of type XVIII collagen was performed in mouse ocular tissue, with polyclonal antibodies to the hinge domain. For wound-healing experiments, excimer laser keratectomy and single linear incisions were performed on mouse corneas. The corneas were harvested at various time points after wounding and processed for immunohistochemistry, in situ hybridization, competitive reverse transcription-polymerase chain reaction (RT-PCR), and Western blot analysis. In the unwounded mouse cornea, type XVIII collagen was expressed by the corneal epithelial cells. Type XVIII collagen was immunolocalized to the mouse corneal epithelium, epithelial basement membrane, Descemet's membrane, ciliary epithelium, lens capsule, retinal inner limiting membrane, and Bruch's membrane. In the early stages of wound healing after excimer laser keratectomy (days 3 and 7), type XVIII collagen staining of the epithelial basement membrane was absent, whereas its localization to Descemet's membrane was unchanged. After linear corneal incisions, however, type XVIII collagen was clearly seen in the stroma and in the epithelial basement membrane. Type XVIII collagen immunolocalization to the subepithelial stromal wound region peaked at 1 week after wounding, and its mRNA showed a corresponding temporal increase in expression within the same region after linear corneal incisions. The results suggest that type XVIII collagen is broadly expressed in ocular tissues and that it may have a role in wound healing, especially after incisional corneal wounds.

Corneal Neovascularization after Excimer Keratectomy Wounds in Matrilysin-Deficient Mice

Matrilysin, matrix metalloproteinase (MMP)-7, is upregulated in the corneal epithelium during wound healing after excimer keratectomy wounds. The purpose of this study was to determine the role of matrilysin in maintaining corneal avascularity during wound healing. Matrilysin-deficient mice (n = 17) and their age-matched wild-type littermates (n = 18) were treated with 193 nm argon-fluoride excimer keratectomy (experiment I). The percentage of corneal surface occupied by neovascularization was measured with a computer image-analysis program adjusted for parallax. In another experiment (experiment II), epithelial closure was monitored with slit lamp biomicroscopy and fluorescein staining, and corneal neovascularization was confirmed by india ink perfusion, electron microscopy, and immunolocalization of CD31 and type IV collagen. Corneal micropocket assays were performed to compare the area of corneal neovascularization in matrilysin-deficient mice and wild-type littermates (experiment III). To determine whether the differences in corneal neovascularization were related to differences in angiogenic factors, the levels of basic fibroblast growth factor (bFGF) were compared with those of vascular endothelial growth factor (VEGF) in matrilysin-deficient and wild-type mouse corneas (experiment IV). The percentages of the corneal surface occupied by neovascularization after excimer laser keratectomy in the matrilysin-deficient mice measured 21.3% +/- 5.2% and 18.7% +/- 5.8% at days 3 and 7, respectively, compared with 5.3% +/- 2.4% and 5.5% +/- 3.4% in the wild-type littermates at days 3 (P < 0.01) and 7, respectively (P < 0.05; experiment I). No significant differences in the rates of epithelial closure of corneal wounds were observed between matrilysin-deficient and wild-type mice after wounding. Corneal neovascularization in the matrilysin-deficient mice was confirmed by india ink present in the corneal stromal blood vessels (extending from the limbus to the wound), immunohistochemical staining, and electron microscopy. Gram, Giemsa, calcofluor white, and acridine orange stains and electron microscopy showed no evidence of corneal infection (experiment II). The area of corneal neovascularization in matrilysin-deficient mice was not significantly different from that of wild-type littermates after implantation of bFGF pellets (0.91 +/- 0.55 mm(2) and 0.77 +/- 0.34 mm(2), respectively; experiment III). The levels of bFGF and VEGF (VEGF, VEGF-B, and VEGF-C) in corneal epithelial cells were not elevated in matrilysin-deficient mice compared with the wild-type mice (experiment IV). Matrilysin may play an important role in maintaining corneal avascularity during wound healing. The differences in corneal neovascularization between matrilysin-deficient mice and wild-type littermates seem unrelated to the bFGF and VEGF levels in the corneal epithelium.

Recurrence of keratitis after excimer laser keratectomy

We report 3 patients who experienced a recurrence of nonherpetic keratitis after excimer laser photorefractive surgery. Two patients had a history of culture-positive adenoviral keratoconjunctivitis, and 1 had a clinical diagnosis of Thygeson’s superficial punctate keratitis (SPK) prior to excimer laser surgery. Patients should be informed that excimer laser surgery may contribute to a recurrence of keratitis and Thygeson’s SPK. Recognition and appropriate treatment can result in resolution and maintenance of a good refractive outcome.

The Effect of Excimer Laser Keratectomy on Corneal Glutathione-related Enzymes in Rabbits

Glutathione related enzymes are involved in the metabolism and detoxification of cytotoxic and carcinogenic compounds as well as reactive oxygen species. Excimer laser is a very useful tool for the treatment of refractive errors and removing superficial corneal opacities. Previous studies have shown that excimer laser may initiate free radical formation in the cornea. In the present study, we evaluated the effect of excimer laser keratectomy on corneal glutathione-related enzyme activities in rabbits. Animals were divided into five groups, and all groups were compared with the controls (group 1), after epithelial scraping (group 2), transepithelial photorefractive keratectomy (PRK) (group 3), traditional PRK (group 4) and deep traditional PRK (group 5). Corneal glutathione peroxidase (GPx), glutathione S -transferase (GST) and glutathione reductase (GR) activities were measured after 24 h. Corneal GPx and GR activities significantly decreased only in group 5 ( p <0.05) but GST activities significantly decreased in all groups when compared with the control group ( p <0.05). In conclusion, excimer laser inhibits the glutathione dependent defense system in the cornea, this effect becomes more prominent after high doses of excimer laser energy and antioxidants may be useful to reduce free radical mediated complications.

Oculocardiac reflex in a nonsedated laser in situ keratomileusis patient

A healthy 21-year-old man had laser in situ keratomileusis (LASIK) in the right eye for a refractive error of −7.0 diopters. The electrocardiogram findings and heart rate were recorded before LASIK; during eye lid speculum insertion, vacuum application, corneal flap preparation, and excimer laser keratectomy; and after the procedure. The pre-LASIK heart rate was 90 pulses/min. Severe bradycardia of 40 beats/min developed during vacuum application, and the procedure was terminated. Severe bradycardia caused by an oculocardiac reflex may occur during LASIK, and patients should be closely monitored during the procedure.

Laser in situ keratomileusis for the correction of myopia and myopic astigmatism

Purpose: To evaluate the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of laser in situ keratomileusis (LASIK) for the correction of myopia and myopic astigmatism. Setting: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. Methods: This retrospective study comprised 69 eyes that had LASIK to correct myopia and 74 eyes that had LASIK to correct myopic astigmatism. The excimer laser keratectomy was performed using a Summit Apex Plus® machine. Refraction, visual acuity, and computerized corneal videokeratography data from the preoperative and postoperative examinations were collected. The astigmatic change was calculated by the Alpins vector analysis method. Results: The preoperative spherical equivalent at the glasses plane in the myopia and myopic astigmatism groups was −8.08 diopters (D) and −9.73 D, respectively. At 6 months, the spherical equivalent and residual corneal astigmatism were −0.25 D and 0.85 D, respectively, in the myopia group and −0.71 D and 0.82 D, respectively, in the myopic astigmatism group. In the myopia group, 88% of eyes were within ±1.0 D of the intended myopia correction and in the myopic astigmatism group, 85% were within ±1.0 D of the targeted spherical equivalent and 90% were within ±1.0 D of the intended astigmatism correction. The uncorrected visual acuity was 20/40 or better in 94.1% of eyes in the myopia group and 92.5% of eyes in the myopic astigmatism group. The SIA magnitude was 0.66 D with the axis randomly distributed in the myopia group. The mean astigmatism correction index was 0.97, the mean magnitude of error was 0.13 D ± 0.62 (SD), and the mean angle of error was −3.70 ± 13.73 degrees in the myopic astigmatism group. Conclusion: Laser in situ keratomileusis had similar predictability, safety, and efficacy in the treatment of myopia and myopic astigmatism. The astigmatism correction was effective, but the results suggest that subjective astigmatism of less than 1.0 D need not be treated with the Summit Apex Plus laser.

New lamellar keratoplasty techniques: posterior keratoplasty and deep lamellar keratoplasty.

Posterior keratoplasty is a new surgical technique that may be valuable in treating patients with corneal decompensation secondary to endothelial dysfunction. There are currently two approaches to posterior keratoplasty. In the first approach, a corneal flap is created using a microkeratome (similar to laser in situ keratomileusis flap), and posterior stromal tissue is excised (by trephination or excimer laser keratectomy). In the second approach, a deep stromal pocket is created across the cornea through a superior scleral incision. A custom-made flat trephine is inserted into the pocket to excise a posterior lamellar disc. Preliminary studies have shown the feasibility of performing these techniques in sighted human eyes. Despite potential advantages, further clinical studies are needed to determine whether these techniques reduce interface scarring, astigmatism and graft rejection, improve visual outcomes, or are potentially an alternative for penetrating keratoplasty.

Effects of Topical Vitamin E on Keratocyte Apoptosis after Traditional Photorefractive Keratectomy

Purpose: To evaluate the keratocyte apoptosis and effects of topical vitamin E on keratocyte apoptosis after photorefractive surgery. Methods: Rabbits were divided into 7 groups, and all groups were compared with controls after epithelial scraping, epithelial scrape and photorefractive keratectomy (PRK) (traditional PRK), transepithelial PRK, production of a corneal flap with microkeratome and laser-assisted in situ keratomileusis (LASIK). The effects of topical Vitamin E treatment were investigated in the traditional PRK group. The terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick-end labelling assay (to detect DNA fragmentation in situ) and light microscopy have been used to detect apoptosis in rabbit cornea. Results: Transepithelial PRK induced minimal keratocyte apoptosis, less than in all other refractive surgical procedures. The greatest amount of keratocyte apoptosis was observed after traditional PRK (p = 0.001), therefore we tested the effects of topical vitamin E in this group. The number of apoptotic keratocytes significantly reduced after vitamin E therapy (p < 0.005). Conclusion: Keratocytes undergo apoptosis after refractive surgery in response to mechanical epithelial removal, preparing of corneal flap and excimer laser stromal photoablation. The topical application of vitamin E immediately after surgery can prevent keratocyte apoptosis, and this result suggests that free radicals may be partly responsible for keratocyte apoptosis after excimer laser keratectomy.