Ultrastructural and immunohistochemical findings after linear excimer laser keratectomy (original) (raw)
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In Situ Collagen Gel Mold as an Aid in Excimer Laser Superficial Keratectomy
Ophthalmology, 1992
The aim of this study is to evaluate the potential use of bovine type I collagen as an adjuvant to excimer laser keratectomy. Method: A suspension of collagen with the capability to polymerize into a gel was applied to the anterior corneal surface of freshly enucleated porcine eyes, using 35.0 diopter (0),45.50, or 52.00 contact lenses as molds. Keratometry, photokeratoscopy, slit-lamp photography, scanning electron microscopy, and light microscopy were performed on the new surfaces. Furthermore, an irregular corneal surface was created and a suspension of collagen was applied to mask protruding irregularities, therefore creating a smooth surface that was subjected to excimer laser keratectomy. Ablation rates for both collagen and cornea were measured. Results: Collagen suspension placed on a cornea and molded with contact lenses created a smooth-surfaced gel that conformed to the shape of the contact lens and adhered to the anterior cornea; it was optically smooth and regular as shown by photokeratoscopy, keratometry, and scanning electron microscopy. The corneal curvature was altered in accordance with the base curvature of the contact lens used. Results of keratometry showed resolution of pre-existing astigmatism without induction of new astigmatism. The ablation rate of the gel was not measurably different than that of cornea; hence, when applied to an irregular corneal surface, a smooth surface was created after excimer laser ablation. Conclusion: This study supports the potential value of collagen gel as an adjuvant to excimer laser keratectomy for removal of corneal irregularities as well as for correction of myopia or hyperopia with or without astigmatism. Ophthalmology 1992;99:1201-1208 The capacity of the 193-nm argon-fluoride excimer laser to remove a precise amount of corneal tissue with submicron accuracy was first suggested by Trokel et al. l Recently, reports of a number of animal studies 2-4 and pre-Originally
Excimer laser treatment of corneal surface pathology: a laboratory and clinical study
British Journal of Ophthalmology, 1991
The argon fluoride excimer laser emits radiation in the far ultraviolet part of the electromagnetic spectrum (193 nm). Each photon has high individual energy. Exposure of materials or tissues with peak absorption around 193 nm results in removal of surface layers (photoablation) with extremely high precision and minimal damage to nonirradiated areas. This precision is confirmed in a series ofexperiments on cadaver eyes and the treatment of 25 eyes with anterior corneal disease (follow-up 6 to 30 months). Multiple zone excimer laser superficial keratectomy is considered the treatment of choice for rough, painful corneal surfaces. Ali patients in this group were pain-free postoperatively. Where good visual potential exists, ablation of a single axial zone is recommended and results in improved visual acuity and reduction of glare. A hyperopic shift was noted in this group.
Specular microscopy of the corneal endothelium after excimer laser photorefractive keratectomy
Journal of Cataract & Refractive Surgery, 1996
Purpose: To evaluate endothelial cell morphology and density after excimer laser photorefractive keratectomy (PRI<). Methods: We used a noncontact specular microscope to examine the central corneal endothelium of 50 eyes of 50 patients who had PRK for an attempted correction between-2.5 and-17.0 diopters (D) (mean-7.8 D) beginning 18 to 24 hours postoperatively. Results: After a follow-up of 11.4 ± 6.1 months (mean ± standard deviation), mean endothelial cell density was 2577.6 ± 402.0 cells/mm2 with rare signs of polymegathism and pleomorphism. Preoperative and untreated fellOW eye endothelial cell density values were used as a control. Paired Student's t-test and analysis of variance results were not significant (P > .05). Conclusion: Excimer laser PRK did not significantly change cell density and morphology.
Cornea, 2006
Purpose: The histologic changes after phototherapeutic keratectomy (PTK) in corneas with granular and macular dystrophy were studied. Methods: We studied 3 corneas of 2 patients (1 granular, 2 macular dystrophy), who underwent penetrating keratoplasty (PK) at 0.8, 2. 16, and 3.25 years after PTK; and 11 corneas (controls) from 10 PK patients (5 granular, 6 macular dystrophy) by light microscopy and by transmission electron microscopy. PTK was performed by using the Asclepion-Meditec MEL 60 excimer laser. Results: After PTK the epithelium (15Y40 versus 5Y100 Km), and the upper stromal collagen lamella thickness (50Y75 versus 50Y100 Km) were less irregular than for the controls. In 1 eye (macular dystrophy) 10 months after PTK an acid mucopolysaccharide-positive band was detected in the subepithelial stroma, which could be removed by hyaluronic acid digestion. This fact suggests that it was Bhaze^formed after PTK, rather than a subepithelial recurrence of the dystrophy. All PTK corneas had deposits in the mid-and posterior stroma. Concerning controls, deposits were detected under the epithelium in all corneas. Electron microscopy of the study corneas revealed a mostly continuous basal lamina, occasionally forming projections into the subepithelial stroma, and large numbers of well-developed hemidesmosomes (5.2 T 0.8 per Km membrane length) present at greater density than in the controls (3.5 T 0.8). Conclusions: In stromal dystrophies, PTK was effective in removing large subepithelial stromal plaques. There were no subepithelial recurrences, and hemidesmosome density was increased.
Regression and wound Healing after Excimer Laser Prk: A Histopathological Study on Human Corneas
European Journal of Ophthalmology, 1997
Background. The results of excimer laser PRK are promising as more than 80% of eyes with up to-6.0 diopters of attempted correction have refractive results within 1.0 diopter of emmetropia. However, throughout the dioptric range some unexpected results have been observed with individual patients showing an aggressive wound healing response with excessive myopic regression and severe corneal haze. Unfortunately, only limited data are available about the cellular and extracellular responses in human corneas after PRK and this information is important to establish adequate postoperative pharmaceutical treatment. Methods. We made a histopathological and immunohistochemical study on 20 human corneal samples from patients with severe corneal haze and myopic regression. The indirect immunofluorescence method was used for demonstration of collagen types I, 1/1, IV laminin, chondroitin sulphate, dermatan sulphate, and keratin. Results. All corneal specimens showed a hyperplastic epithelium. Histologically, most samples. (16/20) showed mainly a loose lamination of extracellular material which could be identified as collagen type IV. The remaining four samples had newly synthesised collagen type 1/1. Conclusions: Our histopathological results indicate that corneal wound healing after excimer laser PRK varies among individuals. In some people epithelial basement proteins, such as collagen type IV, are the main wound healing products, whereas in others mainly collagen type 1/1 is found postoperatively, which does not effect the synthesis of collagen type IV. This suggests the need for individually-tailored postoperative pharmaceutical treatment regimens.
… Ophthalmology & Visual …, 2010
PURPOSE: Riboflavin/ultraviolet A (UVA) cross-linking (CXL) of corneal collagen is a novel method of stabilizing corneal mechanical properties and preventing progression of keratectasias. This study was conducted to investigate whether CXL influences ablation rate, flap thickness, and refractive results of excimer laser procedures ex vivo. METHODS: Corneal epithelium was removed from enucleated porcine eyes, and CXL was performed with riboflavin 0.1% and UVA radiation (365 nm, 3 mW/cm(2)) for 30 minutes. Control eyes received epithelial abrasion only. Diffusion of riboflavin through the cornea was assessed by using infrared-excited, two-photon microscopy of riboflavin autofluorescence, combined with second-harmonic generation of fibrillar collagen. During phototherapeutic keratectomy, corneal thickness was measured by optical coherence pachymetry. During LASIK for myopia, the flap thickness of microkeratome cuts was measured and the induced refractive change assessed by Placido topography. Data were analyzed by Shapiro-Wilk test and Student's t-test. RESULTS: Multiphoton imaging showed a rapid (30-minute) and even distribution of riboflavin throughout the corneal stroma. No difference in ablation rate was measured in treated and untreated corneas (P = 0.90). Mean flap thickness was increased by 44% in cross-linked corneas (P < 0.01). After LASIK for myopia of 4 to 25 D, the mean corneal refractive change was reduced in CXL-treated eyes by 20.1% (P < 0.05). This effect was less pronounced in thinner flaps. CONCLUSIONS: CXL reduces the amount of refractive change after LASIK for myopia. Although the laser ablation rate is unaffected, CXL results in an increased flap thickness. This study suggests the need for adjustment of microkeratome and laser parameters for LASIK after CXL and indirectly endorses the theory of a direct stiffening effect of CXL.
Excimer laser–assisted lamellar keratoplasty for the surgical treatment of keratoconus
Journal of Cataract & Refractive Surgery, 2009
METHODS: This prospective case series comprised patients with keratoconus who had ELLK and were examined preoperatively and 3, 6, 12, and 24 months postoperatively. Outcome measures were uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refraction, computerized videokeratography, pachymetry, and endothelial specular microscopy. RESULTS: Forty-one eyes (41 patients) were examined. The UCVA and BSCVA were significantly better at all follow-up examinations than preoperatively. After the 24-month follow-up (33 patients), the UCVA was better than 20/60 in 11 patients (33.3%) and the BSCVA was 20/40 or better in 29 patients (87.9%). The mean refractive astigmatism was 2.20 diopters (D) and the mean manifest refraction spherical equivalent refraction, À1.18 D. Corneal topographic patterns were regularly astigmatic in 28 (84.8%) of 33 eyes, and the mean corneal thickness (440.0 mm) was significantly greater than preoperatively (553.0 mm). No statistically significant changes in mean corneal endothelial cell density were observed postoperatively. Complications included corneal melting treated with penetrating keratoplasty (PKP) (1 case) and postoperative high refractive error requiring topographically guided excimer laser photorefractive keratectomy (7 cases). CONCLUSIONS: Two-year findings indicate that ELLK is as efficacious as PKP for the surgical treatment of moderate to advanced keratoconus. The procedure is relatively simple. Most steps can be standardized, and there are no time-consuming maneuvers.