Narrow angle light scatter in rabbit corneas after excimer laser surface ablation (original) (raw)
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Experimental Measurement of Corneal Haze After Excimer Laser Keratectomy
Applied Optics, 2001
We developed a model of corneal haze following photorefractive keratectomy ͑PRK͒ in Iber Braun hens and studied optical properties. The animals underwent PRK for Ϫ9.0 diopters of myopia and were divided into groups based on treatment with different wound-healing modulators. At different time points postoperatively, we evaluated haze by slit-lamp microscopy. An experimental device was developed to measure transmittance spatial maps and forward scattering of He-Ne laser light in the excised corneas. Subjective and objective haze measures were compared for each group at the different times. Keratocyte densities were determined by optical microscopy and keratocyte sizes by electron microscopy. The agreement between experimental results and a simple numerical model of scattering suggests that increases in stromal keratocyte density after PRK might explain the degree of corneal haze.
Corneal response to femtosecond laser photodisruption in the rabbit
Experimental Eye Research, 2008
In this report we evaluated the effect of femtosecond laser energy on the development of corneal haze and keratocyte activation in rabbits following intra-stromal photodisruption to create LASIK flaps using a modified commercial femtosecond surgical laser. Three groups of flap parameters were studied: 1.5 microJ/pulse with 10 microm spot separation and complete side cut (Group 1); 3.5 microJ/pulse with 14 microm spot separation and complete side cut (Group 2); 3.5 microJ/pulse with 14 microm spot separation and partial (50 microm) side cut (Group 3). All flaps were left attached without lifting to avoid epithelial contamination. Rabbits were then evaluated pre- and post-operatively by quantitative in vivo and ex vivo confocal microscopy. The achieved flap thickness 1 week after surgery averaged 88.9+/-12.8, 90.8+/-6.9 and 86.5+/-6.8 microm for Groups 1-3 respectively (p=NS). Interface thickness was significantly greater (p<0.05) in the higher energy groups averaging 40.0+/-11.2 and 37.7+/-5.7 microm for Groups 2-3 compared to 28.6+/-4.5 microm for Group 1. Corneal haze was barely detectible and not significantly different between groups, although haze was detected in the region of the side-cuts in Groups 1 and 2. No clinically significant changes in stromal or epithelial thickness were noted. Laser confocal microscopy showed the presence of small diameter cells within the flap interface that resided within disrupted regions of the corneal collagen lamellae. Keratocyte activation was only detected in regions of the 100% side cut and not over the flap interface. In conclusion, the results of this study indicate that photodisruption of the corneal stroma alone without flap elevation regardless of laser energy does not induce significant corneal haze in the rabbit. However, a thicker stromal interface was seen with the higher energy suggesting greater stromal damage.
Effect of beam variables on corneal sensitivity after excimer laser photorefractive keratectomy
British Journal of Ophthalmology, 1997
Aim-To investigate changes in corneal touch sensitivity following excimer laser photorefractive keratectomy (PRK) using diVerent beam configurations. Methods-20 subjects were given a unilateral −3.00 D correction with either a 5 mm (26 µm, n=10) or 6 mm (42 µm, n=10) beam diameter. Thirty subjects underwent a unilateral −6.00 D correction with 5 mm (62 µm, n=10), 6 mm (78 µm, n=10), or multizone (62 µm, n=10) treatments. The multizone treatment was 6 mm in diameter with the depth of the 5 mm treatment. Corneal sensitivity was measured using a slit-lamp mounted Cochet-Bonnet aesthesiometer before and at 1, 3, 6, and 12 months after PRK. Stimulus locations included points lying within the ablated zone (central) and outside (peripheral). These were compared with the equivalent locations in control (untreated) eyes. Results-There was a significant reduction in corneal sensitivity within the central (ablated) zone in all treatment groups after PRK. In most groups a return to full sensitivity was achieved by 6 months with the exception of the multizone treatment group which showed significant corneal hypoaesthesia at 12 months. Peripheral corneal sensitivity was also reduced in this group up to 3 months after the procedure. A comparison between the −3.00 D and −6.00 D treatment groups showed no significant diVerence. However, combining data from all treatment groups, a significant correlation was found between the interocular diVerence in central corneal sensitivity and postoperative haze at 3 and 6 months. Conclusions-For corrections up to −6.00 D ablation depth and treatment zone diameter do not appear to be clinically important determinants of corneal hypoaesthesia. In contrast, postoperative corneal haze appears to correlate with sensitivity loss.
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.
Light-Scattering and Ultrastructure of Healed Penetrating Corneal Wounds
2007
PURPOSE. To investigate quantitatively for the first time the relationship between light-scattering and ultrastructure of semitransparent scars resulting from penetrating wounds in rabbit cornea. METHODS. Penetrating wounds, 2 mm in diameter, were made in the central cornea and allowed to heal for 3.6 to 4.5 years at which time the rabbits were killed. The scar and cornea thick- ness outside
Corneal Light Transmission and Roughness After Refractive Surgery
Optometry and Vision Science, 2010
To determine the relation between the corneal light transmission measurements and the epithelial surface properties in hen corneas after different refractive surgery techniques photorefractive keratectomy, laser in situ keratomileusis, and laser-assisted subepithelial keratomileusis, and a group with only epithelial corneal removal (deepithelialization). Methods. Five groups of hen corneas with different treatments and a control group were analyzed at 30 days. Direct transmittance and corneal light scattering were measured by a scatterometer developed by our group. Quantitative and systematic measurements of external and internal roughness and epithelium thickness were assessed using standard techniques developed for quantitative analysis of microphotographs of the corneal epithelium. Results. Data analysis revealed that the roughness in the epithelial surface was associated with the corneal light transmission. The direct transmittance of light showed a significant correlation with the epithelial roughness in the control (r ϭ Ϫ0.99, p Ͻ 0.05) and photorefractive keratectomy (r ϭ Ϫ0.99, p Ͻ 0.05) groups. However, there was no relation between the epithelial thickness and the corneal light transmission measurements. Conclusions. The experimental results suggested that the roughness of the epithelial surfaces is related to the light transmission in the cornea. (Optom Vis Sci 2010;87:1-•••)
Journal of Huazhong University of Science and Technology [Medical Sciences], 2005
To evaluate the inhibiting effect of Homoharringtonine (HHT) on the corneal haze after excimer laser photorefractive keratectomy (PRK) in rabbits. 18 healthy rabbits which underwent PRK were randomly divided into three groups (A, B and C). The refractive degree of ablation was --10.0DS in each group. Group A was locally treated with a piece of filter paper soaked with 1 rag/ mL HHT for 5 min, and then the entire cornea was repeatedly irrigated with balance solution; Group B was dropped with 0.1 mg/mL HHT after PRK for 3 months; Group C was the control group. Corneal haze, histopathology, response, ect. were investigated. The corneal haze was significantly less in group A, while the difference between group B and group C was insignificant. Keratocytes and fibrocytes in corneal stroma were more active up to 3 months in group B and group C. Intraoperative use of topical HHT can reduce corneal haze after PRK in rabbits.