Fabricio Witzel de Medeiros

Femtosecond Laser and Microkeratome Corneal Flaps: Comparison of Stromal Wound Healing and Inflammation

PURPOSE To examine early postoperative wound healing in rabbit corneas that had LASIK flaps formed with three different models (15 KHz, 30 KhZ, and 60 KHz) of a femtosecond laser compared with flaps formed with a microkeratome. METHODS Thirty-nine rabbit eyes were randomized to receive either no surgery or corneal flaps formed with one of the lasers or the microkeratome. Sixteen eyes also had lamellar cuts with no side cuts with the 30 KHz laser. Animals were sacrificed and corneas processed as frozen sections or fixed for transmission electron microscopy. Frozen sections were evaluated with the TUNEL assay to detect apoptosis, immunocytochemistry for Ki67 to detect cell mitosis, and immunocytochemistry for CD11b to detect mononuclear cells. RESULTS Rabbit corneas that had flaps formed with the 15 KHz laser had significantly more stromal cell death, greater stromal cell proliferation, and greater monocyte influx in the central and peripheral comea at 24 hours after surgery than corneas that had flaps formed with the 30 KHz or 60 KHz laser or the microkeratome. Results of the 60 KHz laser and microkeratome were not significantly different for any of the parameters at 24 hours, except for mitotic stromal cells at the flap margin. Transmission electron microscopy revealed that the primary mode of stromal cell death at 24 hours after laser ablation was necrosis. CONCLUSIONS Stromal cell necrosis associated with femtosecond laser flap formation likely contributes to greater inflammation after LASIK performed with the femtosecond laser, especially with higher energy levels that result in greater keratocyte cell death.

Wavefront analysis comparison of LASIK outcomes with the femtosecond laser and mechanical microkeratomes.

PURPOSE To evaluate differences related to ocular aberrations after customized LASIK for myopia using three different microkeratomes. METHODS Charts of 410 patients who underwent customized LASIK with the Alcon LADARVision4000 excimer laser were reviewed. Patients were stratified according to the device used to create the flap: Moria M2 microkeratome, Bausch & Lomb Hansatome microkeratome, or IntraLase laser. The difference between the wavefront pre- and postoperative value received a positive or a negative sign if the change occurred toward or away from zero, respectively, and it was compared to preoperative minus postoperative manifest refraction spherical equivalent (MRSE). RESULTS Patients showed increase in the aberration level after LASIK with the three devices used in this study. IntraLase spherical aberration change tended to be better than mechanical microkeratomes for higher MRSE values (IntraLase compared to Hansatome, P < or = .023 for MRSE values > or = 4.00 diopters [D]; IntraLase compared to Moria, P < or = .015 for MRSE values > or = 2.00 D). For total aberrations, the improvement values for IntraLase tended to be higher than those for Moria (IntraLase compared to Moria, P < or = .021 for MRSE values > or = 3.00 D). For total higher order aberrations, IntraLase values tended to be better than Moria and Hansatome microkeratomes (IntraLase compared to Hansatome, P < or = .047 for MRSE values between 3.00 and 8.00 D; IntraLase compared with Moria, P < or = .002 for MRSE values > or = 2.00 D). Change in coma root-mean-square was similar for the three groups. CONCLUSIONS The findings suggest the femtosecond laser provides a better platform for LASIK than the commonly used microkeratomes analyzed in this study.

Effect of Femtosecond Laser Energy Level on Corneal Stromal Cell Death and Inflammation

PURPOSE To analyze the effects of variations in femtosecond laser energy level on corneal stromal cell death and inflammatory cell influx following flap creation in a rabbit model. METHODS Eighteen rabbits were stratified in three different groups according to level of energy applied for flap creation (six animals per group). Three different energy levels were chosen for both the lamellar and side cut: 2.7 microJ (high energy), 1.6 microJ (intermediate energy), and 0.5 microJ (low energy) with a 60 kHz, model II, femtosecond laser (IntraLase). The opposite eye of each rabbit served as a control. At the 24-hour time point after surgery, all rabbits were euthanized and the corneoscleral rims were analyzed for the levels of cell death and inflammatory cell influx with the terminal uridine deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and immunocytochemistry for monocyte marker CD11b, respectively. RESULTS The high energy group (31.9+/-7.1 [standard error of mean (SEM) 2.9]) had significantly more TUNEL-positive cells in the central flap compared to the intermediate (22.2+/-1.9 [SEM 0.8], P=.004), low (17.9+/-4.0 [SEM 1.6], P< or =.001), and control eye (0.06+/-0.02 [SEM 0.009], P< or =.001) groups. The intermediate and low energy groups also had significantly more TUNEL-positive cells than the control groups (P< or =.001). The difference between the intermediate and low energy levels was not significant (P=.56). The mean for CD11b-positive cells/400x field at the flap edge was 26.1+/-29.3 (SEM 11.9), 5.8+/-4.1 (SEM 1.6), 1.6+/-4.1 (SEM 1.6), and 0.005+/-0.01 (SEM 0.005) for high energy, intermediate energy, low energy, and control groups, respectively. Only the intermediate energy group showed statistically more inflammatory cells than control eyes (P=.015), most likely due to variability between eyes. CONCLUSIONS Higher energy levels trigger greater cell death when the femtosecond laser is used to create corneal flaps. Greater corneal inflammatory cell infiltration is observed with higher femtosecond laser energy levels.

Corneal stroma PDGF blockade and myofibroblast development.

Myofibroblast development and haze generation in the corneal stroma is mediated by cytokines, including transforming growth factor-beta (TGF-beta), and possibly other cytokines. This study examined the effects of stromal PDGF-beta blockade on the development of myofibroblasts in response to -9.0 diopter photorefractive keratectomy in the rabbit. Rabbits that had haze generating photorefractive keratectomy (PRK, for 9 diopters of myopia) in one eye were divided into three different groups: stromal application of plasmid pCMV.PDGFRB.23KDEL expressing a subunit of PDGF receptor b (domains 2-3, which bind PDGF-B), stromal application of empty plasmid pCMV, or stromal application of balanced salt solution (BSS). The plasmids (at a concentration 1000ng/microl) or BSS was applied to the exposed stroma immediately after surgery and every 24h for 4-5 days until the epithelium healed. The group treated with pCMV.PDGFRB.23KDEL showed lower alphaSMA+ myofibroblast density in the anterior stroma compared to either control group (P<or=0.001). Although there was also lower corneal haze at the slit lamp at one month after surgery, the difference in haze after PDGF-B blockade was not statistically significant compared to either control group. Stromal PDGF-B blockade during the early postoperative period following PRK decreases stromal alphaSMA+ myofibroblast generation. PDGF is an important modulator of myofibroblast development in the cornea.

Biomechanical corneal changes induced by different flap thickness created by femtosecond laser.

OBJECTIVE: To evaluate the impact of the creation of corneal flaps at different thicknesses on the biomechanical properties of swine corneas. METHOD: Twelve swine eyes were obtained to form two groups: 100 µm flap thickness and 300 µm flap thickness. Each eye was submitted to the following examinations: raster topography to investigate corneal curvature alterations, ocular response analyzer to investigate corneal hysteresis change, optical coherence tomography to measure central corneal and flap thickness and sonic wave propagation velocity as a measure of stiffness, before and immediately after flap creation. After flap amputation, surface wave velocity measurements were repeated. RESULTS: Measured flap thicknesses were statistically different for thin and thick flap groups, with an average of 108.5±6.9 and 307.8±11.5 µm respectively. Hysteresis and corneal resistance factor did not change significantly after flap creation in the thin flap group. With thicker flaps, both parameters decreased significantly from 8.0±1.0 to 5.1±1.5 mmHg and from 8.2±1.6 to 4.1±2.5 mmHg respectively. Simulated keratometry values increased in the thick flap group (from 39.5±1 D to 45.9±1.2 D) after flap creation but not in the thin flap group (from 40.6±0.6 D to 41.4±1.0 D). Regarding surface wave velocity analysis, the surgical procedures induced statistically lower results in some positions. CONCLUSION: In the experimental conditions established by this model, thicker flaps presented a greater biomechanical impact on the cornea.

Evaluation of machine learning classifiers in keratoconus detection from orbscan II examinations

PURPOSE: To evaluate the performance of support vector machine, multi‐layer perceptron and radial basis function neural network as auxiliary tools to identify keratoconus from Orbscan II maps. METHODS: A total of 318 maps were selected and classified into four categories: normal (n = 172), astigmatism (n = 89), keratoconus (n = 46) and photorefractive keratectomy (n = 11). For each map, 11 attributes were obtained or calculated from data provided by the Orbscan II. Ten‐fold cross‐validation was used to train and test the classifiers. Besides accuracy, sensitivity and specificity, receiver operating characteristic (ROC) curves for each classifier were generated, and the areas under the curves were calculated. RESULTS: The three selected classifiers provided a good performance, and there were no differences between their performances. The area under the ROC curve of the support vector machine, multi‐layer perceptron and radial basis function neural network were significantly larger than those for all individual Orbscan II attributes evaluated (p<0.05). CONCLUSION: Overall, the results suggest that using a support vector machine, multi‐layer perceptron classifiers and radial basis function neural network, these classifiers, trained on Orbscan II data, could represent useful techniques for keratoconus detection.

Relationship between the biomechanical properties of the cornea and anterior segment measurements

OBJECTIVE: To evaluate the relationship of biomechanical properties, corneal hysteresis and corneal resistance factor with age, sex and various corneal parameters measured with a Pentacam in normal subjects. METHODS: A total of 226 eyes from 113 patients were enrolled in this study. The subjects underwent Ocular Response Analyzer and Pentacam evaluations. A varying-intercept multilevel regression was implemented using Bayesian inference. The predictor variables were age, sex, central corneal thickness, corneal volume at a 7-mm diameter, anterior chamber angle and volume, anterior chamber depth, mean radius of the corneal curvature and corneal astigmatism. RESULTS: Corneal hysteresis ranged from 5.5 to 14.8舁mmHg (mean 10.42±1.74舁mmHg), and the corneal resistance factor ranged from 5.7 to 15.5舁mmHg (mean 10.23±1.88舁mmHg). No predictor variable other than gender and central corneal thickness had a significant correlation with either corneal hysteresis or corneal resistance factor. Corneal hysteresis was positively associated with female sex and with central corneal thickness, and corneal resistance factor was positively associated with central corneal thickness. CONCLUSION: Despite the associations found, only a small fraction of the variance in biomechanical measurements could be explained by the descriptors that were evaluated, indicating the influence of other corneal aspects on the biomechanical characteristics.

Diagnóstico do ceratocone baseado no Orbscan com o auxílio de uma rede neural

PURPOSE: To evaluate an artificial neural network in order to correctly identify Orbscan IITM tests of patients with normal and keratoconus corneas. METHODS: A retrospective analysis included 98 Orbscan IITM tests of 59 subjects and an artificial neural network was created and trained based on the Java Neural Network 1.1 software. Seventy-three tests (59 normal tests and 14 keratoconus examinations) were applied to train the neural network and 25 eyes were used to test the method (19 normal eyes and 6 cases of keratoconus corneas). RESULTS: Backpropagation method was performed to train the neural network to 5% error and 0.2 learning rate. The trained neural network presented sensibility and specificity of 83 and 100% respectively. CONCLUSION: Artificial neural network can accurately help clinicians to classify keratoconus in Orbscan IITM tests.

Doenças do segmento anterior ocular associadas a lentes de contato

Nowadays, contact lenses have shown a larger variety of options in order to meet the needs of different patients. They have become more frequent in the clinical practice and, consequently, the complications related to contact lenses have been more common. This review attempted to describe the main alterations and diseases of the cornea and anterior segment associated with contact lens wearers.

Síndrome de Cogan: relato de caso

Non-luetic interstitial keratitis, deafness and vertigo characterize Cogans syndrome. The most common ocular findings in early Cogans syndrome are bilateral, peripheral, subepithelial numular corneal opacities. The report presents a patient with the evolution of the classic form of Cogans syndrome.