Biomedical subjects

Renato Ambrósio

Publications and source records attributed to Renato Ambrósio.

15 recordsLinked to original sources

PubMed2006

Corneal-thickness spatial profile and corneal-volume distribution: tomographic indices to detect keratoconus.

PURPOSE: To evaluate whether the corneal-thickness spatial profile and corneal-volume distribution differentiate keratoconic corneas from normal corneas using new tomography parameters. SETTING: Subspecialty cornea and refractive practice, Fluminense Federal University, Rio de Janeiro, Brazil. METHODS: Forty-six eyes diagnosed with mild to moderate keratoconus and 364 normal eyes were studied by the Pentacam Comprehensive Eye Scanner. Corneal thickness at the thinnest point and the averages of the points on 22 imaginary circles centered on the thinnest point with increased diameters at 0.4 mm steps were calculated to create a corneal-thickness spatial profile. Corneal volume was calculated within diameters from 1.0 to 7.0 mm with 0.5 mm steps centered on the thinnest point to create the corneal-volume distribution. The percentage increase in thickness and the percentage increase in volume were calculated for each position of the corneal-thickness spatial profile and corneal-volume distribution from their first value. Statistical analysis was done using the Wilcoxon 2-independent-sample test to compare mean levels using S-Plus-4.0 software (MathSoft) and a normal linear model under a Bayesian frame for estimating the mean variation in thickness and volume using the BUGS 0.6 package. RESULTS: Statistically significant differences were observed between the groups (P<.05) in all positions of corneal-thickness spatial profile and corneal-volume distribution and in the percentage increase in thickness and percentage increase in volume between 3.5 mm and 7.0 mm diameters. CONCLUSIONS: Corneal-thickness spatial profile, corneal-volume distribution, percentage increase in thickness, and percentage increase in volume were different between keratoconic corneas and normal corneas and could serve as indices to diagnose keratoconus and screen refractive candidates. Further studies are necessary to evaluate whether these tomographic indices are more sensitive and specific than the classic Placido-based topography.

Cornea↗

PubMed2005

[Corneal wound healing response following different modalities of refractive surgical procedures].

The corneal wound healing response following refractive procedures represents a subject of high relevance, due to its direct influence on the postoperative results. Technical modifications of current refractive procedures, like the automated flap creation with the femtosecond laser, LASEK, PRK with mitomycin C and Epi-LASIK have been proposed as alternatives to traditional LASIK and PRK. Several theoretical advantages have encouraged the diffusion of these new techniques; however, a better understanding of the corneal wound healing response following these procedures is required. The present text proposes a review of the corneal wound healing characteristics following different modalities of refractive surgical procedures.

Corneal Surgery, Laser↗

PubMed2005

Wound healing in the cornea: a review of refractive surgery complications and new prospects for therapy.

PURPOSE: The corneal wound healing response is of particular relevance for refractive surgical procedures since it is a major determinant of efficacy and safety. The purpose of this review is to provide an overview of the healing response in refractive surgery procedures. METHODS: Literature review. RESULTS: LASIK and PRK are the most common refractive procedures; however, alternative techniques, including LASEK, PRK with mitomycin C, and Epi-LASIK, have been developed in an attempt to overcome common complications. Clinical outcomes and a number of common complications are directly related to the healing process and the unpredictable nature of the associated corneal cellular response. These complications include overcorrection, undercorrection, regression, corneal stroma opacification, and many other side effects that have their roots in the biologic response to surgery. The corneal epithelium, stroma, nerves, inflammatory cells, and lacrimal glands are the main tissues and organs involved in the wound healing response to corneal surgical procedures. Complex cellular interactions mediated by cytokines and growth factors occur among the cells of the cornea, resulting in a highly variable biologic response. Among the best characterized processes are keratocyte apoptosis, keratocyte necrosis, keratocyte proliferation, migration of inflammatory cells, and myofibroblast generation. These cellular interactions are involved in extracellular matrix reorganization, stromal remodeling, wound contraction, and several other responses to surgical injury. CONCLUSIONS: A better understanding of the complete cascade of events involved in the corneal wound healing process and anomalies that lead to complications is critical to improve the efficacy and safety of refractive surgical procedures. Recent advances in understanding the biologic and molecular processes that contribute to the healing response bring hope that safe and effective pharmacologic modulators of the corneal wound healing response may soon be developed.

Animals↗

PubMed2003

Corneal cells: chatty in development, homeostasis, wound healing, and disease.

PURPOSE: To provide an overview of cell-cell interactions in the cornea that have a critical role in corneal development, homeostasis, wound healing, and disease. DESIGN: Review. METHODS: Review of the literature. RESULTS; Cell-cell interactions make critical contributions to development, homeostasis, and wound healing in the cornea. Many of these interactions are mediated by cytokines, growth factors, and chemokines. The best characterized are stromal-epithelial interactions between epithelial cells and stromal cells such as keratocytes, keratoblasts, and myofibroblasts. However, interactions also occur between corneal nerves and epithelial cells and between corneal cells (epithelial cells and stromal cells) and corneal immune cells. Although investigations are limited, it is likely that there are interactions between corneal endothelial cells and keratocytes in the posterior stroma. CONCLUSIONS: Cellular communications in the cornea are critical during development, homeostasis, and wound healing. Disorders of cellular communication likely contribute to many corneal diseases.

Animals↗

PubMed2003

Apoptosis, necrosis, proliferation, and myofibroblast generation in the stroma following LASIK and PRK.

The aim of this study was to semi-quantitatively analyze stromal cell apoptosis, stromal cell proliferation, and myofibroblast generation over time points from 4hr to 3 months in rabbit eyes having photorefractive keratectomy (PRK) or laser in situ keratomeliusis (LASIK). Stromal cell necrosis and inflammatory cell infiltration were also studied. PRK for low myopia (-4.5diopters [D]), PRK for high myopia (-9.0D), and LASIK for high myopia (-9.0D) were performed in rabbit eyes, and corneas were obtained for examination at 4, 24, and 72hr, 1 and 4 weeks, and 3 months after surgery. A total of 144 rabbits were included in the study. Stromal cell apoptosis, proliferation, and myofibroblast generation were evaluated semi-quantitatively by TUNEL assay, immunocytochemical analysis of Ki67, and immunocytochemical analysis of alpha-smooth muscle actin, respectively. Stromal cell necrosis and characteristics of other cell types in the stroma were evaluated by electron microscopy. Keratocyte apoptosis and the subsequent proliferation and generation of myofibroblasts were qualitatively and quantitatively different in PRK for high myopia compared to either PRK for low myopia or LASIK for high myopia. Stromal cell necrosis becomes a significant form of cell death by 24hr after injury and may involve corneal fibroblasts, myofibroblasts, and inflammatory cells. Large numbers of polymorphonuclear cells and monocytes invade the cornea by 24hr after surgery and persist for over 1 week. The qualitative and quantitative differences in the cellular wound healing response after PRK for high and low myopia and LASIK for high myopia are likely determinants of the clinical differences in refractive outcome and some of the complications, such as regression and haze, seen after these procedures.

Animals↗

PubMed2003

Effect of ectopic epithelial tissue within the stroma on keratocyte apoptosis, mitosis, and myofibroblast transformation.

The purpose of this study was to examine the effects of the epithelium on processes involved in stromal wound healing. Lamellar epithelial-stromal flaps were produced in rabbit corneas with a microkeratome. Peripheral corneal epithelial tissue, central corneal epithelial tissue, or no epithelial tissue (control) was introduced beneath the flap. Corneas were removed at time points from 4 hr to 1 month after surgery. Tissue sections were analyzed with immunocytochemistry for Keratin 3 (K3) to detect epithelial antigen, terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick-end labelling (TUNEL) assay to detect apoptosis, immunocytochemistry for Ki67 to detect cell proliferation, and immunocytochemistry for alpha-smooth muscle actin (SMA) to detect myofibroblasts. K3 was detected at the level of the interface from 4 hr to 1 month after surgery in corneas in which epithelial tissue was introduced, but not control corneas, with the exception of one that developed epithelial in growth. Keratocyte apoptosis was significantly higher at 4 hr after flap formation in both groups in which corneal epithelial tissue was introduced beneath the flap compared with controls. Keratocyte proliferation was significantly greater at 72 hr in corneas in which epithelial tissue was introduced beneath the flap compared to the controls. Corneas in which epithelial tissue was introduced into the interface, but not control corneas, had stromal cells expressing alpha-SMA in the stroma anterior and posterior to the interface at 1 week and 1 month after surgery. This was also noted in the control cornea in which there was epithelial ingrowth. Signals derived from the corneal epithelium promote keratocyte apoptosis. Keratocyte proliferation is higher in corneas that have lamellar surgery when epithelial tissue is introduced into the interface. Epithelium-derived signals also participate in the generation and/or maintenance of myofibroblasts in the corneal stroma.

Actins↗

PubMed2003

LASIK vs LASEK vs PRK: advantages and indications.

The advent of the excimer laser as an instrument for use in reshaping the corneal stroma was a great step forward in refractive surgery. Laser energy can be delivered on the stromal surface in the photorefractive keratectomy (PRK) procedure or deeper on the corneal stroma by the means of a lamellar surgery in which a flap is created with the microkeratome in the laser in situ keratomileusis (LASIK) procedure. LASIK is currently the dominant procedure in refractive surgery. The main advantage of LASIK over PRK is related to maintaining the central corneal epithelium. This increases comfort during the early post-operative period, allows for rapid visual recovery, and reduces the wound healing response. Reduced wound healing correlates with less regression for high corrections and a lower rate of complications such as significant stromal opacity (haze). PRK, however, remains as an excellent option for mild to moderate corrections, particularly for cases associated with thin corneas, recurrent erosions, or a predisposition for trauma (Martial arts, military, etc.). Recently, a modification of PRK, laser subepithelial keratomileusis (LASEK), was introduced. In the LASEK procedure, an epithelial flap is created and replaced after the ablation. The benefits, if any, of the creation of an epithelial flap compared to traditional PRK are not fully appreciated. Advocates of LASEK suggest that there is less discomfort in the early postoperative period, faster visual recovery, and less haze compared to standard PRK for correction of similar levels of refractive error. Additional long-term clinical studies, along with laboratory research, will be crucial to validate these potential advantages of LASEK procedure.

Humans↗

PubMed2003

Morphology of corneal Basal epithelial cells by in vivo slit-scanning confocal microscopy.

PURPOSE: To determine corneal basal epithelial cell density and morphology in a group of normal corneas and corneas with various conditions. METHODS: The central corneas of a group of 20 normal patients and 27 other patients who either had refractive surgery or had documented corneal pathology were examined with an in vivo slit-scanning confocal microscope. For all these patients in whom a well-defined basal epithelial layer was visualized, the basal cell density, area, and number of sides per cell were determined using customized software. RESULTS: The average basal cell density was 5,274 +/- 575 cells/mm2, the average cell area was 192 +/- 19.6 microm2, and the average number of cell sides was 5.5 +/- 0.1 sides for the group of normal controls. There were no statistically significant differences between basal cell density, cell area, or number of sides between the normal group and any of the other groups in which there were four or more patients. Corneas examined from patients with Fuchs' endothelial dystrophy or bullous keratopathy had hyperreflective basal epithelial cell borders. The measurement of the number of cell sides is not reliable using software developed for endothelial cell counting. CONCLUSION: Corneal basal epithelial cell density and area were found to be remarkably consistent in the variety of corneal disorders that we examined. This finding is further evidence that this aspect of corneal epithelial cell differentiation and maturation is tightly controlled with little variability between individuals even if a corneal condition is present.

Adult↗

PubMed2002

Early pellucid marginal corneal degeneration: case reports of two refractive surgery candidates.

PURPOSE: To report two refractive surgery candidates who demonstrated early corneal topographic findings of pellucid marginal degeneration. METHODS: Case reports. RESULTS: Two candidate patients for corneal laser surgery were examined. The patients had normal examinations, including normal slit lamp biomicroscopy results and corrected visual acuity that was 20/20 or better in each eye. The corneal topography in one eye of patient I and both eyes of patient 2 was characterized by the presence of irregular astigmatism and inferior corneal steepening with a pattern consistent with pellucid marginal degeneration. Marked asymmetry between the eyes was noted. The inferior cornea was thinner than the central cornea in both eyes of each patient. CONCLUSION: Patients with early corneal ectasia often present as refractive surgery candidates with normal corrected visual acuity and normal pachymetry of the central cornea. Corneal topography and regional pachymetry measurements can be used to identify these patients. Patients with pellucid marginal degeneration are not good candidates for refractive surgery because of the potential for poor outcomes and the possibility that iatrogenic thinning of the cornea could lead to progression of the disease.

Aged↗

PubMed2002

Sporadic diffuse lamellar keratitis (DLK) after LASIK.

PURPOSE: To examine the incidence of sporadic diffuse lamellar keratitis (DLK) in a large series of LASIK eyes and to suggest the hypothesis that the etiology of sporadic DLK differs from that of epidemic DLK. METHODS: The incidence and severity of DLK was noted in 1352 consecutive eyes that had primary LASIK for myopia or hyperopia and 217 consecutive eyes that had LASIK enhancement. RESULTS: Twelve of the eyes having primary LASIK had stage 1 DLK and 5 had stage 2 DLK (.9% total). No eyes had stage 3 or stage 4 DLK. Three of the 217 eyes (1.4%) that had LASIK enhancement had stage 1 DLK. The difference in the rate of DLK for primary LASIK compared with LASIK enhancement was not statistically significant (p = 0.69). All eyes responded to intensive corticosteroid therapy, with the addition of flap lifting and irrigation for the eyes with stage 2 DLK. Two of the eyes (one primary LASIK and one LASIK-enhancement) had implanted epithelial nests associated with the DLK. None of the cases of DLK occurred in eyes of patients who had surgery on the same operating day in this series. Two other eyes that had epithelial abrasions more than 3 months after LASIK or LASIK enhancement developed stage 1 DLK. CONCLUSIONS: Many cases of sporadic DLK, including cases associated with epithelial trauma after LASIK, are likely attributable to endogenous factors that trigger inflammation. One trigger is the release of epithelium-derived cytokines such as interleukin-1 that stimulate keratocytes to produce chemokines that are chemotactic to inflammatory cells. Cells likely accumulate at the interface because it is potential space, representing a path of least resistance for cell movement. Some sporadic cases may also be related to exogenous factors such as Betadine. Epidemic DLK is likely associated with exogenous factors that stimulate inflammation, such as endotoxin contaminating sterilizer reservoirs or detergents on instruments.

Epithelium, Corneal↗

PubMedDate not supplied

[Corneal thickness progression from the thinnest point to the limbus: study based on a normal and a keratoconus population to create reference values].

PURPOSE: To study the variation and progression of the pachymetric values from the thinnest point towards the limbus in normal and keratoconic corneas; to establish reference curves for this parameter. METHODS: One hundred eyes with normal corneas and twenty-five eyes with mild keratoconus (stages I and II - Krumeich) were analyzed using the Orbscan. Concentric circles were drawn on the thinnest point of the cornea with increasing radii from 1 to 7 mm. The average results of each circle were calculated and inserted in an Excel table in order to arrange a progression chart for each case starting on the thinnest point. The SPSS software was also used for statistical analysis. Student's t test was then used to compare the found values. RESULTS: The average values on the thinnest point in normal patients was 511.6 microm (standard deviation 30.6). The average values of the thinnest point in patients with keratoconus was 424.4 microm (standard deviation 56.57). Statistically significant different values were reported (p<0.01) for all circles, and for 6 and 7 mm radii p=0.01. CONCLUSION: There is a greater pachymetric variability in patients with keratoconus. Keratoconic corneas also have a faster progression of pachymetric values than healthy eyes. Pachymetric progression complements traditional single point evaluation of corneal thickness and must be considered for the screening at refractive candidates. This parameter may represent an indirect index of the biomechanics of corneal tissue but this hypothesis still needs further studies.

Corneal Topography↗

PubMedDate not supplied

Corneal topographic and pachymetric screening of keratorefractive patients.

PURPOSE: To review the incidence of corneal abnormalities detected in the preoperative examination, using videokeratography and pachymetry that excluded patients from laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). METHODS: We conducted a chart review of consecutive patients who had a preoperative examination and were excluded from refractive surgery. RESULTS: Eighteen patients from 1,392 refractive candidates (1.3%) were designated as poor candidates for LASIK or PRK based on corneal topography and/or pachymetry. Thirteen patients (0.9%) were identified as having keratoconus suspect, keratoconus, or pellucid marginal degeneration. Five patients (0.4%) were excluded due to thin corneas (<490 microm) despite normal corneal topography. CONCLUSIONS: Corneal topography and pachymetry are indispensable tools in the preoperative screening of refractive surgery candidates.

Adult↗

PubMedDate not supplied

Bilateral marginal sterile infiltrates and diffuse lamellar keratitis after laser in situ keratomileusis.

PURPOSE: To report cases of acute bilateral catarrhal infiltrates in the early postoperative period after laser in situ keratomileusis (LASIK). METHODS: Retrospective review of both eyes of two patients. RESULTS: Two patients developed acute bilateral, marginal, catarrhal infiltrates in the early postoperative period after LASIK. Both patients had moderate to severe chronic meibomian gland dysfunction preoperatively. One patient (both eyes) developed grade 3 diffuse lamellar keratitis (DLK) that required both flaps to be lifted for irrigation and cleaning on postoperative day 5. Fungal and bacterial cultures were negative in both eyes of both patients. The condition resolved with intensive topical corticosteroids and fortified antibiotics. Regression of refractive error and the need for enhancement was encountered in all eyes. There was mild recurrence in one eye of each patient with pretreatment with topical corticosteroids prior to enhancement. CONCLUSIONS: Endogenous factors such as chronic blepharitis and meibomian gland dysfunction may trigger inflammation resulting in sporadic cases of catarrhal infiltrates after LASIK. These patients may have chronic inflammatory milieus that can trigger sporadic cases of catarrhal infiltrates after LASIK, with accompanying diffuse lamellar keratitis.

Anti-Bacterial Agents↗

PubMedDate not supplied

Pupil size in refractive surgery candidates.

PURPOSE: To assess pupil size measurements obtained under scotopic and mesopic conditions with the Procyon pupillometer and under photopic conditions with the Humphrey videokeratographer. METHODS: The pupil sizes of 96 candidates for refractive surgery (192 eyes) were measured with the Procyon pupillometer PS2000 SA and the Humphrey Atlas 992 corneal topographer. Anisocoria and pupillary unrest were analyzed according to gender (two groups: 51 females and 45 males), age (five groups: 20 to 30 yr, 31 to 40 yr, 41 to 50 yr, 51 to 60 yr, older than 60 yr) and level of refraction (five groups: >-6.00 D SE, -6.00 to -3.00 D SE, -3.00 to 0 D SE, 0 to +2.50 D SE, +2.50 to +5.00 D SE). RESULTS: The median value of pupil diameter measured with the Procyon pupillometer at the scotopic (0.04 lux), mesopic-low (0.4 lux), and mesopic-high (4 lux) levels of illumination were 6.54+/-0.88 mm; 5.62+/-0.95 mm, and 4.09+/-0.76 mm, respectively. The median pupil size with the Humphrey topographer was 3.65+/-0.62 mm. Pupillary unrest was highest at the mesopic-high level of illumination, with a median value of 0.31+/-0.34 mm. Median pupil size measured with both instruments at all light levels dropped significantly after the fifth decade of life (P<.05, ANOVA). CONCLUSIONS: The Procyon pupillometer and Humphrey videokeratographer revealed an inverse correlation between the pupil size and the age, but no relationship with gender or level of refraction. The Procyon pupillometer provides an objective method for measuring pupil size at controlled light levels with a permanent printed record.

Adult↗

PubMedDate not supplied

Wavefront analysis in normal refractive surgery candidates.

PURPOSE: To quantify the higher order aberrations of refractive surgery candidates and compare the wavefront-determined refractions with manifest refractions refined with a +/- 0.25 Jackson cross cylinder. METHODS: Results of 226 consecutive patients (418 eyes) were analyzed with the WaveScan WavePrint system (VISX, Santa Clara, Calif). Only patients with normal eyes without previous surgery were included. RESULTS: The mean spherical equivalent refraction determined with wavefront analysis was -3.40 +/- 3.14 diopters (D) (range: -10.72 to +5.41 D). The largest amount of higher order aberrations was detected with : a 6-mm pupil diameter (coma 0.14 +/- 0.08 microm; trefoil 0.10 +/- 0.07 microm; spherical aberrations 0.09 +/- 0.07 microm). The mean root-mean-square of higher order aberrations and total aberrations were 0.23 +/- 0.11 microm and 4.00 +/- 2.45 microm, respectively. No statistically significant correlation was noted between higher order aberrations and gender (P = 0.7) or between higher order aberration and refractive level (P > .59). The mean differences in spherical equivalent refraction, sphere, and cylinder between WaveScan measurements and manifest refraction were 0.36 +/- 0.41 D, 0.40 +/- 0.44 D, and 0.28 +/- 0.32 D, respectively. CONCLUSIONS: This study provides reference values for higher order aberrations in normal refractive surgery candidates. Wavefront analysis also proved to be a valuable tool for objectively measuring preoperative refractive error.

Adult↗