Milton Ruiz Alves

Evaluation of corneal shape and biomechanics before LASIK.

The preoperative evaluation is of critical importance for success in laser in situ keratomileusis (LASIK). This examination should fulfill 3 main purposes: counseling and educating the candidates, surgery planning, and screening for cases at higher risk for complications. It is critical to interview each refractive patient to assess their individual needs and to provide realistic expectations. A thorough ophthalmologic examination is mandatory, including specific complementary examinations to characterize many aspects of the cornea and the optics of the eye. In fact, it is notable that refractive surgery has motivated tremendous development for advanced diagnostic methods, among many others advancements and innovations in Ophthalmology. One of the most important aspects of the preoperative examination of LASIK candidates is to screen cases at risk for progressive ectasia.

Effects of age on corneal deformation by non-contact tonometry integrated with an ultra-high-speed (UHS) Scheimpflug camera

PURPOSE To correlate parameters derived from corneal deformation resulting from non-contact tonometry integrated with an ultra-high-speed (UHS) Scheimpflug camera (Oculus Corvis ST, Scheimpflug Technology; Wetzlar, Germany) with age in normal eyes from young patients. METHODS Observational, retrospective study involving one eye randomly selected from study participants, totaling 89 healthy eyes. The Scheimpflug images were taken with an ultra-high-speed camera during each measurement by the corvis ST. The deformation amplitude (DA) and other parameters (e.g., pachy apex, intraocular pressure, 1(st) A time, highest concavity-time, 2(nd) A time, 1(st) A Length, 2(nd) A Length, Wing-Dist, curvature radius highest concavity, curvature radius normal, Vin, Vout) measured by the corvis ST were correlated with age. The Kolmogorov-Smirnov test was applied, and Spearmans correlation test was utilized to evaluate the parameters measured by the Corvis ST and age. RESULTS Mean patient age was 27.50 ± 6.30 years. The highest concavity-time was the only studied parameter statistically significantly correlated to age (i.e., p=0.04, rs=0.18). All other corvis parameters were not correlated to age. This included DA (p=0.319), intraocular pressure (p=0.854), pachy apex (p=0.066), 1(st) A time (p=0.959), 2(nd) A time (p=0.561), 1(st) Length (0.552), 2nd Length (p=0.697), Wing-Dist (p=0.769), curvature radius HC (p=0.145), curvature radius normal (p=0.513), Vin (p=0.980) and Vout (p=0.592). CONCLUSIONS In healthy eyes, age and pressure or biomechanics as derived from the Corvis ST parameters were not associated with exception to highest concavity-time, i.e., the time from starting until the highest concavity is reached.

Correlation between signs and symptoms of ocular surface dysfunction and tear osmolarity with ambient levels of air pollution in a large metropolitan area.

Purpose: To evaluate the effect of high levels of environmental air pollution on tear osmolarity and its possible correlation with clinical signs and symptoms. Methods: This was a panel study involving 71 taxi drivers and traffic controllers from São Paulo, Brazil. Mean individual levels of 24-hour exposure to nitrogen dioxide (NO2) and particulate matter smaller than 2.5 &mgr;m (PM2.5) were assessed on 4 different occasions. On the first and third visits, subjects were submitted to clinical evaluations including the administration of the Ocular Surface Disease Index questionnaire, slit-lamp examination, estimation of tear breakup time (BUT), the Schirmer test, and vital staining of the cornea and conjunctiva. On the second and fourth visits, tear samples were collected for osmolarity assays. Statistical analysis was performed using generalized estimating equations. Results: Although the taxi drivers and traffic controllers in our sample were exposed to high levels of NO2 and PM2.5, few symptoms were reported on the Ocular Surface Disease Index questionnaire. BUT values were reduced, whereas vital staining and Schirmer test mean results were within normal limits, despite considerable variability. A significant and negative correlation was found between PM2.5 levels and tear film osmolarity levels (P < 0.05). An increase of 10 &mgr;g/m3 in PM2.5 was associated with a 10.9 mOsm/kg decrease in tear osmolarity. There also was a negative correlation, although not statistically significant, between NO2 and tear osmolarity. Conclusions: Exposure to air pollution reduces tear film stability and influences tear film osmolarity. Combining clinical examination with the assessment of tear osmolarity may help understand ocular surface response to high levels of air pollution.

Self-evaluation of contact lens wearing and care by college students and health care workers

Purpose. To identify perceptions related to the wear and care and of contact lenses and self-evaluation of the knowledge regarding their cleaning and disinfection. Methods. A survey was conducted by interviewing contact lens wearers among health care workers at a university hospital. Results. Two hundred one contact lens wearers were interviewed. The average age was 23.5 years; 69.2% were female and 71.1% were college students. Approximately 55% did not consider themselves good wearers and declared as the main reason the inadequate maintenance of the contact lenses and their cases. Regarding contact lens care, 79.1% of respondents admitted not performing it correctly. Conclusion. Although the interviewees were health care workers, their self-evaluation regarding contact lens care showed unsatisfactory knowledge and practices related to the use and care of contact lenses.

Ocular Biomechanical Metrics by CorVis ST in Healthy Brazilian Patients

PURPOSE To evaluate ocular biomechanical metrics given by the CorVis ST (Oculus, Inc., Berlin, Germany) in a population of healthy Brazilian patients. METHODS An observational and cross-sectional study involving 1 eye randomly selected from 90 healthy patients. Studied parameters (including deformation amplitude, first applanation time, highest concavity time, second applanation time, first applanation length, second applanation length, curvature radius highest concavity, curvature radius normal, velocity in, and velocity out) derived from the CorVis ST were correlated to central corneal thickness from the Pentacam (Oculus, Inc.). Differences between data on the basis of gender were evaluated. RESULTS Mean patient age was 35.80 ± 12.83 years (range: 21.07 to 78.84 years). Mean central corneal thickness was 547.50 ± 32.00 μm (range: 490 to 647 μm) and mean spherical equivalent refraction was -3.29 ± 3.69 diopters (range: -9.50 to +10.37 diopters). Mean deformation amplitude was 1.05 ± 0.08 mm (range: 0.91 to 1.26 mm). Highest concavity time was 18.38 ± 0.93 ms (range: 16.95 to 21.07 ms). Intraocular pressure was 16.43 ± 2.15 mm Hg (range: 11.50 to 21.0 mm Hg). First applanation time was 8.32 ± 0.33 ms (range: 7.53 to 9.12 ms) and second applanation time was 23.80 ± 0.44 ms (range: 22.76 to 24.95 ms). First applanation length (max) was 2.07 ± 0.38 mm (range: 1.20 to 3.10 mm) and second applanation length (max) was 2.37 ± 0.47 mm (range: 1.33 to 4.12 mm). Curvature radius highest concavity was 11.09 ± 2.06 mm (range: 7.58 to 15.98 mm) and curvature radius normal was 7.59 ± 0.67 mm (range: 6.82 to 11.02 mm). Velocity in was 0.21 ± 0.05 m/s (range: 0.16 to 0.72 m/s) and velocity out was -0.33 ± 0.07 m/s (range: -0.72 to -0.20 m/s). Studied parameters were not associated with gender. CONCLUSIONS Eight of 11 ocular biomechanical metrics given by the CorVis ST were associated with central corneal thickness, but the influence of central corneal thickness on these measurements was low.

Effects of ambient levels of traffic-derived air pollution on the ocular surface: analysis of symptoms, conjunctival goblet cell count and mucin 5AC gene expression.

PURPOSE To quantify ocular symptoms, goblet cells (GC) and mucin 5AC (MUC5AC) gene expression on the conjunctiva of healthy subjects exposed to ambient levels of traffic-derived air pollution and to estimate its correlation with NO2 and particulate matter smaller than 2.5 μm (PM2.5) levels. METHODS Twenty-one taxi drivers or traffic controllers were assessed with the Ocular Surface Disease Index (OSDI) questionnaire and conjunctival impression cytology. MUC5AC mRNA levels were determined based on the cytology of the right eye, and GC density was assessed based on the cytology of the left eye. Mean individual levels of 24-h NO2 and PM2.5 exposure were assessed the day before examination. Possible associations between NO2 or PM2.5 levels, OSDI scores, GC densities and MUC5AC mRNA levels were verified. RESULTS The subjects were exposed to mean PM2.5 levels of 35±12 μg/m(3) and mean NO2 levels of 189±47 μg/m(3). OSDI scores were low (7.4±8) and GC densities were 521±257 and 782±322 cell/mm(2) on the bulbar and tarsal conjunctivas, respectively. The mean GC-derived MUC5AC mRNA expression was 14±7 fM/μg of total RNA. A significant and positive correlation was observed between MUC5AC mRNA levels and tarsal GC density (p=0.018). A trend toward association between PM2.5 levels and tarsal GC cell density (p=0.052) was found. CONCLUSION Exposure to ambient levels of air pollution impacts conjunctival GC density. An increase in MUC5AC mRNA levels may be part of an adaptive ocular surface response to long-term exposure to air pollution.

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.

Ocular surface adverse effects of ambient levels of air pollution

It is widely recognized today that outdoor air pollution can affect human health. Various chemical components that are present in ambient pollution may have an irritant effect on the mucous membranes of the body, particularly those of the respiratory tract. Much less attention has been focused on the adverse effect on the ocular surface, despite the fact that this structure is even more exposed to air pollution than the respiratory mucosa since only a very thin tear film separates the corneal and conjunctival epithelia from the air pollutants. So far, clinical data are the more widespread tools used by ophthalmologists for assessing possible aggression to the ocular surface; however, clinical findings alone appears not to correlate properly with the complaints presented by the patients pointing out the need for further clinical and laboratory studies on the subject. The purpose of this study is to review signs and symptoms associated with chronic long-term exposure to environmental air pollutants on the ocular structures currently defined as the ocular surface and to review clinical and laboratory tests used to investigate the adverse effects of air pollutants on such structures. We also review previous studies that investigated the adverse effects of air pollution on the ocular surface and discuss the need for further investigation on the subject.

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.

Role of reinsertion of the lower eyelid retractor on involutional entropion

AIMS To verify and evaluate the effect of reinsertion of the lower eyelid retractor aponeurosis to correct involutional entropion. METHODS The involutional entropion is one affection that occurs mainly in the lower eyelid of patients over 60 years old. The surgical techniques proposed to correct this condition are based on correction of horizontal laxity—the preseptal orbicularis muscle overrides the pretarsal muscle, and the reinsertion of the lower eyelid retractor aponeurosis. 30 patients clinically diagnosed with involutional entropion and randomly selected underwent reinsertion of the lower eyelid retractor aponeurosis to the tarsal plate, without horizontal shortening or resection of the skin or orbicularis muscle. RESULTS Good anatomical and functional correction was achieved in 96.6% of the patients and no recurrence was observed on 29 month follow up examination. The surgical result was very satisfactory. CONCLUSIONS It was concluded that this procedure is effective and has low recurrence rate, showing the important role of the reinsertion of the lower eyelid retractor aponeurosis in this surgical correction.