Comparability of corneal thickness and opacity depth assessed by OCT and UBM.

OBJECTIVE: To compare the measurement of central thickness and depth of involvement of opacity-bearing corneas at different intensities (mild, moderate, and dense) using different instruments: Visante and Optovue OCTs, ultrasound biomicroscopy (UBM), and ultrasound pachymetry (central thickness). METHODS: Sample of 102 eyes: 70 eyes (68.63 %) with corneal opacity; 32 eyes (31.37%) with normal corneas. Corneal opacity grading included mild (28 eyes, 40.00 %), moderate (27 eyes, 37.57 %), and dense (15 eyes, 21.43 %). Opacity intensity was graded and documented. Central corneal thickness was determined using Optovue and Visante OCTs, ultrasound pachymetry, and UBM VuMax (50 MHz), and depth of corneal opacity, using Optovue and Visante OCTs and UBM. RESULTS: Total corneal thickness of the control group showed differences with a small correction factor using Optovue OCT (534.03 ± 39.88 µm), Visante OCT (523.72±38.70 µm), and ultrasound pachymetry (529.84 ± 39.76 µm), and were higher when compared to UBM (492.06 ± 37.93 µm). In mild opacity, depth measurements were the same with OCT Optovue and Visante and higher than those by UBM. In moderate opacities, there were no differences in measurements by different instruments. In dense opacities, OCT Optovue and Visante measurements were the same and higher than those by UBM. CONCLUSIONS: Central corneal thickness measurements were considered higher in corneas with opacity than in normal corneas. We observed that the greatest thicknesses were measured in corneas with dense opacities. There was a difference between the measurements taken by different instruments, both in central thickness and in opacity depth in cases of mild and dense opacity, and no difference in moderate opacity.

Lens: Management of Cataract Surgery, Cataract Prevention, and Floppy Iris Syndrome.

According to the World Health Organization, cataract is the major cause of reversible visual impairment in the world. It is present as the cause of decreased visual acuity in 33% of the visual impaired citizens. With the increase of life expectancy in the last decades, the number of patients with cataract is expected to grow for the next 20 years. Nowadays, the only effective treatment for cataracts is surgery and its surgical outcomes have been increasingly satisfactory with the technological advancement.Pharmaceutical development has been also responsible for surgical outcomes enhancement. This includes the development of new ophthalmic viscoelastic devices (OVDs), intraocular dyes, mydriatics, miotics, anesthetics, irrigating solutions, and antibiotics. However, the increased costs and demand for cataract surgery may be hard to meet in the future unless clinical preventive and curative options are evaluated.In this chapter, we review the studies that addressed pharmacological applications in cataract.

Spectral-Domain OCT Lens Meridian Position as a Metric to Estimate Postoperative Anatomical Lens Position.

PURPOSE: To evaluate the prediction of postoperative anatomical lens position (ALP) using intraoperative spectral-domain optical coherence tomography (SD-OCT) lens anatomy metrics in patients who underwent femtosecond laser-assisted cataract surgery. METHODS: Intraoperative SD-OCT (Catalys; Johnson & Johnson Vision) and postoperative optical biometry (IOLMaster 700; Carl Zeiss Meditec AG) were used to assess anterior segment landmarks, including lens thickness, lens volume, anterior chamber depth, lens meridian position (LMP), and measured ALP. LMP was defined as the distance from the corneal epithelium to the lens equator, and ALP was defined as the distance from the corneal epithelium to the IOL surface. Eyes were divided into groups according to axial length (> 22.5 mm, 22.5 to 24.5 mm, and > 24.5 mm) and IOL type (Tecnis ZCB00 [Johnson & Johnson Vision]; AcrySof SN-60WF [Alcon Laboratories, Inc], or enVista MX60E [Bausch & Lomb]) to further analyze the correlation between LMP and ALP. Theoretical effective lens position was back-calculated using a specific formula. Primary outcome was correlation between postoperative measured ALP and LMP. RESULTS: A total of 97 eyes were included in this study. Linear regression analysis displayed a statistically significant correlation between intraoperative LMP and postoperative ALP (R2 = 0.522; P < .01). No statistically significant correlation was observed between LMP and lens thickness (R2 = 0.039; P = .06) or between ALP and lens thickness (R2 = 0.02; P = .992). The greatest predictor for ALP was LMP (ß = 0.766, P < .001; R2 = 0.523). CONCLUSIONS: Intraoperative SD-OCT-measured LMP correlated better than anterior chamber depth and axial length to postoperative ALP. Further studies are necessary to analyze the impact of preoperative or intraoperative LMP measurements on postoperative refractive outcomes. [J Refract Surg. 2023;39(3):165-170.].

Refractive Accuracy of Barrett True-K vs Intraoperative Aberrometry for IOL Power Calculation in Post-Corneal Refractive Surgery Eyes.

PURPOSE: To compare the refractive predictability of intraoperative aberrometry (IA, ORA, Alcon) and Barrett True-K/Universal II formulas for intraocular lens (IOL) power calculations in post-corneal refractive surgery and normal eyes. METHODS: Retrospective study of normal and post-corneal refractive surgery eyes that underwent cataract surgery with IA at tertiary academic center. Preoperatively, IOL power calculations were performed using Barrett Universal II (normal eyes) or Barrett True-K (post-corneal refractive surgery eyes) formulas. Intraoperatively, aphakic IA measurements were used for IOL power calculations. Mean absolute refractive prediction error (MAE) and the percentage of eyes with prediction error within ±0.50, ±0.75 and ±1.00 D were calculated. Refractive predictability was also evaluated in short, normal, and long eyes. RESULTS: Two hundred and seventy-three eyes were included in the analysis. No statistically significant differences were observed between the MAE of preoperative formulas and IA for post-hyperopic laser vision correction (LVC), post-myopic LVC, post-radial keratotomy (RK) and normal eyes. For prediction error within ±0.5 D in post-corneal refractive surgery eyes, range of agreement between Barrett True-K and IA ranged from 28% (7/25) of the time in post-RK eyes to 49% (40/81) of the time in post-hyperopic LVC; the corresponding value for Barrett Universal II/IA was 62% (64/103) in normal eyes. When there was disagreement, IA outperformed Barrett True-K in post-hyperopic LVC eyes and Barrett formula outperformed IA in post-myopic LVC, post-RK, and normal eyes. CONCLUSION: IA appears to be comparable to Barrett formulas for IOL power calculations in post-corneal refractive surgery and normal eyes. In post-hyperopic LVC, IA yields better results compared to Barrett True-K formula; in real-life scenarios, IA reveals statistical advantage over the Barrett True-K no history formula for eyes post-hyperopic LVC.

Corneal suture for acute corneal hydrops secondary to post-LASIK ectasia: a case report.

Corneal ectasia is one of the main complications of keratorefractive procedures. In this report, we describe a case of corneal ectasia after laser-assisted in situ keratomileusis), which progressed with acute hydrops and aqueous leakage and required a suture for correction.

Use of virtual reality equipment to assess the manual dexterity of applicants for ophthalmology residency.

PURPOSE: To assess the microsurgery dexterity outcomes of two sequential training evaluations using virtual reality technology. METHODS: This was a multicenter cross-sectional study of all candidates who were accepted as first-year residents at one of six ophthalmology teaching institutions. Residents were subjected to two identical series of standardized, reproducible dexterity tests using virtual reality equipment (Eyesi®): "sequence 1" and "sequence 2." Each sequence consisted of five difficulty levels that were assessed using a proprietary scoring system. The data were tested for normality using the Shapiro-Wilk test. The differences between tests in sequences 1 and 2 were evaluated using the Wilcoxon signed-rank test. RESULTS: The data did not follow a normal distribution. There were improvements from sequence 1 in all the tests (all p values<0.05). The sum of all scores (total score) improved from sequence 1 (median= 152.50) to sequence 2 (median 256.00; p<0.001). There was no correlation between the delta sequence values and the average scores. CONCLUSION: Two sequential training evaluations using virtual reality technology showed relevant improvement in quantifications of microsurgery dexterity. This information should be considered if virtual reality approaches are used for testing purposes, as previous experience may lead to improved test results.

Nasal Polyposis: More than a Chronic Inflammatory Disorder-A Disease of Mechanical Dysfunction-The São Paulo Position.

Introduction The importance of our study lies in the fact that we have demonstrated the occurrence of mechanical dysfunction within polypoid tissues, which promotes the development of polyps in the nasal cavity. Objective To change the paradigm of nasal polyposis (NP). In this new conception, the chronic nasal inflammatory process that occurs in response to allergies, to pollution, to changes in the epithelial barrier, or to other factors is merely the trigger of the development of the disease in individuals with a genetic predisposition to an abnormal tissue remodeling process, which leads to a derangement of the mechanical properties of the nasal mucosa and, consequently, allows it to grow unchecked. Data Synthesis We propose a fundamentally new approach to intervening in the pathological process of NP, addressing biomechanical properties, fluid dynamics, and the concept of surface tension. Conclusion The incorporation of biomechanical knowledge into our understanding of NP provides a new perspective to help elucidate the physiology and the pathology of nasal polyps, and new avenues for the treatment and cure of NP.

Immunofluorescence confocal microscopy of porcine corneas following collagen cross-linking treatment with riboflavin and ultraviolet A.

PURPOSE: To assess ultrastructural stromal modifications in porcine corneas after riboflavin and ultraviolet A (UVA) exposure using immunofluorescence confocal imaging. METHODS: Twenty-five freshly enucleated porcine eyes were enrolled in the study. Five eyes served as control (group I). Twenty eyes had their epithelium removed (groups I, II, IV, and V) and five eyes had their epithelium intact (group III). Groups II and III were cross-linked with riboflavin 0.1% solution (10 mg riboflavin-5-phosphate in 10 mL 20% dextran-T-500) and exposed to UVA (365 nm, 3 mW/cm2) for 30 minutes. Group IV included five eyes soaked with riboflavin without posterior irradiation, and group V included five eyes irradiated, without previous exposure to riboflavin. Ultra-thin sections (8 microm) of the corneas were stained with anti-collagen I and DAPI and their fluorescence was revealed under confocal microscopy. RESULTS: Only the cross-linked corneas (group II) showed a pronounced, highly organized anterior fluorescence zone of 182.5 +/- 22.5 microm. Using DAPI staining, an anterior and concentrated displacement of cell nuclei due to collagen compaction was observed after crosslinking (group II). No structural changes were observed in all other groups. CONCLUSIONS: The cross-linking treatment effect can be directly visualized using confocal fluorescence imaging, allowing for a quantitative analysis. Cross-linked corneas showed a pronounced and limited anterior zone of organized collagen fibers, which was not observed in the other groups. Treatment of the cornea with riboflavin and UVA without previous deepithelialization did not induce any cross-linking effect. Consequently, to facilitate diffusion of riboflavin throughout the corneal stroma, the epithelium should be removed as an important initial step in the treatment.

Spherical aberration and depth of focus in eyes implanted with aspheric and spherical intraocular lenses: a prospective randomized study.

PURPOSE: To compare distance-corrected, near, and intermediate visual acuities as a measurement of depth of focus and spherical aberration of eyes implanted with aspheric and spherical intraocular lenses (IOLs). DESIGN: Randomized prospective study. PARTICIPANTS: One hundred twenty eyes of 60 patients with bilateral cataract implanted with 3 IOL models (AcrySof IQ, AcrySof SN60AT [Alcon Laboratories, Fort Worth, TX], and Sensar AR40 [Allergan Surgical, Irvine, CA]). METHODS: Pupil diameter was analyzed by using a Colvard pupillometer (OASIS Medical, Inc., Glendora, CA) under photopic, mesopic, and scotopic conditions. Distance (6 m), intermediate (1 m), and near (0.33 m) visual acuities were measured with distance correction in place 90 days after surgery. Wavefront analysis (LadarWave; Alcon Laboratories) was performed using 5-mm and measured photopic pupil diameter at 30 and 90 days after surgery. MAIN OUTCOME MEASURES: To evaluate spherical aberration and depth of focus (by means of distance-corrected near and intermediate visual acuity) in patients implanted with aspheric and spherical IOLs. RESULTS: Photopic pupil sizes in each group were similar at 30 days after surgery. At 90 days after surgery, mean logarithm of the minimum angle of resolution distance-corrected near visual acuity (+/-standard deviation [SD]) was 0.50+/-0.20 in the AcrySof IQ group, 0.38+/-0.17 in the AcrySof SN60AT group, and 0.45+/-0.16 in Sensar AR40 group. Mean spherical aberration values (+/-SD) were 0.03+/-0.05 microm in the AcrySof IQ group, 0.24+/-0.04 microm in the AcrySof SN60AT group, and 0.14+/-0.07 microm in the Sensar AR40 group. The AcrySof IQ group showed a statistically significant lower induction of spherical aberration and worse distance-corrected near visual acuity. The AcrySof SN60AT group showed statistically significant higher mean spherical aberration values and better distance-corrected near and intermediate visual acuity. CONCLUSIONS: The reduction of total spherical aberration after aspheric IOL implantation may degrade distance-corrected near and intermediate visual acuity.

[Phakic intraocular lens for presbyopia correction]. / Avaliação de lente intra-ocular fácica para a correção da presbiopia.

PURPOSE: To evaluate clinical and refractive results of anterior chamber multifocal phakic intraocular lens Newlife for presbyopia correction considering uncorrected far and near visual acuity and refraction data and also to evaluate safety of this intraocular lens considering distance and near corrected visual acuity, endothelial cell count and complications. METHODS: Retrospective analysis of a clinical database of 30 patients (51 eyes) who had received a foldable anterior chamber multifocal intraocular lens for presbyopia correction. Data were collected before surgery and at 1, 3, 6, 12 months after the procedure. Statistical variance analysis and multiple comparisons were used to verify possible associations. All complications were described. RESULTS: After surgery the mean spherical equivalent was -0.046 D (+/-0.48) and 87.5% of the eyes could read Parinaud 3 or better (equivalent to J2 or better) without the need of near glasses. Endothelial cell loss was 7.57%. The intraocular lens was explanted in 6 (11.5%) eyes for different reasons. Cataracts were the major cause of lens removal. CONCLUSION: Improvement of mean uncorrected visual acuity and refraction data after multifocal phakic intraocular lens Newlife implantation for presbyopia correction was observed. Established safety criteria (distance and near corrected visual acuity, endothelial cell count and complications) did not confirm the safety of the procedure in the follow-up period.

Complete depigmentation of a small aperture corneal inlay implanted for compensation of presbyopia.

We describe a case of late-onset remarkable depigmentation of a small aperture corneal inlay implanted for presbyopia compensation. The patient was a participant in a clinical trial designed to evaluate the safety and efficacy of the AcuFocusTM ACU-10R160, which is a 10 µm-thick polyimide film tinted with an organic dye. Inlay implantation occurred under mechanical microkeratome Lasik flaps set for a depth of 120 µm. The patient returned to the clinic 11 years after surgery and reported loss of near-vision acuity. Clinical examination showed the complete absence of pigments in the device and the total loss of the initial effect on near vision, despite normal distance vision. Manifest refraction remained stable during the follow-up period. Scheimpflug images characterized the loss of the small aperture effect on incoming light. Confocal analysis revealed small hyper-reflective round images on the endothelium and no signs of inflammation.

A new wavefront sensor with polar symmetry: quantitative comparisons with a Shack-Hartmann wavefront sensor.

PURPOSE: A novel wavefront sensor has been developed. It follows the same principle of the Shack-Hartmann wavefront sensor in that it is based on slope information. However, it has a different symmetry, which may offer benefits in terms of application. METHODS: The new wavefront sensor consists of a set of donut-shaped acrylic lenses with a charge coupled device located at the focal plane. From detection of shift in the radial direction, radial slopes are computed for 2880 points. Theoretical computations for higher order aberrations and lower order aberrations were implemented for the Shack-Hartmann wavefront sensor and the new wavefront sensor, and practical measurements were conducted on several sphere-cylinder trial lenses. RESULTS: The overall mean value of root mean square error (RMSE) (in microns) for theoretical computations was 0.03 for the Shack-Hartmann wavefront sensor and 0.02 for the new wavefront sensor. The mean value of RMSE for lower order aberrations (1-5) was 0.01 and 0.00003, and for higher order aberrations was 0.02 and 0.02, for the Shack-Hartmann and new wavefront sensors, respectively. For practical measurements (sphere, cylinder, axis), the standard deviation was 0.04 diopters (D), 0.04 D, and 4 degrees for the new wavefront sensor and 0.02 D, 0.02 D, and 5 degrees for the Shack-Hartmann wavefront sensor. CONCLUSIONS: Precision of the new wavefront sensor when measuring astigmatic and spherical surfaces is compatible with the Shack-Hartmann wavefront sensor. Centration with this new sensor is an absolute process using the center of the entrance pupil, which is where the line of site passes. This wavefront sensor, similar to the Shack-Hartmann sensor, does not eliminate the possibility of tilt. For more conclusive and statistically valid data, in vivo measurements are needed.

[Evaluation of performance, efficacy and safety of semi-automated lamellar keratoplasty]. / Avaliação da exeqüibilidade, eficácia e segurança do transplante lamelar semi-automatizado de córnea.

PURPOSE: To evaluate the feasibility, efficacy and safety of a manual microkeratome and an artificial anterior chamber for lamellar keratoplasty (ALTK system). METHODS: Twenty-one eyes with superficial corneal opacities were submitted to semi-automated lamellar keratectomy. In recipient eyes keratectomy was performed as in refractive surgery. The donor flap was removed from the preserved corneal shell using the same microkeratome and an artificial anterior chamber. Lamella thickness was measured through ultrasound biomicroscopy (UBM) after surgery. RESULTS: The surgeries were accomplished successfully in 19 eyes. 80% of the flaps obtained in donated corneas and 84.2% of the flaps in recipient eyes had an up to 0.5 mm variation variation of the desired diameter. A high similarity in flap thickness between the donor flap and the recipient cornea was obtained. Postoperative visual acuity of 20/40 or better was observed in 52.6% of the eyes. Complications such as undesired diameter of the flap, a case of perforation in the recipient eye and a case of cornea ectasia were observed. CONCLUSION: The semi-automated lamellar keratoplasty ALTK system showed to be feasible due to the predictability and reproducibility regarding lamella thickness and diameter, efficient in the improvement of postoperative visual acuity and safe due to the low level surgical complication.

Quantitative comparison of different-shaped wavefront sensors and preliminary results for defocus aberrations on a mechanical eye.

PURPOSE: There is a general acceptance among the scientific community of Cartesian symmetry wavefront sensors (such as the Hartmann-Shack (HS) sensor) as a standard in the field of optics and vision science. In this study it is shown that sensors of different symmetries and/or configurations should also be tested and analyzed in order to quantify and compare their effectiveness when applied to visual optics. Three types of wave-aberration sensors were developed and tested here. Each sensor has a very different configuration and/or symmetry (dodecagonal (DOD), cylindrical (CYL) and conventional Hartmann-Shack (HS)). METHODS: All sensors were designed and developed in the Physics Department of the Universidade de São Paulo--São Carlos. Each sensor was mounted on a laboratory optical bench used in a previous study. A commercial mechanical eye was used as control. This mechanical eye has a rotating mechanism that allows the retinal plane to be positioned at different axial distances. Ten different defocus aberrations were generated: 5 cases of myopia from -1D to -5D and 5 cases of hyperopia, from +1D to +5D, in steps of 1D following the scale printed on the mechanical eye. For each wavefront sensor a specific image-processing and fitting algorithm was implemented. For all three cases, the wavefront information was fit using the first 36 VSIA standard Zernike polynomials. Results for the mechanical eye were also compared to the absolute Zernike surface generated from coefficients associated with the theoretical sphere-cylinder aberration value. RESULTS: Precision was analyzed using two different methods: first, a theoretical approach was used by generating synthetic Zernike coefficients from the known sphere-cylinder aberrations, simply by applying sphere-cylinder equations in the backward direction. Then comparisons were made of these coefficients with the ones obtained in practice. Results for DOD, HS and CYL sensors were, respectively, as follows: mean of root mean square (RMSE) for all aberrations, when theoretical Zernike coefficients were used as control, was 0.22, 0.66 and 0.26 microns; RMSE of sphere-cylinder values when compared to autorefractor measurements was 0.18D, 0.22D and 0.35D for sphere, 0.14D, 0.24D and 0.17D for cylinder, 34.36 degrees, 35.16 degrees and 26.36 degrees for axis; RMSE of sphere-cylinder values when theoretical values were used as control was 0.11D, 0.29D and 0.46D for sphere, 0.15D, 0.28D and 0.17D for cylinder, 19.71 degrees, 25.56 degrees and 18.56 degrees for axis. CONCLUSION: The main conclusion is that the symmetry of an optical sensor is not an important consideration when measuring typical eye aberrations such as defocus (myopic and hyperopic), but there are differences. In this sense, the polar symmetry sensors render results that are equivalent to the traditional Cartesian Hartmann-Shack sensor, but furnish an easier method for determining the optical center.

Cyclotorsional and non-cyclotorsional components of eye rotation observed from sitting to supine position.

PURPOSE: Evaluate average cyclotorsional and non-cyclotorsional components (NCY) of eye rotation from sitting to supine, and associate average cyclotorsion to different variables. METHODS: Medical records of patients who underwent bilateral sequential laser refractive surgery were retrospectively evaluated. Recorded variables included the patient's age, refraction, automated keratometry, pupil displacement and eye rotation from sitting to supine position. Measured iris rotation (total rotation, TR) was decomposed into two components: NCY, defined as the common rotation component of each eye of the same patient, and cyclotorsional component (CY), defined as the assumed independent eye rotation for each eye in relation to the face, so that TR=NCY+CY. Cyclotorsion ratio (CR) was calculated as CR=|CY|/|TR|, and used to correlate CY with TR for each eye. RESULTS: Data from 310 eyes of 155 patients were evaluated. TR was +1.43° ±3.41° (-8.30° to +9.20°). Average CYs and NCYs per patient were +1.43°±2.04° (-3.15± to +7.40°) and -0.28°±2.72° (-6.85° to +7.15°), respectively. TR demonstrated that 40.6% and 8.4% of patients presented bilateral excyclotorsion and incyclotorsion, respectively. When excluding NCYs, average CYs demonstrated that 74.2% of patients presented excyclotorsion and 23.9% presented incyclotorsion. CR demonstrated that TR represented from 75% to 125% of average CY in 19.68% of the eyes. TR overestimated and underestimated average CYs above these limits in 52.26% and 28.06% of the eyes, respectively. There was no statistical association between average CYs and the different variables. DISCUSSION: This study demonstrates that most of the rotations previously attributed to torsional components were probably due to NCYs, such as postural misalignments. Apparently, the amplitude of cyclotorsional movements is smaller than observed in previous reports, and could not be associated with any studied variable.

Ultrasound biomicroscopy and Scheimpflug photography of angle-supported phakic intraocular lens for high myopia.

PURPOSE: To evaluate the equivalence of Scheimpflug photography (SP) and ultrasound biomicroscopy (UBM) in determining corneal epithelium-intraocular lens (IOL) and border IOL-iris distances. SETTING: Universität Erlangen-Nuremberg, Erlangen, Germany. METHODS: In 26 eyes of 17 patients who had a NuVita MA20 angle-supported anterior chamber intraocular lens (Chiron-Domilens), SP and UBM were used to evaluate the distance between the endothelium and the anterior IOL face in central and peripheral regions (12 o'clock and 6 o'clock positions) and between the border of the anterior IOL face and the iris. The Wilcoxon test was used for statistical analysis. RESULTS: The mean central endothelium-anterior IOL face distance was 2.01 mm and 2.00 mm by SP and UBM, respectively. The mean peripheral endothelium-anterior IOL border distance was 1.28 mm and 1.58 mm, respectively, and the mean peripheral anterior IOL face-iris distance, 0.89 mm and 0.75 mm, respectively. CONCLUSIONS: The difference between the 2 methods in the central endothelium-anterior IOL face distance was not significant (methods were equivalent), but the difference in the peripheral endothelium-anterior IOL face distance was. This may be the result of difficulty in obtaining the exact transition point between the IOL and the haptics by SP examination. The difference between the 2 methods in the IOL border-iris distance was also significant because of the irregularity of the iris surface; therefore, measurements were performed at different sites along this structure. The significant differences in the peripheral endothelium-IOL and IOL border-iris distances indicate that although both methods are useful, they are not equivalent.

Videokeratoscopes for dioptric power measurement during surgery.

PURPOSE: To evaluate 2 versions of a computerized surgical videokeratoscope that measures a central region of the cornea of approximately 4.0 to 6.0 mm in diameter to provide information on dioptric power and astigmatism. SETTING: Grupo de Optica Oftalmica Universidade de São Paulo, and Departamento de Oftalmologia da Escola Paulista de Medicina, São Paulo, Brazil. METHODS: The first videokeratoscope system with 10 Placido rings is based on a 15 000 fiber-optic illuminated disk attached to the objective lens of a surgical microscope. With this system, the light intensity can be adjusted during surgery for better contrast of the Placido image. The second system with 14 Placido rings is based on a neon light source behind the Placido disk. With both systems, a 480 x 640 pixel resolution charge-coupled device camera and an IBM-compatible personal computer frame grabber were used. Image processing was used for boundary detection of the rings. An axial curvature algorithm based on the spherical surfaces was used to calculate the dioptric power for each examination. Measurements of 4 real spherical surfaces and 4 simulated aspheric surfaces (ellipsotoric surfaces with different apical radii and different shape factors) were performed. RESULTS: Twenty corneas of 10 healthy volunteers were measured on both videokeratoscope systems and an EyeSys System 2000 corneal topographer. The root- mean-square error for the spherical and simulated aspheric surfaces was, respectively, less than 0.20 diopter (D) and 1.30 D for the 10-disk videokeratoscope system and less than 0.16 D and 1.40 D for the 14-disk system. The mean deviation in corneal measurements with both systems was 0.09 mm for the radius of curvature, 0.51 D for dioptric power, and 5 degrees for cylinder. CONCLUSIONS: The results indicate that the 2 surgical videokeratoscopes are sufficiently precise to aid the anterior segment surgeon in reducing residual astigmatism in cataract surgery and keratoplasty.

Nasal polyposis: more than a chronic inflammatory disorder-a disease of mechanical dysfunction - the São paulo position

Introduction: The importance of our study lies in the fact that we have demonstrated the occurrence ofmechanical dysfunction within polypoid tissues, which promotes the development of polyps in the nasal cavity. Objective: To change the paradigm of nasal polyposis (NP). In this new conception, the chronic nasal inflammatory process that occurs in response to allergies, to pollution, to changes in the epithelial barrier, or to other factors is merely the trigger of the development of the disease in individuals with a genetic predisposition to an abnormal tissue remodeling process, which leads to a derangement of the mechanical properties of the nasal mucosa and, consequently, allows it to grow unchecked. Data: Synthesis We propose a fundamentally new approach to intervening in the pathological process of NP, addressing biomechanical properties, fluid dynamics, and the concept of surface tension. Conclusion: The incorporation of biomechanical knowledge into our understanding of NP provides a new perspective to help elucidate the physiology and the pathology of nasal polyps, and new avenues for the treatment and cure of NP (AU)