Estudo comparativo entre as medidas da pressão ocular dos tonômetros de rebote, pneumático e de Goldmann / Comparative study between ocular pressure measurements made by rebot tonometer, pneumatic tonometer, Goldmann tonometry

RESUMO Objetivo: Comparar o resultado entre dois tipos de tonômetros, tendo como padrão ouro a tonometria de aplanação, relacionando com a espessura corneana e suas validações como instrumentos de rastreio populacional. Métodos: Estudo transversal comparativo, realizado com 400 olhos do ambulatório de oftalmologia da Adachi Oftalmologia, em Macapá (Amapá), entre os valores médios da pressão ocular medidos pelo tonômetro Icare®, o Tonômetro Pneumático e o Tonômetro de Aplanação de Goldmann em função da espessura corneana. Foram divididos conforme a ECC em 3 grupos. Grupo 1: 260 olhos com ECC< 530µ; grupo 2: 217 olhos com ECC entre 530µ e 590µ; e, grupo 3: 157 olhos com ECC>590µ. Resultados: A ECC média obtida na paquimetria foi de 557µ, variando de 651µ a 477µ (desvio padrão de 32.9). A PIO média obtida pela TP foi de 19,4 mmHg (com desvio padrão de 2,32); pelo Icare® foi de 16,7mmHg (desvio padrão de 2,12); e, na TAG foi de 15.5 mmHg (desvio padrão de 2,02). Para paquimetrias inferiores a 530µ e superiores a 590µ a PIOm não diferiu significativamente entre a TAG e Icare® (p = 0,232), sendo estatisticamente significativa diferença obtida para córneas com ECC entre 530 e 590 µ. A PIOm obtida pelo TP foi significativamente maior do que a pressão ocular média dos TAG e Icare® (p < 0,001 para ambos) em todos os grupos. Conclusões: Os três métodos podem ser utilizados em campanhas de rastreamento, porém o Icare® se mostrou mais confiável que a TP, com valores obtidos estatisticamente mais confiáveis quando comparados à TP. Existe suficiente concordância entre o Icare e a TAG para recomendar o seu uso.

ABSTRACT Objective: To compare the result between two types of tonometres, using as gold standard the aplanation tonometry, relating to the corneal thickness and its validations as instruments of population screening. Methods: A comparative cross-sectional study was carried out with 400 eyes from the ophthalmology clinic of Adachi Ophthalmology, in Macapá (Amapá), between the mean values of ocular pressure measured by the Icare® tonometro, the Pneumatic Tonometer and the Goldmann Flattening Tonometro as a function of corneal thickness. They were divided according to ECC in 3 groups. Group 1: 260 eyes with ECC <530µ; group 2: 217 eyes with ECC between 530µ and 590µ; and, group 3: 157 eyes with ECC> 590µ. Results: The mean ECC obtained in pachymetry was 557µ, ranging from 651µ to 477µ (standard deviation of 32.9). The mean IOP obtained by PT was 19.4 mmHg (with a standard deviation of 2.32); by Icare® was 16.7mmHg (standard deviation of 2.12); and in the TAG it was 15.5 mmHg (standard deviation of 2.02). For pachymetry less than 530µ and greater than 590µ, PIOm did not differ significantly between TAG and Icare® (p = 0.232), and a statistically significant difference was obtained for corneas with ECC between 530 and 590 µ. The IOP obtained by the PT was significantly higher than the mean ocular pressure of the TAG and Icare® (p <0.001 for both) in all groups. Conclusions: All three methods can be used in screening campaigns, but Icare® proved to be more reliable than TP, with values obtained statistically more reliable when compared to TP. There is sufficient agreement between Icare and TAG to recommend its use.

Comparison of Ultrasound and Scheimpflug Methods for Central Corneal Thickness.

Aim: The central corneal thickness (CCT) of healthy individuals was measured with an ultrasonic pachymeter (UP) and the Scheimpflug imaging system (SIS) and the results were compared to evaluate the agreement between the two methods in this study. Materials and Methods: The 61 subjects who had no ocular pathology or systemic disease except blepharitis were included in the study. CCT measurements of all subjects were performed with the UP (Sonomed 300P Pacscan) and SIS (Nidek Optical biometer AL-Scan) devices and the results were compared. The t test and the Bland-Altman plot were used as the statistical methods. Results: The study sample consisted of 61 cases including 20 males and 41 females. The mean age was 41.8±12.4 (20-58) years for the males and 46.2±9 (24-60) years for the females with no statistically significant difference (P=0.116). The mean CCT measurement of all the 61 subjects was 544.5±31 μm in the right eyes and 547.3±33 μm in the left eyes with UP, 530.7±27.6 μm in the right eyes and 531.6±25.5 μm in the left eyes with SIS. The CCT in the SIS results was an average of 13.8 μm thinner than the UP results in the right eye, 15.7 μm in the left eye and this difference was statistically significant (p=0.001 in right and left eyes). A high degree of agreement was found between the two methods with the Bland-Altman plot. Conclusion: A high degree of agreement was found between SIS and UP regarding CCT measurements and the mean SIS results were 13.8 μm and 15.7 μm thinner than the UP results in the right eyes and left eyes respectively.

Confocal Microscopic Findings of Avellino Corneal Dystrophy According to Disease Severity

PURPOSE: In this study we analyzed and objectified the characteristics of the Avellino corneal dystrophy patients considering disease severity using in vivo confocal microscopy (IVCM). METHODS: Each corneal layer of 36 eyes in 18 patients with Avellino corneal dystrophy was examined using IVCM (ConfoScan 4.0, NIDEK, Co. Ltd., Albignasego, Italy). Patients were classified into 3 groups based on disease severity (mild, moderate, or severe). RESULTS: In the mild group, hyper-reflective granular deposits without dark shadows were observed in the anterior stroma. As the disease progressed, corneal deposits were also found at the posterior stroma and epithelium, and clusters of hyper-reflective corneal deposits resembling stromal opacity were noted. The range of corneal deposits measured using Z-scan optical pachymeter was 111.14 +/- 30.95 um in the mild group, 157.47 +/- 25.00 um in the moderate group, and 193.42 +/- 52.23 um in the severe group (p < 0.05). CONCLUSIONS: The origin of the corneal deposits in Avellino corneal dystrophy may be related to corneal stromal cells and distributed from the corneal epithelial layer to the stromal layer. IVCM might be useful for the standardization of disease severity by digitalizing the range of deposits.

Comparison of Corneal Thickness Measurements with Optical Low Coherence Reflectometry, Orbscan System and Ultrasound Pachymeter

PURPOSE: To investigate the accuracy and reproducibility of Optical Low Coherence Reflectometry (OLCR) corneal thickness measurements compared with the Orbscan system and ultrasound pachymeter (IOPac, Mentor). METHODS: Two examiners measured corneal thicknesses of 78 normal eyes and in 36 eyes that had undergone LASIK, and five sequential measurements of corneal thickness with OLCR, Orbscan system, Mentor, and IOPac were performed. Remeasurements of corneal thickness in 24 normal eyes were performed after two days to investigate intra-examiner reproducibility. RESULTS: The average corneal thickness measured in normal subjects was 536.3+/-23.8 micrometer in OLCR, 542.4+/-25.3 micrometer in the Orbscan system, 535.4+/-23.7 micrometer in Mentor, and 534.2+/-24.1 micrometer in IOPac. The average corneal thickness measured in patients who had undergone LASIK was 487.3+/-30.8 micrometer in OLCR, 492.5+/-36.5 micrometer in the Orbscan system, 487.5+/-30.8 micrometer in Mentor, and 485.3+/-30.8 micrometer in IOPac. There was no statistically significant difference between the four pachymeters. The inter-examiner and intra-examiner reproducibilities were shown to be highly reliable. CONCLUSIONS: The OLCR showed similar measurments of corneal thickness with the Orbscan system and ultrasound pachymeter, and showed no difference in reproducibility with different examiners.

Accuracy of Corneal Thickness Measurement with Ultrasound Pachymeter in Thin Corneas

PURPOSE: Accurate assessment of corneal thickness is important in order to prevent iatrogenic corneal ectasia after laser in situ keratomileusis (LASIK). More accurate measurement is needed in LASIK enhancement because the cornea becomes thin after previous refractive surgery. We evaluated the reliability of corneal thickness measurement with ultrasound pachymeter (USP) in the thin corneas. METHODS: The corneal thickness was measured in the 22 eyes of 11 rabbits. The corneal flap was made with an Automated Corneal Shaper microkeratome (Bausch and Lomb, USA) with 130 micro meter plate and the flap was removed in order to make the cornea thin. Residual stromal bed (RSB) thickness was measured with USP and thickness gauge, and the two measurements were compared. RESULTS: Mean corneal thickness was 404.69 +/- 11.01 micro meter with USP and 133.23 +/- 15.66 micro meter with thickness gauge. RSB thickness measured with thickness gauge was 269.05 +/- 24.19 micro meter and this was not significantly different from the expected RSB thickness, although RSB thickness measured with USP was 388.14 +/- 10.17 micro meter, which was significantly different from the expected RSB thickness (p=0.00). CONCLUSIONS: In the thin corneas, corneal thickness measurement with ultrasound pachymeter is not reliable.

Orbscan System for Measurement of Corneal Thickness

PURPOSE: To investigate the accuracy of Orbscan system in measuring corneal thickness before refractive surgery, the authors conducted a comparative study of Orbscan system and ultrasonic pachymeter in their agreement and repeatability. METHODS: 84 patients (168 eyes) who were examined between December, 2000 and March, 2001 were divided into two groups: those who exceeded -6.00 D, and those who did not. Orbscan and ultrasonic pachymeter were employed. Correlation and regression were analyzed to assess their agreement. The repeatability was measured by analyzing mean, standard deviation, and 95% confidence interval of each method. RESULTS: The average central corneal thickness was 542.3+/-34.2micro meter by Orbscan system, and 528.6+/-29.7micro meter by ultrasonic pachymeter. Correlation coefficient was nearly 1 between them, and therefore we obtained statistically significant linear regression equation. In the analysis of repeatability, 95% confidence interval of Orbscan system was -17.2micro meter~+11.8micro meter which was superior to the interval of ultrasonic pachymeter (-23.2micro meter~+14.4micro meter). CONCLUSION: Orbscan system measurements of corneal thickness was greater than ultrasonic pachymeter measurements by 9 to 19 m. Because Orbscan system also showed superiority in repeatability, it may be a useful method in the clinical field.

Central Corneal Thickness Measured by Ultrasonic Pachymeter in Normal Koreans

Corneal thickness is not only a major indicator of corneal diseases but an important parameter for the safety and the prevention of complications in various refractive surgeries widely performed nowadays.Therefore, we tried to acquire the basic data of corneal thickness in normal Koreans through this study. Central corneal thickness was measured using ultrasonic pachymeter in 460 eyes of 238 normal Koreans and analyzed according to the difference in age, sex, left &right, refractive error, and mean keratometry.Mean CCT was 529.67+/-32.18 micrometer.There is no statistically significant difference in CCT according to the difference in age, sex, left and right, refractive error, and mean keratometry in normal Koreans.

Comparison of Corneal Thickness Measurements with the Orbscan and Ultrasonic Pachymetry

To verify the accuracy and reproducibility of corneal thickness measurements obtained with Orbscan (Orbtek, Inc., Salt Lake City, USA), the measurements were compared with those taken with an ultrasound pachymeter (Omega Compuscan, Storz). Central corneal thickness was measured by each method in 100 eyes of 50healthy subjects. The averages by the two methods were compared. One examiner took the measurements twice by each method in 20 eyes of 10 subjects, and intraexaminer reproducibility was evaluated. Two examiners measured the thickness in 20 eyes of 10 subjects and interexaminer reproducibility was assessed. The average corneal thickness was 550.27+/-3.56 micrometer in the Orbscan measurements and 526.62+/-3.70 micrometer in the ultrasound pachymetry: There was a statistically significant difference between the two methods. Significant difference was noticed but this showed a constant corresponding correlation with the Orbscan showing a 4.4%lower average. The intraexaminer and interexaminer reproducibility showed high reliability(Guttman split-half point<0.99). The Orbscan pachymetry is a highly reliable method and may be widely used in clinical practice.

The Evaluation of the Endothelial Cells after Cataract Extraction and IOL Insertion in Patients with Corneal Guttata

When the corneal endothelium is injured by intraocular surgery, corneal edema occurs above the threshold level. Preoperative examination of corneal endothelium is valuable in prediction the degree of transparency of the cornea. We conducted this study to elucidate what factors affect corneal endothelial cells in performing the cataract extraction and IOL insertion and what is necessary to minimize the corneal endothelial damage. We performed pacoemulsification and IOL insertion in guttata patients, and preoperative and postoperative endothelial examination was done by using specuar microscope and pachymeter. Although the mean of endothelial cell density was diminished from 1498.7cells/mm2 to 1301cells/mm2 after operation. visible edema was not detected by slit lamp examination and visual acuity was improved from 0.15 to 0.48. The older the patient`s age, the longer the time of phaceemulsification; as the ages of the patients are increased, postoperative corneal thicknesses were increased and postoperative endothelial cell densities were decreased. The endothelial cells were relatively well preserved after cataract operation in patients of preoperative diminished endothelial cells. We suggest that when performing the cataract operation in patients of decreased endothelial function, one must use appropriate large amount of viscoelastic substances, and minimize phacoemulsification power and time in as short operation time as possible by accurate surgical technique. We also believe that periodic postoperative endothelial examination is necessary in patients with decreased endothelial function.