Assessment of splanchnic perfusion with gastric tonometry in the immediate postoperative period of cardiac surgery in children

OBJECTIVE - A prospective, nonrandomized clinical study to assess splanchnic perfusion based on intramucosal pH in the postoperative period of cardiac surgery and to check the evolution of patients during hospitalization. METHODS - We studied 10 children, during the immediate postoperative period after elective cardiac surgery. Sequential intramucosal pH measurements were taken, without dobutamine (T0) and with 5mcg/kg/min (T1) and 10 (T2) mcg/kg/min. In the pediatric intensive care unit, intramucosal pH measurements were made on admission and 4, 8, 12, and 24 hours thereafter. RESULTS - The patients had an increase in intramucosal pH values with dobutamine 10mcg/kg/min [7.19± 0.09 (T0), 7.16±0.13(T1), and 7.32±0.16(T2)], (p=0.103). During the hospitalization period, the intramucosal pH values were the following: 7.20±0.13 (upon admission), 7.27±0.16 (after 4 hours), 7.26±0.07 (after 8 hours), 7.32±0.12 (after 12 hours), and 7.38±0.08 (after 24 hours), (p=0.045). No deaths occurred, and none of the patients developed multiple organ and systems dysfunction. CONCLUSION - An increase in and normalization of intramucosal pH was observed after dobutamine use. Measurement of intramucosal pH is a type of monitoring that is easy to perform and free of complications in children during the postoperative period of cardiac surgery.

Major impact of body position on arterial stiffness indices derived from radial applanation tonometry in pregnant and nonpregnant women.

OBJECTIVE: To evaluate the impact of body position on the arterial stiffness indices provided by radial applanation tonometry in pregnant and nonpregnant women. METHODS: Twenty-four young women (18-30 years) in the third trimester of a normal pregnancy and 20 healthy nonpregnant women of the same age were enrolled. In each, applanation tonometry was carried out in the sitting and supine position. The following stiffness indices were analyzed: systolic augmentation index (sAix), sAix adjusted for heart rate (sAix@75) and diastolic augmentation index (dAix), all expressed in % of central aortic pulse pressure. RESULTS: The sAix was apparently not influenced by body position, but the transition from seated to supine was associated with a substantial decrease in heart rate. When correcting for this confounder by calculating the sAix@75, systolic augmentation was substantially lower when individuals were supine (mean ± SD: nonpregnant 3.0 ± 14.4%, pregnant 8.8 ± 9.7%) than when they were sitting (nonpregnant 5.7 ± 13.0%, pregnant 11.1 ± 83%, P = 0.005 supine vs. seated in both study groups, P > 0.2 for pregnant vs. nonpregnant). The influence of body position on the dAix went in the opposite direction (supine: nonpregnant 9.7 ± 6.6%, pregnant 4.4 ± 3.5%; seated: nonpregnant 7.7 ± 5.8%, pregnant 3.3 ± 2.4%, P < 0.00001 supine vs. seated in both study groups, P = 0.001 for pregnant vs. nonpregnant). CONCLUSION: Body position has a major impact on the pattern of central aortic pressure augmentation by reflected waves in healthy young women examined either during third trimester pregnancy or in the nonpregnant state.

Major impact of body position on arterial stiffness indices derived from radial applanation tonometry in pregnant and non pregnant woman

Pendant la grossesse, la pression artérielle reste stable malgré une nette augmentation du volume d'éjection systolique et du débit cardiaque. Cette stabilité vient d'un côté d'une vasodilatation périphérique entraînant une diminution des résistances périphériques et d'un autre côté d'une moindre rigidité des principales artères notamment l'aorte. En conséquence, l'amplitude des ondes de pouls est atténuée, de même que leur vitesse de propagation dans le sens tant antérogade que rétrograde (ondes réfléchies). Les ondes réfléchies tendent ainsi à atteindre l'aorte ascendante plus tard durant la systole, voire durant la diastole, ce qui peut contribuer à diminuer la pression puisée. La prééclampsie perturbe massivement ce processus d'adaptation. Il s'agit d'une maladie hypertensive de la grossesse engendrant une importante morbidité et mortalité néonatale et maternelle. Il est à remarquer que la diminution de la rigidité artérielle n'est pas observée chez les patientes atteintes avec pour conséquence une forte augmentation de la pression systolique centrale (aortique) par les ondes réfléchies. Ce fait a été établi grâce à l'existence de la tonométrie d'aplanation, une méthode permettant l'évaluation non invasive de l'onde de pouls centrale. Dans cette méthode, un senseur de pression piézo-électrique permet de capter l'onde de pouls périphérique, le plus souvent sur l'artère radiale. Par la suite, un algorithme validé permet d'en déduire la forme de l'onde de pouls centrale et de visualiser à quel moment du cycle cardiaque s'y ajoutent les ondes réfléchies. Plusieurs études font état d'une forte augmentation de la pression systolique centrale par les ondes réfléchies chez les patientes atteintes de prééclampsie, suggérant l'utilisation de cette méthode pour le diagnostic et le monitoring voire pour le dépistage de ces patientes. Pour atteindre ce but, il est nécessaire d'établir des normes en rapport notamment avec l'âge gestationnel. Dans la littérature, les données pertinentes actuellement disponibles sont variables, voire contradictoires. Par exemple, les ondes réfléchies proéminentes dans la partie diastolique de l'onde de pouls centrale disparaissaient chez des patientes enceintes au 3eme trimestre comparées à des contrôles non enceintes dans une étude lausannoise, alors que deux autres études présentent l'observation contraire. Autre exemple, certains auteurs décrivent une diminution progressive de l'augmentation systolique jusqu'à l'accouchement alors que d'autres rapportent un nadir aux environs du 6ème mois, suivi d'un retour à des valeurs plus élevées en fin de grossesse. Les mesures effectuées dans toutes ces études différaient dans leur exécution, les patientes étant notamment dans des postions corporelles différentes (couchées, semi-couchées, assises, en décubitus latéral). Or nous savons que le status hémodynamique est très sensible aux changements de position, particulièrement durant la grossesse où l'utérus gravide est susceptible d'avoir des interactions mécaniques avec les veines et possiblement les artères abdominales. Ces différences méthodologiques pourraient donc expliquer, au moins en partie, l'hétérogénéité des résultats concernant l'onde de pouls chez la femme enceinte, ce qui à notre connaissance n'a jamais été exploré. Nous avons mesuré l'onde de pouls dans les positions assise et couchée chez des femmes enceintes, au 3eme trimestre d'une grossesse non compliquée, et nous avons effectué une comparaison avec des données similaire obtenues chez des femmes non enceintes en bonne santé habituelle. Les résultats montrent que la position du corps a un impact majeur sur la forme de l'onde de pouls centrale. Comparée à la position assise, la position couchée se caractérise par une moindre augmentation systolique et, par contraste, une augmentation diastolique plus marquée. De manière inattendue, cet effet s'observe aussi bien en présence qu'en l'absence de grossesse, suggérant que la cause première n'en réside pas dans les interactions mécaniques de l'utérus gravide avec les vaisseaux sanguins abdominaux. Nos observations pourraient par contre être expliquées par l'influence de la position du corps, via un phénomène hydrostatique simple, sur la pression transmurale des artères éloignées du coeur, tout particulièrement celles des membres inférieurs et de l'étage abdominal. En position verticale, ces vaisseaux augmenteraient leur rigidité pour résister à la distension de leur paroi, ce qui y accroîtrait la vitesse de propagation des ondes de pression. En l'état, cette explication reste hypothétique. Mais quoi qu'il en soit, nos résultats expliquent certaines discordances entre les études conduites à ce jour pour caractériser l'influence de la grossesse physiologique sur la forme de l'onde de pouls central. De plus, ils indiquent que la position du corps doit être prise en compte lors de toute investigation utilisant la tonométrie d'applanation pour déterminer la rigidité des artères chez les jeunes femmes enceintes ou non. Il sera aussi nécessaire d'en tenir compte pour établir des normes en vue d'une utilisation de la tonométrie d'aplanation pour dépister ou suivre les patientes atteintes de prééclampsie. Il serait enfin intéressant d'évaluer si l'effet de la position sur la forme de l'onde de pouls central existe également dans l'autre sexe et chez des personnes plus âgées.

Assessing the Glaucoma Quality of Life-15 (GCL-15) Questionnaire, Goldmann Tonometry and Moorfields Motion Displacement Test in Glaucoma Case Finding

Purpose: To compare the performance Glaucoma Quality of Life-15 (GQL-15) Questionnaire, intraocular pressure measurement (IOP Goldmann tonometry) and a measure of visual field loss using Moorfields Motion Displacement Test (MDT) in detecting glaucomatous eyes from a self referred population. Methods: The GQL-15 has been suggested to correlate with visual disability and psychophysical measures of visual function in glaucoma patients. The Moorfields MDT is a multi location perimetry test with 32 white line stimuli presented on a grey background on a standard laptop computer. Each stimulus is displaced between computer frames to give the illusion of "apparent motion". Participants (N=312, 90% older than 45 years; 20.5% family history of glaucoma) self referred to an advertised World Glaucoma Day (March 2009) Jules Gonin Eye Hospital, Lausanne Switzerland. Participants underwent a clinical exam (IOP, slit lamp, angle and disc examination by a general ophthalmologist), 90% completed a GQL-15 questionnaire and over 50% completed a MDT test in both eyes. Those who were classified as abnormal on one or more of the following (IOP >21 mmHg/ GQL-15 score >20/ MDT score >2/ clinical exam) underwent a follow up clinical examination by a glaucoma specialist including imaging and threshold perimetry. After the second examination subjects were classified as "healthy"(H), "glaucoma suspect" (GS) (ocular hypertension and/or suspicious disc, angle closure with SD) or "glaucomatous" (G). Results: One hundred and ten subjects completed all 4 initial examinations; of these 69 were referred to complete the 2nd examination and were classified as; 8 G, 24 GS, and 37 H. MDT detected 7/8 G, and 7/24 GS, with false referral rate of 3.8%. IOP detected 2/8 G and 8/24 GS, with false referral rate of 8.9%. GQL-15 detected 4/8 G, 16/24 GS with a false referral rate of 42%. Conclusions: In this sample of participants attending a self referral glaucoma detection event, the MDT performed significantly better than the GQL-15 and IOP in discriminating glaucomatous patients from healthy subjects. Further studies are required to assess the potential of the MDT as a glaucoma screening tool.

Comparison of rebound tonometry with Goldmann applanation tonometry and correlation with central corneal thickness

BACKGROUND/AIMS: Rebound tonometry (RT) is performed without anaesthesia with a hand held device. The primary aim was to compare RT with Goldmann applanation tonometry (GAT) and to correlate with central corneal thickness (CCT). The secondary aim was to prove tolerability and practicability of RT under "study conditions" and "routine practice conditions." METHODS: In group 1 (52 eyes/28 patients), all measurements were taken by the same physician, in the same room and order: non-contact optical pachymetry, RT, slit lamp inspection, GAT. Patients were questioned about discomfort or pain. In group 2 (49 eyes/27 patients), tonometry was performed by three other physicians during routine examinations. RESULTS: RT was well tolerated and safe. Intraocular pressure (IOP) ranged between 6 mm Hg and 48 mm Hg. No different trends were found between the groups. RT tended to give slightly higher readings: n = 101, mean difference 1.0 (SD 2.17) mm Hg; 84.1% of RT readings within plus or minus 3 mm Hg of GAT; 95% confidence interval in the Bland-Altman analysis -3.2 mm Hg to +5.2 mm Hg. Both RT and GAT showed a weak positive correlation with CCT (r2 0.028 and 0.025, respectively). CONCLUSIONS: RT can be considered a reliable alternative for clinical screening and in cases where positioning of the head at the slit lamp is impossible or topical preparations are to be avoided.

Ocular pulse amplitude in healthy subjects as measured by dynamic contour tonometry

OBJECTIVES: To test whether dynamic contour tonometry yields ocular pulse amplitude (OPA) measurements that are independent of corneal thickness and curvature, and to assess variables of observer agreement. METHODS: In a multivariate cluster analysis on 223 eyes, the relationship between central corneal thickness, corneal curvature, axial length, anterior chamber depth, intraocular pressure, sex, age, and OPA measurements was assessed. Intraobserver and interobserver variabilities were calculated from repeated measurements obtained from 8 volunteers by 4 observers. RESULTS: The OPA readings were not affected by central corneal thickness (P = .08), corneal curvature (P = .47), anterior chamber depth (P = .80), age (P = .60), or sex (P = .73). There was a positive correlation between OPA and intraocular pressure (0.12 mm Hg/1 mm Hg of intraocular pressure; P<.001) and a negative correlation between OPA and axial length (0.27 mm Hg/1 mm of length; P<.001). Intraobserver and interobserver variabilities were 0.08 and 0.02 mm Hg, respectively, and the intraclass correlation coefficient was 0.89. CONCLUSIONS: The OPA readings obtained with dynamic contour tonometry in healthy subjects are not influenced by the structure of the anterior segment of the eye but are affected by intraocular pressure and axial length. We found a high amount of agreement within and between observers.

TONOMETRY REVISITED: PERFUSION-RELATED, METABOLIC, AND RESPIRATORY COMPONENTS OF GASTRIC MUCOSAL ACIDOSIS IN ACUTE CARDIORESPIRATORY FAILURE

Mucosal pH (pHi) is influenced by local perfusion and metabolism (mucosal-arterial Pco2 gradient, DeltaPco2), systemic metabolic acidosis (arterial bicarbonate), and respiration (arterial Pco2). We determined these components of pHi and their relation to outcome during the first 24 h of intensive care. We studied 103 patients with acute respiratory or circulatory failure (age, 63 +/- 2 [mean +/- SEM]; Acute Physiology and Chronic Health Evaluation II score, 20 +/- 1; Sequential Organ Failure Assessment score, 8 +/- 0). pHi, and the effects of bicarbonate and arterial and mucosal Pco2 on pHi, were assessed at admission, 6, and 24 h. pHi was reduced (at admission, 7.27 +/- 0.01) due to low arterial bicarbonate and increased DeltaPco2. Low pHi (<7.32) at admission (n = 58; mortality, 29% vs. 13% in those with pHi >/=7.32 at admission; P = 0.061) was associated with an increased DeltaPco2 in 59% of patients (mortality, 47% vs. 4% for patients with low pHi and normal DeltaPco2; P = 0.0003). An increased versus normal DeltaPco2, regardless of pHi, was associated with increased mortality at admission (51% vs. 5%; P < 0.0001; n = 39) and at 6 h (34% vs. 13%; P = 0.016; n = 45). A delayed normalization or persistently low pHi (n = 47) or high DeltaPco2 (n = 25) was associated with high mortality (low pHi [34%] vs. high DeltaPco2 [60%]; P = 0.046). In nonsurvivors, hypocapnia increased pHi at baseline, 6, and 24 h (all P

Dynamic contour tonometry in keratoconus and postkeratoplasty eyes

PURPOSE: To compare the performance of dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in measuring intraocular pressure in eyes with irregular corneas. METHODS: GAT and DCT measures were taken in 30 keratoconus and 29 postkeratoplasty eyes of 35 patients after pachymetry and corneal topography. Regression and correlation analyses were performed between both tonometry methods and between tonometry methods and corneal parameters. Bland-Altman plots were constructed. RESULTS: DCT values were significantly higher than GAT values in both study groups: +4.1 +/- 2.3 mm Hg (mean +/- SD) in keratoconus and +3.1 +/- 2.5 mm Hg after keratoplasty. In contrast to DCT, GAT values were significantly higher in postkeratoplasty eyes than in keratoconus. The correlation between the 2 tonometry methods was moderate in keratoconus (Kendall correlation coefficient, tau = 0.34) as well in postkeratoplasty eyes (tau = 0.66). The +/-1.96 SD span of the DCT-GAT differences showed a considerable range: -0.42 to +8.70 mm Hg in keratoconus and -1.87 to +7.98 mm Hg in postkeratoplasty eyes. In the keratoconus group, neither DCT nor GAT correlated significantly with any of the corneal parameters. In the postkeratoplasty group, both DCT and GAT measures showed a moderate positive correlation with corneal steepness, but only DCT had a significant negative correlation with the central corneal thickness (tau = -0.33). CONCLUSIONS: DCT measured significantly higher intraocular pressures than GAT in keratoconus and postkeratoplasty eyes. DCT and GAT measures varied considerably, and DCT was not less dependent on biomechanical properties of irregular corneas than GAT.

Methodological considerations and practical recommendations for the application of peripheral arterial tonometry in children and adolescents

Endothelial dysfunction is recognized as the primum movens in the development of atherosclerosis. Its crucial role in both cardiovascular morbidity and mortality has been confirmed. In the past, research was hampered by the invasive character of endothelial function assessment. The development of non-invasive and feasible techniques to measure endothelial function has facilitated and promoted research in various adult and paediatric subpopulations. To avoid user dependence of flow-mediated dilation (FMD), which evaluates nitric oxide dependent vasodilation in large vessels, a semi-automated, method to assess peripheral microvascular function, called peripheral arterial tonometry (Endo-PAT®), was recently introduced. The number of studies using this technique in children and adolescents is rapidly increasing, yet there is no consensus with regard to either measuring protocol or data analysis of peripheral arterial tonometry in children and adolescents. Most paediatric studies simply applied measuring and analysing methodology established in adults, a simplification that may not be appropriate. This paper provides a detailed description of endothelial function assessment using the Endo-PAT for researchers and clinicians. We discuss clinical and methodological considerations and point out the differences between children, adolescents and adults. Finally, the main aim of this paper is to provide recommendations for a standardised application of Endo-PAT in children and adolescents, as well as for population-specific data analysis methodology.

Reproducibility of peripheral arterial tonometry measurements in male cardiovascular patients

BACKGROUND Assessment of endothelial function of the microvasculature by peripheral arterial tonometry (EndoPAT(®)) has gained increasing popularity in patients with cardiovascular risk factors. Only limited knowledge about its reproducibility in patients with coronary artery disease (CAD) is available. We therefore aimed to quantify reproducibility of EndoPAT(®) parameters in patients with stable CAD. DESIGN EndoPAT(®) measurements were performed repeatedly in 78 male patients (age 66 ± 8 years) with CAD on stable medication. We calculated overall mean, standard deviation (SD), coefficient of variation (CV) and intraclass correlation coefficient (ICC) of the following parameters: reactive hyperemic index (RHI), PAT ratio of the postocclusion period 90-150 s as used for calculation of the RHI (PAT ratio90-150 s) and 90-120 s (PAT ratio90-120 s) as used for the often employed Framingham RHI (F-RHI), as well as PAT ratio of the peak hyperemic response (PAT ratiopeak response). Additionally, least significant changes (LSC) for individual subjects and minimum sample sizes for parallel and cross-over design studies were calculated. RESULTS Mean RHI was 1·84 (SD 0·36). For RHI, PAT ratio90-150 s , PAT ratio90-120 s , and PAT ratiopeak response the CVs were 17·0%, 25·4%, 26·1%, and 25·0%, respectively. The ICCs were 0·45, 0·49, 0·48 and 0·51, respectively, and LSC for RHI was 47·2%. CONCLUSIONS CV of RHI in our population was moderate; however, we consider this precision insufficient to monitor changes in individual patients, as they would need to exceed 47% to show a significant change. Further, the poor ICCs reflect the difficulty of detecting treatment effects in homogenous populations, such as patients with stable CAD.

Coupled Biomechanical Response of the Cornea Assessed by Non-Contact Tonometry. A Simulation Study

The mechanical response of the cornea subjected to a non-contact air-jet tonometry diagnostic test represents an interplay between its geometry, the corneal material behavior and the loading. The objective is to study this interplay to better understand and interpret the results obtained with a non-contact tonometry test. A patient-specific finite element model of a healthy eye, accounting for the load free configuration, was used. The corneal tissue was modeled as an anisotropic hyperelastic material with two preferential directions. Three different sets of parameters within the human experimental range obtained from inflation tests were considered. The influence of the IOP was studied by considering four pressure levels (10–28 mmHg) whereas the influence of corneal thickness was studied by inducing a uniform variation (300–600 microns). A Computer Fluid Dynamics (CFD) air-jet simulation determined pressure loading exerted on the anterior corneal surface. The maximum apex displacement showed a linear variation with IOP for all materials examined. On the contrary, the maximum apex displacement followed a cubic relation with corneal thickness. In addition, a significant sensitivity of the apical displacement to the corneal stiffness was also obtained. Explanation to this behavior was found in the fact that the cornea experiences bending when subjected to an air-puff loading, causing the anterior surface to work in compression whereas the posterior surface works in tension. Hence, collagen fibers located at the anterior surface do not contribute to load bearing. Non-contact tonometry devices give useful information that could be misleading since the corneal deformation is the result of the interaction between the mechanical properties, IOP, and geometry. Therefore, a non-contact tonometry test is not sufficient to evaluate their individual contribution and a complete in-vivo characterization would require more than one test to independently determine the membrane and bending corneal behavior.

Radial artery pulse upstroke is not a good marker of left ventricular dysfunction: A comparison of radial tonometry, angiographic and echocardiographic measures of dP/dt

The first derivative of pressure over time (dP/dt) is a marker of left ventricular (LV) systolic function that can be assessed during cardiac catheterization and echocardiography. Radial artery dP/dt (Radial-dP/dt) has been proposed as a possible marker of LV systolic function (Nichols & O’Rourke, McDonald’s Blood Flow in Arteries) and we sought to test this hypothesis. Methods:We compared simultaneously recorded RadialdP/ dt (by high-fidelity tonometry) with LV-dP/dt (by highfidelity catheter and echocardiography parameters analogous to LV-dP/dt) in patients without aortic valve disease. In study 1, beat to beat Radial-dP/dt and LV-dP/dt were recorded at rest and during supine exercise in 12 males (aged 61±12 years) undergoing cardiac catheterization. In study 2, 2D-echocardiography and Radial-dP/dt were recorded in 59 patients (43 men; aged 64±10 years) at baseline and peak dobutamine-induced stress. Three measures at the basal septum were taken as being analogous to LV-dP/dt: (1) peak systolic strain rate, (2) strain rate (SR-dP/dt), and (3) tissue velocity during isovolumic contraction. Results: Study 1; there was a significant difference between resting LV-dP/dt (1461±383 mmHg/s) and Radial-dP/dt (1182±319 mmHg/s; P < 0.001), and a poor, but statistically significant, correlation between the variables (R2 = 0.006; P < 0.001) due to the high number of data points compared (n = 681). Similar results were observed during exercise. Study 2; there was a moderate association between baseline Radial-dP/dt and SRdP/ dt (R2 =−0.17; P < 0.01), but no significant relationship between Radial-dP/dt and all other echocardiographic measures analogous to LV-dP/dt at rest or peak stress (P > 0.05). Conclusion: The radial pressurewaveform is not a reliable marker of LV contractility.

Cling film as a barrier against CJD in Goldmann-type applanation tonometry

Purpose: To determine the feasibility of taking intra-ocular pressure (IOP) readings with Goldmann-type applanation tonometer probe covered with cling film to avoid transmission of Creutzfeldt-Jakob disease (CJD). Methods: Data were collected on two occasions from the right eyes of 30 healthy subjects using a Perkins applanation tonometer. On each occasion, a single tonometry measurement was made with and without cling film covering. Results: Cling film covering brought about a statistically significant IOP bias (-0.8 mmHg on first occasion and -1.17 mmHg on second occasion). The 95% limits of agreement, between readings made with and without cling film covering, were ±3.4 mmHg on first occasion; ±2.5 mmHg on second occasion. A statistically significant reduction of inter-sessional repeatability was observed for readings taken with cling film (±5.2 mmHg) compared to those made without (±3.9 mmHg). Conclusions: Even if the above findings are found to be acceptable, given the known intra-subject variations of this type of tonometry (±4 mmHg), ethical and legal considerations relating to the barrier properties of cling film are likely to prevent its routine use by optometrists. © 2004 The College of Optometrists.

Predicting changes in measured introcular pressure with non-contact tonometry after LASIK

Purpose: Optometrists are becoming more integrally involved in the diagnosis of and care for glaucoma patients in the UK. The correlation of apparent change in non contact tonometry (NCT) IOP measurement and change in other ocular parameters such as refractive error, corneal curvature, corneal thickness and treatment zone size (data available to optometrists after LASIK) would facilitate care of these patients. Setting: A UK Laser Eye Clinic. Methods: This is a retrospective study study of 200 sequential eyes with myopia with or without astigmatism which underwent LASIK using a Hansatome and an Alcon LADARvision 4000 excimer laser. Refraction keratometry, pachymetry and NCT IOP mesurements were taken before treatmebnt and agian 3 months after treatment. The relationship between these variables anfd teh treatment zones were studied using stepwise multiple regression analysis. Results: There was a mean difference of 5.54mmHg comnparing pre and postoperative NCT IOP. IOP change correlates with refractive error change (P < 0.001), preoperative corneal thickness (P < 0.001) and treatment zone size (P = 0.047). Preoperative corneal thickness correlates with preoperative IOP (P < 0.001) and postoperative IOP (P < 0.001). Using these correlations, the measured difference in NCT IIOP can be predicted preoperatively or postoperatively using derived equations.Conclusion: There is a significant reduction in measured NCT IOP after LASIK. The amount of reduction can be calculated using data acquired by optometrists. This is helpful for opthalmologists and optometrists who co-manage glaucoma patients who have had LASIK or with glaucoma pateints who are consideraing having LASIK.

Accuracy of Goldmann, ocular response analyser, Pascal and TonoPen XL tonometry in keratoconic and normal eyes

Aim: The aim of this study was to evaluate the practicality and accuracy of tonometers used in routine clinical practice for established keratoconus (KC). Methods: This was a prospective study of 118 normal and 76 keratoconic eyes where intraocular pressure (IOP) was measured in random order using the Goldman applanation tonometer (GAT), Pascal dynamic contour tonometer (DCT), Reichert ocular response analyser (ORA) and TonoPen XL tonometer. Corneal hysteresis (CH) and corneal resistance factor (CRF), as calculated by the ORA, were recorded. Central corneal thickness (CCT) was measured using an ultrasound pachymeter. Results: The difference in IOP values between instruments was highly significant in both study groups (p<0.001). All other IOP measures were significantly higher than those for GAT, except for the Goldmann-correlated IOP (average of the two applanation pressure points) (IOPg) as measured by ORA in the control group and the CH-corrected IOP (corneal-compensated IOP value) (IOPcc) measures in the KC group. CCT, CH and CRF were significantly less in the KC group (p<0.001). Apart from the DCT, all techniques tended to measure IOP higher in eyes with thicker corneas. Conclusion: The DCT and the ORA are currently the most appropriate tonometers to use in KC for the measurement of IOPcc. Corneal factors such as CH and CRT may be of more importance than CCT in causing inaccuracies in applanation tonometry techniques.