Comparison of intraocular pressure measurement between rebound, non-contact and Goldmann applanation tonometry in treated glaucoma patients

Background: To compare the intraocular pressure readings obtained with the iCare rebound tonometer and the 7CR non‐contact tonometer with those measured by Goldmann applanation tonometry in treated glaucoma patients. Design: A prospective, cross‐sectional study was conducted in a private tertiary glaucoma clinic. Participants or Samples: One hundred nine (54 males : 55 females) patients including only eyes under medical treatment for glaucoma. Methods: Measurement by Goldmann applanation tonometry, iCare rebound tonometry and 7CR non‐contact tonometry. Main Outcome Measures: Intraocular pressure. Results: There were strong correlations between the intraocular pressure measurements obtained with Goldmann and both the rebound and non‐contact tonometers (Spearman r‐values ≥ 0.79, P < 0.001). However, there were small, statistically significant differences between the average readings for each tonometer. For the rebound tonometer, the mean intraocular pressure was slightly higher compared with the Goldmann applanation tonometer in the right eyes (P = 0.02), and similar in the left eyes (P = 0.93); however, these differences did not reach statistical significance. The Goldmann correlated measurements from the non‐contact tonometer were lower than the average Goldmann reading for both right (P < 0.001) and left (P > 0.01) eyes. The corneal compensated measurements from the non‐contact tonometer were significantly higher compared with the other tonometers (P ≤ 0.001). Conclusions: The iCare rebound tonometer and the 7CR non‐contact tonometer measure intraocular pressure in fundamentally different ways to the Goldmann applanation tonometer. The resulting intraocular pressure values vary between the instruments and will need to be considered when comparing clinical versus home acquired measurements.     

Comparison of Diaton transpalpebral tonometer with applanation tonometry in keratoconus

AIM: To investigate the added value of using a Diaton transpalpebral tonometer (DT) to measure IOP in keratoconus. Most type of tonometers use corneal applanation or biomechanical resistance to measure intraocular pressure (IOP); however, these factors can be altered by keratoconus. Specifically, we examined whether DT can detect false-negative low Goldmann applanation tonometry (AT) measurements. METHODS: Patients with keratoconus were recruited from our tertiary academic treatment center. Measurements included AT and DT (in random order) and Scheimpflug imaging. An age- and gender-matched group of control subjects with no history of corneal disease or glaucoma was also recruited. RESULTS: In total, 130 eyes from 66 participants were assessed. In the keratoconus group, mean AT was 11.0 ± 2.6, mean DT 11.2±5.5 (P=0.729), and the two measures were correlated significantly (P=0.006, R=0.323). However, a Bland-Altman plot revealed a wide distribution and poor agreement between both measurements. Previous corneal crosslinking, corneal pachymetry, and Krumeich classification had no effect on measured IOP. CONCLUSION: Measurements obtained using a Diaton tonometer are not affected by corneal biomechanics; however, its poor agreement with Goldmann AT values calls into question the added value of using a Diaton tonometer to measure IOP in keratoconus.     

Intraocular pressure measurement-comparison of dynamic contour tonometry and goldmann applanation tonometry

PURPOSE: The dynamic contour tonometer (DCT, Pascal tonometer, Swiss Microtechnology AG, Port, Switzerland) was recently introduced as a new method of intraocular pressure measurement, supposedly independent of corneal properties. In this study we analyzed the agreement and correlation of dynamic contour tonometry and Goldmann applanation tonometry (GAT) and investigated the influence of central corneal thickness (CCT) and corneal curvature. We also considered preferential patient groups for both methods. METHODS: In a prospective study of 100 eyes without glaucoma, intraocular pressure was measured using dynamic contour tonometry and Goldmann applanation tonometry, followed by measurements of central corneal thickness and corneal curvature. RESULTS: A clear correlation between dynamic contour tonometry and Goldmann applanation tonometry was found (r = 0.693; P < 0.001). Dynamic contour tonometry generally resulted in higher intraocular pressure measurements (median difference + 1.8 mm Hg, mean difference + 2.34 mm Hg). Unlike dynamic contour tonometry, Goldmann applanation tonometry was remarkably affected by central corneal thickness, but neither method was significantly influenced by corneal curvature. Bland-Altman graphs showed remarkable disagreement between dynamic contour tonometry and Goldmann applanation tonometry, which could be partially explained by the influence of central corneal thickness on Goldmann applanation tonometry. To obtain valid readings, dynamic contour tonometry required a more extensive selection of patients than Goldmann applanation tonometry. CONCLUSIONS: Dynamic contour tonometry seems to be a reliable method for intraocular pressure measurement, which unlike Goldmann applanation tonometry is not influenced by central corneal thickness. In clinical practice, advantages from dynamic contour tonometry can be expected for cooperative patients, outpatients, and patients with sufficient bilateral ocular fixation, whereas Goldmann applanation tonometry measurements are more reliable in case of patients with inadequate cooperation, poor vision, or nystagmus.     

Central corneal thickness and Diaton transpalpebral tonometry

Background To examine the effects of central corneal thickness on the measures obtained from transpalpebral tonometry (Diaton), and to identify correlations between intraocular pressure (IOP) measurements with Diaton and the Goldmann applanation tonometer (GAT). Methods In this cross-sectional study, 162 eyes of 81 participants were included. Intraocular pressure measurements were obtained in all patients using Diaton and GAT. Central corneal thickness was determined by ultrasound pachymetry. The participants were stratified by corneal thickness: group I <530 μm (n = 56), group II 530–560 μm (n = 65), and group III >560 μm (n = 41). Results There were moderate correlations between IOP readings obtained using the Diaton and corrected GAT (C-GAT) (r = 0.303; P < 0.0001), and between corrected Diaton (C-Diaton), and C-GAT (r = 0.399; P < 0.0001). The mean Diaton tonometer readings were lower than C-GAT measurements (Diaton-corrected GAT mean difference, 0.9 ± 3.8 mmHg; c-Diaton-corrected GAT mean difference, 0.7 ± 3.5 mmHg). Differences were detected between the groups of patients for the GAT values [2.4 ± 3.6 mmHg for those with the thinnest corneas (<530 μm), 0.7 ± 3.6 mmHg for those with moderate corneas (between 531 μm and 560 μm), and −0.6 ± 3.6 mmHg for those with the thickest (>560 μm) corneas], whereas a significantly lower difference (0.9 ± 3.8 mmHg) was noted for the Diaton values of all individuals. Conclusions The Diaton measurements show moderate correlation with those provided by applanation tonometry. The Diaton tonometer seems to be more affected by the corneal thickness, especially in the thinnest corneas. No author has a financial interest in any product mentioned in the article. No author has a conflict of interest in any product mentioned in the article.     

新型眼压计原理及其在临床中的应用

眼压测量是目前对青光眼进行疗效观察及随访的主要手段之一,眼压计是临床工作中测量眼压的重要工具,修氏眼压计和Goldmann 压平眼压计长期以来为国内外临床医生所广泛应用,近十年来,又出现了一些新型的眼压计,如动态轮廓眼压计（DCT）、I Care回弹眼压计、Tono-Pen眼压计、Diaton眼压计和Proview压眼闪光眼压计等。其原理各异,临床应用价值也众说纷纭。DCT与Goldmann 压平眼压计（GAT）有较好的相关性,且测量值不受角膜性状的影响,但其对于配合差者有较大误差。I Care回弹眼压计、Tono-Pen眼压计、Diaton眼压计和Proview压眼闪光眼压计均为便携式眼压计,测量时不需使用麻醉药,便于青光眼的筛查,但其临床应用较少,测量的准确性仍需进一步研究。（眼科,2012,21： 136-140）     

Measurement of intraocular pressure in LASIK and LASEK patients using the Reichert Ocular Response Analyzer and Goldmann applanation tonometry

PURPOSE: To determine the efficacy of the Reichert Ocular Response Analyzer (ORA) to measure intraocular pressure (IOP) following corneal laser refractive surgery. METHODS: Intraocular pressure was measured using Goldmann applanation tonometry preoperatively and 3 months following LASIK and LASEK for all levels of myopia and low levels of hyperopia. In LASIK eyes, 120-microm flaps were cut using the Hansatome XP. The ORA was used to measure Goldmann correlated IOP and corneal compensated IOP 3 months postoperatively. Postoperative central corneal thickness, hysteresis, and corneal curvature were assessed to determine their relationship with postoperative change in Goldmann applanation tonometry IOP. Efficacy of ORA IOP measurement was analyzed by comparing Goldmann applanation tonometry IOP with Goldmann correlated IOP. RESULTS: LASEK was performed on 35 eyes, and LASIK was performed on 90 eyes. In the LASIK group, mean Goldmann applanation tonometry IOP decreased 3.7+/-2.3 mmHg postoperatively (P=.00). Postoperative Goldmann applanation tonometry did not differ significantly (P=.06) from postoperative ORA Goldmann correlated IOP (10.2+/-2.1 mmHg). In the LASEK group, mean Goldmann applanation tonometry IOP decreased 3.9+/-2.3 mmHg (P=.00). Postoperative Goldmann applanation tonometry did not differ significantly (P=.6) from postoperative ORA Goldmann correlated IOP (10.7+/-2.5 mmHg). Postoperative decrease in Goldmann applanation tonometry IOP did not correlate with age, ablation depth, pre- and postoperative central corneal thickness or corneal hysteresis, or postoperative decrease in corneal curvature. CONCLUSIONS: Intraocular pressure measurements were similar using both the ORA Goldmann correlated IOP and Goldmann applanation tonometry following keratorefractive surgery.     

Three portable tonometers, the TGDc-01, the ICARE and the Tonopen XL, compared with each other and with Goldmann applanation tonometry*.

Three portable tonometers, the TGDc-01, the ICARE and the Tonopen XL, were compared with each other and to Goldmann applanation tonometry in a large group of healthy subjects and patients with ocular hypertension or glaucoma (n = 103). Measurements performed with the ICARE and the Tonopen XL were in good agreement with that of the Goldmann tonometer. Intraocular pressure (IOP) values measured with the TGDc-01 were significantly lower and showed more variability. The 95% limits of agreement (portable tonometer - Goldmann) were -17 to +10 mmHg for the TGDc-01, -6 to +7 mmHg for the ICARE and -6 to +8 mmHg for the Tonopen. Corneal thickness could not explain the differences between an IOP measured with the portable tonometers and an IOP measured with the Goldmann tonometer. Patient comfort was slightly higher for ICARE when compared with the Tonopen.     

Effect of corneal parameters on measurements using the pulsatile ocular blood flow tonograph and Goldmann applanation tonometer

AIMS: To investigate the effect of central corneal thickness and corneal curvature on intraocular pressure measurements using the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer, and to assess the agreement between the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer in intraocular pressure measurement. METHODS: 479 subjects underwent intraocular pressure measurements with the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph. Of these, 334 patients underwent additional measurement of central corneal thickness with an ultrasonic pachymeter and corneal curvature measurement with a keratometer. RESULTS: The intraocular pressure measurements obtained with both the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph varied with central corneal thickness and mean keratometric reading. Intraocular pressure measured using the Goldmann applanation tonometer increased by 0.027 mm Hg per micro m increase in central corneal thickness. Intraocular pressure measured using the pulsatile ocular blood flow tonograph increased by 0.048 mm Hg per micro m increase in central corneal thickness. For an increase of 1 mm of mean corneal curvature there was rise in intraocular pressure of 1.14 mm Hg measured by the Goldmann applanation tonometer and of 2.6 mm Hg measured by the pulsatile ocular blood flow tonograph. When compared to the Goldmann applanation tonometer, the pulsatile ocular blood flow tonograph underestimated at low intraocular pressure and overestimated at higher intraocular pressure. CONCLUSION: Central corneal thickness and corneal curvature affected measurements obtained with the pulsatile ocular blood flow tonograph more than they affected measurements obtained with the Goldmann applanation tonometer.     

Ocuton-S self tonometry vs. Goldmann tonometry; a diurnal comparison study

PURPOSE: To compare 24-hour diurnal intraocular pressure (IOP) measurements obtained using the Ocuton-S applanation self tonometer and the Goldmann tonometer. METHODS: 24-hour diurnal IOP curves were obtained on 14 eyes of 7 trained patients suffering from medically controlled primary open angle glaucoma. IOP was measured every third hour starting at 9 a.m. with a calibrated Goldmann tonometer; one week later, a similar set of measurements was obtained with Ocuton-S self tonometry by the patients. One week later still, ultrasound corneal pachymetry was performed at the same hours. RESULTS: Overall IOP (24-hour mean) did not differ significantly between the different measuring techniques (ANOVA, p = 0.74), but the IOP differed in a statistically significant manner around the clock (ANOVA, p = 0.00006). The mean Goldmann tonometric readings were up to 2.8 mmHg lower than the Ocuton-S values during the daytime (9 a.m. to 9 p.m.), however, during the night (12 midnight to 6 a.m.) mean IOP measured with Goldmann tonometry was 2.2 to 3.3 mmHg higher than the corresponding average of the self tonometry readings. There was a statistically significant interaction between the type of tonometry and the time of the measurement (p = 0.0007). Central corneal thickness (CCT) showed a significant change during the 24-hour period (p = 0.000001). CONCLUSION: IOP shows a different diurnal curve when measured with the Goldmann tonometer and with the Ocuton-S applanation self tonometer. The instruments' readings might be influenced in different ways by the diurnal changes of the corneal thickness. Since Ocuton-S self tonometry underestimates the IOP in the early morning period, a careful evaluation is necessary when nocturnal and early morning IOP elevation is investigated with this technique.     

Comparison of Proview phosphene tonometry with Goldmann applanation tonometry

BACKGROUND: To compare intraocular pressures obtained using a handheld pressure phosphene tonometer (PPT) (Proview, Bausch & Lomb Pharmaceuticals, Inc., Tampa, Fla.) with Goldmann applanation tonometry. METHODS: Comparative case series of 30 randomly selected patients. RESULTS: The readings obtained with the pressure phosphene tonometer display a higher mean and a larger standard deviation than those obtained with the Goldmann applanation tonometer (GAT). Differences between PPT and GAT readings tended to decrease as a function of increased Goldmann levels. The relation of Proview and Goldmann readings (r = 0.32) and the scatterplot were not consistent with the hypothesis that the 2 methods are equivalent. INTERPRETATION: Our results indicate that the pressure phosphene-type handheld tonometry method, which does not appear to provide an accurate and consistent measure of intraocular pressure, is substantially less reliable than the Goldmann method.     

Intraocular pressure difference in Goldmann applanation tonometry versus a transpalpebral tonometer TGDc-01"PRA" in glaucoma patients

PURPOSE: The object of this study was to compare intraocular pressure measurements obtained with the TGDc-01"PRA", a new, transpalpebral indentation tonometer, with those from Goldmann applanation tonometry in normal and glaucomatous eyes. METHODS AND PATIENTS: Forty healthy eyes and 185 eyes suffering from glaucoma were included in the study. For Goldmann tonometry three measurements and for the TGDc-01 ten measurements were performed in a random order. All participants were placed in an upright position for all measurements. RESULTS: In both groups a systematic increase of intraocular pressure was found within the TGDc-01-measurements. Therefore, the first 3 measurements of each device were used for further statistical analysis. No learning curve could be demonstrated for the TGDc-01-measurement with normal eyes. Within the group of normal eyes the mean IOD obtained with the TGDc-01 was 1.84 mmHg lower than the mean IOD obtained with Goldmann tonometry (two-sided Student's t-test; P = 0.003). In the group of glaucomatous eyes, the mean intraocular pressure obtained with the Goldmann tonometry was 19.7 +/- 10.1 mmHg, with the TGDC-01 18.1 +/- 7.1 mmHg (coefficient of correlation r = 0.64, P < 0.001). The mean standard deviation of intraocular pressure measurements with Goldmann tonometry was 1.2 +/- 0.9 mmHg, with the TGDc-01 3.1 +/- 2.1 mmHg. TGDc-01-measurements overestimated intraocular pressure compared to Goldmann tonometry up to values of 16 mmHg and underestimated intraocular pressure at values over 16 mmHg. The difference increased by 5.5 mmHg per 10 mmHg Goldmann tonometry. The probability of success, defined as TGDc-01-recordings within +/- 3 mmHg of the Goldmann tonometry recordings, was less than 53 % between 5 and 20 mmHg and less than 30 % between 20 and 30 mmHg. Intraocular pressure (Goldmann tonometry) over 30 mmHg was always accompanied by TGDc-01-measurements lower than 3 mmHg. CONCLUSION: In eyes with elevated intraocular pressure, the TGDc-01"PRA" significantly underestimated the intraocular pressure measurement when compared to the gold standard, Goldmann tonometry. At present, measurement of the intraocular pressure with the TGDc-01 should not be used for clinical management of patients with glaucoma.     

Screening for glaucoma in a Brisbane general practice — the role of tonometry

Objectives: (1) To pilot, and evaluate, a tonometry training intervention for general practitioners; (2) to evaluate the efficacy of three types of tonometer (Perkins, Schiotz and Tonopen) in the hands of these general practitioners; (3) to evaluate the predictive value of tonometry in screening for glaucoma in a general practice population; and (4) to evaluate the acceptability of tonometry to general practice patients. Design: After being trained, three general practitioners recruited 73 of their patients over 50 years of age to attend for measurement of intraocular pressure by tonometry. Intraocular pressure was initially measured by an ophthalmologist using the Goldmann applanation tonometer, and then recorded in random order by GPs using three types of tonometer — the Perkins, Schiotz and Tonopen. Setting: A group general practice in a middle-class suburb in southern Brisbane. Outcome measures: (1) Comparison of measurements on the Perkins, Schiotz and Tonopen tonometers with that of the ‘gold standard’, the Goldmann Applanation tonometer; (2) Prevalence of disc and perimetric abnormality suggestive of glaucoma among those patients with increased intraocular pressure; and (3) the acceptability of contact tonometry to general practice patients. Results: There was considerable variability between intraocular values obtained across doctors and across instruments (6% to 95% of values within 4 mm of the ‘gold standard’). The Schiotz tonometer provided the most uniform assessment of intraocular pressure across the groups. Nineteen of the 73 patients (26%) had intraocular pressures ≥21 mmHg using the ‘gold standard’. Of these, 18 were followed up with funduscopy, gonioscopy, repeat measurement of intraocular pressure and visual field assessment. Five had persistent elevations of intraocular pressure ≥21 mmHg on subsequent assessment, and two had mild abnormalities of cup—disc ratio with normal fields on testing with Humphrey computerised perimetry. Conclusion: No one hand-held tonometer proved highly accurate in the hands of all three doctors. Even measured optimally, increased intraocular pressure alone was a poor predictor of glaucoma. Of the population screened, two patients (3%) showed evidence of mild cup-disc abnormality requiring follow-up.     

Elastic hysteresis in human eyes is an age‐dependent value

Background: The elastic hysteresis phenomenon is observed when cyclic loading is applied to a viscoelastic system. The purpose of this study was to quantitatively evaluate elastic hysteresis in living human eyes against an external force. Design: Prospective case series. Participants: Twenty‐four eyes of 24 normal human subjects (mean age: 41.5 ± 10.6 years) were recruited. Methods: A non‐contact tonometry process was recorded with a high‐speed camera. Central corneal thickness, corneal thickness at 4 mm from the centre, corneal curvature and anterior chamber depth were measured. Intraocular pressure was also measured using Goldmann applanation tonometry and dynamic contour tonometer. Main Outcome Measures: Energy loss due to elastic hysteresis was calculated and graphed. Results: The mean central corneal thickness was 552.5 ± 36.1 µm, corneal curvature was 7.84 ± 0.26 mm and anterior chamber depth was 2.83 ± 0.29 mm. The mean Goldmann applanation tonometry‐intraocular pressure was 14.2 ± 2.7 mmHg and dynamic contour tonometer‐intraocular pressure was 16.3 ± 3.5 mmHg. The mean energy loss due to elastic hysteresis was 3.90 × 10⁻⁶ ± 2.49 × 10⁻⁶ Nm. Energy loss due to elastic hysteresis correlated significantly with age (Pearson correlation coefficient = 0.596, P = 0.0016). There were no significant correlations between energy loss due to elastic hysteresis and other measurements. Conclusion: Energy loss due to elastic hysteresis in the eyes of subjects was found to positively correlate with age, independent of anterior eye structure or intraocular pressure. Therefore, it is believed that the viscosity of the eye increases with age.     

Comparison of the ICare rebound tonometer with the Goldmann applanation tonometer by experienced and inexperienced tonometrists

PURPOSE: To assess the agreement between ICare rebound tonometer and Goldmann applanation tonometer in the hands of experienced and inexperienced tonometrists. PATIENTS AND METHODS: Two tonometrists, experienced with both Goldmann applanation tonometry (GAT) and ICare Tonometry (ICT) measured intraocular pressure (IOP), in a masked fashion, in 100 patients. In another series of 58 patients, ICT was performed by an inexperienced tonometrist and GAT by an experienced tonometrist. RESULTS: In approximately 80% of patients, the difference in IOP between GAT and ICT was 相似文献   

Assessment of the accuracy and reliability of the Topcon CT80 non‐contact tonometer

Background: The reliability of non‐contact tonometers has been reported extensively in the literature. This study was designed to assess reliability of the new Topcon CT80 non‐contact tonometer in normotensive subjects, using the Goldmann tonometer as the standard. Methods: The accuracy of the Topcon CT 80 non‐contact tonometer was assessed by comparing its IOP assessments with those of the Goldmann applanation tonometer, on 60 right eyes of young healthy subjects with normal intraocular pressures. Each subject’s intraocular pressure was assessed with each technique on two separate occasions, one week apart. The reliability of each technique was determined by the assessment of its inter‐session repeatability using the Bland‐Altman method. The 95 per cent limits of agreement for the two methods were also determined. Results: No statistically significant difference was found between the average intraocular pressures measured with the two techniques (p > 0.05). The inter‐session repeatability indices for the two techniques did not differ significantly (p > 0.05). The mean difference in intraocular measurements between the two techniques was 0.2 ± 1.5 mmHg (mean ± SD) and the 95 per cent limits of agreement were ‐3.14 and +2.74 mmHg, with the non‐contact tonometer returning higher readings than the Goldmann tonometer. Conclusion: In this sample of normotensive subjects, the Topcon CT80 non‐contact tonometer proved to be accurate and as reliable as the Goldmann tonometer in the assessment of intraocular pressure. Thus, it can be used as an objective clinical method for the assessment of normal intraocular pressure.     

Clinical comparison of the ProTon and Tono-Pen tonometers with the Goldmann applanation tonometer.

A clinical evaluation of a new electron ProTon tonometer was performed comparing the values of intraocular pressure (IOP) measured using this instrument with those determined by a similar instrument, Tono-Pen XL, and by Goldmann applanation tonometry. The mean IOP measured in 106 eyes with the ProTon tonometer was not significantly different from that determined with Goldmann applanation, while the IOP values measured with Tono-Pen XL were significantly lower. The 95% limits of agreement between applanation tonometry and ProTon tonometry were between -4 mm Hg and 5 mm Hg and between applanation tonometry and Tono-Pen XL tonometry between -3 mm Hg and 8 mm Hg. The ProTon tonometer appears to have a higher level of accuracy than the Tono-Pen XL tonometer in clinical practice.     

Use of disposable prism tonometry in routine clinical practice

AIM: To establish the reliability, efficacy, and safety of disposable prism tonometry and validate its routine use for screening as well as monitoring of glaucoma. METHODOLOGY: Intraocular pressure (IOP) of 400 eyes of 200 consecutive patients who attended the general ophthalmic clinic was checked with both the Goldmann applanation tonometer and a disposable tonometer prism by an experienced examiner after obtaining informed consent. The data were statistically analysed. RESULTS: The mean difference in the IOP between the two types of prisms was 0.1 mmHg (SD+/-1 mmHg). CONCLUSION: Disposable prism tonometry provides a reliable, effective, and safe alternative to Goldmann reusable prism tonometry for routine screening as well as monitoring of glaucoma with the advantages of eliminating the need for chemical disinfection and therefore eliminating the risk of crossinfection.     

Young's modulus in normal corneas and the effect on applanation tonometry.

OBJECTIVES: To determine the statistically normal range of corneal Young's modulus in young healthy eyes in vivo, and to establish if this variation has a clinically significant influence on intraocular pressure (IOP) measurement using applanation tonometry. METHODS: Central corneal curvature, central corneal thickness (CCT), and applanation IOP (Goldmann tonometer) were measured using standard clinical techniques in one eye of 100 normal human subjects (22.0 +/- 2.9 years) in vivo. The Orssengo-Pye algorithm was used to calculate the corneal Young's modulus of these experimental subjects, and to produce a theoretical model of potential errors in Goldmann applanation tonometry estimates of IOP due to variations of Young's modulus and CCT. RESULTS: Corneal Young's modulus was 0.29 +/- 0.06 MPa [95% confidence interval (CI) 0.17 to 0.40 MPa]. According to the Orssengo-Pye model, the relationship between Young's modulus and the error in applanation IOP is linear; the slope was 23 mm Hg per MPa. An increase from the minimum to the maximum value of the calculated limits of agreement (95% CI) of Young's modulus caused a variation in applanation IOP of 5.35 mm Hg. The anticipated error at the extremes of the limits of agreement (95% CI) of CCT was similar at 4.67 mm Hg. CONCLUSION: Physiological variations in corneal Young's modulus may cause clinically significant errors in Goldmann applanation tonometry estimates of IOP.     

Theoretical basis of goldmann applanation tonometry

For more than 50 years Goldmann applanation tonometry has been the internationally accepted method for measuring intraocular pressure. In Goldmann applanation tonometry, however, some basic physical properties are oversimplified and the method has some flaws and restrictions. This paper is intended to promote the understanding of the methodological basis of Goldmann applanation tonometry and describes the most important factors influencing the measurement of intraocular pressure (e. g., corneal thickness, corneal radius, axial length and corneal morphology). Furthermore, the basic principles of other commonly used tonometer devices will be discussed. New developments are anticipated that will measure the true intraocular pressure more accurately than Goldmann applanation tonometry.     

Comparison of the ICare® rebound tonometer with the Goldmann tonometer in a normal population

The aim of this study was to evaluate the accuracy of measurement of intraocular pressure (IOP) using a new induction/impact rebound tonometer (ICare) in comparison with the Goldmann applanation tonometer (AT). The left eyes of 46 university students were assessed with the two tonometers, with induction tonometry being performed first. The ICare was handled by an optometrist and the Goldmann tonometer by an ophthalmologist. In this study, statistically significant differences were found when comparing the ICare rebound tonometer with applanation tonometry (AT) (p < 0.05). The mean difference between the two tonometers was 1.34 +/- 2.03 mmHg (mean +/- S.D.) and the 95% limits of agreement were +/-3.98 mmHg. A frequency distribution of the differences demonstrated that in more than 80% of cases the IOP readings differed by <3 mmHg between the ICare and the AT. In the present population the ICare overestimates the IOP value by 1.34 mmHg on average when compared with Goldmann tonometer. Nevertheless, the ICare tonometer may be helpful as a screening tool when Goldmann applanation tonometry is not applicable or not recommended, as it is able to estimate IOP within a range of +/-3.00 mmHg in more than 80% of the population.