The relationship between central corneal thickness and Goldmann applanation tonometry

Background: The aim of this study was to investigate the relationship between Goldmann applanation tonometry and central corneal thickness in a large sample of healthy eyes. Method: Five hundred eyes of 500 subjects (253 women, 50.6 per cent and 247 men, 49.4 per cent) were analysed in a prospective healthy population study. Mean age of the sample was 31 ± 8 years. Goldmann applanation tonometry was carried out by one physician. Tonometric values were the mean of three consecutive readings. Subsequently, another physician carried out ultrasonic pachymetry with the DGH 2000 AP ultrasonic pachymeter (DGH Technology Inc, San Diego, USA). Ten measurements were made at the centre of the cornea of each eye. The lowest value was used for analysis. Results: Applanation tonometry and central corneal thickness were correlated (r = 0.184, p < 0.001). There was no significam correlation between corneal thickness and age (r = 0.083, p = 0.065), mean spherical equivalem refraction (r = 0.083, p = 0.065) or visual acuity (r = 0.036, p = 0.187). Conclusion: In normal eyes, there is no statistically significant correlation between changes of intraocular pressure and changes of central corneal thickness but they suggest a relationship between intraocular pressure and central corneal thickness. Goldmann applanation tonometry has a systematic error in accuracy of intraocular pressure readings of healthy eyes caused by its dependence on central corneal thickness. Measurement of corneal thickness by optometrists should be the first step in diagnosing intraocular pressure pathologies.     

正常人中央角膜厚度与Goldmann压平眼压的关系

目的:了解正常人中央角膜厚度(central corneal thickness,CCT)的分布特点并探讨其与压平眼压测量值的关系。方法:采用光学角膜测厚仪及Goldmann压平眼压计检测169名正常人CCT和压平眼压。结果:169名受检者右眼平均CCT为0.547mm(95%可信区间0.443~0.651mm),左眼0.551mm(95%可信区间0.453~0·649)。压平眼压右眼平均15.8mmHg,左眼15.5mmHg。CCT与年龄无相关关系,但与压平眼压测量值显著相关。线性回归分析表明,CCT每增加0.018mm,压平眼压增加1mmHg。结论:CCT变异是眼压测量误差的主要来源。CCT较厚的正常个体可表现"眼压增高"被误诊为高眼压症,而CCT偏薄的原发性开角型青光眼患者则可能因眼压测量"正常"被误诊为正常眼压性青光眼。在诊断青光眼或高眼压症时,特别是在眼压值与其他临床表现不符时,应考虑CCT有无变异。     

不同角膜厚度下动态轮廓眼压计和Goldmann压平眼压计在不同角膜厚度的测量值比较

目的比较动态轮廓眼压计（dynamic contour to-nometry,DCT）和Goldmann压平眼压计（Goldmann applanation tonometry,GAT）在中央角膜厚度（central corneal thickness,CCT）不同的正常眼测量值的差异。方法患者69例（69眼）按CCT不同分为正常组（520～580μm）42眼、变薄组（450～520μm）16眼、增厚组（580～640μm）11眼。各组分别用DCT和GAT测量眼压。结果正常组平均CCT为（574.55±16.40）μm,平均GAT值为（16.62±3.15）mmHg（1kPa=7.5mmHg）,平均DCT值为（16.78±2.86）mmHg,DCT与GAP差异无统计学意义（P〉0.05）,平均GAT-DCT值为（-0.16±0.96）mmHg;变薄组平均CCT为（499.44±16.70）μm,平均GAT值为（14.03±2.72）mmHg,平均DCT值为（17.06±2.72）mmHg,2者差异有统计学意义（P〈0.01）,平均GAT-DCT值为（-3.03±1.32）mmHg;增厚组平均CCT为（605.18±17.90）μm,平均GAT值为（16.91±3.94）mmHg,平均DCT值为（16.80±4.25）mmHg,2者差异无统计学意义（P〉0.05）,平均GAT-DCT值为（0.05±2.47）mmHg。结论在角膜厚度正常眼,DCT值和GAT值较一致;在角膜厚度变薄眼,前者较后者准确;在角膜厚度变厚眼未体现DCT的优越性。     

Clinical comparison of the Keeler Pulsair 2000, American Optical MkII and Goldmann applanation tonometers

The aim of our study was to evaluate the performance of both the Keeler Pulsair 2000 and the American Optical (AO) MkII non-contact tonometers (NCT) and compare these to the reference Goldmann standard using the same group of patients. Forty-five patients (89 eyes) receiving medical treatment for primary open angle glaucoma had their intraocular pressure (IOP) measured with each instrument in a random order using five experienced observers. In the IOP range of the sample (6–27 mmHg) the difference between means for each tonometer was small. The Pulsair 2000 (mean = 19.06 mmHg, SD 6.28) read slightly higher than Goldmann (mean = 18.01 mmHg, SD 4.88), whereas the AO MkII read slightly lower (mean = 16.27 mmHg, SD 5.93). However, all differences were statistically significant ( P < 0.001, repeat measures ANOVA). Correlation coefficients for Pulsair 2000 versus Goldmann was r = 0.82 and for AO MkII versus Goldmann was r = 0.85. In addition, the repeatability for each NCT was assessed using 10 consecutive measurements on a further 10 subjects. The Pulsair 2000 showed significantly greater variation of IOP (mean SD 3.43 mmHg) than the AO MkII (mean SD 1.76 mmHg), confirming the need for taking at least four readings per eye with the Pulsair 2000. These variations are greater than that generally observed with Goldmann, and possible explanations why this occurs are discussed. In conclusion, subject to these limitations, both NCTs should be useful for measuring IOP as part of a screening protocol for glaucoma.     

Dependence of dynamic contour and Goldmann applanation tonometries on peripheral corneal thickness

AIM: To determine the effects of peripheral corneal thickness (PCT) on dynamic contour tonometry(DCT) and Goldmann applanation tonometry (GAT). METHODS: A cross-sectional study. We created a software which calculates the corneal contour (CC) as a function of the radius from the corneal apex to each pixel of the contour. The software generates a central circumference with a radius of 1 mm and the remainder of the cornea is segmented in 5 rings concentric with corneal apex being its diameter not constant around the corneal circumference as a consequence of the irregular CC but keeping constant the diameter of each ring in each direction of the contour. PCT was determined as the mean thickness of the most eccentric ring. Locally weighted scatterplot smoothing (LOWESS) regression was used to determine the pattern of the relationship between PCT and both DCT and GAT respectively. Thereafter, two multivariable linear regression models were constructed. In each of them, the dependant variable was intraocular pressure (IOP) as determined using GAT and DCT respectively. In both of the models the predictive variable was PCT though LOWESS regression pattern was used to model the relationship between the dependant variables and the predictor one. Age and sex were also introduced control variables along with their first-degree interactions with PCT. Main outcome measures include amount of IOP variation explained through regression models (R2) and regression coefficients (B). RESULTS: Subjects included 109 eyes of 109 healthy individuals. LOWESS regression suggested that a 2nd-degree polynomial would be suitable to model the relationship between both DCT and GAT with PCT. Hence PCT was introduced in both models as a linear and quadratic term. Neither age nor sex nor interactions were statistically significant in both models. For GAT model, R2 was 17.14% (F=9.02; P=0.0002), PCT linear term B was -1.163 (95% CI: -1.163, -0.617). PCT quadratic term B was 0.00081 (95% CI: 0.00043, 0.00118). For DCT model R2 was 14.28% (F=9.29; P=0.0002), PCT linear term B was -0.712 (95% CI: -1.052, -0.372), PCT quadratic term was B=0.0005 (95% CI: 0.0003, 0.0007). CONCLUSION: DCT and GAT measurements are conditioned by PCT though this effect, rather than linear, follows a 2nd-degree polynomial pattern.     

Effect of central corneal thickness on Goldmann applanation tonometry measures—a different result with different pachymeters

Purpose To assess whether the use of Orbscan pachymetry, as an alternative to ultrasound pachymetry, had an effect on the IOP-CCT relationship for Goldmann tonometry in normal human eyes. Patients and methods The right eye of 50 healthy subjects, aged 19 to 82 years, were assessed by Orbscan (three scans), and then central corneal thickness (CCT) measured by ultrasound pachymetry (three readings) and Goldmann tonometry performed (three readings). Results Goldmann tonometry indicated average IOP values from 9.7 to 20 mm Hg (group mean 14.3 ± 2.5 mm Hg) that were highly highly correlated with ultrasound pachymetry (r = 0.608, p < 0.001). Orbscan central zone pachymetry (2-mm sample zone) yielded higher values than ultrasound, averaging 0.591 ± 0.044 mm compared to 0.523 ± 0.037 mm (p < 0.001), with the differences between the instruments being proportional to the average thickness (p < 0.001; r = 0.461). Notwithstanding, the Goldmann tonometry values were still highly correlated with the Orbscan central zone thickness data (r = 0.595, p < 0.001); but, due to the difference in the thickness data generated by the two pachymeters, the absolute slope of the IOP–CCT relationship was slightly less if Orbscan measures were used, with or without use of the acoustic factor. Conclusion Orbscan measures of the thickness of a central corneal zone can be used to assess the impact of central corneal thickness on Goldmann tonometry data. Neither of the authors has any financial interest in the production or use of any device mentioned in this article.     

Effect of corneal thickness on intraocular pressure measurements with the Pascal dynamic contour,Canon TX‐10 non‐contact and Goldmann applanation tonometers in healthy subjects

Purpose: To investigate the effects of central corneal thickness (CCT) on intraocular pressure (IOP) measurements of the Pascal dynamic contour tonometry (DCT), Canon TX‐10 non‐contact tonometry (NCT) and Goldmann applanation tonometry measurements (GAT) in healthy subjects. Methods: IOP values of 135 eyes with normal corneas of 135 healthy volunteers were determined by DCT, NCT and by GAT. The CCT was measured using an ultrasonic pachymeter after all IOP determinations had been made. Results: When DCT measurements were compared (IOP = 17.52 ± 2.0 mmHg) with NCT measurements (IOP = 16.54 ± 2.77 mmHg) and GAT measurements (IOP = 15.07 ± 2.35 mmHg), DCT measurements were significantly higher than NCT and GAT (p < 0.001). There was a significant correlation between CCT with both NCT (r = 0.260, p = 0.003) and GAT measurements (r = 0.257, p = 0.005). There was a weak correlation that was not statistically significant between CCT and DCT (r = 0.160, p = 0.079). Conclusion: The IOP measurements with DCT seem to be less dependent on CCT. NCT appears to be more affected by variation in CCT than GAT.     

The effect of contact lens-induced corneal edema on Goldmann applanation tonometry and dynamic contour tonometry

Purpose  To evaluate the effect of contact lens-induced corneal edema on intraocular pressure (IOP) measurements using Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) in Asian subjects. Participants  The study included 40 eyes of 20 normal volunteers with no evidence of ocular disease. Methods  Forty eyes of 20 healthy volunteers were required to wear soft contact lenses for 2 hours to induce corneal swelling. Central corneal thickness (CCT) and IOP were measured before and immediately after contact lens wear using specular microscope, GAT, and DCT. The IOP measurements by GAT and DCT were compared. The changes in the CCT and the IOP measurements after wearing contact lenses were assessed. Results  The mean CCT of the 40 eyes evaluated was 532.6 ± 31.6 μm. The mean IOP was 11.78 ± 2.04 mmHg for the GAT and 14.46 ± 1.89 mmHg for the DCT, and the difference was statistically significant (P < 0.001). After wearing contact lenses, the mean CCT was 553.2 ± 34.3 μm, which was 20.6 ± 12.9 μm greater than before wearing them (P < 0.001). The mean IOP measurements of the GAT and DCT were decreased after wearing the contact lenses. The mean decrease of the GAT values was 0.43 ± 1.95 mmHg, which was not statistically significant (P = 0.175). However, the mean decrease of the DCT readings, which was 0.75 ± 1.74 mm Hg, was statistically significant (P = 0.010). Conclusion  The IOP measurements with DCT were significantly higher than those with GAT in healthy Asian eyes. Although the mean IOP measurements of both the GAT and the DCT were decreased in the edematous cornea, IOP measurements of the DCT were more affected by corneal edema than were the GAT. The authors have no proprietary, commercial, or financial interests in any of the products described in this study.     

On repeated corneal applanation with the Goldmann and two non‐contact tonometers

Background: Several authors believe it is necessary to randomise the order in which contact and non‐contact tonometers are used in comparison studies. This study was carried out to investigate the effect of repeated applanation on the measured intraocular pressure. Methods: One set of measurements per session was made on each of three sessions (one session per day) with the Goldmann and two non‐contact tonometers (Topcon CT80 and Keeler Pulsair EasyEye), in a pre‐determined order, on one randomly selected eye of 120 subjects randomised to one of two groups. For session one, only the non‐contact tonometers were used to assess the intraocular pressure of both groups. For session two, either non‐contact or Goldmann tonometry was performed first and this order was reversed for session 3. Average intraocular pressures were compared between sessions to determine the presence or absence of effects on the intraocular pressure caused by prior repeated applanation with the Goldmann or either one (or both) of the non‐contact tonometers. Results: Prior applanation with a non‐contact tonometer did not cause a significant (p > 0.05) reduction of the mean pressure measured with either non‐contact tonometer. The mean pressure was slightly but significantly (p < 0.05) reduced (for both non‐contact tonometers in both subject groups) when non‐contact tonometry was performed after Goldmann tonometry. There was no significant difference (p > 0.05) between the pressures measured with the Goldmann tonometer prior to and subsequent to non‐contact tonometry, in both subject groups. Conclusion: A small but statistically significant reduction in the intraocular pressure was found following applanation with the Goldmann tonometer but not with either one of two non‐contact tonometers.     

Dynamic contour tonometry (DCT) versus Goldmann applanation tonometry (GAT) - a comparison of agreement and reproducibility

Background

The PASCAL® dynamic contour tonometer (DCT) is a novel device designed for intraocular pressure (IOP) measurements. It is assumed to be largely independent of corneal properties. In a previous study we compared DCT with Goldmann applanation tonometry (GAT) in 100 right eyes with normal corneas. The aim of the present study is to evaluate whether differences DCT-GAT?≥?2.0 mmHg found in the previous study are reproducible and also present in the fellow eye.

Methods

Twenty-three of the 100 patients (M:F?=?8:15, mean age: 36?±?11 SD, range 22–53 years) with a previous difference DCT-GAT?≥?2.0 mmHg were included in the present study. The minimum interval between the initial and the current examination was 3 weeks. The IOP-values of the fellow eyes in this subgroup were assessed in parallel.

Results

The difference DCT-GAT was 2.44?±?0.4 SEM mmHg in the subgroup of the 23 right eyes and 2.03?±?0.5 SEM mmHg for the fellow eyes, compared to 0.94?±?0.5 SEM mmHg in the initial sample of 100 eyes.

Conclusions

In cases with higher difference between DCT-GAT, the difference is reproducible and even present in the fellow eye. We, therefore, assume that the differences are not caused by chance, but by differing biomechanical corneal properties.     

Characterization of the thickness of different corneal zones in glaucoma: effect on dynamic contour,Goldmann and rebound tonometries

Purpose: To characterize five models of corneal thickness circular zoning in a sample of healthy controls and a sample of patients with primary open‐angle glaucoma (POAG) and to determine their effect on Goldmann (GAT), dynamic contour (DCT) and rebound tonometers (RT). Methods: The study participants were 122 controls and 129 cases. Five corneal thickness zoning models (A, B, C, D and E) were constructed. The partitioning pattern consisted of a circle centred at the corneal apex and several concentric rings, until the limbus; the contours of each ring followed the geometry of the corneal contour of each participant. In Model A, the central circle was 1 mm in diameter and five concentric rings were established. Mean was obtained for each zone for both samples and compared between them using a t‐test. The effect on the tonometers of central cornel thickness (CCT) and mean thickness of the zones generated was determined through several linear regression models (one per tonometer and per sample). Results: According to a t‐test, cases and controls differ in zones I [mean difference (MD): 17.93 μm], V (MD: 25.52 μm) and VI (MD: 31.78 μm) of model A (higher values in the cases sample). RT was affected by CCT (controls: B = 0.089; cases: B = 0.081). DCT was affected by zone IV of model A (controls: B = ?0.029; cases: B = ?0.012). GAT was affected by CCT (controls: B = 0.043; cases: B = 0.025) and zone III of model A (controls: B = ?0.045; cases: B = ?0.033). Conclusion: Our results highlight the importance of the thickness of other regions of the cornea different from its main centre in discriminating between healthy controls and patients with POAG and in IOP measurements made using DCT, GAT and RT.     

Comparison of tonometry with the Keeler air puff non-contact tonometer "Pulsair" and the Goldmann applanation tonometer

Intraocular pressure (IOP) readings were performed with the Keeler Air-Puff Non-Contact Tonometer "Pulsair" in 126 patients before (NCT1) and after (NCT2) applanation-tonometry with the Goldmann device (GAT). For the whole population of 126 patients, in each of whom only one eye was selected, there was a significant difference of the mean IOP measurement, but the difference between the two measurement methods was only slightly significant when the NCT was applied before the GAT, and highly significant vice versa. Also the variation of the NCT-measurements was significantly larger than that for the GAT, while the before- and after GAT measurements had equal variations. If only the measurements under 18 mmHg mean GAT are taken into account (n = 101), the difference between GAT and NCT1 was not significant (p = 0.437), as opposed to the GAT-measurements above 18 mmHg, where a highly significant difference between the means was found (p = 0.0033). In most cases, the IOP-readings were underestimated using NCT. The Non Contact Tonometer "Pulsair" could be used for IOP-readings in patients with increased risk of infection, as well as in those with known allergic reactions to topical anesthetic agents, with poor or absent fixation ability, with corneal edema, and postoperative after anterior-segment surgery. The possibility of IOP-measurement in a reclined position is a true advantage of the Non-Contact Tonometer presented here. A measuring strategy for the above-mentioned applications is presented.     

Effects of central corneal thickness,central corneal power,and axial length on intraocular pressure measurement assessed with goldmann applanation tonometry

Purpose  To determine the effects of central corneal thickness (CCT), central corneal power (CCP), and axial length (AL) on the measurement of intraocular pressure (IOP) using Goldmann applanation tonometry, and the effects of CCP and AL on CCT. Methods  Charts of 147 consecutive patients undergoing preoperative examinations for cataract surgery between April 2006 and April 2007 in our clinic were reviewed retrospectively. CCT, CCP, and AL were measured by ultrasonic pachymeter (Micropach Model 200P, Sonomed, Lake Success, N.Y. USA), autorefractokeratometer (KR 8800, Topcon, Tokyo, Japan), and ultrasound biometry (EZ Scan AB 5500+ Sonomed, Lake Success, N.Y. USA). Pearson correlation analysis and multiple linear regression analysis were used as indicated, and only one eye of each subject was included in the statistical analysis. Results  Ninety-eight eyes of 98 patients were included in the study. IOP and CCT were significantly and positively correlated (P < 0.001), and CCT and CCP (P = 0.001) were inversely correlated. Multiple regression analysis showed that the effect of CCT on IOP was statistically significant (P < 0.001), but the effects of CCP and AL on IOP were not significant (P = 0.614, P = 0.831, respectively). IOP increased by 0.29 mmHg for each 10 μm increase in CCT. Conclusions  CCT, but not CCP or AL, significantly affected IOP readings obtained by Goldmann applanation tonometry. The effect of CCP on IOP was weak and not significant despite the significant inverse correlation between CCT and CCP.     

非接触式眼压计与Goldmann压平眼压计测量眼压的比较

目的 :比较非接触式眼压计 ( NCT)和 Goldm ann压平眼压计测量眼压的差异。方法 :对 112例 ( 2 2 0眼 )志愿者分别进行 NCT和 Goldmann压平眼压计眼压测量及中央角膜厚度测量 ,并对其中 16 8眼进行自动验光检查。结果 :NCT和 Goldmann眼压计眼压测量值分别为 1.98± 0 .6 9k Pa和 2 .34± 0 .77k Pa。 NCT眼压测量值较 Goldmann眼压测量值偏低 0 .36± 0 .37k Pa( P<0 .0 5 )。眼压在 1.33～ 2 .6 7k Pa内 ,二种眼压计测量眼压值偏差最小。角膜厚度和眼球屈光度与 NCT眼压测量值分别呈明显正相关和负相关。结论 :NCT眼压测量值较Goldmann眼压测量值偏低 ,NCT眼压值为临界眼压时 ,应应用 Goldm ann压平眼压计校正     

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.     

Effects of central corneal thickness and corneal curvature on the intraocular pressure measurement by Goldmann applanation tonometer and ocular blood flow pneumatonometer

PURPOSE: To assess the effects of central corneal thickness (CCT) and corneal curvature (CC) on the measurements of intraocular pressure (IOP) using Goldmann applanation tonometer (GAT) and the ocular blood flow pneumatonometer (OBFT). METHODS: 104 patients were recruited from a glaucoma clinic. The CCT was measured using ultrasound pachymetry and the mean radius of CC using a keratometer. The IOP of each eye was measured using both GAT and the OBFT in a random order. Right eyes only were analysed for statistical purposes. RESULTS: The mean (+/-SD) IOP by GAT and OBFT was 18.2 mmHg (+/-4.4) and 18.2 mmHg (+/-4.0), respectively, with no statistically significant difference. IOP measurement with both instruments varied with CCT and CC. GAT showed an IOP increase of 0.40 mmHg per 10 microm increase of CCT and OBFT showed an increase of 0.38 mmHg in IOP per 10 microm increase of CCT. Multiple regression analysis showed that the effect of CCT was statistically significant (P<0.001) on IOP recorded by both the GAT and OBFT but CC did not have a statistically significant effect on IOP recordings performed by either technique. CONCLUSION: IOP measurements by GAT and OBFT are positively correlated with CCT with both tonometers being similarly affected. There was no significant correlation between CC and IOP measured by either tonometer.     

Effect of central corneal thickness on intraocular pressure and comparison of Topcon CT‐80 non‐contact tonometry with Goldmann applanation tonometry

Background

To compare intraocular pressure (IOP) measurements obtained with the Topcon CT‐80 non‐contact tonometer (NCT) and Goldmann applanation tonometer (GAT), in different ranges of IOP in normal and glaucoma subjects, and to assess the influence of central corneal thickness (CCT) on the IOP measurements in Asian Indian eyes.

Methods

Four hundred and two eyes of 402 subjects (193 newly diagnosed primary open angle glaucoma [POAG] and 209 normal) were enrolled for this prospective study. For each eye, IOP was measured with GAT by a glaucoma specialist and NCT by a trained optometrist. The IOP values were compared among the tonometers in the three different IOP ranges (≤ 12 mmHg, 13–20 mmHg and ≥ 21 mmHg) using Bland–Altman graphs. Correlation between GAT and NCT was assessed by Pearson correlation co‐efficient. CCT was measured with ultrasound pachymetry and its correlation with GAT and NCT was analysed using linear regression analysis.

Results

The mean paired difference of IOP between NCT and GAT was 1.556 ± 2.69 mmHg (r = 0.26, p = 0.006) at IOP range of ≤ 12 mmHg, ?1.665 ± 2.6 mmHg (r = 0.51, p < 0.0001) in IOP range of 13–20 mmHg and ?2.202 ± 3.44 mmHg (r = 0.82, p < 0.0001) in the IOP range of ≥ 21 mmHg. Linear regression analysis showed a mean IOP variation of 0.27 mmHg per 10 μm change in CCT for NCT (p < 0.0001) and IOP change of 0.19 mmHg per 10 μm change in CCT for GAT (p = 0.01).

Conclusion

In this study of normotensive and POAG subjects, the Topcon CT‐80 NCT showed an overestimation of IOP at the lower range and underestimation of IOP in normal and higher ranges of IOP. Clinicians should keep in mind that CCT influences IOP measurement with both types of tonometer and that the IOP readings obtained with these tonometers are not interchangeable.

     

Performance of the rebound,noncontact and Goldmann applanation tonometers in routine clinical practice

Purpose: To compare rebound tonometry (RBT) and noncontact tonometry (NCT) using Goldmann applanation tonometry (GAT) as reference. Methods: The study sample was comprised of 108 eyes of 108 subjects consecutively examined at a general ophthalmology clinic. The order of use of the three tonometers was randomized at the study outset. The difference between the methods was plotted against the mean to compare the tonometers. The hypothesis of zero bias was examined by a paired t‐test and 95% limits of agreement (LoA) were also calculated. Differences with respect to GAT were assessed according to the international standard for ocular tonometers (ISO 8612). Results: Mean intraocular pressures (IOPs ± SD) obtained using the three instruments were GAT 17.5 ± 3.8 mmHg; RBT 18.5 ± 5.5 mmHg and NCT 17.4 ± 5.6 mmHg. The 95% LoA were from ?7.9 to +7.7 mmHg for NCT–GAT and from ?6.8 mmHg to +8.7 mmHg for RBT–GAT. A difference with respect to GAT under ±1 mmHg was observed in 11.1% of the eyes measured by NCT and 18.5% of eyes measured by RBT. According to the IOP ranges established by the ISO 8612, differences from GAT measurements greater than ±5 mmHg were always above the accepted level of 5%. Correlations between IOP and central corneal thickness (CCT) were significant for all three tonometers. Conclusions: The rebound and noncontact tonometer behaved similarly when used to measure IOP taking GAT measurements as the reference standard. Neither tonometer fulfilled ISO 8612 requirements. Both were similarly influenced by CCT.     

中央角膜厚度、角膜曲率对Goldmann压平眼压计和非接触眼压计测量结果的影响

目的 探讨中央角膜厚度和角膜曲率对Goldmann压平眼压计(GAT)和非接触眼压计(NCT)测量结果 的影响.方法 比较性研究.选择120例门诊患者作为研究对象.应用超声角膜测厚仪测量患者中央角膜厚度,采用多功能验光仪测量角膜曲率,应用GAT和NCT测量受检者双眼眼压.应用SPSS 12.0统计学软件进行数据处理.采用直线回归法比较两种眼压计的测量结果 ,采用多重线性同归法分析中央角膜厚度、角膜曲率与两种眼压计所测眼压值的关系,应用Bland-Altman法比较NCT和GAT两种方法 对眼压测最结果 的影响.结果 GAT与NCT测量的平均眼压值分别为(18.4±4.0)mm Hg(1 mm Hg=0.133 kPa)和(17.0±4.6)mm Hg,差异有统计学意义(r=0.835,P=0.000).GAT和NCT测量的眼压值均受中央角膜厚度和角膜曲率的影响.中央角膜厚度每增加1μm,GAT测量眼压值增加0.039 mm Hg,而NCT测量眼压值增加0.064 mm Hg.角膜曲率半径每增加1 mm,GAT测最眼压值减少2.648 mm Hg,NCT测量眼压值减少3.190 nun Hg.中央角膜厚度对NCT测量眼压值的影响较其对于GAT测量眼压值的影响大.随着眼压的升高,NCT测最眼压值呈现出由低于GAT测量值到高于GAT测量值的逐渐变化趋势.结论 中央角膜厚度和角膜曲率均会影响NCT和GAT测量眼压值,而且中央角膜厚度对NCT测量眼压值的影响较其对GAT测量眼压值的影响大.     

动态轮廓眼压计监测LASIK手术前后眼压变化

目的比较动态轮廓眼压计(DCT)、Goldmann压平式眼压计(GAT)及非接触式眼压计(NCT)测量接受准分子激光原位角膜磨镶术(LASIK)患者眼压值的差异。设计前瞻性临床试验研究。研究对象接受LASIK治疗的近视患者70例(140眼)。方法对上述患者于术前、术后1周,1、6个月用三种不同眼压计分别测量眼压,比较各时间点、各种眼压计之间的差异。同时记录手术前、后中央角膜厚度,取其两者差为角膜切削深度的值。主要指标眼压值(IOP)和角膜切削深度。结果术后1周,1、6个月DCT测量值(16.74±1.96mmHg、16.67±1.90mmHg、16.42±2.12mmHg)与其术前值(17.36±2.32mmHg)比较差异无统计学意义(F=1.346,P=0.06)。术后GAT和NCT测量值均呈下降趋势,与术前测量值比较差异有统计学意义(GAT:F=101.217,P=0.000;NCT:F=171.466,P=0.000),并且下降值与角膜切削深度成正相关关系(GAT:r=0.86,P=0.000;NCT:r=0.87,P=0.000),但术后三个时间段测量值比较差异无统计学意义(GAT术后三个时间点q值为0.216、0.677、0.461,P值分别为0.461、0.097、0.117;NCT术后三个时间点q值为0.215、0.585、0.370,P值分别为0.436、0.436、0.100)。结论LASIK术后GAT和NCT测量值明显下降,而DCT测量值无显著变化,其测量值较前两者更为可靠。(眼科,2007,16:344-347)