Transpalpebral measurement of intraocular pressure using the Diaton tonometer versus standard Goldmann applanation tonometry

Background  

Diaton transpalpebral tonometry is a new version of TGDc-01 transpalpebral tonometry. The aim of this study is to evaluate the reliability of this method, and to compare the results with those of corrected Goldmann applanation tonometry (c-GAT), which is the “gold standard” for the clinical measurement of IOP.     

Comparison of intraocular pressure measurements with the digital tonometer TGDc-01 'PRA' and the Goldmann applanation tonometer

BACKGROUND: To compare intraocular pressure (IOP) measurements obtained with the digital tonometer TGDc-01 'PRA' with those from a Goldmann applanation tonometer (GAT). METHODS: The IOP in 176 eyes of 88 healthy volunteers was measured prospectively in a sitting position. One single measurement, generated by the TGDc-01 PRA, was compared with a single reading from the GAT. RESULTS: Mean IOP values were 13.0 +/- 3.7 mm Hg for the TGDc-01 PRA (range, 4-22 mm Hg) and 14.9 +/- 3.2 mm Hg for the GAT (range, 8-27 mm Hg). The mean difference was 1.9 mm Hg with a standard deviation of 2.77 mm Hg, and this was statistically significant (p < 0.001, paired t test). CONCLUSIONS: In comparison to the GAT, the TGDc-01 PRA underestimated IOP on an average of 1.9 mm Hg. Only 50.6% of all measurements were within the +/-2 mm Hg difference range. Thus, the TGDc-01 PRA has no high coincidence degree with the GAT. Both methods were not equivalent.     

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.     

Deviations between transpalpebral tonometry using TGDc-01 and Goldmann applanation tonometry depending on the IOP level

Background Recent comparisons between transpalpebral tonometry using TGDc-01 and Goldmann applanation tonometry were performed in populations with IOPs between 10 and 20 mmHg. The purpose of this study was to evaluate device deviations depending on different IOP levels (range 5–40 mmHg).Methods A total of 68 eyes of 68 patients were included and assigned to four IOP levels according to an initial applanation tonometry assessment: level I, <10 mmHg (n=8); level II, 10–19 mmHg (n=20); level III, 20–29 mmHg (n=20); and level IV, 30 mmHg (n=20). Two independent and randomized observers performed three replicate measurements per eye—observer 1 using TGDc-01 tonometry, and observer 2 using Goldmann applanation tonometry. Intraindividual deviations between measurement results were investigated concerning clinical relevance by medians and quartiles, concerning statistical significance by pairwise sign tests; p values <0.05 indicate local statistical significance.Results In patients with initial IOP 20 mmHg, TGDc-01–based tonometry significantly underestimated the IOP as based on Goldmann applanation tonometry (p<0.001). This effect increased with increasing IOP: IOP level III median difference (TGDc-01 – Goldmann) –1.3 mmHg (interquartile range, –2.5, –0.4), IOP level IV median difference –2.7 mmHg (–3.7, –1.0). In patients with initial IOP <10 mmHg, an at least gradual underestimation by TGDc-01 tonometry (p=0.219; median difference, –0.6, –1.6, 0) was observed. A total 18% of patients showed device deviations >±3 mmHg, and even 35% of those patients with initial IOP 30 mmHg.Conclusions TGDc-01–based tonometry demonstrated an increasing underestimation of IOP with increasing IOP levels when compared with the current standard method of Goldmann applanation tonometry.     

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     

Ocular response analyzer versus Goldmann applanation tonometry for intraocular pressure measurements

PURPOSE: To establish correlations between intraocular pressure (IOP) measurements obtained with the ocular response analyzer (ORA) and the Goldmann applanation tonometer (GAT). The effects of central corneal thickness on the measures obtained were also examined. METHODS: This was a cross-sectional study. IOP was determined in 48 eyes of 48 patients with glaucoma In all patients, central corneal thickness (CCT) was measured by ultrasound pachymetry. RESULTS: ORA readings were consistently higher than GAT measurements (Goldmann-correlated IOP - IOP GAT mean difference, 7.2 +/- 3.5 mm Hg; corneal-compensated IOP - IOP GAT mean difference, 8.3 +/- 4.0 mm Hg) However, differences were not constant and increased with increasing IOP GAT readings, both with respect to Goldmann-correlated IOP (slope = 0.623, P < 0.0001) and corneal-compensated IOP (slope = 0.538, P < 0.0001). Both pressure measurements provided by the ORA showed significant correlation with CCT (CCT versus Goldmann-correlated IOP: r = 0.460, P = 0.001; CCT versus corneal-compensated IOP: r = 0.442, P = 0.001). No significant effects of corneal curvature or refraction on any of the pressures were observed. CONCLUSIONS: The ORA significantly overestimates IOP compared with the GAT. Differences between both sets of measures increase as the GAT-determined IOP increases. ORA readings seem to be affected by central corneal thickness.     

Reliability of intraocular pressure measurement with the Goldmann applanation tonometer in epidemiological studies

The reproducibility of intraocular pressure (IOP) measurement with the Goldmann applanation tonometer was investigated as part of a population-based epidemiological study. Sixty-two subjects were examined in a first measurement session. The IOP was measured three times consecutively in both eyes according to a fixed protocol. The mean standard deviation (SD) of these measurements was 0.8 mmHg. The mean intraobserver variation for the first measurement was 1.64 (SD 2.07) mmHg. For the median of the three measurements the intra-observer variation was 1.50 (SD 1.96) mmHg. The mean inter-observer values were 1.79 (SD 2.41) mmHg for the first measurement and 1.60 (SD 2.15) mmHg for the median measurement. The correlation coefficient between the median values of the three measurements of both observers was 0.81. No systematic differences were found between the two observers. Using the median value of three consecutive measurements reduced the inter-observer variation by 11% and the intra-observer variation by 9% compared with a single measurement.     

Pressure phosphene tonometry versus Goldmann applanation tonometry for measuring intraocular pressure before and after LASIK

PURPOSE: To compare pressure phosphene tonometry with Goldmann applanation tonometry for measuring intraocular pressure (IOP) before and after LASIK. METHODS: Forty-three (18 men and 25 women) consecutive healthy patients underwent complete pre- and postoperative LASIK ophthalmologic assessments including manifest and cycloplegic refraction, keratometry, and central corneal thickness. Three repetitive sets of pressure phosphene tonometry and Goldmann applanation tonometry measurements were performed the day before and 3 months following uneventful LASIK. RESULTS: Mean preoperative spherical equivalent refraction was -4.70 +/- 2.50 diopters (D) (range: -1.50 to -12.90 D) and mean preoperative keratometry was 43.95 +/- 1.08 D. After LASIK, spherical equivalent refraction was +0.23 +/- 0.11 D and mean keratometry was 39.46 +/- 2.28 D. Preoperative pressure phosphene tonometry (12.16 +/- 1.58 mmHg) and Goldmann applanation tonometry (12.01 +/- 1.55 mmHg) IOP measurements were similar. Postoperative IOP was 10.30 +/- 1.16 mmHg with Goldmann applanation tonometry and 12.20 +/- 1.62 mmHg with pressure phosphene tonometry. The postoperative IOP difference between Goldmann applanation tonometry and pressure phosphene tonometry was 0.15 +/- 1.12 mmHg (P = .41). The mean change in pachymetry after LASIK was 68.73 +/- 73 microm. The change in Goldmann applanation between preoperative and postoperative LASIK values was 1.71 +/- 1.43 mmHg (P < .0001), a change that was strongly correlated with changes in corneal thickness (R = 0.75, P < .0001) and keratometry (R = 0.72, P < .0001). No such correlations were found with pressure phosphene tonometry. CONCLUSIONS: Goldmann applanation tonometry-measured IOP decrease after LASIK is strongly correlated with a decrease in central corneal thickness and changes in keratometry, whereas pressure phosphene tonometry-measured IOP is independent of corneal thickness. Pressure phosphene tonometry appears to be a more reliable method for recording tonometry in these patients.     

Effect of corneal astigmatism on intraocular pressure measurement using ocular response analyzer and Goldmann applanation tonometer

Purpose  

To assess the effect of corneal astigmatism on intraocular pressure (IOP) measurements using an Ocular Response Analyzer (ORA) and a Goldmann applanation tonometer (GAT).     

新型非接触式眼压分析仪ORA与Goldmann压平眼压计的比较

目的比较新型非接触式眼压分析仪ORA与Goldmann压平式眼压计测量眼压的差异,以评价ORA眼压测量仪在临床眼压测量中的应用价值。方法本院门诊127例237眼分别由专人进行非接触眼压测量仪ORA与Goldmann压平式眼压计测量,并同时用超声角膜测厚仪测量角膜厚度。结果127例病人237眼,Goldmann压平眼压值和ORA直接测量结果（IOPG）分别为（17.94±6.50）mmHg和（18.88±7.93）mmHg,两者比较差异有显著统计学意义（P=0.000）;正常人群平均角膜厚度为（546.19±36.34）μm,经角膜厚度-眼压公式校正IOPG平均值为17.42±3.92mmHg,ORA经自带软件处理后的眼压值（IOPcc）平均为（17.50±4.38）mmHg,两者比较差异无统计学意义（P=0.681）,IOPG校正前两者比较差异有统计学意义（P=0.024）。结论新型非接触式眼压分析仪ORA的直接测量值与Goldmann压平眼压计的测量值相近略高,ORA的测量分析值IOPcc是排除角膜因素影响更接近真实的眼压结果。     

Icare回弹式眼压计与Goldmann压平眼压计眼压测量结果的比较

背景Icare回弹式眼压计作为一种新式眼压计,有必要对它的临床应用价值进行评估。目的通过比较分析Icare回弹式眼压计和Goldmann压平眼压计（GAT）的眼压测量结果,探讨Icare的临床价值。方法可疑青光眼、青光眼、屈光不正及部分健康体检者78例共152眼同时接受Icare、GAT眼压测量,受检眼先行Icare测量,然后再进行GAT测量,2次测量间隔3～5min。对比分析两种眼压计的测量结果。结果使用Icare和GAT测得的眼压均值分别为（19．16±5．03）mmHg和（18．41±4．52）mmHg,96眼（63．2％）两者的眼压差值≤1mmHg,二者的测量值差异虽有统计学意义,但二者的变化呈明显正相关（r=0．940,P〈0．01）。当Icare眼压测量值〈16mmHg时,Icare的眼压测量值低于GAT,而当Icare眼压测量值≥16mmHg时恰好相反;CCT偏薄、正常以及偏厚的情况下,Icare的眼压测量值均高于GAT的眼压测量值。Icare、GAT的眼压测量值和CCT间呈正相关（r=0．341,P〈0．01;r=0．333,P〈0．01）。结论与GAT眼压计比较,Icare回弹式眼压计易操作,测量结果可靠,临床实用性更强。     

Goldmann压平眼压计与非接触式眼压计测量眼压的对比研究

目的:比较Goldmann压平眼压计(Goldmannapplanationtonometer,GAT)与非接触眼压计(non-contacttonometer,NCT)测量眼压的差异,以评价NCT与GAT测量的相关性。方法:对265例志愿者(529眼)分别采用Goldmann压平眼压计与非接触眼压计测量眼压。结果:非接触眼压计的测量结果低于Goldmann压平眼压计,且差异有显著性(19.13vs23.43,t=22.644,P<0.01),随眼压值的升高,两者相差幅度增大,差异在眼压〉30mmHg时更为明显,但相关系数逐渐变小。结论:非接触眼压计眼压测量值较Goldmann眼压测量值偏低,非接触眼压计眼压值为临界眼压时,需应用Gold-mann压平眼压计校正,以便及时发现病理性眼压升高,避免青光眼的漏诊和失治。     

The validity of a digital eyelid tonometer (TGDc-01) and its comparison with Goldmann applanation tonometry – a pilot study

PURPOSE: To determine the intra- and inter-examiner repeatability of a new eyelid tonometer, and its agreement with Goldmann applanation tonometry (GAT). MATERIALS AND METHODS: Forty normal subjects were recruited and their intraocular pressure was measured by two examiners using the eyelid tonometer. Examiner 1 carried out the first set of measurement, followed by examiner 2, and then examiner 1 again. Finally, a third examiner was responsible for GAT measurement. Five readings were obtained from the eyelid tonometer by each examiner each time and were masked, and three readings were obtained from GAT. The mean readings from the eyelid tonometer and GAT were used for analysis. RESULTS: The intra-examiner repeatability for the eyelid tonometer was better (around +/-5 mmHg 95% of the cases) than the inter-examiner repeatability (around +/-8 mmHg 95% of the cases). The mean difference between the eyelid tonometer and GAT was small from examiner 1 (<0.5 mmHg). However, the limits of agreement were greater than the clinically acceptable level of +/-3 mmHg. Examiner 2 gave an even greater difference from GAT. CONCLUSIONS: Similar to other recent studies, we have found that this eyelid tonometer does not provide good agreement with GAT. Different examiners could position the instrument differently and this eyelid tonometer is suggested for screening purposes only.     

Clinical comparison of the Icare tonometer and Goldmann applanation tonometry

PURPOSE: To compare a new method of intraocular pressure (IOP) measurement, using the Icare tonometer, with Goldmann applanation tonometry (GAT). PATIENTS AND METHODS: Two observers obtained IOP readings in 292 eyes (143 right and 149 left) of 153 subjects, using the Icare without topical anesthetic. A GAT reading was subsequently obtained by a consultant ophthalmologist, without the knowledge of the Icare readings. Central corneal thickness (CCT) was obtained on all eyes with ultrasound pachymetry. Patient comfort after IOP measurement was assessed in a consecutive subset of patients. RESULTS: The intraclass correlation coefficient between the 2 modalities of IOP measurement was r=0.95 for the right and r=0.93 for the left eye. The mean difference (Icare-GAT) between the IOP measured by the 2 methods was 0.4 mm Hg in the right eye (SD 3.0, 95% confidence interval -5.5 to 6.3), and 0.8 mm Hg in the left eye (SD 3.0, confidence interval -4.7 to 6.2). GAT measurements did not vary with CCT [correlation coefficient=0.09 (P=0.25) right and 0.14 (P=0.09) left eyes]. However, IOP measured with Icare tonometry increased with increasing CCT [correlation coefficient=0.16 (P=0.05) right and 0.21 (P=0.01) left eyes]. For every 100-microm increase in CCT, the difference (Icare-GAT) increased by 1 mm Hg. Of the 38 consecutive patients surveyed, 28 (73.7%) rated the Icare more comfortable than GAT, with only 2 (5.3%) rating it less comfortable (P<0.001). CONCLUSIONS: There is good correlation between the 2 methods of IOP measurement, even at extremes of IOP. The Icare instrument was easy to use and recorded rapid and consistent readings with minimal training. It seems to be more comfortable than GAT and obviates the need for topical anesthesia.     

Intraocular pressure difference in Goldmann applanation tonometry versus Perkins hand-held applanation tonometry in overweight patients

Objective

To analyze the increase in intraocular pressure (IOP) caused by anatomic and physiologic factors in overweight patients when using Goldmann applanation tonometry.

Design

A prospective cohort study.

Participants

Seventy average-weight individuals who had no difficulties with IOP measurements at the slit lamp and 12 obese patients with suspected glaucoma who could position the head at the slit lamp only with great effort participated.

Intervention

The authors compared IOP values between slit-lamp-mounted Goldmann applanation tonometry and Perkins hand-held tonometry.

Main outcome measure

The difference in Goldmann and Perkins IOP measurements was examined.

Results

In the group of obese patients, the mean IOP was 20.9 ± 2.28 mmHg (mean ± standard deviation; range, 18–26 mmHg) for the right eye and 21.4 ± 3.16 mmHg (range, 16–28 mmHg) for the left eye when determined by Goldmann tonometry and 16.3 ± 2.39 mmHg (range, 13–20 mmHg) for the right eye and 16.3 ± 2.42 (range, 11–19 mmHg) for the left eye when determined by Perkins tonometry. The mean decrease was 4.5 ± 1.3 mmHg (range, 3–7 mmHg) for the right eye and 4.9 ± 1.9 mmHg (range, 2–9 mmHg) for the left eye. In the control group, the mean difference between the two types of tonometers for the right eye was 0.34 ± 0.69 mmHg and for the left eye was 0.33 ± 0.82 mmHg. Patients who had a falsely elevated IOP on Goldmann tonometry had an average body mass index of 34 ± 3.82 (range, 28.5–41.9); most were female (5:1 ratio).

Conclusion

The authors believe simultaneous breath-holding and thorax compression, with subsequent increase in venous pressure, may be a causative factor for transitory elevations of IOP. Perkins tonometry in obese patients may help avoid a false diagnosis of glaucoma caused by transitory elevations in IOP.     

Level of disagreement between Proview phosphene tonometer and Goldmann applanation tonometer intraocular pressure readings

PURPOSE: To evaluate the agreement of intraocular pressure (IOP) readings obtained with the Proview phosphene tonometer and those obtained by Goldmann applanation tonometry as well as the effect of regular use of the Proview on patients' anxiety about their glaucoma. METHODS: One hundred thirty-five consecutive patients with glaucoma, 35 designated as controls, were enrolled in a 10-month randomized prospective clinical trial. The study patients but not the controls used the Proview outside the office. At office visits IOP was measured by an ophthalmologist with the Goldmann applanation tonometer (GAT) as well as by examiners and patients using the Proview. Patients in the treatment group (n = 100) were asked to measure and record their IOP at home as well. Using ANOVA, we examined the relationship between demographic variables and the level of agreement between the Proview readings and those measured by GAT at the final office visit. All participants also were asked to complete a questionnaire regarding their anxiety about their IOP at the baseline and final office visits. The primary outcome measure was the level of agreement of the Proview measurements with those obtained by GAT. Secondary outcome measures included patients' anxiety about their glaucoma. RESULTS: The absolute mean difference between GAT and Proview readings at the final visit was 3.5 +/- 2.9 mm Hg (median, 2.8 mm Hg). The treatment group reported significantly less anxiety about their glaucoma after 4 to 6 weeks of using the Proview (P = .024). CONCLUSIONS: There was considerable discrepancy between Proview and GAT readings. However, regular use of the Proview tonometer significantly reduced patients' anxiety about their glaucoma.     

动态轮廓眼压计与Goldmann压平眼压计及非接触眼压计测量眼压的对比研究

目的探讨动态轮廓眼压计(DCT)与Goldmann压平眼压计(GAT)及非接触眼压计(NCT)测量眼压的准确性,并比较三种眼压计测量结果与中央角膜厚度(CCT)的相关性。设计前瞻性、比较性病例系列。研究对象连续选取90例(90眼)10~76岁正常人。方法采用KONAN非接触式角膜内皮镜测量CCT后,对所有入选者单眼以随机顺序采用Pascal型DCT、GAT及Topcon型NCT测量眼压。测量结果两两比较,并将眼压值与CCT进行直线回归分析。主要指标眼压值,Pearson相关系数。结果 90例正常人DCT眼压平均值(17.33±2.71 mm Hg)明显高于GAT(14.27±2.81 mm Hg)(P=0.000)及NCT(14.67±2.93 mm Hg)(P=0.000),平均差异分别为(3.06±2.01)mm Hg和(2.67±2.20)mm Hg;GAT与NCT之间平均差异为(-0.39±2.29)mm Hg(P=0.105)。DCT与GAT眼压值之间相关系数r=0.736(P=0.000);与NCT眼压值之间相关系数r=0.699(P=0.000)。GAT、NCT眼压值与CCT均明显相关(r=0.370,P=0.000;r=0.508,P=0.000);DCT眼压值与CCT无明显相关性(r=0.051,P=0.639)。DCT和GAT的差值与年龄无明显相关性(r=0.064,P=0.052)。结论 DCT测量的眼压值虽高于GAT及NCT,但不受CCT的影响,可能较GAT和NCT测量的眼压值更接近真实值。     

Transpalpebral tonometer for measuring intraocular pressure

Two new portable instruments--an ophthalmotonometer (TGDc-01) and a pressure indicator (IGD-02)--which make it possible to measure the intraocular pressure (IOP) through the eyelid, were worked out. The operation of both instruments is based on determining the acceleration of freely falling rod after its interaction with the elastic eye surface. The readings of TGDc-01 correlate with the genuine IOP, and those of IGD-2--with the tonometric pressure for Maklakov's tonometer with a weight of 10 g. The accuracy of both instruments is sufficient for clinical purposes; there is no need to use anesthetics or to sterilize the instruments, which are easy in usage. They can be used not only in ophthalmologic examination rooms but also at home.     

Comparison of intraocular pressure measured by Pascal dynamic contour tonometry and Goldmann applanation tonometry

AIMS: To compare the intraocular pressure (IOP) measurements obtained using the Pascal dynamic contour tonometer (PDCT) with the standard Goldmann applanation tonometer (GAT) and to correlate these with central corneal thickness (CCT) in patients with normal corneas. METHODS: A prospective, masked, comparative case series of 116 eyes from patients attending a glaucoma clinic. IOP was measured with PDCT by one examiner and with GAT by a masked, independent examiner. A mean of six CCT readings was used for analysis. RESULTS: IOP measured by the two instruments correlated significantly (r=0.77; P<0.0001). IOP measured by GAT correlated strongly with CCT (r=0.37, P=0.0001) whereas the relationship between IOP measured by PDCT and CCT approached significance (r=0.17, P=0.073). The differences between GAT and PDCT measured IOP also correlated strongly with CCT (r=0.37, P<0.0001). The 95% limits of agreement between GAT and PDCT were +/-4.2 mmHg. Dividing the eyes into three groups on the basis of CCT, demonstrated those in the thickest tertile showed a poorer agreement between instruments and the GAT measured significantly higher IOP in this group (P=0.003) while the PDCT showed no significant differences with different CCTs (P=0.37). CONCLUSION: Demonstration of the relative independence of PDCT IOP measurements from CCT supports a potential clinical role for this instrument, particularly for subjects with CCT outside the normal range.