Measurement of the intraocular pressure with the “transpalpebral tonometer” TGDc-01 in comparison with applanation tonometry

Background An irregular corneal surface compromises IOP measurement by Goldmann applanation tonometry. In such cases accurate measurement without corneal contact would be desirable. The new eyelid tonometer TGDc-01 measures IOP without corneal contact through the eyelid. The aim of the study was to evaluate the accuracy of the eyelid tonometer compared with Goldmann applanation tonometry (cornea thickness-corrected values) in subjects without corneal alterations.Methods IOP was measured in 199 eyes of 103 subjects without corneal alterations by means of two different methods. Measurements with the transpalpebral tonometer TGDc-01 and the Goldmann applanation tonometer were performed within 5 min in random order.Results The mean difference between lid tonometry and Goldmann applanation tonometry was 0.71 mmHg, SD ±2.467 mmHg. In the reliability analysis the intraclass correlation coefficient was 0.8620. Compared with Goldmann applanation tonometry 66.4% of the IOP readings measured by lid tonometry were in an interval of ±2 mmHg, 81.0% in an interval of ±3 mmHg. The maximum of deviation was –6 mmHg and +6 mmHg, respectively. The Bland and Altman plots are shown.Conclusions Lid tonometry correlates sufficiently with Goldmann applanation tonometry, but in more than 10% of the measurements the IOP readings differed by more than 3 mmHg. The eyelid tonometer may be helpful as a screening tool when Goldmann applanation tonometry is not applicable.     

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.     

Prospective comparison of the new indentation tonometer TGdC-01, the non-contact tonometer PT100 and the conventional Goldmann applanation tonometer

BACKGROUND: This study aimed to compare the results of newer tonometric techniques with standard tonometry for the examples of the Goldmann applanation tonometry (GAT), the indentation tonometer "TGDc-01" and the non-contact tonometer "PT 100". PATIENTS: The study was conducted on a total of 52 healthy subjects. The IOP was measured in each subject on both eyes with all three methods. There were 27 males (51.9 %), 25 females (48.1 %) with an average age of 28.5 years, with a minimum of 13 and a maximum of 79 years. RESULTS: There was no statistically significant difference between the non-contact and the Goldmann applanation tonometry. The measurements were 0.4 mmHg lower, no difference for the left or right side was seen. For IOP higher than 15 mmHg - 0.88 mmHg lower and for IOP lower 15 mmHg - 0.15 mmHg. The results for the "TGDc01" were 0.82 mmHg lower than GAT, the standard deviation was a little higher with 2.9 mmHg compared to 2.67 mmHg for GAT. For IOP higher than 15 mmHg they rose up to - 2.28 mmHg, for IOP lower than 15 mmHg the results for "TGDc-01" were only - 0.2 mmHg lower. There was also an effect with respect to the side, on the right eye the difference was significant with 3.03 mmHg (p = 0.006), in contrast to the left eye with 2.69 mmHg (p = 0.235). For "TGDc01" the standard deviation was higher with 2.9 mmHg compared to 2.6 mmHg for "PT 100". CONCLUSIONS: The non-contact tonometer showed no clinical relevant difference compared with GAT for measuring IOP. The indentation tonometer showed differences for precision, for higher tension IOP the measurement was lower compared with GAT. There was also a significant side difference using the "TGDc-01".     

Transpalpebral measurement of intraocular pressure using the TGDc-01 tonometer versus standard Goldmann applanation tonometry

Background A recently developed digital tonometer for transpalpebral intraocular pressure (IOP) measurement, distributed by Corneal, Inc., allows the noninvasive measurement of IOP for screening purposes.Method We measured the IOP of 218 eyes in 109 patients of the Interdisciplinary Uveitis Center of the University of Heidelberg with intact corneal epithelium. IOPs were measured first with the TGDc-01 tonometer, and then by means of Goldmann tonometry. IOPs were recorded by two independent examiners. The mean of three measurements obtained with the TGDc-01 was taken, whereas only one measurement was performed with the Goldmann tonometer.Results The mean difference between the TGDc-01 and Goldmann measurements was 3.7 mmHg. The standard deviation of the differences was ±4.06 mmHg. Thus measurements acquired with the TGDc-01 may range 4.4 mmHg above or 11.8 mmHg below the values given by Goldmann tonometry.Conclusion The IOP values obtained with the TGDc-01 were in poor agreement with Goldmann tonometry. We found a higher variation as well as a bias towards lower IOP values with the TGDc-01. It is a question of clinical judgement as to how far these deviating measurements can be accepted for screening purposes. Because the IOPs obtained with the TGDc-01 are generally lower and less accurate than those obtained with the Goldmann tonometer we believe that the TGDc-01 is not a reliable tool for IOP measurement in clinical routine.This work was presented at the 101st meeting of the German Society of Ophthalmology, Berlin, 2003     

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.     

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.     

Clinical evaluation of the new TGDc-01 "PRA" palpebral tonometer: comparison with contact and non-contact tonometry.

PURPOSE: The TGDc-01 "PRA" (Ryazan State Instrument, Ryazan, Russia) tonometer is a new portable small-sized tonometer that measures intraocular pressure (IOP) through the eyelid. The purpose of this study is to assess the repeatability of the TGDc-01 IOP measurements by comparing them against those obtained with Goldmann tonometer and with those from Perkins applanation tonometer, Xpert (Reichert, Depew, NY) noncontact tonometer, and Tono-Pen XL (Medtronic Solan, Jacksonville, FL) digital tonometer. METHODS: Fifty-eight right eyes of 58 young subjects were measured with each of the tonometers. Noncontact tonometry was performed first, followed by Goldmann and Perkins applanation tonometer (in random order), digital Tono-Pen XL, and finally TGDc-01 tonometer (sitting and supine position). Correlation analysis was used to evaluate the relationship between the Goldmann tonometer and the remaining tonometers used in this study. Plotting the difference between the methods against mean was also done to compare the tonometers. The hypothesis of zero bias was examined by a paired t-test. The 95% limits of agreement (LoA) were also calculated. RESULTS: TGDc-01 showed no statistical difference between the IOP measurements obtained in sitting and supine positions. A poor relationship between the TGDc-01 and Goldmann tonometer was found (r = 0.173; p = 0.001). Although the mean differences between Goldmann and Tonopen XL, Xpert, and TGDc-01 IOP measurements were statistically significant, the wider 95% LoA was observed when comparing the Goldmann and TGDc-01 tonometers. Computation of the 95% LoA resulted in a wide bias range when comparing the TGDc-01 with all the tonometers used in this study. CONCLUSIONS: The TGDc-01 "PRA" tonometer was not comparable with the other techniques used in the study. The wide dispersion range of the values obtained shows low repeatability of the TGDc-01 for screening purposes. These results could be because of the technique of measurement and/or interindividual variables.     

Goldmann-Applanationstonometrie und dynamische Konturtonometrie

BACKGROUND: The aim of the study was to compare intraocular pressure (IOP) measurements between Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) during product certification according to the international requirements for ophthalmic instruments (tonometers, ISO 8612:2001). METHODS: The study included 160 eyes of 80 subjects. IOP measurements were performed four times consecutively on each instrument in randomized order. The difference of mean IOP measurements between GAT and DCT was analyzed. Furthermore, Bland and Altman analysis was performed to assess agreement between the instruments. RESULTS: The mean difference between DCT and GAT IOP measurements was 0.30+/-2.18 mmHg. At low to normal IOP values of 7-16 mmHg and higher IOP values of > or =23 mmHg, the difference between DCT IOP measurements and GAT IOP measurements increased in the opposite direction (1.44+/-1.59 mmHg and -1.47+/-2.57 mmHg). The Bland and Altman analysis revealed a fixed bias of -0.4+/-2.0 mmHg. CONCLUSIONS: The test tonometer DCT exceeds the requirements for the international standard for tonometers ISO 8612:2001. The results are valid for a central corneal thickness of 540+/-40 microm.     

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.     

Evaluation des mobilen TGDc-01-Tonometers und Vergleich mit dem Applanationstonometer nach Goldmann

PURPOSE: The aim of this study was to evaluate patients' acceptance and intraocular pressure (IOP) readings of a new digital mobile tonometer (TGDc-01) and compare it to Goldmann applanation tonometry.METHOD: Measurements repeated five times with the TGDc-01 and three times with Goldmann tonometry were performed in 100 eyes of 100 patients by two independent investigators. Patients' acceptance of both techniques was evaluated by a visual analogue scale (VAS).RESULTS: The mean IOP with the TGDc-01 yielded 15.4 mmHg for investigator 1 and 12.7 mmHg for investigator 2 (range: 4-43 mmHg). Results of the measurements with Goldmann tonometry showed 17.6 mmHg for investigator 1 and 17.3 mmHg for investigator 2 (9-42 mmHg). The IOP difference of the two tonometry methods was highly significant (p<0.001). The intraobserver variability was 29% for investigator 1 and 8% for investigator 2. Mean IOP values of the two investigators taken with the TGDc-01 differed significantly (p<0.01) from each other by a mean of 2.6 mmHg.CONCLUSIONS: The new mobile tonometer TGDc-01 is better accepted by patients but IOP values are significantly lower compared to Goldmann tonometry and variability is high. Regarding glaucoma diagnostics it seems to be less suitable than Goldmann tonometry.     

How does Central Cornea Thickness Influence Intraocular Pressure during Applanation and Contour Tonometry?

Background: Golmann applanation tonometry represents a well-established procedure for measuring intraocular pressure (IOP). This implies the necessity of an accurate measurement of IOP with the reference tonometer. One example is the contour tonometer Pascal with a measuring probe, adapted to the cornea geometry, for measuring the IOP and the ocular pulse amplitude. There is controversy of how strongly corneal thickness affects the measurement of IOP. We thus analysed, for a number of eyes, the correlation of IOP, as measured by two types of applanation tonometers and one contour tonometer and the central corneal thickness.Methods: In all 158 patient eyes were investigated in a clinical comparison of applanation tonometers AT 870 and Ocuton-A. The study was performed by a trained ophthalmologist and the comparison was in accordance with international standard ISO 8612. In addition, the corneal thickness in the vertex was repeatedly determined using an Oculus Pentacam. The potential effect of central corneal thickness on the IOP as measured by the mentioned tonometers was statistically evaluated by rank correlation analysis.Results: We found that the measured IOP values for the three investigated tonometers were not normally distributed. The central corneal thickness values, in contrast, measured on 158 eyes by means of an ultrasound pachymeter and additionally on 235 eyes by the Pentacam, obeyed a Gaussian distribution. For the correlation analysis of both parameters the Spearman linear rank correlation coefficient (r) was considered. We found a very weak (|r| < 0.2) correlation between central corneal thickness and IOP for all 3 tonometers. The softness of the correlation is also illustrated by a large standard deviation of the regression line. A comparison of the different devices for corneal-thickness measurements shows less variance and a smaller variation coefficient when the ultrasoundpachymeter AL-1000 is used.Conclusions: The measured values for IOP are only very weakly correlated to the central corneal thickness. For the 3 tonometer types studied there is no need to correct the indicated pressure values according to the central corneal thickness of the investigated eye. Clinical comparisons according to the ISO 8612 standard between a tonometer under test and a reference Goldmann applanation tonometer are always a time-consuming procedure. Additional measures to determine the central corneal thickness of every investigated eyes are dispensable.     

The iCare rebound tonometer: comparisons with Goldmann tonometry, and influence of central corneal thickness

Purpose:  To assess agreement between the iCare rebound tonometer and Goldmann tonometry and to assess the influence of central corneal thickness and the value of scleral rebound tonometer readings.
Methods:  Prospective single-centre cross-sectional study comparing iCare rebound tonometer (RT) intraocular pressure (IOP) readings taken from corneal and scleral locations to Goldmann applanation tonometer (GAT) readings in 100 subjects attending ophthalmology clinics.
Results:  There was a significant difference between RT and GAT, with RT tending to overestimate IOP. The mean difference between RT and GAT measurements was 3.36 mmHg. The mean difference between the log of RT and the log of GAT measurements was 0.2356, a ratio of 1.27 ( P  < 0.0001). A formula derived from a linear regression analysis suggested that a 10% increase in CCT increased the RT IOP reading by 9.9%. Scleral RT readings showed no relationship to GAT readings.
Conclusions:  The rebound tonometer cannot replace the Goldmann tonometer in the office setting given the wide limits of agreement between the two devices. Corneal rebound tonometer readings are influenced by CCT whereas scleral rebound tonometer readings are of no value.     

Clinical evaluation of a new tonometer on the basis of international standard ISO 8612

BACKGROUND: There is a continuous process of development of new tonometer types following different measurement principles on the tonometer market. A new tonometer working on the dynamic contour measurement principle is currently available for ophthalmologists. This device has special properties, since it determines the intraocular pressure as well as the ocular pulse amplitude. So far, clinical comparison measurements exist between the new tonometer Pascal and the applanation tonometer by Goldmann albeit without any reference to a standard. Besides, these measurements cover only a small pressure range between 7 mmHg and 23 mmHg which is not sufficient for medical diagnosis. PATIENTS AND METHODS: This new tonometer was investigated by clinical comparison measurements according to the currently valid international standard for human eye tonometers (ISO 8612). The tested tonometer determines the intraocular pressure without fluorescein. In an ophthalmogical hospital in Berlin the clinical comparison measurements were carried out by ophthalmologists on 127 patients according to the methods and criteria of the above-mentioned standard. A calibrated AT 870 from the Haag-Streit company served as reference tonometer. RESULTS: The different cornea surface geometries of individual eyes, the variation of tear liquid volume, and also the different elastic properties of the human eye due to a large variation in rigidity led to measurements of intraocular pressure by this tonometer with an excessively high number of outliers p (i) (i = 1, ..., 3) per group (p (1) = 16.28 %, p (2) = 8.85 %, p (3) = 15.69 %, 5.0 % outliers per group only are permitted for the differences method), which do not correspond to the requirements of the international standard for tonometers ISO 8612. This is also shown by application of total method of least squares of regression line (slope a = 0.964, interception b = 2.868 mmHg, standard deviation s (y) = 2.628 mmHg). CONCLUSIONS: The test of conformity of results of clinical comparison measurements to the international standard for tonometers ISO 8612 is the target of this work. The measurement results of the investigated tonometer are analysed and discussed according to this standard. Statements about the medical application of this medical measurement device for ophthalmologists are presented. According to the presented investigations the requirements of this international standard are not fulfilled by the tonometer Pascal.     

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.     

Comparison of the iCare rebound tonometer and the Goldmann applanation tonometer over a wide IOP range

Background The aim of this study was to compare the intraocular pressure (IOP) results measured by the iCare rebound tonometer with those obtained by the Goldmann applanation tonometer (GAT) over a wide range of IOP values. Furthermore, the comfort level of the iCare measurement was evaluated. Method The study included 75 eyes of 75 patients. The patients were divided into three groups (7–15 mmHg n = 25, 16–22 mmHg n = 25, 23–60 mmHg n = 25). The measurements were taken by two independent observers in a masked fashion. All patients were asked about discomfort during the iCare measurement. To establish the agreement between the two devices, a Bland-Altman analysis was performed. Results Overall, the 95% confidence interval of the differences between the two devices was −8.67 to 10.25 mmHg and in 62.7%, the iCare measurement was within ±3 mmHg of the GAT measurements. The distribution of the differences in IOP was similar, from 7–22 mmHg. In the higher IOP range (23–60 mmHg), however, the deviation was almost twice as large. The measurement with the iCare tonometer was well tolerated; 100% of the patients denied any discomfort. Conclusions The iCare tonometer is a mobile alternative to GAT in a low to moderate IOP range, but our findings show a greater deviation than previously reported. In high IOP values, measurements with the iCare tonometer do not correlate well with GAT.     

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.     

iCare iC100与Corvis ST测量眼压的重复性和一致性比较

目的：比较iCare iC100回弹式眼压计（iC100）和Corvis ST角膜生物力学分析仪（CST）测量眼压的重 复性和一致性，分析iC100测量的眼压与角膜生物力学特性的关系。方法：系列病例研究。本研究 于2020年6─10月在沈阳爱尔眼视光医院职工或白内障患者中招募志愿者50例（50眼），其中健康 眼23例（23眼），白内障患者27例（27眼）。分别使用CST、iC100和Goldmann压平眼压计（GAT）测量 眼压，每只眼睛连续测量3次，各眼压计测量眼压值分别记为bIOP、IOPiC100和IOPGAT。角膜生物力 学特征参数和中央角膜厚度（CCT）采用CST进行测量。使用组内相关系数（ICC）评价眼压计的重 复性；使用单因素方差分析及Bland-Altman分析比较眼压计的一致性；使用Pearson相关系数及简单 线性回归分析各眼压计与CCT的关系，使用Pearson相关系数或非参数Spearman分析角膜生物力学 参数与3种眼压计测量值的关系，使用多重线性回归分析iC100测量值与角膜生物力学特性的关系。 结果：bIOP、IOPGAT和IOPiC100分别为（14.79±1.73）、（14.46±2.00）、（14.18±2.80）mmHg，三者差异无 统计学意义。CST、GAT和iC100的眼压测量值可重复性较好（ICC=0.729、0.973、0.923，P<0.001）。 Bland-Altman分析表明，IOPiC100和bIOP、IOPGAT和IOPiC100、IOPGAT和bIOP之间具有良好的一致性。 IOPGAT、IOPiC100与CCT均存在正相关关系（R2 =0.122，P=0.013；R2 =0.183，P=0.002），bIOP与CCT无 相关性。bIOP、IOPGAT与IOPiC100均与第1次压平时间（TA1）、第1次压平时的硬度参数（SP-A1）、第 2次压平长度（LA2）、第2次压平速度（VA2）呈正相关（均P<0.05）；与第1次压平速度（VA1）、第2次 压平时间（TA2）、最大压陷时的变形幅度（HC-DA）、形变比例（DAR）、综合半径（IR）呈负相关（均 P<0.05）；与最大压陷的时间（HC-time）不相关。多元线性回归模型具有统计学意义（F=26.177， P<0.001，调整R2 =0.507），纳入模型的2个自变量DAR、TA2对IOPiC100的影响均有统计学意义（t=-4.341，P<0.001； t=-2.080，P=0.043）。结论：iC100的眼压测量值重复性良好，与GAT及Corvis ST眼压测量 值之间的一致性良好，并且受CCT影响。但与CCT相比，角膜生物力学特性对iC100的眼压测量值 影响更大。     

Comparison of iCare tonometer and Goldmann applanation tonometry in normal corneas and in eyes with automated lamellar and penetrating keratoplasty

Purpose

To compare intraocular pressure (IOP) measurements with Goldmann applanation tonometry (GAT) and iCare tonometry in normal and post-keratoplasty corneas and to assess the influence of central corneal thickness (CCT), corneal curvature (CC), and corneal astigmatism (CA) on IOP.

Methods

This prospective cross-sectional study included one eye of 101 subjects with normal corneas (58 healthy subjects, 43 glaucoma); and 90 post-keratoplasty patients: 34 penetrating keratoplasties (PK); 20 automated-lamellar-therapeutic keratoplasties (ALTK); 19 Descemet-stripping-automated-endothelial keratoplasties (DSAEK); 17 edematous grafts. All subjects underwent GAT and iCare IOP measurements in random order, and CCT, CC, and CA evaluation. The Bland–Altman method and multivariate regression analysis were used to assess inter-tonometer agreement and the influence of CCT, CC, and CA on IOP.

Results

iCare significantly underestimated IOP in all groups compared with GAT (GAT minus iCare of 3.5±3.5 mm Hg, P<0.001), but overestimated IOP in the edematous grafts (GAT minus iCare of −6.5±1.9 mm Hg, P<0.001). In normal corneas, both tonometer measurements were directly related to CCT values; iCare readings appeared inversely related to CC. There was no significant relationship between IOP and CCT, CC and CA in post-keratoplasty eyes, except between CC and iCare measurements for PK eyes.

Conclusions

The agreement between GAT and iCare was clinically acceptable in control, ALTK and DSAEK groups, and poor in PK and edematous grafts eyes. In normal corneas, GAT was significantly affected by CCT; iCare was influenced by CCT and CC. The iCare appeared less influenced by corneal edema when compared with GAT. High IOP readings taken with both tonometers in grafts should raise suspicion of true elevated IOP.     

Relation between corneal thickness and intraocular pressure measurement by noncontact and applanation tonometry.

PURPOSE: To assess whether there is a significant difference in intraocular pressure (IOP) measurements between noncontact and applanation methods and if so, whether the difference is correlated with corneal thickness. SETTING: I?ik Eye Clinic, Ankara, Turkey. METHODS: This prospective study comprised 120 eyes of 60 randomly selected patients. Noncontact tonometry, applanation tonometry, and pachymetry were performed in each eye. The results were compared and an analysis was performed to determine whether there was a correlation between the differences in IOP measurements and corneal thickness in the entire group and in subgroups composed of the halves and quarters of the group. RESULTS: The mean IOP in the entire group was 20.38 mm Hg +/- 4.97 (SD) with the noncontact tonometer and 18.84 +/- 4.47 mm Hg with the Goldmann applanation tonometer. The difference between the measurements with the noncontact method and those with the applanation method was statistically significant (P <.01) except in cases having a corneal thickness between 513 microm and 539 microm (P >.01). There was a positive correlation between corneal thickness and the difference in measurements by noncontact and applanation tonometry, and the magnitude of correlation was greater in cases with thicker corneas. CONCLUSION: The reliability of tonometers decreased with increasing corneal thickness, in which case higher readings were found, especially with the noncontact tonometer.     

The non-contact tonometer. Its value and limitations

A review of the literature and a comparative study against Goldmann applanation tonometers suggests that the non-contact tonometer is reliable for measuring intraocular pressures within the normal range. In addition, the non-contact tonometer eliminates the need for corneal contact and topical anesthesia, thereby avoiding the potential problems of corneal abrasion, spread of infection, and drug reactions. The instrument can be used reliably by paramedical personnel and has particular value in mass screening and possibly in studies of topical antiglaucoma drugs. The non-contact tonometer is less reliable in patients with elevated intraocular pressure, since comparative studies against the Goldmann applanation tonometers have shown poorer correlations in the higher pressure ranges. The instrument is also limited by an abnormal cornea or poor fixation, which may interfere with accurate pressure measurements. Furthermore, the non-contact tonometer is less portable than many tonometers and more expensive than most.