Comparisons between Pascal dynamic contour tonometry, the TonoPen, and Goldmann applanation tonometry in patients with glaucoma

Validation of intraocular pressure measurement using tonometer AVIA across different postures: A Bland Altman analysis

AIMS/OBJECTIVES

Tonometry is a fundamental procedure in the diagnosis and management of glaucoma. Different tonometers have been proposed but none are as accurate as the Goldman applanation tonometry (GAT). Nonetheless, due to the limitations of GAT, mobile tonometry methods became prevalent. This study aims to examine the reliability of the Tono-Pen AVIA® (TPA) in measuring intraocular pressure (IOP) across different postures.

METHODS

A total of 196 eyes were prospectively examined for IOP changes using GAT and TPA. IOP measurements were taken across different postures using the TPA. Reliability of measurements was compared using interclass correlation coefficients (ICC), while agreement was represented using Bland-Altman analysis. Pearson r coefficient was used to measure correlations.

RESULTS

When compared to GAT (14.5 ± 4.4 mmHg), IOP readings were significantly higher for TPA at both seated (16.5 ± 4.5 mmHg; p < 0.001) and supine (16.9 ± 5.7; p < 0.001) positions. The ICC values for GAT and TPA among seated and supine patients were 0.79 (0.54-0.90) and 0.76 (0.48-0.87) indicating good reliability between the readings. There were significantly positive correlations between GAT and TPA at both seated (r = 0.626, p < 0.001) and supine (r = 0.727, p < 0.001) positions. Per Bland-Altman analysis, limits of agreement were -8.57 to 4.37 for GAT and seated TPA and -10.34 and 5.34 for GAT and supine TPA.

CONCLUSION

Good reliability exists between IOP measurements using GAT and TPA. However, the devices are not interchangeable and therefore cannot be used reciprocally in the same patient.

The relationship between intraocular pressure and glaucoma: An evolving concept

Intraocular pressure (IOP) is the most important modifiable risk factor for glaucoma and fluctuates considerably within patients over short and long time periods. Our field's understanding of IOP has evolved considerably in recent years, driven by tonometric technologies with increasing accuracy, reproducibility, and temporal resolution that have refined our knowledge regarding the relationship between IOP and glaucoma risk and pathogenesis. The goal of this article is to review the published literature pertinent to the following points: 1) the factors that determine IOP in physiologic and pathologic states; 2) technologies for measuring IOP; 3) scientific and clinical rationale for measuring diverse IOP metrics in patients with glaucoma; 4) the impact and shortcomings of current standard-of-care IOP monitoring approaches; 5) recommendations for approaches to IOP monitoring that could improve patient outcomes; and 6) research questions that must be answered to improve our understanding of how IOP contributes to disease progression. Retrospective and prospective data, including that from landmark clinical trials, document greater IOP fluctuations in glaucomatous than healthy eyes, tendencies for maximal daily IOP to occur outside of office hours, and, in addition to mean and maximal IOP, an association between IOP fluctuation and glaucoma progression that is independent of mean in-office IOP. Ambulatory IOP monitoring, measuring IOP outside of office hours and at different times of day and night, provides clinicians with discrete data that could improve patient outcomes. Eye care clinicians treating glaucoma based on isolated in-office IOP measurements may make treatment decisions without fully capturing the entire IOP profile of an individual. Data linking home blood pressure monitors and home glucose sensors to dramatically improved outcomes for patients with systemic hypertension and diabetes and will be reviewed as they pertain to the question of whether ambulatory tonometry is positioned to do the same for glaucoma management. Prospective randomized controlled studies are warranted to determine whether remote tonometry-based glaucoma management might reduce vision loss and improve patient outcomes.

Real-world agreement of same-visit Tono-Pen vs Goldmann applanation intraocular pressure measurements using electronic health records

Purpose

To compare intraocular pressure (IOP) obtained with Tono-Pen (TP) and Goldmann applanation (GAT) using large-scale electronic health records (EHR).

Design

Retrospective cohort study.

Methods

A single pair of eligible TP/GAT IOP readings was randomly selected from the EHR for each ophthalmology patient at an academic ophthalmology center (2013-2022), yielding 4550 eligible measurements. We used Bland-Altman analysis to describe agreement between TP/GAT IOP differences and mean IOP measurements. We also used multivariable logistic regression to identify factors associated with different IOP readings in the same eye, including demographics, glaucoma diagnosis, and central corneal thickness (CCT). Primary outcome metrics were discrepant measurements between TP and GAT as defined by two methods: Outcome A (normal TP despite elevated GAT measurements), and Outcome B (TP and GAT IOP differences ≥6 mmHg).

Result

The mean TP/GAT IOP difference was 0.15 mmHg ( ± 5.49 mmHg 95% CI). There was high correlation between the measurements (r = 0.790, p < 0.001). We found that TP overestimated pressures at IOP <16.5 mmHg and underestimated at IOP >16.5 mmHg (Fig. 4). Discrepant measurements accounted for 2.6% (N = 116) and 5.2% (N = 238) for outcomes A and B respectively. Patients with thinner CCT had higher odds of discrepant IOP (OR 0.88 per 25 μm increase, CI [0.84-0.92], p < 0.0001; OR 0.88 per 25 μm increase, CI [0.84-0.92], p < 0.0001 for outcomes A and B respectively).

Conclusion

In a real-world academic practice setting, TP and GAT IOP measurements demonstrated close agreement, although 2.6% of measurements showed elevated GAT IOP despite normal TP measurements, and 5.2% of measurements were ≥6 mmHg apart.

Comparison of Intraocular Pressure Measurements With Goldmann Applanation Tonometry, Tonopen XL, and Pascal Dynamic Contour Tonometry in Patients With Descemet Membrane Endothelial Keratoplasty

PRCIS

IOP measured with Tonopen and DCT was higher than GAT in eyes that underwent DMEK.

PURPOSE/AIM OF THE STUDY

To compare intraocular pressure (IOP) measurements measured based on Goldmann applanation tonometry (GAT), Tonopen XL, and Pascal Dynamic Contour Tonometry (DCT) in patients who had undergone descemet membrane endothelial keratoplasty (DMEK) and to appraise the influence of central corneal thickness (CCT) on IOP measurements.

MATERIALS AND METHODS

Thirty-four eyes (from 34 patients) who underwent DMEK at least 1 month before the study were included. We performed Tonopen XL, GAT, and DCT IOP measurements at 10 min intervals. Bland-Altman plots were used to assess agreement between GAT, Tonopen XL, and DCT. Spearman rank correlation was used to calculate the deviation from GAT readings by each device and correlate the readings with the CCT variable.

RESULTS

The mean IOP values with GAT, Tonopen XL, and DCT were 14.9±5.8, 16.2±5.5, and 19.2±5.0, respectively. Statistically significant differences between GAT and Tonopen XL and between GAT and DCT were noted ( r =0.942 [0.885-0.971]; P =0.0001 and r =0.942 [0.885-0.971]; P =0.0001, respectively). DCT tended to return a higher IOP relative to GAT and Tonopen XL. CCT and IOP readings obtained by GAT, Tonopen XL, and DCT did not show a statistically significant correlation with each other.

CONCLUSION

IOP as measured with both Tonopen and DCT was found to be higher than GAT in eyes that underwent DMEK surgery although the techniques showed a good correlation. After DMEK surgery, all 3 measurement techniques can be practical in routine postoperative examinations, however it is recommended to measure IOP with the same device during patient follow-up.

How should we measure intraocular pressure in the era of coronavirus disease 2019? Balancing infectious risk, cleaning requirements, and accuracy

PURPOSE OF REVIEW

Accurate and precise measurement of intraocular pressure (IOP) is a vitally important component of the ophthalmic examination. There are multiple methods of tonometry, each of which has considerations in light of the ongoing severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic. This review discusses these considerations and compares various tonometer methods with the gold standard of Goldmann applanation tonometry (GAT).

RECENT FINDINGS

The SARS-CoV-2 virus may spread via droplets, microaerosols, or direct contact in the ophthalmology clinic. Tonometry poses a high risk of contamination. The accuracy and reliability of various methods of tonometry with single-use disposable equipment has been compared with Goldmann applanation tonometry.

SUMMARY

Goldmann applanation tonometry with disposable applanation tips, Tono-pen, and iCare employ single use tips to decrease the risk of cross-contamination of infectious agents. Review of the literature demonstrates good correlation between these devices and GAT, although the published level of agreement between devices varies.

How to Measure Intraocular Pressure: An Updated Review of Various Tonometers

Intraocular pressure (IOP) is an important measurement that needs to be taken during ophthalmic examinations, especially in ocular hypertension subjects, glaucoma patients and in patients with risk factors for developing glaucoma. The gold standard technique in measuring IOP is still Goldmann applanation tonometry (GAT); however, this procedure requires local anesthetics, can be difficult in patients with scarce compliance, surgical patients and children, and is influenced by several corneal parameters. Numerous tonometers have been proposed in the past to address the problems related to GAT. The authors review the various devices currently in use for the measurement of intraocular pressure (IOP), highlighting the main advantages and limits of the various tools. The continuous monitoring of IOP, which is still under evaluation, will be an important step for a more complete and reliable management of patients affected by glaucoma.

Smart Contact Lenses with a Transparent Silver Nanowire Strain Sensor for Continuous Intraocular Pressure Monitoring

Continuous intraocular pressure (IOP) monitoring can provide a paradigm shift in the management of patients with glaucoma as a facile alternative to conventional diagnostic methods. However, the low sensitivity and functional instability of current IOP sensors have limited their clinical utility in the management of glaucoma. Here, we have developed a smart contact lens integrated with a transparent silver nanowire IOP strain sensor and wireless circuits for noninvasive, continuous IOP monitoring. After confirming the robust stability of the IOP sensor within the smart contact lens in the presence of tears and repeated eyelid blink model cycles, we were able to monitor IOP changes on polydimethylsiloxane model eyes in vitro. In vivo tests demonstrated that our fully integrated wireless smart contact lens could successfully monitor the change in IOP in living rabbit eyes, which was clearly validated by the conventional invasive tonometer IOP test. Taken together, we could confirm the feasibility of our smart contact lens as a noninvasive platform for continuous IOP monitoring of glaucoma patients.

Real-world comparison between the Tonopen and Goldmann applanation tonometry in a university glaucoma clinic

PURPOSE

To determine whether Tonopen intraocular pressure (IOP) measurements by Ophthalmic technicians are interchangeable with Goldmann applanation tonometry (GAT) by a specialist in our glaucoma clinic.

METHODS

Ophthalmic technician Tonopen and glaucoma specialist GAT IOP measurements were performed on both undilated eyes of 300 consecutive patients during the same visit to our glaucoma clinic.

RESULTS

Among all 600 eyes of 300 patients (age 65.4, range: 23-92 years, male: 44.3%), Tonopen and GAT IOPs were similar (15.5 ± 0.6 vs. 15.4 ± 0.7 mmHg, respectively, p = 0.63) and directly correlated (r² = 0.58, p < 0.0001). However, among 120 patients with bilateral primary open-angle glaucoma GAT IOP was significantly higher than Tonopen in the right eyes (17.1 ± 1.1 vs. 16.2 ± 0.9 mmHg, p = 0.024) and in the left eyes (17.0 ± 1.0 vs. 16.3 ± 1.0 mmHg, p = 0.029). In all 300 right eyes, Tonopen underestimated IOP in 48.3% of eyes and overestimated in 39% (difference range: ( - )14 to ( + )12 mmHg), with IOP difference >  ± 3 mmHg in 34% of eyes. In eyes with GAT IOP ≥ 22 mmHg, Tonopen IOP was significantly lower (24.7 ± 2.6, range: 11-43 mmHg vs. 28.2 ± 2.2, range: 22-43 mmHg, p = 0.0002, mean difference: - 3.6 ± 1.7 mmHg), and the Tonopen measured IOP ≤ 21 mmHg in 33.3% of eyes. In eyes with Tonopen IOP ≤ 10 mmHg GAT measured IOP of 11-17 mmHg in 65.7% of eyes.

CONCLUSIONS

Tonopen may mask a third of eyes with elevated IOP and two third of eyes with potentially above-goal IOP. The Tonopen may not be interchangeable with GAT or sufficiently reliable for patient management or screening in our glaucoma clinic. However, further study is recommended to assess the limitations of the Tonopen IOP measurements in eyes with higher or lower GAT IOPs.

CLINICAL TRIALS REGISTRATION

The Institutional review board, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY does not require this retrospective study to register.

Comparison of Dynamic Contour Tonometry and Non-contact Tonometry in Older Patients Presenting with Headache or Vision Loss

Background:

Dynamic Contour Tonometry (DCT) is touted to be the most accurate tonometer for Intraocular Pressure (IOP) measurement. Non-Contact “air puff” Tonometry (NCT) may be the most commonly used tonometer for screening of IOP. Elevated IOP is important to exclude in patients presenting with headache or vision loss.

Objective:

To determine the agreement between DCT and NCT.

Methods:

The IOP of adult patients 50 years of age or older presenting with headache or vision loss for possible temporal artery biopsy were prospectively recorded. NCT and DCT measurements were obtained within thirty minutes. The right eye IOP measurements were compared with paired t-test, and Bland- Altman plot analysis. The left eye IOP measurements were subsequently analyzed for confirmation of results.

Results:

There were 106 subjects with complete right eye data, and 104 subjects with complete left eye data. The average age was 72 years, and 70% were female. The NCT IOP was on average 3.9 mm Hg lower in the right eye, and 3.5 mm Hg lower in the left eye compared with DCT. (p<.001) In the right eye the Bland-Altman analysis showed the 95% agreement interval between the two tonometers was -2.5 to 10.4 mmHg and in the left eye -3.0 to 9.9 mmHg.

Conclusion:

The IOP from NCT and DCT should not be used interchangeably because their level of disagreement includes clinically important discrepancies of up to 10 mm Hg.

Comparison of Goldmann Applanation, Noncontact Air Puff, and Tono-Pen XL Tonometry in Normal Controls versus Glaucoma Patients at a University Hospital in Riyadh, Saudi Arabia

PURPOSE:

The purpose of this study is to compare intraocular pressure (IOP) measured by the Goldmann applanation tonometer (GAT), the Tono-Pen XL (TPXL), and a noncontact airpuff tonometer (NCT) in glaucoma patients and normal controls.

METHODOLOGY:

In the current study, two groups of individuals were recruited; the first group included glaucoma patients (glaucoma group) while the second one was a glaucoma-free group. The IOP was measured through GAT, NCT, and TPXL for the same participants by three different physicians in both groups. Measurements through the three devices were compared statistically. Correlations between different methods of assessment were also assessed.

RESULTS:

In the glaucoma group, the mean IOP measured was 16.0 ± 5.5 mmHg (range, 6–40 mmHg) with GAT 20.5 ± 6.9 mmHg (range, 10–52 mmHg) with the TPXL, and 20.2 ± 6.5 mmHg (range, 8–50 mmHg) with the NCT. In the control group, the mean IOP was 14.0 ± 2.7 mmHg (range, 9–19 mmHg) with GAT, 17.3 ± 3.8 mmHg (range 6–30 mmHg) with the TPXL, and 17.9 ± 3.9 mHg (range 10–27 mmHg) with the NCT.

CONCLUSION:

IOP measurements were approved among the three devices with relatively higher readings using both NTC and TPXL. All three methods are required to address different situations that present in the daily clinical and surgical practice.

Tonometers-which one should I use?

Although several factors are known to play a role in the development and progression of glaucoma, intraocular pressure (IOP) remains the only modifiable risk factor. Medical and surgical treatments for glaucoma both aim to reduce IOP to minimize disease progression. Tonometry is therefore an essential element of the ophthalmological exam. There are several types of tonometers available currently. These range from well-established instruments that have been in clinical use for decades to new devices, which are the result of recent technological advances. The various instruments have advantages and disadvantages that affect their suitability for a given setting, purpose, and patient population. In this review, we aim to describe the most commonly available tonometers today along with their advantages, disadvantages, and applicability.

Prospective Comparative Analysis of 4 Different Intraocular Pressure Measurement Techniques and Their Effects on Pressure Readings

PURPOSE

To compare intraocular pressure (IOP) measurement using the Goldmann applanation tonometry (GAT) without fluorescein, with fluorescein strips, with fluorescein droplets, and IOP measurement with Tono-Pen Avia (TPA).

PATIENTS AND METHODS

This was a prospective comparative clinical analysis. It was performed in clinical practice. The study population consisted of 40 volunteer patients, 1 eye per patient. All patients who were 18 years and older having routine ophthalmological examination were eligible to participate. Active corneal abrasions and/or ulcers, previous glaucoma surgery, or prostheses interfering with GAT measurement were excluded. GAT IOP was measured first without fluorescein, then with fluorescein strip, then with fluorescein droplet, and finally with the TPA device. The main outcome measure was central corneal IOP.

RESULTS

Mean±SD IOP measurements for GAT without fluorescein, with fluorescein strip, with fluorescein droplet, and for TPA groups were 12.65±3.01, 14.70±2.82, 15.78±2.64, and 16.33±3.08 mm Hg, respectively. Repeated-measures analysis of variance corrected with the Greenhouse-Geisser estimate ([Latin Small Letter Open E]=0.732) showed that measuring technique had a significant effect on IOP measurements (F2.20,85.59=34.66, P<0.001). The pairwise post hoc testing showed statistically significant mean differences (P≤0.001) between all techniques except when GAT with fluorescein droplet was compared with TPA (P=0.222). The Bland-Altman analyses showed 95% limits of agreement maximum potential discrepancies in measurement ranging from 5.89 mm Hg in the GAT with fluorescein strip versus droplet compared with 11.83 mm Hg in the GAT with fluorescein strip versus TPA comparison.

CONCLUSIONS

IOP measurement technique significantly impacted the values obtained. The ophthalmologist should ensure consistent measurement technique to minimize variability when following patients.

Ageing and ocular surface immunity

Foreword

It gives me pleasure to introduce the 4th edition of the EGS Guidelines. The Third edition proved to be extremely successful, being translated into 7 languages with over 70000 copies being distributed across Europe; it has been downloadable, free, as a pdf file for the past 4 years. As one of the main objectives of the European Glaucoma Society has been to both educate and standardize glaucoma practice within the EU, these guidelines were structured so as to play their part.

Glaucoma is a living specialty, with new ideas on causation, mechanisms and treatments constantly appearing. As a number of years have passed since the publication of the last edition, changes in some if not all of these ideas would be expected.

For this new edition of the guidelines a number of editorial teams were created, each with responsibility for an area within the specialty; updating where necessary, introducing new diagrams and Flowcharts and ensuring that references were up to date. Each team had writers previously involved with the last edition as well as newer and younger members being co-opted.

As soon as specific sections were completed they had further editorial comment to ensure cross referencing and style continuity with other sections.

Overall guidance was the responsibility of Anders Heijl and Carlo Traverso. Tribute must be made to the Task Force whose efforts made the timely publication of the new edition possible.

Roger Hitchings

Chairman of the EGS Foundation

www.eugs.org

The Guidelines Writers and Contributors 

Augusto Azuara Blanco

Luca Bagnasco

Alessandro Bagnis

Keith Barton

Christoph Baudouin

Boel Bengtsson

Alain Bron

Francesca Cordeiro

Barbara Cvenkel

Philippe Denis

Christoph Faschinger

Panayiota Founti

Stefano Gandolfi

David Garway Heath

Francisco Goni

Franz Grehn

Anders Heijl

Roger Hitchings

Gabor Hollo

Tony Hommer

Michele Iester

Jost Jonas

Yves Lachkar

Giorgio Marchini

Frances Meier Gibbons

Stefano Miglior

Marta Misiuk-Hojo

Maria Musolino

Jean Philippe Nordmann

Norbert Pfeiffer

Luis Abegao Pinto

Luca Rossetti

John Salmon

Leo Schmetterer

Riccardo Scotto

Tarek Shaarawy

Ingeborg Stalmans

Gordana Sunaric Megevand

Ernst Tamm

John Thygesen

Fotis Topouzis

Carlo Enrico Traverso

Anja Tuulonen

Ananth Viswanathan

Thierry Zeyen

The Guidelines Task Force 

Luca Bagnasco

Anders Heijl

Carlo Enrico Traverso

Augusto Azuara Blanco

Alessandro Bagnis

David Garway Heath

Michele Iester

Yves Lachkar

Ingeborg Stalmans

Gordana Sunaric Mégevand

Fotis Topouzis

Anja Tuulonen

Ananth Viswanathan

The EGS Executive Committee 

Carlo Enrico Traverso (President)

Anja Tuulonen (Vice President)

Roger Hitchings (Past President)

Anton Hommer (Treasurer)

Barbara Cvenkel

Julian Garcia Feijoo

David Garway Heath

Norbert Pfeiffer

Ingeborg Stalmans

The Board of the European Glaucoma Society Foundation 

Roger Hitchings (Chair)

Carlo E. Traverso (Vice Chair)

Franz Grehn

Anders Heijl

John Thygesen

Fotis Topouzis

Thierry Zeyen

The EGS Committees 

CME and Certification 

Gordana Sunaric Mégevand (Chair)

Carlo Enrico Traverso (Co-chair)

Delivery of Care 

Anton Hommer (Chair)

EU Action 

Thierry Zeyen (Chair)

Carlo E. Traverso (Co-chair)

Education 

John Thygesen (Chair)

Fotis Topouzis (Co-chair)

Glaucogene 

Ananth Viswanathan (Chair)

Fotis Topouzis (Co-chair)

Industry Liaison 

Roger Hitchings (Chair)

Information Technology 

Ingeborg Stalmans (Chair)

Carlo E. Traverso (Co-chair)

National Society Liaison 

Anders Heijl (Chair)

Program Planning 

Fotis Topouzis (Chair)

Ingeborg Stalmans (Co-chair)

Quality and Outcomes 

Anja Tuulonen (Chair)

Augusto Azuara Blanco (Co-chair)

Scientific 

Franz Grehn (Chair)

David Garway Heath (Co-chair)

Determination of normal values of intraocular pressure and central corneal thickness in healthy premature infants-a prospective longitudinal study

PURPOSE

To evaluate the longitudinal change of intraocular pressure (IOP) and central corneal thickness (CCT) in healthy premature infants.

METHODS

Premature infants born at 28 weeks' gestational age were included in this prospective, single-center longitudinal study. IOP was measured by handheld applanation tonometer (Tono-Pen Avia); CCT measurements were performed by ultrasonic pachymeter. Examinations were held at 32 weeks' gestational age initially and at 2-week intervals thereafter for a total of 5 consecutive measurements by the same ophthalmologist.

RESULTS

A total of 110 right eyes of 110 healthy premature infants were analyzed. The mean IOP at 32 weeks' gestational age was 18.28 ± 2.78 mm Hg; mean CCT, 670.56 ± 55.72 μm. Mean IOP and CCT thereafter were 16.13 ± 2.20 mm Hg and 613.67 ± 48.11 μm in week 34, 14.67 ± 2.04 mm Hg and 579.24 ± 43.73 μm in week 36, 13.49 ± 2.08 mm Hg and 551.91 ± 40.75 μm in week 38, and 13.21 ± 1.94 mm Hg and 546.18 ± 38.70 μm in week 40. The longitudinal changes of mean IOP and CCT values between 5 consecutive measurements were statistically significant (P < 0.001, for each).

CONCLUSIONS

IOP and CCT values decrease longitudinally in healthy premature infants between 32 and 40 weeks' gestational age. Elevated IOP values, which were identified in the early premature period, seem to be associated with higher CCT values.

Can higher end tonometers be used interchangeably in routine clinical practice?

Context:

Precise intraocular pressure (IOP) measurement is important in glaucoma practise. Various instruments are available today to accurately measure IOP. Thus, the question arises about which instrument to use and whether all of them can be used interchangeably.

Aims:

To assess the agreement between noncontact tonometer (NCT), rebound tonometer (RBT), Goldmann applanation tonometer (GAT), and dynamic contour tonometer (DCT) in measuring IOP.

Subjects and Methods:

499 eyes of 250 patients were evaluated during a period of 24 months from September 2010 to August 2012 and measurement of IOP by NCT, RBT, GAT, and DCT was done in the given sequence. The agreement was assessed by use of the Bland–Altman plot keeping GAT as a gold standard technique.

Results:

The mean IOP value of NCT, RBT, GAT, and DCT was 15.9 ± 5.5, 15.9 ± 5.8, 15.9 ± 4.9, and 16.0 ± 4.7 mm of Hg, respectively. The limits of agreement of GAT with DCT, NCT, and RBT were found to be +5.4 to −5.2, −4.7 to +4.6, and −5.2 to +5.1 mm of Hg, respectively.

Conclusions:

A positive and strong correlation was found between newer tonometers and GAT, but the limit of agreement was clinically unacceptable. The use of a single tonometer should be practised at a glaucoma clinic for a patient at each follow-up.

Detecting IOP Fluctuations in Glaucoma Patients

Lowering intraocular pressure (IOP) remains the guiding principle of glaucoma management. Although IOP is the only treatable risk factor, its 24-hour behavior is poorly understood. Current glaucoma management usually relies on single IOP measurements during clinic hours, even though IOP is a dynamic parameter with rhythms dependent on individual patients. It has further been shown that most glaucoma patients have their highest IOP measurements outside clinic hours. The fact that these IOP peaks go largely undetected may explain why certain patients progress in their disease despite treatment. Nevertheless, single IOP measurements have determined all major clinical guidelines regarding glaucoma treatment. Other potentially informative parameters, such as fluctuations in IOP and peak IOP, have been neglected, and effects of IOP-lowering interventions on such measures are largely unknown. Continuous 24-hour IOP monitoring has been an interest for more than 50 years, but only recent technological advances have provided clinicians with a device for such an endeavor. This review discusses current uses and shortcomings of current measurement techniques, and provides an overview on current and future methods for 24-hour IOP assessment. It may be possible to incorporate continuous IOP monitoring into clinical practice, potentially to reduce glaucoma-related vision loss.

Comparisons of the Tono-Pen® and Goldmann Applanation Tonometer in the Measurement of Intraocular Pressure of Primary Open Angle Glaucoma Patients in a Hospital Population in Southwest Nigeria

OBJECTIVE

The aim of this study was to compare intraocular pressure (IOP) measured with the Tono-Pen® to that measured using the Goldmann applanation tonometer (GAT) in patients with primary open angle glaucoma attending a glaucoma clinic.

SUBJECTS AND METHODS

A comparative clinic-based observational study was conducted involving 75 patients (39 men and 36 women) attending a glaucoma clinic in Southwest Nigeria. A pretested structured questionnaire was used to collect sociodemographic data. The Tono-Pen and the GAT were used to measure the IOP in each patient. Central corneal thickness (CCT) was measured with an ultrasonic pachymeter, and the corrected GAT value was calculated for each patient. The Tono-Pen readings were compared with the uncorrected and corrected GAT readings. Descriptive and comparative analyses were performed. Values for p < 0.05 were considered statistically significant.

RESULTS

The mean age of the participants was 60.39 ± 16.71 years. The mean IOP using the Tono-Pen was 21.1 ± 6.8 mm Hg versus the mean uncorrected GAT value of 17.1 ± 6.9 mm Hg and the corrected GAT value of 18.9 ± 7.5 mm Hg. The mean CCT was 510.5 ± 29.6 µm. The mean differences between the Tono-Pen reading and uncorrected and corrected GAT readings were 3.9 ± 2.6 and 2.1 ± 3.5 mm Hg, respectively. Gender (Tono-Pen vs. GAT; p = 0.981 vs. 0.437) and corneal thickness (p = 0.057) did not significantly affect the IOP value. Of the 75 patients, 68 (90.7%) preferred the Tono-Pen to the GAT.

CONCLUSION

In this study, the Tono-Pen gave a higher value for IOP than the uncorrected and corrected GAT values. Gender and corneal thickness did not significantly affect the measurements. Most patients found the Tono-Pen more acceptable than the GAT.

Fundamentals and Advances in Tonometry

According to the World Health Organization, glaucoma is the leading cause of irreversible blindness worldwide. Although intraocular pressure (IOP) is not considered any more to be a defining feature of the disease, its lowering remains the only treatment option for glaucoma. Therefore, accurate and precise measurement of IOP is the cornerstone of glaucoma. Intraocular pressure is a highly dynamic physiological parameter with individual circadian rhythms. The main limitation of current tonometry methods remains the static and mostly office-based nature of their measurements. This review provides a brief historical overview on tonometry and discusses current tonometry instruments. In recent years, approaches to 24-hour IOP monitoring have been introduced, and there is hope that they may become part of routine clinical management in the future.

Comparison of three methods of tonometry in normal subjects: Goldmann applanation tonometer, non-contact airpuff tonometer, and Tono-Pen XL

Objective

We aimed to compare intraocular pressure (IOP) measurements via three different tonometers: the Goldmann applanation tonometer (GAT), the Tono-Pen^® XL (TPXL), and a non-contact airpuff tonometer (NCT).

Methods

This was a cross-sectional study of 200 eyes from 200 patients. Right eyes of all patients were included in this study. IOP was measured via GAT, NCT, and TPXL by three physicians. Each physician used one of the tonometers. Measurements via the three devices were compared.

Results

The mean IOP was 15.5±2.2 mmHg (range 10–22) with the GAT, 16.1±3.0 (range 9–25) with the TPXL, and 16.1±2.8 (range 10–26) with the NCT. Bland–Altman analysis showed that the mean difference between measurements from the NCT and the GAT was 0.6±2.3 mmHg. The mean difference between the TPXL and GAT measurements was 0.7±2.5 mmHg. The mean difference between the NCT and TPXL measurements was −0.02±3.0 mmHg. There was no significant difference between the groups according to a one-way analysis of variance (ANOVA) test. P-values were 0.998 for NCT–TPXL, 0.067 for NCT–GAT, and 0.059 for TPXL–GAT.

Conclusion

The NCT and TPXL provide IOP measurements comparable to those of the gold standard GAT in normotensive eyes.

Repeatability and accuracy of applanation resonance tonometry in healthy subjects and patients with glaucoma

PURPOSE

To evaluate the repeatability and accuracy of the applanation resonance tonometer (ART) used in the automatic servo-controlled version, and to evaluate the influence of central corneal thickness (CCT) on the ART intraocular pressure (IOP) measurements.

METHODS

This prospective, randomized, single-centre study included one eye of 153 subjects (35 healthy volunteers and 118 patients with glaucoma). All participants underwent ultrasonic CCT measurement, followed by IOP evaluation with Goldmann applanation tonometer (GAT) and ART in random order. A single operator measured the IOP with each tonometer three times. Intra-examiner variability was evaluated using the coefficient of variation (CoV), intraclass correlation coefficient (ICC) and test-retest differences. Intermethod agreement was assessed using the Bland-Altman method. Linear regression analysis was used to evaluate the relationship between IOP measurements and CCT.

RESULTS

The mean IOP was 17.7 ± 4.4 mmHg with GAT and 20.6 ± 5.3 mmHg with ART (p < 0.001). CoV and ICC were, respectively, 5 ± 3% and 0.99 for GAT, and 8 ± 4% and 0.96 for ART (intermethods differences, p = 0.001). The ART test-retest differences significantly increased with increasing mean IOP (p = 0.003). The mean IOP difference (ART minus GAT) was 3.0 ± 4.0 mmHg, which increased with increasing mean IOP (p < 0.001). Both GAT IOP and ART IOP readings were significantly directly related to the CCT values (p = 0.03 and p = 0.004, respectively; intermethods difference, p = 0.32).

CONCLUSIONS

The ART intra-examiner repeatability was excellent, although significantly lower than that of GAT, and decreased at higher IOP levels. ART significantly overestimated GAT IOP measurements, especially at higher IOP range. Both GAT and ART appeared similarly influenced by CCT value.

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 Goldmann Tonometry and Dynamic Contour Tonometry in Normal and Descemet Stripping Endothelial Keratoplasty Eyes

PURPOSE

This study aimed to compare intraocular pressures (IOP) measured by dynamic contour tonometry (DCT) with Goldmann tonometry (GAT) in Descemet stripping endothelial keratoplasty (DSEK) eyes. The agreeability between the 2 established methods and their relation to central corneal thickness (CCT) was also studied.

DESIGN

A comparative case series.

METHODS

Forty-six eyes of DSEK were enrolled at least 3 months after the procedure. Thirty-five other eyes of the same patient cohort served as control. Intraocular pressures were measured by DCT and GAT by 2 different examiners in a randomized manner. Central corneal thickness was measured by ultrasonic pachymetry. Statistical analysis was used for the calculation of means, SD, coefficient of determination, linear regression, and Bland and Altman plot. Statistical significance was considered as P < 0.05.

RESULTS

Mean CCT was 624.49 μm and 518.41 μm in DSEK and control eyes, respectively. Mean IOP by GAT and DCT, respectively, was 19.4 and 21.5 mm Hg in DSEK eyes and 15.12 and 17.6 mm Hg in controls. Descemet stripping endothelial keratoplasty eyes showed universally higher IOP by either method in comparison with normal controls. Dynamic contour tonometry reading was significantly higher than GAT in both (P < 0.05) groups. The correlation between IOP and CCT was not significant in DSEK eyes (P > 0.05).

CONCLUSIONS

A higher baseline IOP is to be expected in DSEK eyes, which is independent of corneal thickness. Both GAT and DCT can be used as a standard method to measure IOP in DSEK eyes, but their readings cannot be used interchangeably.

Test retest variability of TonoPen AVIA

The study was conducted to evaluate the intra-session repeatability of Tonopen AVIA (TPA). 180 eyes of 180 patients (50 eyes with glaucoma, 130 eyes of controls) were recruited for this observational study. The mean age of patients enrolled in the study was 43.9 ± 16.7 yrs (84 males, 96 females). Mean IOP recorded with Tonopen AVIA was 19.5 ± 9.5 mmHg, 19.4 ± 9.6 mmHg and 19.3 ± 9.2 mmHg, respectively in the first, second and third instances (P = 0.656). The intraclass correlation coefficient (ICC) ranged from 0.996 (95% CI: 0.956 - 0.998) for glaucoma subjects to 0.958 (95% CI: 0.934 - 0.975) for controls. The coefficient of variation in the study population ranged from 3.47% (glaucoma patients) to 8.10% (healthy controls), being 6.07% overall. The coefficient of repeatability varied between 2.96 (glaucoma patients), 3.35 (healthy controls) to 3.24 (overall). Thus, the Tonopen Avia shows good intrasessional repeatability of IOP in both glaucomatous patients and healthy subjects.

Comparison of Goldmann applanation and dynamic contour tonometry in a population of Mexican open-angle glaucoma patients

To compare intraocular pressure (IOP) measurements obtained with Goldmann applanation (GAT) and dynamic contour tonometry (DCT) in a Mexican population. 40 glaucoma patients were included in this cross-sectional observational cohort study. IOP measurements were performed in the following order: DCT, ultrasonic pachymetry and GAT, with a 5-minute difference between each measurement, between 8 am and 2 pm. Only DCT measurements of good quality (Q ≤ 3) were accepted. GAT measurements were made three times with the same Goldmann tonometer, previously checked for calibration errors, and the mean was used for statistical purposes. The IOP (mean [standard deviation], 95 % confidence interval [CI]) measured with the Goldmann tonometer (13.2 [2.4], 12.4-14.0 mmHg) was significantly lower than that obtained with the DCT (18.4 [3.3], 17.0-19.2 mmHg), p < 0.0001. Pearson's correlation coefficients between CCT and IOP measured with GAT and DCT were (r = 0.24, 95 % CI = 0.07-0.52, p = 0.133) and (r = 0.13, 95 % CI = -0.19 to 0.43, p = 0.412), respectively. The concordance correlation coefficient between GAT and DCT was r c = 0.3, 95 % CI = 0.17-0.41). DCT seems to overestimate the IOP as compared to GAT. Additionally, although there was a good correlation between the IOP measurements assessed with either GAT or DCT, the agreement was poor.

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.

Comparison of Goldmann and Pascal tonometry in relation to corneal hysteresis and central corneal thickness in nonglaucomatous eyes

Objective:

To compare measurements obtained by Goldmann applanation tonometry (GAT) and Pascal dynamic contour tonometry (DCT), and to study their relationship to corneal thickness and biomechanical properties in nonglaucomatous eyes.

Methods:

This is a prospective and randomized study of 200 eyes from 200 non-glaucomatous subjects who underwent intraocular pressure (IOP) measurements by GAT and DCT. The two methods were compared and assessed for agreement by means of the Bland–Altman plot. Central corneal thickness (CCT) and corneal hysteresis (CH) were obtained by ultrasound pachymeter and Ocular Response Analyzer, respectively. The effect of CH and CCT was correlated with the DCT/GAT IOP differences.

Results:

Mean age was 57.4 ± 14.7 years (range 24–82 years). Mean IOP measurements obtained were 16.7 ± 3.2 mmHg by GAT and 19.4 ± 3.3 mmHg by DCT. DCT showed a statistically significant higher mean IOP (2.7 ± 1.9 mmHg, P < 0.001) compared with GAT. Mean CCT and CH were 546.5 ± 40 μm and 10.85 ± 2.0 mmHg, respectively. The differences in IOP (DCT – GAT) were significantly correlated with CCT and CH (Pearson’s correlation coefficient r = −0.517 and −0.355, P < 0.0001, respectively). The difference between the two correlation coefficients was statistically significant (P < 0.05, Z-statistic). According to the Bland–Altman plot, the results of the two methods were clinically different.

Conclusion:

Significantly higher IOP readings were obtained by DCT than by GAT in nonglaucomatous subjects. The IOP differences between the two methods were associated with CCT and CH, suggesting that DCT was less dependent on corneal parameters. Each method provides clinically different IOP values, indicating that DCT and GAT should not be used interchangeably.

Hand-held dynamic contour tonometry

PURPOSE

We present a prototype of the hand-held dynamic contour tonometer (HH-DCT) and prospectively compare this HH-DCT with the well-established Perkins applanation tonometer (PAT) and the TonoPenXL (TPXL).

METHODS

In a prospective, single-centre, randomized study, intraocular pressure (IOP) readings were taken in random order using HH-DCT, PAT and TPXL tonometers. Intra-observer variability was calculated for each observer and compared between three experienced ophthalmologists and an inexperienced medical student.

RESULTS

Ninety-two corneas of 92 healthy participants were enrolled. IOP [mean mmHg ± standard deviation (SD)] as measured by HH-DCT was 16.97 ± 2.71, by PAT 13.98 ± 2.52 and by TPXL 13.34 ± 2.68. The range of three consecutive IOP readings differed significantly between the devices [p < 0.001; mean range: 1.45 ± 1.07 (HH-DCT), 1.87 ± 0.97 (PAT) and 2.08 ± 1.77 (TPXL)]. There was no difference of the range in all devices between the ophthalmologists and the medical student (HH-DCT p = 0.68, PAT p = 0.54, TPXL p = 0.48).

CONCLUSION

IOP readings measured by HH-DCT are significantly higher than by PAT and TPXL. The differences of IOP measurements are in good accordance with previous studies using the slit-lamp-mounted DCT (SL-DCT) and Goldmann Applanation Tonometry, where SL-DCT readings were 1-3.2 mmHg higher. HH-DCT seems to give more constant results, which can be seen in the lower intra-observer variability compared to PAT and TPXL.

Tonometry methods in the pediatric emergency department

The measurement of intraocular pressure is perhaps the most important clinical parameter contributing to the diagnosis of glaucoma. This report describes the most commonly used methods of tonometry (to measure intraocular pressure). Considering the common options of Goldmann applanation tonometry (GAT), Schiotz tonometry (ST), and Tono-Pen tonometry (TP), the TP is the easiest to use in the emergency department. It is subject to some degree of inaccuracy. In the pediatric emergency department, a child with a painful eye is likely to require deep sedation to achieve an accurate measurement.

A clinical comparison of dynamic contour tonometry versus Goldmann applanation tonometry

BACKGROUND AND OBJECTIVE

To compare the intraocular pressures (IOP) obtained with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) and to determine the dependency of both devices on corneal structure.

PATIENTS AND METHODS

One hundred forty eyes of 70 patients were included. Cases with corneal pathologies, former glaucoma diagnosis, and systemic diseases were excluded. All eyes underwent measurements of central corneal thickness (CCT) and corneal curvature. IOP measurements were obtained with GAT and DCT. The agreement of measurements was statistically analyzed.

RESULTS

The correlation of IOP values obtained with DCT and GAT was statistically significant. The mean DCT values were 0.46 ± 2.55 mm Hg higher than those of GAT, but this difference was statistically insignificant. Bland-Altman plots showed reasonable inter-method agreement between DCT and GAT measurements. GAT readings were significantly affected by CCT, but DCT measurements were affected by age and corneal curvature.

CONCLUSION

DCT is a reliable method of assessing IOP and is less dependent on central corneal thickness. This new technology may be a promising step forward in the management of glaucoma. Further studies are required to validate these observations.

The effect of deep sclerectomy on intraocular pressure of normal-tension glaucoma patients: 1-year results

PURPOSE

To study the intraocular pressure (IOP)-reducing effect of deep sclerectomy on normal-tension glaucoma (NTG) patients.

METHODS

We retrospectively analysed 21 eyes of 18 consecutive NTG patients who had undergone deep sclerectomy with mitomycin-C and a collagen implant.

RESULTS

Median (range) preoperative IOP was 15.1 mmHg (9.3-20.8) and median follow-up time 13 months (12-18). At the 1-year follow-up visit, median IOP was significantly (P < 0.001) reduced to 10.5 mmHg (4-15) with median IOP reduction from preoperative values of 37% (12-78). Laser goniopuncture was performed in 10 eyes (48%) 1-16 months postoperatively. After 13 months' follow-up, a complete success at 20%, 25% and 30% IOP reduction levels was achieved in 67%, 62% and 52% of eyes, respectively. Few complications were encountered, but these included reduced visual acuity, problems with conjunctiva, microperforation, hyphaema, Dellen formation and encapsulated bleb. We encountered no complications related to postoperative hypotony.

CONCLUSION

Deep sclerectomy with a collagen implant and mitomycin-C was a safe and effective method for reducing IOP in NTG patients during 1-year follow-up.

Association between corneal hysteresis and central corneal thickness in glaucomatous and non-glaucomatous eyes

PURPOSE

We aimed to determine corneal hysteresis values (CH) using the ocular response analyser (ORA) in non-glaucomatous and glaucomatous eyes and their relationship with central corneal thickness (CCT).

METHODS

Corneal hysteresis, intraocular pressure (IOP) as measured by Goldmann applanation tonometry (GAT) and CCT were prospectively evaluated in 74 non-glaucoma subjects with IOP < 21 mmHg and in 108 patients with treated primary open-angle glaucoma (POAG). One eye in each subject was randomly selected for inclusion in the analysis.

RESULTS

Mean (+/- standard deviation [SD]) age was 59.2 +/- 14.2 years in the non-glaucoma group and 62.4 +/- 9.8 years in the glaucoma group. Mean (+/- SD) GAT IOP was 15.7 +/- 2.65 mmHg and 16.38 +/- 2.73 mmHg in the non-glaucoma and glaucoma groups, respectively. There was no statistically significant difference between the two groups in mean age (p = 0.396) or mean GAT IOP (p = 0.098). Mean (+/- SD) CH was 10.97 +/- 1.59 mmHg in the non-glaucoma and 8.95 +/- 1.27 mmHg in the glaucoma groups, respectively. The difference in mean CH between the two groups was statistically significant (p < 0.0001). There was a strong positive correlation between CH and CCT in the non-glaucoma group (r = 0.743) and a significantly (p = 0.001) weaker correlation (r = 0.426) in the glaucoma group.

CONCLUSIONS

Corneal hysteresis was significantly lower in eyes with treated POAG than in non-glaucomatous eyes. The corneal biomechanical response was strongly associated with CCT in non-glaucoma subjects, but only moderately so in glaucoma patients. It can be assumed that diverse structural factors, in addition to thickness, determine the differences in the corneal biomechanical profile between non-glaucomatous and glaucomatous eyes. Corneal hysteresis could be a useful tool in the diagnosis of glaucoma.

Comparison of dynamic contour tonometry with Goldmann applanation tonometry in glaucoma practice

PURPOSE

To compare intraocular pressure (IOP) readings taken using dynamic contour tonometry (DCT) with IOP readings taken with Goldmann applanation tonometry (GAT) in eyes with glaucoma or ocular hypertension.

METHODS

The present study included 100 eyes in 100 patients with glaucoma or ocular hypertension. After pachymetry DCT and GAT were performed. Intraocular pressures as measured with DCT and GAT were compared with one another and with central corneal thickness (CCT).

RESULTS

Mean DCT IOP measurements (20.1 +/- 4.3 mmHg) were significantly (p < 0.001) higher than GAT IOP values (17.9 +/- 4.7 mmHg). The mean difference between DCT and GAT measurements was 2.1 mmHg (range -3.4 to 9.7 mmHg). The difference followed a normal distribution. Measurements made with DCT and GAT correlated significantly with one another (Spearman's rho = 0.761, p < 0.001). Neither GAT nor DCT measurements showed a significant correlation with CCT (537 +/- 39 microm, range 458-656 microm). Multivariate regression analysis has shown that the difference between DCT and GAT is influenced significantly by ocular pulse amplitude (r = -0.334, p = 0.001) and it is not influenced by CCT (r = -0.106, p = 0.292).

CONCLUSIONS

In eyes with glaucoma or ocular hypertension, DCT facilitates suitable and reliable IOP measurements which are in good concordance with GAT readings. Variation in CCT cannot by itself explain the differences in measurements taken with DCT and GAT in a number of eyes.

Correlation of intraocular pressure measured with goldmann and dynamic contour tonometry in normal and glaucomatous eyes

PURPOSE

To compare intraocular pressure (IOP) values measured by both Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) in both normal and glaucomatous eyes, and to determine the relationship between these parameters and central corneal thickness (CCT).

PATIENTS AND METHODS

Forty-seven subjects with primary open-angle glaucoma and 38 normal subjects attended a 12-hour session during which IOP was assessed at 7 time points, every 2 hours, by both GAT and DCT. CCT was also assessed at the same visit. Mean IOP was calculated for each eye of each subject by each method from the 7 diurnal IOP measurements obtained.

RESULTS

Mean IOP was higher when measured by DCT than by GAT in both normal (by 1.1 mm Hg, P<0.0001) and glaucomatous (by 1.6 mm Hg, P<0.0001) eyes. IOP measurements by GAT and DCT were moderately correlated in both normal (r(2)=0.354, P<0.0001) and glaucomatous (r(2)=0.552, P<0.0001) eyes. In normal eyes, there was a weak positive correlation between GAT IOP and CCT (r(2)=0.088, slope=0.022 mm Hg/microm, P=0.009) and no correlation between DCT IOP and CCT (r(2)=0.007, slope=0.005 mm Hg/microm, P=0.468). In glaucomatous eyes, there was no correlation between GAT IOP and CCT (r(2)=0.006, slope=0.007 mm Hg/microm, P=0.473) and a weak inverse correlation between DCT IOP and CCT (r(2)=0.075, slope=-0.021 mm Hg/microm, P=0.008).

CONCLUSIONS

Both GAT and DCT are affected by CCT, albeit in different ways. Normal and glaucomatous eyes exhibit different relationships between CCT and IOP measured by either GAT or DCT. The relationships between CCT and transcorneal IOP measurements are complex and incompletely characterized, which limits the clinical interpretation of GAT and DCT measurements of IOP in both normal and glaucomatous eyes.

Most common mistakes in measuring intraocular pressure

<zakljucak> Zlatni standard za merenje IOP je tehnika GAT koja je tacna, ali ne i potpuno precizna, tako da ce se u cilju dobijanja sto preciznijih vrednosti IOP morati koristiti i druge tonometrijske tehnike.

Pascal, ICare and Goldmann applanation tonometry--a comparative study

PURPOSE

To compare intraocular pressure (IOP) measurements by Pascal, ICare and Goldmann applanation tonometry (GAT), to evaluate the effects of central corneal thickness (CCT) and curvature on IOP measurement and to estimate the intra-observer variability.

METHODS

A prospective, single-centre study of 150 eyes with a wide range of pressures. Six masked IOP measurements/method; corneal thickness and curvature were studied for each eye. GAT was the reference.

RESULTS

IOPPascal and IOPICare correlated with IOPGAT (r = 0.91, 0.89). Mean ICare measurement exceeded GAT by 2 mmHg. Pascal measured higher than GAT at low IOPs and lower at high IOPs. For every 10 mmHg increase in IOP above 31 mmHg, Pascal measured 2 mmHg lower than GAT and vice versa. CCT was correlated significantly with IOPGAT (r = 0.23) and IOPICare (r = 0.43) but not with IOPPascal (P = 0.12). CCT was correlated with age. In a subgroup (>50 years), ICare and the difference between IOPGAT and IOPPascal were affected significantly by the CCT, whereas IOPGAT and IOPPascal were not. Corneal curvature was correlated significantly with IOPGAT (r = -0.27) and IOPPascal (r = -0.26) but not with IOPICare (P = 0.60). Intra-observer variability within each set of six measurements was approximately 2 mmHg, irrespective of method.

CONCLUSION

This study showed a reasonable overall correlation and concordance between the IOP obtained with the three instruments. None of the methods were completely independent of the biomechanical properties of the cornea. ICare showed a significant dependency upon CCT, whereas GAT and Pascal showed a significant dependency on corneal curvature. All methods showed intra-observer variability, which leaves room for further improvement of methods.

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.

Intraocular pressure measurements following Descemet stripping endothelial keratoplasty

PURPOSE

The effect of increased corneal thickness after Descemet stripping endothelial keratoplasty (DSEK) on intraocular pressure (IOP) measurement has not been previously studied. It is uncertain if this increase in corneal thickness would artificially elevate IOP reading by Goldmann tonometry [GAT] (Haag-Streit, Konig, Switzerland). Therefore the effect of DSEK-related thick cornea on IOP measurement was investigated using three different techniques.

DESIGN

Prospective cross-sectional study.

METHODS

Participants were recruited from a single tertiary referral center. Fifty eyes of 38 patients with successful DSEK at least three months prior to testing were evaluated. At the time of the study, none of the participants had clinically detectable corneal edema. IOP was measured with GAT, pneumatonometry, and dynamic contour tonometry (DCT) in an unmasked randomized sequence. Central corneal thickness (CCT) was measured by ultrasonic pachymetry.

RESULTS

Mean CCT was 701 +/- 68 microm. The mean IOP +/- standard deviation (SD) was 15.9 +/- 4.9 mm Hg for GAT, 20.3 +/- 4.5 mm Hg for pneumatonometry, and 19.8 +/- 4.4 mm Hg for DCT. Pneumatonometry and DCT IOP measurements were significant higher than GAT (P < .01). In contrast, the difference between pneumatonometry and DCT readings was not statistically significant (P = .28). The correlations between IOP and corneal thickness were not significant in this cohort (P > .05).

CONCLUSIONS

Falsely elevated GAT, as expected in thick corneas, was not demonstrated after DSEK. High IOP reading by GAT therefore should raise suspicion of elevated IOP in DSEK eyes.

Poor agreement between Goldmann and Pascal tonometry in eyes with extreme pachymetry

AIM

To compare the intraocular pressure (IOP) measurements obtained using the Pascal dynamic contour tonometer (PDCT) with the standard Goldmann applanation tonometry (GAT) and to correlate them with the central corneal thickness (CCT) in a non-glaucomatous population.

METHODS

We prospectively measured IOP using PDCT and GAT in random order in 100 normal eyes. CCT was analysed with an ultrasonic pachymeter in each case. Statistical analysis of baseline and stratified data included intraclass correlation coefficient (ICC), Lin correlation, and Bland-Altman analysis to evaluate the agreement between both techniques.ResultsGAT was used first in 51 eyes and PDCT in 48 cases. Mean IOP was 14.8 mm Hg with GAT and 20.3 mm Hg with PDCT. Mean pachymetry was 553.23 micrometres (microm) (SD: 4.7 microm). Global agreement of IOP between GAT and PDCT was 0.09 by ICC and 0.170 by Lin correlation. When CCT values ranged between 540 and 545 microm, the agreement between both tonometers was optimal (ICC 0.54 and Lin 0.61). Outside these pachymetry values, agreement between both tonometers diminished dramatically.

CONCLUSION

Statistically significant agreement between both devices was reached only at intermediate pachymetry readings in contrast with other studies that show excellent global agreement between GAT and PDCT.

Comparison of dynamic contour tonometry and goldmann applanation tonometry in deep lamellar and penetrating keratoplasties

PURPOSE

To compare the measurements of intraocular pressure (IOP) with dynamic contour tonometry (DCT) and Goldmann applanation tonometry (GAT) in eyes with corneal graft and to evaluate the influence of corneal thickness (CCT), corneal curvature (CC), and astigmatism on these methods.

DESIGN

Prospective, observational cross-sectional study.

METHODS

Eighteen eyes of 18 patients after penetrating keratoplasty (PKP) and 14 eyes of 14 patients after deep lamellar keratoplasty (DLKP) underwent IOP evaluation with DCT and GAT, and measurements of CCT, CC, and astigmatism. Bland-Altman plots were used to evaluate the agreement between tonometers. Multivariate regression analysis was used to evaluate the influence of ocular structural factors and running suture on IOP measurements obtained with both tonometers.

RESULTS

IOP values obtained by DCT and GAT were strongly correlated in all eyes (r = .91; P < .001). DCT values measured 2.5 +/- 1.7 mm Hg higher than GAT readings (P < .001). A reduction of the mean IOP difference between DCT and GAT with an increase in IOP values (P < .001) was found. Regression analysis showed no effect of CCT, CC, astigmatism, and running suture on both DCT and GAT readings, either in DLKP or in PKP eyes.

CONCLUSIONS

We found a good overall correlation between both tonometers but the agreement between instruments differs in high or low IOP ranges. The wide and varying 95% limits of agreement between DCT and GAT indicates that DCT provides IOP measurements on deep lamellar and penetrating keratoplasties which can be used in the clinical practice.