Comparison of ICare tonometer with Goldmann applanation tonometer in glaucoma patients

Limbal rebound tonometry: clinical comparisons and applications

PURPOSE

The accuracy of contact tonometry may be compromised in cases with disorders affecting central corneal bio-mechanical properties. This study examined the reliability of rebound tonometry (RT) on the area of corneo-scleral limbus, instead of the conventional central corneal area, and the correlation of findings with ocular biometric parameters.

METHODS

This is a prospective cross-sectional study performed at the Department of Ophthalmology of the University Hospital of Heraklion, in Crete, Greece. Consecutive cataract surgery candidates without concomitant ocular pathology, apart from cataract, were included. RT was performed on the central cornea (central RT, CRT) as well as on the limbus and scleral spur area (limbal RT, LRT). Findings were correlated with Goldmann applanation tonometry (GAT) as well as axial length (AL), central corneal thickness (CCT), and corneal curvature (CC) measurements.

RESULTS

LRT readings were significantly correlated with central CRT as well as with GAT readings, whereas respective correlations with other parameters examined were not statistically significant.

CONCLUSIONS

LRT may be used as an alternative tool in clinical practice to determine intraocular pressure when conventional devices and techniques might be inadequate or unreliable.

Agreement of patient-measured intraocular pressure using rebound tonometry with Goldmann applanation tonometry (GAT) in glaucoma patients

This study aims to determine the agreement of patient-measured intraocular pressure (IOP) using rebound tonometry with ophthalmologist-measured IOP using Goldmann applanation tonometry (GAT). Fifty-three glaucoma patients used rebound tonometry (Icare ONE, Icare Finland Oy., Finland) to measure their own IOP in ambient environments for 1 week, 5 times per day. Clinic IOP measurements were performed by ophthalmologists using GAT and by patients using rebound tonometry on examination days 1, 4 and 7 of the same week. The agreement between the two tonometries was evaluated by modified Bland-Altman plots and intra-class correlation coefficient (ICC) was determined. Differences in ICCs of them among the three examination days were evaluated by bootstrap resampling analysis. Respective within-measurement ICC of GAT and rebound tonometry were 0.98 and 0.94 on Day 1, 0.98 and 0.93 on Day 4, and 0.96 and 0.92 on Day 7. In a modified Bland-Altman plot, the mean difference ±1 standard deviation (SD) between the two tonometries was 0.15 ± 0.65 mmHg (p = 0.682). Between-measurement ICC were 0.66, 0.76 and 0.73 on the 3 examination days. There was no significant difference among ICCs. In conclusion, patient-measured IOP using rebound tonometry and ophthalmologist-measured IOP using GAT demonstrate good agreement.

Self-tonometry as a complement in the investigation of glaucoma patients

PURPOSE

To evaluate the reliability of intraocular pressure measured by patients with glaucoma themselves using a new hand-held tonometer and to observe whether the intraocular pressure (IOP) variations have the same pattern on different days while glaucoma treatment is constant.

METHODS

Eighty-seven patients diagnosed with open-angle glaucoma or ocular hypertension were recruited to the study. Intraocular pressure measured using Goldmann applanation tonometry (GAT) was compared with IOP measured using tonometry at baseline and on the second visit. Patients measured their IOP at home using the hand-held tonometers.

RESULTS

The mean difference between GAT and iCare^® values varies from 0 to 1 mmHg. Seventy-eight per cent of iCare^® measurements were within 3 mmHg of the GAT measurements. Approximately 64% of the study eyes had higher IOP in the morning than in the afternoon/evening. Circadian patterns differed between consecutive days in 47% of the study eyes. There were IOP peaks outside office hours in up to 16% of the study eyes.

CONCLUSION

Measurements made using rebound self-tonometry are accurate and could be used to complement the investigation of patients with glaucoma. Intraocular pressure curves provide valuable data usable when adapting glaucoma treatment.

Comparison of ICare and IOPen vs Goldmann applanation tonometry according to international standards 8612 in glaucoma patients

AIM

To compare IOPen and ICare rebound tonometry to Goldmann applanation tonometry (GAT) according to International Standards Organization (ISO) 8612 criteria.

METHODS

Totally 191 eyes (n=107 individuals) were included. Criteria of ISO 8612 were fulfilled: 3 clusters of IOP, measured by GAT, were formed. The GAT results were given as mean±standard deviation.

RESULTS

GAT (19.7±0.5 mm Hg) showed a significant correlation to ICare (19.8±0.5 mm Hg) (r=0.547, P<0.001) and IOPen (19.5±0.5 mm Hg) (r=0.526, P<0.001). According to ISO 8612 criteria in all 3 IOP groups the number of outliers (of the 95% limits of agreement) exceeded 5% for ICare and IOPen vs GAT: No.1 (n=68) 29.4% and 22.1%, No.2 (n=62) 35.5% and 37.1%, No.3 (n=61) 26.2% and 42.6%, respectively.

CONCLUSION

The strict requirements of the ISO 8612 are not fulfilled in a glaucoma collective by ICare and IOPen at present. As long as the Goldmann tonometry is applicable it should be used first of all for reproducible IOP readings. ICare and IOPen tonometry should be considered as an alternative tool, if application of Goldmann tonometry is not possible.

Wound stability and surgically induced corneal astigmatism after transconjunctival single-plane sclerocorneal incision cataract surgery

PURPOSE

To compare intraocular pressure (IOP) immediately after cataract surgery, and surgically induced corneal astigmatism (SIA) and corneal shape changes between eyes with transconjunctival single-plane sclerocorneal incisions (TSSIs) and eyes with clear corneal incisions (CCIs).

METHODS

Bilateral eyes of 64 patients undergoing phacoemulsification were randomized to undergo 2.4-mm temporal TSSI or CCI. IOP was measured preoperatively, and in the immediate postoperative periods. SIA was determined using vector analysis, and corneal shape changes and irregular astigmatism were evaluated using a videokeratography preoperatively, and in the early postoperative periods.

RESULTS

Wound hydration was performed in 23 eyes (35.9 %) of the TSSI group and in 60 (93.8 %) of the CCI group (P < 0.0001). Mean IOP was significantly higher in the TSSI group than in the CCI group at 30, 60, and 120 min postoperatively (P ≤ 0.0179). SIA tended to be smaller in the TSSI group than the CCI group, but the difference was not significant. The higher order irregular astigmatism was smaller in the TSSI group than in the CCI group at 2 days (P = 0.0312). The videokeratography revealed a wound-related flattening postoperatively in both groups; this change disappeared within 4 weeks in the TSSI group, whereas it persisted until 12 weeks in the CCI group.

CONCLUSION

IOP was significantly higher immediately after TSSI than after CCI and required less wound hydration, suggesting better stability with TSSI. Higher order irregular astigmatism and wound-related corneal flattening were smaller after TSSI than after CCI in the early periods, suggesting that fewer corneal shape changes with TSSI.

Systematic Review of Current Devices for 24-h Intraocular Pressure Monitoring

Glaucoma is a common optic neuropathy that can lead to irreversible vision loss, and intraocular pressure (IOP) is the only known modifiable risk factor. The primary method of treating glaucoma involves lowering IOP using medications, laser and/or invasive surgery. Currently, we rely on in-office measurements of IOP to assess diurnal variation and to define successful management of disease. These measurements only convey a fraction of a patient's circadian IOP pattern and may frequently miss peak IOP levels. There is an unmet need for a reliable and accurate device for 24-h IOP monitoring. The 24-h IOP monitoring devices that are currently available and in development fall into three main categories: self-monitoring, temporary continuous monitoring, and permanent continuous monitoring. This article is a systematic review of current and future technologies for measuring IOP over a 24-h period.

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)

The measurement of intraocular pressure over positive soft contact lenses by rebound tonometry

PURPOSE

To investigate if the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over disposable hydrogel (etafilcon A) contact lenses (CL) is affected by the positive power of the CLs.

METHODS

The experimental group comprised 26 subjects, (8 male, 18 female). IOP measurements were undertaken on the subjects' right eyes in random order using a Rebound Tonometer (ICare). The CLs had powers of +2.00D and +6.00D. Measurements were taken over each contact lens and also before and after the CLs had been worn.

RESULTS

The IOP measure obtained with both CLs was significantly lower compared to the value without CLs (t test; p<0.001) but no significant difference was found between the two powers of CLs.

CONCLUSIONS

Rebound tonometry over positive hydrogel CLs leads to a certain degree of IOP underestimation. This result did not change for the two positive lenses used in the experiment, despite their large difference in power and therefore in lens thickness. Optometrists should bear this in mind when measuring IOP with the rebound tonometer over plus power contact lenses.

Glaucoma management after corneal transplantation surgeries

PURPOSE OF REVIEW

Intraocular pressure (IOP) elevation and glaucoma progression following corneal transplantation, specifically, penetrating keratoplasty, Descemet's stripping endothelial keratoplasty, and Boston keratoprosthesis, are well described causes of ocular morbidity. Depending on the procedure performed, the incidence of glaucoma is highly variable. Several etiologic factors have been identified, the most common being synechial angle closure and corticosteroid-induced IOP elevation. The purpose of this review is to describe the various treatment strategies for glaucoma following corneal transplantation.

RECENT FINDINGS

Medications and laser treatments are usually first-line therapies for postoperative IOP elevation. Surgical intervention, including filtering surgery and glaucoma drainage devices, may be necessary to control IOP and prevent progressive glaucomatous damage.

SUMMARY

Glaucoma is a common complication of corneal transplantation, and the degree of aggressiveness is often related to the indication for corneal surgery. Although postoperative IOP elevation may be controlled with medical therapy alone, refractory cases may require glaucoma surgery. In all cases, early detection and intervention are necessary to optimize patient outcomes.

The Icare HOME (TA022) Study: Performance of an Intraocular Pressure Measuring Device for Self-Tonometry by Glaucoma Patients

PURPOSE

To evaluate the Icare HOME (TA022) device (Icare Oy, Vanda, Finland) for use by glaucoma patients for self-tonometry.

DESIGN

Prospective performance evaluation of a medical device.

PARTICIPANTS

One hundred eighty-nine participants with glaucoma or suspected glaucoma were recruited from the Wilmer Eye Institute, Baltimore, Maryland, between July 2014 and April 2015.

METHODS

Participants had standardized training and had to be able use the Icare HOME device independently. Subjects also had to be able to obtain the first intraocular pressure (IOP) measurement within 5 mmHg of Goldmann applanation tonometry (GAT). Those certified obtained 3 IOP measures using the HOME device, and these were compared with Icare TA01i and GAT IOP measurements.

MAIN OUTCOME MEASURES

The agreement between Icare HOME and reference tonometers was used to assess precision. The intraclass correlation coefficient was used to assess within-patient reliability for the HOME device.

RESULTS

Eighteen of 189 recruited patients were ineligible to take part in the study. Forty-four of 171 patients (25.7%) started but failed to complete the study: 7 stopped because of time concerns, 10 of 171 patients (6%) stopped because of difficulty using the device during certification, and 27 of 171 patients (16%) failed to be certified based on IOP. The HOME and GAT measurements agreed within 5 mmHg in 116 of 127 participants (91.3%); 2 participants (1.6%) had a difference of more than 7 mmHg. The mean difference between the Icare HOME and GAT measurements was -0.33 mmHg (standard deviation, 3.11 mmHg). The overall intraclass correlation coefficient for the HOME device was 0.92 (95% confidence interval, 0.89-0.95).

CONCLUSIONS

Not all participants could learn how to use the Icare HOME device, but for those who could, most were able to obtain measurements similar to those obtained by GAT. The Icare HOME device is safe and reliable for self-tonometry, but nearly 1 in 6 individuals may fail to certify in use of the device based on large differences in IOP when comparing GAT with the Icare HOME measurements. The device has the potential to address an unmet need by providing more frequent IOP measurements in a patient's day to day life.

Comparison of intraocular pressure measurements with different contact tonometers in young healthy persons

AIM

To analyze the correlation of Goldmann applanation tonometer (GAT), I-Care tonometer and Tono-Pen tonometer results in young healthy persons, and to investigate the influence of central corneal thickness (CCT) on intraocular pressure (IOP) measurements recorded with these tonometers.

METHODS

We conducted a pilot clinical study in 78 eyes of 78 subjects aged 22-28 years old (44 women and 34 men; mean age 23.8±1.19y). IOP was measured using GAT, I-Care and Tono-Pen tonometers, followed by measurements of CCT. Statistical analysis was performed using SPSS 20.0.

RESULTS

The mean IOPs and standard deviation (±SD) for GAT, I-Care and Tono-Pen were 15.62±2.281 mm Hg, 16.29±2.726 mm Hg and 16.32±2.393 mm Hg, respectively. The mean CCT was 555.15±29.648 µm. Clear positive correlations between GAT and I-Care, GAT and Tono-Pen, and I-Care and Tono-Pen tonometers were found (r=0.867, P<0.001; r=0.861, P<0.001; r=0.915, P<0.001, respectively). In comparison between devices, Bland-Altman analysis showed a significant mean difference (MD) in the measurements by GAT and I-Care of -0.679 mm Hg and by GAT and Tono-Pen of -0.705 mm Hg ( P<0.001), but there was no significant difference between I-Care and Tono-Pen ( P>0.05). Both non-gold standard tonometers were affected by CCT; that is, both I-Care and Tono-Pen tonometer values were significantly higher with higher CCT means (>555 µm; MD=-1.282, P<0.001; MD=-0.949, P<0.001, respectively) compared with GAT.

CONCLUSION

Both I-Care and Tono-Pen tonometers overestimated IOP compared with the GAT values. Either the I-Care or Tono-Pen tonometer could be used instead of GAT because there was no significant difference between their results. Higher CCT values (>555 µm) were associated with overestimated IOP values.

Comparison of Intraocular Pressure Measurements Obtained by Icare PRO Rebound Tonometer, Tomey FT-1000 Noncontact Tonometer, and Goldmann Applanation Tonometer in Healthy Subjects

PURPOSE

To compare intraocular pressure (IOP) measurements obtained by Icare PRO rebound tonometer (RT), Tomey FT-1000 noncontact tonometer (NCT), and Goldmann applanation tonometer (GAT) in healthy subjects, and to investigate the influence of central corneal thickness (CCT) on IOP measurements.

METHODS

A total of 132 eyes of 66 healthy subjects were included in the study. All IOP measurements were applied in a sitting position and always in the same order (RT, NCT, and GAT). CCT was measured by noncontact anterior segment optical coherence tomography.

RESULTS

The mean CCT was 523.5±31.2 μm. The mean IOPs with GAT, NCT, and RT measurements were 14.56±2.77, 13.42±2.99, 14.18±2.55 mm Hg, respectively. A significantly good agreement was found between RT and GAT measurements (P=0.515). The mean difference between RT and GAT measurements was -0.38 mm Hg. An underestimation was found in NCT measurements compared with GAT ones as defined from paired comparisons (P=0.003). The mean difference between NCT and GAT measurements was -1.14 mm Hg. There was no significant difference between NCT and RT readings (P=0.069). The mean difference between NCT and RT measurements was -0.76 mm Hg. There was a significant correlation between GAT-NCT (r=0.740, P<0.001), GAT-RT (r=0.743, P<0.001), NCT-RT (r=0.729, P<0.001) measurement methods. The increment in measured IOP for a 10 μm increase in CCT was 0.16, 0.33, and 0.18 mm Hg for the GAT, NCT, and RT, respectively.

CONCLUSIONS

The IOP readings with the new Icare PRO RT showed good correlation with those obtained by GAT. Tomey FT-1000 NCT underestimated the IOP compared with GAT.

A Comparative Study of Rebound Tonometry With Tonopen and Goldmann Applanation Tonometry Following Vitreoretinal Surgery

PURPOSE

To investigate agreement in intraocular pressure (IOP) measurements among Icare rebound tonometry, Tonopen tonometry, and Goldmann applanation tonometry following vitreoretinal surgery.

DESIGN

Reliability analysis of tonometers.

METHODS

Fifty-eyes of 50 adults undergoing vitreoretinal surgery were enrolled. IOP was measured on first postoperative day using Icare (Tiolat, Helsinki, Finland), followed by Tonopen (Reichert, Depew, New York, USA) and Goldmann (Haag-Streit USA, Mason, Ohio, USA) in randomized order. Intraclass correlation coefficients (ICC) and Bland-Altman plots were calculated for all subcategories.

RESULTS

Icare successfully measured IOP in all eyes, while Goldmann was unmeasurable in 6 eyes (12%) and Tonopen in 1 eye (2%). Mean IOP by Icare, Tonopen, and Goldmann was 15.9 ± 8.9, 16.9 ± 6.2, and 16.0 ± 7.3 mm Hg, respectively (P = .76). Type of intraocular tamponade, status of lens, status of cornea, gauge of instrumentation, and history of prior vitrectomy did not result in significant differences among the 3 tonometers. ICC was excellent (>0.75) in all subgroups, except at IOP <10 and ≥ 23 mm Hg (based on Icare). In eyes with IOP <10 mm Hg, Icare underestimated IOP (mm Hg; P = .01) compared to Goldmann (2.0 ± 2.1) and Tonopen (3.5 ± 2.4), whereas at IOP ≥ 23 mm Hg Icare was overestimated (P = .01) compared to Goldmann (3.77 ± 3.49) and Tonopen (4.97 ± 3.33). Overall, differences in IOP were ≤ 3 mm Hg in 58% of eyes for Icare-Tonopen, 72% for Tonopen-Goldmann, and 62% for Icare-Goldmann.

CONCLUSION

IOP measurements using Icare rebound tonometry, Tonopen, and Goldmann tonometry are in excellent agreement following vitreoretinal surgery. However, Icare overestimates at IOP ≥ 23 and underestimates at IOP <10 mm Hg.

Comparison of Intraocular Pressure Measurements Obtained by Rebound, Noncontact, and Goldmann Applanation Tonometry in Children

PURPOSE

To compare intraocular pressure (IOP) among rebound, noncontact, and Goldmann applanation tonometry (GAT) and their relationships to central corneal thickness in children.

DESIGN

Diagnostic protocol comparison and evaluation.

METHODS

In right eyes of 419 children, mean IOP, rates of successful measurement with 3 tonometries, and intermethod agreement by Bland-Altman plot were assessed. The influences of central corneal thickness, and of average IOP of 3 tonometries on IOP differences between tonometries, were evaluated.

RESULTS

The mean age was 8.89 ± 3.41 years (3-15 years). There was significant difference in mean IOP of each tonometry; GAT showed the lowest values (P < .05). The IOP was successfully measured by noncontact tonometry in 89%, by rebound tonometry in 75%, and by GAT in 64% of children less than 10 years old, and in 100%, 98%, and 94% of children older than 10 years, respectively. The IOP of each tonometer positively correlated with central corneal thickness (P < .05). The mean differences and limits of agreement were 0.81 ± 6.19 mm Hg (noncontact minus rebound), 2.56 ± 4.62 mm Hg (rebound minus GAT), and 1.81 ± 4.76 mm Hg (noncontact minus GAT). Rebound and noncontact tonometry overestimated IOP relative to GAT for thicker central corneal thicknesses. Rebound tonometry overestimated IOP relative to GAT and noncontact tonometry at higher average IOP of 3 tonometries.

CONCLUSIONS

Rebound, noncontact, and Goldmann applanation tonometries can be considered appropriate methods for children, though noncontact tonometry is the most accessible. Given the risk of false-positive diagnosis of pediatric glaucoma, attention should be devoted to children with IOP within a suspicious range or thicker cornea.

Intraocular Pressure Changes during Accommodation in Progressing Myopes, Stable Myopes and Emmetropes

Purpose

To investigate the changes of intraocular pressure (IOP) induced by 3-diopter (3 D) accommodation in progressing myopes, stable myopes and emmetropes.

Design

Cross-sectional study.

Participants

318 subjects including 270 myopes and 48 emmetropes.

Methods

195 progressing myopes, 75 stable myopes and 48 emmetropes participated in this study. All subjects had their IOP measured using iCare rebound tonometer while accommodative stimuli of 0 D and 3 D were presented.

Main Outcome Measures

IOP values without accommodation and with 3 D accommodation were measured in all subjects. Baseline IOPs and IOP changes were compared within and between groups.

Results

There was no significant difference in IOPs between progressing myopes, stable myopes and emmetropes when no accommodation was induced (17.47±3.46, 16.62±2.98 and 16.80±3.62 respectively, p>0.05). IOP experienced an insignificantly slight decrease after 3 D accommodation in three groups (mean change -0.19±2.16, -0.03±1.68 and -0.39±2.65 respectively, p>0.05). Subgroup analysis showed in progressing myopic group, IOP of children (<18 years old) declined with accommodation while IOP of adults (≥18 years) increased, and the difference was statistically significant (p = 0.008). However, after excluding the age factor, accommodation induced IOP changes of high progressing myopes (≤-6 D), low, moderate and non-myopes (>-6 D) was not significantly different after Bonferroni correction (p = 0.838).

Conclusions

Although no difference was detected between the baseline IOPs and accommodation induced IOP changes in progressing myopes, stable myopes and emmetropes, this study found accommodation could cause transient IOP elevation in adult progressing myopes.

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.

The effect of corneal biomechanical properties on rebound tonometer in patients with normal-tension glaucoma

PURPOSE

To evaluate the effects of corneal biomechanical properties on intraocular pressure (IOP) measured with the ICare, and to compare IOP readings obtained with ICare, Ocular Response Analyzer (ORA), and Goldmann applanation tonometry (GAT) in normal-tension glaucoma (NTG) and normal subjects.

DESIGN

Prospective, cross-sectional, comparative study.

METHODS

IOP was measured with ICare, ORA, and GAT. All subjects had corneal hysteresis (CH) and corneal resistance factor (CRF), which were measured with ORA; and central corneal thickness (CCT), axial length, spherical equivalent, and keratometry.

RESULTS

This study enrolled 97 eyes of 97 NTG patients and 89 eyes of 89 normal subjects. CCT, CH, and CRF in NTG patients were significantly lower than those in normal subjects (P = .033, P = .006, and P = .003). The difference in IOP between techniques was highly significant in NTG patients (P < .001), while there was no significant difference in IOP values between techniques in normal controls (P = .931). ICare readings were significantly lower than corneal-compensated IOP in NTG patients (P = .014). CH and CRF were significantly associated with IOP measurements with ICare in NTG and normal subjects (P < .001). The greater difference between IOPcc and ICare in NTG patients was significantly influenced by the lower CH (P < .001).

CONCLUSIONS

Since ICare is a convenient way to measure IOP, ICare is a reasonable option as an alternative tonometer in NTG patients. However, the clinician must consider that the corneal biomechanical characteristics in NTG can cause ICare to underestimate IOP.

Comprasion of ICare rebound tonometer and Goldmann applanation tonometer in high myopia

Purpose. To compare intraocular pressure (IOP) measurements with the Goldmann applanation tonometer (GAT) and the ICare rebound tonometer (RBT) in high myopic eyes. Patients and Methods. This randomized prospective study included 40 eyes of 40 patients with high myopia. All patients' central corneal thickness (CCT), anterior chamber depth (ACD), axial length (AXL), keratometry, and refractive measurements were recorded and followed by IOP measurement with RBT and GAT. Results. The average CCT, AXL, and ACD were determined to be 514.65 ± 32 μm, 27.65 ± 2.22 mm, and 3.25 ± 0.51 mm, respectively. Mean K was 43.27 ± 1.4 D and mean spherical equivalent was −11.31 ± 4.30 D. The mean IOP values obtained by RBT and GAT were 17.18 ± 3.72 mmHg and 16.48 ± 3.19 mmHg, respectively. The deviations of RBT readings from corrected GAT values were highly correlated with CCT values (r = 0.588, P = 0.0001). The mean corrected GAT reading was 17.49 ± 3.01 mmHg. Linear regression analysis showed that a CCT change of 10 μm resulted in an RBT reading deviation of 0.57 mmHg. The Bland-Altman scatter-plot and McNemar test showed a clinically good level of agreement between the two tonometers. Conclusion. This study found a good agreement level between the two tonometers in high myopic patients and that RBT measurements are influenced by CCT variations.

Accommodation-induced intraocular pressure changes in progressing myopes and emmetropes

PURPOSE

To investigate the changes of intraocular pressure (IOP) and anterior eye segment biometric parameters under different accommodative statuses in progressing myopes and emmetropes.

METHODS

Forty-six progressing myopes and 40 emmetropes participated in this study. All the subjects had their IOP and anterior eye segment biometric parameters (including corneal thickness, anterior chamber depth, anterior chamber angle width, and lens thickness) measured using iCare rebound tonometer and VisanteTM anterior segment-optical coherence tomography while accommodative stimuli of 0, 3, and 6D were presented.

RESULTS

There was no significant difference in IOP between progressing myopes and emmetropes when no accommodation was induced (16.22±4.11 vs 17.01±3.72, respectively, t=-0.93, P>0.05). However, IOP significantly increased with accommodation in progressing myopes (mean change +1.02±2.07 mm Hg from 0D to 6D, F=5.35, P<0.01), but remained unchanged (mean change -0.76±3.22 mm Hg from 0D to 6D, F=1.46, P>0.05) in emmetropes. Meanwhile, we found that their anterior chamber depth decreased (P<0.01), anterior chamber angle narrowed (P<0.01), and lens thickened (P<0.01) significantly with accommodation, both in progressing myopes and emmetropes.

CONCLUSIONS

Although no difference was detected between the IOPs of progressing myopes and emmetropes without accommodation, accommodation could induce transient IOP elevation in progressing myopes. Simultaneously, we found that their anterior chamber depth decreased, anterior chamber angle narrowed, and lens thickened with accommodation. Although emmetropes showed the similar anterior eye segment structure changes, their IOPs did not increase with accommodation. Our study indicated that IOP elevation with accommodation in progressing myopes might be related to myopia progression.

Immediate changes in intraocular pressure after clear corneal micro-incision versus small-incision cataract surgery

PURPOSE

We sought to examine changes in intraocular pressure (IOP) in the immediate period after clear corneal micro-incision cataract surgery (MICS) and after small-incision cataract surgery (SICS).

METHODS

Sixty-eight eyes of 34 patients scheduled for coaxial phacoemulsification were randomized into one of two groups: (a) eyes that were to undergo a 2.0-mm MICS, and (b) a 2.65-mm SICS. At the conclusion of surgery, the IOP was adjusted to the range between 15-40 mmHg with stromal hydration. The IOP was measured using a rebound tonometer preoperatively, at the conclusion of surgery, and at 3, 6, 9, 12, and 15 min postoperatively. The Seidel test and anterior segment-optical coherence tomography were performed at 20 min postoperatively.

RESULTS

Mean IOP at the conclusion of surgery was 27.7 ± 4.7 mmHg in the MICS group and 29.7 ± 5.1 mmHg in the SICS group (p = 0.1239). In both groups, mean IOP decreased to the preoperative level within 9 min postoperatively and did not change significantly for up to 15 min. Mean IOP was similar between the MICS and SICS groups throughout the observation period (p ≥ 0.1239). Hypotony (≤10 mmHg), positive Seidel test, and loss of wound coaptation were not detected in all eyes.

CONCLUSIONS

After adjusting the IOP to a relatively high level at the conclusion of surgery, the IOP decreased within 9 min and was stable within 15 min without hypotony. The IOP was comparable between eyes after MICS and SICS, and both incisions virtually closed within 20 min postoperatively.

Assessment of IcareONE rebound tonometer for self-measuring intraocular pressure

PURPOSE

To evaluate the precision of the IcareONE rebound tonometer, which was developed for self-measuring intraocular pressure (IOP) and to compare IcareONE measurement with Goldmann applanation tonometry (GAT).

METHODS

Twenty-four healthy eyes and 81 glaucomatous eyes were enrolled. IOP measurements (three times per session) with IcareONE were made in a random order by an ophthalmologist (Icare(O)) and by the subject (Icare(S)). Intraclass correlation coefficients (CCs), kappa values and mean values of IOP were compared among the two types of Icare recordings and GAT. Bland-Altman analysis was used to assess agreement between methods. Multiple regression analysis was performed to identify the subject factors that influenced the discordant measurements between IcareONE and GAT.

RESULTS

The mean value of Icare(O) and Icare(S) measurements was 13.5±5.2 and 13.5±5.4 mmHg, respectively, neither of which was significantly different from GAT (13.8±4.4). The intrarater CC of Icare(O) and Icare(S) was 0.968 and 0.885, respectively. The intermethod CC and weighted kappa between Icare(O) and Icare(S) were 0.907 and 0.684, respectively. All pairwise correlations between the two types of IOP measurement showed coefficients of determination >0.8. Bland-Altman analysis did not show any proportional biases. Multiple regression analysis revealed that the differences between GAT and Icare(O) or Icare(S) were positively correlated with central corneal thickness (CCT) and negatively correlated with age.

CONCLUSIONS

Intraocular pressure measurements with IcareONE by a physician and by the subject showed excellent agreement with GAT measurements; IcareONE measurements between a physician and the subject had high intrarater reliability, and good agreement thicker CCT led IcareONE measurement to overestimate IOP, while higher age caused it to underestimate IOP compared with GAT.

Short-term effect of standard automated perimetry testing on intraocular pressure in patients with open-angle glaucoma

Purpose. To evaluate the short-term effect of standard automated perimetry (SAP) testing on intraocular pressure (IOP) in patients with open-angle glaucoma (OAG). Methods. We tested 45 patients (71 eyes) with OAG that had stable IOP under medical treatment. IOP was measured four times using an iCare rebound tonometer (RBT) immediately before, immediately after, 10 minutes after, and 20 minutes after SAP testing. Logistic regression analyses were performed to determine the relationships among SAP test duration, mean deviation of the SAP result, type of glaucoma medications, patient age, and significant IOP change (exceeding 2 mmHg) from baseline IOP. Results. The mean baseline IOP was 13.29 ± 3.06 mmHg. Although IOP changes immediately and 20 minutes after SAP testing were not statistically significant, the IOP change 10 minutes after SAP testing (-0.57 ± 1.84 mmHg) was statistically significant. However, the changes were within the margin of error of the RBT. Test duration, mean deviation, patient age, and type of glaucoma medications did not have a significant influence on IOP change (all P > 0.14). Conclusions. IOP measured by RBT did not vary significantly after SAP testing in patients with OAG. It may be not necessary to reject IOP measured after SAP testing in patients with OAG.

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.

Comparison of IOPen rebound tonometer with Goldmann applanation tonometer at different IOP levels

AIM

To compare the accuracy of IOPen rebound tonometer with Goldmann applanation tonometer (GAT) in individuals with low, normal and high intraocular pressure (IOP) and to evaluate the effect of central corneal thickness (CCT) on IOP measurements.

METHODS

This cross-sectional study consisted of 159 participants. IOP of one eye of each subject was measured consecutively with IOPen and GAT. Then CCT was measured using an ultrasonic pachymeter. Based on GAT IOP readings, participants were divided into low, normal and high IOP groups. Correlation between tonometers and CCT was calculated by spearman's correlation coefficient. Agreement between tonometers was evaluated using Bland-Altman method.

RESULTS

Non-significant underestimation of IOP by IOPen was observed in low IOP group (Mean difference: 0.20mmHg; P=0.454) and also in normal IOP group (Mean difference: 0.56mmHg; P=0.065). However, IOPen significantly overestimated IOP in high IOP group (Mean difference: 1.06mmHg; P=0.038). The 95% limits of agreement (LoA) width between IOPen and GAT IOPs were 7.84, 8.57 and 14.27mmHg in low, normal and high IOP groups, respectively. Low IOP group had thinner corneas compared to high IOP group (P=0.034). IOP measurements taken by IOPen were not influenced by CCT (P=0.099) while poor correlation between CCT and GAT was found (R=0.17, P=0.032). Using receiver operating characteristic (ROC) curve, cutoff value of 18.75mmHg was determined for IOPen with sensitivity of 98.1 and specificity of 97.2%.

CONCLUSION

Accuracy of IOPen is comparable to GAT in patients with low or normal IOP but IOPen overestimates IOP at high IOP levels. CCT does not affect IOP readings with IOPen.

Comparison of the new rebound tonometer with Goldmann applanation tonometer in a clinical setting

PURPOSE

To evaluate the clinical usefulness of a new rebound tonometer, Icare(®) PRO (Icare PRO), by comparison with Goldmann applanation tonometry (GAT) in a study on patients with glaucoma.

METHODS

One hundred and seventy-two eyes of 86 subjects were enrolled in this study. All of the subjects were examined with an autorefractometer, Icare PRO, slit-lamp biomicroscope, GAT, ultrasound A-scan and pachymeter. Three intraocular pressure (IOP) measurements were obtained by Icare PRO and GAT. The intraobserver reliabilities were established by calculating the intraclass correlation coefficients. The Bland-Altman plot was used to compare the Icare PRO and GAT.

RESULTS

There was a good correlation between the IOP measurement by GAT and that by Icare PRO (r = 0.6995, p < 0.001). The intraclass correlation coefficients of Icare PRO and GAT were 0.778 and 0.955, respectively. The IOP differences between Icare PRO and GAT (mean: 1.92 mmHg; SD: 3.29 mmHg; 95% limit of agreement: -4.52 to 8.37 mmHg) did not vary over the wide range of central corneal thickness (p = 0.498), age (p = 0.248), axial length (p = 0.277) or spherical equivalent (p = 0.075).

CONCLUSIONS

Although IOP with Icare PRO was higher than that with GAT, especially at lower GAT IOP value, Icare PRO was found to be a reliable method and showed a good correlation with GAT. The IOP difference between Icare PRO and GAT was not affected by the central corneal thickness, age, axial length or spherical equivalent. Icare PRO can be expected not only to be a good screening tool but also to be a good substitute for GAT.

Comparison of handheld rebound tonometry with Goldmann applanation tonometry in children with glaucoma: a cohort study

OBJECTIVE

To test agreement of two methods to measure intraocular pressure (IOP): rebound tonometry (RBT) and gold standard Goldmann applanation tonometry (GAT) in children with glaucoma.

DESIGN

Observational prospective cohort study.

SETTING

Tertiary paediatric glaucoma clinic at a single centre.

PARTICIPANTS

102 individuals attending a paediatric glaucoma clinic, mean (SD) age 11.85 (3.17), of whom 53 were male.

PRIMARY AND SECONDARY OUTCOME MEASURES

Intraocular pressure, central corneal thickness, child preference for measurement method.

RESULTS

Limits of agreement for intraobserver and interobserver were, respectively, (-2.71, 2.98) mm Hg and (-5.75, 5.97) mm Hg. RBT frequently gave higher readings than GAT and the magnitude of disagreement depend on the level of IOP being assessed. Differences of 10 mm Hg were not uncommon. RBT was the preferred method for 70% of children.

CONCLUSIONS

There is poor agreement between RBT and GAT in children with glaucoma. RBT frequently and significantly overestimates IOP. However, 'normal' RBT readings are likely to be accurate and may spare children an examination under anaesthesia (EUA). High RBT readings should prompt the practitioner to use another standard method of IOP measurement if possible, or consider the RBT measurement in the context of clinical findings before referring the child to a specialist clinic or considering EUA.

Intraocular pressure in a cohort of healthy eastern European schoolchildren: variations in method and corneal thickness

Background

Intraocular pressure (IOP) in the developing eye of a child is not always easy to measure and there is no technique that is known to be the most accurate for the young eye. Measurements are needed on many cohorts of children with different tonometers to determine how the values correlate between instruments, whether corneal parameters affect readings and whether correlations between age and IOP values can be discerned. The aim of this study was to undertake a comparative analysis of three different tonometers on a group of healthy children to see whether differences exist and whether these may be related to central corneal thickness and/or radius of curvature. In addition, the study adds to the relatively small body of literature on IOP in the growing eye which will collectively allow trends to be identified and ultimately norms to be established.

Methods

IOP was measured on 115 eyes in a group of Polish children, aged between 5–17 years (mean ± standard deviation [SD] 11.3 ± 3.0 years) using three different tonometers: non-contact (NCT), the ICare and Goldmann applanation (GAT). Readings obtained were compared between instruments and with central corneal thickness and radius of curvature.

Results

The ICare tonometer provided statistically higher IOP values (16.9 ± 3.4 mmHg) than the GAT (14.7 ± 2.9 mmHg) regardless of corneal thickness and whether or not a correction factor was applied. A correlation was found between central corneal thickness (CCT) and IOP values obtained with all three tonometers but only the IOP values detected with the ICare tonometer showed a statistically significant correlation with radius of curvature (p < 0.004). No correlations with age or gender were found for IOP values measured with any of the instruments.

Conclusions

IOP measurements on children vary significantly between instruments and correlations are affected by the corneal thickness. Further studies on children are needed to determine which instrument is most appropriate and to derive a normative IOP scale for the growing eye.

Icare ONE rebound versus Goldmann applanation tonometry in children with known or suspected glaucoma

PURPOSE

To compare Icare ONE tonometry by clinic examiner and parent/guardian to Goldmann applanation in children with known/suspected glaucoma; to evaluate the trend in intraocular pressure (IOP) with 4 repeated measurements using Icare ONE; and to evaluate the feasibility of instructing parents on the use of the Icare ONE device in the clinic setting.

DESIGN

Nonrandomized, prospective clinical study.

METHODS

Patients with known or suspected glaucoma were recruited from the Duke pediatric glaucoma clinic. Parent(s) of all subjects gave informed consent (and children gave assent) for participation in this research study. IOP was measured using Icare ONE by clinic examiner and parent/guardian, then using Goldmann applanation (masked physician). Each parent/guardian completed an ease-of-use survey.

RESULTS

Sixty eyes (60 children) were included. Absolute value of mean IOP difference (ICare ONE clinic examiner vs Goldmann applanation) was 3.3 ± 4.0 mm Hg (P = .001). Icare ONE IOP by clinic examiner was within 3 mm Hg of Goldmann applanation in 68% (n = 41 eyes). In eyes with >3 mm Hg difference, Icare ONE was higher than Goldmann applanation in 84%. IOP demonstrated a statistically significant downward trend with repeated sequential measurements with Icare ONE (P = .0053, r(2) = 0.9894). All parents accomplished Icare ONE tonometry on at least 1 eye; 98% reported it was "easy to learn to use."

CONCLUSION

Icare ONE tonometry appears accurate and well-tolerated compared to Goldmann applanation, and holds promise for clinic and home tonometry in children. IOP trends downward with successive measurements using Icare ONE, demonstrating a possible effect from presumed patient relaxation.

Evaluation of the Icare-ONE rebound tonometer as a self-measuring intraocular pressure device in normal subjects

PURPOSE

To compare Icare ONE rebound self-tonometer (ICRBT) measurements with Goldman applanation tonometry (GAT).

METHODS

A trained examiner instructed each of 60 normal subjects on use of the ICRBT. Each subject then took two measurements of his/her own pressure using the ICRBT. Finally, a different examiner, who was masked to the earlier readings, measured IOP by GAT. Bland–Altman limits of agreement (LOA), intraclass correlation coefficients (ICCs), Kappa values, and paired t-test were used to assess the agreement between the two methods. Pearson’s correlation coefficient was used for correlation analysis.

RESULTS

All of the subjects were able to obtain correct measurements with ICRBT after three attempts. The mean intraocular pressure with ICRBT and GAT measurements were 16.0 ± 3.3 mmHg and 13.7 ± 2.5 mmHg respectively. The mean difference between patient’s ICRBT and technician’s GAT measurements was 2.3 mmHg (p < 0.001). In 63% (38/60) of the cases the IOP difference (ICRBT − GAT) was within ± 3 mmHg. The weighted Kappa for the IOP measurements of the two methods was 0.49 (95% CI: 0.30–0.68, p < 0.001), indicating acceptable agreement. A significantly positive correlation was found between ICRBT IOP measurements and central corneal thickness (CCT) (r = 0.48, p < 0.001). In addition, the difference in IOP measurements (ICRBT − GAT) between the two methods was positively correlated with CCT (r = 0.31, p = 0.015), indicating that greater thickness is associated with greater differences between the two methods.

CONCLUSION

The ICRBT was reliable in the hands of normal subjects, and may be used for self-monitoring of IOP. ICRBT measurements generally overestimated GAT measurements.

[Comparison of the iCare tonometer with the Goldmann tonometer in Malawi]

BACKGROUND

The risk for glaucoma is 4-5 times higher in patients from sub-Saharan Africa. Thus, especially in developing countries an easy and effective method for assessing the intraocular pressure (IOP) is needed.

METHODOLOGY

In this hospital-based survey 150 eyes were divided into 3 groups concerning the IOP (group I < 16 mmHg, group II 16-23 mmHg and group III > 23 mmHg) and underwent examination with ultrasound pachymetry followed by iCare tonometry (ICT) and Goldmann applanation tonometry (GAT). Agreement of the measurements by two tonometers was assessed with the Bland-Altman method and the influence of the central corneal thickness (CCT) on the ICT measurements was determined.

RESULTS

The mean difference between the IOD measured with GAT and ICT was 0.84 ± 2.63 mmHg. The differences were similar in all three groups (0.77-0.97 mmHg), however, the standard deviation in group III (4.04 mmHg) was greater than in groups I (1.98 mmHg) and II (1.79 mmHg). The mean CCT was 513.51 ± 36.22 µm.

CONCLUSIONS

The agreement of measurements by GAT and ICT was good for lower IOP values but less accurate in patients with higher IOP values (group III). A dependency of the CCT on the ICT measurements was observed. In comparison to other countries the lowest CCTs were found in Malawian patients.

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.

Home tonometry for management of pediatric glaucoma

PURPOSE

To use iCare rebound tonometry in the home setting for documentation of diurnal intraocular pressure (IOP) fluctuations in children.

DESIGN

Nonrandomized, prospective clinical study.

METHODS

Pediatric ophthalmology clinic patients were recruited between October 2009 and February 2010 who were able to cooperate with IOP measurement by iCare rebound tonometry and whose caregiver was willing and able to obtain iCare measurements at home. The child's IOP was measured first by iCare tonometry followed by a second method (Goldmann applanation [GAT]). The caregiver was instructed on the use of the iCare tonometer. The subject's IOP was measured by the caregiver at home at designated time periods for at least 2 consecutive days.

RESULTS

Seventeen children (17 eyes) with known or suspected glaucoma and 11 normal children were included. Excellent reliability was obtained by caregivers in 70% of iCare measurements. Mean difference between iCare and GAT in clinic was 2.0 ± 4.0 mm Hg, P = .08. Daily IOP fluctuation occurred in both subjects with glaucoma and normal subjects. In children with known or suspected glaucoma, relative peak and trough IOPs occurred in the early morning (45%) and late evening (43.5%), respectively. Comparison of the peak IOP measured at home vs in the clinic was >6 mm Hg in 5 of 16 subjects (31%) and affected glaucoma management in several subjects.

CONCLUSIONS

In selected children with glaucoma, home tonometry by iCare rebound tonometry was reliable, easily performed by caregivers, and well tolerated, and offered IOP information valuable in clinical management.

Comparing applanation tonometry and rebound tonometry in glaucomatous and ocular hypertensive eyes

PURPOSE

To describe Goldmann applanation tonometer (GAT) and rebound tonometer (RT) agreement in measuring intraocular pressure (IOP) in glaucomatous and ocular hypertensive (OH) eyes and to evaluate central corneal thickness (CCT) influence on RT readings.

METHODS

A total of 347 eyes were enrolled and IOP measured between 9 and 11 am. Rebound tonometry was performed first (RT1), followed by 3 consecutive GAT measurements and by a second RT reading (RT2), within a 5-minute span. Mean IOP (±SD) values were compared by means of paired t-test. Agreement between GAT and RT1 (test 1) and RT2 (test 2) was evaluated with Bland-Altman method, whereas a linear function described the relationship between CCT and IOP taken with RT.

RESULTS

Mean IOP (±SD) taken with RT1, GAT, and RT2 was 18.1±4.3, 15.6±3.3, and 16.3±3.9 mmHg, respectively. Readings were within ±3 mmHg in 63.7% and 86.7% of eyes for test 1 and 2, respectively. A significant (p<0.001) proportional bias was noted on both tests (95% limits of agreement: -2.3/7.4 and -3.6/5.0 mmHg for test 1 and 2, respectively). Agreement between instruments decreased for increasing IOP. Rebound tonometry readings increased by 4.6 and 4.1 mmHg for RT1 and RT2, respectively, for each 100-µm CCT increase.

CONCLUSIONS

When used first, RT significantly overestimated IOP compared with GAT. Differences became clinically negligible when RT was used immediately after GAT. Repeated applanation tonometry may explain this observation. Agreement between instruments was acceptable for low IOP, but worsened with increasing IOP values. RT is significantly influenced by CCT. Goldmann applanation tonometer and RT should not be used interchangeably.

Validity and limits of the rebound tonometer (ICare®): clinical study

PURPOSE

The aim of this study was to evaluate the measurement of intraocular pressure (IOP) using a new induction/impact rebound tonometer (ICare®) compared with Goldmann applanation tonometry (GAT). We also aimed to quantify the systematic and random errors (bias) of the 2 methods, to evaluate the sensitivity and specificity of the ICare® tonometer in identifying patients with 21 mmHg or more measured with the GAT, and to study the influence of corneal thickness on IOP measurement with the 2 tonometers.

METHODS

We compared the IOP values obtained with the 2 instruments in 97 patients.

RESULTS

Analysis based on the Bland and Altman method revealed that the IOP values recorded with the ICare® tonometer were slightly higher than those obtained with the GAT. The estimated bias for right eye measurements was 0.78 mmHg with 95% limits of agreement ±3.55 mmHg. This overestimation, which is not clinically relevant, was confirmed when we used the IOP values corrected according to central corneal thickness for data analysis. The sensitivity and specificity were 0.90 and 0.95, respectively.

CONCLUSIONS

The ICare® tonometer proved to be comparable with other nonconventional tonometers and can be used by nonophthalmologists and paramedical personnel during screening tests of populations. In addition, the ICare® tonometer could be considered a valid alternative to GAT when GAT is not available.

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.

A history of intraocular pressure and its measurement

Doctors have not always associated elevated intraocular pressure with the vision loss from glaucoma. Although several individuals appear to have noted firmness of the eye in this condition as far back as the 10th century, elevated intraocular pressure was not routinely assessed until the latter part of the 19th century. von Graefe developed the first instrument for measuring intraocular pressure in 1865. The first reasonably accurate instrument was the Maklakoff applanation tonometer of the late 19th century; it was in widespread use throughout Eastern Europe until relatively recently. Schiötz developed an indentation tonometer that was widely used throughout the world during the first two thirds of the 20th century. Goldmann's applanation tonometer of 1950 began the era of truly accurate intraocular pressure measurement. It is still the most widely used tonometer in the world. Other devices such as the McKay-Marg tonometer (or its offspring the Tono-Pen), the pneumatonometer, and airpuff applanation tonometers are gaining adherents. The dynamic contour tonometer is the first totally new concept in tonometry in over 100 years. It is probably the most accurate of all the tonometers and is relatively independent of corneal biomechanical properties unlike its predecessors. Transpalpebral tonometers are attractive as they do not require topical anesthesia; however, they add the biomechanical properties of the eyelid to the list of potential errors and have not proven very accurate. The future should, hopefully, bring tonometers that can give diurnal or even longer indications of intraocular pressure variation. Although intraocular pressure elevation (or its absence) no longer can be counted on for diagnostic purposes, the role of intraocular pressure in the management of glaucomatous optic neuropathy remains critical.

Icare rebound tonometry in children with known and suspected glaucoma

BACKGROUND

Accurate intraocular pressure (IOP) measurement, important in managing pediatric glaucoma, often presents challenges. The Icare rebound tonometer shows promise for screening healthy children and has been reported comparable with Goldmann applanation in adults with glaucoma. The purpose of this study was to evaluate the Icare tonometer against Goldmann applanation for clinic IOP measurement in pediatric glaucoma.

METHODS

This was a prospective study comparing Icare versus Goldmann tonometry in pediatric glaucoma. Children with known or suspected glaucoma were recruited from scheduled clinic visits. IOP was measured with the Icare tonometer by a clinician and subsequently measured with Goldmann applanation tonometry (GAT) by a different single masked clinician.

RESULTS

A total of 71 eyes of 71 children with known or suspected glaucoma were included. IOP by GAT ranged from 9 to 36 mm Hg. Icare readings ranged from 11 to 44 mm Hg. Mean difference between Icare and GAT was 2.3 ± SD 3.7 mm Hg, p < 0.0001. Icare IOPs were within ± 3 mm Hg of GAT in 63%. Icare IOPs were ≥GAT IOPs in 75%. The following factors were not associated with Icare IOPs greater than GAT: child's age, glaucoma diagnosis, strabismus, nystagmus, central corneal thickness, Icare instrument-reported reliability, number of glaucoma surgeries or medications, corneal abnormalities, and visual acuity.

CONCLUSIONS

IOP by Icare tonometry was within 3 mm Hg of IOP by GAT in 63% and greater than GAT in 75%. This device may be reasonable to estimate IOP in selected children with known or suspected glaucoma whose IOP cannot otherwise be obtained in clinic; however, correlation of Icare IOPs with clinical findings must continue to be considered in each case.

Clinical evaluation of the IOPen® in a glaucomatous population

The aim of this study was to evaluate the level of agreement of measurements of intraocular pressure (IOP) taken by a rebound tonometer (IOPen®), in comparison to a reference Goldmann applanation tonometer (GAT) in a glaucomatous population. Both eyes from 60 patients were assessed with the two tonometers, the induction tonometry was performed first by an experienced optometrist, and the GAT by an ophthalmologist. In this study, statistically significant differences were found when comparing the IOPen® tonometer with the GAT tonometer (p < 0.001), mean differences were -4.81 ± 4.31 and -4.76 ± 5.76 mmHg (mean ± S.D.) for the right eye and left eye respectively These values represent an underestimation in the present population by the IOPen® when compared with the GAT. Frequency distribution of differences demonstrated that in more than 71.6% of the measurements the IOP readings differed by more than 3 mmHg between the two tonometers. These results suggest that IOPen® should be used with great caution in the determination of IOP.