Comparison of the Tono-Pen to the Goldmann applanation tonometer

Meta-Analysis of Tonometer Correction Formulae to Determine True Normal Intraocular Pressures Across a Diverse Range of Species

OBJECTIVE

To utilize previously published tonometer correction formulae to investigate whether true intraocular pressure (IOP) is relatively conserved across a diverse range of vertebrate species.

ANIMALS STUDIED

Tonometer correction formulae for 21 species.

PROCEDURES

A literature search was performed to identify prior studies containing correction formulae for non-invasive tonometers used in normal animal and human subjects. In all cases, direct manometry was compared to non-invasive tonometry values. Where necessary, multiple correction regression formulae were combined to generate a single representative formula using a meta-analysis generic inverse variance method. A subsequent literature search was then performed to collect uncorrected IOP values of normal animals and humans using a variety of non-invasive tonometers. These IOP values were then corrected using the relevant correction formula.

RESULTS

Sixty-five tonometer correction formulae and 104 studies containing IOP values in normal animals and humans acquired using non-invasive tonometry met the inclusion criteria. Corrected IOP values were calculated for 21 species using 13 types of non-invasive tonometers. Overall corrected and uncorrected mean IOP values were typically within a range of 10 to 25 mmHg (corrected: 16/21 species, uncorrected: 14/21 species). Differences between overall mean corrected and uncorrected IOP values ranged from 0.2 to 15.3 mmHg with an average of 6.1 mmHg difference.

CONCLUSIONS

True normal IOP is relatively conserved across a diverse range of vertebrate species despite uncorrected values from individual tonometers suggesting otherwise. Maintaining true IOP between 10 and 25 mmHg appears to be important in ocular physiology in many vertebrates.

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.

Intraocular Pressure Changes during Hemodiafiltration with Two different Concentrations of Sodium in the Dialysate

Simple Summary

An increase in intraocular pressure during chronic hemodialysis is linked to ocular complications, such as glaucoma. The behavior of intraocular pressure during hemodiafiltration is unknown. Changes in intraocular pressure with a sodium dialysate concentration fixed at 138 mmol/L and an individualized concentration were studied in 13 patients with end-stage renal disease treated with hemodiafiltration. Up to 31% patients presented an episode of intraocular hypertension without differences between sodium profiles. A large variability in intraocular pressure within patients and a high prevalence of transient intraocular hypertension were found.

Abstract

Ocular complications are common among end-stage renal disease patients and some complications had been linked to increments of intraocular pressure (IOP) during hemodialysis. The changes of IOP during hemodiafiltration (HDF) have been scarcely investigated and the potential influence of the sodium dialysate concentration is unknown. The aim of this study was to compare the IOP changes during HDF with sodium dialysate concentration, either fixed or individualized. Thirteen end-stage renal disease patients participated in the study; they were treated with HDF using a dialysate sodium profile fixed at 138 mmol and another session with an individualized sodium profile. The intraocular pressure was measured before and after each session and every 30 min during HDF. Both groups had a similar HDF prescription, blood pressure, and biochemical parameters. At the end of hemodiafiltration, sodium concentration decreased only in the fixed sodium profile group. The number of patients with at least an episode of intraocular hypertension during HDF ranged from 5 (19%) to 8 (31%) without significant differences between right and left eye nor between dialysate sodium concentration. During HDF, there is a large variability of IOP; transient events of intraocular hypertension are highly prevalent in this sample, and they are not related to the sodium dialysate concentration.

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.

Telehealth and Screening Strategies in the Diagnosis and Management of Glaucoma

Telehealth has become a viable option for glaucoma screening and glaucoma monitoring due to advances in technology. The ability to measure intraocular pressure without an anesthetic and to take optic nerve photographs without pharmacologic pupillary dilation using portable equipment have allowed glaucoma screening programs to generate enough data for assessment. At home, patients can perform visual acuity testing, web-based visual field testing, rebound tonometry, and video visits with the physician to monitor for glaucomatous progression. Artificial intelligence will enhance the accuracy of data interpretation and inspire confidence in popularizing telehealth for glaucoma.

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 the iCare, Tono-Pen, non-contact airpuff, and Goldmann applanation tonometers in eyes with corneal edema after penetrating keratoplasty

BACKGROUND

To compare the utility of the iCare, Tono-Pen, and non-contact airpuff (NCT) tonometers with the Goldmann applanation tonometer (GAT) for measuring intraocular pressure (IOP) in patients with corneal edema after penetrating keratoplasty (PKP) and to assess the effects of central corneal thickness (CCT) and corneal curvature (CC) on IOP measurements.

METHODS

Thirty-two eyes of 27 patients with corneal edema after PKP due to corneal abnormalities and 43 control eyes of 30 patients with normal corneas were recruited. Before IOP measurements, all patients underwent a baseline examination, including auto-refraction, keratometry, slit lamp biomicroscopy, and CCT measurement. IOP was measured using the devices in the same order: first the NCT, followed by the iCare, Tono-Pen, and GAT. The differences between the iCare, Tono-Pen, NCT, and GAT were calculated with repeated-measures analysis of variance. The Bland-Altman method was used to assess the agreement between the iCare, Tono-Pen, and NCT versus the GAT. The influences of CCT and CC on IOP measurement were evaluated by correlation analysis using Pearson's correlation coefficient.

RESULTS

Mean IOP measurements were significantly higher with the NCT and Tono-Pen than with the GAT in the PKP and control groups. When compared with GAT, iCare showed significantly higher IOP readings in the control group, but the IOP readings did not differ between the iCare and GAT in the PKP group. Poor agreement was noted between the NCT and GAT in both groups. The Tono-Pen showed clinically acceptable agreement with GAT in control eyes and poor agreement in PKP eyes. The agreement between the iCare and GAT appeared to be clinically acceptable in both groups. Correlation analysis of the results from control eyes showed that the IOP measurements with the GAT and NCT were weakly related to CCT and moderately correlated with CC. The iCare IOP readings were weakly correlated with CCT and CC.

CONCLUSION

In the PKP group, the NCT and Tono-Pen significantly overestimated IOP, whereas the iCare IOP readings were similar to those obtained using the GAT. Poor agreement was noted between the NCT and GAT as well as between the Tono-Pen and GAT, but the iCare showed clinically acceptable agreement with GAT. In normal corneas, the GAT, NCT, and iCare were affected by CCT and CC. The iCare tonometer was less affected by corneal edema than were the NCT and the Tono-Pen. The iCare appears to be a useful device for IOP measurement in eyes with corneal edema after PKP.

Comparison of Three Different Tonometers in Eyes with Angle Closure

SIGNIFICANCE

Precise measurement of intraocular pressure (IOP) is essential when diagnosing and managing glaucoma. We compared the IOP readings of three different tonometers and analyzed agreement among tonometers in eyes with high IOPs.

PURPOSE

The purpose of this study was to compare the IOP readings obtained using a Goldmann applanation tonometer (GAT), a rebound tonometer (RT), and a Tono-Pen (TP) in angle-closure eyes with elevated IOP before and after medical IOP-lowering therapy.

METHODS

Twenty-five eyes of 25 patients with angle closure and IOPs of greater than 30 mmHg were enrolled. Intraocular pressure was measured using RT (iCare Pro), TP (Tono-Pen XL), and GAT before and after medical treatment. The mean IOP readings of the tonometers were compared before and after treatment. The agreement among the tonometers was assessed via Bland-Altman analysis.

RESULTS

The measurements from 22 eyes of 22 patients were suitable for statistical analyses. Before medical treatment, the mean TP-IOP was significantly lower than the mean GAT-IOP (44.0 ± 10.3 vs. 50.4 ± 8.9 mmHg, respectively; P < .001), but no significant difference was evident between the RT-IOP and the GAT-IOP (50.8 ± 10.9 vs. 50.4 ± 8.9 mmHg, respectively; P = .79). After IOP-lowering treatment, the mean GAT-IOP (14.9 ± 4.7 mmHg) did not differ from either the mean RT-IOP (15.6 ± 4.4 mmHg) or the mean TP-IOP (15.4 ± 5.0 mmHg; P = .05 and P = .18, respectively). The random measurement error among tonometers was greater for high IOP readings.

CONCLUSIONS

Compared with RT or GAT, TP underestimated IOP in angle-closure eyes with a GAT-IOP of greater than 30 mmHg. Intraocular pressure reading agreement among the three tonometers was lower in eyes with high IOP.

Risk Factors for Early Intraocular Pressure Elevation After Cataract Surgery in a Cohort of United States Veterans

INTRODUCTION

Cataract surgery is the most frequently performed surgery in the Veterans Health Administration (VHA). A well-known complication is a transient but potentially harmful elevation in intraocular pressure (IOP) within the 24-h postoperative period. The purpose of this study is to investigate the risk factors for IOP elevation 1 d after cataract surgery in a cohort of United States (US) veterans.

MATERIALS AND METHODS

The study included 784 patients who underwent cataract surgery between April 2013 and April 2016 at a single Veterans Affairs medical center in Providence, RI. One thousand one hundred thirty-seven cataract surgeries were considered in total. Institutional Review Board (IRB) approval was obtained through the Providence Veterans Affairs Medical Center (PVAMC). Logistic regression, adjusted for patients with bilateral surgeries, was used to evaluate risk factors for first postoperative day IOP elevation (≥28 mmHg). The main outcome measure was elevated IOP on postoperative day 1 (POD1) after cataract surgery.

RESULTS

The average patient age was 74 yr. Ninety-eight percent (1,110/1,137) of cases involved male patients; 75.3% (856/1,137) of the cataract surgeries were performed by resident surgeons. Type II diabetes mellitus (DM) was present in 41% (461/1,137), alpha-1 blocker use in 31% (358/1,137), ocular hypertension (ocular HTN) in 4% (44/1,137), and glaucoma in 11% (126/1,137) of cases. Twenty-two percent (232/1,137) of eyes had elevated IOP. Independent risk factors were a history of ocular HTN (OR: 8.74 [4.03-18.9]), glaucoma (OR: 3.54 [2.17-5.75]), a preoperative IOP ≥22 mmHg (OR: 2.51 [1.12-5.62]), and complicated cataract surgery (OR: 2.45 [1.18-5.08]), defined as vitreous loss, anterior capsular tear (ACT), posterior capsular tear (PCT), or presence of zonular lysis.

CONCLUSION

These findings suggest that cataract surgery patients with ocular HTN, glaucoma, a preoperative IOP ≥22 mmHg, or significant intraocular complications may benefit from prophylactic ocular anti-hypertensive medication.

A comparison of NCT, Goldman application tonometry values with and without fluorescein

Purpose

The aim of the study was to statistically compare intraocular pressure (IOP) values measured using noncontact tonometer (NCT), Goldmann applanation tonometry (GAT) with fluorescein (fGAT), and GAT without fluorescein (nGAT). The study was also performed to test whether the values obtained using each technique change in accordance with the central corneal thickness (CCT) and refractive and keratometric values.

Study design

This study was a prospective study of 188 eyes of 94 healthy volunteers. Methods: IOP was measured using fGAT, nGAT and NCT. CCT, refractive values, and keratometric values were measured, and the correlations and differences in the IOP for each tonometer were investigated.

Results

The mean IOP values obtained with the NCT, nGAT, and fGAT were 17.5±3.7, 12.3±2.7, and 12.5±2 mmHg. The mean CCT was 538.2±34.4 µm, the mean refractive value was 0.9±1.2 D, and the mean keratometric value was 43.5±1.5 D. NCT was positively correlated with fGAT and GAT values and was significantly higher than both the values. There were no differences between fGAT and GAT values. No correlation was observed between the CCT and keratometric and refractive values and the difference between NCT and nGAT or fGAT.

Conclusion

Differences in the measurements obtained using nGAT and fGAT were insignificant (P>0.05). Both values were positively correlated with NCT measurements (r =0.354, P<0.05) and were independent of CCT, keratometry, and refraction values. nGAT appears to be suitable for use in routine clinic 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.

Intraocular Pressure Changes Following Intravitreal Melphalan and Topotecan for the Treatment of Retinoblastoma With Vitreous Seeding

PURPOSE

To investigate the impact of intravitreal chemotherapy on intraocular pressure (IOP) in children with retinoblastoma.

METHODS

This was a retrospective study of 10 eyes of 10 patients with retinoblastoma (7 males, 3 females, mean age: 33.6 ± 9.4 months) with vitreous seeding injected with intravitreal melphalan and topotecan. IOP was measured with Tonopen (Reichert, Inc., Buffalo, NY) at baseline prior to injecting and then repeatedly following each intravitreal injection.

RESULTS

Mean pre-injection IOP was 8.2 ± 2.3 mm Hg (range: 4 to 12 mm Hg). Mean IOP 1 to 30 seconds after intravitreal melphalan (first injection) was 45.4 ± 14.3 mm Hg. The IOP of 89.5% of patients declined to 29 mm Hg or less in a mean 153.3 ± 97.5 seconds. Mean IOP 1 to 30 seconds after intravitreal topotecan (second injection) was 44.5 ± 11.0 mm Hg, which decreased to 31.0 ± 5.0 mm Hg by 150 seconds after injection. No significant relationship was found between age and post-injection IOP elevation. IOP exceeded the calculated mean arterial perfusion pressure in four encounters.

CONCLUSIONS

Intravitreal chemotherapy caused a transient rise in IOP. Post-injection IOP elevations can reach levels that may exceed mean arterial pressure. [J Pediatr Ophthalmol Strabismus. 2017;54(3):185-190.].

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.

Comparison of Goldmann applanation tonometer, Tono-Pen and noncontact tonometer in children

Background:

To evaluate the agreement of Goldmann applanation tonometer (GAT) with Tono-Pen and noncontact tonometer (NCT) for measurement of intraocular pressure (IOP) in pediatric age group and to evaluate the correlation between central corneal thickness (CCT) and IOP measured with the tonometers used.

Materials and Methods:

IOP was measured in 200 eyes in a group of Indian children, aged between 8 and 18 years using three different tonometers: NCT, the Tono-Pen and GAT. All IOP readings were made in the office settings by the same examiner. Readings obtained were compared between the instruments and with the CCT for each tonometer. Tonometer inter-method agreement was assessed by the Bland–Altmann method. The relations of CCT with absolute IOP values and inter-tonometer differences were analyzed by linear regression.

Results:

The mean age was 13.37 ΁ 3.51 years. The mean IOP values recorded with NCT; Tono-Pen and GAT were 14.38, 15.63, and 12.44 mmHg, respectively. Both Tono-Pen and NCT recorded statistically higher IOP values than the GAT (P = 0.00) regardless of the CCT. The percentage increase of IOP measured over GAT was 15.66% for NCT and 25.70% for Tono-Pen which was also statistically significant. A correlation was found between CCT and IOP values obtained with all the three tonometers.

Conclusion:

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.

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.

Change in intraocular pressure during scleral depression

PURPOSE

Manometric studies have found that intraocular pressure (IOP) rises 116-350 mmHg during scleral depression in surgical settings. No information is available regarding the effect of scleral depression on IOP in routine clinical settings. The aim of this study is to quantify the change in IOP that occurs when scleral depression is performed on normal eyes in a routine clinical setting.

METHODS

A total of 28 eyes from 28 normal subjects were included. Tono-Pen tonometry was performed while scleral depression was performed in each of the two quadrants: superotemporal (ST) and inferonasal (IN). A post-procedure IOP measurement was obtained following each scleral depression examination. Both ST and IN quadrants were tested on all eyes, with the quadrant tested first chosen at random (15 ST, 13 IN).

RESULTS

The mean IOP during scleral depression was 65.3 mmHg ST and 47.8 mmHg IN, with a maximum recorded IOP of 88 mmHg. The mean change in IOP for the ST quadrant was 51.9 ± 17.3 mmHg and 46.4 ± 16.0 mmHg for the right and left eyes, respectively. The mean change in IOP for the IN quadrant was 45.3 ± 22.7 mmHg and 16.8 ± 15.8 mmHg for the right and left eyes, respectively.

CONCLUSIONS

Scleral depression as performed in a routine office setting produces wide fluctuations in IOP and may impair ocular perfusion. Additional studies are needed to determine the long-term consequences of routine scleral depression.

Non-continuous measurement of intraocular pressure in laboratory animals

Glaucoma is a leading cause of blindness, which is treatable but currently incurable. Numerous animal models therefore have both been and continue to be utilized in the study of numerous aspects of this condition. One important facet associated with the use of such models is the ability to accurately and reproducibly measure (by cannulation) or estimate (by tonometry) intraocular pressure (IOP). At this juncture there are several different approaches to IOP measurement in different experimental animal species, and the list continues to grow. We feel therefore that a review of this subject matter is timely and should prove useful to others who wish to perform similar measurements. The general principles underlying various types of tonometric and non-tonometric techniques for non-continuous determination of IOP are considered. There follows discussion of specific details as to how these techniques are applied to experimental animal species involved in the research of this disease. Specific comments regarding anesthesia, circadian rhythm, and animal handling are also included, especially in the case of rodents. Brief consideration is also given to possible future developments.

The circadian changes of intraocular pressure and ocular perfusion pressure after tafluprost compared with travoprost in normal tension glaucoma

PURPOSE

To compare the 24-h changes of intraocular pressure (IOP) and mean ocular perfusion pressure (MOPP) obtained with tafluprost versus travoprost in patients with normal-tension glaucoma (NTG).

METHODS

This study is a randomized crossover study of 50 patients newly diagnosed with NTG who received either tafluprost or travoprost given once at 9 PM for 2 months, after which they were crossed over to the other medication for another 2 months. IOP and blood pressure were measured for 24 h before starting the treatment and after finishing the first and second treatment periods.

RESULTS

Forty-one patients completed the study. The mean (±standard deviation) 24-h IOP was 16.8±2.0 mmHg at baseline, 14.4±2.2 mmHg on tafluprost, and 13.6±1.8 mmHg on travoprost. Both prostaglandin monotherapies significantly reduced mean 24-h IOP as compared with baseline (P<0.001, P<0.001, respectively), and travoprost demonstrated a lower mean 24-h IOP than tafluprost (P=0.044). Both treatments significantly reduced the IOP from baseline at every point over 24 h. At 3 individual time points, travoprost provided a lower IOP than tafluprost: at 4 PM (13.8±2.7 vs. 14.8±2.6 mmHg, P=0.041), at 6 PM (13.5±2.5 vs. 14.4±2.5 mmHg, P=0.006), and at 8 PM (13.3±2.5 vs. 14.5±2.4 mmHg, P=0.029). Both tafluprost and travoprost significantly increased the 24-h MOPP (P=0.008, P=0.002, respectively), and travoprost demonstrated a greater 24-h MOPP than tafluprost (P=0.027).

CONCLUSIONS

Both tafluprost and travoprost were effective in lowering IOP and increasing MOPP throughout 24 h in NTG. However, travoprost reduced IOP greater than tafluprost in the late afternoon and evening.

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.

The impact of corneal edema on intraocular pressure measurements using goldmann applanation tonometry, Tono-Pen XL, iCare, and ORA: an in vitro model

PURPOSE

Among other corneal biomechanical properties, Goldmann applanation tonometry (GAT) has been shown to depend on corneal edema. New tonometry devices have been designed, such as the Tono-Pen XL, iCare, and ocular response analyzer (ORA), to measure the intraocular pressure (IOP) accurately. This study aims to investigate the influence of corneal edema on the accuracy of these IOP-measuring devices in an in vitro model.

METHODS

A model of an artificial anterior chamber was developed using a guided trephination system. Eight donor corneas not suitable for keratoplasty were clamped into this artificial anterior chamber. All corneas showed signs of stromal edema. Intracameral pressure (ICP) was adjusted manometrically to 10, 20, 30, 40, and 50 mm Hg. The central corneal thickness (CCT) was determined by ultrasonic pachymetry. For each manometrically defined ICP, tonometry was performed using the iCare, Tono-Pen XL, GAT, and ORA.

RESULTS

The mean CCT increased from 616.1±29.6 µm to 626.9±36.1 µm. At 10 mm Hg, GAT yielded a higher ICP than those manometrically adjusted (10.4±3.3 mm Hg); at all other ICP levels, GAT yielded lower ICP levels than those adjusted. The Tono-Pen XL and iCare showed the greatest difference at 10 mm Hg, with the Tono-Pen XL yielding a value of 14.0±4.0 mm Hg and the iCare yielding a value of 12.5±2.6 mm Hg. All other results of the 2 devices fell within a range of ±2 mm Hg from the adjusted ICP. The ORA provided accurate results only at "physiological" ICP levels with a maximum difference of 2.6 mm Hg at 30 mm Hg. At higher ICP levels, corneal hysteresis decreased significantly with increasing ICP. None of the measurement devices revealed a statistically relevant dependence on CCT in this experimental setting.

CONCLUSIONS

The Tono-Pen XL and the iCare yielded the most accurate ICP values across all the adjusted ICP values. This may be because of their relatively small contact area with the cornea and, consequently, greater independence from corneal biomechanical properties. The ORA yielded accurate measurement results only at physiological ICP levels. As anticipated, GAT underestimated ICP. The Tono-Pen XL and the iCare should therefore be used to determine IOP in patients suffering from corneal edema, such as bullous keratopathy or Fuchs endothelial dystrophy.

Intraocular pressure, ultrasonographic and echobiometric findings of juvenile Yacare caiman (Caiman yacare) eye

OBJECTIVE

The aim was to determine the intraocular pressure (IOP), the ultrasonographic and echobiometric findings in the eyes of juvenile Yacare caiman (Caiman yacare).

ANIMALS

Twenty-two healthy caimans from a breeding farm in Brazilian Pantanal.

PROCEDURES

Intraocular pressure was measured under physical restraint and topical anesthesia by applanation tonometry. Five individual measurements of each eye were recorded by the same examiner. B-mode ultrasonography was performed with a 10-MHz linear transducer, and the anterior chamber depth, lens thickness, vitreous depth, and axial globe length were measured. Unpaired and paired t-tests were used to assess data. Pearson's test was used to assess correlations between IOP and ocular structures (P < 0.05).

RESULTS

Mean ± SD IOP of the 44 eyes studied was 9.56 ± 2.69 mmHg, (range 5.4-15.6 mmHg). IOP did not differ significantly between right and left eyes or between genders (P > 0.05). Echobiometric measurements did not differ significantly between eyes and genders (P > 0.05). Intraocular structures measured in male and female subjects were, respectively, 2.61 ± 0.13 and 2.55 ± 0.18 mm for anterior chamber depth, 7.60 ± 0.17 and 7.54 ± 0.20 mm for lens thickness, 6.83 ± 0.20 and 6.90 ± 0.22 mm for vitreous chamber depth, and 17.55 ± 0.25 and 17.54 ± 0.29 mm for axial globe length. Correlations were not observed (P > 0.05).

CONCLUSION

Reference values of tonometry and distances of intraocular structures of Yacare caiman were described. IOP did not correlate with echobiometric measurements in this crocodilian. The ultrasonographic appearance was similar to other domestic and wild species.

Comparison of Tono-Pen AVIA intraocular pressure measurements performed at limbus with central corneal Tono-Pen AVIA intraocular pressure

PURPOSE

To compare Tono-Pen AVIA (TPA) intraocular pressure (IOP) measurements performed at the limbus with central corneal Tono-Pen AVIA (TPA) intraocular pressure.

METHODS

Fifty-one patients attending our outpatient department with a best corrected visual acuity of ≥ 20/40, no corneal disease, and no astigmatism greater than 1.5 diopters underwent routine ophthalmological examination. Patients with ametropia greater than or equal to ± 5 diopters, a history of recent contact lens wear, and central corneal thickness of <480 µm or >550 µm were excluded from the study. IOP was recorded first in the corneal center, followed by tonometry measurements obtained from the temporal, nasal, superior, and inferior limbus using TPA. IOP measurements were compared using the paired t test. Correlation was derived by Pearson correlation coefficient, and regression equations were derived.

RESULTS

The mean age of patients in our study was 43.86 ± 15.39 years. The mean TPA IOP from the central cornea was 16.59 ± 3.75 mm Hg. There was a statistically significant difference between Tono-Pen IOP from the central cornea and that recorded from all 4 limbal positions (P < 0.001). There was a positive correlation between the central and the limbal IOP obtained with Tono-Pen. Correlation was maximum for the temporal limbus.

CONCLUSIONS

Limbal TPA IOP is significantly higher than central TPA IOP. There remains a good correlation between central and limbal IOP. This was found to be greatest for the temporal limbus.

Repeatability of intraocular pressure measurements with Icare PRO rebound, Tono-Pen AVIA, and Goldmann tonometers in sitting and reclining positions

BACKGROUND

Icare PRO (ICP) is a new Rebound tonometer that is able to measure intraocular pressure (IOP) in both sitting and reclining positions. In this study, the gold standard Goldmann tonometer (GAT) was compared to ICP and Tono-Pen AVIA (TPA). Hypothesis was that repeatability of GAT is superior to ICP and TPA.

METHODS

36 eyes of 36 healthy caucasian individuals, 13 male and 26 females, 17 right and 19 left eyes have been included in this prospective, randomized, cross-sectional study. The study was conducted at a single site (Dept. of Ophthalmology, University Hospital Zurich, Switzerland). Primary outcome measures were Intraclass correlation coefficients (ICC) and coefficients of variation (COV) and test-retest repeatability as visualized by Bland-Altman analysis. Secondary outcome measures were IOP in sitting (GAT, ICP and TPA) and in reclining (ICP and TPA) position.

RESULTS

Mean IOP measured by GAT was 14.9 ± 3.5 mmHg. Mean IOP measured by ICP was 15.6 ± 3.1 mmHg (with TPA 14.8 ± 2.7 mmHg) in sitting and 16.5 ± 3.5 mmHg (with TPA 17.0 ± 3.0 mmHg) in reclining positions. COVs ranged from 2.9% (GAT) to 6.9% (ICP reclining) and ICCs from 0.819 (ICP reclining) to 0.972 (GAT).

CONCLUSIONS

Repeatability is good with all three devices. GAT has higher repeatability compared to the two tested hand-held devices with lowest COVs and highest ICCs. IOP was higher in the reclining compared to the sitting position.

TRIAL REGISTRATION

The study was registered to the Clinical Trials Register of the US National Institute of Health, NCT01325324.

The difference in intraocular pressure readings between 3 applanation tonometers is independent of central corneal thickness, in glaucomatous and nonglaucomatous eyes

PURPOSE

To look at tonometry differences between 3 tonometers and to correlate this difference with central corneal thickness (CCT) in glaucomatous and nonglaucomatous eyes.

METHODS

A total of 145 patients were recruited (39 with glaucoma). Intraocular pressure (IOP) was carried out using the Tonosafe (TS), Tono-Pen XL (TP), and Goldmann applanation tonometer (GAT). CCT was also performed using a digital pachymeter.

RESULTS

The TS underestimated IOP when compared with the GAT by a mean (±SD) of 1.03±2.14 mm Hg (P<0.001). The TP when compared to the GAT overestimated IOP by a mean (±SD) of +1.09±6.38 mm Hg (P=0.071). We found only 31% of TP readings to be within ±2 mm Hg of the GAT readings and only 60% to be within ±4 mm Hg of the GAT readings. Correlation was poor (F=0.247) between the GAT and TP with the coefficient of determination being 0.061. The difference in IOP was independent of CCT and a diagnosis of glaucoma.

CONCLUSIONS

The TS, when compared with the GAT, underestimates IOP with a tendency for this to increase in the higher range of IOP readings. The TP is poorly correlated with the GAT.

The effect of ketamine on intraocular pressure in pediatric patients during procedural sedation

OBJECTIVES

Ketamine is one of the most commonly used procedural sedation and analgesia (PSA) agents in pediatric emergency departments (PEDs). It is considered a very safe and reliable agent, with limited respiratory suppression, hemodynamic effects, and adverse outcomes. However, physicians are often reluctant to use ketamine for patients with eye injuries due to a concern that ketamine might increase intraocular pressure (IOP). The objective was to measure IOP in previously healthy children receiving ketamine for PSA for a reason other than eye injury.

METHODS

This was a prospective noninferiority study of patients seen in an academic tertiary care children's hospital emergency department (ED) who required ketamine for PSA. The authors measured IOP in the right eye as soon as possible after ketamine had been administered and then at 2.5, 5, and 10 minutes after ketamine had been administered.

RESULTS

Eighty patients were enrolled (28 between 1 and 5 years of age, 26 between 6 and 10 years, 26 between 11 and 15 years); 49 (61%) were male. Procedures requiring PSA included fracture/dislocation reduction (63%), abscess incision and drainage (16%), laceration repair (11%), dental abscess incision and drainage (6%), and other (4%). The mean total ketamine dosage was 1.6 mg/kg (95% confidence interval [CI] = 1.4 to 1.7). The mean initial IOP was 17.5 mm Hg (95% CI = 16.4 to 18.6 mm Hg) and at 2.5 minutes was 18.9 mm Hg (95% CI = 17.9 to 19.9 mm Hg). The mean difference was 1.4 mm Hg (95% CI = 0.4 to 2.4 mm Hg). Using a noninferiority margin of 2.6 mm Hg (15%), noninferiority (no significant elevation in IOP) was demonstrated with 95% confidence between the first and second readings.

CONCLUSIONS

 Ketamine does not significantly increase IOP in pediatric patients without eye injuries receiving typical PSA dosages in the PED. Further study should assess its safety in patients with ocular injury.

Comparison of Tono-Pen and Goldmann applanation tonometers for measurement of intraocular pressure in healthy children

PURPOSE

To assess the agreement of intraocular pressure (IOP) measured with the Tono-Pen and the Goldmann applanation tonometer (GAT) in normal children and adolescents.

METHODS

A total of 439 subjects from birth to <18 years of age without anterior segment anomalies or glaucoma had their IOP measured with the two instruments by separate, masked examiners in the office or under general anesthesia.

RESULTS

On average, the Tono-Pen measured values slightly lower than the GAT for IOP <11 mm Hg and slightly higher than the GAT for IOP >11 mm Hg in the office setting. Using the average of GAT and Tono-Pen IOPs to estimate the true IOP, the average difference (GAT - Tono-Pen) was 0.4 mm Hg at IOP of 10 mm Hg and -3.0 mm Hg at IOP of 20 mm Hg. The 95% limits of agreement on the average difference between instruments were ± 6.4 mm Hg in the office setting and ± 6.8 mm Hg under general anesthesia. Larger differences between instruments were found with younger age. Standard error of measurement with the Tono-Pen was 1.44 mm Hg and 1.82 mm Hg for the office and anesthesia settings, respectively. Thicker corneas were associated with higher IOP with both the GAT and the Tono-Pen.

CONCLUSIONS

In normal children, average differences between IOP measured by Tono-Pen and GAT were small, although there was substantial test-retest variability. Younger age was associated with larger average differences, as was higher IOP in the office setting.

Comparison of intraocular pressure measurement using 4 different instruments following penetrating keratoplasty

PURPOSE

To compare intraocular pressure (IOP) measurements after penetrating keratoplasty (PK) using Goldmann applanation tonometry (GAT; Haag-Streit USA), TonoPen XL (Reichert Inc), Pascal Dynamic Contour tonometer (PDCT; Swiss Microtechnology AG), and Ocular Response Analyzer (ORA; Reichert Inc) and to analyze effects and correlation of corneal thickness and curvature on these measurements.

DESIGN

Prospective, cross-sectional study.

METHODS

SETTINGS

Departments of Ophthalmology, University of Auckland and Auckland District Health Board, New Zealand.

STUDY POPULATION

Thirty-one eyes of 31 participants with previous PK.

OBSERVATIONS

IOP measured using GAT, TonoPen, PDCT, and ORA. Central corneal thickness (CCT) and corneal astigmatism were assessed by Pentacam rotating Scheimpflug tomography.

MAIN OUTCOME MEASURE

Degree of agreement in IOP measures and correlation with CCT and corneal astigmatism.

RESULTS

Mean age was 44.5 ± 21.0 years and mean time since PK was 27.7 ± 28.2 months (range 3.0-122.4 months). Mean CCT was 585 ± 149 μm and mean corneal astigmatism 5.5 ± 3.8 diopters. There was no significant difference in IOP measured by GAT and TonoPen; however, both PDCT (2.12 mm Hg, P < .01) and ORA (6.29 mm Hg, P < .01) measured significantly higher IOPs compared to GAT. ORA showed the least agreement with GAT. Significant correlation was identified between each pair of measurement techniques. No instruments correlated significantly with CCT. Only PDCT showed no significant correlation with corneal astigmatism. However, no IOP measures correlated with corneal astigmatism if sutures in situ or less than 1 year post-PK.

CONCLUSIONS

TonoPen or PDCT are the most suitable alternatives for measuring IOP in PK eyes where GAT readings are difficult to obtain. PDCT also offers the advantage of being independent of both CCT and corneal astigmatism.

Effect of instrument orientation on the accuracy of intraocular pressure measurements in human cadaveric eyes: manometric evaluation of the model 30 classic Pneumatonometer and Tono-Pen XL

PURPOSE

To determine the effects of probe orientation on the accuracy of intraocular pressure (IOP) measurements obtained with pneumatonometry (Model 30 Classic Pneumatonometer, Reichert Ophthalmic Instruments, Depew, NY) and with a handheld electronic tonometer (Tono-Pen XL, Reichert Ophthalmic Instruments, Depew, NY).

MATERIALS AND METHODS

Six enucleated human eyes were obtained fewer than 24 hours postmortem. IOP was maintained at 10, 20, and 30 mm Hg, sequentially, via liquid column manometry. At each IOP setpoint, the eyes were positioned to mimic a sitting, supine, and prone patient. Pneumatonometry was performed in the sitting and supine orientations. Tono-Pen measurements were performed in the sitting, supine, and prone orientations. Accuracy was analyzed using multifactor repeated measures analysis of variance, and one-sample t tests.

RESULTS

At all IOP setpoints, for both instruments, probe orientation had no significant effect on the IOP measurement (pneumatonometer P=0.58; Tono-Pen P=0.85). At all 3 setpoints (10, 20, and 30 mm Hg) the pneumatonometer overestimated IOP (P<0.0001; P<0.0001; P=0.005, respectively). The Tono-Pen overestimated IOP at the 10 mm Hg setpoint (P<0.0001), but underestimated IOP at the 20 and 30 mm Hg setpoints (P=0.03; P<0.0001, respectively).

CONCLUSIONS

Under experimental conditions, probe orientation had no significant effect on IOP measurements for either instrument, suggesting that both can be used without correction in the tested orientations. In enucleated human cadaveric eyes, the pneumatonometer overestimated IOP at all setpoints. The handheld electronic tonometer overestimated IOP at 10 mm Hg, but underestimated IOP at the higher setpoints. It is unknown if these findings are generalizable to human eyes in vivo.

The effect of orbital decompression surgery on refraction and intraocular pressure in patients with thyroid orbitopathy

PURPOSE

To investigate the effect of orbital decompression surgery in thyroid orbitopathy (TO) on both refractive status and intraocular pressure (IOP).

PATIENTS AND METHODS

A prospective, multicentre, consecutive audit of patients undergoing thyroid decompression surgery. Indications for surgery included cosmetically unacceptable proptosis or corneal exposure. Exclusion criteria included the following: previous orbital surgery, glaucoma, corneal disease, steroid use in the preceding 12 months, or an acute optic neuropathy. Automated refraction, keratometry, pachymetry, Hertel exophthalmometry, and IOP were recorded at 1 month pre- and 3 months postoperatively. IOP using the Tono-Pen (mean of three readings) was measured in the primary, upgaze, and downgaze positions.

RESULTS

Data were collected from 52 orbits of 33 patients (East Grinstead, New York, and Adelaide). There was no significant difference between pre- and postoperative data for sphere, cylinder, or central corneal thickness (CCT). The mean spherical equivalent was -0.43 ± 1.49 D pre-operatively and -0.28 ± 1.52 D postoperatively. The steepest meridian of corneal curvature was 93.1 degrees pre- and 94.2 degrees postoperatively, with no significant difference. Mean IOP significantly decreased when measuring by Goldmann applanation tonometry (GAT) (2.28 mm Hg, (*) P=0.001) and Tono-Pen (3.06 mm Hg, (*) P=<0.0001). IOP measured in upgaze was significantly greater than that in the primary position. Regression analysis between change in IOP and either Hertel exophthalmometry or the number of orbital walls decompressed was non-significant ((*)Student's t-test).

CONCLUSION

Patients with TO undergoing orbital decompression had, on average, with-the-rule astigmatism not affected by orbital decompression surgery. IOP was significantly reduced by decompression surgery although no relationship between IOP and the degree of decompression was observed.

Evaluation of the Perkins handheld applanation tonometer in horses and cattle

The objective of this study was to evaluate and validate the accuracy of the Perkins handheld applanation tonometer for measuring intraocular pressure (IOP) in horses and cattle. Both eyes of 10 adult horses and cattle were evaluated in a postmortem study. The eyes from 10 clinically normal adult horses and cattle were also examined after bilateral auriculopalpebral nerve block and topical anesthesia for an in vivo study. IOP was measured postmortem using direct manometry (measured with an aneroid manometer) and tonometry (measured with a Perkins handheld applanation tonometer). The correlation coefficients (r(2)) for the data from the postmortem manometry and Perkins tonometer study were 0.866 for horses and 0.864 for cattle. In the in vivo study, IOP in horses was 25.1 ± 2.9 mmHg (range 19.0~30.0 mmHg) as measured by manometry and 23.4 ± 3.2 mmHg (range 18.6~28.4 mmHg) according to tonometry. In cattle, IOP was found to be 19.7 ± 1.2 mmHg (range 18.0~22.0 mmHg) by manometry and 18.8 ± 1.7 mmHg (range 15.9~20.8 mmHg) by tonometry. There was a strong correlation between the IOP values obtained by direct ocular manometry and the tonometer in both horses and cattle. Our results demonstrate that the Perkins handheld tonometer could be an additional tool for accurately measuring IOP in equine and bovine eyes.

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.

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.

Short-term effect of intravitreal injection of Ranibizumab (Lucentis) on intraocular pressure

PURPOSE

To investigate short-term effect on intraocular pressure (IOP) after intravitreal injection of ranibizumab (Lucentis) (IVIL).

MATERIALS AND METHODS

This prospective study included 1 eye of 54 patients (64+/-12 y) with wet age-related macular degeneration treated with IVIL. IOP measurements with TonoPen were taken: immediately before and 5 seconds, 5, 10, 15, 30, 60 minutes, and 1 day after IVIL. Axial length (with ultrasound biometry) was assessed in 24 eyes. The analysis included IOP difference at various time points and between phakic and pseudophakic eyes and the relationship between axial length and IOP increases after 5 seconds.

RESULTS

Mean IOP were 16.3+/-3.0 mm Hg (range: 12.0 to 21.3), 44.1+/-10.6 (22.0 to 59.3), 29.0+/-9.6 (15.0 to 49.0), 25.8+/-7.9 (16.0 to 45.0), 23.7+/-6.6 (15.7 to 39.0), 21.9+/-5.6 (14.7 to 37.0), 18.8+/-6.1 (10.0 to 35.0), and 16.1+/-3.0 (11.0 to 21.0), respectively, for time points immediately before, 5 seconds, 5, 10, 15, 30, 60 minutes, and 1 day after IVIL. Differences between before IVIL and after IVIL IOP were statistically significant after 5 seconds, 5, 10, 15, and 30 minutes (P=0.0001); however, were not significant after 1 hour (P=0.064) and 1 day (P=0.449). Differences between phakic and pseudophakic eyes were not significant (P>0.05). The relationship between shorter axial length and IOP increase after 5 seconds was significant (linear regression analysis; R=0.28, P=0.007).

CONCLUSIONS

IVIL causes a considerable short-term transient rise in IOP. The IOP increase after IVIL can be statistically significant at 0 to 30 minutes after injection in both phakic and pseudophakic eyes, and tends to be greater in shorter eyes.

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.