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

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.

Validation of rebound tonometry for intraocular pressure measurement in the rabbit

Rabbits play a growing role in research into glaucoma surgical models and ocular drug delivery models. However, the lack of an accurate method for measuring intraocular pressure (IOP) in this animal has been a significant deficit. In this study we validated the use of the TonoVet rebound tonometer and provide conversion tables for its use in rabbits. Experiments were performed on 18 adult New Zealand White rabbits. The TonoVet measurements were obtained and compared to manometric readings by anterior chamber (AC) cannulation. The TonoVet position and 'd' (dog or cat) and 'p' (other species) modes were compared. The sensitivity of the TonoVet tonometer in assessing IOP changes was also tested. There was a strong linear correlation for both the 'd' mode (mean slope = 0.84 ± 0.03, r(2) = 0.99 ± 0.03) and the 'p' mode (mean slope = 0.64 ± 0.02, r2 = 0.97 ± 0.01) of the TonoVet with manometric IOP. However, the TonoVet had a tendency to underestimate IOP compared to manometry and conversion formulae were possible to calculate for both modes. The orientation of the TonoVet handle had no effect on IOP reading, as long as the groove was horizontal. No significant differences were observed when comparing right and left eyes (P > 0.05). IOP recovered four days after cannulation. Younger rabbits had lower IOP compared with older rabbits (P < 0.01). Timolol produced a 2.5 mmHg reduction in IOP 2 h later as detected by the TonoVet. Using the conversion table presented, the TonoVet is a reliable and precise tool for the measurement of IOP in rabbits.

[Evaluation of the self-tonometer Icare ONE in comparison to Goldmann applanation tonometry]

OBJECTIVE

The aim of this clinical study was to demonstrate the practicability of self-measured intraocular pressure and to evaluate the reliability by comparing the data with those obtained by Goldmann applanation tonometry (GAT).

METHODS

A total of 40 patients aged between 44 and 82 years with glaucoma were introduced to the handling of the tonometer. The self-measurements were done for 1-3 days following the medical measurement by GAT. The data were saved as "correct" or in the case of wrong handling as "false". The impressions of the patients were obtained by a questionnaire.

RESULTS

A total number of 191 single measurements were registered by the Icare ONE and of these there were 97 (50.8%) signed "false". Of the patients 45% reached a maximum difference of ±5 mmHg between GAT and self-measurement in every single measurement. In the subgroup of under 60-year-old patients 70% reached this result. There were no indications of a systematic error. Of the probands 60% considered the handling of the Icare ONE as difficult. Nevertheless, 80% could imagine using the self-tonometer at home.

CONCLUSIONS

The differences between the self-measurements and the GAT were highly fluctuating in some cases. In the group of patients younger than 60 years the agreement was better, so problems with the handling of the Icare ONE may be an important factor. However, the acceptance in the patients tested was high and continuous pressure measurements at home could be reasonable. Advancements in the handling and reliability are needed to improve clinical application of the measured values.

Does rebound tonometry probe misalignment modify intraocular pressure measurements in human eyes?

Purpose. To examine the influence of positional misalignments on intraocular pressure (IOP) measurement with a rebound tonometer. Methods. Using the iCare rebound tonometer, IOP readings were taken from the right eye of 36 healthy subjects at the central corneal apex (CC) and compared to IOP measures using the Goldmann applanation tonometer (GAT). Using a bespoke rig, iCare IOP readings were also taken 2 mm laterally from CC, both nasally and temporally, along with angular deviations of 5 and 10 degrees, both nasally and temporally to the visual axis. Results. Mean IOP ± SD, as measured by GAT, was 14.7 ± 2.5 mmHg versus iCare tonometer readings of 17.4 ± 3.6 mmHg at CC, representing an iCare IOP overestimation of 2.7 ± 2.8 mmHg (P < 0.001), which increased at higher average IOPs. IOP at CC using the iCare tonometer was not significantly different to values at lateral displacements. IOP was marginally underestimated with angular deviation of the probe but only reaching significance at 10 degrees nasally. Conclusions. As shown previously, the iCare tonometer overestimates IOP compared to GAT. However, IOP measurement in normal, healthy subjects using the iCare rebound tonometer appears insensitive to misalignments. An IOP underestimation of <1 mmHg with the probe deviated 10 degrees nasally reached statistical but not clinical significance levels.

Evaluation of intraocular pressure in conscious Hermann's tortoises (Testudo hermanni) by means of rebound tonometry

OBJECTIVE

To determine intraocular pressure (IOP) in healthy Hermann's tortoises (Testudo hermanni).

ANIMALS

26 outdoor-housed Hermann's tortoises (13 males and 13 females); body weight ranged from 255 to 2,310 g, and age ranged from 4 to > 50 years.

PROCEDURES

After a preliminary ophthalmic evaluation was performed, IOP was measured by means of a rebound tonometer in both eyes of each tortoise. Three measurements were obtained for each eye; successive measurements were obtained from alternate eyes. Each measurement was based on the mean of 6 values automatically provided by the rebound tonometer. Statistical analysis was used to evaluate correlations between variables and to identify sex- or size-related IOP variations, and changes in IOP over multiple measurements.

RESULTS

Mean ± SEM IOP of the 52 eyes was 15.74 ± 0.20 mm Hg (range, 9 to 22 mm Hg). Results for t tests did not reveal significant differences in IOP between the right and left eyes or between males and females. A significant moderate negative correlation (r = -0.41; r(2) = 0.169) between IOP and body weight was detected. Results of repeated-measures ANOVA revealed a significant increase in IOP over multiple measurements.

CONCLUSIONS AND CLINICAL RELEVANCE

Rebound tonometry was a practical and rapid means of determining IOP in small- to medium-sized tortoises that required minimal manual restraint of the animals. Establishing IOP values in healthy Hermann's tortoises will provide a reference frame for use during complete ophthalmic examinations, thus allowing clinicians to diagnose a broader spectrum of ocular pathological conditions in tortoises.

Intraocular pressure during femtosecond laser pretreatment of cataract

PURPOSE

To analyze the course of intraocular pressure (IOP) during femtosecond laser pretreatment to cataract surgery.

SETTING

Launceston Eye Institute, Tasmania, Australia.

DESIGN

Interventional prospective study.

METHODS

Femtosecond laser pretreatment was performed using the Catalys Precision Laser System with Liquid Optics Interface. The IOP was measured using a rebound tonometer (iCare PRO) during different stages of surgery and analyzed by number of docking attempts, vacuum time, treatment time, and central corneal thickness (CCT).

RESULTS

The mean baseline IOP in the 25 eyes was 17.5 mm Hg ± 2.4 (SD). During vacuum application, the mean IOP rise was 11.4 ± 3.3 mm Hg. Peak IOPs were recorded immediately after laser capsulotomy and lens fragmentation (mean 36.0 ± 4.4 mm Hg; mean increase from baseline 18.5 ± 4.7 mm Hg) and remained above baseline 2 minutes after the procedure (26.6 ± 4.0 mm Hg) (P<.001). Multiple regression analysis found no association between IOP rise and number of docking attempts, vacuum time, treatment time, or CCT.

CONCLUSION

Femtosecond laser pretreatment was associated with a mean peak increase in IOP of 18.5 mm Hg from baseline and appeared to be safe and well tolerated.

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.

The use of the iCare tonometer reduced the need for anesthesia to measure intraocular pressure in children

PURPOSE

To determine whether the introduction of iCare rebound tonometry in a pediatric ophthalmology clinic resulted in fewer examinations under anesthesia to evaluate children with glaucoma.

METHODS

The medical records of consecutive glaucoma patients were retrospectively reviewed. The numbers of examinations under anesthesia (EUAs) and office visits that included measurement of intraocular pressure (IOP) were compared for three periods relative to introduction of the Icare (Icare Finland Oy, Helsinki, Finland) rebound tonometer into our clinical practice: before device introduction, learning/transition period, and routine use.

RESULTS

A total of 87 subjects were included: 48 subjects met inclusion criteria for the first period; 58 patients met inclusion criteria for the third period (some subjects straddled all three periods). The average patient age for the first period was 4.2 years and 4.9 years (P = 0.3) for the third period. The number of EUAs performed before the introduction of the Icare was 55 and after the introduction of the Icare was 18 (P < 0.001). The number of office visits at which IOP was measured increased from 34 to 151 (P < 0.001). Data from the transition period suggest a trend and a short learning period.

CONCLUSIONS

The use of Icare tonometry decreased the need for EUAs to evaluate children with glaucoma and significantly increased successful IOP measurement in clinic.

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.

Precision and accuracy of the ICare tonometer - Peripheral and central IOP measurements by rebound tonometry

PURPOSE

The purpose of this study was to evaluate the ICare tonometers precision and accuracy and the extent to which intraocular pressure (IOP) measurements are influenced by measuring position.

METHODS

This was carried out by comparing the central and peripheral ICare-IOP readings and comparing ICare- with the Goldmann applanation tonometer (GAT)-IOP readings. IOP was measured using the ICare rebound tonometer on the right eye of 40 subjects, straight at the centre of the cornea (CS), straight 2 mm from the nasal and temporal limbus (NS and TS), and in 10 degrees nasally and temporally angled positions measured from the same location as CS (NA and TA). The IOP was also assessed with the GAT.

RESULTS

Central IOP (CS) was significantly (p < 0.001) greater than peripheral measurements (NS, TS, NA and TA) by approximately 3-4 mmHg. Centre IOP (CS) significantly overestimated by mean 2 mmHg and the peripheral measurements significantly underestimates approximately 1.4-2 mmHg compared with GAT readings.

CONCLUSION

The ICare tonometer may be useful in a routine clinical setting for IOP screening, but the ICare measurement is not a substitute for the GAT measurement, when a precise and accurate IOP is desired.

Effects of trabeculectomy on posture-induced intraocular pressure changes over time

INTRODUCTION

To determine whether trabeculectomy affects postural-induced changes in intraocular pressure (IOP), and whether it is maintained.

METHODS

Thirty-six eyes of 36 patients with open-angle glaucoma who were scheduled for their initial trabeculectomy with adjunctive mitomycin C were prospectively examined. The IOP was measured in the sitting and the lateral decubitus position with an ICare rebound tonometer before, and 1, 3, and 12 months after trabeculectomy.

RESULTS

Twenty-nine eyes of 29 patients completed this study. The mean baseline IOP measured with the ICare tonometer was 17.4 ± 4.9 mmHg in the sitting position and 21.3 ± 5.6 mmHg in the lateral decubitus position (p < 0.001). This postural IOP difference, +3.9 mmHg, was reduced to +1.3 ± 1.7 mmHg at 1 month and to +0.8 ± 1.5 mmHg at 3 months after the trabeculectomy (p < 0.001 and p = 0.004 respectively). This decrease in the degree of posture-dependent IOP change was maintained at +1.7 ± 2.2 mmHg at 1 year postoperatively (p < 0.001). In three cases, the postural IOP changes returned to the baseline level, and all three had a failed bleb.

CONCLUSIONS

Our results indicate that trabeculectomy not only reduces the IOP but also reduces the degree of posture-induced changes in the IOP. Our findings also speculate that measuring the postural IOP changes after trabeculectomy might provide a clue on the functioning of a filtering bleb.

Performance of the rebound, noncontact and Goldmann applanation tonometers in routine clinical practice

PURPOSE

To compare rebound tonometry (RBT) and noncontact tonometry (NCT) using Goldmann applanation tonometry (GAT) as reference.

METHODS

The study sample was comprised of 108 eyes of 108 subjects consecutively examined at a general ophthalmology clinic. The order of use of the three tonometers was randomized at the study outset. The difference between the methods was plotted against the mean to compare the tonometers. The hypothesis of zero bias was examined by a paired t-test and 95% limits of agreement (LoA) were also calculated. Differences with respect to GAT were assessed according to the international standard for ocular tonometers (ISO 8612).

RESULTS

Mean intraocular pressures (IOPs ± SD) obtained using the three instruments were GAT 17.5 ± 3.8 mmHg; RBT 18.5 ± 5.5 mmHg and NCT 17.4 ± 5.6 mmHg. The 95% LoA were from -7.9 to +7.7 mmHg for NCT-GAT and from -6.8 mmHg to +8.7 mmHg for RBT-GAT. A difference with respect to GAT under ± 1 mmHg was observed in 11.1% of the eyes measured by NCT and 18.5% of eyes measured by RBT. According to the IOP ranges established by the ISO 8612, differences from GAT measurements greater than ± 5 mmHg were always above the accepted level of 5%. Correlations between IOP and central corneal thickness (CCT) were significant for all three tonometers.

CONCLUSIONS

The rebound and noncontact tonometer behaved similarly when used to measure IOP taking GAT measurements as the reference standard. Neither tonometer fulfilled ISO 8612 requirements. Both were similarly influenced by CCT.

Comparison of intraocular pressure measurement between rebound, non-contact and Goldmann applanation tonometry in treated glaucoma patients

BACKGROUND

To compare the intraocular pressure readings obtained with the iCare rebound tonometer and the 7CR non-contact tonometer with those measured by Goldmann applanation tonometry in treated glaucoma patients.

DESIGN

A prospective, cross-sectional study was conducted in a private tertiary glaucoma clinic.

PARTICIPANTS OR SAMPLES

One hundred nine (54 males : 55 females) patients including only eyes under medical treatment for glaucoma.

METHODS

Measurement by Goldmann applanation tonometry, iCare rebound tonometry and 7CR non-contact tonometry.

MAIN OUTCOME MEASURES

Intraocular pressure.

RESULTS

There were strong correlations between the intraocular pressure measurements obtained with Goldmann and both the rebound and non-contact tonometers (Spearman r-values ≥ 0.79, P < 0.001). However, there were small, statistically significant differences between the average readings for each tonometer. For the rebound tonometer, the mean intraocular pressure was slightly higher compared with the Goldmann applanation tonometer in the right eyes (P = 0.02), and similar in the left eyes (P = 0.93); however, these differences did not reach statistical significance. The Goldmann correlated measurements from the non-contact tonometer were lower than the average Goldmann reading for both right (P < 0.001) and left (P > 0.01) eyes. The corneal compensated measurements from the non-contact tonometer were significantly higher compared with the other tonometers (P ≤ 0.001).

CONCLUSIONS

The iCare rebound tonometer and the 7CR non-contact tonometer measure intraocular pressure in fundamentally different ways to the Goldmann applanation tonometer. The resulting intraocular pressure values vary between the instruments and will need to be considered when comparing clinical versus home acquired measurements.

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.

The effect of hydrogel and silicone hydrogel contact lenses on the measurement of intraocular pressure with rebound tonometry

PURPOSE

To assess the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over disposable hydrogel (etafilcon A) and silicone hydrogel (senofilcon A) contact lenses (CLs) of different powers.

METHODS

The experimental group comprised 36 subjects (19 male, 17 female). IOP measurements were undertaken on the subject's right eyes in random order using a rebound tonometer (ICare). The CLs had powers of +2.00D, -2.00D and -6.00D. Six measurements were taken over each contact lens and also before and after the CLs had been worn.

RESULTS

A good correlation was found between IOP measurements with and without CLs (all r≥0.80; p<0.05). Bland Altman plots did not show any significant trend in the difference in IOP readings with and without CLs as a function of IOP value. A two-way ANOVA revealed a significant effect of material and power (p<0.01) but no interaction. All the comparisons between the measurements without CLs and with hydrogel CLs were significant (p<0.01). The comparisons with silicone hydrogel CLs were not significant.

CONCLUSIONS

Rebound tonometry can be reliably performed over silicone hydrogel CLs. With hydrogel CLs, the measurements were lower than those without CLs. However, despite the fact that these differences were statistically significant, their clinical significance was minimal.

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.

The influence of refractive errors on IOP measurement by rebound tonometry (ICare) and Goldmann applanation tonometry

PURPOSE

To evaluate the effect of refractive errors and central corneal thickness (CCT) on the measurement of intraocular pressure (IOP) by ICare rebound tonometer (RT), and its agreement with measurements by Goldmann applanation tonometer (GAT).

PATIENTS AND METHODS

Two observers measured the IOP by using RT and GAT in four groups of healthy volunteers with emmetropic (n = 78), hyperopic (n = 83), myopic (n = 87) and astigmatic (n = 79) eyes. Refraction was assessed by an autorefractometer. CCT was assessed by ultrasound pachymetry.

RESULTS

In all groups, no significant interobserver difference was seen in IOP values detected by both tonometers (Wilcoxon signed-rank test not significant). In all groups, IOP values were higher as measured by RT than by GAT (paired t-test p = 0.000): mean RT-GAT difference was higher in myopic eyes (+1.6 +/- 1.8 mmHg), and it was less than 1 mmHg in the other groups. RT-GAT difference was correlated to the refraction (p < 0.001), and it was greater when an higher IOP was detected by RT (significant correlation between RT-GAT difference and IOP by RT, p < 0.001). Compared with GAT values, the IOP readings by RT were greater than 2 mmHg in respectively 17.9% (emmetropic), 13.3% (hyperopic), 34.5% (myopic) and 7.6% (astigmatic) of the eyes. With both tonometers, in all groups the IOP values were correlated with CCT (p < 0.05), but the discrepancy between RT and GAT values was not related to CCT.

CONCLUSIONS

In all groups of subjects, higher IOP values were detected by RT; the IOP readings exceed the GAT values usually in a range of less than 1 mmHg, except when RT detects IOP >18 mmHg and generally in myopic eyes; RT-GAT discrepancy is related to the refractive error, but not to CCT.