Transpalpebral tonometry: reliability and comparison with Goldmann applanation tonometry and palpation in healthy volunteers

Influence of unilateral eyelid spasms and botulinum toxin treatment on intraocular pressure measured by transpalpebral tonometer

PURPOSE

Eyelid spasms might be associated with elevated intraocular pressure (IOP) in hemifacial spasm (HFS) patients. IOP assessment using a Goldmann applanation tonometer (GAT) is often compromised by eyelid spasms. This study aimed to assess the effect of HFS on IOP measurements using the transpalpebral tonometer Diaton® before and after treatment with botulinum toxin type A (BTX-A) and compared Diaton® and GAT measurements after treatment with BTX-A.

METHODS

IOP measurements were obtained with Diaton® in 27 patients with moderate-to-severe HFS before and after treatment with BTX-A. After treatment, the IOP was also measured using GAT and the results were compared with the ones measured with a Diaton®. The patients underwent automated perimetry, OCT, and pachymetry for screening to glaucoma.

RESULTS

Mean IOP with Diaton® was 11 ± 3.42 mmHg before treatment in the affected eye and 9 ± 2.98 mmHg in the contralateral eye. This difference was statistically significant (P = 0.012). However, after treatment with BTX-A, no interocular difference was found in IOP obtained with Diaton® (P = 0.204) or GAT (P = 0.971). Comparison between GAT and Diaton® measurements showed no significant differences after BTX-A treatment between the affected (P = 0.212) and contralateral eye (P = 0.971).

CONCLUSIONS

A significant reduction in IOP measurements on the affected side of HFS patients was observed after treatment with BTX-A, demonstrating that eyelid spasms may increase the IOP. No significant difference was observed between Diaton® and GAT measurements after the application of BTX-A. No differences were found in automated perimetry, OCT, and CCT when comparing affected eyes with contralateral eyes.

Comparison of intraocular pressure measurements between Easyton transpalpebral tonometry and Perkins, iCare iC100 and Corvis ST, and the influence of corneal and anterior scleral thickness

PURPOSE

To compare intraocular pressure (IOP) measurements between Easyton transpalpebral tonometry and Perkins, iCare iC100 and Corvis ST. Also, to assess the influence of corneal characteristics and anterior scleral thickness (AST) on the IOP measurements.

METHODS

Sixty-nine eyes from 69 healthy subjects were included. IOP was measured by Easyton, Perkins, iC100 and Corvis ST (corrected IOP, bIOP; and non-corrected IOP, IOPnct). Other variables studied were AST, axial length (AL), and Corvis parameters: Length 1, velocity 1, length 2, velocity 2, peak distance, radius, deformation amplitude, and central corneal thickness (CCT). Pearson correlation, limits of agreement (LoA), and multiple regression analysis were calculated.

RESULTS

No significant differences in IOP between Easyton and Perkins, iC100, and bIOP were observed (all p > 0.05), being significant only between Perkins and IOPnct ( - 1.49 mmHg, p < 0.001). Bland-Altman graphs showed that the mean difference between Perkins and Easyton was 0.07 mmHg (p < 0.001), and LoA  - 7.49 to + 7.39 mmHg. Significant correlations were found between the measurements of Perkins and iC100, IOPnct, bIOP (r = 0.710, 0.628, 0.539; p < 0.001 respectively), iC100 and IOPnct, bIOP (r = 0.627, 0.513; p < 0.001, respectively). The multivariate regression analysis revealed that differences between Perkins and Easyton (adjusted R2 = 0.25) were influenced by AL (B = 1.28, p < 0.008), length 1 (B = 3.13, p < 0.018), and the radius (B = 1.26, p < 0.010). Differences between Perkins and bIOP (adjusted R2 = 0.21) were affected by the CCT (B = 0.029, p < 0.003).

CONCLUSIONS

There are no significant differences in the IOP measurements between Perkins and Easyton, iC100 or bIOP. Length 1, radius, and CCT have limited influence on these differences, while AST did not show any effect.

Anatomical and physiological considerations in scleral lens wear: Intraocular pressure

Intraocular pressure (IOP) is maintained through complex and interrelated systems which control aqueous production and drainage, and it has been suggested that scleral lens (SL) wear may disrupt these vital homeostatic processes. This review provides an overview of anatomical and physiological processes that control IOP, identifies potential effects of SLs on these regulatory mechanisms, and examines studies that have attempted to quantify the effect of SLs on IOP. Lack of access to the cornea during SL wear makes accurate assessment of IOP challenging; therefore, a range of different assessment techniques and instruments have been employed to quantify IOP during and following SL wear. Some studies have evaluated IOP using standard techniques prior to lens application and following lens removal, or through a large central fenestration. Other studies have utilised instruments that facilitate assessment of IOP on the peripheral cornea or conjunctiva overlying the sclera (e.g. Schiotz, transpalpebral, and pneumatonometry). Two studies have recently evaluated changes in optic nerve structure during SL wear. Conflicting results have been reported on this topic, much of which examines changes in IOP in healthy subjects over limited periods of time. Currently, only a few studies have reported on long-term effects of SL wear on IOP in habitual SL wearers (after lens removal). Future research in this area must not only consider the fact that ocular conditions treated with SLs may potentially alter corneal biomechanical properties which can influence IOP, but also that these properties may be further altered by SL wear. Monitoring other risk factors for glaucoma (permanent alterations in optic nerve physiology, visual field defects) could provide a more comprehensive assessment of potentially increased risk of glaucomatous optic neuropathy due to SL wear. Ongoing clinical assessment of optic nerve structure and function is advisable in patients at risk for glaucoma who require SLs.

Methods for measuring intraocular pressure: disadvantages and advantages

This review of the literature is devoted to the comparison of tonometers based on various operating principles, their advantages and disadvantages. The principles of operation of each considered in the review tonometer are discussed. The features of the structure and mechanisms for measuring the intraocular pressure of various tonometers are highlighted, on the basis of which the anatomical features and other factors that have the greatest impact on the reliability of measurement and accounting of the data obtained in clinical practice are determined.

Identification of the Optimal Model for the Prediction of Diabetic Retinopathy in Chinese Rural Population: Handan Eye Study

BACKGROUND

To identify an optimal model for diabetic retinopathy (DR) prediction in Chinese rural population by establishing and comparing different algorithms based on the data from Handan Eye Study (HES).

METHODS

Five algorithms, including multivariable logistic regression (MLR), classification and regression trees (C&RT), support vector machine (SVM), random forests (RF), and gradient boosting machine (GBM), were used to establish DR prediction models with HES data. The performance of the models was assessed based on the adjusted area under the ROC curve (AUROC), sensitivity, specificity, and accuracy.

RESULTS

The data on 4752 subjects were used to build the DR prediction model, and among them, 198 patients were diagnosed with DR. The age of the included subjects ranged from 30 to 85 years old, with an average age of 50.9 years (SD = 3.04). The kappa coefficient of the diagnosis between the two ophthalmologists was 0.857. The MLR model revealed that blood glucose, systolic blood pressure, and body mass index were independently associated with the development of DR. The AUROC obtained by GBM (0.952), RF (0.949), and MLR (0.936) was similar and statistically larger than that of CART (0.682) and SVM (0.765).

CONCLUSIONS

The MLR model exhibited excellent prediction performance and visible equation and thus was the optimal model for DR prediction. Therefore, the MLR model may have the potential to serve as a complementary screening tool for the early detection of DR, especially in remote and underserved areas.

Comparison of Pneumatonometry and Transpalpebral Tonometry Measurements of Intraocular Pressure during Scleral Lens Wear

SIGNIFICANCE

As scleral lens wear becomes more common, understanding the impact of these lenses upon ocular physiology is critically important. Studies on the effect of scleral lens wear upon intraocular pressure (IOP) have used different instruments and have reported conflicting results.

PURPOSE

The purpose of this study was to compare assessment of IOP during scleral lens wear using pneumatonometry and transpalpebral tonometry.

METHODS

Twenty healthy subjects wore a small-diameter (15.2 mm) and a large-diameter (18.0 mm) scleral lens on the right eye, each for 1 hour in randomized order. IOP was assessed with pneumatonometry and transpalpebral tonometry on both eyes before lens application, immediately after lens application, after 1 hour of lens wear, and immediately after lens removal. Paired t test compared mean IOP in the study eye to the control eye. Repeated-measures ANOVA was performed to take instrumentation, lens diameter, and their interaction into account in an analysis of the change in IOP in the study eye.

RESULTS

Mean peripheral IOP measured with pneumatonometry was not significantly different from baseline at any subsequent measurement. Measurements with transpalpebral tonometry, however, were significantly different during scleral lens wear immediately after application and after 1 hour of wear with both diameter lenses (P < .005), but were not significantly different after either sized lens was removed. Repeated-measures ANOVA revealed that the instrument used to measure IOP was a significant factor in IOP changes found during lens wear (P ≤ .001).

CONCLUSIONS

Assessment of IOP during scleral lens wear varies based upon the instrument that is used. Although further studies are clearly needed to further elucidate this issue, clinicians should continue to monitor optic nerve structure and function in scleral lens wearers, as they do in all patients.

Effects of Scleral Contact Lenses for Keratoconus Management on Visual Quality and Intraocular Pressure

Purpose

To evaluate the visual acuity level achieved by scleral contact lens (CL) fitting in patients affected by keratoconus and to evaluate possible intraocular pressure (IOP) changes during the scleral CL wear using a transpalpebral tonometer.

Methods

In a prospective case series a comparison was made between visual acuity obtained with glasses, RGP and 16.8mm diameter scleral CL in 30 consecutive patients affected by keratoconus. IOP was tested during scleral CL wear by transpalpebral Diaton Tonometer (DT) and also by Goldmann Applanation Tonometer (GAT) before and after scleral CL wear.

Results

The mean logMAR visual acuity improved from 0.2±0.25SD with glasses and 0.1±0.02SD with RGP, to −0.002±0.041SD when using the scleral CL (p<0.05). The mean IOP value before scleral CL wear was 12.93mmHg±2.20SD when measured with GAT and 7.85mmHg±2.27SD when measured with DT. During scleral CL wear, IOP was assessed through DT, with a mean value of 8.86mmHg±2.36SD; values were stable after 8 hours of scleral CL use. Immediately after scleral CL removal, the mean IOP measured with GAT was 12.85mmHg ±2.40SD and the mean IOP measured with DT was 7.66mmHg±1.88SD. Therefore, during scleral CL wear, it was evidenced a small but statistically significant increase of the mean IOP value (1.01mmHg; p<0.01), with a reversion to values prior to application when scleral CL was removed.

Conclusion

Scleral CLs remarkably improved visual acuity in keratoconus patients when compared to glasses or RGP contact lenses. Even if it was evidenced a small increase of the mean IOP value during their wear, it may not be significant in otherwise healthy eyes. Statistical analysis demonstrated good agreement between GAT and DT but their numerical values presented a constant gap, that should be taken into account when there is a need to relate the DT values to the reference ones.

Design, methodology, and preliminary results of the follow-up of a population-based cohort study in rural area of northern China: Handan Eye Study

Background:

Handan Eye Study (HES), a large population-based cohort study in rural area of northern China, was one of the few studies focusing on the major eye diseases of rural Chinese population. The aim of this study was to introduce the design, methodology and to assess the data quality of the follow-up phase of HES.

Methods:

All participants were recruited in Yongnian county of Handan city between 2012 and 2013. Main outcomes were measured by visual quality scales and ocular examinations. We performed the Chi-square test to make comparison of categorical data among groups, One-way analysis of variance and Kruskal-Wallis test was applied to make comparison of continuous data among groups, a post-hoc test was done to make further pairwise comparison. Inter-class correlation coefficients (ICCs) and Kappa coefficients were used to evaluate the consistency between different operators. Logistic regression was used to explore the influence factors of death, odds ratio (OR) and 95% confidence interval (CI) were used to estimate the effect size of each influence factor.

Results:

The follow-up rate was 85.3%. Subjects were classified into three groups: the follow-up group (n = 5394), the loss to follow-up group (n = 929), and the dead group (n = 507), comparison of their baseline information was done. Compared with the other two groups, age of the dead group (66.52 ± 10.31 years) was the oldest (Z = 651.293, P < 0.001), male proportion was the highest (59.0%) (χ² = 42.351, P < 0.001), only 65.9% of the dead finished middle school education (Z = 205.354, P < 0.001). The marriage percentage, body mass index (BMI), best-corrected visual acuity (BCVA), and intra-ocular pressure of the dead group was the lowest either. Spherical equivalent error (SER) of the dead group was the highest. Besides, history of smoking, hypertension, diabetes, and heart disease were more common in the dead group. Multivariate analysis showed that age (OR = 1.901, 95% CI: 1.074–1.108), gender (OR = 0.317, 95% CI: 0.224–0.448), and BCVA (OR = 0.282, 95% CI: 0.158–0.503) were associated with death. While between the follow-up group and the loss to follow-up group, there was only difference on age, gender, BMI, systolic blood pressure and SER. The Cronbach coefficients of all scales used in the follow-up were ≥0.63 and the cumulative variances were ≥0.61, indicating good reliability and validity. The ICCs and Kappa coefficients between different operators were ≥0.69.

Conclusions:

HES has a high follow-up rate and a low risk of loss to follow-up bias. Age, gender, and BCVA are influence factors of death. Specifically, male subjects are at a higher risk of death than female, age is a risk factor of death while BCVA is a protective factor for death.

Change in intraocular pressure during point-of-care ultrasound

INTRODUCTION

Point-of-care ocular ultrasound (US) is a valuable tool for the evaluation of traumatic ocular injuries. Conventionally, any maneuver that may increase intraocular pressure (IOP) is relatively contraindicated in the setting of globe rupture. Some authors have cautioned against the use of US in these scenarios because of a theoretical concern that an US examination may cause or exacerbate the extrusion of intraocular contents. This study set out to investigate whether ocular US affects IOP. The secondary objective was to validate the intraocular pressure measurements obtained with the Diaton® as compared with standard applanation techniques (the Tono-Pen®).

METHODS

We enrolled a convenience sample of healthy adult volunteers. We obtained the baseline IOP for each patient by using a transpalpebral tonometer. Ocular US was then performed on each subject using a high-frequency linear array transducer, and a second IOP was obtained during the US examination. A third IOP measurement was obtained following the completion of the US examination. To validate transpalpebral measurement, a subset of subjects also underwent traditional transcorneal applanation tonometry prior to the US examination as a baseline measurement. In a subset of 10 patients, we obtained baseline pre-ultrasound IOP measurements with the Diaton® and Tono-Pen®, and then compared them.

RESULTS

The study included 40 subjects. IOP values during ocular US examination were slightly greater than baseline (average +1.8mmHg, p=0.01). Post-US examination IOP values were not significantly different than baseline (average -0.15mmHg, p=0.42). In a subset of 10 subjects, IOP values were not significantly different between transpalpebral and transcorneal tonometry (average +0.03mmHg, p=0.07).

CONCLUSION

In healthy volunteer subjects, point-of-care ocular US causes a small and transient increase in IOP. We also showed no difference between the Diaton® and Tono-Pen® methods of IOP measurement. Overall, the resulting change in IOP with US transducer placement is considerably less than the mean diurnal variation in healthy subjects, or pressure generated by physical examination, and is therefore unlikely to be clinically significant. However, it is important to take caution when performing ocular ultrasound, since it is unclear what the change in IOP would be in patients with ocular trauma.

[Glaucoma attack following Hughes tarsoconjunctival flap: what should be done?]

PURPOSE

The aim of this article is to present a case of acute glaucoma arising in a closed eye 10 days after lower eyelid reconstruction by Hughes tarsoconjunctival flap technique and to discuss clinical strategies to avoid this complication.

CASE REPORT

A 61-year-old hyperopic patient presented with a basal cell carcinoma of the lower eyelid. After 2-step tumor resection eyelid reconstruction was performed by Hughes tarsoconjunctival flap technique but 1 week later the patient presented with headache and pain in the contralateral eye. Acute glaucoma was diagnosed and successfully treated (mannitol, aceatazolamide i.v., topical pilocarpine and iridotomy). Some days later the patient came back with relapsed headache and pain in the closed eye. Although the intraocular pressure (IOP) could not be measured acute glaucoma of the right eye as well was suspected and the patient was treated again with mannitol and acetazolamide. As the pain resolved under this therapy the closed eyelid was not opened at this time but the lid reopening was performed at the regular time point (4 weeks postoperatively).

CONCLUSIONS

To the best of our knowledge this is the first published case of an acute glaucoma arising in a topically uncontrolled treatable eye with sutured eyelids. The risk of insufficient treatable acute glaucoma should be included in the patient informed consent when planning eyelid reconstruction by Hughes tarsoconjunctival flap technique. The case supports experimental research efforts to establish techniques of transpalpebral IOP measurement.

Comparative evaluation of Diaton and Goldmann applanation tonometers

AIM

To evaluate the agreement between intra-ocular pressure (IOP) measurements with the Diaton and the Goldmann applanation tonometers (GAT).

METHODS

In this cross-sectional observational study, a total of 196 eyes of 196 participants (66 patients with glaucoma, 130 healthy subjects) were included. IOP measurements were obtained from all patients using the Diaton and GAT.

RESULTS

The average age of the patients enrolled in this study was 48.3 ± 14.6 years (range 18-79). The overall mean IOP measured by the Diaton was 17.2 ± 6.4 mm Hg, while that in glaucoma patients was 17.9 ± 6.2 mm Hg and in the control group 15.8 ± 4.9 mm Hg. Pearson's correlation coefficient showed a moderate correlation in IOP measurements by the two instruments in healthy controls (r = 0.460, p < 0.01); however, the same correlation for the glaucomatous subjects was noted to be poor (r = 0.261, p = 0.57). The limits of agreement (95% confidence intervals) ranged from -9.9 to +11.2 and from -15.3 to +19.7 mm Hg in healthy controls and glaucoma patients, respectively.

CONCLUSION

The Diaton measurements do not correlate well with those provided by applanation tonometry. The two tonometers show very wide limits of agreement so they may not be used interchangeably in clinical practice for the measurement of IOP.

Diaton tonometry: an assessment of validity and preference against Goldmann tonometry

BACKGROUND

To assess agreement between the Diaton, a new transpalpebral tonometer, and Goldmann applanation tonometry, the accepted gold standard.

DESIGN

Comparative study of two devices in a hospital setting.

PARTICIPANTS

Two hundred and fifty-one patients attending the eye casualty and general ophthalmology clinics at St James' University Hospital, Leeds between February and December 2009.

METHODS

Intraocular pressure was measured using Goldmann applanation tonometry and Diaton tonometry by one examining ophthalmologist. Patient preference for either technique was also recorded.

MAIN OUTCOME MEASURES

Intraocular pressure measured by Diaton was compared with intraocular pressure measured by Goldmann applanation tonometry. Limits of agreement were determined using the Bland-Altman method.

RESULTS

Two hundred and fifty right eyes underwent both Goldmann applanation tonometry and Diaton tonometry. Mean intraocular pressure was 13.8 ± 3.6 mmHg using Goldmann applanation tonometry and 13.2 ± 4.3 mmHg using Diaton tonometry. Upper and lower limits of agreement were +8.4 mmHg and -9.6 mmHg, respectively. Order of intraocular pressure measurement and positioning did not influence limits of agreement in a clinically significant manner. Overall, more patients expressed preference for Diaton tonometry (40.2%) than Goldmann applanation tonometry (30.3%). Those aged 50 or less were more likely to prefer Diaton tonometry.

CONCLUSIONS

The Diaton tonometer is portable, lightweight, user-friendly and well tolerated by patients. However, it shows poor agreement with Goldmann applanation tonometry, thereby precluding it from being regarded as a substitute in routine clinical practice.

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.

Transpalpebral measurement of intraocular pressure using the Diaton tonometer versus standard Goldmann applanation tonometry

BACKGROUND

Diaton transpalpebral tonometry is a new version of TGDc-01 transpalpebral tonometry. The aim of this study is to evaluate the reliability of this method, and to compare the results with those of corrected Goldmann applanation tonometry (c-GAT), which is the "gold standard" for the clinical measurement of IOP.

METHODS

IOP was measured in 212 eyes of 129 subjects by means of two different methods. Measurements with two tonometers were performed in random order, and the measurements of central cornea thickness were performed with ultrasound pachymetry.

RESULTS

The average IOP reading was 15.46 ± 5.68 mmHg for c-GAT and 13.84 ± 5.12 mmHg for Diaton tonometer. The mean difference between c-GAT and Diaton tonometer was 1.62 ± 3.60 mmHg (p < 0.05). Compared with c-GAT, 39.6% of IOP readings (84 eyes) by Diaton tonometer was in an interval of ± 1 mmHg; 59.4% (126 eyes) was in an interval of ± 2 mmHg, and 76.4% (162 eyes) was in an interval of ± 3 mmHg. For the subjects whose age was from 20 to 50, the mean difference of IOP readings by two tonometers was 0.53 ± 3.24 mmHg.

CONCLUSIONS

We cannot recommend Diaton as a substitute or alternative method for GAT for diagnosis and follow-up of patients with abnormal IOPs, but it may be helpful as a screening tool, especially for subjects whose age is between 20 and 50 years and for healthy subjects.

Effects of corneal thickness on intraocular pressure measured with three different tonometers

PURPOSE

To compare intraocular pressure (IOP) measured by a Goldmann applanation tonometer (GAT), a noncontact tonometer (NCT), and a portable noncontact tonometer (PNCT) in eyes of healthy volunteers, and to determine if a significant correlation exists between the IOP and the central corneal thickness (CCT).

METHODS

A total of 144 healthy participants were randomly assigned to one of two groups; in the first group, IOP was measured first with the NCT and then with the GAT. In the second group, IOP was measured first with the PNCT and then with the GAT. Subsequently, the CCT of all subjects was measured with an ultrasonic pachymeter.

RESULTS

The IOPs determined by the GAT and NCT and were strongly correlated, as were those determined by the GAT and PNCT, in both groups. However, a Bland-Altman plot showed that the correlations between the GAT and NCT and between the GAT and the PNCT measurements were not significant. With all three instruments, the IOP readings varied with the CCT. The mean IOPs obtained with the GAT increased by 0.23 mmHg with each 10-microm increase in CCT (0.23 mmHg/10 microm). The comparable value for the NCT was 0.29 mmHg/10 microm, and that for the PNCT was 0.31 mmHg/10 microm.

CONCLUSIONS

For measurements of IOP in normal eyes, the GAT is the tonometer least affected by the CCT, compared with the PNCT and NCT. A PNCT is more likely to be affected by variations in CCT than the GAT.

Central corneal thickness and Diaton transpalpebral tonometry

BACKGROUND

To examine the effects of central corneal thickness on the measures obtained from transpalpebral tonometry (Diaton), and to identify correlations between intraocular pressure (IOP) measurements with Diaton and the Goldmann applanation tonometer (GAT).

METHODS

In this cross-sectional study, 162 eyes of 81 participants were included. Intraocular pressure measurements were obtained in all patients using Diaton and GAT. Central corneal thickness was determined by ultrasound pachymetry. The participants were stratified by corneal thickness: group I <530 microm (n = 56), group II 530-560 microm (n = 65), and group III >560 microm (n = 41).

RESULTS

There were moderate correlations between IOP readings obtained using the Diaton and corrected GAT (C-GAT) (r = 0.303; P < 0.0001), and between corrected Diaton (C-Diaton), and C-GAT (r = 0.399; P < 0.0001). The mean Diaton tonometer readings were lower than C-GAT measurements (Diaton-corrected GAT mean difference, 0.9 +/- 3.8 mmHg; c-Diaton-corrected GAT mean difference, 0.7 +/- 3.5 mmHg). Differences were detected between the groups of patients for the GAT values [2.4 +/- 3.6 mmHg for those with the thinnest corneas (<530 microm), 0.7 +/- 3.6 mmHg for those with moderate corneas (between 531 microm and 560 microm), and -0.6 +/- 3.6 mmHg for those with the thickest (>560 microm) corneas], whereas a significantly lower difference (0.9 +/- 3.8 mmHg) was noted for the Diaton values of all individuals.

CONCLUSIONS

The Diaton measurements show moderate correlation with those provided by applanation tonometry. The Diaton tonometer seems to be more affected by the corneal thickness, especially in the thinnest corneas.

Evaluation of the impedance tonometers TGDc-01 and iCare according to the international ocular tonometer standards ISO 8612

BACKGROUND

Two new tonometers have been introduced that are based on the impedance principle. Both the TGDc-01 (transpalpebral measurement) and the iCare (corneal measurement) do not require corneal anaesthesia. The present work presents an evaluation of both devices.

METHODS

Comparative measurements using one of the new tonometers and applanation tonometry were performed by one investigator according to the international standard for ocular tonometer (ISO 8612). Measurements were performed on 445 eyes without corneal pathology from 243 patients. Six measurements were performed for iCare and 3 for TGDc, immediately followed by 3 applanation tonometry measurements.

RESULTS

The correlation coefficient with respect to applanation tonometry was 0.81 for TGDc and 0.95 for iCare. TGDc-01 measurements showed an average deviation of 3.1 +/- 2.6 mmHg to those of Perkins applanation tonometry. The maximum difference was 28.7 mmHg below and 9.8 mmHg above the results of applanation tonometry. iCare showed an average deviation of 2.5 +/- 1.1 mmHg to Goldmann tonometry. The maximum difference was 14.5 mmHg below and 9.8 mmHg above.

CONCLUSIONS

The results of both new tonometers showed a good correlation with the reference applanation tonometric methods, but the strict requirements of ISO 8612 are not fulfilled by either tonometer at present. Additionally, transpalpebral measurements with the TGDc-01 showed unacceptably high variability.

Are Disposable Prisms an Adequate Alternative to Standard Goldmann Tonometry Prisms in Glaucoma Patients?

PURPOSE

To evaluate the accuracy and reliability of 2 single-use tonometry devices (Tonosafe and Tonojet) as an alternative to standard Goldmann prisms in patients attending dedicated glaucoma clinics.

DESIGN

Prospective experimental study with human subjects.

PARTICIPANTS

Two hundred forty glaucoma patients who attended 2 glaucoma clinics at the Stepping Hill Hospital between January and February 2005.

METHODS

During each examination, intraocular pressure (IOP) was measured 3 times, using the standard Goldmann prism, Tonosafe, and Tonojet, respectively. The prism sequence was predetermined at random using a computer, and the measurements were taken at 5-minute intervals. Data were analyzed using the Bland-Altman method of differences.

MAIN OUTCOME MEASURE

Intraocular pressure.

RESULTS

Intraocular pressure ranged from 6 to 68 mmHg. Linear regression analysis indicated that there was a proportional bias between Goldmann and Tonosafe (r2 = 0.368, P<.001), especially for values higher than 25 mmHg. On the other hand, there was no statistically significant proportional bias between Goldmann and Tonojet (r2 = 0.006, P = 0.14).

CONCLUSIONS

Caution should be exercised when using Tonosafe prisms in the presence of IOP higher than 25 mmHg. On the other hand, Tonojet is an adequate and useful alternative to the Goldman tonometer for glaucoma patients.

Corneal structure and biomechanics: impact on the diagnosis and management of glaucoma

PURPOSE OF REVIEW

Highlights recent studies relating to the impact of corneal structure and biomechanical properties on glaucoma evaluation and management.

RECENT FINDINGS

Central corneal thickness has been shown to play a role in the interpretation of intraocular pressure. Central corneal thickness has also been suggested as a glaucoma risk factor. The potential role of other corneal factors, such as stromal makeup, in the accurate measurement of intraocular pressure and the assessment of glaucoma risk remains to be determined.

SUMMARY

Improved understanding of central corneal thickness and corneal biomechanical properties may someday lead to a better understanding of glaucoma risk and its assessment.

Goldmann-Applanationstonometrie und dynamische Konturtonometrie

BACKGROUND

The aim of the study was to compare intraocular pressure (IOP) measurements between Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT) during product certification according to the international requirements for ophthalmic instruments (tonometers, ISO 8612:2001).

METHODS

The study included 160 eyes of 80 subjects. IOP measurements were performed four times consecutively on each instrument in randomized order. The difference of mean IOP measurements between GAT and DCT was analyzed. Furthermore, Bland and Altman analysis was performed to assess agreement between the instruments.

RESULTS

The mean difference between DCT and GAT IOP measurements was 0.30+/-2.18 mmHg. At low to normal IOP values of 7-16 mmHg and higher IOP values of > or =23 mmHg, the difference between DCT IOP measurements and GAT IOP measurements increased in the opposite direction (1.44+/-1.59 mmHg and -1.47+/-2.57 mmHg). The Bland and Altman analysis revealed a fixed bias of -0.4+/-2.0 mmHg.

CONCLUSIONS

The test tonometer DCT exceeds the requirements for the international standard for tonometers ISO 8612:2001. The results are valid for a central corneal thickness of 540+/-40 microm.