Tonometers-which one should I use?

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.

Corneal biomechanics and diagnostics: a review

PURPOSE

Corneal biomechanics is an emerging field and the interest into physical and biological interrelations in the anterior part of the eye has significantly increased during the past years. There are many factors that determine corneal biomechanics such as hormonal fluctuations, hydration and environmental factors. Other factors that can affect the corneas are the age, the intraocular pressure and the central corneal thickness. The purpose of this review is to evaluate the factors affecting corneal biomechanics and the recent advancements in non-destructive, in vivo measurement techniques for early detection and improved management of corneal diseases.

METHODS

Until recently, corneal biomechanics could not be directly assessed in humans and were instead inferred from geometrical cornea analysis and ex vivo biomechanical testing. The current research has made strides in studying and creating non-destructive and contactless techniques to measure the biomechanical properties of the cornea in vivo.

RESULTS

Research has indicated that altered corneal biomechanics contribute to diseases such as keratoconus and glaucoma. The identification of pathological corneas through the new measurement techniques is imperative for preventing postoperative complications.

CONCLUSIONS

Identification of pathological corneas is crucial for the prevention of postoperative complications. Therefore, a better understanding of corneal biomechanics will lead to earlier diagnosis of ectatic disorders, improve current refractive surgeries and allow for a better postoperative treatment.

Comparison of intraocular pressure measured by iCare tonometers and Goldmann applanation tonometer

OBJECTIVE

To evaluate the relationship between the Goldmann applanation tonometer (GAT) and the iCare PRO and iCare IC200 tonometers in measuring intraocular pressure (IOP) in adult eyes with a diagnosis of glaucoma or glaucoma suspect.

PARTICIPANTS AND METHODS

One hundred and one eyes from 101 participants diagnosed with glaucoma or glaucoma suspect were evaluated in this study. IOP was measured by iCare PRO and iCare IC200 tonometers in a randomized sequence followed by IOP measurements by the GAT tonometer and then central corneal thickness measurements. After the IOP measurements, participants scored their comfort level using a visual analog scale with each tonometer. Intraclass correlation coefficient (ICC) and Bland-Altman analysis were used to investigate the agreement among tonometers. SPSS and Microsoft Excel programs were used for statistical analysis.

RESULTS

Overall, there was good agreement among the 3 tonometers used in this study. The ICC for the iCare PRO and the iCare IC200 was 0.95 (p < 0.001), and the ICC for the iCare PRO and the GAT and the iCare IC200 and the GAT was >0.80 (p < 0.001). However, both iCare tonometers underestimated IOP by approximately 2 mm Hg compared with the GAT. Furthermore, 84% of iCare readings fall within ±5 mm Hg of GAT measurements. Neither body mass index nor central corneal thickness affected the IOP agreement among the tonometers. Participant response on visual analog scale rated IOP measurements by iCare tonometers to be more comfortable than the GAT.

CONCLUSION

Our results demonstrated a good agreement between iCare tonometers and GAT; but iCare tonometers underestimated IOP compared to the GAT.

International comparisons of intraocular pressures, as measured by Tono-Pen and Goldmann applanation tonometry, in healthy adults: A meta-analysis

BACKGROUND

Investigate intraocular pressure (IOP), as measured by Tono-Pen (TP) and Goldmann applanation tonometry (GAT), in healthy adults. Provide an updated synthesis of multinational, primary studies, reported during the 10-year period 2011 to 2021 and offer an evidence-based benchmark, against which IOP can be evaluated across subject variables and pathologies. Three primary research questions are investigated: Is there a statistically significant difference between IOP measured by TP and GAT? If yes, is the difference clinically significant? Is measurement of IOP affected by the country or setting location, in which the measurements are made?

METHODS

An aggregate meta-analysis was conducted on 22 primary studies, from 15 different countries. IOP measurements were made from each healthy adult subject, with both the TP and GAT. Primary studies were identified and data extracted according to recommended preferred reporting items for systematic reviews and meta-analysis protocol guidelines. Meta-analysis summary results are reported as the point estimate of the raw mean difference of IOP.

RESULTS

Meta-analysis reveals a statistically significant difference in raw mean differences in IOP, when measured by TP and GAT, in the healthy adult population. Tono-Pen IOP measurements are higher than GAT IOP measurements. The point estimate for the summary effect size = -0.73 mm Hg, P = .03. The prediction interval for the true effect size, in 95% of all comparable populations, is -4.03 to 2.58 mm Hg. There is no clinically significance difference in IOP when measured by TP and GAT. Meta-regression analysis reveals statistically significant differences in measurement of IOP by countries, R2 analog = 0.75, P = .001. There is no statistically significant difference in measurement of IOP as a function of measurement location setting, R2 analog = -0.17, P = .65.

CONCLUSIONS

IOP measured by TP are marginally higher compared to GAT, in the healthy adult population. However, from a clinical practice perspective, TP and GAT produce similar IOP measurements. There is evidence of significant variabilities in IOP measurements as a function of country. IOP measurements collected in a research laboratory setting are similar to IOP collected in a clinical setting. Results have implications for the primary care physician requiring a portable, inexpensive, reliable, and easily administered instrument to assess IOP.

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.

The short-term effects of intranasal steroids on intraocular pressure in pediatric population

PURPOSE

To evaluate the effect of intranasal mometasone furoate (INMF) on short-term intraocular pressure (IOP) alterations in children with allergic rhinitis (AR).

METHODS

Children diagnosed with AR and to whom INMF nasal spray had been firstly prescribed were enrolled. Cases with any ocular diseases except for refractive errors were excluded. Complete ophthalmologic examinations including IOP measurements using Tonopen XL were performed before the treatment as well as at the first and sixth weeks of follow-up. Demographics and ophthalmologic findings were noted and statistically analyzed.

RESULTS

Study population consisted of 62 right eyes of 62 children with a mean age of 8.55 ± 3.14 years. Of them, 29 were female (46.8%) and 33 were male (53.2%). Dilated fundoscopy revealed an enlarged Cup/Disc ratio in 12 eyes (19.4%). Family history of glaucoma was positive in 13 cases (21.0%). Mean best corrected visual acuity was found as 0.05 ± 0.08 logMAR. Initial IOP was 17.1 ± 2.3 mmHg; whereas it was measured as 18.2 ± 2.0 mmHg and 17.3 ± 2.1 mmHg at the first and sixth weeks of follow-up, respectively (p < 0.001). Both at the first and sixth weeks of follow-up, significant IOP rise was present in children with a positive family history of glaucoma (p < 0.001 and p = 0.003, respectively). Besides, increased IOP was found in participants with cupping revealed on fundoscopy at the first week of follow-up (p = 0.044).

CONCLUSION

Since children have greater risk for steroid-induced ocular hypertensive response than adults, ophthalmologic evaluation must be recommended in children receiving intranasal steroids.

A Prospective Analysis of the Simplified Student Sight Savers Program on Open-Angle Glaucoma Cost Burden in Underserved Communities

(1) Background: Glaucoma is a leading cause of irreversible blindness worldwide. Unfortunately, no noticeable symptoms exist until mid- to late-stage glaucoma, leading to substantial costs to the patient and the healthcare system. (2) Methods: The Student Sight Savers Program, an initiative started at Johns Hopkins University, was designed to meet the needs of community screening for glaucoma. Several medical students at the Rocky Vista University in Saint George, Utah, were trained, and screened patients at local fairs and gathering places using a modified version of this program. Patients found to have elevated pressure (>21 mmHg) or other ocular abnormalities were referred for an ophthalmological examination. (3) Results: Individuals from medically underserved areas/populations (MUA/Ps) were nearly three times as likely to have elevated intraocular pressure as individuals not in underserved areas (p = 0.0141). A further analysis demonstrates that medical students can help reduce medical costs for patients and the healthcare system by providing referrals to ophthalmologists and reaching populations that are not usually screened for glaucoma. (4) Conclusions: Allowing medical students to perform community-based glaucoma screening events in MUA/Ps using handheld tonometers may decrease the cost burden associated with late diagnosis, and raise awareness about glaucoma, especially in underserved populations.

Comparison of Three Tonometers in Measuring Intraocular Pressure in Eyes That Underwent Myopic Laser in situ Keratomileusis and Photorefractive Keratectomy

Objective

Methods

Results

Conclusion

Comparison of Non-contact Tonometry and Goldmann Applanation Tonometry Measurements in Non-pathologic High Myopia

Purpose

To compare intraocular pressure (IOP) values obtained using Goldmann applanation tonometry (IOPGAT) and non-contact tonometry (IOPNCT) in a non-pathologic high myopia population.

Methods

A total of 720 eyes from 720 Chinese adults with non-pathologic high myopia were enrolled in this cross-sectional study. Demographic and ocular characteristics, including axial length, refractive error, central corneal thickness (CCT), and corneal curvature (CC) were recorded. Each patient was successively treated with IOPNCT and IOPGAT. Univariate and multivariable linear regression analyses were conducted to detect factors associated with IOPNCT and IOPGAT, as well as the measurement difference between the two devices (IOPNCT−GAT).

Results

In this non-pathologic high myopia population, the mean IOPNCT and IOPGAT values were 17.60 ± 2.76 mmHg and 13.85 ± 2.43 mmHg, respectively. The IOP measurements of the two devices were significantly correlated (r = 0.681, P &lt; 0.001), however, IOPNCT overestimated IOPGAT with a mean difference of 3.75 mmHg (95% confidence interval: 3.60–3.91 mmHg). In multivariate regression, IOPNCT was significantly associated with body mass index (standardized β = 0.075, p = 0.033), systolic blood pressure (SBP) (standardized β = 0.170, p &lt; 0.001), and CCT (standardized β = 0.526, p &lt; 0.001). As for IOPGAT, only SBP (standardized β = 0.162, p &lt; 0.001), CCT (standardized β = 0.259, p &lt; 0.001), and CC (standardized β = 0.156, p &lt; 0.001) were significantly correlated. The mean IOPNCT−GAT difference increased with younger age (standardized β = −0.134, p &lt; 0.001), higher body mass index (standardized β = 0.091, p = 0.009), higher SBP (standardized β = 0.074, p = 0.027), thicker CCT (standardized β = 0.506, p &lt; 0.001), and lower IOPGAT (standardized β = −0.409, p &lt; 0.001).

Conclusion

In the non-pathologic high myopia population, IOPNCT overestimated IOPGAT at 3.75 ± 2.10 mmHg. This study suggests that the difference between the values obtained by the two devices, and their respective influencing factors, should be considered in the clinical evaluation and management of highly myopic populations.

Common causes of visual impairment in the elderly

Background

Aging is not a disease; rather, it is a process. As people age, visual impairment (VI) becomes more common. In 2010, the overall prevalence rate of vision impairment in all races was 25.66% in individuals aged ≥ 80 years, according to the estimate of the National Eye Institute at the National Institutes of Health. This review aimed to address the common causes of VI in the elderly.

Methods

In this narrative review, an electronic search of the PubMed/MEDLINE database was conducted using "visual impairment" and "elderly" for the period between January 2010 and April 2021, to include randomized clinical trials and observational studies concerning VI in the elderly. The selected time period was chosen to provide an updated review.

Results

The search yielded 2955 articles published over the period of more than 11 years. The relevant randomized clinical trials or observational studies were included and reviewed. Cataracts, refractive errors, open-angle glaucoma, age-related macular degeneration, and diabetic retinopathy were the most common age-related ocular disorders leading to VI if untreated in the elderly. The loss of visual acuity can adversely affect quality of life in the elderly. Difficulty with activities of daily living related to VI can lead to social isolation, depression, and anxiety. Loss of vision in the elderly is linked to an increased risk of falls, hip fracture, depression, and poor quality of life.

Conclusions

The most common causes of VI in the elderly are cataracts and refractive errors. VI in most ocular diseases is more prevalent in women than in men due to longer lifespan. The overall prevalence of the main causes of VI in the elderly is expected to increase; therefore, health policymakers should consider this when planning for the health-enhancement program of the population.

Measures of disease activity in glaucoma

Glaucoma is the leading cause of irreversible blindness globally which significantly affects the quality of life and has a substantial economic impact. Effective detective methods are necessary to identify glaucoma as early as possible. Regular eye examinations are important for detecting the disease early and preventing deterioration of vision and quality of life. Current methods of measuring disease activity are powerful in describing the functional and structural changes in glaucomatous eyes. However, there is still a need for a novel tool to detect glaucoma earlier and more accurately. Tear fluid biomarker analysis and new imaging technology provide novel surrogate endpoints of glaucoma. Artificial intelligence is a post-diagnostic tool that can analyse ophthalmic test results. A detail review of currently used clinical tests in glaucoma include intraocular pressure test, visual field test and optical coherence tomography are presented. The advanced technologies for glaucoma measurement which can identify specific disease characteristics, as well as the mechanism, performance and future perspectives of these devices are highlighted. Applications of AI in diagnosis and prediction in glaucoma are mentioned. With the development in imaging tools, sensor technologies and artificial intelligence, diagnostic evaluation of glaucoma must assess more variables to facilitate earlier diagnosis and management in the future.

A Review of Ophthalmic Telemedicine for Emergency Department Settings

BACKGROUND

Patients presenting to emergency departments for ophthalmic emergencies benefit from prompt evaluation. However, Few emergency departments (EDs) have ophthalmologists on call, and eye care provided in EDs without ophthalmic services can be inaccurate.

METHODS

We review the current state of ophthalmic telemedical care in EDs and highlight important considerations when implementing telemedicine in this setting.

RESULTS

Telemedicine allows ophthalmologists to work with on-site emergency care providers to interview and examine patients remotely in EDs, enabling proper assessment of patient history, visual acuity, pupils, intraocular pressure, as well as the anterior and posterior segment. To date, patients' perceptions of this new model of care have been largely positive.

DISCUSSION

The use of telemedical consultations for remote evaluation of patients with ophthalmic complaints stands to improve the quality of care provided to patients and extend the reach of remote ophthalmologists. The onset of the COVID-19 pandemic and the risk of in-person care further highlights the potential for telemedicine to augment existing models of emergency care.

Goldmann Tonometry and Corneal Biomechanics

Glaucoma is the second cause of irreversible blindness in the world. Intraocular pressure (IOP) is a recognized major risk factor for the development and progression of glaucomatous damage. Goldmann applanation tonometry (GAT) is internationally accepted as the gold standard for the measurement of IOP. The purpose of this study was to search for correlations between Goldmann tonometry and corneal mechanical properties and thickness by means of in vitro tests. IOP was measured by the Goldmann applanation tonometer (GIOP), and by a pressure transducer inserted in the anterior chamber of the eye (TIOP), at increasing pressure levels by addition of saline solution in the anterior chamber of enucleated pig eyes (n = 49). Mechanical properties were also determined by inflation tests. The GAT underestimated the real measurements made by the pressure transducer, with most common differences in the range 15–28 mmHg. The difference between the two instruments, highlighted by the Bland–Altman test, was confirmed by ANOVA, normality tests, and Mann–Whitney’s tests, both on the data arranged for infusions and for the data organized by pressure ranges. Pearson correlation tests revealed a negative correlation between (TIOP-GIOP) and both corneal stiffness and corneal thickness. In conclusion, data obtained showed a discrepancy between GIOP and TIOP more evident for softer and thinner corneas, that is very important for glaucoma detection.

Correlation between corneal thickness, keratometry, age, and differential pressure difference in healthy eyes

To determine the use of differential pressure difference (DPD), in air-puff differential tonometry, as a potential biomechanical measure of the cornea and elucidate its relationship with the intraocular pressure (IOP), central corneal thickness, corneal curvature, and age. This study comprised 396 eyes from 198 patients and was conducted at Acibadem University, School of Medicine, Department of Ophthalmology, Istanbul, Turkey. The central corneal curvature and refraction of the eyes were measured using an Auto Kerato-Refractometer (KR-1; Topcon Corporation, Tokyo, Japan). IOP and central corneal thickness were measured using a tono-pachymeter (CT-1P; Topcon Corporation, Tokyo, Japan), wherein two separate readings of IOP were obtained using two different modes: 1-30 and 1-60. The difference between these two readings was recorded as the DPD. The factors affecting the DPD were determined by stepwise multiple linear regression analysis. DPD varied over a dynamic range of - 3.0 to + 5.0 mmHg and was weakly correlated with the central corneal thickness (r = 0.115, p < 0.05). DPD showed no significant correlation with IOP 1-30 (p > 0.05). A weak but statistically significant (p < 0.05) positive correlation of DPD was observed with age (r = 0.123), Kavg (r = 0.102), and the CCT (r = 0.115). There was a significant correlation between DPD and Kavg, CCT, and age. There was no significant correlation between DPD and IOP 1-30. Age-related changes in the corneal ultrastructure may be a plausible explanation for the weak positive association between age and DPD. The proposed method may prove a valid non-invasive tool for the evaluation of corneal biomechanics and introduce DPD in the decision-making of routine clinical practice.

Corrected Intraocular Pressure Variability with Central Corneal Thickness Measurement

Purpose

To evaluate variability in measured intraocular pressure (IOP) values when correlated with central corneal thickness measurements obtained by both ultrasonic and optical tools.

Patients and Methods

We included 46 eyes of 46 healthy subjects (age range 35–76 years). Exclusion criteria for the current study were patients with confirmed diagnosis of glaucoma, glaucoma suspect patients and those having corneal opacities, scars or prior cornea-based laser vision correction. Central corneal thickness (CCT) was measured using two methods: ultrasonically (CCT1) by pachymeter and optically (CCT2) using anterior-segment optical coherence tomography (AS-OCT). The IOP was measured in all subjects using Goldmann applanation tonometry (GAT).

Results

No significant difference was detected comparing intraocular pressure values and CCT-corrected intraocular pressure (IOPcc1 and IOPcc2) (P=0.47 and P=0.06, respectively) among the study participants. A significant negative correlation was found between corneal thickness-corrected IOP values and the measured central corneal thickness by both optical and ultrasonic tools (P=0.004 and P=0.001, respectively).

Conclusion

Intraocular pressure appears to be dependent and positively correlated with CCT changes. However, this does not appear to depend largely on methods used for measuring the CCT in the current study. Corrected intraocular pressure is negatively correlated to both ultrasonically and optically measured central corneal thickness.

Comparative Assessment of The Goldmann Applanation and Noncontact Tonometers in Intraocular Pressure Measurements in a Sample of Glaucoma Patients in the Cape Coast Metropolis, Ghana

Objectives:

The objective of the study was to explore the usage of the Goldmann applanation tonometry and noncontact tonometry interchangeably in the measurement of intraocular pressure (IOP) in glaucoma patients.

Materials and Methods:

The study involved 441 clinically diagnosed glaucoma patients receiving care at a referral facility. IOP measurements were obtained using both the Noncontact tonometer and Goldmann applanation tonometer The repeatability of the measures was analyzed by comparing the repeated measures of the devices using paired t-test and calculating the correlation coefficient. A Bland–Altman analysis was used to determine the limits of agreement between the two procedures.

Results:

There were 271 (61.5%) males and 170 (38.5%) females and their age ranged from 18 to 73 years (mean age = 49.37; standard deviation ± 14.81 years). The findings of the study showed significantly lower readings (P < 0.001) of the GAT (right eye = 17.40 ± 7.48 mmHg; left eye = 16.80 ± 7.49 mmHg) compared to the NCT (right eye = 20.15 ± 8.30 mmHg; left eye = 19.74 ± 8.31 mmHg). There was a strong positive correlation between the GAT and NCT findings in the right eye (r = 0.871, n = 441, P < 0.001) and in the left eye (r = 0.887, n = 441, P < 0.001). There was a wide limit of agreement between NCT and GAT measurements.

Conclusion:

There was statistically significant higher measures obtained with NCT than the GAT but did not exceed the allowable inter-device difference. There was a strong positive correlation between GAT and NCT measurements. However, it is strongly recommended that these devices are not used interchangeably in the monitoring of IOP in glaucoma due to the wide range of limits of agreement.

Effect of trabeculectomy and Ahmed glaucoma valve implantation surgery on corneal biomechanical changes

PURPOSE

To evaluate alterations in corneal biomechanical properties before and 6 months after conventional trabeculectomy (TRAB) and Ahmed glaucoma valve (AGV) implantation.

METHODS

Thirty-nine eyes of 39 patients were evaluated retrospectively. Complete ophthalmological examinations including evaluation of corneal biomechanical properties using the Ocular Response Analyzer were performed before and after 6 months postoperatively. A mean of four measurements for corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann correlated intraocular pressure (IOPg), and corneal compensated intraocular pressure (IOPcc) was recorded. The participants had undergone trabeculectomy or shunt surgery as the first surgical procedure for glaucoma treatment of uncontrolled IOP with maximum antiglaucoma eyedrops.

RESULTS

There were 20 eyes of 20 patients in trabeculectomy group and 19 eyes of 19 patients in AGV implantation group. There was no significant difference between two groups in terms of sex, age, eye laterality, lens status, antiglaucoma drug usage, preoperatively measured Mean Deviation of Humphrey Visual Field Analyzer, CH, CRF, IOPcc, and IOPg (p > 0.05). CH and CRF increased significantly after shunt surgery (p < 0.001). CH increased in trabeculectomy group postoperatively (p < 0.001); however, CRF showed a small amount of decrease, but this reduction was not statistically significant (p > 0.05). CH and CRF showed higher increase after AGV surgery than trabeculectomy surgery (p < 0.05). There was no significant correlation between IOP changes and CH-CRF changes in both TRAB and AGV groups (p > 0.05).

CONCLUSION

According to our results, surgical technique differences may have an impact on postoperative corneal biomechanical outcomes. AGV surgery offers better corneal biomechanical results than standard trabeculectomy in 6-month follow-up.

Biomechanically-Corrected Intraocular Pressure Compared To Pressure Measured With Commonly Used Tonometers In Normal Subjects

PURPOSE

To compare the biomechanically-corrected intraocular pressure (bIOP) measured by the Corvis ST (Oculus, Wetzlar, Germany) with IOP measurements made by other commonly used tonometers; and to test the correlations between IOP measures and central corneal thickness.

METHODS

One randomly-selected eye from each of 94 healthy subjects was assessed. The bIOP was determined by the CorVis ST and compared with the IOP measurements made by standard Goldmann Applanation Tonometer (GAT: Haag-Streit AG, Bern, Switzerland), the Icare (Icare Finland Oy, Vantaa, Finland), and the Ocular Response Analyzer (ORA-IOPcc: Reichert, New York, USA). Corneal thickness was assessed by the Oculus Pentacam. The correlation between bIOP and the other devices and between CCT were assessed using the Pearson correlation test or Spearman's rho test accordingly to the distribution of these values. The Bland-Altman method and intraclass correlation coefficients (ICC) were used to assess the agreement of bIOP results with IOP obtained with other techniques. The limits of agreement (LoA) were determined as the mean difference ±1.96 SD of the mean differences. In all tests, the significance level was considered to be 0.05.

RESULTS

Mean and SD of the bIOP were 16.11±1.66 mmHg. Significant differences were found between the bIOP and other IOP measurements (GAT, 3.02±2.60 mmHg, p<0.001, Icare, 1.51±2.95 mmHg, p<0.001, IOPcc, 1.09±1.96 mmHg, p<0.001). The lowest and highest mean differences in IOP were with the IOPcc and GAT, respectively. Interestingly, there were no significant differences in bIOP, GAT-IOP and ORA-IOPcc between the eyes with thin or thick corneal thicknesses, with Icare-IOP being the only exception (p<0.001).

CONCLUSION

The Corvis bIOP has a higher correlation with the IOPcc by ORA, which are also compensated for the effects of corneal biomechanics and have less association with corneal thickness relative to the uncorrected GAT and Icare measurements.