Underestimation Of Intraocular Pressure Research Articles

Validation of the Reichert® Tono-Vera® Vet rebound tonometer in normal exvivo canine eyes.

To determine the accuracy of the Reichert® Tono-Vera® Vet rebound tonometer for canine intraocular pressure (IOP) measurement. Five normal canine exvivo globes. The anterior chambers of five freshly enucleated normal canine eyes were cannulated and connected to a reservoir of Plasma-Lyte A and a manometer. Starting at a manometric IOP of 5 mmHg, the pressure was progressively increased to 80 mmHg by raising the reservoir. Triplicate IOP measurements were taken with the Tono-Vera® Vet from the central cornea using the dog setting and compared to the manometric pressure by linear regression analysis and Bland-Altman plots. There was a strong positive linear regression trend when comparing central corneal Tono-Vera® Vet IOPs to manometric pressures (r2 = .99) with solid agreement between the two methods. Compared to manometric IOPs, the Tono-Vera® Vet underestimated IOPs at higher pressures ≥70 mmHg. Measurement of IOPs from the central cornea with the Tono-Vera® Vet provided accurate results over a large range in normal canine globes compared to direct manometry. The mild to moderate underestimation of IOPs at high pressures was not considered clinically relevant.

Correlation Between Central Corneal Thickness and Intraocular Pressure with the Goldmann Applanation Tonometer

Purpose: The aim of this review is to investigate the correlation between central corneal thickness (CCT) and Intraocular pressure with the Goldmann applanation tonometer (GAT).
 Materials and Methods: A literature search using Medline database was conducted for the years 1946 to 2022 to explore the relationship between central corneal thickness and Intraocular pressure measured by the Goldmann applanation tonometer. The search was restricted to studies published in English language. The first 80 articles were reviewed and five relevant studies were selected in this analysis.
 Findings: Impacts of central corneal thickness on Intraocular pressure were investigated in five studies. Overestimation of intraocular pressure is associated with thick cornea while underestimation of intraocular pressure was associated with thin cornea
 Implications to Theory, Practice and Policy: Central corneal thickness can affect the result of Intraocular pressure measurement with the Goldmann applanation tonometer (GAT) . Assessment of central corneal thickness (CCT) is necessary for correct interpretation of IOP measurements obtained with the Goldmann applanation tonometer (GAT).

Assessment of corneal sublayer thickness changes in glaucoma patients using optical coherence tomography and correlation of epithelial layer thinning with dry eye monitoring

In this study, we aimed to assess the central corneal epithelial thickness (CET), central corneal stromal thickness (CST), and total central corneal thickness (CCT) thinning relationships with dry eye development monitoring and underestimated measurement of intraocular pressure (IOP) in primary open-angle glaucoma (POAG) patients treated with timolol, dorzolamide, and brimonidine. This longitudinal cohort study included 106 patients with POAG. All patients underwent a detailed ophthalmic examination. In addition, CET, CST, and CCT were measured using anterior segment optical coherence tomography (AS-OCT). Subsequently, the cohort was divided into three groups based on the therapy administered. The Tomec group received monotherapy with benzalkonium chloride (BAK)-preserved timolol+dorzolamide fixed combination. The Alphagan group received monotherapy with purite-preserved brimonidine, and the Combigan group received monotherapy with BAK-preserved timolol+brimonidine fixed combination. CET, CST, and CCT did not show a statistically significant decrease in the Alphagan group (p>0.05). However, the Tomec and Combigan groups showed significantly reduced measurements, except for stromal thickness (p<0.05). Finally, a significant positive correlation was found between changes in tear break-up time (TBUT) and CET during the follow-up period (r=0.637, p=0.001). CET and CCT thinning were higher in the Tomec and Combigan groups than in the Alphagan group. Furthermore, although CCT reduction was significant in the Tomec and Combigan groups, its effect on IOP underestimation was approximately 1%. Furthermore, the positive correlation between CET and TBUT suggests that CET measurement with AS-OCT may also be useful in dry eye monitoring.

Comparison of the iCare rebound tonometer and the Perkins applanation tonometer in children under general anesthesia

The goal of the study was to compare Perkins applanation tonometry and iCare rebound tonometry, evaluating their correlation and agreement in a diverse pediatric population under general anaesthesia (GA). Children undergoing an eye examination under GA between November 2019 and March 2020 were included. Intraocular pressure (IOP) was measured successively using the Perkins applanation tonometer and the iCare IC200 rebound tonometer. Ultrasonic central pachymetry and axial length were measured. One hundred and thirty-eight eyes of 72 children were included. The mean age was 2.87years. IOP measurements obtained with the two tonometers were statistically and significantly highly correlated (r=0.8, P<0.001), although the iCare overestimated IOP by an average of 3.37mmHg (SD±4.48). The agreement between the two methods was moderate; the 95% agreement limits ranged from -5.41 to +12.15mmHg (r=0.5, P<0.001). The IOP difference between the two tonometers was weakly but significantly correlated with mean IOP (r=0.52; P=0.006). No correlation was found with axial length and pachymetry. In this study, the IOP values obtained using the Perkins applanation tonometer and the iCare IC200 rebound tonometer were well correlated. The iCare tended to overestimate the IOP, especially for high IOP values. However, no underestimation of IOP was found with this device, hence its potential for glaucoma screening in children.

Analysis of the influence of corneal properties and densitometry on applanation and rebound tonometry in primary open angle glaucoma

To evaluate the influence of corneal densitometry on portable applanation (Perkins) and rebound (iCare ic100 and PRO) tonometry. A secondary goal was to assess if there was a relationship between various corneal properties and the severity of primary open angle glaucoma (POAG). Seventy-five eyes of 75 patients with primary open angle glaucoma were studied, divided by severity into 3 groups: 25 mild, 25 moderate and 25 advanced. Intraocular pressure (IOP) was measured 3 times in each participant with a Perkins applanation tonometer (PAT), a handheld version of the Goldman applanation tonometer (GAT), an iCare PRO and an iCare ic100. Mean values were then calculated. Corneal topography with the Pentacam HR (Oculus, Wetzlar, Germany) was also performed in all individuals. Mean age and sex were comparable in all groups, as were densitometry values (P>0.05). The mean visual field defect (MD) was 2.85 (±1.23) dB in the mild glaucoma group, 8.26 (±1.90) dB in the moderate group and 15.66 (±3.46) dB in the advanced group. Three multivariate regression analyses were performed. The first and second calculations assessed the effect of IOP obtained with iCare ic100 and PAT as dependent variables with age, sex, CCT and mean keratometry (Km) within the glaucoma subgroups and the global sample. The third analysis was carried out to assess the relationship between corneal densitometry as the dependant variable and the aforementioned corneal parameters among the glaucoma groups. In the first multivariate regression analysis, a statistically significant correlation was found between ic100 rebound tonometry and CCT in the POAG global sample (coef. 0.117; IC [-0.21-(-0.01)]; P=0.025). No statistically significant correlation was found in the subgroup analyses. In the second multivariate analysis, no significant correlation was found between PAT and CCT, Km, age or sex (P>0.05). In the third analysis, densitometry was correlated with age in all glaucoma subgroups (P<0.001) and with CCT in the moderate glaucoma subgroup (coef. -0.037; IC [-0.67-(-0.01)]; P=0.021). Tonometry appeared to be minimally influenced by corneal densitometry, with a mild positive linear correlation seen (R=0.03). IOP values were similar with 3 of the tonometers: PAT 16.07 (±3.18) mmHg, PRO 16.27 (±3.42) mmHg and ic100 15.17 (±4.28) mmHg. There was, however, a significant underestimation of IOP with ic100 (-0.89mmHg) compared to PAT (P=0.007). Corneal densitometry did not show significant differences between glaucoma severity groups. A positive correlation was seen with CCT and both corneal densitometry and age. No correlation was found with keratometry or severity of glaucoma. The influence of corneal densitometry on IOP measurements appears weak, with little clinical relevance identified.

Evaluating Intraocular Pressure After Myopic Photorefractive Keratectomy: A Comparison of Different Tonometers.

All devices evaluated in this study showed a significant underestimation in intraocular pressure (IOP) measurement after myopic photorefractive keratectomy (PRK), Goldmann tonometer more than others. Corneal biomechanics indicated a different influence on the different kinds of tonometry. The aim was to investigate the reliability of Goldmann applanation tonometry (GAT), rebound tonometry (RT), ocular response analyzer (ORA), Corvis ST (CST), and dynamic contour tonometry (DCT) in IOP evaluation after myopic PRK. One eye of 145 patients who underwent myopic PRK for a refractive defect ranging from -10.25 to -0.50 D (mean -4.69±2.00 D) was included in this retrospective comparative study. A complete eye visit with corneal tomography and IOP measurement with GAT, DCT, ORA, RT, and CST was performed before surgery and at 1, 3, and 6 months follow-up. Values provided by each device were tested and compared at each follow-up. Correlation analyses were run between changes in IOP and the corneal, morphologic and biomechanical parameters were measured after PRK. GAT, DCT, ORA, RT, and CST showed a significant (P<0.01) underestimation of IOP at 6 months follow-up. GAT showed the greatest underestimation (-14.1%) and stronger correlations with corneal deformation parameter changes, whereas ORA, DCT, and RT appeared to be less conditioned by these variations. At 6 months follow-up DCT, ORA, RT, and CST provided IOP values with nonsignificant differences compared with GAT before PRK. Each tested tonometer showed a significant IOP underestimation after myopic PRK. As this was most observed with GAT compared with all devices, we suggest DCT, ORA, RT, or CST to evaluate IOP in these patients following surgery.

TonoVet Plus®: Higher reliability and repeatability compared with Tono-Pen XL™ and TonoVet® in rabbits.

To evaluate the accuracy and repeatability of the Tono-Pen XL™, TonoVet® and TonoVet Plus® tonometers by manometric evaluation, and to establish adjustment equations for intraocular pressure (IOP) estimates in rabbits. Rabbits. A postmortem study was conducted on seven rabbit eyes to verify the correlation between manometry and tonometry with an artificial incremental increase in IOP from 5 and 60mmHg. A clinical study was conducted to evaluate accuracy and to establish reference values for the species, with measurement of IOP in 17 animals, for 2 consecutive days, with the same tonometers and calibrations used in the postmortem evaluations. There were strong linear trends for all evaluated tonometers. In the in-vivo evaluation, the mean IOP values were: 14.23±1.75 (Tono-Pen XL™); 13.89±2.07 (TonoVet® calibration mode 'd'); 8.88±1.24 (TonoVet calibration mode 'p'); 18.59±1.94 (Tonovet Plus®). There was a significant difference in the two evaluation times for the two TonoVet® calibration modes. The adjustment equations generated from the manometry for the evaluated tonometers were: Y=0.2570X+2.219 (Tono-Pen XL™), Y=0.2289X+2.389 (TonoVet® 'd'), Y=0.4043X+4.062 (TonoVet® 'p'), Y=0.1233X+0.3644 (TonoVet Plus®) (X is device-estimated IOP). All evaluated tonometers were well correlated with the manometry, with an underestimation of IOP by all devices. Applying adjustment formulas may compensate for systematic errors. TonoVet Plus® was well tolerated, and showed better repeatability and reliability in successive evaluations.

Photorefractive surgery with excimer laser and its impact on the diagnosis and follow-up of glaucoma. A review

Excimer laser refractive surgery is a procedure performed worldwide to solve refractive errors and reduce dependence on glasses or contact lenses. There has been an increase in the number of procedures performed around the world. Myopia is the most common indication for corneal photorefractive surgery. Myopic patients have a higher risk of developing some type of glaucoma in their lifetime, such as primary open-angle glaucoma and others. Refractive surgery ablates central corneal stromal tissue, altering its thickness and biomechanics, which in turn makes it difficult to accurately measure intraocular pressure (IOP), since it underestimates it. This underestimation of IOP may delay the diagnosis of de novo glaucoma in patients with a history of refractive surgery. Each patient who wishes to undergo corneal refractive surgery should undergo a thorough glaucoma examination in order to monitor and detect the possible development and / or progression of glaucoma. A very useful practical approach is to perform a series of IOP measurements before and after surgery, when the eye is already stable, and the difference between the averages of the two sets of readings can then be used as a personalised correction factor for postoperative IOP monitoring in that eye. Also, if there is any suspicion of a possible glaucoma, paraclinical tests, such as coherent optical tomography of the retinal nerve fibre layer (RNFL), visual fields and photos of the optic nerve should be requested. All this data prior to refractive surgery should be provided to these patients, so that they can save it and give it to their treating ophthalmologists in the future.

PHOTOREFRACTIVE SURGERY WITH EXCIMER LASER AND ITS IMPACT ON THE DIAGNOSIS AND FOLLOW-UP OF GLAUCOMA. A REVIEW.

Excimer laser refractive surgery is a procedure performed worldwide to solve refractive errors and reduce dependence on glasses or contact lenses. There has been an increase in the number of procedures performed around the world. Myopia is the most common indication for corneal photorefractive surgery. Myopic patients have a higher risk of developing some type of glaucoma in their lifetime, such as primary open-angle glaucoma and others. Refractive surgery ablates central corneal stromal tissue, altering its thickness and biomechanics, which in turn makes it difficult to accurately measure intraocular pressure (IOP), since it underestimates it. This underestimation of IOP may delay the diagnosis of de novo glaucoma in patients with a history of refractive surgery. Each patient who wishes to undergo corneal refractive surgery should undergo a thorough glaucoma examination in order to monitor and detect the possible development and / or progression of glaucoma. A very useful practical approach is to perform a series of IOP measurements before and after surgery, when the eye is already stable, and the difference between the averages of the two sets of readings can then be used as a personalised correction factor for postoperative IOP monitoring in that eye. Also, if there is any suspicion of a possible glaucoma, paraclinical tests, such as coherent optical tomography of the retinal nerve fibre layer (RNFL), visual fields and photos of the optic nerve should be requested. All this data prior to refractive surgery should be provided to these patients, so that they can save it and give it to their treating ophthalmologists in the future.

Pneumotonometer Accuracy Using Manometric Measurements after Radial Keratotomy, Clear Corneal Incisions and Lamellar Dissection in Porcine Eyes

ABSTRACT Purpose/Aim of the study Measured intraocular pressure (IOP) after corneal incisions may not be reflective of the true IOP because of changes in corneal biomechanical properties. The purpose of this study is to investigate the effect of various corneal incisions on pneumotonometer accuracy in enucleated porcine eyes. Materials and Methods A pneumotonometer was used to measure IOP (IOPp) at manometrically controlled pressure levels of 10, 20, 30 and 40 mmHg in enucleated porcine eyes. IOP measurements at each level were repeated after one of the following corneal incisions: radial keratotomy (8 eyes), lamellar dissection (10 eyes), clear cornea standard phacoemulsification incisions (10 eyes). The pneumotonometer error, defined as the difference between IOPp and manometric pressure (IOPm), was calculated for each pressure level. The error before the corneal incisions was compared to the error after the corneal incisions to assess the accuracy of the pneumotonometer. Results The pneumotonometer underestimates true IOP at all pressure levels, both before and after the corneal procedures. There was a statistically significant greater underestimation of IOP after radial keratotomy incisions at pressure levels of 20, 30 and 40 mmHg (p = .013, 0.004, and 0.002, respectively). There was no statistically significant difference in the amount of pneumotonometer underestimation error after lamellar dissection or standard cataract incisions. Conclusion The pneumotonometer underestimates true IOP in enucleated porcine eyes at all pressure levels between 10–40 mmHg. Radial keratotomy incisions caused a statistically significant greater underestimation error in pneumotonometry measurements at pressures of 20–40 mmHg. Lamellar dissection and clear corneal cataract incisions did not cause an additional error in pneumotonometry measurements in enucleated porcine eyes.

Dynamic Scheimpflug Ocular Biomechanical Parameters in Healthy and Medically Controlled Glaucoma Eyes.

To evaluate the relationship between biomechanical parameters measured with a dynamic Scheimpflug analyzer and glaucoma. Cross-sectional observational data of 47 eyes of 47 consecutive subjects with medically controlled primary open-angle glaucoma and 75 eyes of 75 healthy subjects examined with a dynamic Scheimpflug analyzer (Corvis ST) were retrospectively investigated. Eight biomechanical parameters were compared between eyes with and without glaucoma using multivariable models adjusting for intraocular pressure (IOP), central corneal thickness, age, and axial length. In multivariable models, glaucoma was negatively correlated with A1 time (P<0.001, coefficient=-0.5535), A2 time (P=0.008, coefficient=-0.1509), radius (P=0.011, coefficient=-0.4034), and whole eye movement (P<0.001, coefficient=-0.0622). Negative correlation between glaucoma and 3 parameters (A1 time, A2 time, and radius) consistently indicate larger deformability of the cornea and negative correlation between glaucoma and whole eye movement indicate smaller eye movement, in glaucoma eyes. There were significant correlations of many biomechanical parameters with other baseline factors (8 parameters with IOP, 2 with central corneal thickness, 4 with age, and 7 with axial length). Eyes with medically controlled glaucoma were more deformable than healthy eyes, which may increase the risk of optic nerve damage through an underestimation of IOP and biomechanical vulnerability of the globe. Many parameters showed a significant correlation with baseline factors, suggesting the importance of adjustment for these confounding factors when evaluating the correlation between biomechanical parameters and ocular diseases. These results suggest the relevance of measuring biomechanical properties of glaucoma eyes for accurate IOP measurement and risk assessment.

Association of Diabetes With Central Corneal Thickness Among a Multiethnic Asian Population

Thicker or thinner central corneas may lead to either overestimation or underestimation of intraocular pressure, which is the most important causal and treatable risk factor for glaucoma. However, the findings on the associations between diabetes, random glucose, and glycated hemoglobin A1c (HbA1c) with central corneal thickness (CCT) are conflicting. To evaluate the associations between diabetes, random glucose, and HbA1c with CCT in a multiethnic Asian population. Cross-sectional analysis of the Singapore Epidemiology of Eye Diseases (SEED) Study conducted from 2004 to 2011. A total of 10 033 Chinese, Malay, and Indian individuals 40 years or older residing in Singapore were recruited. Participants with incomplete information on diabetes status (448 participants), prior refractive or cataract surgery (1940 eyes), and corneal edema or dystrophy (29 eyes) were excluded. A meta-analysis was conducted to estimate the overall association of diabetes with CCT. Standardized clinical examinations and interviewer-administered questionnaire to collect information about demographic, systemic, and ocular factors. Measurement of CCT using ultrasound pachymetry. A total of 8846 adults (mean [SD] age, 57.9 [9.9] years; 4447 women [50.3%]) (17 201 eyes) were included in the final analyses. The CCT profile was similar among participants with and without diabetes (mean [SD] CCT, 545.3 [33.7] μm vs 544.8 [33.9] μm; P = .39). Following adjustments of age, sex, ethnicity, corneal curvature, axial length, and body mass index, CCT was a mean (SD) of 4.9 (0.8) μm (95% CI, 3.3-6.5 μm) thicker in patients with diabetes than those without diabetes. Multivariable analyses also showed that thicker CCT was associated with higher random glucose (per 10 mg/dL [to convert to mmol/L, multiply by 0.0555], β = 0.3; 95% CI, 0.2-0.4) and higher HbA1c (per percentage, β = 1.5; 95% CI, 1.0-2.1) (all P < .001). These associations were significant in the subgroup with diabetes but not in the subgroup without diabetes. A meta-analysis including 12 previous population- and clinical-based studies showed that CCT was 12.8 μm (95% CI, 8.2-17.5 μm) thicker in eyes of patients with diabetes. These findings suggest that diabetes and hyperglycemia were associated with thicker CCT. This study provides useful information on the interpretation of intraocular pressure in patients with diabetes.

Effect of central corneal thickness on intraocular pressure and comparison of Topcon CT‐80 non‐contact tonometry with Goldmann applanation tonometry

BackgroundTo compare intraocular pressure (IOP) measurements obtained with the Topcon CT‐80 non‐contact tonometer (NCT) and Goldmann applanation tonometer (GAT), in different ranges of IOP in normal and glaucoma subjects, and to assess the influence of central corneal thickness (CCT) on the IOP measurements in Asian Indian eyes.MethodsFour hundred and two eyes of 402 subjects (193 newly diagnosed primary open angle glaucoma [POAG] and 209 normal) were enrolled for this prospective study. For each eye, IOP was measured with GAT by a glaucoma specialist and NCT by a trained optometrist. The IOP values were compared among the tonometers in the three different IOP ranges (≤ 12 mmHg, 13–20 mmHg and ≥ 21 mmHg) using Bland–Altman graphs. Correlation between GAT and NCT was assessed by Pearson correlation co‐efficient. CCT was measured with ultrasound pachymetry and its correlation with GAT and NCT was analysed using linear regression analysis.ResultsThe mean paired difference of IOP between NCT and GAT was 1.556 ± 2.69 mmHg (r = 0.26, p = 0.006) at IOP range of ≤ 12 mmHg, −1.665 ± 2.6 mmHg (r = 0.51, p < 0.0001) in IOP range of 13–20 mmHg and −2.202 ± 3.44 mmHg (r = 0.82, p < 0.0001) in the IOP range of ≥ 21 mmHg. Linear regression analysis showed a mean IOP variation of 0.27 mmHg per 10 μm change in CCT for NCT (p < 0.0001) and IOP change of 0.19 mmHg per 10 μm change in CCT for GAT (p = 0.01).ConclusionIn this study of normotensive and POAG subjects, the Topcon CT‐80 NCT showed an overestimation of IOP at the lower range and underestimation of IOP in normal and higher ranges of IOP. Clinicians should keep in mind that CCT influences IOP measurement with both types of tonometer and that the IOP readings obtained with these tonometers are not interchangeable.

Intraocular Pressure Changes and Relationship With Corneal Biomechanics After SMILE and FS-LASIK.

The purpose of this article was to evaluate intraocular pressure (IOP) changes and investigate the relationship with corneal biomechanics after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). A total of 193 eyes of 193 patients who underwent SMILE and FS-LASIK procedures were included in this retrospective study. Data were collected preoperatively and postoperatively, including Goldmann-correlated IOP (IOPg), corneal-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) by ocular response analyzer, noncontact intraocular pressure (IOPNCT) by noncontact tonometer, and Ehlers, Shah, Dresden, Kohlhaas, Orssengo/Pye by the Pentacam corrected system. Changes in both groups and differences between groups were evaluated. Multiple linear regression models were constructed to explore factors influencing IOP changes. In SMILE, the IOPg, IOPcc, IOPNCT, and Kohlhaas decreased significantly at 1 month postoperatively (P < 0.01), whereas with the Ehlers formula they significantly increased (P < 0.01). IOPs decreased at 3 and 6 months compared with all preoperative values except Ehlers values (P < 0.01), but there was no significant difference between 3 and 6 months (P > 0.05). In FS-LASIK, the IOPg, IOPcc, and IOPNCT decreased significantly at 1 month (P < 0.01), whereas in the Ehlers and Shah formulas they significantly increased (P < 0.01). Compared with preoperative values, the IOPs decreased at 3 and 6 months except in the Ehlers and Shah formulas (P < 0.01). Only IOPg and IOPcc differed between 3 and 6 months (P < 0.05). The Ehlers and Shah formulas were closer to the preoperative IOP for both groups, with variation approximately 1 mm Hg at 6 months postoperatively. Preoperative IOP, postoperative corneal resistance factor, corneal hysteresis, and flat keratometry were enrolled into the regression equations. IOP underestimation after SMILE or FS-LASIK was related to corneal biomechanics as well as preoperative IOP and flat keratometry. IOP after SMILE seem to remain more stable. Accordingly, the Ehlers and Shah formulas were closer to the preoperative IOP. It may be useful to estimate future IOP with the best-fit models after surgery.

Factors Influencing Intraocular Pressure Changes after Laser In Situ Keratomileusis with Flaps Created by Femtosecond Laser or Mechanical Microkeratome.

The aim of this study is to describe factors that influence the measured intraocular pressure (IOP) change and to develop a predictive model after myopic laser in situ keratomileusis (LASIK) with a femtosecond (FS) laser or a microkeratome (MK). We retrospectively reviewed preoperative, intraoperative, and 12-month postoperative medical records in 2485 eyes of 1309 patients who underwent LASIK with an FS laser or an MK for myopia and myopic astigmatism. Data were extracted, such as preoperative age, sex, IOP, manifest spherical equivalent (MSE), central corneal keratometry (CCK), central corneal thickness (CCT), and intended flap thickness and postoperative IOP (postIOP) at 1, 6 and 12 months. Linear mixed model (LMM) and multivariate linear regression (MLR) method were used for data analysis. In both models, the preoperative CCT and ablation depth had significant effects on predicting IOP changes in the FS and MK groups. The intended flap thickness was a significant predictor only in the FS laser group (P < .0001 in both models). In the FS group, LMM and MLR could respectively explain 47.00% and 18.91% of the variation of postoperative IOP underestimation (R2 = 0.47 and R2 = 0.1891). In the MK group, LMM and MLR could explain 37.79% and 19.13% of the variation of IOP underestimation (R2 = 0.3779 and 0.1913 respectively). The best-fit model for prediction of IOP changes was the LMM in LASIK with an FS laser.

Evaluation of a new rebound tonometer for self-measurement of intraocular pressure

Background/aimsTo compare the accuracy of self-obtained, partner-obtained and trainer-obtained measurements using the handheld Icare Home rebound tonometer with Goldmann applanation tonometry (GAT), and to evaluate the acceptability to subjects of...

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

PurposeTo investigate if the accuracy of intraocular pressure (IOP) measurements using rebound tonometry over disposable hydrogel (etafilcon A) contact lenses (CL) is affected by the positive power of the CLs. MethodsThe experimental group comprised 26 subjects, (8 male, 18 female). IOP measurements were undertaken on the subjects’ right eyes in random order using a Rebound Tonometer (ICare). The CLs had powers of +2.00D and +6.00D. Measurements were taken over each contact lens and also before and after the CLs had been worn. ResultsThe IOP measure obtained with both CLs was significantly lower compared to the value without CLs (t test; p<0.001) but no significant difference was found between the two powers of CLs. ConclusionsRebound tonometry over positive hydrogel CLs leads to a certain degree of IOP underestimation. This result did not change for the two positive lenses used in the experiment, despite their large difference in power and therefore in lens thickness. Optometrists should bear this in mind when measuring IOP with the rebound tonometer over plus power contact lenses.

A Comparison of the Icare Pro Rebound Tonometer with Applanation Tonometry in Healthy Infants

Aims: To study the accuracy and patient tolerability of the new Icare Pro rebound tonometer (ICPRO) compared with applanation tonometry in infants aged under 24 months. Methods: Prospective observational study of 50 consecutive patients with expected normal intraocular pressure (IOP). One eye of each patient was examined sequentially using an ICPRO and Perkins applanation tonometer (PAT) to obtain a single adequate IOP measurement for each device. Agreement was assessed using Bland-Altman analysis. An objective assessment of patient tolerance of IOP measurement was also recorded. Results: Mean age of patients was 12.6 months. Correlation of IOP measurement between PAT and ICPRO was moderate (r=0.384, p=0.0059). ICPRO underestimated IOP in 88% of cases: IOP was measured significantly lower with ICPRO (9.18±1.57 mmHg) compared to PAT (12.4±2.95 mmHg, p<0.001). The 95% limit of agreement (LOA) was -8.6 to 2.2 mmHg. Subgroup analysis showed ICPRO underestimated IOP most in infants over 12 months (mean: 4.8mmHg, 95% LOA:-9.5 to 0.2mmHg, p<0.0001). Measurement of IOP with the ICPRO was significantly better tolerated, causing distress and crying in 6%, compared to 62% with PAT (p<0.0001). IOP underestimation with ICPRO was significantly greater when infants were crying during PAT measurement (5.26±2.83) compared to when infants were not crying during PAT measurement (1.97±1.83, p<0.0001). Conclusions: ICPRO appears to be safe, tolerable and of adequate accuracy for the screening of IOP in infants. It consistently significantly underestimated IOP, therefore high or borderline IOPs measured with the ICPRO should be repeated with applanation tonometry to prevent missing cases of raised IOP.

Corneal Biomechanical Properties Affect Goldmann Applanation Tonometry in Primary Open-angle Glaucoma

To study differences in corneal biomechanical properties between primary open-angle glaucoma (POAG) and central corneal thickness (CCT)-matched control subjects and their effect on intraocular pressure (IOP) measurement. Thirteen eyes of 13 POAG subjects and 15 eyes of 15 normal subjects underwent corneal topography; IOP using Goldmann applanation tonometry (GAT), dynamic contour tonometry (DCT), and corneal compensated IOP (IOPcc) using the Reichert ocular response analyzer (ORA); corneal hysteresis; and CCT. Results from POAG and control eyes were then compared using t tests. Ages in the POAG group were slightly greater than that in the control group. CCT was closely matched between groups. Significant differences were found between GAT versus DCT and GAT versus IOPcc within both groups: Mean GAT IOP was not significantly different between POAG and controls, whereas mean DCT IOP did show a significant difference between groups as did mean IOPcc. The delta differences, GATΔDCT and GATΔIOPcc, were of greater magnitude in POAG subjects when compared with controls. Corneal hysteresis was significantly lower in POAG subjects. The delta differences between GAT and newer measures of IOP are greater in magnitude in patients with POAG than in the normal controls, independent of CCT. This is likely due to differences in the corneal biomechanical properties with POAG corneas being softer than healthy corneas, which causes greater underestimation of IOP by GAT in POAG than controls. Underestimation of IOP could affect treatment decisions and outcomes in POAG.

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

To compare the accuracy of IOPen rebound tonometer with Goldmann applanation tonometer (GAT) in individuals with low, normal and high intraocular pressure (IOP) and to evaluate the effect of central corneal thickness (CCT) on IOP measurements. This cross-sectional study consisted of 159 participants. IOP of one eye of each subject was measured consecutively with IOPen and GAT. Then CCT was measured using an ultrasonic pachymeter. Based on GAT IOP readings, participants were divided into low, normal and high IOP groups. Correlation between tonometers and CCT was calculated by spearman's correlation coefficient. Agreement between tonometers was evaluated using Bland-Altman method. Non-significant underestimation of IOP by IOPen was observed in low IOP group (Mean difference: 0.20mmHg; P=0.454) and also in normal IOP group (Mean difference: 0.56mmHg; P=0.065). However, IOPen significantly overestimated IOP in high IOP group (Mean difference: 1.06mmHg; P=0.038). The 95% limits of agreement (LoA) width between IOPen and GAT IOPs were 7.84, 8.57 and 14.27mmHg in low, normal and high IOP groups, respectively. Low IOP group had thinner corneas compared to high IOP group (P=0.034). IOP measurements taken by IOPen were not influenced by CCT (P=0.099) while poor correlation between CCT and GAT was found (R=0.17, P=0.032). Using receiver operating characteristic (ROC) curve, cutoff value of 18.75mmHg was determined for IOPen with sensitivity of 98.1 and specificity of 97.2%. Accuracy of IOPen is comparable to GAT in patients with low or normal IOP but IOPen overestimates IOP at high IOP levels. CCT does not affect IOP readings with IOPen.