The Effect of Yoga on Intraocular Pressure Using the "iCare HOME2" Tonometer.

BACKGROUND: Various yoga positions may have an unfavorable impact on intraocular pressure (IOP) and may therefore be seen as a potential risk factor for the progression of glaucoma. The new "iCare HOME2" is a handheld self-tonometer for IOP measurements outside clinical settings. This is the first study to evaluate the immediate effect of common yoga postures on the IOP of healthy and glaucomatous eyes using the "iCare HOME2" self-tonometer and to compare the time of IOP recovery in both groups. METHODS: This is a single-center, prospective, observational study including 25 healthy and 25 glaucoma patients performing the following yoga positions: "legs up" (Viparita Karani), "bend over" (Uttanasana), "plough pose" (Halasana), and the "down face dog" (Adho Mukha Svanasana) for 90 s each, with a 2-min break in between. IOP was measured with the "iCare HOME2" before, during, and after each position. RESULTS: IOP significantly increased in all eyes in all positions (p < 0.05), showing no statistically significant difference between healthy or glaucomatous eyes (p > 0.05). The mean rise in IOP in healthy subjects was 1.6 mmHg (SD 1.42; p = 0.037), 14.4 mmHg (SD 4.48; p < 0.001), 7.5 mmHg (SD 4.21; p < 0.001), and 16.5 mmHg (SD 3.71; p < 0.001), whereas in glaucoma patients, IOP rose by 2.8 mmHg (SD 2.8; p = 0.017), 11.6 mmHg (SD 3.86; p < 0.001), 6.0 mmHg (SD 2.24; p < 0.001), and 15.1 mmHg (SD 4.44; p < 0.001) during the above listed yoga positions, repsectively. The highest increase in IOP was seen in the down face position, reaching mean IOP values above 31 mmHg in both study groups. IOP elevation was observed immediately after assuming the yoga position, with no significant change during the following 90 s of holding each pose (p > 0.05). All IOP values returned to baseline level in all individuals, with no significant difference between healthy and glaucoma participants. CONCLUSION: Our data show that common yoga positions can lead to an acute IOP elevation of up to 31 mmHg in healthy as well as glaucoma eyes, with higher IOP values during head-down positions. Given that IOP peaks are a major risk factor for glaucomatous optic neuropathy, we generally advise glaucoma patients to carefully choose their yoga exercises. If and to what extent practicing yoga leads to glaucoma progression, however, remains unclear and warrants further research.

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

OBJECTIVE: To determine the accuracy of the Reichert® Tono-Vera® Vet rebound tonometer for canine intraocular pressure (IOP) measurement. ANIMALS STUDIED: Five normal canine ex vivo globes. PROCEDURES: 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. RESULTS: 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. CONCLUSIONS: 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.

A new mouse-fixation device for IOP measurement in awake mice.

Glaucoma is an irreversible blinding eye disease. The mechanisms underlying glaucoma are complex. Up to now, no successful remedy has been found to completely cure the condition. High intraocular pressure (IOP) is an established risk factor for glaucoma and the only known modifiable factor for glaucoma treatment. Mice have been widely used to study glaucoma pathogenesis. IOP measurement is an important tool for monitoring the potential development of glaucomatous phenotypes in glaucoma mouse models. Currently, there are two methods of IOP measurement in mice: invasive and non-invasive. As the invasive method can cause corneal damage and inflammation, and most of the noninvasive method involves the use of anesthetics. In the course of our research, we designed a mouse fixation device to facilitate non-invasive measurements of mouse IOPs. Using this device, mouse IOPs can be accurately measured in awake mice. This device will help researchers to accurately assess mouse IOP without the use of anesthetics.

Comparison of intraocular pressure in New Zealand White rabbits measured using rebound and applanation tonometers and four different methods of physical restraint.

AIMS: To compare intraocular pressure (IOP) measurements obtained in rabbits using rebound (TV) and applanation (TPV) tonometers with four different methods of physical restraint. METHODS: A total of 20 New Zealand White rabbits (40 eyes) were included in this study. IOP readings were obtained from both eyes using the two different tonometers. The rabbits were placed on a table and restrained by wrapping in a cloth (Method I), by scruffing with rear support (Method II), by wrapping in a cloth and cupped in the hands (Method III), or by a box restrainer (Method IV). RESULTS: The mean IOP measurement obtained by TPV was higher than that obtained with the TV for all handling methods. Mean differences (TV-TPV, in mmHg) in IOP were -5.3 (95% Cl = -6.5 to -4.1) for Method 1, -4.7 (95% Cl = -6.2 to -3.29) for Method II, -4.9 (95% Cl = -6.2 to -3.7) for Method III and -7.6 (95% Cl = -9.2 to -5.9) for Method IV. Using the TV tonometer, mean IOP for Method IV was higher than for Method I (mean difference 2.1 (95% Cl = 1.1-3.1)), whereas using the TPV tonometer, mean IOP for Method IV was significantly higher than Method I, II, and III (mean differences: 4.4 (95% Cl = 2.6-5.9), 3.7 (95% Cl = 2-5.3) and 3.8 (95% Cl = 2-5.4), respectively). According to Bland-Altman plots, IOP readings for TPV tended to be higher than those for TV with all handling methods, but with a lack of agreement. The mean difference and 95% limits of agreement for the differences between TV and TPV were -5.4 mmHg (-12.5-1.9 mmHg), -4.7 mmHg (-12.9-3.5 mmHg), -4.9 mmHg (-12-2.2 mmHg), and -7.5 mmHg (-17.4-2.3 mmHg), with Methods I, II, III, and IV, respectively. Comparing TV and TPV, only 7.5%, 12.5%, 27.5%, and 15% of IOP measurements from 20 rabbits were within the range considered clinically acceptable for IOP (± 2 mmHg) for Method I, II, III, and IV, respectively. CONCLUSION AND CLINICAL RELEVANCE: In conclusion, the physical restraint method should be recorded when IOP is measured in rabbits, and TV and TPV tonometers cannot be used interchangeably (high bias and low proportion of measurements within ± 2 mmHg).

Corneal biomechanics and glaucoma beyond the bidirectional impact of intraocular pressure and corneal deformation response / Biomecânica corneana e glaucoma além do impacto bididirecional da pressão intraocular e da resposta da deformação corneana

ABSTRACT The purpose of this study was to highlight the impact of biomechanical corneal response in available in vivo tonometry methods for glaucoma management. Systematic review of non-contact air-puff tonometers that analyzes the corneal deformation response, with special focus on the investigation of the correlation of derived parameters with intraocular pressure measurements. The two actual and commercially available in vivo corneal tonometers provide promising information about biomechanical characteristics of the cornea and its relation to glaucoma, allowing the development of new protocols to evaluate, diagnose, and manage this disease.

RESUMO O objetivo deste estudo é destacar o impacto da resposta biomecânica corneana em métodos de tonometria in vivo disponíveis para o manejo do glaucoma. Trata-se de revisão sistemática de tonômetros de ar que analisa a resposta à deformação corneana, com foco especial na investigação da correlação dos parâmetros derivados com as medições da pressão intraocular. Os dois tonômetros mais recentes e comercialmente disponíveis fornecem informações promissoras sobre as características biomecânicas da córnea e sua relação com o glaucoma, permitindo o desenvolvimento de novos protocolos para avaliar, diagnosticar e controlar a doença.

Comparison of intraocular pressure in healthy brachycephalic and nonbrachycephalic cats using the Icare® TONOVET Plus rebound tonometer.

OBJECTIVE: To compare intraocular pressure using the Icare® TONOVET Plus rebound tonometer in healthy brachycephalic and nonbrachycephalic cats. ANIMALS STUDIED: Both eyes of 78 healthy cats were investigated in this study. Cats were divided into two groups: brachycephalic (n = 39) and nonbrachycephalic (n = 39). PROCEDURES: Nose position and muzzle ratio were photographically recorded and analyzed. Physical and ophthalmic examinations were performed. Intraocular pressure was measured using the Icare® TONOVET Plus rebound tonometry instrument. Quantitative mean values were statistically compared using an unpaired t-test at a significance level of p < .05. RESULTS: Mean values of the nose position and muzzle ratio were significantly lower in the brachycephalic group (20.14 ± 5.43%, 9.61 ± 3.29%) compared with the nonbrachycephalic group (29.21 ± 4.30%, 13.97 ± 6.01%). The mean intraocular pressure for brachycephalic cats (15.76 ± 0.50 mmHg) was significantly lower (p < .001) than for nonbrachycephalic cats (18.77 ± 0.49 mmHg). CONCLUSIONS: Intraocular pressure was significantly lower in brachycephalic cats using the Icare® TONOVET Plus rebound tonometer. Intraocular pressure values obtained in this study could be used as a guideline for measurements obtained using this tonometry device in healthy brachycephalic and nonbrachycephalic cats.

Acupuncture treatment of glaucoma based on radar plots: A protocol for an overview of systematic reviews.

BACKGROUND: Glaucoma is the second most blinding eye disease in the world. Currently, lowering the intraocular pressure through various methods is the main treatment of glaucoma. Acupuncture has been effectively and safely used in the treatment of glaucoma. However, the evidence for the efficacy of acupuncture in the treatment of glaucoma is controversial, leading to inconsistent findings from systematic evaluations at abroad and home. Therefore, this protocol aims to provide a multivariate evaluation on the quality of evidences from current systematic reviews (SRs) and/or meta-analyzes (MAs) of acupuncture in the treatment of glaucoma, and literature quality, thus providing an intuitive and reliable evidence synthesis and basis for clinical decision making. METHODS: MAs/SRs about the acupuncture treatment of glaucoma will be searched online, including Chinese Biomedical Literature Database (CBM), China Science and Technology Journal Database (VIP), China National Knowledge Infrastructure (CNKI), WanFang Database (WF), Web of Science, Embase, PubMed, and Cochrane Library. Two investigators will independently screen literatures according to inclusion and exclusion criteria and extract data. A multivariate evaluation of the included literature will be performed by depicting radar plots in 6 aspects as follows: Year of publication, study type, SRs assessment through the Assessment of Multiple Systematic Reviews 2 (AMSTAR 2), literature quality assessment through the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA), homogeneity, and publication bias. The Grading of Recommendations Assessment, Development, and Evaluation evidence quality assessment tool will be used to grade and evaluate the quality of outcome indicators of the included literatures. RESULTS: This study will be submitted for publication in a peer-reviewed journal. CONCLUSION: We would like to provide a visual and scientific approach for clinical decision making of acupuncture treatment of glaucoma through a accessible and useful assessment of systematic reviews.

COMPARISON OF INTRAOCULAR PRESSURE MEASUREMENT USING REBOUND AND APPLANATION TONOMETRY IN LOGGERHEAD (CARETTA CARETTA) SEA TURTLES.

This study aimed to evaluate intraocular pressure (IOP) estimates in healthy eyes of Caretta caretta using rebound tonometry in comparison with applanation tonometry. Twenty-three healthy C. caretta (housed at the Marine Turtle Research Center) without preexisting ophthalmic disease were enrolled in the study. IOP measurements were obtained by the same ophthalmologist, with the turtle in ventral recumbency between 2:30 p.m. and 4:30 p.m., using a rebound tonometer (RT; TonoVet) in dog calibration mode, and after topical anesthesia, an applanation tonometer (AT; Tono-Pen) in both eyes. The average of three readings per instrument was used for analysis. The agreement between the two tonometers was assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC). Moreover, differences in IOP between the two tonometers were analyzed using the Mann-Whitney test. Moderate agreement was found between the two tonometers (ICC, 0.663; 95% confidence interval, 0.206-0.857). The median, Q1, and Q3 IOP obtained with AT (6.2, 4.7, and 9.1 mm Hg) were significantly lower (P = 0.001) than that obtained with RT (9.7, 8.3, and 11.6 mm Hg). It was not possible to obtain an instrument automatically generated mean of four values with AT because of retraction of the globe by the animals, and IOP measurement was unsuccessful in 7 eyes. In conclusion, IOP readings from the RT were statistically higher than those from the AT. RT proved to be more feasible because of the light, short-lasting contact with the cornea.

Implanted Microsensor Continuous IOP Telemetry Suggests Gaze and Eyelid Closure Effects on IOP-A Preliminary Study.

Purpose: To explore the effect of gaze direction and eyelid closure on intraocular pressure (IOP). Methods: Eleven patients with primary open-angle glaucoma previously implanted with a telemetric IOP sensor were instructed to view eight equally-spaced fixation targets each at three eccentricities (10°, 20°, and 25°). Nine patients also performed eyelid closure. IOP was recorded via an external antenna placed around the study eye. Differences of mean IOP between consecutive gaze positions were calculated. Furthermore, the effect of eyelid closure on gaze-dependent IOP was assessed. Results: The maximum IOP increase was observed at 25° superior gaze (mean ± SD: 4.4 ± 4.9 mm Hg) and maximum decrease at 25° inferonasal gaze (-1.6 ± 0.8 mm Hg). There was a significant interaction between gaze direction and eccentricity (P = 0.003). Post-hoc tests confirmed significant decreases inferonasally for all eccentricities (mean ± SEM: 10°: -0.7 ± 0.2, P = 0.007; 20°: -1.1 ± 0.2, P = 0.006; and 25°: -1.6 ± 0.2, P = 0.006). Eight of 11 eyes showed significant IOP differences between superior and inferonasal gaze at 25°. IOP decreased during eyelid closure, which was significantly lower than downgaze at 25° (mean ± SEM: -2.1 ± 0.3 mm Hg vs. -0.7 ± 0.2 mm Hg, P = 0.014). Conclusions: Our data suggest that IOP varies reproducibly with gaze direction, albeit with patient variability. IOP generally increased in upgaze but decreased in inferonasal gaze and on eyelid closure. Future studies should investigate the patient variability and IOP dynamics.

Comparación entre el tonómetro de rebote IC200 y el tonómetro de aplanación Perkins en sujetos sanos y pacientes con glaucoma congénito / Comparision of intraocular pressure measured using the new icare 200™ rebound tonometer and the Perkins™ applanation tonometer in healthy subjects and in patients with primary congenital glaucoma

Objetivo Comparar las medidas de presión intraocular (PIO) obtenidas con el tonómetro de rebote iCare 200 (IC200) con las obtenidas mediante la versión portátil del tonómetro de aplanación Goldmann, Perkins (GAT) en pacientes con glaucoma congénito primario (GCP) y en sujetos sanos. Material y métodos Se incluyeron 42 sujetos sanos (G1) y 40 pacientes con GCP (G2). Se incluyó un ojo por paciente. Se recogieron las variables clínicas de interés: sexo, edad, grosor corneal central (GCC) y se midió la PIO mediante los tonómetros IC200 y GAT en el mismo orden, en consulta. Se estudió la concordancia entre tonómetros mediante el coeficiente de correlación intraclase y el gráfico de Bland Altman. La influencia de las variables se analizó mediante test de regresión lineal. Resultado Las medias de PIO obtenidas mediante IC200 y GAT fueron: G1=15,91 (2,57) vs. 15,06 (2,12) mmHg (diferencia de medias, DM=0,84 (0,50) mmHg; p=0,101) y en el G2=20,10 (6,37) vs.19,12 (5,62) (DM=0,98 [1,36]; p=0,474). Se observó excelente concordancia entre IC200/GAT en ambos los grupos (coeficiente de correlación intraclase=G1: 0,875 [IC 95%: 0,768-0,933; p<0,001]; G2: 0,924 [IC 95% 0,852-0,961; p<0,001]), así como la influencia del GCC en la diferencia entre tonómetros en el G1 (B=0,021; IC 95%: 0,005-0,037; p=0,008), sin significación estadística en el G2. Conclusión Se ha encontrado una excelente concordancia entre ambos tonómetros, IC200 y GAT tanto en sujetos sanos como en pacientes con GCP, con una tendencia a la sobreestimación de la PIO de IC200 sobre Perkins. No se ha demostrado la influencia del GCC en los pacientes con GCP (AU)

Objective To compare intraocular pressure (IOP) measurements obtained using the Icare 200™ (IC200) rebound tonometer and the hand-held version of the Goldmann Applanation Tonometer (Perkins™ tonometer, GAT) in patients with primary congenital glaucoma (PCG) and in healthy subjects Material and method a total of 42 eyes of healthy subjects (G1) and 40 patients with PCG (G2) were analysed. The following clinical data were collected: gender, age, Cup/Disc ratio, central corneal thickness (CCT). IOP was determined in the examination room using the IC200 and GAT tonometers, in the same order Agreement between both tonometers was determined using the intraclass correlation coefficient (ICC) and Bland-Altman plot. A linear regression analysis was used to establish the IOP was affected by the studied variables. Results Mean IOP between both tonometers (IC200 minus GAT) was: G1=15.91 (2.57) mmHg vs. 15.06 (2.12) mmHg (mean difference, MD=0.84 (0.50) mmHg; P<.101) and G2=20.10 (6.37) vs.19.12 (5.62) (MD=0.98 (1.36); P=.474). Excellent agreement was found between IC200 and GAT in both groups (ICC=G1: 0.875 (95% CI; 0.768-0.933; P<.001); G2: 0.924 (95% CI; 0.852-0.961; P<.001), and there was a statistically significant correlation between the IOP difference measured with IC200 and GAT and CCT in G1 (B=0.021; 95% CI; 0.005–0.037; P=.008), but was not statistically significant in G2. Conclusion There was excellent agreement between the IC200 and GAT tonometers, both in healthy subjects and PCG, with a trend to overestimate IOP when measured with IC200. There was no influence by CCT on IOP measurements in patients with PGC (AU)

Continuous 24-hour measurement of intraocular pressure in millimeters of mercury (mmHg) using a novel contact lens sensor: Comparison with pneumatonometry.

PURPOSE: To address the unmet need of continuous IOP monitoring, a Pressure-Measuring Contact Lens (PMCL) was developed to measure IOP in millimeters of mercury (mmHg) continuously over 24 hours. The present study assessed the reliability of the novel PMCL. METHODS: In this prospective open-label clinical study, healthy and open-angle glaucoma (OAG) subjects were fitted with the PMCL, and pneumatonometry was performed on study eyes (in absence of the PMCL) and on fellow eyes before, during, and after provocative tests. The primary outcome measures were (1) mean IOP difference between same-eye measurements, and (2) percentage of timepoints at which IOP measured by the PMCL was within 5 mmHg of that measured by pneumatonometry in the fellow eye. RESULTS: Eight subjects were analysed (4 healthy, 4 OAG). The average difference in successive IOP measurements made by pneumatonometry and with the PMCL was 2.0±4.3mmHg at placement-time, and 6.5±15.2mmHg at removal time. During water drinking test, a significant increase in IOP was detected both by PMCL in the study eye (2.4±2.5mmHg, p = 0.03) and by pneumatonometry in the fellow eye (1.9±1.9mmHg, p = 0.02). Over the 24-hour recording, 88.0% of IOP variations measured by the PMCL were within 5mmHg of that measured with the pneumatonometer in the fellow eye. A transient corneal erosion of severe intensity was observed following removal of the PMCL on one single eye, and may have affected measurement accuracy in that eye. CONCLUSIONS: This study is a proof-of-concept for this novel PMCL, and its results are encouraging, with a fair accuracy in IOP values measurement and good sensitivity to subtle IOP variations.

Agreement of Corrected Intraocular Pressure Values Between Corvis ST and Pentacam in Patients With Keratoconus, Subclinical Keratoconus, and Normal Cornea.

PURPOSE: To analyze the agreement of corrected intraocular pressure (IOP) values between Corvis ST (ΔIOP1) and Pentacam (ΔIOP2) in patients with keratoconus (KC), subclinical KC (sub-KC), and normal cornea. METHODS: In total, 235 eyes were divided into KC, sub-KC, and control groups. Differences in ΔIOP1 (biomechanically corrected IOP minus uncorrected IOP) and ΔIOP2 (central corneal thickness-corrected amounts of IOP) were analyzed within and among groups. Topographical and biomechanical differences were compared among the 3 groups. Factors affecting differences between ΔIOP1 and ΔIOP2 were analyzed. Agreement analysis of ΔIOP2 and ΔIOP1 was performed by Bland-Altman plots for all 3 groups. RESULTS: Mean ΔIOP1 was highest in the KC group (1.23 ± 0.84 mm Hg), followed by sub-KC and control groups (all P < 0.05). Deformation amplitude ratio at 2 mm (DA-2 mm), integrated radius, stiffness parameter at first applanation, and Corvis biomechanical index values significantly differed between sub-KC and control groups. The differences between ΔIOP1 and ΔIOP2 were affected by stiffness parameter at first applanation, after adjusting for central corneal thickness and age, in all 3 groups. The lowest agreement between ΔIOP2 and ΔIOP1 was observed in the KC group (mean difference: 1.90 mm Hg; 95% limit of agreement ranged from -0.2 to 3.9 mm Hg). CONCLUSIONS: Among the 3 groups in this study, the KC group exhibited the worst consistency between ΔIOP2 and ΔIOP1. For the sub-KC and control groups, corrected IOP values derived by Pentacam were similar to Corvis ST. Ophthalmologists should carefully consider the mechanical properties of eyes with KC during IOP management.

The use of infrared thermal imaging in tonometry with a Scheimpflug camera.

Infrared thermal imaging is currently used in almost every field of medicine. This paper presents the novel use of thermography in ophthalmology - using a thermal camera to assess correct intraocular pressure measurement depending on the position of the patient's head during non-contact tonometry. For the analysed group of 10 healthy subjects, thermographic images of the face were recorded before and after intraocular pressure testing. Pressure was tested with a non-contact tonometer with a Scheimpflug camera. For the acquired 20: 2D images (thermograms), an analysis of the characteristic areas of the face determined temperature changes of the patient's face in contact with the tonometer frame. Analysis and processing of the acquired thermograms was carried out in MATLAB® with the Image Processing Toolbox. The results clearly showed a decrease in the patient's face temperature where the face was in contact with tonometer supports. Temperature changes in the patient's face provide valuable information about the correct position of their head in the device, which directly translates into measurement quality. Therefore, the analysis of changes in the patient's face temperature both before and after the examination can be a tool for assessing correct patient positioning in the tonometer supports.

Evaluation of the effect of disposable tonometer cover brand on performance of Tono-Pen Vet in canine eyes.

PRIMARY OBJECTIVE: To evaluate the effect of latex tip cover manufacturer on accuracy and repeatability of Tono-Pen Vet™ in canine eyes. ANIMAL STUDIED: Twelve enucleated globes from six dogs. PROCEDURES: The anterior chamber was cannulated and connected to a calibrated manometer. Intraocular pressure (IOP) measurements were obtained using the Tono-Pen Vet and TONOVET Plus at manometric IOP ranging from 5 to 80 mmHg. At each IOP, the Tono-Pen Vet was used with a new Ocu-Film™ latex tip cover (the only manufacturer-approved brand of cover) followed by a new Softips™ latex tip cover. For comparison, the TONOVET Plus was also used at each IOP with a new disposable rebound probe. Measured IOP values were analyzed by linear regression and intraclass correlation coefficient (ICC). RESULTS: Tono-Pen Vet accuracy was unaffected by tip cover manufacturer or by frequent change in cover. Using ICC analysis, repeatability of measurements using either tonometer was good to excellent at physiologic IOP levels but variably decreased with both devices at supraphysiologic IOP. CONCLUSIONS: Neither tip cover manufacturer nor frequent changes in tip cover adversely affect Tono-Pen Vet accuracy. Measurement repeatability with Tono-Pen Vet and TONOVET Plus is widely variable at supraphysiologic IOP. Therefore, minor changes in IOP >25 mmHg should not be used to make clinical decisions without considering this variability.

Intraocular pressure measurements using the TONOVET® rebound tonometer: Influence of the probe-cornea distance.

PURPOSE: To demonstrate the effect of different probe-cornea distances during intraocular pressure (IOP) data acquisition in dogs and rats. ANIMALS STUDIED: Twenty-four conscious dogs and 15 anesthetized Wistar rats. METHODS: Three interchangeable three-dimensional printed polylactide plastic spacer collars were used in place of the original Icare TonoVet® collar piece, which provided different distances (4, 6, and 8 mm) between the instrument's probe and the corneal surface. IOP values were obtained in sequence by a single observer, with the tonometer probe at a 4-, 6-, and 8-mm distance from the corneal surface. The dogs were gently restrained, and the rats were anesthetized with isoflurane. RESULTS: Intraocular pressure values obtained at 4, 6, and 8 mm from the TonoVet® probe to corneal surface distance in both dogs and rats were significantly different (P < .01). There was a small positive correlation between IOP (mm Hg) and probe-cornea distance (mm) (rs  = 0.39 for dogs and rs  = 0.51 for rats). In dogs, the mean IOP (± SD mm Hg) obtained at different distances were 16.2 ± 3.0 at 4 mm; 17.6 ± 3.4 at 6 mm; and 19.8 ± 3.8 at 8 mm. In rats, IOP values were 8.2 ± 1.5 at 4-mm; 9.4 ± 1.8 at 6-mm; and 10.5 ± 1.5 mm Hg at 8-mm distance. CONCLUSIONS: Probe-cornea distance of the Icare TonoVet® significantly affects IOP readings, even within the 4- to 8-mm range recommended by the manufacturer.

Comparison of the Icare ic100 Rebound Tonometer and the Goldmann Applanation Tonometer in 1,000 Eyes.

BACKGROUND: Measurement of intraocular pressure (IOP) forms a crucial component in the diagnosis and management of glaucoma. Many devices have been developed to measure IOP with Goldmann applanation tonometry (GAT) considered the gold standard for IOP measurement. OBJECTIVES: The objective was to compare the IOP measured using Icare ic100 and GAT. METHODS: This cross-sectional study measured IOP in 1,000 eyes (500 left and 500 right) using the Icare ic100 and GAT. Central corneal thickness (CCT) was measured using a hand-held pachymeter. IOP measurements were investigated in all eyes, by IOP substrata, by CCT group, by number of topical glaucoma medications, and diagnosis. RESULTS: There was moderate agreement between ic100 and GAT IOP measurements (intraclass correlation coefficient 0.73). Mean IOP was significantly lower when measured by ic100 than by GAT (12.1 vs. 16.2 mm Hg, p < 0.0001). Mean ic100 IOPs were also significantly lower than mean GAT IOPs within each IOP strata ≤12 (7.9 vs. 9.7 mm Hg, p < 0.0001), 13-21 (12.1 vs. 16.6 mm Hg, p < 0.0001), and ≥22 (18.4 vs. 25.2 mm Hg, p < 0.0001) and within each subanalysis. CONCLUSIONS: The Icare tonometer consistently under estimated IOP compared to GAT, irrespective of CCT ranges and other subgroup analyses. The mean difference of 4.2 mm Hg can have significant clinical implications, particularly in the management of glaucoma patients.

A Comparison of Applanation and Rebound Tonometers in Young Chicks.

PURPOSE: To assess the validity of and compare applanation and rebound tonometry readings of intraocular pressure in alert normal chicks from ages 3 to 45 days. METHODS: Intraocular pressures (IOPs) were measured weekly in awake White Leghorn chicks, from ages 3-45 days (n = 22-30 per age group), with both applanation Tono-Pen and rebound TonoLab tonometers. Three repeated measurements on individual eyes were used to derive variance data for both instruments at each age. Calibration curves were also derived for each instrument and each age, weekly from ages 10-45 days (n = 3-4 per age group), from in situ manometry data collected over IOP settings of 0 to 100 mmHg in 5 mmHg steps in cannulated eyes. RESULTS: The TonoLab showed less within measurement variability, but more variability with age, than the Tono-Pen. The coefficient of variation ranged from 3.8-8.3% for the TonoLab, compared to 11.0-19.7% for the Tono-Pen across all ages. For the youngest, 3 day-old chicks, mean IOPs recorded with the Tono-Pen and TonoLab were not significantly different (17.0 ± 5.6 and 15.2 ± 3.7 mmHg, respectively, P = .27). However, with increasing age, IOP readings significantly increased for the TonoLab (P < .001), whereas Tono-Pen readings did not. Compared to manometry settings, the Tono-Pen tended to underestimate IOPs while the TonoLab overestimated IOPs over the range 20-60 mmHg, saturating thereafter; there were also age-dependent differences for the TonoLab. CONCLUSIONS: Both the Tono-Pen and TonoLab gave IOP readings that differed from manometry settings in normal young chicks over some or all of the ages tested. These results reinforce the importance of calibrating clinical tonometers in animal studies involving IOP as a key variable.

Short-Term and Long-Term Variability of Intraocular Pressure Measured with an Intraocular Telemetry Sensor in Patients with Glaucoma.

PURPOSE: To evaluate the short-term and long-term variability of intraocular pressure (IOP) in eyes with primary open-angle glaucoma. DESIGN: Prospective study. PARTICIPANTS: Twenty-two patients previously implanted with a sulcus-based IOP sensor (EyeMate, Implandata GmbH, Germany). METHODS: Twenty-two patients previously implanted with the EyeMate were requested to obtain at least 4 IOP measurements daily. Data were grouped according to the eye and the medication so that an eye treated with a particular medication was considered as one group, and the same eye treated with a different medication during the observation period was considered as a different group. A day was divided into 7 periods: night, midnight to 5:59 am; early, 6 am to 7:59 am; morning, 8 am to 10:59 am; noon, 11 am to 1:59 pm; afternoon, 2 pm to 5:59 pm; evening, 6 pm to 8:59 pm; and late, 9 pm to 11:59 pm. Short-term variability during a particular period was defined as the variability in IOP measurements obtained during that period on different days within 3 months of each other. Long-term variability was defined as the variability in IOP measurements obtained during a particular period on different days over a period of 1 year or more. Variability was assessed using intraclass correlation coefficients (ICCs). RESULTS: The mean age of study participants was 67.8 ± 6.8 years and 36.4% were women. The mean follow-up duration of patients was 19.2 ± 21.3 months (median, 9 months; range, 1-58 months). Overall, 92 860 IOP measurements over 15 811 measurement days were obtained and analyzed during the study period. The number of measurements obtained from each eye ranged from 1 daily to 277 daily. Intraclass correlation coefficients for short-term variability among the 7 periods during the day ranged from 0.52 (morning) to 0.66 (early). Long-term ICCs ranged from 0.29 (night) to 0.51 (late). CONCLUSIONS: Continual IOP monitoring showed that IOP has moderate short-term and high long-term variability in glaucoma patients. These findings demonstrate that single IOP measurements do not characterize day-to-day variations in IOP. Moreover, they show the importance of continual IOP monitoring in glaucoma patients.

Estimation of intraocular pressure in normal canine eyes utilizing the newly introduced TonoVet Plus and TonoPen Avia, and their comparison to the established TonoVet.

PURPOSE: To evaluate the IOP values obtained from normal canine eyes, by means of the TonoVet Plus (TVP) and TonoPen Avia (TPA), and compare them to an established tonometer, the TonoVet (TV). METHODS: Tonometry was performed bilaterally in 50 healthy dogs, age 1-11 years. The rebound tonometers (TV and TVP) were used first (in a random order), and then, one drop of tetracaine hydrochloride was applied to each eye, and approximately one minute later the IOP was estimated using the TPA. The mean ± standard deviation (SD) was calculated for each tonometer and a paired Student's t test was used to compare the IOP values between tonometers. A P value ≤ .05 was considered significant. The agreement between tonometers was assessed by a Bland-Altman plot. RESULTS: The mean ± SD (range) IOP values were 15.0 ± 3.2 mm Hg (7-22), 19.2 ± 3.1 mm Hg (11-25), and 12.8 ± 2.9 mm Hg (6-19), for the TV, TVP, and TPA, respectively. The IOP values obtained by each tonometer were significantly different compared to the other two (P < .0001). There was a good agreement with fixed bias between all tonometers. CONCLUSIONS: The average IOP values of the TVP were significantly higher than those of the TV, which were significantly higher than those of the TPA, in normal canine eyes. Knowing the normal IOP values for these tonometers and the bias between them will help the clinician with the interpretation of IOP values obtained by these devices and compare between them.

Use of a novel telemetric sensor to study interactions of intraocular pressure and ganglion-cell function in glaucoma.

AIMS: (1) To test the feasibility of simultaneous steady-state pattern electroretinogram (ssPERG) and intraocular pressure (IOP) measurements with an implanted IOP sensor. (2) To explore the scope of this approach for detecting PERG changes during IOP manipulation in a model of lateral decubitus positioning (LDP; lateral position). METHODS: 15 healthy controls and 15 treated glaucoma patients participated in the study. 8 patients had an IOP sensor (Eyemate-IO, Implandata Ophthalmic Products GmbH) in the right eye (GLAIMP) and 7 had no sensor and with glaucoma in the left eye. (1) We compared PERGs with and without simultaneous IOP read-out in GLAIMP. (2) All participants were positioned in the following order: sitting1 (S1), right LDP (LDR), sitting2 (S2), left LDP (LDL) and sitting3 (S3). For each position, PERG amplitudes and IOP were determined with rebound tonometry (Icare TA01i) in all participants without the IOP sensor. RESULTS: Electromagnetic intrusions of IOP sensor read-out onto ssPERG recordings had, due to different frequency ranges, no relevant effect on PERG amplitudes. IOP and PERG measures were affected by LDP, for example, IOP was increased during LDR versus S1 in the lower eyes of GLAIMP and controls (5.1±0.6 mmHg, P0.025=0.00004 and 1.6±0.6 mmHg, P0.025=0.02, respectively) and PERG amplitude was reversibly decreased (-25±10%, P0.025=0.02 and -17±5%, P0.025, respectively). CONCLUSIONS: During LDP, both IOP and PERG changed predominantly in the lower eye. IOP changes induced by LDP may be a model for studying the interaction of IOP and ganglion-cell function.