Modulation of Human Intraocular Pressure Using a Pneumatic System.

Noninvasive intraocular pressure (IOP) measurement in mice is critically important for understanding the pathophysiology of glaucoma. Rebound tonometry is one of the methods that can be used for obtaining such measurements. We evaluated the ability of the rebound tonometer (RT) to determine IOP differences among various mouse strains and whether differences in corneal thickness may affect IOP measurements in these animals. Five different commonly used mouse strains (BALB/C, CBA/CAHN, AKR/J, CBA/J, and 129P3/J) were used. IOP was measured in eyes from 12 nonsedated animals (6 male and 6 female) from each strain at 2 to 3 months of age using the RT. IOPs were measured in all animals, on 2 different days between 10 AM and 12 PM. Subsequently, a number of eyes from each strain were cannulated to provide a calibration curve specific for that strain. Tonometer readings for all strains were converted to apparent IOP values using the calibration data obtained from the calibration curve of the respective strain. For comparison purposes, IOP values were also obtained using the C57BL/6 calibration data previously reported. IOP for the 5 strains, male and female animals, and the different occasion of measurement were compared using repeat measures analysis of variance. The central corneal thickness (CCT) of another group of 8 male animals from each of the 5 strains was also measured using an optical low coherence reflectometry (OLCR) pachymeter modified for use with mice. CCT values were correlated to mean IOPs of male animals and to the slopes and intercept of individual strain calibration curves. Noninvasive IOP measurements confirm that the BALB/C strain has lower and the CBA/CAHN has higher relative IOPs than other mouse strains while the AKR/J, the CBA/J, and the 129P3/J strains have intermediate IOPs. There is a very good correlation of apparent IOP values obtained by RT with previously reported true IOPs obtained by cannulation. There was a small but statistically significant difference in IOP between male and female animals in 2 strains (129P3/J and AKR/J) with female mice having higher relative IOPs. No correlation between CCT and IOP was detected. CCT did not correlate with any of the constants describing the calibration curves in the various strains. Noninvasive IOP measurement in mice using the RT can be used to help elucidate IOP phenotype, after prior calibration of the tonometer. CCT has no effect on mouse IOP measurements using the RT.

The Induction/Impact Tonometer: a New Instrument to Measure Intraocular Pressure in the Rat

PurposeThis is a 2-part study to investigate the agreement between pneumatonometry and direct pressure transducer intraocular pressure (IOP) measurements in a perfusion organ culture (POC) model where (1) the perfusion fluid column is open to atmospheric pressure, holding IOP constant to permit evaluation of the impact of negative pressure (NP) on IOP measurements, and (2) the perfusion fluid column is a closed system, allowing IOP to vary with NP application.MethodsThe first part incorporated a fluid column open to atmospheric pressure, maintaining IOP constant to permit evaluation of the effect of applied NP on IOP measurement accuracy. In the second part, the POC column was closed, allowing IOP to vary with NP application and permit evaluation of agreement between pneumatonometry and pressure transducer measurements. In each part, four perfused tissues were used in thirteen paired pre-set IOP (10, 20, 25, 30 mmHg) and NP (0, 5, 10, 15, 20 mmHg) combinations, resulting in a total of 1040 paired measurements (520 per study). The difference in IOP measurements (Δ IOP = Excursion tonometry – pressure transducer) was calculated at each paired configuration.ResultsDuring the first part, the mean Δ IOP was −0.7 ± 1.6 mmHg across all measurements. During the second part, the mean Δ IOP across all measurements was +0.7 ± 1.4 mmHg. At NP settings of −5, −10, −15, and −20 mmHg, across all pre-set IOPs, the mean IOP reduction via Excursion tonometry was 3.1 ± 0.3, 5.6 ± 1.3, 8.5 ± 1.7 and 11.2 ± 1.8 mmHg, respectively.ConclusionMeasurement of IOP via Excursion tonometry yields results within the accuracy range of the pneumatonometry device (per manufacturer) and is minimally impacted by NP application. The IOP-lowering results are consistent with previous studies and further support the effectiveness of the Multi-Pressure Dial in lowering IOP relative to atmospheric pressure.

To examine the effects of multiple intraocular pressure (IOP) measurements on the correlation of response to glaucoma medication between fellow eyes. Latanoprost was applied to the first eye and then to both eyes of 16 patients with either primary open-angle glaucoma or ocular hypertension. IOP measurements were performed twice on different days for each of three periods: at baseline, during treatment of the first eye only and for both eyes. IOP decreases in the first and second eyes were evaluated with ∆IOP 1 (=IOP at baseline-IOP after treatment) and ∆IOP 2 (=∆IOP 1-IOP fluctuation of the contralateral eye). The correlation of IOP decreases between the fellow eyes was analyzed by linear regression analysis using the Pearson correlation coefficient, r. No significant correlations of ∆IOP1 between fellow eyes were found regardless of the number of IOP measurements. ∆IOP2 was significantly correlated between fellow eyes using two post-treatment IOP measurements, but not with a single post-treatment IOP. Using multiple post-treatment IOP measurements may improve the prediction of a fellow eye's response to glaucoma medication in one-eye trials.

Purpose. The purpose of this study was to investigate the influence of corneal topography and thickness on intraocular pressure (IOP) and pulse amplitude (PA) as measured using the Ocular Blood Flow Analyzer (OBFA) pneumatonometer (Paradigm Medical Industries, Utah, USA). Methods. 47 university students volunteered for this crosssectional study: mean age 20.4 yrs, range 18 to 28 yrs; 23 male, 24 female. Only the measurements from the right eye of each participant were used. Central corneal thickness and mean corneal radius were measured using Scheimpflug biometry and corneal topographic imaging respectively. IOP and PA measurements were made with the OBFA pneumatonometer. Axial length was measured using A-scan ultrasound, due to its known correlation with these corneal parameters. Stepwise multiple regression analysis was used to identify those components that contributed significant variance to the independent variables of IOP and PA. Results. The mean IOP and PA measurements were 13.1 (SD 3.3) mmHg and 3.0 (SD 1.2) mmHg respectively. IOP measurements made with the OBFA pneumatonometer correlated significantly with central corneal thickness (r = +0.374, p = 0.010), such that a 10 µm change in CCT was equivalent to a 0.30mmHg change in measured IOP. PA measurements correlated significantly with axial length (part correlate = –0.651, p < 0.001) and mean corneal radius (part correlate = +0.459, p < 0.001) but not corneal thickness. Conclusions. IOP measurements taken with the OBFA pneumatonometer are correlated with corneal thickness, but not axial length or corneal curvature. Conversely, PA measurements are unaffected by corneal thickness, but correlated with axial length and corneal radius. These parameters should be taken into consideration when interpreting IOP and PA measurements made with the OBFA pneumatonometer.

This study aims to determine the effect of corneal cross-linkage (CXL) on intraocular pressure (IOP) in keratoconus patients. Methods: A quasi-experimental study was carried out at the Cornea Clinic of Al Ibrahim Eye Hospital Malir, Karachi. A total of 60 eyes of 36 subjects with progressive keratoconus with the age range of 15 to 31 years were fulfilling the criteria of the study. Subjects were selected with convenient sampling and subjects with a previous history of CXL were excluded from the study. A complete history of the patient, clinical examination with slit-lamp biomicroscopy, and visual acuity (VA) with Snellen chart were recorded. Intraocular pressure (IOP) measurements of each subject were recorded with Goldman Applanation Tonometer (GAT) before and immediately after 15 minutes of CXL and on the 2nd day of CXL, 1month, and 3 months after CXL. SPSS version 22 was used to analyze the data. Results: The average preoperative measured intraocular pressure (IOP) was 20.22 +/- 3.97 mmHg. There was a statistically significant decrease in IOP measurements 18.96 +/- 3.73 mmHg on the same day after the corneal cross linkage procedure with (P 0.001) while there was no statistically significant change in intraocular pressure (IOP) measurements was observed on the 2nd day, 1 month and 3 months after CXL. The postoperative mean of IOP measurements was 19.61 +/- 3.47 mmHg on the 2nd day, 19.67 +/- 3.14 mmHg on 1 month, and 19.33 +/- 3.64 mmHg at 3 months respectively. Conclusion: This study shows that reductions in intraocular pressure (IOP) measurements were observed on the immediate response of corneal cross-linkage (CXL) on the same day. This change might be due to immediate alteration in the biomechanics of the cornea during corneal cross-linkage. These changes return to the normal position later because no change was seen on different follow-ups of patients after CXL in eyes with keratoconus.

Intraocular pressure (IOP) is a dynamic parameter with variations over 24-hours in the eye. For the diagnosis and treatment of IOP-related diseases such as glaucoma, clinically established spot IOP measurements cannot capture the full circadian rhythm of IOP in patients. As a result, a 24-hour IOP profile would be immensely beneficial and clinically relevant for the treatment of IOP related diseases. Continuous and non-invasive IOP measurements have been made possible with the introduction of contact lens sensors (CLS). Upon corneal changes due to IOP variations, deformation from the cornea is directly transferred to the contact lens by surface tension forces. An electrical circuit embedded into the lens tracks the resulting deformation of the CLS and a wireless system delivers the signal to an external reader. However, despite the thin build of the inductive sensing CLS, the passive nature of the circuit is not selectively sensitive to IOP when worn on the human eye. Environmental changes near the CLS invalidates the previously established linear resonant frequency to IOP relationship. In this thesis, the environmental influences from the human eye were shown on a silicone model eye, and a new inductive sensing CLS was designed and fabricated to remove the environmental influences. The rigid-flex CLS includes a rigid passive inductor-capacitor (LC) resonator placed beside another a separate LC resonator with higher flexibility. The flexible LC resonator is sensitive to intraocular pressure change as well as environmental influences; while the rigid coil only senses the environmental conditions. Results show the feasibility of removing the environmental influence from IOP measurements with the rigid-flex contact lens sensor.

Intraocular pressure (IOP) measurement is critical in diagnosing and managing eye conditions. This study aims to assess the comparability of three alternative devices for measuring IOP: Noncontact tonometer, Icare rebound tonometer, and Tono-Pen. A cross-sectional study included 172 adult participants (87 males and 85 females) who underwent IOP and central corneal thickness (CCT) assessments. IOP was measured using Noncontact (Canon TX-20), Icare (Icare TA01i), and Tono-Pen (Tonopen XL). CCT was measured with the built-in pachymetry of the Noncontact tonometer. Correlation coefficients and Bland-Altman analyses were conducted to assess the relationships and agreements between these tonometers. Participants were grouped based on IOP and CCT levels. The mean of the standard deviation of the three tonometer results was calculated to evaluate measurement result variability. One-way analysis of variance was conducted for comparing between the groups. IOP measurements among the three devices were not significantly different, indicating their comparability. Correlation analysis revealed strong correlations between the tonometers. Bland-Altman analysis showed good agreement, with the Icare rebound tonometer and Tono-Pen exhibiting narrower limits of agreement. Furthermore, IOP levels influenced measurement result variability, with higher IOP levels associated with greater variance. This study demonstrates that the alternative devices examined can provide reliable IOP measurements. It highlights the potential of these alternative devices for IOP measurement. These findings have implications for clinical practice, offering practitioners additional tools for accurate IOP assessment.

IntroductionTo investigate the effect of applying negative pressure (vacuum) to the periocular space on intraocular pressure (IOP) and retrobulbar pressure (RBP) by use of the Multi-Pressure Dial (MPD) system (Equinox Ophthalmic, Inc.).MethodsTwo eyes of two full body cadavers were studied. In each subject, the retrobulbar space, posterior segment and intra-goggle space were cannulated to provide direct IOP, RBP and intra-goggle pressure measurements via a pressure transducer data acquisition system. The goggles of the MPD system were placed over the eyes of each subject, and multiple test runs were performed, with negative pressure settings programmed to 5, 10 and 20 mmHg. IOP and RBP measurements were continuously obtained during each run and plotted against time for analysis.ResultsFor both subjects, the mean reduction (± standard deviation) in IOP was 1.6 ± 0.9 (10%), 3.5 ± 1.8 (23%) and 5.6 ± 2.0 (37%) mmHg at programmed negative pressure levels of − 5, − 10 and − 20 mmHg, respectively. The overall mean change in RBP (mmHg) during negative pressure application was 0.02 ± 0.14 at − 5 mmHg, 0.03 ± 0.19 at − 10 mmHg and − 0.01 ± 0.18 at − 20 mmHg. In both subjects, the magnitude of RBP change during application of negative pressure fell below the uncertainty of the measurement system.ConclusionsThe application of negative pressure to the periocular space with the MPD decreases IOP but does not affect RBP.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40123-021-00442-2.

Background: To compare intraocular pressure (IOP) measurements in silicone filled eyes by Goldmann applanation tonometer (GAT) and air puff tonometer (APT).Aim: The purpose of this study was to evaluate the role of APT by comparing the measurements of IOP made using it with those made using a GAT.Methods: In this prospective comparative study, 40 eyes with silicone oil tamponade were included.IOP was measured by GAT and air puff tonometer at least 1 month from vitrectomy.Results: in eyes with silicone oil, IOP was 21.35±12.34mmHg and 19.46±5.29 mmHg using GAT and APT, respectively (p>0.05) and this difference was not statistically significant (p=0.074).In addition, no significant correlation was detected between IOP measurements using both techniques and gender, and lens status.Conclusion: It seems that GAT provided higher IOP measurements by 3.34 mmHg (95% CI = 2.15 to 4.53 mmHg) on average compared with APT but the difference between the two IOP measurements was statistically nonsignificant (p >0.05), in silicone filled eyes.The further assessment of available methods for IOP measurement could possibly establish the most accurate technique for IOP estimation in silicone filled eyes.

Purpose To evaluate the relationship between intraocular pressure (IOP) measurements obtained with Pulsair EasyEye (PEE) and Ocular Response Analyser (ORA) in healthy subjects.Methods Sixty‐five eyes from 65 healthy subjects were prospective and consecutively evaluated. All of them underwent a full optometric examination, including central corneal thickness (CCT), and IOP measured with both PEE and ORA devices. Differences between IOP measurements between both tonometers were analyzed.Results Statistically differences were found between IOP measurements of PEE (IOPk) and ORA Goldmann‐corrected IOP (IOPg; p=0.001). IOPk and ORA corneal resistance‐corrected IOP (IOPcc) were also statistically different (p=0.025). However, no differences between IOPg and IOPcc were found (p=0.952). Mean differences between IOPg‐IOPk, IOPcc‐IOPk and IOPg‐IOPcc (±SD) were 0.71±1.66, 0.70±2.46 and 0.01±1.54 mmHg respectively. Pearson correlation coefficients showed that IOPk, IOPg, IOPcc were significantly correlated (p&lt;0.001): r=0.816 for IOPk‐IOPg, r=0.826 for IOPcc‐IOPg and r=0.587 IOPcc‐IOPk.Conclusion There are statistically differences between mean IOP values measured with PEE and ORA. ORA tonometer provides higher IOP values than PEE in most of the cases. IOPk, IOPcc and IOPg have, at least, moderate positive linear correlations between them.

Intraocular pressure (IOP) is known to be subject to daily fluctuations, the occurrence of which is a risk factor for progression of glaucoma. Control of IOP during the day by drugs is an important therapeutic target. We set out to compare the IOP control of travoprost and latanoprost taking into account the time since last instillation and the time of IOP measurement. This was a prospective, cross-sectional observational study with some retrospective data collection. Private ophthalmologists were selected to each recruit ten patients with primary open-angle glaucoma and/or ocular hypertension receiving either travoprost or latanoprost as monotherapy. Clinical endpoints included IOP measurements and percentage of patients attaining predefined target IOPs. Six patient subgroups were defined according to: (a) IOP measurement time: before 1200h, 1200h-1600h and after 1600h, and (b) time since last intake (<24 hours, >24 hours). Analyses comprised chi(2) and Wilcoxon tests, ANOVA, logistic regressions and adjustment by propensity score. In total, 2052 patients treated with travoprost (n = 1704) or latanoprost (n = 348) participated in the study. Treatment groups were comparable at baseline, except for a longer treatment duration in latanoprost-treated patients. When the interval between the last treatment instillation and IOP measurement (treatment/IOP interval) was <24 hours (n = 1241), 82% of travoprost-treated patients attained pre-defined target IOP versus 67% with latanoprost (p < 0.0001). This difference was greatest after 1600 h, when the mean IOP was 16.5 mm Hg for travoprost-treated patients and 17.7 mm Hg for latanoprost-treated patients (p = 0.0025). When the treatment/IOP interval was >24 hours (n = 461), travoprost was superior to latanoprost, i.e. more patients using travoprost attained the predefined target IOP (78.5% vs 68.3%; p = 0.0344), and the mean IOP value was lower in the travoprost group (16.8 vs 17.8 mm Hg; p = 0.0016). After adjustments for confounding factors, similar results were obtained. According to this observational survey, travoprost appears to reduce evening and mean diurnal IOP more effectively than latanoprost. Latanoprost IOP control appears to be more sensitive to time since the last dose.

PurposeTo use machine learning to predict the risk of intraocular pressure peaks at6 a.m. in primary open-angle glaucoma patients and suspects.MethodsThis cross-sectional observational study included 98 eyes of 98 patients whounderwent a 24-hour intraocular pressure curve (including the intraocularpressure measurements at 6 a.m.). The diurnal intraocular pressure curve wasdefined as a series of three measurements at 8 a.m., 9 a.m., and 11 a.m.from the 24-hour intraocular pressure curve. Two new variables wereintroduced: slope and concavity. The slope of the curve was calculated asthe difference between intraocular pressure measurements at 9 a.m. and 8a.m. and reflected the intraocular pressure change in the first hour. Theconcavity of the curve was calculated as the difference between the slopesat 9 a.m. and 8 a.m. and indicated if the curve was bent upward or downward.A classification tree was used to determine a multivariate algorithm fromthe measurements of the diurnal intraocular pressure curve to predict therisk of elevated intraocular pressure at 6 a.m.ResultsForty-nine (50%) eyes had intraocular pressure measurements at 6 a.m. >21mmHg, and the median intraocular pressure peak in these eyes at 6 a.m. was26 mmHg. The best predictors of intraocular pressure measurements >21mmHg at 6 a.m. were the intraocular pressure measurements at 8 a.m. andconcavity. The proposed model achieved a sensitivity of 100% and aspecificity of 86%, resulting in an accuracy of 93%.ConclusionsThe machine learning approach was able to predict the risk of intraocularpressure peaks at 6 a.m. with good accuracy. This new approach to thediurnal intraocular pressure curve may become a widely used tool in dailypractice and the indica tion of a 24-hour intraocular pressure curve couldbe rationalized according to risk stratification.

Corneal collagen cross-linking (CCL) with riboflavin and ultraviolet A irradiation has recently been introduced for treatment of corneal ectasia. Yet a CCL-induced increase in corneal rigidity may interfere with intraocular pressure (IOP) measurements. In an investigation of the effect of CCL on the accuracy of IOP measurements, IOP readings before and after CCL were compared. Ten human eye bank corneas were de-epithelialized and mounted on an artificial anterior chamber. The hydrostatically controlled reference pressure in the chamber was adjusted from 10 to 40 mm Hg in 5-mm Hg steps. IOP was measured by Goldmann applanation tonometry (GAT; Haag Streit, Könitz, Switzerland), dynamic contour tonometry (DCT; Pascal tonometer; Ziemer Ophthalmics, Port, Switzerland), and the TonoPen XL (TP; Tono-Pen XL, Medtronic, Jacksonville, FL) before and after CCL, which was performed with a 0.1% riboflavin solution and 30 minutes of UVA irradiation. Before CCL, GAT, and DCT readings showed an excellent concordance with the manometric reference pressure, whereas TP overestimated the true IOP. After CCL, the reliability of IOP readings decreased with all three tonometers. This decrease resulted in a slight overestimation of mean IOP, but there were also some potentially dangerous underestimations in some individual corneas. The mean (+/-SD) difference between IOP readings after and before CCL was +1.8 (3.5) mm Hg for DCT, +2.9 (6.1) mm Hg for GAT, and +3.1 (8.3) mm Hg for TP (P <or= 0.002 for DCT versus GAT or TP). In this in vitro model on human corneas, CCL resulted in an overestimation of true IOP by all the tested tonometers. Although the magnitude of this effect was small, care should be taken when measuring IOP with GAT after CCL, as it results in less accurate, much more variable IOP readings.

To compare intraocular pressure (IOP) control in eyes with or without clear corneal phacoemulsification following trabeculectomy. The study group included 30 eyes that underwent uneventful clear corneal phacoemulsification and foldable intraocular lens implantation following trabeculectomy without antimetabolites. Thirty eyes that had undergone filtering surgery without cataract extraction were selected as controls. Case and control groups were matched with respect to age, gender, IOP, number of glaucoma medications, glaucoma type (primary open-angle glaucoma/pseudoexfoliative glaucoma), trabeculectomy time and follow-up. Comparisons between the study and control groups (intergroup) and within the same group at different time-points (intragroup) were performed for IOP, glaucoma medications and bleb morphology. Success rates were investigated by Kaplan-Meier survival analysis and the factors influencing final success by logistic regression. Intraocular pressure (p = 0.04) and glaucoma medications (p = 0.001) increased during an average follow-up of 26.1 +/- 9.9 months in both groups. Intragroup differences became statistically significant after the 6-month visit, but intergroup differences remained insignificant. Bleb height decreased significantly following phacoemulsification in the study group (p = 0.017). Success rates decreased with time in both groups, with no intergroup difference (p = 0.46). The final success rate was negatively correlated with IOP and number of glaucoma medications used at the study entry, while there was a positive correlation between the baseline and final success rates. Trabeculectomy success decreased in a time-dependent manner in eyes with and without subsequent phacoemulsification. Uncomplicated clear corneal phacoemulsification was not found to have any additional unfavorable influence on IOP control in eyes with filtering blebs.