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.

Intraocular pressure measurements in paediatric glaucoma: A narrative review on accuracy, tolerability, and ease of use.

INTRODUCTION: Numerous tonometers are available to measure intraocular pressure (IOP) in children with glaucoma. This review aims to discuss IOP measurement techniques and principles and compare the accuracy, tolerability and ease of use of available tonometers in measuring IOP in paediatric glaucoma patients. MATERIALS AND METHODS: A review of observational studies was conducted to discuss the accuracy, tolerability and ease of use of tonometers in measuring IOP in children with glaucoma. RESULTS: Goldmann applanation tonometry (GAT) and its portable handheld versions remain the gold standard in measuring IOP. Tono-Pen (Reichert Ophthalmic Instruments, Depew, New York, USA) and rebound tonometer (RBT) both correlate well with GAT. Although both tonometers tend to overestimate IOP, Tono-Pen overestimates more than RBT. Overestimation is more remarkable in higher IOP and corneal pathologies (such as but not limited to scarred cornea and denser corneal opacity). RBT was better tolerated than other tonometers in children and was easier to use in children of all ages. CONCLUSIONS: RBT is the preferred tonometer for measuring IOP in children with glaucoma, as it is less traumatic, time efficient and does not require fluorescein dye or anaesthesia. However, examiners should use a second tonometer to confirm elevated IOP readings from the RBT.

A novel intraocular pressure predicting method based on hyperelastic mechanical model of cornea.

Measuring intraocular pressure (IOP) is crucial and remains challenging in diagnosing glaucoma, as it is associated with cornea deformation during inflation. In this study, a three-dimensional analytical model based on hyperelastic constitutive relationship to predict correlation between cornea vertex displacement and the IOP is proposed. The analytical model is validated by rigorous experiments. Rabbit corneas were selected for this study and their mechanical properties were obtained using uniaxial tensile tests. To mimic the environment in which the cornea exists, an artificial anterior chamber equipped with water-injection pipelines was constructed to study the relationship between the corneal vertex displacement with IOP value in practical situation. The experimental results of rabbits corneas prove that the IOP can be deduced based on the measured corneal vertex displacement by the analytical model. Furthermore, subtle difference occurs when comparing the calculated human IOPs with those measured by medical equipment, demonstrating that the proposed method is suitable for monitoring the IOP of human. This novel IOP predicting method provides new inspiration for the design of eyepieces, as well as the preoperative preparation for laser surgery and evaluation of corneal damage.

In vivo assessment of the ocular biomechanical properties in patients with idiopathic normal pressure hydrocephalus.

PURPOSE: Idiopathic normal pressure hydrocephalus (iNPH) is associated with an increased prevalence of open-angle glaucoma, attributed to variations of the pressure gradient between intraocular and intracranial compartments at the level of the lamina cribrosa (LC). As ocular biomechanics influence the behavior of the LC, and a lower corneal hysteresis (CH) has been associated to a higher risk of glaucomatous optic nerve damage, in this study we compared ocular biomechanics of iNPH patients with healthy subjects. METHODS:  Twenty-four eyes of 24 non-shunted iNPH patients were prospectively recruited. Ocular biomechanical properties were investigated using the ocular response analyzer (Reichert Instruments) for the calculation of the CH, corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg), and corneal-compensated intraocular pressure (IOPcc). Results were compared with those of 25 eyes of 25 healthy subjects. RESULTS:  In iNPH eyes, the median CH value and interquartile range (IQR) were 9.7 mmHg (7.8-10) and 10.6 mmHg (9.3-11.3) in healthy controls (p = 0.015). No significant differences were found in IOPcc [18.1 mmHg (14.72-19.92) vs. 16.4 mmHg (13.05-19.6)], IOPg [15.4 mmHg (12.82-19.7) vs. 15.3 mmHg (12.55-17.35)], and CRF [9.65 mmHg (8.07-11.65) vs. 10.3 mmHg (9.3-11.5)] between iNPH patients and controls. CONCLUSIONS:  In iNPH patients, the CH was significantly lower compared to healthy subjects. This result suggests that ocular biomechanical properties may potentially contribute to the risk of development of glaucomatous optic nerve damage in iNPH patients.

A mechanical model of ocular bulb vibrations and implications for acoustic tonometry.

In this study, we propose a comprehensive mechanical model of ocular bulb vibrations and discuss its implications for acoustic tonometry. The model describes the eye wall as a spherical, pre-stressed elastic shell containing a viscoelastic material and accounts for the interaction between the elastic corneoscleral shell and the viscoelastic vitreous humor. We investigate the natural frequencies of the system and the corresponding vibration modes, expanding the solution in terms of scalar and vector spherical harmonics. From a quantitative point of view, our findings reveal that the eyebulb vibration frequencies significantly depend on IOP. This dependency has two origins: "geometric" stiffening, due to an increase of the pre-stress, and "material" stiffening, due to the nonlinearity of the stress-strain curve of the sclera. The model shows that the second effect is by far dominant. We also find that the oscillation frequencies depend on ocular rigidity, but this dependency is important only at relatively large values of IOP. Thus close to physiological conditions, IOP is the main determinant of ocular vibration frequencies. The vitreous rheological properties are found to mostly influence vibration damping. This study contributes to the understanding of the mechanical behavior of the eye under dynamic conditions and thus has implications for non-contact intraocular pressure measurement techniques, such as acoustic tonometry. The model can also be relevant for other ocular pathological conditions, such as traumatic retinal detachment, which are believed to be influenced by the dynamic behavior of the eye.

Even-number measurement bias with Goldmann applanation tonometry in patients with glaucoma and glaucoma suspects.

CLINICAL RELEVANCE: Goldmann applanation tonometry is widely used for the diagnosis and management of glaucoma and its use is considered standard of care. However, the precision of this method may be reduced by a clinician tendency to round to even numbers. BACKGROUND: Studies have previously demonstrated an even-number measurement bias with Goldmann applanation tonometry during examination of a general patient population. Since it has not been determined whether this bias persists among glaucoma suspects and patients with glaucoma, further investigation was conducted. METHODS: A retrospective analysis was conducted on a random sample from a large dataset of >69,000 patients seen during a six-year period at an urban, academic primary eye care service. Patients without suspicion of glaucoma, patients with a suspicion of glaucoma, and patients with glaucoma were selected who had Goldmann tonometry performed. Chart reviews were performed to confirm status, and even/odd-numbered Goldmann tonometry measurement frequencies were compared. RESULTS: The analysis included 961 controls, 506 glaucoma suspects, 159 ocular hypertensives not taking medication, and 314 patients taking medications who carried a diagnosis of glaucoma or ocular hypertension. Among controls the Goldmann tonometry even/odd digit proportions were 62.8%/37.2% (N = 961, p < 0.0001), and the even-number bias persisted among the other groups with specific even/odd distributions being 61.9%/38.1% (N = 506, p < 0.0001) for glaucoma suspects not taking medications, 66.0%/34.0% (N = 159, p < 0.0001) for ocular hypertensives not taking medications, and 64.3%/35.7% (N = 314, p < 0.0001) for glaucoma/ocular hypertension patients taking medications. CONCLUSION: An even-number measurement bias with Goldmann tonometry may be prevalent even when the examiner is aware of there being greater importance for intraocular pressure measurement accuracy.

Efficacy of the positioning system when measuring canine intraocular pressures with the Reichert® Tono-Vera® Vet rebound tonometer.

OBJECTIVE: To compare intraocular pressure (IOP) measurements in dogs taken with the Reichert® Tono-Vera® Vet rebound tonometer with and without the automatic positioning system. ANIMALS STUDIED: Measurements were taken on 49 eyes from 26 Beagle-derived dogs with variable genetics-four non-glaucomatous and 22 ADAMTS10-mutant dogs affected with different stages of open-angle glaucoma. Seventeen of the 26 dogs were measured 2-4 times on different days with variable intervals since IOP-lowering medications were administered. PROCEDURES: In each dog, tonometry was performed with the Tono-Vera® Vet using three different methods in a randomized order: (Method 1) Average of three readings with an automatic positioning system; (Method 2) one reading with an automatic positioning system; and (Method 3) average of three readings obtained without the automatic positioning system. Statistical analyses included one-way ANOVA, Tukey pairwise comparisons, and Bland-Altman plots (MiniTab®). RESULTS: With each of the three tonometry methods, 116 measurements were taken, resulting in 348 total IOP measurements with a range of 12.8-49.9 mmHg. The means and standard deviations for each method were 25.4 ± 6.9 mmHg (Method 1), 26.0 ± 7.2 mmHg (Method 2), and 26.9 ± 7.7 mmHg (Method 3), with no significant differences (p = .27). Mean IOP variances were also not significantly different between tonometry methods (p = .24 to .78). CONCLUSIONS: Because mean IOPs and their standard deviations were not statistically different between the three tonometry methods, we conclude that Tono-Vera® Vet measurements conducted without the aid of the positioning system still provide reliable results.

Reliability of Intraocular Pressure Measurements in a Low-Contact Drive-Through Setting.

PRCIS: Drive-through intraocular pressure (IOP) measurement using iCare tonometry is a promising method of low-contact, high-throughput IOP monitoring. However, owing to its vulnerability to variable measurement technique and local air currents, the iCare may overestimate IOPs. PURPOSE: During the COVID-19 pandemic, a drive-through IOP measurement protocol using the iCare tonometer was established to facilitate low-contact monitoring of select glaucoma patients. As the iCare may be prone to error due to variable measurement technique and local air currents, we endeavored to assess the reliability of drive-through IOP measurements by comparing them with recent measurements taken in clinic settings. METHODS: Inclusion criteria were patients with drive-through IOP measurements performed from April 28 to October 11, 2020; exclusion criteria were pre-drive-through IOPs >21 mmHg. Drive-through IOP measurements were compared with the closest previous and/or subsequent in-clinic IOP measurements. Data were gathered using the Sight Outcomes Research Collaborative (SOURCE) data repository. RESULTS: The post-exclusion study group consisted of 314 patients receiving a total of 868 drive-through IOP measurements, all of whom had prior in-clinic measurements, and 56.8% of whom had subsequent in-clinic measurements. Drive-through IOPs were, on average, +2.4 mmHg (+14.5%; SD 4.9) higher than in-clinic IOPs. Further sub-analysis of the data showed a difference of +2.1 mmHg OD and +2.6 mmHg OS. Compared with the closest previous in-clinic visit, the difference was +2.4 mmHg OU (+2.1 mmHg OD, +2.7 mmHg OS); compared with the closest subsequent in-clinic visit, the difference was +2.3 mmHg OU (+2.1 mmHg OD, +2.5 mmHg OS). 68.6% of all drive-through IOPs were higher than corresponding in-clinic IOPs; 21.1% were lower. 25.9% of drive-through IOPs were higher by more than 5 mmHg, whereas 3.9% of drive-through IOPs were lower by more than 5 mmHg. DISCUSSION: As teleophthalmology becomes an ever more important tool in glaucoma patient care, drive-through or walk-through IOP monitoring methods are likely to play an increasing role. However, our data reveals potential inaccuracies in drive-through iCare IOP measurements which tended to overestimate IOP. It is advisable to confirm large changes in IOP with in-clinic measurement before making management decisions. CONCLUSION: With better optimization of accuracy and reliability of measurements, drive-through tonometry is a promising, high-throughput, low-contact method of measuring IOP.

Reliability of Measurements Using Ocular Response Analyzer as a Screening Tonometer and Corneal Hysteresis Values in the Presence or Absence of Glaucomatous Changes in Fundus.

PRCIS: Use of the Ocular Response Analyzer (ORA) as a screening tonometer in clinical practice yielded reliable measurements in over 80% of eyes screened. Including corneal hysteresis (CH) data in screening may improve the accuracy of glaucoma detection. PURPOSE: To examine measurement reliability when the ORA is used as a screening tonometer, and to compare CH measurements in eyes with and those without glaucomatous changes in the fundus. PATIENTS AND METHODS: 1488 eyes of 747 patients (mean age: 53.5 ± 20.4 y, range: 6-94 y) underwent intraocular pressure (IOP) measurement using ORA as screening. The percentage of eyes with a waveform score ≥6, the recommended threshold indicating reliability, was calculated. Eyes that had waveform score ≥6 and had undergone fundus photography and optical coherence tomography were assessed for the presence or absence of glaucomatous changes in fundus from optical coherence tomography and fundus images, and CH was compared between the 2 groups. RESULTS: Mean ± SD (range) of ORA measurements were: Goldmann-correlated IOP 14.9 ± 4.8 (1.0-63.2) mm Hg, corneal-compensated IOP 16.2 ± 4.7 (3.2-73.6) mm Hg, CH 9.7 ± 1.5 (0.0-20.6) mm Hg, and waveform score 7.3 ± 1.5 (0.1-9.7). Eighty-four percent of eyes had a waveform score ≥6. Among 192 eyes (127 patients, aged 53.5 ± 18.0 y) with waveform score ≥6 and evaluable for glaucomatous changes in the fundus, 53 eyes were determined as positive and 139 eyes as negative. CH was 9.6 ± 1.4 (6.8-13.3) mm Hg in the positive group and 10.2 ± 1.2 (6.9-13.3) mm Hg in the negative group, and was significantly lower in the positive group ( P =0.003). CONCLUSION: When using ORA as a screening tonometer, reliable results were obtained in ~80% of the eyes. CH was lower in the glaucomatous change-positive group compared with the glaucomatous change-negative group, but the ranges overlapped between the 2 groups.

A first-in-human pilot study of a novel electrically-passive metamaterial-inspired resonator-based ocular sensor embedded contact lens monitoring intraocular pressure fluctuations.

Glaucoma is a leading cause of blindness with no cure, but early treatment and effective monitoring can often slow the progression of the disease. Monitoring of glaucoma is based on the measurement of intra-ocular pressure (IOP) that is a physiological parameter related to the mechanical state and parameters of the eye. Conventionally, diagnosing and assessing the progression of glaucoma is based on the method of measuring IOP discretely at clinics. Recent studies have demonstrated the importance of continuously monitoring IOP for 24 h to elucidate the effect of circadian rhythm. In this work, a metamaterial-inspired electrically-passive sensor-embedded contact lens is presented to monitor the IOP fluctuations based on a first-in-human pilot study. The sensor inside the contact lens is an electrically passive, metamaterial-based resonator that can be measured using a wearable antenna patch. The system has been tested with six healthy volunteers during an experiment to induce deliberate IOP changes via water-loading and placing the individuals in supine position using a recliner seat. The initial data compared with tonometer measurements suggest that the system can be used to assess the variation of IOP continuously.

Comparison of Three Methods of Tonometry in Patients with Inactive Thyroid-Associated Orbitopathy.

INTRODUCTION: Intraocular pressure (IOP) measurement in patients with thyroid-associated orbitopathy (TAO) can be difficult and misleading, particularly in patients with diplopia and eye deviation (esotropia or hypotropia). However, when measuring IOP, it is also necessary to pay sufficient attention to TAO patients without diplopia in primary gaze direction and without motility disorder that might not be readily apparent. PURPOSE: The aim of this study was to evaluate the accuracy of measurement of intraocular pressure (IOP) using three different types of tonometers: the rebound tonometer (iCARE), the Goldmann applanation tonometer (GAT) and the non-contact airpuff tonometer (NCT) in patients with inactive TAO.  Materials and Methods: A total of 98 eyes of 49 adult patients with TAO were examined. The study group included 36 females and 13 males, with an age range of 19-70 years and a median age of 55.0. All the patients had evidence of thyroid disease,  a history of mild to moderate TAO, no clinical signs or symptoms of active disease, and no diplopia in direct gaze direction. In addition to a comprehensive eye examination, all the patients underwent measurement of intraocular pressure with three tonometers: NCT, iCARE, and GAT. The measurements with these three devices were compared. RESULTS: The mean IOP was 18.1 ± 2.4 mmHg (range 13-25 mmHg) with GAT, 22.3 ±5.0 mmHg (range 13-35 mmHg) with NCT, and 18.0 ±2.4 mmHg (range 13.3-26 mmHg) with iCARE. The mean difference between the GAT and iCARE measurements (using the Bland-Altman analysis) was -0.1 ±1.16 mmHg (limits of agreement -2.4 to 2.1). The mean difference between the GAT and NCT measurements was 4.2 ±3.6 mmHg (limits of agreement -2.8 to 11.2). The mean difference between the iCARE and NCT measurements was -4.3 ±3.7 mmHg (limits of agreement -11.6 to 2.9). No significant difference was found between GAT and iCARE (p = 1.000). However, there was a significant difference between GAT and NCT (p < 0.0001), as well as between iCARE and NCT (p < 0.0001).  Conclusions: In patients with TAO, NCT significantly overestimates IOP values compared to the GAT and ICare. By contrast, the iCARE rebound tonometer provides IOP measurements comparable to the gold standard GAT in these patients.

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

PURPOSE: Eyelid spasms might be associated with elevated intraocular pressure (IOP) in hemifacial spasm (HFS) patients. IOP assessment using a Goldmann applanation tonometer (GAT) is often compromised by eyelid spasms. This study aimed to assess the effect of HFS on IOP measurements using the transpalpebral tonometer Diaton® before and after treatment with botulinum toxin type A (BTX-A) and compared Diaton® and GAT measurements after treatment with BTX-A. METHODS: IOP measurements were obtained with Diaton® in 27 patients with moderate-to-severe HFS before and after treatment with BTX-A. After treatment, the IOP was also measured using GAT and the results were compared with the ones measured with a Diaton®. The patients underwent automated perimetry, OCT, and pachymetry for screening to glaucoma. RESULTS: Mean IOP with Diaton® was 11 ± 3.42 mmHg before treatment in the affected eye and 9 ± 2.98 mmHg in the contralateral eye. This difference was statistically significant (P = 0.012). However, after treatment with BTX-A, no interocular difference was found in IOP obtained with Diaton® (P = 0.204) or GAT (P = 0.971). Comparison between GAT and Diaton® measurements showed no significant differences after BTX-A treatment between the affected (P = 0.212) and contralateral eye (P = 0.971). CONCLUSIONS: A significant reduction in IOP measurements on the affected side of HFS patients was observed after treatment with BTX-A, demonstrating that eyelid spasms may increase the IOP. No significant difference was observed between Diaton® and GAT measurements after the application of BTX-A. No differences were found in automated perimetry, OCT, and CCT when comparing affected eyes with contralateral eyes.

Relationship Between Intraocular Pressure and Age: A Population-Based Study in Nepal.

PRCIS: Intraocular pressure (IOP) decreased with age in a population-based study in Nepal, from a mean of 14.1 mm Hg among those 60-64 years old to 13.0 mm Hg among those 80 years old or older. PURPOSE: Few studies have assessed the distribution of IOP from the Indian subcontinent, despite its large population and high burden of glaucoma. The objective of this study was to assess the distribution of IOP measurements from adults living in a lowland region of Nepal. METHODS: In a population-based cross-sectional study, all individuals aged 60 years and older from an area of lowland Nepal were invited for an IOP assessment with a rebound tonometer. RESULTS: Of 160 communities (28,672 people aged ≥60 y) enrolled, 79 (13,808 people aged ≥60 y) were randomly selected for IOP testing. Of those eligible, 10,017 (72.5%) individuals underwent tonometry. Mean IOP decreased monotonically over 5-year age groups, from 14.1 mm Hg (SD: 3.6) among those aged 60-64 years to 13.0 mm Hg (SD: 4.2) among those 80 years or older. The 97.5th percentile IOP measurement was 21.0 mm Hg for all age groups. In adjusted analyses, younger age, self-reported diabetes, and higher population density were each associated with higher IOP, and self-reported cataract surgery was associated with lower IOP. CONCLUSIONS: Mean IOP was lower among older individuals in Nepal, consistent with many studies from East Asia and in contrast to many studies from western populations. These results suggest that ethnic background might be a consideration when diagnosing ocular hypertension.

Current Innovations in Intraocular Pressure Monitoring Biosensors for Diagnosis and Treatment of Glaucoma-Novel Strategies and Future Perspectives.

Biosensors are devices that quantify biologically significant information required for diverse applications, such as disease diagnosis, food safety, drug discovery and detection of environmental pollutants. Recent advancements in microfluidics, nanotechnology and electronics have led to the development of novel implantable and wearable biosensors for the expedient monitoring of diseases such as diabetes, glaucoma and cancer. Glaucoma is an ocular disease which ranks as the second leading cause for loss of vision. It is characterized by the increase in intraocular pressure (IOP) in human eyes, which results in irreversible blindness. Currently, the reduction of IOP is the only treatment used to manage glaucoma. However, the success rate of medicines used to treat glaucoma is quite minimal due to their curbed bioavailability and reduced therapeutic efficacy. The drugs must pass through various barriers to reach the intraocular space, which in turn serves as a major challenge in glaucoma treatment. Rapid progress has been observed in nano-drug delivery systems for the early diagnosis and prompt therapy of ocular diseases. This review gives a deep insight into the current advancements in the field of nanotechnology for detecting and treating glaucoma, as well as for the continuous monitoring of IOP. Various nanotechnology-based achievements, such as nanoparticle/nanofiber-based contact lenses and biosensors that can efficiently monitor IOP for the efficient detection of glaucoma, are also discussed.

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).

Contact Lens Sensor with Anti-jamming Capability and High Sensitivity for Intraocular Pressure Monitoring.

Contact lens sensors provide a noninvasive approach for intraocular pressure (IOP) monitoring in patients with glaucoma. Accurate measurement of this imperceptible pressure variation requires highly sensitive sensors in the absence of simultaneously amplifying IOP signal and blinking-induced noise. However, current noise-reduction methods rely on external filter circuits, which thicken contact lenses and reduce signal quality. Here, we introduce a contact lens strain sensor with an anti-jamming ability by utilizing a self-lubricating layer to reduce the coefficient of friction (COF) to remove the interference from the tangential force. The sensor achieves exceptionally high sensitivity due to the strain concentration layout and the confined occurrence of sympatric microcracks. The animal tests prove our lens can accurately detect IOP safely and reliably.

Do ophthalmology residents know how to check the calibration of a Goldmann applanation tonometer?

PURPOSE: The purpose of this observational study was to determine whether ophthalmology residents know how to check Goldmann applanation tonometer (GAT) calibration. METHODS: The step-by-step technique for checking the calibration of a GAT was taken from the manufacturer's manual and developed into a mark sheet. Ophthalmology residents in years 2-8 of training from 11 hospitals were individually observed and assessed checking calibration of a GAT. Participation was voluntary. Contact between participants was minimised to prevent communication about the study. RESULTS: Sixty-eight per cent (n = 30) of eligible ophthalmology residents (years 2-8) from 11 hospitals (three teaching hospitals and eight local general hospitals) were observed checking GAT calibration. Only 33% (n = 10; 95% CI: 16-50%) of ophthalmology residents were able to correctly check GAT calibration. Those participants who were previously taught (p = 0.046) or assessed (p = 0.015) were more likely to be successful in GAT calibration. CONCLUSIONS: Most ophthalmology residents were unable to correctly check GAT calibration. Although better than previously published results, this observational study shows that further training and assessment is required for ophthalmology residents to learn the technique of checking GAT calibration.

Prediction model of contact forces and IOP during digital palpation of porcine eyes.

Frequent intraocular pressure (IOP) measurements are desirable in the diagnosis and management of glaucoma. Most current tonometers utilize some form of corneal deformation to estimate the IOP, since trans-scleral tonometry suffers from loss of sensitivity. Tran-scleral and trans-palpebral tonometry, however, offer a pathway towards a non-invasive home tonometry. This article presents a mathematical model capturing the relationship between the IOP and the displacements imposed onto the sclera by externally applied forces. Similar to manual digital palpation tonometry, trans-scleral mechanical palpation makes use of two force probes that are advanced in a specific order and distance. Data from the applied forces and displacements, along with concurrent measurements of IOP is used to produce a phenomenological mathematical model. The experiments were carried out on enucleated porcine eyes. Two models are presented. Model 1 predicts IOP vs forces and displacements, while Model 2 predicts the baseline IOP (prior to applying the forces) as a function of the measured forces and displacements. The proposed models result in IOP errors of 1.65 mmHG and 0.82 mmHg, respectively. Model parameters were extracted using least-squares-based system identification methods. The results show that the proposed models can be used to estimate the baseline IOP with accuracy of ±1 mmHg over a pressure range of 10-35 mmHg, solely from measurement of tactile forces and displacements.

Evaluation of the agreement and reliability of Transpalpebral Tonometers compared with Goldmann Applanation Tonometer - A systematic Review and Meta-Analysis Protocol.

In 2020, the global prevalence of glaucoma was estimated to be 76 million and it was projected to increase to 111.8 million by 2040. Accurate intraocular pressure (IOP) measurement is imperative in glaucoma management since it is the only modifiable risk factor. Numerous studies have compared the reliability of IOP measured using transpalpebral tonometers and Goldmann applanation tonometry (GAT). This systematic review and meta-analysis aims to update the existing literature with a reliability and agreement comparison of transpalpebral tonometers against the gold standard GAT for IOP measurement among individuals presenting for ophthalmic examinations. The data collection will be performed using a predefined search strategy through electronic databases. Prospective methods-comparison studies published between January 2000 and September 2022 will be included. Studies will be deemed eligible if they report empirical findings on the agreement between transpalpebral tonometry and Goldmann applanation tonometry. The standard deviation and limits of agreement between each study and their pooled estimate along with weights and percentage of error will be reported using a forest plot. Cochrane's Q test and the I2 statistic will be used to assess heterogeneity, and the publication bias will be investigated using a funnel plot, Begg's and Egger's tests. The review results will provide additional evidence on the reliability of transpalpebral tonometers that, in turn, could possibly assist practitioners to make informed decision about using it as a screening or diagnostic device for clinical practice, outreach camps, or home-based screening. Institutional Ethics Committee registration number: RET202200390. PROSPERO Registration Number: CRD42022321693.

Assessment of intraocular pressure measurement between Goldman applanation tonometer, rebound tonometer, non-contact tonometer, and its correlation with central corneal thickness.

Purpose: To compare readings of intraocular pressure (IOP) taken with the Goldmann applanation tonometer (GAT), the non-contact tonometer (NCT), and the rebound tonometer (RBT), and to compare their correlation with central corneal thickness (CCT). Methods: This was a prospective, cross-sectional, observational study to which patients above 18 years of age were enrolled. A total of 400 eyes of 200 non-glaucomatous patients underwent IOP recordings using the GAT, NCT, and RBT, and CCT was also noted. Informed consent of the patients was taken. The IOP readings taken via the three methods were compared and correlated with CCT. Paired t test was used to compare the two devices. Simple and multivariate linear regression analyses were used to study the relationship between factors. A P value less than 0.05 was considered significant. Correlation was determined using the Pearson correlation coefficient, and a Bland-Altman graph was plotted. Results: Mean IOP measured by the NCT was 15.65 ± 2.80 mmHg, by the RBT was 14.23 ± 3.05 mmHg, and by the GAT was 14.69 ± 2.97 mmHg. The mean CCT was 510.61 ± 33.83 microns. The difference between mean IOP recorded by the NCT and that by the RBT was 1.41 ± 2.39 mmHg, between the NCT and GAT was 0.95 ± 2.03 mmHg, and between the GAT and RBT was 0.45 ± 2.22 mmHg. The difference between the IOP values was statistically significant (P < 0.005). All tonometers showed a statistically significant correlation with CCT, but it was observed that the NCT had a stronger correlation (0.4037). Conclusion: The IOP readings taken by all the three methods were comparable; however, RBT values were closer to GAT values. CCT did influence the IOP values, and this should be kept in mind while evaluating.