Accurate Intraocular Pressure Research Articles

Agreement of tonometer for measuring intraocular pressure in Wistar rats: a systematic review

Glaucoma is the most common cause of irreversible blindness in the world. It is associated with elevated intraocular pressure (IOP). Fluctuations in tonometer readings have implications for glaucoma research, where accurate IOP measurements are vital for evaluating disease progression and treatment efficacy. Researchers should carefully select the appropriate tonometer and consider biases associated with different tonometers. Validation against standard measurements can improve IOP measurement accuracy in rat models. In conclusion, this systematic review will emphasize on the importance of selecting the appropriate tonometer for IOP measurement in rat models, considering potential biases and their implications for glaucoma research. Accurate and consistent IOP measurement in rat models is crucial for understanding glaucoma pathophysiology and developing effective treatments. This systematic review aims to assess agreement among tonometers used for measuring IOP in Wistar rat models primarily focusing on TonoLab, TonoVet, and Tono-pen. The review was conducted using PRISMA guidelines. Two articles were included for qualitative synthesis. The studies compared manometric IOP with TonoLab, rebound tonometer, and Tono-pen XL readings. It was observed that TonoLab consistently underestimated IOP, while Tono-pen XL tended to overestimate IOP compared to manometric measurements. The study’s findings will help researchers in making decisions about tonometer selection, leading to more reliable outcomes in glaucoma research using rat models. Further research, specifically RCT’s (randomized controlled trial) is needed to confirm the results and enhance IOP measurement precision in rat models.

Temperature Self-Compensating Intelligent Wireless Measuring Contact Lens for Quantitative Intraocular Pressure Monitoring.

Flexible bioelectronic devices that can perform real-time and accurate intraocular pressure (IOP) monitoring in both clinical and home settings hold significant implications for the diagnosis and treatment of glaucoma, yet they face challenges due to the open physiological environment of the ocular. Herein, we develop an intelligent wireless measuring contact lens (WMCL) incorporating a dual inductor-capacitor-resistor (LCR) resonant system to achieve temperature self-compensation for quantitative IOP monitoring in different application environments. The WMCL utilizes a compact circuitry design, which enables the integration of low-frequency and high-frequency resonators within a single layer of a sensing circuit without causing visual impairment. Mechanically guided microscale 3D encapsulation strategy combined with flexible circuit printing techniques achieves the surface-adaptive fabrication of the WMCL. The specific design of frequency separation imparts distinct temperature response characteristics to the dual resonators, and the linear combination of the dual resonators can eliminate the impact of temperature variations on measurement accuracy. The WMCL demonstrates outstanding sensitivity and linearity in monitoring the IOP of porcine eyes in vitro while maintaining satisfactory measurement accuracy even with internal temperature variations exceeding 10 °C. Overcoming the impact of temperature variations on IOP monitoring from the system level, the WMCL showcases immense potential as the next generation of all-weather IOP monitoring devices.

Remote and low-cost intraocular pressure monitoring by deep learning of speckle patterns.

Glaucoma, a leading cause of global blindness, disproportionately affects low-income regions due to expensive diagnostic methods. Affordable intraocular pressure (IOP) measurement is crucial for early detection, especially in low- and middle-income countries. We developed a remote photonic IOP biomonitoring method by deep learning of the speckle patterns reflected from an eye sclera stimulated by a sound source. We aimed to achieve precise IOP measurements. IOP was artificially raised in 24 pig eyeballs, considered similar to human eyes, to apply our biomonitoring method. By deep learning of the speckle pattern videos, we analyzed the data for accurate IOP determination. Our method demonstrated the possibility of high-precision IOP measurements. Deep learning effectively analyzed the speckle patterns, enabling accurate IOP determination, with the potential for global use. The novel, affordable, and accurate remote photonic IOP biomonitoring method for glaucoma diagnosis, tested on pig eyes, shows promising results. Leveraging deep learning and speckle pattern analysis, together with the development of a prototype for human eyes testing, could enhance diagnosis and management, particularly in resource-constrained settings worldwide.

Real-time in vivo monitoring of intraocular pressure distribution in the anterior chamber and vitreous chamber for diagnosis of glaucoma.

Glaucoma causes irreversible vision loss due to optic nerve damage and retinal cell degeneration. Since high intraocular pressure (IOP) is a major risk factor for glaucoma development, accurate IOP measurement is crucial, especially intravitreal IOP affecting the optical nerve and cells. However, conventional methods have limits in selectively and directly detecting local retina pressure. Here, we present continuous measurements of local IOP values in the anterior chamber and vitreous chamber of living animals using minimally invasive probes with pressure-sensitive transistors. After inducing glaucoma in animal models, we compared the local IOP distribution between normal and glaucomatous eyes. We also compared IOP values detected in the cornea using tonometry measurements. Our findings revealed that glaucoma induced higher IOP in the vitreous chamber than in the anterior chamber, indicating that measuring IOP in the vitreous chamber is key to the glaucoma model. This progress offers future directions for diagnosis and treatment of glaucoma.

Assessing Agreement and Variability Among Alternative Devices for Intraocular Pressure Measurement: A Comparative Study.

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.

Development and validation of an intuitive biomechanics-based method for intraocular pressure measurement: a modal analysis approach

BackgroundCurrent intraocular pressure (IOP) measurements based on non-contact tonometry are derived from statistics-driven equations and lack biomechanical significance, which often leads to under-estimation in post-refractive surgery cornea. This study aims to introduce and validate modal analysis-derived intraocular pressure (mIOP) as a novel method generated through Legendre-based modal decomposition of the anterior corneal contour; it provides an accurate and intuitive IOP measurement from an energy-based perspective.MethodsThis retrospective study included 680 patients. Healthy participants were divided into reference (n = 385) and validation (n = 142) datasets, and the others underwent either femtosecond-assisted laser in situ keratomileusis (FS-LASIK, n = 58) or transepithelial photorefractive keratectomy (TPRK, n = 55). Corneal curvature of the right eyes was extracted from raw serial cross-sectional images of the cornea generated by Corvis ST, a noncontact tonometer with a high-speed Scheimpflug-camera. Legendre expansion was then applied to the corneal curvature to obtain the modal profiles (i.e., temporal changes of the coefficient for each basis polynomial [modes]). Using the reference dataset, feature selection on the modal profiles generated a final mIOP model consisting of a single parameter: total area under curve (frames 1–140) divided by the area under curve of the rising phase (frames 24–40) in the fourth mode, i.e. the M4 ratio. Validation was performed in both the healthy validation and postoperative datasets. IOP-Corvis, pachymetry-corrected IOP, biomechanically corrected IOP, and mIOP values were compared. For the FS-LASIK and TPRK groups, pairwise postoperative IOP changes were analyzed through repeated measures analysis of variance, and agreement was examined through Bland–Altman analysis. Using a finite element analysis based three-dimensional model of the human cornea, we further compared the M4 ratio with the true intraocular pressure within the physiological range.ResultsThe M4 ratio-based mIOP demonstrated weak to negligible association with age, radius of corneal curvature, and central corneal thickness (CCT) in all validation analyses, and performed comparably with biomechanically corrected IOP (bIOP) in the refractive surgery groups. Both remained nearly constant postoperatively and were not influenced by CCT changes. Additionally, M4 ratio accurately represented true intraocular pressure in the in silico model.ConclusionsmIOP is a reliable IOP measurement in healthy and postrefractive surgery populations. This energy-based, ratio-derived approach effectively filters out pathological, rotational, misaligned movements and serves as an interpatient self-calibration index. Modal analysis of corneal deformation dynamics provides novel insights into regional corneal responses against pressure loading.

Commentary: Decoding the intraocular pressure conundrum surrounding the core of COR.

The concept of intraocular pressure (IOP) gained popularity around the 19th century. It was during that time when Albrecht von Graefe developed the first IOP measuring instrument, the Maklakoff applanation tonometer, in 1865. Somewhere around the 10th century, it started off as an assessment of the firmness of the eyeball.[1] Currently, we possess cutting-edge technology like dynamic contour tonometry to provide in vivo IOP measurements. IOP control is an important component of glaucoma management, and therein lies the importance of accurate IOP measurement and documentation. Consensual Ophthalmotonic Reaction The concept of consensual ophthalmotonic reaction (COR) has been a point of debate for several decades now.[2] There have always been claims for and against this phenomenon. Though inconclusive, this theory needs to be taken into account in view of the sensitive nature of the disease. The accompanying article represents the largest evaluation to date of the untreated fellow eye response after unilateral trabeculectomy. The author’s suggestion raises the possibility of a real risk of IOP increase in the fellow eye following ipsilateral glaucoma surgery.[3] Nearly a third of patients needed an intervention to control IOP in the entire study population. COR – The Gray Area Surrounding the How and Why The authors of the accompanying article report that contralateral eye IOP was increased following ipsilateral glaucoma surgery. However, some works of literature have reported conflicting results and noted a drop in IOP, while some agreed.[4–7] The pathophysiology for this increase or decrease of IOP following ipsilateral glaucoma surgery is unclear and not well known. Possible Hypothesis and Postulations Surrounding COR Several hypotheses have been made to explain COR, but all are not entirely accepted. Some suggest that topical medication either works on the fellow eye via the bloodstream or acts centrally on IOP control mechanisms after systemic absorption. Smith et al. disproved it with the use of pindolol and stated that the IOP falls after topical and intravenous administration of pindolol.[8] Pindolol treatment is used to help decrease IOP in the contralateral untreated eye, which is unlikely to have resulted from systemic absorption of the drug. This theory can also not explain the COR seen in mechanical alteration of IOP, such as following laser trabeculoplasty and tonography. Leplat hypothesized the existence of a nervous mechanism that causes changes in IOP in one eye to provoke a reflex alteration in pressure in the contralateral eye.[9] Moreover, the Collaborative Initial Glaucoma Treatment Study (CIGTS) showed a moderate drop in IOP in the contralateral eye, but the findings were not statistically significant and were found to be transient. Hence, it is inferred that this COR does not warrant any clinical management.[10] It is postulated that post-trabeculectomy, the increased IOP in the fellow eye could be due to a reflex increase in aqueous humor production, an effort of the eyes to compensate for the low IOP of the operated eye. The ocular central nervous system (CNS) reflex mechanism would trigger an increase in aqueous production both in the ipsilateral and the contralateral eyes, resulting in a buildup of IOP in the contralateral eye. It is also possible that the IOP fluctuations in the nonsurgical eye are due to changes in the blood flow or circulation to the eye or due to the body’s overall response to the surgery.[4] COR and Minimally Invasive Glaucoma Surgery Though trabeculectomy has been the gold standard for the past few decades, minimally invasive glaucoma surgery (MIGS) is now taking up space in the world of glaucoma. Currently, there is a paucity of data regarding the efficacy of MIGS, but it is a sought-after mode of treatment. So, studies also need to focus on COR in MIGS patients to see if any similar responses are seen in that category. Conclusion Changes in IOP are possible after glaucoma surgery due to a multitude of factors coming into play, suggesting that the fellow eye needs to be carefully monitored after glaucoma surgery in one eye. In many instances, the fellow eye is often the one with useful vision. Failure to recognize and monitor IOP changes carefully may unnecessarily delay treatment and appropriate management of these eyes. In addition, fellow eyes already damaged by glaucomatous processes may be at significant risk of glaucoma progression due to higher IOP levels. Although the evidence for the existence of COR is strengthened, larger studies with more patients in each glaucoma category may shed light on its exact biological role.

Comparison of intraocular pressure readings with Perkins, Tonopen, iCare 200, and iCare Home to manometry in cadaveric eyes.

To compare intraocular pressure (IOP) readings obtained with Perkins tonometry, iCare Home, iCare 200, and Tonopen to IOP readings obtained with the manometer of a perfusion system to assess the accuracy and reproducibility of each method of tonometry at set pressures. The IOP of human cadaveric eyes (n=2) was measured using a manometer inserted into the eye through the optic nerve. IOP measurements were obtained using a Perkins tonometer, iCare Home, iCare 200, and Tonopen. These measurements were compared to set point IOP measurements of a manometer to determine accuracy and reproducibility of each device. Mean IOP readings obtained with the Perkins tonometer compared to manometer readings demonstrated a difference of -1.0±5.0 mm Hg (P=0.45), indicating a lower reading on average than manometery although not significant. Mean IOP difference between iCare 200 and manometer was 5.3±2.2 mm Hg (P<0.0001). Mean difference in IOP between iCare Home and manometer was 3.5±2.4 mm Hg (P=0.0004). Mean IOP difference compared to manometer was 4.6±4.0 mm Hg for the Tonopen (P<0.0001). IOP measurements obtained with the Perkins tonometer demonstrated a standard deviation of 5.0 mm Hg while the Tonopen measurements demonstrated a 4.0 mm Hg standard deviation. In comparison, iCare 200 and iCare Home demonstrated 2.2 and 2.4 mm Hg standard deviation, respectively. Applanation tonometry produces more accurate IOP readings than rebound tonometry or Tonopen, however it demonstrates greater variability than the other forms of tonometry. Rebound tonometry is more reproducible but tends to over-estimate IOP.

Laser vision correction in glaucoma; myths and reality

AbstractLaser vision correction has been a well‐established, rapidly developing, safe and widely used technique for refractive error correction. Nevertheless, there are several drawbacks for its use in specific groups of patients. A classic contraindication has been patients with glaucoma. These include those with diagnosed glaucoma and even glaucoma suspects. The main concern remains the evaluation of the intraocular pressure (IOP) after refractive surgery. Newer technology has been helpful in achieving accurate IOP measurements bypassing to an extend the biomechanical changes and thinning of the cornea induced by laser correction. Use of conversion factors may well be applied. Perioperative care of these patients has also been an issue as corticosteroids drops are used, sometimes for a prolonged period of time potentially causing a rise in IOP. Choosing between superficial techniques and LASIK, the former inducing high intraocular pressure during flap dissection is also a question to be answered. In addition, following up those patients to assess possible glaucoma progression can be challenging. Thorough preoperative assessment is mandatory with functional and anatomical testing of the optic nerve. This is especially important so new glaucoma disease is not missed especially in high myopes. Last but not least patients on glaucoma treatment usually have a compromised ocular surface due to the long‐term effects of topical drops. This fact has to be taken into consideration when deciding to proceed or not with laser refractive surgery. In conclusion the glaucoma patient and the glaucoma suspect are challenging patients regarding the potential laser vision correction. Several factors need to be considered in order to make the correct decision. So, myths andreality are analysed that either defeat or support the argument that under the laser vision correction can be safely performed in carefully selected glaucoma eyes.

A portable applanation tonometer for accurate intraocular pressure measurements

Accurate intraocular pressure (IOP) measurement in a convenient way is critical for the diagnosis and treatment in glaucoma development. In this study, we present a prototype of a portable tonometer by utilizing a new applanation method. The tonometer consists of two components: a capacitive force sensor (CFSen) and a portable displacement platform (PorDP). The capacitance output of CFSen and moving distance of PorDP reflects the force exerted on the eye and the corneal applanate area respectively. A numerical model based on finite element method (FEM) has been developed to analyze the tonometer performance. In addition, the tonometer has been validated on in vitro pig eyes, from which an analytical relationship of IOP, capacitance of CFSen and moving distance of PorDP has been established. Different from the traditional applanation-based tonometer which measures the force and area at single corneal applanate state, our tonometer takes readings at several corneal applanating phases. By considering multiple corneal applanation states, the measurement error of the tonometer is in the range of −0.38 to +0.67 mmHg and the resolution is less than 1 mmHg. We believe this approach provides a technological platform to develop an advanced tonometer for accurate IOP monitoring.

Newer glaucoma surgeries: A review

With sophisticated diagnostic modalities used in glaucoma now-a-days, the demand for more accurate and precise intraocular pressure control is also rising. Glaucoma has seen myriad of treatment modalities including medical, laser and surgical. This article focuses on the newer glaucoma surgeries, viz-a-viz microinvasive glaucoma surgeries (MIGS) that has seen immense experimental and clinical research with favourable results. MIGS works via various mechanisms, by-passing trabecular meshwork by implanting a stent or excising the trabecular tissue, enhancing aqueous outflow through Schlemm’s canal or suprachoroidal space, and shunting the aqueous to the subconjunctival space. In this article we describe each of these procedures with the results on their efficacy and safety.

Changes of Corneal Thickness and Intraocular Pressure in Type II Diabetic Patients

Aims. The purpose of the present paper is to present the results of central corneal thickness &amp; intraocular pressure measurements in diabetic patients with or without retinopathy, and compare the results with non-diabetic control patients. Methods. Total number was 152 patients were 152 eyes The study group was divided into 3 groups as following: 50 non diabetic (control). 50 diabetic type II with no diabetic retinopathy. 52 diabetic type II patient with diabetic retinopathy. Correlation analysis was performed to assess the association between glycosylated hemoglobin levels&amp; Intraocular pressures and retinal changes among subgroups. Results. Demographic characteristics of study and control groups were similar (P&gt;0.05). Mean CCT 553.62 with Std deviation (14.47) in control cases and 622.27 with Std deviation (507.09) in diabetic cases which is more than control however the distinction failed to reach applied math significance were (p value= &gt; 0.05). additionally, CCT and diabetic retinopathy association was significant were CCT in diabetic patients with no retinal changes was 563.96 Std deviation (18.85) and in diabetic patients with retinopathy was 670.45 Std deviation (717.2) and P value = 0.004 (significant). There was significant correlation between increased corneal thickness and intraocular pressure were p-value = 0.002. Conclusions. We found that the central cornea of diabetic patients is thicker when compared with non-diabetic patients. Thicker central cornea associated with diabetes mellitus should be taken into consideration while obtaining accurate intraocular pressure measurements in diabetics.

An Ultrasensitive Contact Lens Sensor Based On Self‐Assembly Graphene For Continuous Intraocular Pressure Monitoring

AbstractElevated intraocular pressure (IOP) is the leading cause of glaucoma. As glaucoma is an irreversible neurological eye disease, it is urgent to realize timely and accurate IOP detection for diagnostic and therapeutic purposes. Here, a contact lens sensor for continuous IOP monitoring using self‐assembly graphene (SAG), is developed. The combination of face‐to‐face water transfer printing and micro‐electromechanical systems technology can realize the batch preparation of such a sensor. The sensor has good light transmittance and temperature stability. It exhibits an ultra‐high IOP sensitivity of 1.0164 mV mm Hg−1 on a silicone eye, and 3.166 mV mm Hg−1 in vitro on the porcine eye with remarkable linearity. The sensitivity of the proposed sensor is high enough to be read by a commercial radio frequency identification read–write system for continuous wireless monitoring of IOP. Furthermore, the as‐prepared sensor can work as normal for 24 h in phosphate buffer saline.

An Intraocular Pressure Measurement Technique Based on Acoustic Radiation Force Using an Ultrasound Transducer: A Feasibility Study.

High intraocular pressure (IOP) is one of the major risk factors for glaucoma, and thus accurate IOP measurements should be performed to diagnose and treat glaucoma early. In this study, a novel technique for measuring the IOP based on acoustic radiation force was proposed, and its potential was experimentally demonstrated. The proposed technique uses the acoustic radiation force to generate axial displacement on the ocular surface while simultaneously measuring the degree of deformation. In order to verify that the ocular displacement induced by the acoustic radiation force is related to the IOP, the experiment was conducted by fabricating a 5 MHz single element transducer and gelatin phantoms with different stiffness values. Our experimental results show that there is a close relationship between the ocular displacement by the acoustic radiation force and the IOP obtained by a commercial tonometer. Therefore, the proposed acoustic radiation force technique can be a promising candidate for measuring the IOP.

Comparison of Central Corneal Thickness and Endothelial Cell Density in Patients with Various Types of Glaucoma and Patients without Glaucoma: A Case-control Study

Introduction: Corneal affection in glaucoma patients is very high due to various risk factors that may lead to unforeseen and unplanned deleterious effects on the cornea leading to vision loss. Accurate intraocular pressure determination requires corneal thickness measurement and uncontrolled intraocular pressures, use of long term medication, intra ocular surgeries including cataract and glaucoma shunt surgeries may cause significant endothelial loss. Therefore, adequate planning and management and follow-up in these patients is required weighing all the long term consequences and emphasis the need for implementing adequate precautions. Aim: To evaluate and compare the Central Corneal Thickness (CCT) and corneal Endothelial Cell Density (ECD) in patients with glaucoma and without glaucoma by specular microscopy. Materials and Methods: A case-control study conducted in a Shekar Eye Hospital, Bengaluru, Karnataka, India, was conducted from August 2016 till April 2018 on a total 182 eyes from 182 patients were evaluated comprising of 91 cases and 91 controls. All participants underwent a detailed ophthalmological examination including slit lamp biomicroscopy, Intraocular Pressure (IOP) measurement, and CCT and ECD measurement by Tomey EM 3000 noncontact specular microscopy. The Statistical analysis was completes using Statistical Package For the Social Sciences (SPSS) 18.0 and R environment version 3.2.2 software’s. Results: The CCT of the glaucoma patients and the controls showed no significant difference (p-value=0.172). The CCT was comparatively thicker in Ocular Hypertension (OHTN) patients and thinner in Normal Tension Glaucoma (NTG) however statistical significance was not established. The mean ECD of controls was 2509.05±298.48 (cells/mm3) and that of cases was 2465.68±392.91 (cells/mm3) (p-value=0.404). The difference in the ECD amongst the glaucoma subgroups was not statistically significant (p-value=0.588). However, a lower ECD were seen in Pseudoexfoliation Glaucoma (PXG) and Primary Angle Closure Glaucoma (PACG) subgroups. Conclusion: No significant difference was found in CCT and endothelial cell in cornea of patients with and without glaucoma. Normal Tension Glaucoma (NTG) patients have comparatively thinner corneas and OHTN patients had thicker corneas. There was no significant correlation established between ECD of Normal corneal vs. Glaucoma and its subgroups.

The influence of diabetes mellitus type 2 on the central corneal thickness

Background/Aim. Complications of diabetes mellitus (DM) in the eye are the leading cause of blindness in the world. Although research on eye complications of DM is mainly focused on retinal damage, changes in the cornea are also associated with DM. Central corneal thickness (CCT) reflects the metabolic status of the cornea and is also affected by DM. Knowledge of CCT changes that occur within DM is important for accurate IOP measurement, diagnosis, and monitoring of patients with glaucoma. The aim of the study was to examine the effect of DM type 2 on the central corneal thickness. Methods. The study was designed as a clinical, cross-sectional, observational study. It consists of 96 patients, divided into two groups. The first group consisted of 49 patients diagnosed with DM type 2. The second group was the control group and consisted of 47 healthy subjects. The DM group was divided into subgroups depending on the status of diabetic retinopathy, the length of DM treatment, and the levels of glycosylated hemoglobin (HbA1C). Results. A statistically significant difference in CCT was observed among DM patients and the control group. Analyzing only DM patients, the highest CCT values were observed in patients who had HbA1C &gt; 7.0%, as well as those who have treated DM for more than 15 years, with a statistically significant difference in relation to the corresponding patient sub-groups (p = 0.002 and p = 0.037, respectively). No statistically significant difference was observed depending on the status of retinopathy. Intraocular pressure (IOP) was statistically significantly higher in patients with DM compared to the control group. Conclusion. Our research demonstrated that the status of retinopathy had no statistically significant influence on CCT. Knowing that the increase in CCT also affects the measured IOP values, this research will be useful in better understanding and control of the patients who have glaucoma in addition to DM type 2.

Simulation of Air Puff Tonometry Test Using Arbitrary Lagrangian-Eulerian (ALE) Deforming Mesh for Corneal Material Characterisation.

Purpose: To improve numerical simulation of the non-contact tonometry test by using arbitrary Lagrangian-Eulerian deforming mesh in the coupling between computational fluid dynamics model of an air jet and finite element model of the human eye. Methods: Computational fluid dynamics model simulated impingement of the air puff and employed Spallart–Allmaras model to capture turbulence of the air jet. The time span of the jet was 30 ms and maximum Reynolds number was, with jet orifice diameter 2.4 mm and impinging distance 11 mm. The model of the human eye was analysed using finite element method with regional hyperelastic material variation and corneal patient-specific topography starting from stress-free configuration. The cornea was free to deform as a response to the air puff using an adaptive deforming mesh at every time step of the solution. Aqueous and vitreous humours were simulated as a fluid cavity filled with incompressible fluid with a density of 1000 kg/m3. Results: Using the adaptive deforming mesh in numerical simulation of the air puff test improved the traditional understanding of how pressure distribution on cornea changes with time of the test. There was a mean decrease in maximum pressure (at corneal apex) of 6.29 ± 2.2% and a development of negative pressure on a peripheral corneal region 2–4 mm away from cornea centre. Conclusions: The study presented an improvement of numerical simulation of the air puff test, which will lead to more accurate intraocular pressure (IOP) and corneal material behaviour estimation. The parametric study showed that pressure of the air puff is different from one model to another, value-wise and distribution-wise, based on cornea biomechanical parameters.

Assessment of intraocular pressure with an artificial model eye mimicking human eye

AbstractPurposeGiven that clinical significance of intraocular pressure (IOP), accurate IOP measurements are crucial. However, measurement of IOP is affected by corneal properties such as thickness, curvature, and biomechanical properties. To derive the quantitative relationship between corneal variables and IOP, it is valuable to create a theoretical model that represents these various properties of the cornea. We have constructed optically transparent artificial eye phantoms, which have closely similar to a human eye. The purpose of this study is to evaluate the clinical applicability of artificial eye by understanding and quantifying the IOP measurement.MethodThe artificial model eye has made of polydimethylsiloxane (PDMS) and its inside is filled with glycerol solution. We developed three different shapes of model eye to reflect the variation in corneal diameter and radius of curvature. Corneal properties (i.e., elasticity) were varied according to the formulation of PDMS (Young’s modulus: 1.7 MPa, 0.7 Mpa, and 0.4 MPa) and corneal thickness was differed by varying the concentration of ethylene glycol. The effect of each variable on the measurement of IOP was examined quantitatively using Goldmann applanation tonometry.ResultsThe IOP of the model eye showed significant positive correlation with corneal thickness in all shapes of model eye (all p &lt; 0.001). The range of the IOP changed according to Young’s modulus of model eye. (12–80 mmHg, 1–80 mmHg, and 1–32 mmHg in model eyes with 1.7 MPa, 0.7 MPa, and 0.4 MPa, respectively). Relationship between the IOP and thickness differed depending on the Young’s modulus of the model eye.ConclusionsThe IOP of the developed artificial eyeball was successfully measured by Goldmann applanation tonometer in a similar manner to a real human eye. This finding suggests that the artificial model eye may have a value as an independent, reproducible sample that allows comparison of tonometers.

Influence of Ocular Dimensional Change on 24-Hour Intraocular Pressure Measurement With Contact Lens Sensor.

We measured changes in the corneal morphology and intraocular pressure (IOP) before and after the use of contact lens sensor (CLS). Then, we investigated whether the ocular dimensional change affected the measured IOP value with CLS. In this prospective study, we examined 112 eyes of glaucoma patients. We measured the IOP fluctuation using a Sensimed Triggerfish CLS. We measured the corneal morphology before and after making measurements using a CLS in anterior segment optic coherent optical coherence tomography and measured the IOP with a Goldmann applanation tonometer. We investigated the correlation between these ocular dimensional changes and the last IOP value with CLS. Measurement with the CLS significantly increased the IOP (P=0.0305), made the corneal thickness (CT) significantly thicker (P<0.001), and increased the steeper meridian (P=0.0026). The last value of IOP-patterns recorded with CLS was significantly correlated with the IOP immediately after the measurement with Goldmann applanation tonometer (P=0.0134), was not significantly correlated with central and peripheral CT. The difference of steeper and flatter curvature between before and after measurement significantly correlated with the last value of IOP-patterns recorded with CLS. Measurement with a CLS affects the IOP, CT, and corneal steeper meridian. From the last value of IOP-related patterns recorded with CLS, CLS could perceive accurate IOP. The change of corneal curvature might affect CLS output values.

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

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