Accuracy Of Intraocular Pressure Measurements Research Articles

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.

Ocular Biomechanics and Glaucoma.

Biomechanics is a branch of biophysics that deals with mechanics applied to biology. Corneal biomechanics have an important role in managing patients with glaucoma. While evidence suggests that patients with thin and stiffer corneas have a higher risk of developing glaucoma, it also influences the accurate measurement of intraocular pressure. We reviewed the pertinent literature to help increase our understanding of the biomechanics of the cornea and other ocular structures and how they can help optimize clinical and surgical treatments, taking into consideration individual variabilities, improve the diagnosis of suspected patients, and help monitor the response to treatment.

Early influence of endotamponade on corneal biomechanical parameters, central corneal thickness and accuracy of intraocular pressure measurement

To define the influence of air, SF6 gas and silicon oil 1000cs tamponade injection and oil tamponade removal on corneal biomechanics, central corneal thickness and intraocular pressure. 77 eyes referred to vitrectomy were divided into 4 groups: 19 to air tamponade, 21 to SF6 tamponade, 19 to oil tamponade, 18 to oil tamponade removal. Pre- and postoperative corneal hysteresis, corneal resistance factor, corneal thickness, Goldman intraocular pressure (GAT) and corneal compensated intraocular pressure (IOPcc) were analysed. GAT and IOPcc did not change after the air or SF6 tamponade. The oil tamponade injection caused increase in GAT and IOPcc, while the oil removal caused reduction in those parameters. In all groups, preoperative and postoperative values of GAT and IOPcc did not differ. There was no change in corneal thickness and biomechanics after air, SF6 or oil tamponade while after removal of oil those parameters are decreased. The air, SF6 and oil tamponade does not change the corneal thickness and corneal biomechanics. The removal of oil causes decrease in corneal thickness and biomechanics which can lead to bias in intraocular pressure measurement. GAT and IOPcc did not differ in eyes pre- and post-vitrectomy, being similarly reliable measure.

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.

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.

Accuracy of Intraocular Pressure Measurements of Eyes with Therapeutic Contact Lenses after Vitrectomy

Purpose: To evaluate the accuracy of intraocular pressure (IOP) measurements obtained by a rebound and non-contact tonometer in eyes with a therapeutic contact lens (CL) after vitrectomy.Methods: In 60 eyes of 60 patients who underwent vitrectomy for vitreoretinal disease, IOP was measured using a rebound tonometer (iCare ic200®; IOPRT) and non-contact computerized air puff tonometer (CT-80, IOPNCT), before and after wearing a CL (Purevision2®, +0.0 diopter). The mean IOP of three consecutive measurements were analyzed, and a comparative analysis with IOP measured by a Goldman applanation tonometer (IOPGAT) was performed.Results: The mean IOPRT without and with the CL was 12.55 ± 5.43 and 13.12 ± 5.13 mmHg, respectively, showing a statistically significant difference (p = 0.02) and strong positive correlation (r = 0.90, p < 0.001). The mean IOPNCT with and without the CL was 12.18 ± 3.24 and 12.17 ± 3.14 mmHg, showing no statistically significant difference (p = 0.17). The consistency with IOPGAT (12.57 ± 5.22 mmHg) was highest in IOPRT without the CL, followed by IOPRT with the CL, IOPNCT without the CL, and IOPNCT with the CL (intraclass correlation coefficients = 0.955, 0.945, 0.856, and 0.850, respectively). In addition, the rebound tonometer successfully measured IOP, regardless of whether the CL was worn; however, the non-contact tonometer failed to measure IOP in seven eyes without the CL and nine with the CL. No difference was observed according to intraocular tamponade type.Conclusions: A rebound tonometer can be used as an alternative IOL measuring method in eyes for which it is difficult to use a Goldman applanation tonometer due to the postoperative presence of a therapeutic CL.

A comparison of goldmann applanation tonometry and rebound tonometry measurements among patients attending a glaucoma clinic in Southwest Nigeria.

The accurate measurement of intraocular pressure (IOP) is a fundamental basic examination in daily ophthalmic practice and is important in managing many ophthalmic diseases and conditions such as glaucoma, uveitis, and following trauma. Accurate measurement of IOP is particularly important in glaucoma because the intraocular pressure is the most important modifiable risk factor in its management. To compare intraocular pressure (IOP) measurements obtained with the Goldmann applanation (GAT) tonometer to intraocular pressure measurements obtained with the iCare rebound tonometer (RBT) and evaluate the suitability of the iCare tonometer for routine clinical use among adult patients attending a glaucoma clinic in Southwest, Nigeria. The study was a comparative cross-sectional study. A total of 132 eyes of 132 patients were recruited for the study. Three consecutive IOP measurements were obtained with each of the instruments by the same observer. A difference in IOP of ± 3 mmHg between the two instruments was considered clinically significant in this study. The mean IOP measurement from GAT was 15.18 mmHg (±4.26 mmHg) and 16.32 mmHg (±4.48 mmHg) from RBT. The mean central cornea thickness was 520.66 μm (±33.34). Pearson's correlation (r = 0.84) revealed a strong statistically significant correlation between GAT and RBT measurements and paired student t-test revealed a statistically significant difference in the means of IOP obtained by the GAT and RBT. There was a tendency for RBT to yield higher IOP measurements. The intraocular pressure measurements obtained with iCare RBT and GAT though strongly correlated, showed statistically significant differences in the means. The impact of central cornea thickness on measurements obtained by GAT and RBT was statistically insignificant. The iCare rebound tonometer, cannot replace GAT for routine use in the glaucoma clinic.

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 & 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& Intraocular pressures and retinal changes among subgroups. Results. Demographic characteristics of study and control groups were similar (P>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= > 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.

Comparison of Intraocular Pressure before and after Laser in Situ Keratomileusis Measured with Applanation Tonometry, Non Contact Tonometry and Rebound Tonometry

Abstract Background Measurement of intraocular pressure (IOP) plays a central role throughout ophthalmology. It is part of routine ophthalmologic examinations and important in the management and follow-up of patients with glaucoma. While elevated IOP remains the most important risk factor for development and progression of open angle glaucoma, at least half of the population diagnosed with open angle glaucoma is asymptomatic. Objectives The aim of our study is to compare the accuracy of intraocular pressure measurement before and after Laser in situ keratomeulsis (LASIK) surgery using three different types of Tonometers: Goldmann Applanation tonometry (GAT), Non contact tonometry (NCT) and Rebound tonometry (I care), considering the change in the central corneal thickness (CCT). Patients and Methods In this study Eighty eyes of 40 patients with mean age of 27.00±6.00 years were scheduled for LASIK..Central corneal thickness before and after surgery was obtained by Ultrasound (US) pachymetry.IOP values were measured before and after surgery using three different types of Tonometers: Goldmann Applanation tonometry, Non contact tonometry and Rebound tonometry. Results The results revealed that lower post-operative IOP measurements using all techniques. The least affected technique was Non –contact with IOP change 16%, followed by GAT with IOP change 18%, and finally Rebound with IOP change 19 %, respectively. The percentage of change in CCT between pre- and post- LASIK surgery measured with the Ultrasound pachymetry was statistically highly significant. There was a clinical significant correlation between Percentage of tissue ablation (PTA) and IOP change for GAT, NCT and rebound tonometry. Also, there was a significant correlation between Residual stromal bed (RSB) and IOP change for GAT and NCT. There was no clinical significant correlation between Ablation depth (AD) and percentage of change of IOP measurements pre and post LASIK, except for IOP measured with GAT when AD < 40.00 µm. Conclusion Refractive surgery causes significant lowering of IOP as measured using Goldmann applanation tonometry, non contact tonometry and rebound tonometry. The least affected tonometry post LASIK is non contact tonometry. The reduction was correlated to the percentage of tissue ablated. The ideal method to measure IOP in post-LASIK patients would be a device that is free of corneal factors.

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.

Effect of airway device and depth of anesthesia on intra-ocular pressure measurement during general anesthesia in children: A randomized controlled trial.

Background and Aims:Accurate measurement of intraocular pressure (IOP) under anaesthesia is essential for diagnosis and further management of pediatric glaucoma patients. However, depth of anaesthesia and use of airway device like laryngeal mask airway (LMA) or endotracheal tube can influence IOP values measured. We planned this study to compare change of IOP with facemask or LMA. Change of IOP at varying depth of anaesthesia was also assessed.Material and Methods:After Institutional ethical clearance and informed parental consent, 89 children of glaucoma aged 0-12 years were included in this prospective randomized controlled trial. The children were randomized to facemask (Group M) and LMA (Group L). Sevoflurane was the sole general anaesthetic used in both the groups and IOP were recorded after induction, at BIS 40-60, after LMA insertion (Group L), at BIS 60-80 and BIS more than 80.Results:The IOP values did not differ significantly between the groups at BIS 40-60 and at BIS 60-80. Moreover, pre and post LMA insertion IOP values were also comparable in Gr L (p = 0.11). However, significant increase in IOP values were observed with increasing BIS values within each group. The mean IOP in Group M at BIS 40-60 was 13.41 ± 4.04 as compared to 14.18 ± 3.64 at BIS 60-80 (p = 0.003). There was a similar pattern observed in Group L, where mean IOP at BIS 40-60 & BIS 60-80 was 14.13 ± 4.90 and 15.52 ± 4.57 respectively (p < 0.001).Conclusion:Either facemask or classic LMA can be safely used as per anaesthesiologist's preference without any significant effect on IOP. BIS monitoring may be used during IOP measurement in paediatric glaucoma suspects for accurate assessment of IOP.

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.

Highly Transparent and Sensitive Graphene Sensors for Continuous and Non-invasive Intraocular Pressure Monitoring.

Intraocular pressure (IOP) is the prime indicator for the diagnosis and treatment of glaucoma. IOP has circadian rhythm changes and is dependent on body gestures; therefore, a single measurement in the clinic can be misleading for diagnosis. Herein, few-layer graphene is utilized to develop non-invasive sensors with high transparency, sensitivity, linearity, and biocompatibility for 24 h continuous IOP monitoring. The graphene Wheatstone bridge consisting of two strain gauges and two compensating resistors is designed to improve the sensitivity and accuracy of IOP measurement. Testing results on a silicone eyeball indicate that the output voltage of the sensor is proportional to the IOP fluctuation. Under the various ranges and speeds of IOP fluctuation, the sensor exhibits excellent performance of dynamic cycles and step responses with an average sensitivity of 150 μV/mmHg. With the linear relationship, the average relative error between the calibrated IOP and the standard pressure is maintained at about 5%. More than 100 cycles and interval time measurements illustrate that the sensor possesses significant stability, durability, and reliability. Furthermore, a wireless system is designed for the sensor to realize IOP monitoring using a mobile phone. This sensor, with the average transparency of 85% and its ease of fabrication, as well as its portability for continuous IOP monitoring, brings new promise to the diagnosis and treatment of glaucoma.

A new method for detecting the outer corneal contour in images from an ultra-fast Scheimpflug camera

BackgroundThe Corvis® ST tonometer is an innovative device which, by combining a classic non-contact tonometer with an ultra-fast Scheimpflug camera, provides a number of parameters allowing for the assessment of corneal biomechanics. The acquired biomechanical parameters improve medical diagnosis of selected eye diseases. One of the key elements in biomechanical measurements is the correct corneal contour detection, which is the basis for further calculations. The presented study deals with the problem of outer corneal edge detection based on a series of images from the afore-mentioned device. Corneal contour detection is the first and extremely important stage in the acquisition and analysis of corneal dynamic parameters.ResultA total of 15,400 images from the Corvis® ST tonometer acquired from 110 patients undergoing routine ophthalmologic examinations were analysed. A method of outer corneal edge detection on the basis of a series of images from the Corvis® ST was proposed. The method was compared with known and commonly used edge detectors: Sobel, Roberts, and Canny operators, as well as others, known from the literature. The analysis was carried out in MATLAB® version 9.0.0.341360 (R2016a) with the Image Processing Toolbox (version 9.4) and the Neural Network Toolbox (version 9.0). The method presented in this paper provided the smallest values of the mean error (0.16%), stability (standard deviation 0.19%) and resistance to noise, characteristic for Corvis® ST tonometry tests, compared to the methods known from the literature. The errors were 5.78 ± 9.19%, 3.43 ± 6.21%, and 1.26 ± 3.11% for the Roberts, Sobel, and Canny methods, respectively.ConclusionsThe proposed new method for detecting the outer corneal contour increases the accuracy of intraocular pressure measurements. It can be used to analyse dynamic parameters of the cornea.

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.

Whether lowering intraocular pressure is needed for thyroid associated ophthalmopathy with intraocular hypertension

Patients with thyroid associated ophthalmopathy often have elevated intraocular pressure. Patients and doctors are often confused about whether intraocular hypertension in thyroid associated ophthalmopathy needs to be lowered. There are several theories on the possible causes of this kind of increased intraocular pressure: restriction and compression of the globe by fibrotic and enlarged rectus muscles, increased episcleral venous pressure resulting from orbital congestion and venous outflow obstruction, and increased resistance to trabecular outflow. In addition, the patient's eye position and the device for measuring intraocular pressure also have great impacts on the accuracy of intraocular pressure measurement. At the same time, there are very few patients with thyroid associated ophthalmopathy combined with primary glaucoma. Therefore, whether patients with elevated intraocular pressure need to be treated depends on the specific clinical manifestations of the thyroid associated ophthalmopathy. Intraocular pressure of most patients can be lowered by active treatment for thyroid associated ophthalmopathy; antiglaucoma medical therapy may be necessary for patients whose intraocular pressure cannot be lowered; only very few cases of glaucoma require antiglaucoma drugs or surgery. (Chin J Ophthalmol, 2019, 55:811-813).

Accuracy of intraocular pressure measurements between non-contact tonometer and ICare rebound tonometer

Accuracy of intraocular pressure measurements between non-contact tonometer and ICare rebound tonometer

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.

Changes in Corneal Biomechanical Properties After Descemet Membrane Endothelial Keratoplasty.

To evaluate the course of corneal biomechanical properties (corneal hysteresis and corneal resistance factor) after Descemet membrane endothelial keratoplasty (DMEK) in patients with Fuchs endothelial dystrophy (FECD). In this prospective study, we consecutively included 49 patients with FECD with an indication for DMEK. Central corneal thickness, measured using the Oculus Pentacam, and corneal hysteresis (CH) and corneal resistance factor (CRF), both measured using the Reichert Ocular Response Analyzer, were examined preoperatively, 3 months, and 6 months after DMEK. CH was significantly increased 6 months postoperatively (8.66 ± 2.50 mm Hg) compared with preoperative baseline (7.43 ± 1.56 mm Hg). Preoperative CRF (7.89 ± 1.68 mm Hg) increased significantly 6 months after DMEK (8.49 ± 1.71 mm Hg). Preoperative central corneal thickness showed a significant decrease from 629 ± 58 μm to 550 ± 40 μm after 3 months and 535 ± 40 μm after 6 months postoperatively. DMEK affects both measured corneal biomechanical properties in patients with FECD: CH and CRF. This has to be taken into account for the accuracy of intraocular pressure measurements.