Comparison of ICare and IOPen vs Goldmann applanation tonometry according to international standards 8612 in glaucoma patients

AIM： To compare IOPen and ICare rebound tonometry to Goldmann applanation tonometry（GAT） according to International Standards Organization（ISO） 8612 criteria.METHODS： Totally 191 eyes（n =107 individuals） were included. Criteria of ISO 8612 were fulfilled： 3 clusters of IOP, measured by GAT, were formed. The GAT results were given as mean±standard deviation.RESULTS： GAT（19.7±0.5 mm Hg） showed a significant correlation to ICare（19.8±0.5 mm Hg）（r =0.547, P 〈0.001）and IOPen（19.5 ±0.5 mm Hg）（r =0.526, P 〈0.001）.According to ISO 8612 criteria in all 3 IOP groups the number of outliers（of the 95% limits of agreement）exceeded 5% for ICare and IOPen vs GAT： No.1（n =68）29.4% and 22.1%, No.2（n =62） 35.5% and 37.1%, No.3（n =61） 26.2% and 42.6%, respectively.CONCLUSION： The strict requirements of the ISO 8612 are not fulfilled in a glaucoma collective by ICare and IOPen at present. As long as the Goldmann tonometry is applicable it should be used first of all for reproducible IOP readings. ICare and IOPen tonometry should be considered as an alternative tool, if application of Goldmann tonometry is not possible.

Comparison of Diaton transpalpebral tonometer with applanation tonometry in keratoconus

AIM： To Investigate the added value of using a Diaton transpalpebral tonometer （DT） to measure lOP in keretoconus. Most type of tonometers use corneal applanation or biomechanical resistance to measure intraocular pressure （lOP）; however, these factors can be altered by keratoconus. Specifically, we examined whether DT can detect false-negative low Goldmann applanation tonometry （AT） measurements. METHODS： Patients with keratoconus were recruited from our tertiary academic treatment center. Measurements included AT and DT （in random order） and Scheimpflug imaging. An age- and gender-matched group of control subjects with no history of corneal disease or glaucoma was also recruited. RESULTS： In total, 130 eyes from 66 participants were assessed. In the keratoconus group, mean AT was 11.0± 2.6, mean DT 11±5.5 （P =0.729）and the two measures were correlated significantly（P=0.006, R=0.323）. However, a Bland-Altman plot revealed a wide distribution and poor agreement between both measurements. Previous corneal crosslinking, corneal pachymetry, and Krumeich classification had no effect on measured IOP. CONCLUSION： Measurements obtained using a Diaton tonometer are not affected by corneal biomechanics; however, its poor agreement with Goldmann AT values calls into question the added value of using a Diaton tonometer to measure lOP in keratoconus.

Measurement of Intraocular Pressure after LASIK by Dynamic Contour Tonometry

Changes of corneal properties induced by laser in situ keratomileusis （LASIK） results in low inaccurate intraocular pressure （IOP） readings by Goldmann applanation tonometry （GAT）. Before and after LASIK, the applied value of IOP, measured by dynamic contour tonometry （DCT） in comparison to GAT, was evaluated. Before and 1, 4 weeks after LASIK, the IOP in 30 cases （60 eyes） was measured by GAT and DCT respectively. The obtained results were statistically processed by SPSSll. 5 statistical software. The results showed that central corneal thickness （CCT） could affect GAT measurements but not DCT measurements. The comparison of IOP one and 4 weeks after LASIK revealed that the readings from GAT was separately decreased by 5.00±1.12 and 5.45±1.13 mmHg as compared with those before LASIK, while those from DCT had no significant difference. It was concluded that LASIK-induced changes of CCT could influence the accuracy of GAT measurements, but had no influence on those from DCT. DCT was more beneficial to the measurements of IOP in normal eyes and those subject to LASIK surgery.

Dynamic Contour Tonometry,Tono-Pen XL^(■),and Goldmann Applanation Tonometry in Comparison to Intracameral Intraocular Pressure(IOP)Measurements in Patients with Corneal Pathologies

Purpose: The accuracy of Goldmann applanation tonometry (GAT) has been shown to depend on several biomechanical properties of the cornea. Newer tonometry devices (e.g., the Dynamic Contour Tonometer PASCAL? [DCT] and the Tono-Pen? XL [TP]) have been designed to accurately measure intraocular pressure (IOP) independent of corneal thickness (CCT) and pathology. This study investigates the influence of corneal pathologies on the accuracy of these IOP measuring devices, and compares this accuracy to that of direct intracameral IOP measurement. Methods: 8 eyes of 8 patients suffering from corneal pathologies scheduled for penetrating keratoplasty, and 10 eyes of 10 patients scheduled for cataract surgery (control group) were examined. Before surgery, the anterior chamber was cannulated at the temporal corneal limbus. In a closed system, the intraocular pressure (IOP) was directly set to 10, 20, and 30 mmHg with a manometric water column. Intraocular pressure measurements taken by GAT, DCT, and TP were compared to intracameral measurements obtained by a precision reference pressure sensor. Results: Control group: All three methods showed good agreement with the intracameral readings (mean deviation of all three devices, -0.9 mmHg). Group with corneal pathologies: The TP yielded the most exact IOP values in the group with corneal pathologies when taking all diagnoses into account. The mean deviations from the intracameral IOP measurements were -0.9 mmHg ± 3.2 mmHg (mean ± SD) for TP, -2.9 mmHg ± 3.3 mmHg for GAT, and -5.0 mmHg ± 7.9 mmHg for DCT. For bullous keratopathy, the most exact IOP readings were obtained by the TP (mean deviation -0.2 mmHg ± 3.5 mmHg). The TP and GAT devices underestimated IOP in the patients with Fuchs’ endothelial dystrophy;all 3 devices underestimated adjusted IOP after keratoplasty. DCT showed the greatest deviations from adjusted IOP in the case of non-herpetic scars. In the control group, none of the devices showed a statistically relevant dependency on CCT. Nevertheless, in the group with corneal pathologies, only TP showed no dependency on CCT. Conclusion: Our results suggest that the Tono-Pen XL? is the most accurate measurement device to determine IOP in patients with corneal pathologies, especially in patients suffering from corneal edema (bullous keratopathy). GAT yielded surprisingly exact IOP values in patients suffering from irregular corneal surface. DCT showed a high degree of deviation from the adjusted IOP, and should not be used to determine IOP in corneas with the disorders listed here.

Assessment of intraocular pressure measured by Reichert Ocular Response Analyzer,Goldmann Applanation Tonometry,and Dynamic Contour Tonometry in healthy individuals

AIM: To investigate the accuracy of intraocular pressure (IOP) as measured by a Reichert Ocular Response Analyzer (ORA), as well as the relationship between central corneal thickness (CCT) and IOP as measured by ORA, Goldmann applanation tonometry (GAD, and dynamic contour tonometry (DCT). METHODS: A total of 158 healthy individuals (296 eyes) were chosen randomly for measurement of IOP. After CCT was measured using A-ultrasound (A-US), IOP was measured by ORA, GAT, and DCT devices in a randomized order. The IOP values acquired using each of the three tonometries were compared, and the relationship between CCT and IOP values were analyzed separately. Two IOP values, Goldmann-correlated IOP value (IOPg) and corneal-compensated intraocular pressure (IOPcc), were got using ORA. Three groups were defined according to CCT: 1) thin cornea (CCT<520 mu m); 2) normal-thickness cornea (CCT: 520-580 mu m); and 3), thick cornea (CCT>580 mu m) groups. RESULTS: In normal subjects, IOP measurements were 14.95 2.99mmHg with ORA (IOPg), 15.21+/- 2.77mmHg with ORA(IOPcc),1522+/- 2.77mmHg with GAT,and 15.49+/- 2.56mmHg with DCT. Mean differences were 0.01+/- 2.29mmHg between IOPcc and GAT (P >0.05) and 0.28+/- 2.20mmHg between IOPcc and DC (P >0.05). There was a greater correlation between IOPcc and DCT (r =0.946, P =0.000) than that between IOPcc and GAT (r=0.845, P=0.000). DCT had a significant correlation with GAT (r=0.854, P=0.000). GAT was moderately correlated with CCT (r=0.296, P<0.001), while IOPcc showed a weak but significant correlation with CCT (r =0.155, P =0.007). There was a strong negative correlation between CCT and the difference between IOPcc and GAT (r=-0.803, P=0.000), with every 10 m increase in CCT resulting in an increase in this difference of 0.35mmHg. The thick cornea group (CCT>580 mu m) showed the least significant correlation between IOPcc and GAT (r=0.859, 0.000); while the thin cornea group (CCT< 520 mu m) had the most significant correlation between IOPcc and GAT (r= 0.926, P =0.000). The correlated differences between IOPcc and DCT were not significant in any of the three groups (P>0.05). CONCLUSION: Measurement of IOP by ORA has high repeatability and is largely consistent with GAT measurements. Moreover, the ORA measurements are affected only to a small extent by CCT, and are likely to be much closer to the real IOP value than GAT.

Endothelial impairment evaluation by peripheral arterial tonometry in pediatric endocrinopathies:A narrative review

Endothelial dysfunction(ED)is characterized by an imbalance between vasodilator and vasoconstriction agents.Several pathological conditions clinically diagnosed in childhood and adolescence are characterized by ED and increased risk for early development of microangiopathic and macroangiopathic impairment,in particular type 1 diabetes mellitus(T1DM),T2DM,obesity,metabolic syndromeand pituitary dysfunction associated to various endocrinopathies.More recently insulin resistance following chemotherapy or radiotherapy for tumors,bone marrow transplantation for hematological malignancies(i.e.,cancer survivors),or immunosuppressive treatment for solid organ transplantation has been observed.Assessment of ED by means of non-invasive techniques is the gold standard for early ED detection before clinical manifestation.It is aimed to recognize patients at risk and to avoid the development and progression of more serious illnesses.Reactive hyperemia-peripheral artery tonometry is a noninvasive technique to assess peripheral endothelial function by measuring modifications in digital pulse volume during reactive hyperemia,and represents a non-invasive,reproducible and operator-independent tool able to detect precocious ED.This narrative review aimed to provide an overview of the most important papers regarding ED detection by EndoPat 2000 in children and adolescents with different endocrine diseases.A comprehensive search of English language articles was performed in the MEDLINE database without using other search filters except the publication interval between 2005 and 2020.

Twenty-four hours intraocular pressure in keratoconic eyes assessed by applanation tonometry and Tono-Pen AVIA

AIM:To assess intraocular pressure(IOP)during the daily curve of intraocular pressure(DCPo)in keratoconic eyes and compare Goldmann applanation tonometer(GAT),without and with astigmatism correction(n GAT and c GAT)and Tono-Pen AVIA(TPA)assessment methods.METHODS:Thirty-nine keratoconic eyes of 24 patients were assessed.DCPo was evaluated with five IOP measurements;four were performed with a GAT(n GAT and c GAT),and a Tono-Pen AVIA(TPA)at various times throughout the day.RESULTS:Mean IOP DCPo values(mm Hg)were:n GAT,9.9±2.6;c GAT,11.3±2.6;TPA 12.3±3.1.Mean IOP DCPo differences(mm Hg)and Spearman’s correlation coefficients were as follows:c GATc-n GAT,1.32±1.31,r_(s)=0.879(P<0.01);c GAT-TPA,-1.02±2.08,r_(s)=0.723(P<0.01);and n GAT-TPA,-2.35±2.23,r_(s)=0.730(P<0.01).Bland-Altman analysis for agreement between c GAT-TPA and n GAT-TPA mean IOP DCPo measurements revealed a mean difference of 1.02(95%CI,0.35-1.70)and 2.35(95%CI,1.62-3.07)mm Hg,respectively.Regression analysis yielded the following equation:TPA IOP=5.49+0.775×c GAT-0.015×ACD-0.299×corneal astig matism,which allowed us to infer TPA IOP values from other parameters.CONCLUSION:In keratoconic eyes,IOP peaks of DCPo measurements are identified at 6 a.m.,independent of the tonometer.The mean DCPo values are:TPA>c GAT>n GAT.IOP TPA measures are predictive of c GAT values,adjusted according to anterior chamber depth and corneal astigmatism.

Radial Applanation Tonometry as an Adjuvant Tool in the Noninvasive Arterial Stiffness and Blood Pressure Assessment

Since antiquity, the human arterial pulse represents an important parameter in the clinical assessment. Besides being routinely assessed in the medical practice, such pulse is not observed in its completeness yet, once many of the data obtained through it cannot be evaluated using conventional methods. Taking into account such methods, the measurement of arterial blood pressure using sphygmomanometry, although broadly widespread in the assessment and follow-up of patients who require accompaniment of their cardiovascular status, is not able to properly guide about parameters related to the central hemodynamic status, the latter most strongly associated with cardiovascular risk. Such incapability is due to the centrifugal augmentation of the pressures taken at different points of the arterial bed, based on the properties of the closed arterial system through which the blood flow travels. In this context, methodologies capable of assessing central parameters estimated using the pulse wave analysis, such as applanation tonometry, represent a promising adjuvant for evaluating patients with cardiovascular diseases, by providing detailed information concerning hemodynamic parameters otherwise inaccessible. In this scenario, the present review focuses on the applanation tonometry and its assessment on the radial artery, highlighting the importance of this method in the cardiovascular assessment, as well as its relevance in the clinical practice, when determining parameters peripherally obtained capable of estimating the central hemodynamic status.

Transpalpebral intraocular pressure measurement by Diaton compared to Goldman applanation tonometer in myopic eyes before and after transepithelial photorefractive keratectomy in Saudi Arabia

AIM:To compare intraocular pressure(IOP)measured via the trans palpebral IOP(tp IOP)method using a Diaton or with a Goldman applanation tonometer(GAT)and study the determinants of IOP difference in eyes undergoing transepithelial photorefractive keratectomy(TPRK)for myopia.METHODS:This cross-sectional validation study was held in 2020 in an eye hospital in Saudi Arabia.IOP was measured by Diaton and GAT before treatment,after one week,and one month of TPRK.It is considered if IOP difference by Diaton and GAT was less than±2 mm Hg acceptable.The IOP difference was tested if correlated to spherical equivalent(SE),central corneal thickness(CCT),age,gender,or tp IOP.RESULTS:Totolly 200 myopic eyes of 100 patients were included in the study.The mean difference of IOP measured by two methods before TPRK,1wk,and 1mo after TPRK were 0.790,-0.790,and-0.920 mm Hg,respectively(P<0.001).Diaton could measure IOP effectively 89.5%eyes before TPRK and 82%and 84%at 1wk and 1mo after TPTK,respectively.At week 1,IOP differences were significantly correlated to baseline CCT(P=0.02)and tp IOP at week 1(P<0.001).One month after TPRK,only tp IOP was significantly correlated to the difference in IOP(P<0.001).CONCLUSION:Diaton is a good screening tool for IOP before TPRK.It helps in monitoring IOP after surgery.Although more practical,it is less efficient than GAT.In eyes with high myopia and low tp IOP before surgery,IOP post-TPRK by Diaton and GAT could differ.

Comparison of IOPen rebound tonometer with Goldmann applanation tonometer at different IOP levels

AIM:To compare the accuracy of IOPen rebound tonometer with Goldmann applanation tonometer(GAT) in individuals with low,normal and high intraocular pressure(IOP) and to evaluate the effect of central corneal thickness(CCT) on IOP measurements.METHODS:This cross-sectional study consisted of 159 participants.IOP of one eye of each subject was measured consecutively with IOPen and GAT.Then CCT was measured using an ultrasonic pachymeter.Based on GAT IOP readings,participants were divided into low,normal and high IOP groups.Correlation between tonometers and CCT was calculated by spearman’s correlation coefficient.Agreement between tonometers was evaluated using Bland-Altman method.RESULTS:Non-significant underestimation of IOP by IOPen was observed in low IOP group(Mean difference:0.20mmHg;P=0.454) and also in normal IOP group(Mean difference:0.56mmHg;P=0.065).However,IOPen significantly overestimated IOP in high IOP group(Mean difference:1.06mmHg;P=0.038).The 95% limits of agreement(LoA) width between IOPen and GAT IOPs were 7.84,8.57 and 14.27mmHg in low,normal and high IOP groups,respectively.Low IOP group had thinner corneas compared to high IOP group(P=0.034).IOP measurements taken by IOPen were not influenced by CCT(P=0.099) while poor correlation between CCT and GAT was found(R=0.17,P=0.032).Using receiver operating characteristic(ROC) curve,cutoff value of 18.75mmHg was determined for IOPen with sensitivity of 98.1 and specificity of 97.2%.CONCLUSION:Accuracy of IOPen is comparable to GAT in patients with low or normal IOP but IOPen overestimates IOP at high IOP levels.CCT does not affect IOP readings with IOPen.

Dependence of dynamic contour and Goldmann applanation tonometries on peripheral corneal thickness

AIM：To determine the effects of peripheral corneal thickness（PCT）on dynamic contour tonometry（DCT）and Goldmann applanation tonometry（GAT）.METHODS：A cross-sectional study.We created a software which calculates the corneal contour（CC）as a function of the radius from the corneal apex to each pixel of the contour.The software generates a central circumference with a radius of 1 mm and the remainder of the cornea is segmented in 5 rings concentric with corneal apex being its diameter not constant around the corneal circumference as a consequence of the irregular CC but keeping constant the diameter of each ring in each direction of the contour.PCT was determined as the mean thickness of the most eccentric ring.Locally weighted scatterplot smoothing（LOWESS）regression was used to determine the pattern of the relationship between PCT and both DCT and GAT respectively.Thereafter,two multivariable linear regression models were constructed.In each of them,the dependant variable was intraocular pressure（IOP）as determined using GAT and DCT respectively.In both of the models the predictive variable was PCT though LOWESS regression pattern was used to model the relationship between the dependant variables and the predictor one.Age and sex were also introduced control variables along with their first-degree interactions with PCT.Main outcome measures include amount of IOP variation explained through regression models（R2）and regression coefficients（B）.RESULTS：Subjects included 109 eyes of 109 healthy individuals.LOWESS regression suggested that a 2nd-degree polynomial would be suitable to model the relationshipbetween both DCT and GAT with PCT.Hence PCT was introduced in both models as a linear and quadratic term.Neither age nor sex nor interactions were statistically significant in both models.For GAT model,R2was 17.14%（F=9.02;P=0.0002）,PCT linear term B was-1.163（95%CI：-1.163,-0.617）.PCT quadratic term B was 0.00081（95%CI：0.00043,0.00118）.For DCT model R2was 14.28%（F=9.29;P=0.0002）,PCT linear term B was-0.712（95%CI：-1.052,-0.372）,PCT quadratic term was B=0.0005（95%CI：0.0003,0.0007）.CONCLUSION：DCT and GAT measurements are conditioned by PCT though this effect,rather than linear,follows a2nd-degree polynomial pattern.

Eye rubbing-induced changes in intraocular pressure and corneal thickness measured at five locations, in subjects with ocular allergy

AIM: To assess the effects of eye rubbing on corneal thickness(CT) and intraocular pressure(IOP)measurements obtained 0-30 min after habitual eye rubbing in symptomatic patients.METHODS: Measurements of IOP and CT were obtained at five locations(central, temporal, superior,nasal and inferior) before, and every 5min for 30 min interval after 30 s of eye rubbing, for 25 randomly selected eyes of 14 subjects with ocular allergy and 11age-matched normals. Differences in measurements were calculated in each group [Baseline measurements minus measurements recorded at each time interval after eye rubbing(for IOP), and for each corneal location(for CT)]and comparison were then made between groups(allergic versus control) for differences in any observed effects.RESULTS: Within groups, baseline mean IOPs in the allergic patient-group(14.2 ±3.0 mm Hg) and in the control group(13.1±1.9 mm Hg) were similar at all times,after eye rubbing(P 】0.05, for all). The maximum reduction in IOP was 0.8 mm Hg in the control subjects and the maximum increase was also 0.8 mm Hg in the allergic subjects. Between groups(allergic versus control), the changes in IOP remained under 1 mm Hg at all times(P =0.2) after 30 min of eye rubbing. Between 0and 30 min of CT measurements after eye rubbing, the mean central CT(CCT), inferior CT(ICT), superior CT(SCT), temporal CT(TCT) and nasal CT(NCT) did not vary significantly from baseline values in the control and allergic-subject groups(P 】0.05, for both). Between both groups, changes in CT were similar at all locations(P 】0.05)except for the TC which was minimally thinner by about4.4 μm(P =0.001) in the allergic subjects than in the control subjects, 30 min following 30 s of eye rubbing.CONCLUSION: IOP measured in allergic subjects after30 s of habitual eye rubbing was comparable with that obtained in normal subjects at all times between 0 and30 min. Although, CT in the allergic subjects were similar to those of the control subjects at all times, it varied between +10 and-7.5 μm following eye rubbing, with the temporal cornea showing consistent reductions in thickness in the subjects with allergy. However, this reduction was minimal and was considered to not be clinically relevant.

Diagnosis and management of splanchnic ischemia

Splanchnic or gastrointestinal ischemia is rare and randomized studies are absent. This review focuses on new developments in clinical presentation, diagnostic approaches, and treatments. Splanchnic ischemia can be caused by occlusions of arteries or veins and by physiological vasoconstriction during low-flow states. The prevalence of significant splanchnic arterial stenoses is high, but it remains mostly asymptomatic due to abundant collateral circulation. This is known as chronic splanchnic disease (CSD). Chronic splanchnic syndrome (CSS) occurs when ischemic symptoms develop. Ischemic symptoms are characterized by postprandial pain, fear of eating and weight loss. CSS is diagnosed by a test for actual ischemia. Recently, gastro-intestinal tonometry has been validated as a diagnostic test to detect splanchnic ischemia and to guide treatment. In single- vessel CSD, the complication rate is very low, but some patients have ischemic complaints, and can be treated successfully. In multi-vessel stenoses, the complication rate is considerable, while most have CSS and treatment should be strongly considered. CT and MR-based angiographic reconstruction techniques have emerged as alternatives for digital subtraction angiography for imaging of splanchnic vessels. Duplex ultrasound is still the first choice for screening purposes. The strengths and weaknesses of each modality will be discussed. CSS may be treated by minimally invasive endoscopic treatment of the celiac axis compression syndrome, endovascular antegrade stenting, or laparotomy-assisted retrograde endovascular recanalization and stenting.The treatment plan is highly individualized and is mainly based on precise vessel anatomy, body weight, co- morbidity and severity of ischemia.

Evaluation of Corvis ST tonometer with the updated software in glaucoma practice

AIM: To evaluate the agreement of biomechanically corrected intraocular pressure(b-IOP) and central corneal thickness(CCT) measurements obtained with the updated Corvis ST tonometer versus Goldmann applanation tonometry(GAT) and optical-based corneal pachymetry(OB-CCT) in controls, patients with ocular hypertension(OHT) and primary open angle glaucoma(POAG).Additionally, we examined the differences in corneal deformation parameters provided by the updated Corvis ST among the three groups.METHODS: For each participant, GAT IOP, OB-CCT and measurements with a Corvis ST with updated software were obtained.Bland-Altman analysis was used to assess the agreement between the two measurement methods.RESULTS: A consecutive series of 80 eyes from 80 participants(30 with POAG, 25 with OHT and 25 normal controls) were included in this prospective study.The mean GAT IOP of all eyes was 17.2±3.6 mm Hg, and the mean b-IOP was 15.9±3.7 mm Hg(Spearman’s rho=0.767, P<0.001).The 95% limits of agreement(Lo As) ranged from-3.1 mm Hg to 5.5 mm Hg for GAT IOP and b-IOP.b-IOP was not correlated with OB-CCT(Spearman’s rho=-0.13 P=0.917).Meanwhile there was a weak positive corelation between OB-CCT and GAT IOP–b-IOP difference(Spearman’s rho=0.378, P=0.001).The mean OB-CCT was 549.5±36.4 μm, and the Corvis-CCT was 556.1±41.5 μm(Spearman’s rho=0.900, P<0.001).No statistically significant difference in the new indices provided by the updated Corvis ST was detected among the three groups.Compared with control eyes, POAG eyes had a significantly reduced applanation time 2 after adjusting for OB-CCT and GAT IOP(P=0.048).CONCLUSION: Corvis b-IOP and CCT correlate well with GAT IOP and OB-CCT.b-IOP is not affected by CCT, which might be an advantage, especially in thick or thin corneas.Corvis ST yields shorter applanation time 2 measurements in patients with POAG, which might reflect altered corneal viscoelasticity.

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

AIM:To compare intraocular pressure(IOP)readings obtained with Perkins tonometry,i Care Home,i Care 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.METHODS: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,i Care Home,i Care 200,and Tonopen.These measurements were compared to set point IOP measurements of a manometer to determine accuracy and reproducibility of each device.RESULTS: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.CONCLUSION: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.

Modeling and Simulation of Human Cornea for the Measurement of Intraocular Pressure (IOP) through Eyelid

This article describes a study based on the use of an instrumented form of applanation and indentation tonometry through eyelid.The methods and devices which are available for the measurement of intraocular pressure(IOP)have their own limitations.These cause discomfort to the patients during IOP measurement.Also these methods,used to measure IOP over cornea,need anesthesia.In the present work,an attempt is made to develop a device for the measurement of IOP through eyelid which eliminates the need of anesthesia and enhance the patient’s comfort and convenience of the clinician.To represent the results of proposed technique,the human eye modeled with cornea,sclera and also with the eyelid,is used.Furthermore,simulation results of stress values for the range of IOP i.e.5-40 mm of Hg are presented and discussed comparatively with eyelid and without eyelid i.e.directly‘on cornea’methods.

On the Validity of the Imbert-Fick Law: Mathematical Modelling of Eye Pressure Measurement

Ophthalmologists rely on a device known as the Goldmann applanation tonometer to make intraocular pressure (IOP) measurements. It measures the force required to press a flat disc against the cornea to produce a flattened circular region of known area. The IOP is deduced from this force using the Imbert-Fick principle. However, there is scant analytical justification for this analysis. We present a mathematical model of tonometry to investigate the relationship between the pressure derived by tonometry and the IOP. An elementary equilibrium analysis suggests that there is no physical basis for traditional tonometric analysis. Tonometry is modelled using a hollow spherical shell of solid material enclosing an elastic liquid core, with the shell in tension and the core under pressure. The shell is pressed against a rigid flat plane. The solution is found using finite element analysis. The shell material is anisotropic. Values for its elastic constants are obtained from literature except where data are unavailable, when reasonable limits are explored. The results show that the force measured by the Goldmann tonometer depends on the elastic constant values. The relationship between the IOP and the tonometer readings is complex, showing potentially high levels of inaccuracy that depend on IOP.

Effects of baffie and intraocular pressure on aerosols generated in the noncontact tonometer measurement during COVID-19

AIM: To investigate the effects of baffle and intraocular pressure(IOP) on the aerosols generated in the noncontact tonometer(NCT) measurement and provide recommendations for the standardized use of the NCT during coronavirus disease 2019(COVID-19). METHODS: This clinical trial included 252 subjects(312 eyes) in The Eye Hospital, Wenzhou Medical University from March 7, 2020, to March 28, 2020. Sixty subjects(120 eyes) with normal IOP were divided into two groups. One group used an NCT without a baffle, another group used an NCT with a baffle. Another 192 subjects(192 eyes) were divided into four groups: Group A;(without a baffle+normal IOP), Group A;(without a baffle+high IOP), Group B;(with a baffle+normal IOP) and Group B;(with a baffle+high IOP). Particulate matter(PM) 2.5 and PM10 generated by all subjects were quantified during the NCT measurement. The IOP values were recorded simultaneously. Effects of baffle and IOP on aerosols generated during the NCT measurement were analyzed.RESULTS: In the normal eye group with a baffle, the aerosol density decreased in a wave-like shape near the NCT with the increase in the number of people measured for IOP, demonstrating no cumulative effect. However, in the normal eye group without a baffle, there was a cumulative effect. PM2.5 and PM10 in Group A;were higher than Group A;(both P<0.001). The PM2.5 and PM10 in Group B;were higher than Group B;(P<0.01, P<0.001 respectively). The PM10 of Group B;was lower than Group A;(P<0.01). PM2.5 in Group B;were lower than Group A;(P<0.01). The median of per capita PM2.5 and PM10 in the combined Group A;+A;were 0.80 and 1.10 μg/m;respectively, which were higher than 0.20 and 0.60 μg/m;in the combined Group B;+B;(both P<0.01). The median of per capita PM2.5 and PM10 in the combined Group A;+B;were 0.10 and 0.20 μg/m;respectively, which were lower than 1.30 and 1.70 μg/m;in the combined Group A;+B;(both P<0.001).CONCLUSION: More aerosols could be generated in patients with high IOP. After the NCT is equipped with a baffle, per capita aerosol density generated decreased significantly near the NCT;And with the increase in the number of people measured for IOP, the aerosols gradually dissipated near the NCT, demonstrating no cumulative effect. Therefore, it is suggested that the NCT should be equipped with a baffle, especially for patients with high IOP.

MEASUREMENTS OF INTRAOCULAR PRESSURE THROUGH0UT THE PREGNANCY IN PAKISTANI WOMEN

Background. Decrease in intraocular pressure (IOP) during pregnancy has been reported by previous studies,but amount of decrease varies from study to study. Moreover,previous studies have concentrated on the last trimester of pregnancy or one reading per trimester. IOP changes throughout the pregnancy have never been described. Therefore,the present study was planned to determine IOP throughout the pregnan cy,after placing control on IOP affecting factors.Subjects and methods. Thirty-six pregnant and same numbers of non-pregnanat women of the same age group were studied. IOP measurements were taken at four week intervals throughout the pregnancy,with the Goldmann applanation tonometer.Results. As compared to control subjects,up to 8th week,IOP remained the same. At 12th week,it becomes significantly lower. The IOP differences between fIrst and second (P<0. 05),and second and third (P<0. 001 ) trimesters of pregnancy were significant. In every subject, IOP decreased during pregnancy.However,there were variations among individuals in the extent of IOP decrease Conclusbos. With advancing pregnancy, intraocular pressure decreases. Knowledge of the normal level of intraocular pressure in various stages of pregnancy may help glaucoma screeners.

EFFECT OF THIRD TRIMESTER OF PREGNANCYON DIURNAL VARIATION OF OCULAR PRESSURE

This study was planned to evaluate the effect of pregnancy on diurnal variation of intraocular pressure(IOP) after placing control on all the IOP affecting factors. The IOP was measured with the Goldmann ap-planation tonometer. Both in the control and 3rd trimester subjects, the peak of mean IOP appeared in themorning when the subJects waked, and the trough of mean IOP happened at 2 am to 4 am. The diurnal in-traocular pressure curves revealed that the lOP peaks were 15.4±0. 9 and 12. 9±0. 6 mmHg in the controland third trimester pregnant subjects, respectively. Whereas the trough were 13.1±0. 4 and 11. 8±0. 3mmHg, respectively. The mean diurnal variation were 2. 3±0. 6 mmHg (P<O.01 ), and 1.1±0. 8mmHg in the control and third trimester subjects, respectively. There are two main findings of presentstudy: first, compared with non-pregnant control subjects, the IOP was significantly lower (P<0.001 ) inthe third trimester pregnant subjects. Second, in the third trimester of pregnancy, the lower IOP level wasassociated with the less degree of IOP fluctuations at various hours of the day.