Dynamic Contour Tonometer Research Articles

The Alteration of Intraocular Pressure and Ocular Pulse Amplitude by Retrobulbar Anaesthesia-A Search for Risk Factors for Serious Complications Due to Retrobulbar Anaesthesia.

Our goal was to assess the impact of retrobulbar anaesthesia on ocular pressure and perfusion development and to find out if there were systemic or biometric parameters of patients affecting them in order to understand the effect of retrobulbar anaesthesia better. Methods: Changes in intraocular pressure (IOP) and ocular pulse amplitude (OPA) using a dynamic contour tonometer (DCT) were noted before and after retrobulbar anaesthesia (RBA) in combination with five minutes of oculopression at 40 mmHg in 134 patients. Only results with a quality Q 1-3 were considered for further statistical analysis. Systemic and ophthalmic parameters were noted and their impact was tested using linear regression. Results: IOP decreased from 18.9 ± 7.2 mmHg to 15.4 ± 6.3 mmHg (n = 71, p = 0.001) after first RBA. The dosage of midazolam administered during premedication was found to increase IOP significantly after first RBA (B = 3.75; R2 = 0.38). Ocular pulse amplitude decreased significantly from 3.8 ± 1.7 mmHg to 3.0 ± 1.9 mmHg after first RBA (n = 72, p < 0.001). This change was found to be dependent on the presence of diabetes mellitus (n = 68, p = 0.048). Conclusions: IOP and OPA decrease after RBA and oculopression. Caution is needed with midazolam premedication due to potential IOP increase. Patients with diabetes and pre-existing retinal or optic nerve damage should consider alternative anaesthesia methods, such as eye drops or general anaesthesia, due to the observed decrease in OPA after RBA and oculopression.

In Vivo Corneal Biomechanical Response to Three Different Laser Corneal Refractive Surgeries.

To compare the effects of three common refractive surgeries on corneal biomechanics. Two hundred seven patients who had refractive surgery were included in this study, of whom 65 received transepithelial photorefractive keratectomy (tPRK), 73 received femtosecond laser-assisted laser in situ keratomileusis (FSLASIK), and 69 received small incision lenticule extraction (SMILE). Each patient had biomechanical measurements using the Corvis ST (Oculus Optikgeräte GmbH) preoperatively and at 3 and 6 months postoperatively. The measurements included five parameters expected to be associated with corneal biomechanics: deformation amplitude ratio at 2 mm (DAR2), integrated inverse radius (IIR), stiffness parameter at first applanation (SP-A1), highest concavity time (HCT), and the updated stress-strain index (SSIv2). The variations in these parameters postoperatively among the three surgeries, and their relationship with corneal thickness (CCT) and intraocular pressure measured by the Dynamic Contour Tonometer (DCT-IOP) were analyzed. SP-A1 decreased significantly from preoperatively to 3 months postoperatively in all three groups, whereas DAR2 and IIR increased significantly, all indicating stiffness losses. Between 3 and 6 months postoperatively, the results were inconsistent, with DAR2 decreasing (indicating stiffness increases) and IIR increasing (denoting stiffness decreases) in the FS-LASIK and SMILE groups. The decrease in SSIv2 (the only measure of corneal material stiffness) postoperatively was comparatively less pronounced at both 3 and 6 months postoperatively. On the other hand, HCT remained generally stable after all three surgeries. Unlike DAR2, IIR, and SP-A1, the changes postoperatively in stiffness parameters HCT and SSIv2 were independent of the corresponding changes in both DCT-IOP and CCT. Among the stiffness parameters considered, SSIv2 was not correlated with CCT or DCT-IOP, and holds promise for representing the corneal material stiffness and how it remains largely unaffected by refractive surgeries. Overall, FS-LASIK had the most significant impact on corneal stiffness, followed by SMILE, and finally tPRK. [J Refract Surg. 2024;40(5):e344-e352.].

The influence of altitude on the differences between Goldmann tonometry and Pascal dynamic contour tonometry: An ecological meta-analysis.

A meta-analysis found that including atmospheric pressure as altitude in generalized linear models reveals higher differences between Goldmann tonometry and Pascal dynamic contour tonometry at higher altitudes, with the difference increasing in thinner corneas. To examine the difference in intraocular pressure (IOP) measurements by using Goldman applanation tonometry (GAT) and dynamic contour tonometer (DCT) tonometry in published literature and determine the influence of central corneal thickness (CCT), age, and altitude on that difference. Articles that compare GAT and DCT were selected for an extensive literature review, and the location and altitude of the research centers were found online. CCT and age were analyzed as covariates, when available. A total of 157 studies including 24,211 eyes of 20,214 patients were included in the study. The results showed that the difference between DCT and GAT was higher at higher altitudes above sea level and increased with thinner corneas. However, the results were different in eyes with corneal transplants, where altitude and CCT had less influence, and in those post-refractive surgery where age was found to influence the difference. Theoretical correction formulas using altitude, CCT, and age were derived from this meta-analysis, but their accuracy and usefulness in clinical practice need validation. The findings suggest that there is a higher risk of underestimating IOP when the Goldmann tonometer is used at a higher altitude, particularly in eyes with glaucoma, thinner corneas, or corneal refractive surgery. Further research is needed to validate the accuracy of the correction formulas derived from this meta-analysis in clinical practice.

Estimating pulsatile ocular blood volume from intraocular pressure, ocular pulse amplitude, and axial length.

The purpose of this study was to develop a method of estimating pulsatile ocular blood volume (POBV) from measurements taken during an ophthalmic exam, including axial length and using a tonometer capable of measuring intraocular pressure (IOP) and ocular pulse amplitude (OPA). Unpublished OPA data from a previous invasive study was used in the derivation, along with central corneal thickness (CCT) and axial length (AL), as well as IOP from the PASCAL dynamic contour tonometer (DCT) and intracameral (ICM) measurements of IOP for 60 cataract patients. Intracameral mean pressure was set to 15, 20, and 35 mmHg (randomized sequence) in the supine position, using a fluid-filled manometer. IOP and OPA measurements were acquired at each manometric setpoint (DCT and ICM simultaneously). In the current study, ocular rigidity (OR) was estimated using a published significant relationship of OR to the natural log of AL in which OR was invasively measured through fluid injection. Friedenwald's original pressure volume relationship was then used to derive the estimated POBV, delivered to the choroid with each heartbeat as a function of OR, systolic IOP (IOPsys), diastolic IOP (IOPdia), and OPA, according to the derived equation POBV = log (IOPsys/IOPdia) / OR. Linear regression analyses were performed comparing OPA to OR and calculated POBV at each of the three manometric setpoints. POBV was also compared to OPA/IOPdia with all data points combined. Significance threshold was p < 0.05. OR estimated from AL showed a significant positive relationship to OPA for both DCT (p < 0.011) and ICM (p < 0.006) at all three manometric pressure setpoints, with a greater slope for lower IOP. Calculated POBV also showed a significant positive relationship to OPA (p < 0.001) at all three setpoints with greater slope at lower IOP, and a significant negative relationship with IOPdia. In the combined analysis, POBV showed a significant positive relationship to OPA/ IOPdia (p < 0.001) in both ICM and DCT measurements with R2 = 0.9685, and R2 = 0.9589, respectively. POBV provides a straight-forward, clinically applicable method to estimate ocular blood supply noninvasively. Higher IOP in combination with lower OPA results in the lowest values of POBV. The simplified ratio, OPA/ IOPdia, may also provide a useful clinical tool for evaluating changes in ocular blood supply in diseases with a vascular component, such as diabetic retinopathy and normal tension glaucoma. Future studies are warranted.

Innovative approaches to measuring intraocular pressure

AbstractAlthough different factors have been implicated in the development and progression of glaucoma, intraocular pressure (IOP) remains the main modifiable risk factor. Goldmann applanation tonometer (GAT) considers the “gold standard” for measuring IOP. The main deficiency of GAT, however, is the static nature of its measurements and that it is dependent on corneal biomechanics, central corneal thickness as well as scleral stiffness. The single measurement of IOP for the management of glaucoma provides limited information since it does not take into account the natural fluctuation of IOP, individual ranges, IOP peaks or variations throughout the day. Although the role of IOP fluctuations in glaucoma progression is not clearly defined, there is consensus on the importance of understanding the circadian profiles of IOP in glaucoma patients. Given the limitations of GAT for the actual measurement of IOP, different tonometers have been designed with the aim of advancing in self‐tonometry as Icare HOME, or obtaining independent measurements of corneal biomechanics, as Ocular Response Analyser (ORA), Pascal dynamic contour tonometer or the Corvis ST tonometer. Research to monitor IOP is based on three different strategies: (1) self‐tonometry; (2) permanent monitoring of the IOP; and (3) the temporary monitoring of the IOP. Currently, the sensors in contact lenses allow the IOP profiles to be recorded semi‐continuously for 24 hours with a minimally invasive technique, independent of the patient's position and the activity performed, opening new perspectives in the knowledge and management of glaucoma.

Evaluation of ocular pulse amplitude changes after the retinal detachment repair.

The study was conducted to determine the ocular pulse amplitude (OPA) changes, measured with a dynamic contour tonometer (DCT), after surgical retinal detachment repair. This was a prospective and comparative study. Thirty patients (30 eyes) who had undergone uncomplicated unilateral scleral buckling and encircling procedures for quadrant or half-retinal rhegmatogenous retinal detachment were referred for DCT one day before the surgery was performed, on the 1st, 7th, and 30th postoperative day. Methods of descriptive (arithmetical mean, standard deviation) and analytical statistics (analysis of variance) were used to analyze the data and evaluate the significance of the difference. A value of P less than 0.05 was considered statistically significant. The data were evaluated for normality with the single-sample Kolmogorov-Smirnov test. OPA values decreased significantly after scleral buckling procedures (p < 0.0001), but regained near to preoperative values one month after the surgery. OPA tends to decrease after retinal detachment surgery. Restoring patients' vision with scleral buckling and encircling procedures gives early changes in blood supply to the choroid and ocular nerve, and since OPA is an indirect parameter of choroidal vascularization, measuring these values can help make an insight into ocular hemodynamics.

Changes in ocular pulse amplitude and posterior ocular structure parameters in type 1 diabetic children without diabetic retinopathy.

Background:It is important to determine changes in posterior ocular structures in the early period before retinopathy develops in pediatric patients with type 1 diabetes mellitus (DM).Objective:To evaluate inner plexiform layer (IPL), ganglion cell layer (GCL), and retinal nerve fiber layer (RNFL) thicknesses, as well as the relationship between choroidal thickness (CT) and ocular pulse amplitude (OPA) in type 1 diabetic children without diabetic retinopathy (DR).Design:A prospective observational study.Methods:Group 1 (n = 44) consisted of pediatric patients with type 1 DM without DR, and Group 2 (n = 65) of pediatric control subjects. Both intraocular pressure (IOP) and OPA were measured using a dynamic contour tonometer. CT, IPL, GCL, and RNFL were all measured using spectral domain optical coherence tomography (OCT).Results:The mean IOP and OPA values were 16.67 ± 2.34 and 1.85 ± 0.34, respectively, in group 1, and 15.14 ± 2.17 and 1.65 ± 0.25 in Group 2 (p = 0.001 for both). The mean subfoveal CT value was 294.30 ± 67.61 μm in group 1 and 394.42 ± 69.65 μm in Group 2 (p < 0.001). The mean GCL and RNFL values were 1.09 ± 0.11 and 96.46 ± 11.69, respectively, in group 1, and 1.14 ± 0.09 and 101.73 ± 9.33 in Group 2 (p = 0.005 and p = 0.008, respectively).Conclusions:IOP and OPA values were higher, and CT, GCL, and RNFL values were lower in children with type 1 DM during the early stages than in the healthy control group. These findings suggest that CT may be a marker of retinal involvement in children with type 1 DM without DR.

Effects of childhood obesity on ocular pulse amplitude and intraocular pressure.

To assess intraocular pressure and ocular pulse amplitude changes in obese children and adolescents using dynamic contour tonometry. 137 cases, 64 obese and 73 healthy children, who were both age-matched and gender-matched, comprised the study population in this cross-sectional study. Children with body mass index values >95% for sex and age were regarded as obese. Participants underwent detailed ophthalmological examinations, including intraocular pressure measurement using a Pascal dynamic contour tonometer. Relationships between intraocular pressure and ocular pulse amplitude measurements and age, sex, obesity, pubertal status, and insulin resistance were investigated. Bilateral ocular pulse amplitude was lower while intraocular pressure was higher in the obese group than in the control group (p<0.001). No significant relationship was observed between insulin resistance and intraocular pressure or ocular pulse amplitude (p>0.005). No correlation was determined between systolic and diastolic blood pressure, homeostasis model assessment for insulin resistance, or blood lipid levels and intraocular pressure and ocular pulse amplitude. Our results show that obesity caused an increase in intraocular pressure and a decrease in ocular pulse amplitude independently of insulin resistance in children and adolescents. Prospective studies involving long-term follow-up of cases are now needed to assess the probable adverse effects of these ocular findings in obese children.

Changes in intra-ocular pressure, ocular pulse amplitude and choroidal thickness after trabeculectomy

ABSTRACT Clinical relevance Glaucoma is one of the most common causes of blindness. Although high intra-ocular pressure (IOP) is the most important risk factor, ocular blood flow also has an effect on prognosis. Background The aim of this study was to investigate the IOP, ocular pulse amplitude (OPA) and choroidal thickness (CT) changes after trabeculectomy and to determine whether trabeculectomy has an effect on ocular blood flow. Methods This retrospective, comparative case series was conducted with 33 eyes of 33 patients who underwent trabeculectomy due to uncontrolled glaucoma. The fellow eyes of 20 patients who were followed up with medical therapy were included as a control group. IOP and OPA were evaluated using a dynamic contour tonometer. Subfoveal choroidal thickness (SFCT) was obtained with enhanced depth imaging (EDI) mode of Spectralis-OCT. Results The mean IOP was 21.6 ± 6.3 mmHg at baseline and 13.8 ± 0.9 mmHg after trabeculectomy (p ˂ 0.001), and the mean OPA was 4.1 ± 1.5 at baseline and 2.6 ± 1.6 mmHg after trabeculectomy (p ˂ 0.001). The mean SFCT was 292.2 ± 63.2 µm at baseline and 303.8 ± 70.4 µm after trabeculectomy (p = 0.024). The change in OPA was strongly positively correlated with the change in IOP (r = 0.597, p ˂ 0.001) and SFCT change was positively correlated with OPA change (r = 0.34, p = 0.05). There was no difference between the two groups in terms of IOP, OPA and SFCT values measured after trabeculectomy (respectively, p = 0.264, p = 0.627 and p = 0.949). Conclusion The large IOP decrease following trabeculectomy causes a decrease in OPA and choroidal thickening. On the other hand, trabeculectomy has no effect on OPA change.

Changes in ocular pulse amplitude and choroidal thickness in childhood obesity patients with and without insulin resistance.

To compare choroidal thickness (CT) and ocular pulse amplitude (OPA) in childhood obesity with insulin resistance (IR) and without IR. Seventy-three childhood obesity and 62 healthy children, who were both age-matched and gender-matched, comprised the study population in this prospective study. Obesity was determined as having a body mass index (BMI) - standard deviation (SD) score that was > 2 SD.Intraocular pressure (IOP) and OPA were measured using a dynamic contour tonometer. The CT measurements were performed using enhanced depth imaging optical coherence tomography at three locations, comprising at the fovea, at a position 500 µm nasal, and also at a position 500 µm temporal to the fovea. Mean BMI value was 28.72 ± 4.85 in the patients with childhood obesity and 21.47 ± 1.14 in the control group. The mean IOP and OPA values were determined 15.90 ± 2.30 and 14.10 ± 2.16 mm Hg, 1.50 ± 0.28 and 1.74 ± 0.32 mm Hg in the patients with childhood obesity and the control group, respectively (p < 0.001, p < 0.001). The mean subfoveal CT value was 350.50 ± 81.51 μm in the eyes with childhood obesity and 390.02 ± 71.50 μm in those of the control group (p = 0.003). When the patient groups with and without IR were compared, no significant difference was found between CT, OPA and IOP values (p > 0.005). Our results showed that both OPA and CT values were significantly decreased in childhood obesity patients. We suggest further studies to verify longitudinal changes in OPA and CT, as also the evaluation of these parameters in other populations.

Intraocular pressure elevation after vitrectomy-Goldmann applanation tonometry measures lower intraocular pressure than dynamic contour tonometry

HintergrundDas dynamische Konturtonometer PASCAL (DCT) ist ein digitales, der natürlichen Hornhautgeometrie angepasstes Kontakttonometer. Verglichen wurde das DCT mit dem Goldmann-Applanationstonometer (GAT).MethodikIn einer prospektiven Querschnittstudie wurden 100 Augen vor und nach Pars-plana-Vitrektomie (ppV) vergleichend mit dem GAT und DCT gemessen. Verwendete Endotamponaden waren verschiedene Gase und Silikonöle. Erfasst wurden der präoperative intraokulare Druck (IOD), postoperative Druckveränderungen und die Intertonometerdifferenz.ErgebnissePräoperativ lag der mittlere IOD mit dem GAT gemessen bei 15,8 ± 5,2 mm Hg und dem DCT bei 17,5 ± 5,9 mm Hg. Am ersten postoperativen Tag stieg bei Augen, die mit Gas versorgt wurden, der Druck im Mittel um 2,5 mm Hg (p = 0,035) an. Das DCT erfasste 18 Augen (19,1 %) mit einem postoperativen IOD von ≥ 25 mm Hg. Postoperativ maß das GAT den IOD im Schnitt 2,5 mm Hg niedriger und bei expansiver Gasendotamponade im Mittel um 3,0 mm Hg niedriger als das DCT. Bei IOD-Werten von postoperativ über 20 mm Hg lag das GAT im Mittel 4,7 mm Hg unter dem DCT. Zehn von 18 Augen mit IOD ≥ 25 mm Hg wurden mit dem GAT nicht als hypertensiv (≥ 25 mm Hg) erkannt. Bei 13 % maß das DCT am 1. postoperativen Tag einen um mindestens 6 mm Hg höheren IOD als das GAT. In einem Extremfall wurde der IOD mit dem GAT bei Gasendotamponade um 12 mm Hg unterschätzt.SchlussfolgerungPostoperative Druckanstiege nach ppV sind gefürchtete Komplikationen und können zu irreversiblem Visusverlust führen. Abhängig von der verwendeten Endotamponade misst das GAT den IOD niedriger als das DCT – besonders bei Druckspitzen durch expansive Gase. Die postoperative IOD-Messung nach ppV ist bedeutend und die Messwerte von GAT und DCT können abweichen.

Association of obstructive sleep apnea/hypopnea syndrome with glaucomatous optic neuropathy and ocular blood flow.

The present study aimed to investigate the prevalence of glaucomatous optic neuropathy in patients with obstructive sleep apnea/hypopnea syndrome (OSAHS). In total, 83 subjects (45 cases of severe OSAHS and 38 controls) underwent polysomnographic assessment and were evaluated for the severity of the disease using the Apnea-Hypopnea index. A detailed ophthalmologic exam was then performed, including measurement of the intraocular pressure (IOP) with a Goldmann applanation tonometer and Pascal dynamic contour tonometer (DCT), recording of the ocular pulse amplitude measured by the Pascal DCT, standard automated perimetry and retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) thickness evaluation using optical coherence tomography. Ocular blood flow was assessed using color Doppler imaging (CDI) and ophthalmic artery indices were evaluated, including peak systolic blood velocity, end diastolic blood velocity and resistivity index (RI). There was a significant difference in the mean IOP between controls (11.03±3.85 mmHg) and cases of severe OSAHS (18.06±3.39 mmHg) when the IOP was measured by DCT (P<0.0001), but not with the Goldmann applanation tonometer (IOP, 13.97±2.85 mmHg for controls and 14.89±3.21 mmHg for cases of severe OSAHS; P=0.0877). Significant negative correlations were observed between RNFL thickness and RI (P=0.0011) in cases of severe OSAHS, as well as between GCC thickness and RI (P<0.008) in all subjects. Furthermore, a negative correlation between RI and RNFL thickness in severe cases of OSAHS suggested a hemodynamically induced vulnerability of RNFL in OSAHS. The correlation between RI and GCC thickness in all subjects suggested that impaired perfusion, more prominent in OSAHS, leads to structural changes. Therefore, cases of severe OSAHS should be monitored for changes in RNFL and GCC thickness, as well as CDI findings. Furthermore, patients with increased ophthalmic artery RIs should be monitored for changes in the GCC, regardless of the etiology of the RI increase.

Heartbeat-Induced Corneal Axial Displacement and Strain Measured by High Frequency Ultrasound Elastography in Human Volunteers.

PurposeThe purpose of this study was to establish in vivo data acquisition and processing protocols for repeatable measurements of heartbeat-induced corneal displacements and strains in human eyes, using a high-frequency ultrasound elastography method, termed ocular pulse elastography (OPE).MethodsTwenty-four volunteers with no known ocular diseases were recruited for this study. Intraocular pressure (IOP) and ocular pulse amplitude (OPA) were measured using a PASCAL Dynamic Contour Tonometer (DCT). An in vivo OPE protocol was developed to measure heartbeat-induced corneal displacements. Videos of the central 5.7 mm of the cornea were acquired using a 50-MHz ultrasound probe at 128 frames per second. The radiofrequency data of 1000 frames were analyzed using an ultrasound speckle tracking algorithm to calculate corneal displacements and quantify spectral and temporal characteristics. The intrasession and intersession repeatability of OPE- and DCT-measured parameters were also analyzed.ResultsThe in vivo OPE protocol and setup were successful in tracking heartbeat-induced corneal motion using high-frequency ultrasound. Corneal axial displacements showed a strong cardiac rhythm, with good intrasession and intersession repeatability, and high interocular symmetry. Corneal strain was calculated in two eyes of two subjects, showing substantially different responses.ConclusionsWe demonstrated the feasibility of high-frequency ultrasound elastography for noninvasive in vivo measurement of the cornea's biomechanical responses to the intrinsic ocular pulse. The high intrasession and intersession repeatability suggested a robust implementation of this technique to the in vivo setting.Translational RelevanceOPE may offer a useful tool for clinical biomechanical evaluation of the cornea by quantifying its response to the intrinsic pulsation.

Ganglion cell layer thickening in patients suffering from Obstructive Sleep Apnea-Hypopnea syndrome with long Mean Apnea-Hypopnea Duration during sleep.

To study the effects of mean apnea-hypopnea duration (MAD), a useful indicator of blood oxygenation, on peripapillary retinal nerve fiber layer (RNFL), macular ganglioncell toinner plexiform layer (GC-IPL) and macular retinal thickness in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS). Sixty-five patients recently diagnosed with OSAHS and 35 healthy individuals were enrolled in this cross-sectional study. OSAHS patients were divided according to their MAD values into group 1 with 16 participants (MAD:10-15.5s), group 2 with 17 participants (MAD:15.5-19s), group 3 with 17 participants (MAD:19-30s) and group 4 with 15 participants (MAD > 30s). The average and sectorial values of RNFL, GC-IPL and retinal thickness were measured by SS-OCT (DRI OCT Triton, Topcon). Intraocular pressure was recorded by Goldmann Applanation and Pascal Dynamic Contour Tonometer (DCT-IOP). The average RNFL and retinal thicknessvalues were higher in group 4, but did not reach statistical significance. With the exception of the central 1mm at the fovea, GC-IPL was always thickened in group 4, and significant differences were evident when its average value was compared with group 2 (p = 0.03), its superior and inferior-nasal values were compared with group 2 (p = 0.02,p = 0.006,respectively) and group 3 (p = 0.01, p = 0.02,respectively), its superior-temporal value was compared with group 3 (p = 0.003) and the control group (p = 0.03), and its superior-nasal value was compared with group 2 (p = 0.03), group 3 (p = 0.001) and the control group (p = 0.03). DCT-IOP was significantly positively correlated with the duration of sleepin whichoxygen saturation(SaO2 ) was decreased under90% (r = 0.359, p = 0.01). We report a novel observation of GC-IPL thickening in OSAHS patients experiencing long MAD, a parameter which incorporates the severity of breathing events during sleep. Higher DCT-IOP was noted with advancing hypoxemia.

Variations of Intraocular Pressure Measured by Goldmann Applanation Tonometer, Tono-Pen, iCare Rebound Tonometer, and Pascal Dynamic Contour Tonometer in Patients With Corneal Edema After Phacoemulsification.

Edematous corneas had lower Goldmann applanation tonometer (GAT) intraocular pressure (IOP) compared with other tonometers. A significant, mild negative correlation between central corneal thickness (CCT) and GAT IOP was found in a group of significant edematous corneas with CCT increases of >100 µm. To compare the IOP that was randomly obtained with the GAT, Tono-Pen, iCare, and Pascal dynamic contour tonometer in patients with corneal edema after phacoemulsification. Corneal edema was quantified by CCT measurement. The agreement between IOP measurements assessed by different instruments was evaluated using Bland-Altman plots. The relationship between CCT and IOP was investigated using the coefficient of correlation. The CCT and IOP were compared between the periods of postsurgical edema and after its resolution. The mean age of 60 patients was 75.9±7.8 years. CCT increased significantly after surgery, by an average of 96.1±39.9 µm (P<0.001). Relative to the IOPs measured with the GAT in edematous eyes: the mean difference in Tono-Pen IOPs was 4.7 mm Hg; 95% limits of agreement (LOA), -0.3 to 9.6 mm Hg. For iCare, was 2.3 mm Hg; 95% LOA, -2.2 to 6.8 mm Hg. For Pascal dynamic contour tonometer, was 3.0 mm Hg; 95% LOA, -0.4 to 6.5 mm Hg. Edematous corneas had significantly lower GAT IOP than Tono-Pen IOP; 12.3±3.2 versus 16.9±3.1 (P=0.02). Pearson correlation coefficients (r) showed a high correlation between the 4 tonometers in eyes without edema. There was a significant, mild negative correlation between CCT and GAT IOP (r=-0.25, P=0.02) in a group of significant edematous corneas with CCT increases of >100 µm: GAT IOP decreased by 3.1 mm Hg for every 10-µm increase in CCT. IOP readings with GAT tended to be lower than those obtained with the other tonometers, especially the Tono-Pen. GAT IOP readings in cases of severe corneal edema should be interpreted with caution.

The retinal venous pressure at different levels of airway pressure.

To investigate retinal venous pressure (RVP) as a function of airway pressure (AirP) during the Valsalva maneuver (VM) in human subjects. Forty-three healthy volunteers (age, 22.0 (2.3) years) (median and interquartile range) were investigated using the following instruments: dynamic contour tonometer, contact lens dynamometer (CLD), and aneroid manometer. The following measurements were performed in their left eyes: tonometry and dynamometry during VM at different levels of airway pressure (AirP = 0, 10, 20, 30, and 40mmHg). The median RVP during spontaneous breathing (AirP = 0) was 19.7 (6.4) (median in mmHg (interquartile range)) and the intraocular pressure (IOP) in mydriasis was 16.3 (3.1) mmHg. Spontaneous pulsation occurred in 58.1% of the subjects. RVP increased nonlinearly. The coefficient of variation of four individual measurements of RVP at each pressure level averaged 8.1 (7.6) %. At different AirP levels of 10, 20, 30, and 40mmHg, the following RVPs were measured: 29.6 (12.6); 34.2 (12.8); 38.0 (10.5); and 40.3 (11.0), respectively. The rise of RVP (Δ RVP) during VM was significantly higher than that of Δ IOP (p< 0.0001, Wilcoxon test). Δ RVP between 0 and 40mmHg AirP was 20.6mmHg and Δ IOP 1.5mmHg. The steepest slope of the RVP/AirP curve was observed at the first step from 0 to 10mmHg of AirP (∆ RVP = 9.9mmHg). A nonlinear relationship between RVP and AirP was found during VM. Small rises in AirP increase the RVP and affect retinal circulation.

Effectiveness of 4 tonometers in measuring IOP after femtosecond laser-assisted LASIK, SMILE, and transepithelial photorefractive keratectomy.

To test the performance of 4 tonometers in estimating intraocular pressure (IOP) after 3 forms of refractive surgery. Eye Hospital, Wenzhou Medical University, China. Prospective case series. Patients matched for preoperative age, corneal thickness, and myopic correction enrolled for femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK), small-incision lenticule extraction (SMILE), or transepithelial photorefractive keratectomy (tPRK) were included in the study. For each patient, 4 measurements of IOP were obtained preoperatively and 3 months postoperatively, using the Goldmann applanation tonometer (GAT-IOP), the Dynamic Contour Tonometer (DCT-IOP), corneal-compensated IOP (IOPcc) from the Ocular Response Analyzer, and biomechanically corrected IOP (bIOP) from the Corvis ST. Overall corneal stiffness was also estimated based on the stiffness parameter (SP-A1) provided by the Corvis ST. The study included 144 eyes of 144 patients. Among the 3 procedures, the smallest variances between preoperative and postoperative IOP estimates and SP-A1 values were observed with the tPRK, followed by SMILE and FS-LASIK. In the tPRK group, no significant differences were observed in both bIOP (-0.18 ± 1.63 mm Hg) and DCT-IOP (-.64 ± 2.34 mm Hg), whereas they were larger and significant in GAT-IOP (-1.78 ± 2.29 mm Hg) and IOPcc (-2.77 ± 1.84 mm Hg). In FS-LASIK and SMILE groups, although there were similar significant reductions in IOP postoperatively, these reductions were still lower in bIOP and DCT-IOP than those in GAT-IOP and IOPcc. The bIOP and DCT-IOP were the least affected IOP estimates between the 3 refractive surgery procedures considered. It was evident that tPRK produced significantly smaller reductions in IOP readings than did FS-LASIK and SMILE.

The Effects of Surgical Treatment on Retina-Choroidal Findings in Patients With Obstructive Sleep Apnea Syndrome

The purpose of this study was to determine the effect of surgical treatment on ocular findings in obstructive sleep apnea syndrome (OSAS). The authors studied 34 eyes of 34 newly diagnosed OSAS patients. The sleep study was performed before and 6 months after expansion sphincter pharyngoplasty (ESP). Retinal nerve fiber layer (RNFL), choroidal thickness (CT), and retinal arteriolar caliber (RAC) analyses were performed using spectral-domain optical coherence tomography. Intraocular pressure (IOP) and ocular pulse amplitude were performed using the Pascal dynamic contour tonometer. The preoperative and postoperative Apnea Hypopnea Index scores and average oxygen saturation values were significantly different (P = .0001 and P = .001, respectively). There was no significant difference between the preoperative and postoperative RNFL thicknesses (P > .05). The preoperative subfoveal, nasal, temporal CT, and IOP were significantly different from the postoperative measurements (P = .006, P = .05, P = .036, and P = .0001, respectively). ESP had a significant influence on CT and IOP in patients with OSAS, maintaining a decrease in CT and IOP 6 months after surgery. The determination of these ocular findings may be useful to show the positive effects of ESP. [Ophthalmic Surg Lasers Imaging Retina. 2020;51:35-42.].

Effectiveness of the Goldmann Applanation Tonometer, the Dynamic Contour Tonometer, the Ocular Response Analyzer and the Corvis ST in Measuring Intraocular Pressure following FS-LASIK

ABSTRACTPurpose: To test the performance of the four tonometers in providing IOP measurements that were free of the effects of corneal biomechanics changes caused by refractive surgery.Methods: Four tonometers were employed to provide IOP measurements for 65 participants who accepted Femtosecond laser-assisted LASIK (FS-LASIK). The measurements included GAT-IOP by the Goldmann Applanation Tonometer, DCT-IOP by the Dynamic Contour Tonometer, Goldmann-correlated IOP (ORA-IOPg) and corneal-compensated IOP (ORA-IOPcc) by the Ocular Response Analyzer, and uncorrected IOP (CVS-IOP) and biomechanically corrected IOP (CVS-bIOP) by the Corvis ST. Statistical analyses were performed to assess the association of the differences in IOP caused by FS-LASIK with central corneal thickness (CCT), mean corneal curvature (Km), age, refractive error correction (REC), optical zone diameter (OZD), ablation zone diameter (AZD), residual stromal bed thickness (RSB) and RSB ratio (RSB/CCT). Multiple linear regression models were constructed to explore factors influencing IOP changes.Results: All four tonometers exhibited significant differences between IOP measurements taken pre and post-surgery except for CVS-bIOP in the low to moderate myopia group (t = 1.602, p = .12). CVS-bIOP, followed by DCT-IOP, provided the best agreement between pre and post-FS-LASIK measurements with the lowest differences in IOP and the narrowest limits of agreement. The pre-post IOP differences were also significantly associated with the reduction in CCT in only GAT-IOP, ORA-IOPg, and CVS-IOP. CVS-bIOP and ORA-IOPcc were the only measurements that were not correlated with CCT, Km or age both before and after FS-LASIK.Conclusions: The biomechanically corrected bIOP from the Corvis ST provided post-FS-LASIK measurements that were in closest agreement with those obtained before surgery. In comparison, GAT-IOP, ORA-IOPg, ORA-IOPcc, and CVS-IOP appeared to be more influenced by the changes in corneal biomechanics caused by FS-LASIK.

Impact of corneal parameters on intraocular pressure measurements in different tonometry methods

To evaluate the impact of central corneal thickness (CCT) and corneal curvature on intraocular pressure (IOP) measurements performed by three different tonometers. IOP in 132 healthy eyes of 66 participants was measured using three different tonometry techniques: Goldmann applanation tonometer (GAT), Pascal dynamic contour tonometer (DCT), and ICare rebound tonometer (RT). CCT and corneal curvature were assessed. In healthy eyes, DCT presents significantly higher values of IOP than GAT (17.34±3.69 and 15.27±4.06 mm Hg, P<0.0001). RT measurements are significantly lower than GAT (13.56±4.33 mm Hg, P<0.0001). Compared with GAT, DCT presented on average 2.51 mm Hg higher values in eyes with CCT<600 µm and 0.99 mm Hg higher results in eyes with CCT≥600 µm. The RT results were lower on average by 1.61 and 1.95 mm Hg than those obtained by GAT, respectively. Positive correlations between CCT in eyes with CCT<600 µm were detected for all IOP measurement techniques, whereas a similar relationship was not observed in eyes with thicker corneas. A correlation between IOP values and keratometry in the group with CCT<600 µm was not detected with any of the tonometry methods. In thicker corneas, a positive correlation was found for GAT and mean keratometry values (R=0.369, P=0.005). The same method should always be chosen for routine IOP control, and measurements obtained by different methods cannot be compared. All analysed tonometry methods are dependent on CCT; thus, CCT should be taken into consideration for both diagnostics and monitoring.