Assessment of True Intraocular Pressure: The Gap Between Theory and Practical Data

Corneal Biomechanics in Non-infectious Uveitis Measured by Corvis ST: A Pilot Study

PURPOSE

To assess differences between corneal biomechanical properties in patients with non-infectious uveitis and healthy subjects using CorVis.

METHODS

77 patients with non-infectious uveitis and 47 control subjects were recruited. Biomechanical parameters were measured: deformation amplitude (DA), A-1 length and A-2 length (L1, L2), A-1 velocity and A-2 velocity (V1, V2), peak distance (PD) and HC radius (highest concavity radius). AUC ROC and correlation between clinical variables and biomechanical properties were determined.

RESULTS

Lower HC Radius and IOPb and higher DA and V1 was found in uveitis group. Statistical differences between cases using systemic medications and those with topical treatment were found in L1. Differences were showed between those cases with active and inactive uveitis in PD, DA, V2 and L2. The biomechanical parameter with the best discriminatory capacity of uveitis disease was HC Radius.

CONCLUSION

Differences in corneal biomechanical properties between non-infectious uveitis and healthy eyes were found.

Twenty-Four-Hour Intraocular Pressure in Chronic Primary Angle-Closure Disease

PRCIS

Primary angle closure and primary angle closure glaucoma may exhibit normal intraocular pressure. Twenty-four-hour intraocular pressure fluctuation is highest in primary angle closure glaucoma. The degree of peripheral anterior synechiae was associated with a 24-hour intraocular pressure pattern in primary angle-closure disease without laser iridotomy.

PURPOSE

The purpose of this study was to study 24-hour intraocular pressure (IOP) patterns in eyes with chronic primary angle-closure disease and evaluate associations between peripheral anterior synechiae (PAS) and 24-hour IOP pattern.

PATIENTS AND METHODS

In this prospective cohort study, 59 eyes of 35 Asian patients with chronic primary angle-closure disease underwent complete ocular examinations at Ramathibodi Hospital, Mahidol University. Twenty-four-hour IOP records were obtained using Goldmann applanation tonometry at 2-hour intervals. Peak, mean, and trough 24-hour IOP values and 24-hour IOP fluctuation (difference between peak and trough values) were compared among groups. None of the participants received any treatment before complete data collection.

RESULTS

Even univariable analysis demonstrated a significant difference in peak, mean, and trough IOP and 24-hour IOP fluctuation between the 3 groups; the magnitude of trough IOP was not higher than 21 mmHg in all groups. In multivariable analysis, PAC and PACG eyes showed significantly higher peak IOP ( P =0.020 and 0.006, respectively) and 24-hour IOP fluctuation ( P =0.048 and 0.001, respectively) compared with PACS eyes. In comparison between combined PACS and PAC eyes versus PACG eyes, PACG eyes revealed significantly higher 24-hour IOP fluctuation. The degree of PAS was associated with peak and mean IOP values and with 24-hour IOP fluctuation in PAC and PACG eyes.

CONCLUSIONS

Twenty-four-hour IOP fluctuation was highest in PACG eyes. Although PAC and PACG eyes showed higher peak IOP and 24-hour IOP fluctuation values, compared with PACS eyes, trough IOP in PAC and PACG eyes were mostly below 21 mmHg. In addition, the degree of PAS was associated with a 24-hour IOP pattern in either PAC or PACG eyes.

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

Purpose

To compare readings of intraocular pressure (IOP) taken with the Goldmann applanation tonometer (GAT), the non-contact tonometer (NCT), and the rebound tonometer (RBT), and to compare their correlation with central corneal thickness (CCT).

Methods

This was a prospective, cross-sectional, observational study to which patients above 18 years of age were enrolled. A total of 400 eyes of 200 non-glaucomatous patients underwent IOP recordings using the GAT, NCT, and RBT, and CCT was also noted. Informed consent of the patients was taken. The IOP readings taken via the three methods were compared and correlated with CCT. Paired t test was used to compare the two devices. Simple and multivariate linear regression analyses were used to study the relationship between factors. A P value less than 0.05 was considered significant. Correlation was determined using the Pearson correlation coefficient, and a Bland-Altman graph was plotted.

Results

Mean IOP measured by the NCT was 15.65 ± 2.80 mmHg, by the RBT was 14.23 ± 3.05 mmHg, and by the GAT was 14.69 ± 2.97 mmHg. The mean CCT was 510.61 ± 33.83 microns. The difference between mean IOP recorded by the NCT and that by the RBT was 1.41 ± 2.39 mmHg, between the NCT and GAT was 0.95 ± 2.03 mmHg, and between the GAT and RBT was 0.45 ± 2.22 mmHg. The difference between the IOP values was statistically significant (P < 0.005). All tonometers showed a statistically significant correlation with CCT, but it was observed that the NCT had a stronger correlation (0.4037).

Conclusion

The IOP readings taken by all the three methods were comparable; however, RBT values were closer to GAT values. CCT did influence the IOP values, and this should be kept in mind while evaluating.

The Japan Glaucoma Society guidelines for glaucoma 5th edition

We are pleased to bring you the 5th edition of the Glaucoma Clinical Practice Guidelines. Clinical practice guidelines are based on evidence (scientific grounds). It is a document that presents the treatment that is the most appropriate for the patient. "Glaucoma Clinical Guidelines" was first published in 2003. This was the first guideline for glaucoma treatment in Japan. The principle of glaucoma treatment is to lower intraocular pressure. Means for lowering intraocular pressure includes drugs, lasers, and surgery; Glaucoma is a disease that should be considered as a complex syndrome rather than a single condition. Therefore, the actual medical treatment is not as simple as one word. This time we set the Clinical Questionnaire with a focus on glaucoma treatment. We hope that you will take advantage of the 5th edition.

Comparison between dynamic contour tonometry and Goldmann applanation tonometry correcting equations

In order to investigate the reliability of correcting GAT formulas in comparison with dynamic contour tonometry (DCT), this study included 112 right eyes of 112 healthy subjects aged from 21 to 77 years, whose eyes underwent to a full ophthalmologic exam. IOP was measured in each eye with DCT and then with GAT. IOP values obtained with GAT were corrected with 10 equations and then compared with those provided by DCT. Participants mean age was 42.24 ± 14.08 years; mean IOP measured with DCT was 17.61 ± 2.87 and 15.50 ± 2.47 mmHg, measured with GAT. The mean discordance between DCT and GAT measurements was 2.11 ± 2.24 mmHg. All the correcting formulas, but Srodka one (p ˂ 0.001), tend to increase the difference between GAT and DCT. According to these results Śródka equation provides the best correction, reducing the difference between the two IOP measurement methods of - 0.03 ± 0.85 mmHg. Other equations do not provide a valid improvement of the agreement between the two methods or they provide a worsening of the agreement.

Comparison of different correction formulas and measurement methods for the accurate determination of intraocular pressure after SMILE and FS-LASIK surgery

Background

To compare the accuracy of non-contact tonometry, Pentacam, and corneal visualization Scheimpflug technology (Corvis ST) for the measurement of intraocular pressure (IOP) after small incision lenticule extraction (SMILE) or femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery.

Methods

A total of 49 patients (98 eyes) undergoing FS-LASIK or SMILE surgery at West China Hospital, Sichuan University from January to March 2021 were enrolled in this prospective, comparative, self-controlled study. IOP values were measured with non-contact tonometer, Pentacam, and Corvis ST before surgery and 1 month after surgery. Pentacam-derived postoperative IOP values were corrected using five correction formulas (Ehlers, Shah, Dresden, Orssengo-Pye, and Kohlhaas), while Corvis ST-derived values were corrected using a single formula.

Results

In the SMILE group, no significant differences were observed between the IOP values corrected with the Shah formula before and after surgery (t = 0.17, P = 0.869), whereas postoperative IOP values corrected with the other formulas were significantly different from the corresponding preoperative measurements (P < 0.05). In the FS-LASIK group, postoperative IOP values corrected with the Ehlers, Shah, or Corvis ST formulas were significantly different from the corresponding preoperative IOP measurements (P < 0.05), but no significant differences were observed between pre- and postoperative IOP values corrected with the Dresden (t =  − 0.08, P = 0.941), Orssengo-Pye (t =  − 0.52, P = 0.604), or Kohlhaas (t = 1.22, P = 0.231) formulas.

Conclusions

Pentacam’s Shah correction formula seemed to be the most appropriate method for accurately measuring postoperative IOP in patients undergoing SMILE surgery, while the Dresden, Orssengo-Pye, and Kohlhaas correction formulas of Pentacam were identified as the most reliable methods for estimating IOP in patients after FS-LASIK surgery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02620-7.

Effect of manual upper eyelid elevation on intraocular pressure measurement by noncontact tonometer

PURPOSE

To evaluate whether manual upper eyelid elevation (MUEE) affects intraocular pressure (IOP) values obtained with a noncontact tonometer (NT).

METHODS

This cross-sectional study included 122 eyes of 122 non-glaucomatous adults. All patients underwent IOP measurement using both NT and Goldmann applanation tonometer (GAT). The order of measurements was NT without MUEE, NT with MUEE, and GAT. Both eyes of each patient were measured and one of the eyes was randomly selected for inclusion in the study. Central corneal thickness (CCT) and palpebral fissure height (PFH; distance between upper and lower eyelids) was recorded.

RESULTS

The patients' mean age was 43.91 ± 12.36 (20-61) years and 62.3% were women. Mean IOP values measured by NT without MUEE, NT with MUEE, and GAT were 15.98 ± 2.39, 15.84 ± 2.53, and 14.33 ± 2.3 mmHg, respectively. There was no statistically significant difference in mean IOP between NT without and with MUEE (p = 0.506). Mean IOP values obtained by NT with and without MUEE were significantly higher than those obtained by GAT (p < 0.001). The difference in IOP values measured by NT without and with MUEE was positively correlated with PFH (r = 0.214; p = 0.018). CCT and IOP values obtained by NT without MUEE and GAT were positively correlated (r = 0.300; p = 0.001 and r = 0.311; p = 0.001, respectively).

CONCLUSION

MUEE does not have a significant effect on IOP measurements by NT. The difference between IOP measured by NT without and with MUEE increases with greater PFH.

A stochastic approach to estimate intraocular pressure and dynamic corneal responses of the cornea

IntraOcular Pressure (IOP) is one of the most informative factors for monitoring the eye-health. This is usually measured by tonometers. However, the outputs of the tonometers depend on the physical and geometrical properties of the cornea. Therefore, the common practice is to develop a numerical model to generate some correction factors. The main challenge here is the accuracy and efficiency of a numerical model in predicting the IOP and Dynamic Corneal Response (DCR) of each patient. This study addresses this issue by developing a two-step surrogate model based on adaptive sparse Polynomial Chaos Expansion (PCE) for fast and accurate prediction of the IOP. In this regard, first, an FE model of the cornea has been developed to predict the DCR parameters. This FE model has been replaced with a PCE-based surrogate model to speed up the simulation step. The uncertainties in the geometry and material model of the cornea have been propagated through the surrogate model to estimate the distributions of the DCR parameters. In the second step, the combination of DCR parameters and the input parameters provide a proper parameter space for developing an efficient data-driven PCE model to predict the IOP. Moreover, sensitivity analysis by using PCE-based Sobol indices has been performed. The results demonstrate the accuracy and efficiency of the proposed method in predicting the IOP. Sensitivity analysis revealed that IOP measurement was influenced mostly by deflection amplitude and applanation time. The analysis indicates the importance of the interactions between the parameters.

Corneal-compensated intraocular pressure, Goldmann-correlated intraocular pressure and their associated factors in the geriatric population, a population-based study

PURPOSE

To determine the distribution of corneal-compensated intraocular pressure (IOPcc), Goldmann-correlated intraocular pressure (IOPg) and their associated factors in a geriatric population.

METHODS

The present cross-sectional study was performed in individuals above 60 years of age in Tehran, the capital of Iran. The sampling was performed using multi-stage random cluster sampling method. All participants underwent preliminary ocular examinations, and then imaging by Pentacam HR and IOL master 500. Measurement of IOPg, IOPcc, and corneal biomechanical indices including corneal hysteresis (CH) and corneal resistant factor (CRF) was performed in a random sub-sample using ocular response analyzer (ORA).

RESULTS

The mean IOPg and IOPcc were 16.76 ± 4.71 mmHg and 19.05 ± 4.67 mmHg, respectively. There were no statistically significant differences in both IOPg (p = 0.891) and IOPcc (p = 0.248) between males and females. Based on the multiple linear regression models, both IOPg and IOPcc showed a statistically significant direct relationship with CRF (P < 0.001) and a significant inverse relationship with CH (P < 0.001 for IOPg and IOPcc), anterior chamber angle (ACA) (p = 0.006 for IOPg and p = 0.017 for IOPcc), and spherical equivalent refractive error (p = 0.032 for IOPg and p = 0.046 for IOPcc).

CONCLUSION

Mean IOPg and IOPcc in the present study were higher compared to most previous studies. Corneal biomechanical indices including CH and CRF, refractive error and anterior chamber angle were independent associated factors of IOPg and IOPcc in the present study. There was no significant relationship between ORA-derived IOP values and CCT.

The Effect of an Eyelid Speculum on Intraocular Pressure Measurement in Newborns

PURPOSE

To evaluate the effect of an eyelid speculum on intraocular pressure (IOP) measurements in newborns.

METHODS

A total of 54 eyes of 27 newborns were involved in the study. The IOP measurements were obtained under topical anesthesia with the Icare PRO (Icare Finland Oy) before and after inserting the infant type of Barraquer wire eyelid speculum. A paired t test was used to compare the measurements.

RESULTS

The mean IOP without the eyelid speculum was 9.04 ± 2.13 mm Hg (range: 6.00 to 13.20 mm Hg) in the right eye and 9.26 ± 1.59 mm Hg (range: 7.10 to 13.00 mm Hg) in the left eye. With the eyelid speculum in place, the mean IOP was 11.91 ± 2.23 mm Hg (range: 9.10 to 15.80 mm Hg) in the right eye and 11.70 ± 1.89 mm Hg (range: 8.40 to 14.50 mm Hg) in the left eye (P ≤ .001). The mean differences in IOP between measurements with and without the eyelid speculum were 2.87 ± 2.23 mm Hg (range: 0.20 to 5.20 mm Hg) in the right eye and 2.44 ± 1.48 mm Hg (range: 0.00 to 4.90 mm Hg) in the left eye. The mean difference in IOP between measurements with and without the eyelid speculum for all eyes was 2.65 ± 1.89 mm Hg (range: 0.00 to 5.20 mm Hg). There was no correlation between the difference in IOP after the placement of the eyelid speculum and postconceptual age or weight at the examination (r = 0.11, P = .41, r = 0.32, P = .14, respectively).

CONCLUSIONS

The Barraquer wire eyelid speculum caused an increase in IOP in newborns under topical anesthesia without a significant difference between postconceptual age and sex in both eyes. The average IOP rise after the eyelid speculum was inserted was 2.65 mm Hg. This effect should be considered when interpreting IOP measurements in newborns. [J Pediatr Ophthalmol Strabismus. 2022;59(1):13-16.].

Comparison of intraocular pressures estimated by rebound and applanation tonometry in dogs with lens instability: 66 cases (2012-2018)

OBJECTIVE

To compare intraocular pressures (IOPs) estimated by rebound and applanation tonometry for dogs with lens instability.

ANIMALS

66 dogs.

PROCEDURES

Medical records of dogs examined between September 2012 and July 2018 were reviewed for diagnoses of anterior (ALL) or posterior (PLL) lens luxation or lens subluxation.

RESULTS

Estimates of IOP obtained with rebound and applanation tonometry significantly differed from each other for all types of lens instability considered collectively (mean ± SE difference between tonometric readings, 8.1 ± 1.3 mm Hg) and specific types of lens instability considered individually (mean ± SE difference between tonometric readings: ALL, 12.8 ± 2.5 mm Hg; PLL, 5.9 ± 1.7 mm Hg; subluxation, 2.8 ± 0.8 mm Hg). Median (range) differences between rebound and applanation tonometer readings for dogs with ALL was 5 mm Hg (-9 to 76 mm Hg), with PLL was 3 mm Hg (-1 to 19 mm Hg), and with lens subluxation was 3 mm Hg (-9 to 18 mm Hg). In eyes with ALL, rebound tonometer readings exceeded applanation tonometer readings on 44 of 60 (73%) occasions.

CONCLUSIONS AND CLINICAL RELEVANCE

Rebound tonometry yielded higher estimates of IOP than did applanation tonometry in eyes with ALL and with all types of lens luxation considered collectively. Estimates of IOP in eyes with lens instability should ideally be obtained with both rebound and applanation tonometers. Veterinarians with only one type of tonometer should interpret results for dogs with lens instability concurrent with physical examination findings.

Different Effects of Aging on Intraocular Pressures Measured by Three Different Tonometers

This study aimed to compare intraocular pressures (IOP) using different tonometers, Goldmann applanation (IOP_GAT), non-contact (IOP_NCT), and rebound (IOP_RBT), and to assess the effects of aging and central corneal thickness (CCT) on the measurements. The IOP_GAT, IOP_NCT, IOP_RBT, mean patient age (65.1 ± 16.2 years), and CCT (521.7 ± 39.2 µm) were collected retrospectively from 1054 eyes. The differences among IOPs were compared by the paired t-test. Possible correlations between devices, age, and CCT were assessed by linear regression analyses. The effects of age and CCT on the IOP reading were assessed by mixed-effects regression models. The IOP_GAT values were 2.4 and 1.4 mmHg higher than IOP_NCT and IOP_RBT, respectively; the IOP_NCT was 1.0 mmHg lower than IOP_RBT (p < 0.0001 for all comparisons). The IOPs measured by each tonometer were highly correlated with each other (r = 0.81–0.90, t = 45.2–65.5). The linear regression analyses showed that age was negatively correlated with IOP_NCT (r = −0.12, t = −4.0) and IOP_RBT (r = −0.14, t = −4.5) but not IOP_GAT (r = 0.00, t = −0.2); the CCT was positively correlated with IOP_GAT (r = 0.13, t = 4.3), IOP_NCT (r = 0.29, t = 9.8), and IOP_RBT (r = 0.22, t = 7.2). The mixed-effect regression models showed significant negative correlations between age and IOP_NCT (t = −2.6) and IOP_RBT (t = −3.4), no correlation between age and IOP_GAT (t = 0.2), and a significant positive correlation between CCT and the tonometers (t = 3.4–7.3). No differences between IOP_GAT and IOP_RBT were seen at the age of 38.8 years. CCT affects IOPs from all tonometers; age affects IOP_NCT and IOP_RBT in different degrees. IOP_RBT tended to be higher than IOP_GAT in young subjects, but this stabilized in middle age and became higher in older subjects.

The Precision of a New Anterior Segment Optical Coherence Tomographer and Its Comparison With a Swept-Source OCT-Based Optical Biometer in Patients With Cataract

PURPOSE

To assess the precision of a new spectral-domain optical coherence tomographer (SD-OCT)/Placido topographer (MS-39; CSO) and its comparison with a swept-source OCT (SS-OCT) biometer (Argos; Movu, Inc) in patients with cataract.

METHODS

Fifty-three right eyes from 53 patients were examined by two experienced operators three times using both devices randomly. Employing the within-subject standard deviation (S_w), test-retest variability, coefficient of variation, and intraclass correlation coefficient to evaluate intraoperator repeatability and interoperator reproducibility; the double-angle plots to analyze astigmatism; and Bland-Altman plots and 95% limits of agreement to verify the agreement between devices.

RESULTS

The SD-OCT/Placido tomographer showed high precision, with coefficient of variation of 0.44% or less, intraclass correlation coefficient of 0.945 or greater for all parameters, test-retest variability of 4.21 µm or less for central corneal thickness (CCT), 0.03 mm or less for anterior chamber depth (ACD) and aqueous depth (AQD), and 0.25 diopters (D) or less for mean keratometry (Km), J₀, and J₄₅. The inter-device differences in Km, J₀, and J₄₅ were statistically insignificant, whereas the remaining were statistically but not clinically significant. The 95% limits of agreement of CCT, ACD, AQD, Km, J₀, and J₄₅ were -3.70 to 15.25 µm, -0.06 to 0.04 mm, -0.06 to 0.04 mm, -0.28 to 0.35 D, -0.27 to 0.26 D, and -0.27 to 0.21 D, respectively. The double-angle plot confirmed the high agreement in astigmatism.

CONCLUSIONS

For CCT, ACD, AQD, Km, and astigmatism measurements in patients with cataract, the new SD-OCT/Placido tomographer has excellent precision and high agreement with the Argos SS-OCT biometer, and can be used interchangeably. [J Refract Surg. 2021;37(9):616-622.].

The effect of intraocular pressure elevation and related ocular biometry changes on corneal OCT speckle distribution in porcine eyes

The aim of this study was to evaluate the influence of increase in intraocular pressure (IOP) and cooccurring changes in ocular biometry parameters on the corneal optical coherence tomography (OCT) speckle distribution in ex-vivo experiments on porcine intact eyes. Twenty-three eyeballs were used in the inflation test where IOP in the anterior chamber was precisely set from 10 mmHg to 40 mmHg in steps of 5 mmHg and where eye biometry was utilized (IOL Master 700). To assess the influence of the duration of the experiment on the OCT speckle statistics, the second experiment was performed with 10 eyeballs at the constant IOP of 15 mmHg. Based on the OCT scans of central cornea (Copernicus REVO), spatial maps of the scale parameter (a) and the shape parameter (v) of the gamma distribution speckle model were estimated. The means of both parameters for each spatial map were computed within the 2 mm of the central stroma. Both distributional parameters statistically significantly varied with IOP and time (one way repeated measures ANOVA, all p-values < 0.001). The a parameter revealed a faster statistically significant increase in IOP up to 25 mmHg, regardless of time. Central corneal thickness (CCT), the anterior chamber depth, and the mean equivalent spherical power varied significantly with IOP, whereas CCT and axial length changed statistically significantly with time. Statistically significant correlation was found between CCT and the a parameter, after removing IOP as a confounding factor (r = -0.576, p < 0.001). The parameters of the gamma distribution can be used not only for identifying IOP induced changes in the optical scattering within the corneal stroma, but also in corneal geometry. The approach of corneal speckle analysis could be potentially utilized for an indirect and noninvasive assessment of some properties of corneal stroma.

Correlation between corneal thickness, keratometry, age, and differential pressure difference in healthy eyes

To determine the use of differential pressure difference (DPD), in air-puff differential tonometry, as a potential biomechanical measure of the cornea and elucidate its relationship with the intraocular pressure (IOP), central corneal thickness, corneal curvature, and age. This study comprised 396 eyes from 198 patients and was conducted at Acibadem University, School of Medicine, Department of Ophthalmology, Istanbul, Turkey. The central corneal curvature and refraction of the eyes were measured using an Auto Kerato-Refractometer (KR-1; Topcon Corporation, Tokyo, Japan). IOP and central corneal thickness were measured using a tono-pachymeter (CT-1P; Topcon Corporation, Tokyo, Japan), wherein two separate readings of IOP were obtained using two different modes: 1-30 and 1-60. The difference between these two readings was recorded as the DPD. The factors affecting the DPD were determined by stepwise multiple linear regression analysis. DPD varied over a dynamic range of - 3.0 to + 5.0 mmHg and was weakly correlated with the central corneal thickness (r = 0.115, p < 0.05). DPD showed no significant correlation with IOP 1-30 (p > 0.05). A weak but statistically significant (p < 0.05) positive correlation of DPD was observed with age (r = 0.123), Kavg (r = 0.102), and the CCT (r = 0.115). There was a significant correlation between DPD and Kavg, CCT, and age. There was no significant correlation between DPD and IOP 1-30. Age-related changes in the corneal ultrastructure may be a plausible explanation for the weak positive association between age and DPD. The proposed method may prove a valid non-invasive tool for the evaluation of corneal biomechanics and introduce DPD in the decision-making of routine clinical practice.

[Comparison of Goldmann tonometry with air-puff tonometry. A study of 159 patients in Abidjan]

PURPOSE

The goal of this study was to compare the intraocular pressure (IOP) values obtained with each of the tonometry methods as well as to study the effect of corneal pachymetry on the measurements obtained by each method.

MATERIAL AND METHODS

We carried out a cross-sectional, descriptive, analytical, prospective study in the ophthalmology department of a multispecialty clinic in Abidjan (Ivory Coast) from April 2018 to August 2018. Patients aged 15 and over were included in the study. Over this period, IOP was measured by Goldman Applanation Tonometer (HaagStreit, AT 900, Switzerland) and air-puff Tonopachymeter (Nidek, NT 530 P, Japan), which also permitted measurement of central optical corneal pachymetry. The data analyzed focused on socio-demographic characteristics, ophthalmologic history, tonometry, and central corneal pachymetry. The comparison of the values obtained by both devices and the effect of central corneal thickness (CCT) on tonometry were analyzed using EpiDataAnalysis V2.2.2.183 software.

RESULTS

We examined 318 eyes of 159 patients whose mean age was 40±12.57 years, range 16 to 82 years. The gender ratio was 1. A past ophthalmologic history was noted in 79.2% of patients. The mean IOP by Goldmann applanation tonometry was 12.75±3.17mmHg, and that by non-contact air-puff tonometry was 13.83±3.80mmHg. The mean central corneal thickness was 530.50±32.61μm. The difference between IOP measured by non-contact tonometry and that measured by contact tonometry was statistically significant, with P=0.00. There was no statistically significant relationship between central corneal pachymetry and contact tonometry (P=0.80). However, there was a statistically significant relationship between non-contact tonometry and central pachymetry (P=0.00). The values obtained with the air-puff tonometer are more affected by central corneal thickness.

CONCLUSION

The values obtained by Goldmann applanation tonometry are not equivalent to those obtained by non-contact air-puff tonopachymetry.

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

PRCIS

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.

PURPOSE

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.

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Reliability of Intraocular Pressure Measurement by Goldmann Applanation Tonometry After Refractive Surgery: A Review of Different Correction Formulas

Myopia is one of the main risk factors for the onset of open-angle glaucoma. One of the first steps to assess glaucoma occurrence is the measurement of the intraocular pressure (IOP) by the Goldmann applanation tonometry (GAT). Even if this device is considered to be the gold standard for such measurements, it is affected by several sources of errors. Among these, there are the corneal thickness and curvature, both modified by corneal refractive surgery (CRS), that nowadays has become a very popular method to treat refractive errors. Indeed, CRS, by modifying the corneal shape and structure, causes an underestimation of the IOP measurements. In the literature, several IOP correction formulas to utilize with different devices have been proposed to overcome this problem. This paper aims to review the various correction formulas applied to the GAT in the attempt to improve the reliability of this measurement.

Comparative intraocular pressure measurements using three different rebound tonometers through in an ex vivo analysis and clinical trials in canine eyes

Objective

To evaluate the clinical relevance of intraocular pressure (IOP) measured with three different rebound tonometers in an ex vivo analysis and clinical trials in dogs.

Animals and procedures

Ex vivo analysis and clinical trials were performed separately. For the ex vivo analysis, eight enucleated eyes were obtained from four Beagle dogs. IOP values measured with TONOVET^® (TV‐IOP), TONOVET‐Plus^® (TVP‐IOP), and SW‐500^® (SW‐IOP) were compared with manometric IOPs. For clinical trials, each tonometer was evaluated separately, depending on whether TVP‐IOP was higher or lower than 14 mm Hg. One‐way repeatedmeasures analysis of variance, simple linear regression analysis, and Bland‐Altman plots were used for statistical analyses.

Results

In ex vivo analysis, TV‐IOP and TVP‐IOP were not significantly different from manometric IOP. However, SW‐IOP underestimated IOP compared to manometry. Higher discrepancy was observed in TV‐IOP and SW‐IOP with an increase in manometric IOP. In clinical trials, no significant difference was observed between TV‐IOP (9.73 ± 2.92) and TVP‐IOP (11.36 ± 2.23) when TVP‐IOP was lower than 14 mm Hg, but SW‐IOP (8.70 ± 3.03) was significantly lower than TVP‐IOP. TV‐IOP (15.96 ± 6.47) and SW‐IOP (13.09 ± 3.72) were significantly lower than TVP‐IOP (20.08 ± 6.60) when the IOP was higher than 14 mm Hg of TVP‐IOP.

Conclusions

This study demonstrates that the TONOVET^® and TONOVET‐Plus^® provide a useful approach for ex vivo analysis. In clinical trials, results of TV‐IOP and SW‐IOP were significantly lower than of TVP‐IOP when IOP was higher than 14 mm Hg of TVP‐IOP. The characteristics of rebound tonometers should be considered in clinical settings.

In vivo measures of anterior scleral resistance in humans with rebound tonometry

PURPOSE

To measure regional variations in anterior scleral resistance (ASR) using a ballistic rebound tonometer (RBT) and examine whether the variations are significantly affected by ethnicity and refractive error (RE).

METHODS

ASR was measured using a RBT (iCare TA01) following calibration against the biomechanical properties of agarose biogels. Eight scleral regions (nasal, temporal, superior, inferior, inferior-nasal, inferior-temporal, superior-nasal and superior-temporal) were measured at locations 4mm from the limbus. Subjects were 130 young adults comprising three ethnic groups whose RE distributions [MSE (D) ± S.D.] incorporated individuals categorised as without-myopia (NM; MSE ≥ -0.50) and with-myopia (WM; MSE < -0.50); British-White (BW): 26 NM + 0.52 ± 1.15D; 22 WM -3.83 ± 2.89D]; British-South-Asian (BSA): [9 NM + 0.49 ± 1.06D; 11 WM -5.07 ± 3.76D; Hong-Kong-Chinese (HKC): [11 NM + 0.39 ± 0.66D; 49 WM -4.46 ± 2.70D]. Biometric data were compiled using cycloplegic open-field autorefraction and the Zeiss IOLMaster. Two- and three-way repeated measures analysis of variances (anovas) tested regional differences for RBT values across both refractive status and ethnicity whilst stepwise forward multiple linear regression was used as an exploratory test.

RESULTS

Significant regional variations in ASR were identified for the BW, BSA and HKC (p < 0.001) individuals; superior-temporal region showed the lowest levels of resistance whilst the inferior-nasal region the highest. Compared to the BW and BSA groups, the HKC subjects displayed a significant increase in mean resistance for each respective region (p < 0.001). With the exception of the inferior region, ethnicity was found to be the chief predictor for variation in the scleral RBT values for all other regions. Mean RE group differences were insignificant.

CONCLUSIONS

The novel application of RBT to the anterior sclera confirm regional variation in ASR. Greater ASR amongst the HKC group than the BW and BSA individuals suggests that ethnic differences in anterior scleral biomechanics may exist.

Validation and comparison of four handheld tonometers in normal ex vivo canine eyes

OBJECTIVES

To determine the accuracy and precision of the Icare^® TONOVET Plus rebound tonometer and the Tono-Pen AVIA Vet™ applanation tonometer for intraocular pressure (IOP) measurement in normal ex vivo canine eyes and comparison to earlier models of these tonometers.

ANIMALS & PROCEDURES

The anterior chambers of six normal dog eyes were cannulated ex vivo. IOP was measured with the TONOVET (TV01), TONOVET Plus, Tono-Pen Vet™, and Tono-Pen AVIA Vet™ at manometric IOPs ranging from 5 to 70 mm Hg. Data were analyzed by linear regression, ANOVA and Bland-Altman plots. A P value ≤ .05 was considered significant.

RESULTS

Intraocular pressure values obtained using the TONOVET Plus and TV01 were significantly more accurate than with the Tono-Pen VET and Tono-Pen AVIA Vet, particularly at higher IOPs (30-70 mm Hg). Accuracy was not significantly different between any of the devices in the low to normal physiologic IOP range (5-25 mm Hg). Level of precision was high for all devices, though the TONOVET Plus was more precise than the Tono-Pen Vet in the 5-25 mmHg range and the TV01 was more precise than the Tono-Pen AVIA Vet over the whole IOP range.

CONCLUSIONS

All devices underestimated IOP, particularly at higher pressures. Rebound tonometers were more accurate over the full range of IOP tested and in the high IOP range; however, there were no significant differences in accuracy among devices in the physiologic IOP range. All tonometers can provide clinically useful IOP readings in dogs, but rebound and applanation tonometers should not be used interchangeably.

Effect of Manual Upper Eyelid Elevation on Intraocular Pressure Measurement by Four Different Tonometers

SIGNIFICANCE

This study is the first to show that the manual upper eyelid elevation (manual UEE) that is commonly used to prevent disruption of the IOP measurement due to blinking or upper eyelid contact with the tip of the tonometer does not affect the IOP values.

PURPOSE

We investigated whether manual UEE affects the IOP readings using three rebound tonometers (Icare TA01i, Icare PRO, and Icare ic100) and Goldmann applanation tonometry (GAT).

METHODS

One eye was measured for 101 patients (56 eyes of primary open-angle glaucoma patients and 45 healthy subjects). The IOPs were measured without and with manual UEE. Each IOP was measured twice; the measurement order using the tonometers was randomly selected. In addition, palpebral fissure height (distance between the upper and lower eyelids) was measured.

RESULTS

The IOPs without manual UEE were 12.1 ± 2.9, 13.3 ± 2.7, 11.7 ± 2.9, and 16.0 ± 3.2 mmHg (Icare TA01i, Icare PRO, Icare ic100, and GAT), and those with manual UEE were 12.3 ± 3.0, 13.3 ± 2.8, 11.7 ± 2.9, and 16.0 ± 3.3, respectively. No significant difference was found between the IOP without and with manual UEE (IOP difference; all, P > .50; paired t test). Multiple linear regression analyses revealed that palpebral fissure height did not affect IOP difference for any of the tonometers.

CONCLUSIONS

Simple manual UEE when measuring the IOP has little effect on the IOP obtained using all current rebound tonometers and GAT.

A clinical method for estimating the modulus of elasticity of the human cornea in vivo

BACKGROUND

To develop a method, using current clinical instrumentation, to estimate the Young's modulus of the human cornea in vivo.

METHODS

Central corneal curvature (CCC), central corneal thickness(CCT), intraocular pressure (IOP) was measured with the Goldmann tonometer (IOPG) and the Pascal Dynamic Corneal Tonometer(PDCT) in one eye of 100 normal young human subjects (21.07 ± 2.94 years) in vivo. The Orssengo and Pye algorithm was used to calculate the Young's modulus of the corneas of these subjects.

RESULTS

The Young's modulus(E) of the corneas of the subjects using the PDCT and IOPG results (Ecalc) was 0.25 ± 0.10MPa, and without the PDCT results (Eiopg) was 0.29 ± 0.06MPa. The difference in these results is due to the difference in tonometry results between the two instruments, as the mean PDCT result for the subjects was 16.89 ± 2.49mmHg and the IOPG result 15.06 ± 2.71mmHg. E was affected by the CCC of the subjects but more particularly by the CCT and IOP measurements. Corneal stiffness results are also presented.

CONCLUSION

Two methods have been developed to estimate the Young's modulus of the human cornea in vivo using current clinical instrumentation. One method (Ecalc) is applicable to the general corneal condition, and Eiopg to the normal cornea, and these results can be used to calculate corneal stiffness.

Finite element simulation of Goldmann tonometry after refractive surgery

BACKGROUND

The problem of accuracy of intraocular pressure (IOP) measurement using Goldmann Applanation Tonometry (GAT) after a refractive surgery is still unresolved. In this study a numerical simulation of refractive surgery and GAT is proposed as a method to evaluate accuracy of the correction formula for GAT reading after changes in corneal curvature and thickness.

METHODS

In the finite element analysis the effect of the corneal shell buckling was taken into account. This effect is responsible for the nonlinear relation of Goldmann applanation tonometer measurement and intraocular pressure. Goldmann applanation tonometry was simulated for different ablation depths and values of intraocular pressure levels.

FINDINGS

The results of the simulation indicate a strong relation between the Goldmann applanation reading and the intraocular pressure level for values greater than nominal (about 16 mmHg). The estimation error of the intraocular pressure after changes in corneal geometry, is lower than 1 mmHg for IOP = 32 mmHg and lower than 3 mmHg for IOP = 48 mmHg.

INTERPRETATION

The proposed correction formula of Goldmann applanation tonometry occurred to be useful in the cases after the corneal refractive surgery regardless of the intraocular pressure values and ablation depth.

Effects of vitamin D deficiency on intraocular pressure values obtained by ocular response analyzer

PURPOSE

To compare corneal biomechanical properties measured with ocular response analyzer (ORA) and intraocular pressure (IOP) measurements in patients with vitamin D deficiency and in healthy cases.

METHODS

One hundred and twenty eyes of 120 subjects (between the ages of 19 and 78) who applied to university's outpatient clinic were evaluated: 41 lacks of vitamin D (Group 1), 39 insufficient vitamin D (Group 2) and 40 controls (Group 3). Corneal hysteresis, corneal resistance factor, Goldmann-correlated IOP and corneal compensated IOP of patients were measured by ORA.

RESULTS

The mean ages were 48.9 ± 12.1, 52.8 ± 13.6 and 52.1 ± 13.9 in groups 1, 2 and 3, respectively (p = 0.370). Mean IOPcc values were 16.5 ± 3.6 (8.1-27.3), 16.7 ± 2.7 (12.0-22.7) and 16.3 ± 3.3 (10.8-27.4) mmHg (p = 0.889); mean IOPg values were 16.8 ± 5.0 (6.5-39.5), 16.3 ± 2.9 (10.3-23.0) and 15.9 ± 3.2 (10.0-26.0) mmHg (p = 0.539); mean CH values were 10.8 ± 1.9 (8.3-19.0), 11.4 ± 1.6 (6.9-14.0) and 11.2 ± 1.5 (7.5-13.2) (p = 0.257); mean CRF values were 10.5 ± 2.7 (7.4-25.0), 11.1 ± 1.5 (6.8-13.5) and 10.5 ± 1.2 (7.7-12.8) (p = 0.282) in groups 1, 2 and 3, respectively. There was no statistical difference between the groups in terms of IOPcc, IOPg CH and CRF. However, mean CH values were found less in the lack of vitamin D group.

CONCLUSION

The CH values were lower, and the IOPg values were higher in cases of vitamin D deficiency. Corneal biomechanical differences in patients with lack of vitamin D were not statistically significant.

Comparability of three intraocular pressure measurement: iCare pro rebound, non-contact and Goldmann applanation tonometry in different IOP group

Background

Measurement of intraocular pressure (IOP) is essential for glaucoma patients. Many factors such as central corneal thickness (CCT) can affect the accuracy of IOP measurement. The purpose of this study was to evaluate the agreement of IOP measured by non-contact tonometer (NCT), iCare pro rebound tonometer (iCare), and Goldmann applanation tonometer (GAT) in different IOP group.

Methods

This was a Hospital-based cross-sectional study. Two hundred subjects were enrolled in this study. All subjects underwent IOP measurement using an NCT–iCare–GAT sequence. Bland-Altman, Pearson correlation and intraclass correlation analysis were performed using SPSS 17.0 software. The influence of CCT on each IOP measurement methods was evaluated by linear regression analysis.

Results

The mean difference (Δ) of NCT–GAT did not differ from (Δ) iCare–GAT in IOP < 10 and 10–21 mmHg group. However, (Δ) NCT–GAT was significantly higher than (Δ) iCare–GAT in IOP 22–30 and > 30 mmHg group (P < 0.05). Bland–Altman analysis showed significant agreement between the three devices (P < 0.01). IOP measurements of the three methods were significantly correlated with CCT (P < 0.01).

Conclusions

ICare pro shows a higher agreement with GAT over a wide range of IOP compared with NCT. The consistency between the three tonometers was similar in a low and normal IOP range. However, NCT shows a greater overestimate of IOP in moderate and higher IOP group. The variability of IOP measurement affected by CCT is NCT > iCare pro > GAT.

[Modern view on ocular hypertension]

Increased intraocular pressure is the main, and the only modifiable risk factor in the development of glaucoma. This review analyzes studies on differential diagnostics of ocular hypertension and risk factors of its conversion to glaucoma, and gives recommendations based on literature data for the most correct algorithm for management of patients with ocular hypertension.

Dual Optical Signal-based Intraocular Pressure-sensing Principle Using Pressure-sensitive Mechanoluminescent ZnS:Cu/PDMS Soft Composite

This paper presents a novel principle for intraocular pressure (IOP)-sensing (monitoring) based on a pressure-sensitive soft composite in which a dual optical signal is produced in response to impulsive pressure input. For the initial assessment of the new IOP sensing principle, a human eye is modeled as the spherically shaped shell structure filled with the pressurized fluid, including cornea, sclera, lens and zonular fiber, and a fluid-structure interaction (FSI) analysis was performed to determine the correlation between the internal pressure and deformation (i.e., strain) rate of the spherical shell structure filled with fluid by formulating the finite element model. The FSI analysis results for human eye model are experimentally validated using a proof-of-conceptual experimental model consisting of a pressurized spherical shell structure filled with fluid and a simple air-puff actuation system. In this study, a mechanoluminescent ZnS:Cu- polydimethylsiloxane (PDMS)-based soft composite is fabricated and used to generate the dual optical signal because mechanically driven ZnS:Cu/PDMS soft composite can emit strong luminescence, suitable for soft sensor applications. Similar to the corneal behavior of the human eye, inward and outward deformations occur on the soft composite attached to the spherical shell structure in response to air puffing, resulting in a dual optical signal in the mechnoluminescence (ML) soft composite.

Characterization of Corneal Biomechanical Properties and Determination of Natural Intraocular Pressure Using CID-GAT

Purpose

The intraocular pressure (IOP) measured using Goldmann Applanation Tonometry (GAT) is confounded by individual corneal properties. We investigated a modified method that removes the confoundment by incorporating corneal properties into the Imbert-Fick's law is investigated.

Method

Porcine eyes were pressurized between 10 and 40 mm Hg using a manometer. The eyes were indented using a flat cylindrical indenter. A modified corneal indentation device (CID) procedure was used to obtain the corneal moduli E_qs. The calculated IOP_NC from the Imbert-Fick's Law using the corneal moduli E_qs was compared to the natural IOP_N, measured using pressure sensor inserted into the eye.

Results

Test results showed that IOP-dependent corneal modulus E_qs is a primary confounding factor in IOP calculation. The average elastic modulus E_qs is 0.173 ± 0.018 MPa at 20 mm Hg, and increases with IOP at a linear rate of 0.0066 MPa per mm Hg (r = 0.997, P < 0.001). Incorporation of individual E_qs into IOP_NC calculation showed that IOP_NC are in good agreement with reference IOP_N (slope = 0.999, r = 0.939, P < 0.001).

Conclusions

The IOP-dependent corneal modulus E_qs is a primary confounding factor in IOP calculation. A modified CID-GAT procedure to obtain natural cornea-independent IOP_NC is developed and verified in this study. The CID-GAT IOP modification may be used in place of conventional GAT when the confounding effects in eyes with atypical cornea (e.g., laser-assisted in situ keratomileusis [LASIK] thinned) are significant.

Translational Relevance

Confoundment from corneal properties results in IOP measurement errors. The study showed that the CID-GAT method can significantly reduce the confounding corneal errors.

Validation of the Icare® TONOVET plus rebound tonometer in normal rabbit eyes

To determine the accuracy and precision of the Icare^® TONOVET Plus rebound tonometer for measuring intraocular pressure (IOP) in normal rabbit eyes, as well as compare it to three other commercially available tonometers: the Icare^® TONOVET (TV01), Tono-Pen Vet™, and Tono-Pen AVIA Vet™. The anterior chambers of both eyes of three New Zealand White rabbits were cannulated, post-mortem. IOP was measured using each of the above four tonometers at manometric pressures ranging between 5 mmHg and 70 mmHg. Data were analyzed by linear regression, ANOVA, and Bland-Altman plots. A p-value of ≤0.05 was considered significant for all statistical tests. IOP values obtained with the TONOVET Plus (in 'lapine' mode) were significantly closer to manometric IOP than those obtained with the other tonometers tested. The TV01 (in 'd' dog setting) and Tono-Pen AVIA Vet™ were significantly more accurate compared to the Tono-Pen Vet™. All tonometers had high levels of precision, though the TONOVET Plus and TV01 were significantly more precise compared to the Tono-Pen AVIA Vet™. All tonometers tended to underestimate IOP, particularly at high pressures, however the TONOVET Plus was highly correlated with manometric IOP in the clinically relevant range of 5-50 mmHg. The TONOVET Plus is an appropriate choice of instrument for measuring IOP in rabbit eyes in both research and clinical settings.

An Update on Corneal Biomechanics and Architecture in Diabetes

In the last decade, we have witnessed substantial progress in our understanding of corneal biomechanics and architecture. It is well known that diabetes is a systemic metabolic disease that causes chronic progressive damage in the main organs of the human body, including the eyeball. Although the main and most widely recognized ocular effect of diabetes is on the retina, the structure of the cornea (the outermost and transparent tissue of the eye) can also be affected by the poor glycemic control characterizing diabetes. The different corneal structures (epithelium, stroma, and endothelium) are affected by specific complications of diabetes. The development of new noninvasive diagnostic technologies has provided a better understanding of corneal tissue modifications. The objective of this review is to describe the advances in the knowledge of the corneal alterations that diabetes can induce.

Citius, Altius, Fortius: Agreement between Perkins and Dynamic Contour Tonometry (Pascal) and the Impact of Altitude

Introduction

To ascertain differences in intraocular pressure (IOP) measurement and their repeatability between dynamic contour tonometry (DCT) and Goldmann/Perkins applanation tonometry (GAT) at two different atmospheric pressures.

Materials and methods

Forty-one eyes of 41 healthy consenting subjects were enrolled for this observational, cross-sectional study. Pachymetry and IOP measurements with DCT and GAT for both eyes of each subject at Acapulco (0 m from sea level) and at Mexico City (2,234 m from sea level) were done by the same observer. The IOP was compared between tonometers at each of the altitudes, and also for repeatability of each tonometer at different altitudes. Pearson's correlation coefficient and Bland-Altman plots were used to assess reliability of measurements and their differences at the two altitudes.

Results

The mean age of patients was 41.7 (28-66 years); 22 were females. Mean IOP with DCT was 16.1 ± 2.2 mm Hg at sea level and 15.9 ± 2.1 mm Hg at 2,234 m above sea level, not a significant difference. Mean GAT IOP at the two altitudes was 13.1 ± 1.8 and 11.5 ± 1.7 mm Hg respectively, a statistically sig -nificant difference. In contrast, central corneal thickness (CCT) was not significantly changed (548.3 to 549.4 μm, p = 0.496).

Conclusion

Repeatability of single-observer measurements with GAT remains clinically acceptable, but not at different altitudes. The DCT seems to more consistently measure a similar IOP at different altitudes in the same subjects. The two tonometers may not be used interchangeably in the serial follow-up of patients at any of the altitudes.How to cite this article: Albis-Donado O, Bhartiya S, Gil-Reyes M, Casale-Vargas G, Arreguin-Rebollar N, Kahook MY. Citius, Altius, Fortius: Agreement between Perkins and Dynamic Contour Tonometry (Pascal) and the Impact of Altitude. J Curr Glaucoma Pract 2018;12(1):40-44.

Clinical evaluation of a new correction algorithm for dynamic Scheimpflug analyzer tonometry before and after laser in situ keratomileusis and small-incision lenticule extraction

PURPOSE

To compare a biomechanically corrected intraocular pressure (bIOP) algorithm provided by the dynamic Scheimpflug analyzer (Corvis ST) with Goldmann applanation tonometry IOP (Goldmann IOP) and standard dynamic Scheimpflug analyzer IOP measurements before and after laser in situ keratomileusis (LASIK) and refractive lenticule extraction small-incision lenticule extraction (SMILE) surgeries.

SETTING

Smile Eye Clinic, Munich, Germany, and University of Liverpool, Liverpool, United Kingdom.

DESIGN

Retrospective case series.

METHODS

Patients scheduled for LASIK and patients scheduled for small-incision lenticule extraction for myopia or myopic astigmatism were included. The preoperative and postoperative evaluations included Goldmann, Scheimpflug tomography, and dynamic Scheimpflug analyzer IOP measurements.

RESULTS

The study comprised 14 patients in the LASIK group and 22 patients in the small-incision lenticule extraction group. Preoperative Goldmann IOP and Scheimpflug analyzer IOP values showed significant positive correlation with central corneal thickness (CCT) (P = .05 for LASIK; P = .003 for small-incision lenticule extraction). No significant correlation was found between bIOP and CCT (P > .05). After both surgeries, there were significant decreases in Goldmann IOP (-3.2 mm Hg ± 3.4 [SD] and -3.2 ± 2.1 mm Hg, respectively; both P < .001) and Scheimpflug analyzer IOP (-3.7 ± 2.1 mm Hg and -3.3 ± 2.0 mm Hg, respectively, both P < .001) compared with preoperative readings, whereas bIOP did not differ significantly (0.1 ± 2.1 mm Hg and 0.8 ± 1.8 mm Hg, respectively; P = .80 and P = .273, respectively).

CONCLUSIONS

The bIOP readings before and after LASIK and small-incision lenticule extraction were neither significantly different nor correlated with CCT. In contrast, both Goldmann IOP and Scheimpflug analyzer IOP had significant reductions postoperatively and showed significant correlation with CCT preoperatively.

Higher Intraocular Pressure Levels Associated With Lower Hysteresis In Type 2 Diabetes

Aim:

To investigate the differences of corneal biomechanic characteristics using Ocular Response Analyzer (ORA, Reichert; USA) on type 2 diabetics and healthy subjects.

Methods:

One hundred eyes of 100 subjects (between the ages of 17-91) who applied to Adnan Menderes University’s Ophthalmology Clinic between January-March 2015 were included in this study, 50 diabetics (Group 1) and 50 healthy controls (Group 2). The eyes included in the study were randomly chosen. Corneal Hysteresis (CH), Corneal Resistance Factor (CRF), Goldmann correlated Intraocular Pressure (IOPg) and corneal compensated Intraocular Pressure (IOPcc) of patients were measured by ORA. Detailed ophthalmological examinations were done for every subject. Kolmogorov-Smirnov test was used to analyze the distribution of quantitative variables and t test was used for the data that were normally distributed. Any p value <0.05 was considered as statistically significant.

Results:

The mean ages were 63.3±9.0 and 61.7±11.6 in Group 1 and 2, respectively (p=0.459). 25 (50.0%) were female, 25 (50.0%) were male in Group 1 and 26 (52.0%) were female, 24 (48.0%) were male in Group 2 (p=1.000). Mean IOPcc values were 17.8±3.6 (12.1-29.0) and 16.0±3.1 (10.9-23.8) mmHg (p=0.006); mean IOPg values were 16.9±3.5 (10.9-25.9) and 15.4±2.9 (9.0-24.7) mmHg (p=0.032); mean CH values were 9.9±1.5 (6.1-13.3) and 10.5±1.7 (6.5-15.7) (p=0.080) and mean CRF values were 10.4±1.6 (7.5-14.0) and 10.5±1.7 (6.6-15.4) (p=0.730) in Groups 1 and 2, respectively.

Conclusions:

There was no any statistical difference between the groups in terms of CH and CRF. However, mean CH and CRF values were found less in diabetic group. Corneal biomechanical differences seen in diabetic patients may be associated with a statistically significantly higher IOP measurements.

Upcoming Methods and Specifications of Continuous Intraocular Pressure Monitoring Systems for Glaucoma

Glaucoma is the leading cause of irreversible blindness and vision loss in the world. Although intraocular pressure (IOP) is no longer considered the only risk factor for glaucoma, it is still the most important one. In most cases, high IOP is secondary to trabecular meshwork dysfunction. High IOP leads to compaction of the lamina cribrosa and subsequent damage to retinal ganglion cell axons. Damage to the optic nerve head is evident on funduscopy as posterior bowing of the lamina cribrosa and increased cupping. Currently, the only documented method to slow or halt the progression of this disease is to decrease the IOP; hence, accurate IOP measurement is crucial not only for diagnosis, but also for the management. Due to the dynamic nature and fluctuation of the IOP, a single clinical measurement is not a reliable indicator of diurnal IOP; it requires 24-hour monitoring methods. Technological advances in microelectromechanical systems and microfluidics provide a promising solution for the effective measurement of IOP. This paper provides a broad overview of the upcoming technologies to be used for continuous IOP monitoring.

A microscale optical implant for continuous in vivo monitoring of intraocular pressure

Intraocular pressure (IOP) is a key clinical parameter in glaucoma management. However, despite the potential utility of daily measurements of IOP in the context of disease management, the necessary tools are currently lacking, and IOP is typically measured only a few times a year. Here we report on a microscale implantable sensor that could provide convenient, accurate, on-demand IOP monitoring in the home environment. When excited by broadband near-infrared (NIR) light from a tungsten bulb, the sensor's optical cavity reflects a pressure-dependent resonance signature that can be converted to IOP. NIR light is minimally absorbed by tissue and is not perceived visually. The sensor's nanodot-enhanced cavity allows for a 3-5 cm readout distance with an average accuracy of 0.29 mm Hg over the range of 0-40 mm Hg. Sensors were mounted onto intraocular lenses or silicone haptics and secured inside the anterior chamber in New Zealand white rabbits. Implanted sensors provided continuous in vivo tracking of short-term transient IOP elevations and provided continuous measurements of IOP for up to 4.5 months.

Noninvasive Intraocular Pressure Measurement in Animals Models of Glaucoma

Intraocular pressure (IOP) elevation is a critical risk factor for development and progression of glaucoma. As such, measuring IOP in animal models of the disease is important for any research work trying to understand the pathophysiologic mechanisms of glaucoma. Noninvasive IOP measurement in animals uses methods that have been adapted from use on humans. Calibration of the instruments used for the specific animal and even strain used is critically important for allowing meaningful comparisons of results. We describe below the methods used for noninvasive IOP measurement in animals that are relevant to glaucoma research.

Clinical Evaluation of Methods to Correct Intraocular Pressure Measurements by the Goldmann Applanation Tonometer, Ocular Response Analyzer, and Corvis ST Tonometer for the Effects of Corneal Stiffness Parameters

PURPOSE

To evaluate the effectiveness of methods to correct intraocular pressure (IOP) measurements obtained using the Goldmann applanation tonometer (GAT), the ocular response analyzer (ORA), and the Corvis ST tonometer (CVS) for the effects of corneal stiffness parameters: central corneal thickness (CCT), corneal curvature (R), and age in a Chinese population.

PATIENTS AND METHODS

Data were collected for 99 eyes of 99 participants. Whereas cornea-corrected IOP was obtained directly from ORA (ORA-IOPcc), cornea correction in GAT and CVS was implemented using multiparameter equations developed earlier. The study also included IOP measurements by the dynamic contour tonometer, which is thought to be less affected by corneal stiffness parameters than other tonometers. Statistical analyses were performed to determine the association of both uncorrected and corrected IOP with the main stiffness parameters: CCT, R, and age.

RESULTS

After correction, a significantly decreased association between the GAT (from r=0.15 to r=-0.02), ORA (from r=0.24 to r=-0.19), and CVS (from r=0.47 to r=0.004) IOP measurements and the CCT was found, to levels below that with the dynamic contour tonometer-IOP (r=0.11). The IOP measurements made by the 4 tonometers, both uncorrected and corrected, did not correlate with age. The same was true for R except with ORA-IOPcc (r=0.23).

CONCLUSIONS

CCT accounted for the majority of variance in IOP, whereas age and R had a much smaller effect. The IOP correction processes studied were successful in reducing reliance of IOP measurements, especially those by GAT and CVS, on CCT in a healthy Chinese population.

Ocular pulse amplitude in different types of glaucoma using dynamic contour tonometry: Diagnosis and follow-up of glaucoma

The aim of the present study was to compare the ocular pulse amplitude (OPA) in patients with different types of glaucoma using dynamic contour tonometry (DCT), to evaluate ocular and systemic factors associated with the OPA and to verify whether OPA measured by DCT is an independent predictor for glaucoma diagnosis. A total of 217 eyes of 217 participants in the following five groups were included in this cross-sectional study: Chronic angle closure glaucoma (CACG), primary open angle glaucoma, normal tension glaucoma (NTG), suspected open angle glaucoma (SOAG) and normal control (NC). The following tests were simultaneously performed during a single visit: Intra-ocular pressure (IOP), OPA, cup-to-disk (C/D) ratio, mean damage (MD) and loss variance (LV). OPAs were compared in each group. The association between OPA and IOP, age, C/D ratio, MD and LV was detected. OPA analysis prior to and after trabeculectomy was also performed to assess its prognostic value. Among the 217 individuals, the OPA was consistent with the IOP, both measured by DCT, along with the MD and LV. Patients with CACG and SOAG had higher OPA values than those with NTG and normal controls. Compared with patients aged >30 years, the OPA was significantly lower in younger patients, while they may not have been affected by different C/D ratios. After trabeculectomy, the OPA had significantly decreased compared with the values prior to surgery. In conclusion, the present study showed that the OPA is correlated with the IOP determined by DCT. CACG and SOAG patients had higher OPA values than patients with other types of glaucoma. OPA measured by DCT may be a predictor for glaucoma diagnosis and prognosis.

Comparison of intraocular pressure measurements using Goldmann tonometer, I-care pro, Tonopen XL, and Schiotz tonometer in patients after Descemet stripping endothelial keratoplasty

PURPOSE

Post-Descemet stripping endothelial keratoplasty (DSEK) patients are prone for intraocular pressure (IOP) elevations and glaucoma. Corneal characteristics influence various IOP measuring devices in various ways. The aim of this study was to evaluate the agreement between four different IOP measuring devices: Goldmann applanation tonometer (GAT), I-care pro, Tonopen XL, and Schiotz tonometr in patients who underwent DSEK.

METHODS

This was a prospective comparative study using a convenience cohort of post-DSEK patients with compact grafts. Post-DSEK patients had IOP measured using GAT, I-care Pro, Tonopen XL, and Schiotz tonometer. Measurements were compared and agreement assessed. Wilcoxon signed-rank test was used for comparison of means as variables did not show a normal distribution. Bland-Altman plots were used for assessing agreement.

RESULTS

Thirty eyes of 24 patients were included in the study. Mean time from DSEK surgery was 25.31 ± 13.05 months. Mean IOP with GAT, I-care pro, Tonopen XL, and Schiotz tonometer was 13.99 ± 3.76, 13.92 ± 3.36, 13.31 ± 3.89, and 12.83 ± 4.07, respectively. GAT, I-care pro, and Tonopen XL had similar mean IOP measurements (P = 0.135 and P = 0.551, respectively), while Schiotz tonometry measurements were higher (P = 0.046). Bland-Altman plots show good agreement between GAT, Tonopen XL, and I-care pro. GAT and Schiotz tonometry show less agreement, with large variations in the differences of measured IOP.

CONCLUSIONS

IOP measurements in post-DSEK patients showed good agreement between GAT and either Tonopen XL or I-care pro. Schiotz tonometer has large variations in this patient group. IOP measurements and IOP difference between devices were not dependent on central corneal thickness.

Agreement among Goldmann applanation tonometer, iCare, and Icare PRO rebound tonometers; non-contact tonometer; and Tonopen XL in healthy elderly subjects

PURPOSE

To evaluate the inter-device agreement among the Goldmann applanation tonometer (GAT), iCare and Icare PRO rebound tonometers, non-contact tonometer (NCT), and Tonopen XL tonometer.

METHODS

Sixty healthy elderly subjects were enrolled. The intraocular pressure (IOP) in each subject's right eye was measured thrice using each of the five tonometers. Intra-device agreement was evaluated by calculating intraclass correlation coefficients (ICCs). Inter-device agreement was evaluated by ICC and Bland-Altman analyses.

RESULTS

ICCs for intra-device agreement for each tonometer were >0.8. IOP as measured by iCare (mean ± SD, 11.6 ± 2.5 mmHg) was significantly lower (p < 0.05) than that measured by GAT (14.0 ± 2.8 mmHg), NCT (13.6 ± 2.5 mmHg), Tonopen XL (13.7 ± 4.1 mmHg), and Icare PRO (12.6 ± 2.2 mmHg; Bonferroni test). There was no significant difference in mean IOP among GAT, NCT, and Tonopen XL. Regarding inter-device agreement, ICC was lower between Tonopen XL and other tonometers (all ICCs < 0.4). However, ICCs of GAT, iCare, Icare PRO, and NCT showed good agreement (0.576-0.700). The Bland-Altman analysis revealed that the width of the 95% limits of agreement was larger between the Tonopen XL and the other tonometers ranged from 14.94 to 16.47 mmHg. Among the other tonometers, however, the widths of 95% limits of agreement ranged from 7.91 to 9.24 mmHg.

CONCLUSION

There was good inter-device agreement among GAT, rebound tonometers, and NCT. Tonopen XL shows the worst agreement with the other tonometers; therefore, we should pay attention to its' respective IOP.

CLINICAL TRIAL REGISTRATION

Japan Clinical Trials Register; number: UMIN000011544.

The effect of Timolol 0.5% on the correction of myopic regression after LASIK

BACKGROUD

Postlaser in situ keratomileusis (post-LASIK) refractive regression is defined as the gradual, partial, or total loss of initial correction that limits the predictability, efficiency, and long-term stability of LASIK. Our study assesses the effect of Timolol 0.5% on the correction of myopic regression after LASIK.

METHODS

This prospective, randomized, controlled study included 62 eyes of 62 patients with myopic regression of -1.18 ± 0.86 diopters (D) after myopic LASIK. They were randomly assigned into either Group 1 who received Timolol 0.5% eye drops for 3 months or Group 2 who received artificial tears as control (during treatment). Patients were followed an additional 2 months after cessation of eye drops treatment (posttreatment).

RESULTS

During treatment in Group 1, as the mean true intraocular pressure (IOPT) lowered significantly, regression stopped. As the mean IOPT increased significantly posttreatment and returned to its pretreatment level, regression recurred. The effective rate of Timolol therapy dropped from 62.5% during treatment to 40.6% posttreatment. On the contrary in Group 2, although the mean IOPT did not change significantly, regression continually happened as time passed. During treatment, the mean IOPT, uncorrected visual acuity, spherical equivalent (SE), and corneal refractive power showed significant difference between the 2 groups. In Group 1, the differences of effective rate of Timolol therapy between each of the 2 subgroups of age, gender, preoperative SE (PSE), or pretreatment time (how long we start treatment with Timolol post-LASIK) were not statistically significant.

CONCLUSION

IOP-lowering eye drop Timolol was effective for the correction of myopic regression when a 0.5-D or greater myopic shift is detected after LASIK in patients regardless of age, gender, PSE, or anytime we started the treatment only if regression happened. However, the myopic regression recurred after cessation of Timolol treatment.

Repeatability of Central Corneal Thickness Measurement Using Rotating Scheimpflug Camera in Dry and Normal Eyes

PURPOSE

To compare the repeatability of central corneal thickness (CCT) measurement using the Pentacam between dry eyes and healthy eyes, as well as to investigate the effect of artificial tears on CCT measurement.

METHODS

The corneal thicknesses of 34 patients with dry eye and 28 healthy subjects were measured using the Pentacam. One eye from each subject was assigned randomly to a repeatability test, wherein a single operator performed three successive CCT measurements time points-before and 5 min after instillation of one artificial teardrop. The repeatability of measurements was assessed using the coefficient of repeatability and the intraclass correlation coefficient.

RESULTS

The coefficient of repeatability values of the CCT measurements in dry and healthy eyes were 24.36 and 10.69 μm before instillation, and 16.85 and 9.72 μm after instillation, respectively. The intraclass correlation coefficient was higher in healthy eyes than that of in dry eyes (0.987 vs. 0.891), and it had improved significantly in dry eyes (0.948) after instillation of one artificial teardrop. The CCT measurement fluctuated in dry eyes (repeated-measures analysis of variance, P<0.001), whereas no significant changes were detected in healthy eyes, either before or after artificial tear instillation.

CONCLUSIONS

Central corneal thickness measurement is less repeatable in dry eyes than in healthy eyes. Artificial tears improve the repeatability of CCT measurements obtained using the Pentacam in dry eyes.

A Comparative Analysis of Goldmann Tonometry Correction

PURPOSE

The measurement of intraocular pressure (IOP) by Goldmann applanation tonometry (GAT) is based on assumptions about corneal parameters. To correct for variations in corneal curvature and thickness, a number of equations have been proposed. This study evaluates the in vivo accuracy of these equations from individuals with primary open-angle glaucoma and compared them with measurements taken using the Pascal dynamic contour tonometer (DCT), which makes no assumptions about the corneal geometry or biomechanics.

PARTICIPANTS AND METHODS

The study included 108 participants with primary open-angle glaucoma (47 male and 61 female) with an age range of 39 to 81 years. Participants were recruited from the Glaucoma Clinic at Wroclaw Medical University. A full ophthalmologic examination was conducted on all participants. Participants were divided into 3 groups depending on IOP as measured by GAT. Six formulae were applied and the results were compared with measurements taken with DCT.

MAIN OUTCOME MEASURES

To determine as to which formula provides the closest value to IOP measured with DCT.

RESULTS

For IOP values ≤29 mm Hg, 2 of the formulae showed the smallest and comparable mean differences and SDs between corrected IOP values obtained with GAT and those measured with DCT. For IOP≥30 mm Hg, the formula derived from the model of corneal applanation that takes into account corneal buckling showed the closest agreement with measurements taken using DCT.

CONCLUSIONS

Correction formulae provide widely varying results and their appropriateness can depend on the IOP values.