Corrected Intraocular Pressure Research Articles

The lack of causal link between myopia and intraocular pressure: Insights from cross-sectional analysis and Mendelian randomization study

ObjectiveThis study aimed to explore the potential causal relationship between intraocular pressure (IOP) and myopia. MethodsThe study included 3,459 patients who underwent corneal refractive surgery at our institution between 2021 and 2023. Preoperative data on IOP, spherical equivalent (SE), axial length (AL), and corneal thickness (CCT) were collected. The association between IOP and myopia was investigated through rank correlation analysis, and causal inference was examined using Mendelian randomization (MR) methods, including MR-Egger, weighted median, mode-based estimation, simple mode, and inverse variance weighted (IVW) approaches. Utilizing summary statistics from genome-wide association studies (GWAS), IOP was considered as the exposure, with myopia as the outcome variable. IVW method was employed for the primary analysis, supplemented by sensitivity analyses. ResultsCross-sectional analysis revealed a non-significant association between corrected IOP (cIOP) and myopia (r = -0.019, P = 0.12). MR analysis indicated a non-significant genetic causal relationship between cIOP and myopia under the IVW method (OR = 1.001; 95 % CI [0.999–1.003], P = 0.22), a finding corroborated in replication samples (OR = 0.98; 95 % CI [0.96–1.00], P = 0.099). ConclusionThis study did not find a direct causal link between IOP and the development of myopia. These findings challenge the traditional role attributed to IOP in the progression of myopia and highlight the complex, multifactorial process of myopia development. This provides a new perspective on understanding the intricate mechanisms behind myopia progression.

Corneal stress‒strain index in relation to retinal nerve fibre layer thickness among healthy young adults.

To determine the relationship between corneal stress-strain index (SSI) and retinal nerve fibre layer (RNFL) thickness. 1645 healthy university students from a university-based study contributed to the analysis. The RNFL thickness was measured by high-definition optical coherence tomography (HD-OCT), axial length (AL) was measured by IOL Master, and corneal biomechanics including SSI, biomechanical corrected intraocular pressure (bIOP), and central corneal thickness (CCT) were measured by Corvis ST. Multivariate linear regression was performed to evaluate the relationship between the SSI and RNFL thickness after adjusting for potential covariates. The mean age of the participants was 19.0 0.9 years, and 1132 (68.8%) were women. Lower SSI was significantly associated with thinner RNFL thickness ( =8.601, 95% confidence interval [CI] 2.999-14.203, = 0.003) after adjusting for age, CCT, bIOP, and AL. No significant association between SSI and RNFL was found in men, while the association was significant in women in the fully adjusted model. The association was significant in the nonhigh myopic group ( for trend = 0.021) but not in the highly myopic group. Eyes with greater bIOP and lower SSI had significantly thinner RNFL thickness. Eyes with lower SSI had thinner RNFL thickness after adjusting for potential covariates, especially those with higher bIOP. Our findings add novel evidence of the relationship between corneal biomechanics and retinal ganglion cell damage.

Retropupillary iris-claw lens

Aim: To evaluate the preoperative and intraoperative indications, postoperative complications, incidence of secondary glaucoma, and visual outcome in patient who underwent iris-claw implantation during cataract surgery and effect of vitrectomy on postoperative intraocular pressure (IOP). Material and Methods: A retrospective study was conducted from January 2016 to February 2020. One hundred eighty-seven eyes of 187 patients who underwent iris-claw lens implantation, with minimum 1 month follow-up, were included in the study. Analysis of records was done for preoperative, intraoperative findings and was recorded and postoperative best corrected visual acuity (BCVA) and IOP were noted in each follow-up. Results: Mean preoperative BCVA of 187 eyes was 1.78 logMAR (SD 0.68), which increased to 0.61 ± 0.50, 0.36 ± 0.26, 0.21 ± 0.16 logMAR at postoperative day 1, day 7, and 1 month, respectively. Most common indications included phacodonesis (17.65%), small dilating and nondilating pupil (11.22%), zonular dialysis (6.41%), and pseudoexfoliation in (4.81%). Few patients (6.94%) had preexisting corneal pathologies which lend up in intraoperative complications that lead to iris-claw implantation. Mean IOP in vitrectomized eye after 1 month was 15.53 (SD 2.16) mm Hg and those of nonvitrectomized was 16 (SD 1.90) mm Hg. Posterior capsular rent and whole capsular bag loss were the most common intraoperative indications. Incidence of secondary glaucoma was 2.13%. Irregular pupil was the most common anterior segment finding at 1 month postoperatively. Conclusion: Retropupillary iris-claw implantation is one of the safe and least complicated methods of managing intraoperative complications which gives good visual acuity and prevent patient from the trauma of multiple surgeries.

Effect of myopia and astigmatism deepening on the corneal biomechanical parameter stress-strain index in individuals of Chinese ethnicity.

Purpose: To investigate the differences in corneal biomechanical parameter stress-strain index (SSI) among different degrees of myopic eyes in Chinese individuals and to analyze the relevant factors of the SSI. Methods: This study analyzed the right eyes of 240 participants (240 eyes) aged 18-34years. The participants were divided into low-, moderate-, high-, and ultra-high myopia groups according to their spherical equivalent (SE), with 60 eyes included in each group. Spherical, cylinder, and SE were measured via automatically integrated optometry. Intraocular pressure (IOP) was measured using a non-contact tonometer. AL was measured using an IOLMaster device. Corneal curvature and central corneal thickness (CCT) were measured using a Pentacam. SSI and biomechanical corrected IOP (bIOP) were measured via corneal visualization Scheimpflug technology (Corvis ST). The statistical analyses included one-sample Kolmogorov-Smirnov tests and normal distribution histogram methods, Levene variance homogeneity tests, Pearson's correlation analyses, multiple linear stepwise regression analyses, one-way ANOVA, and LSD t-tests. Results: The mean (±SD) age of the 240 participants was (24.97 ± 4.16) years. The SSI was positively correlated with spherical, cylinder, SE, CCT, IOP, and bIOP and negatively correlated with K1 and AL (r = 0.475, 0.371, 0.497, 0.169, 0.291, 0.144, -0.154, and -0.464, respectively; all p < 0.05), but were not correlated with age, K2, or Km (all p > 0.05). Multiple linear regression analysis performed with SSI as the dependent variable, and spherical, cylinder, K1, CCT, and IOP as independent variables produced the following regression equation: SSI = 0.989 + 0.017 spherical + 0.042 cylinder +0.018 IOP (R 2 = 0.402, F = 31.518, p < 0.001). The SSI values in the low-, moderate-, high-, and ultra-high myopia groups were 0.945 ± 0.135, 0.940 ± 0.128, 0.874 ± 0.110, and 0.771 ± 0.104, respectively. The values decreased sequentially, and the differences between pairs were statistically significant (all p < 0.05), except for that between the low- and moderate-myopia groups (p > 0.05). Conclusion: SSI decreased with increasing myopia and astigmatism in the Chinese participants. The SSI was significantly lower in high and ultra-high myopia, especially ultra-high myopia. These findings indicate that increased corneal elasticity may be related to the pathogenesis of high and ultra-high myopia.

Repeatability and comparison of Corvis ST parameters before and after accelerated transepithelial corneal cross-linking in keratoconus eyes

AIM: To evaluate the repeatability and comparison of corneal visualization scheimpflug technology (Corvis ST) parameters in keratoconus eyes before and after accelerated transepithelial corneal cross-linking (ATE-CXL). METHODS: Thirty eyes of 30 progressive keratoconus patients were included in the prospective study. Three repeated corneal biomechanical measurements were performed preoperatively and one month postoperatively by Corvis ST. The interclass correlation coefficient (ICC) and 95% confidence interval (CI), Cronbach’ α, repeatability coefficient (RC), and coefficient of variation (CV) were used to evaluate the repeatability of Corvis ST parameters. Paired t test or Wilcoxon rank test was used to evaluate the differences between preoperative and postoperative data. RESULTS: At preoperative, 26 of 39 (66.67%) parameters showed good to excellent repeatability, 6 (15.38%) showed moderate, and 7 (17.95%) showed poor repeatability. Similarly, 34 (87.18%) parameters showed good to excellent repeatability, 3 (7.69%) showed moderate, and 2 (5.13%) showed poor repeatability after ATE-CXL. After ATE-CXL 1mo, the intraocular pressure (IOP), biomechanical corrected IOP (bIOP), first applanation time (A1T), Radius, deformation amplitude at the first applanation (A1DA), deflection length at the maximum deformation (HCDLL) and stiffness parameter at first applanation (SP A1) parameters increased, while the steep keratometry (Ks), flat keratometry (Kf), mean keratometry (Kmean), second applanation time (A2T), DA Ratio Max (2 mm) and integrated radius parameters decreased (all P&lt;0.05). CONCLUSION: The repeatability of the Corvis ST parameters before and 1mo ATE-CXL follow up were both acceptable, and the corneal stiffness was improved after 1-month ATE-CXL.

Glaucoma characteristics evaluation in myopia – A clinical study

Glaucoma is the leading cause of irreversible blindness, one of the risk factor recognised being high myopia. Intra ocular pressure may be normal in myopic patients, with optic nerve head glaucoma characteristics. Eye ball elongation and optic nerve head tilting may be present in patients with high myopia that will represent field defects mimicking glaucoma. Treating patients with myopia having suspected aspects of glaucoma may be a challenge but even more challenging is the diagnosis of glaucoma in myopic patients.: To evaluate the association of glaucoma features with myopia. To create the awareness regarding the long term follow up.: Patients in the age group of 15 to 45 years who had attended our institution over a period of one year who fulfilled the inclusion and exclusion criteria were subjected for this study. Fifty four patients who were diagnosed to have moderate or high degree myopia were selected for this analytical study. They were subjected to vision, ocular examination, tonometry and results obtained were analysed.: In our study moderate myopes constituted 55.5% and high myopes were 44.5%. The mean Intra ocular pressure and the mean corrected Intra ocular pressure in high myopes were observed to be higher than in moderate myopia. It was observed that higher prevalence of glaucoma was observed in high myopes.: There is a clinically as well as statistically significant difference between mean Intra ocular pressure and mean corrected Intra ocular pressure. So mean corrected Intra ocular pressure should be measured .From our study, there is a clear indication that there is increased prevalence of glaucoma in high myopes.

Association between Corneal Stiffness Parameter at the First Applanation and Keratoconus Severity.

Objective The study aimed to evaluate the character of corneal stiffness parameter at the first applanation (SP-A1) in normal and keratoconus eyes and explore the association between SP-A1 and keratoconus severity indicators. Methods A total of 351 normal and 351 keratoconus eyes were included in the current study. Keratoconus was diagnosed according to the corneal topography map and slit-lamp examination. The severity of keratoconus was classified to mild (steep keratometry (Ks) < 48D), moderate (48 ≤ Ks < 55D), and severe (Ks ≥ 55D). The SP-A1 was measured using the Corvis ST software. The correlation analyses and receiver operating characteristic (ROC) curve were performed in the current analysis. ResultsThe SP-A1 values of keratoconus were lower than that of normal eyes (72.11 (57.02, 83.08) mmHg/mm vs 110.89 (100.45, 122.47) mmHg/mm, P < 0.001). With the severity of keratoconus increasing, the SP-A1 decreased and the value of SP-A1 was 79.54 (70.30, 90.93) mmHg/mm, 65.11 (53.14, 77.46) mmHg/mm, and 47.59 (37.50, 62.14) mmHg/mm in mild, moderate, and severe keratoconus eyes, respectively (P < 0.001). The negative association between SP-A1 and Ks was found in mild, moderate, and severe keratoconus eyes (r mild = -0.171, rmoderate = -0.317, rsevere = −0.288, all P < 0.05). A positive association between SP-A1 and the thinnest corneal thickness (TCT) was found in all eyes (rnormal = 0.687, rmild = 0.519, rmoderate = 0.488, rsevere = 0.382, all P < 0.05). SP-A1 was found to be statistically positively associated with intraocular pressure (IOP), biomechanical corrected IOP (bIOP), time from the initiation of air puff until the first applanation (A1T), corneal velocity at the second applanation (A2V), and negatively associated with deformation amplitude (DA), peak distance (PD), corneal velocity at the first applanation (A1V), time from the initiation of air puff until the second applanation (A2T), and DA Ratio Max [2 mm] both in normal and keratoconus eyes (all P < 0.05). The ROC analysis indicated that the AUC (95% CI) of SP-A1 was 0.952 (0.934–0.967) and 0.930 (0.904–0.951) in detecting keratoconus eyes and mild keratoconus eyes from normal eyes, respectively. Conclusions The SP-A1 value decreased while the keratoconus severity increased. It was lower in keratoconus than that in normal eyes and could be helpful in identifying keratoconus eyes from normal eyes. Further researches would be warranted to expand the clinical utility of SP-A1.

Transient effect of suction on the retinal neurovasculature in myopic patients after small-incision lenticule extraction.

To characterize retinal neurovasculature changes after small-incision lenticule extraction (SMILE) in myopic patients. Ophthalmic Center, the Second Affiliated Hospital of Guangzhou Medical University, China. Prospective interventional study. The corrected distance visual acuity/uncorrected distance visual acuity, corrected intraocular pressure (CIOP), and corneal tomography were evaluated at baseline (PRE), postoperative day (POD) 1, and POD 7. Ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were measured. The vessel area densities (VADs, %), vessel skeleton densities (VSDs, %), vessel diameter index (VDI), and fractal dimensions (Dbox) of the superficial vascular plexus (SVP) and deep vascular plexus (DVP) were measured in a circular area (ϕ 2.5 mm) centered on the fovea. A total of 38 myopic patients were recruited. The GCIPL thickness was increased after SMILE at POD 1 and POD 7 (P < .01) but no significant changes in the pRNFL thickness. The VAD, VSD, and Dbox of the SVP were decreased at POD 1 (P < .01), but not at POD 7. The VDI in small vessels of the SVP and DVP was decreased at POD 1 (P < .05) and increased at POD 7 (P < .05). Changes in CIOP were positively correlated with changes in the GCIPL thickness. Changes in CIOP were negatively correlated with changes in the VAD of small vessels and the Dbox of total vessels in the DVP. Changes in CIOP were negatively correlated with the VSD and VDI of small vessels in the DVP and changes in the VDI of big vessels in the SVP. The transient fluctuations in the retinal neurovasculature after SMILE may represent a characteristic homeostasis pattern in patients after refractive surgery.

Transient Effect of Suction on Retinal Neuro-vasculature in Myopic Patients after Small Incision Lenticule Extraction

In Brief Purpose: To characterize retinal neurovasculature changes after small-incision lenticule extraction (SMILE) in myopic patients. Setting: Ophthalmic Center, the Second Affiliated Hospital of Guangzhou Medical University, China. Design: Prospective interventional study. Methods: The corrected distance visual acuity/uncorrected distance visual acuity, corrected intraocular pressure (CIOP), and corneal tomography were evaluated at baseline (PRE), postoperative day (POD) 1, and POD 7. Ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were measured. The vessel area densities (VADs, %), vessel skeleton densities (VSDs, %), vessel diameter index (VDI), and fractal dimensions (Dbox) of the superficial vascular plexus (SVP) and deep vascular plexus (DVP) were measured in a circular area (ϕ 2.5 mm) centered on the fovea. Results: A total of 38 myopic patients were recruited. The GCIPL thickness was increased after SMILE at POD 1 and POD 7 (P < .01) but no significant changes in the pRNFL thickness. The VAD, VSD, and Dbox of the SVP were decreased at POD 1 (P < .01), but not at POD 7. The VDI in small vessels of the SVP and DVP was decreased at POD 1 (P < .05) and increased at POD 7 (P < .05). Changes in CIOP were positively correlated with changes in the GCIPL thickness. Changes in CIOP were negatively correlated with changes in the VAD of small vessels and the Dbox of total vessels in the DVP. Changes in CIOP were negatively correlated with the VSD and VDI of small vessels in the DVP and changes in the VDI of big vessels in the SVP. Conclusions: The transient fluctuations in the retinal neurovasculature after SMILE may represent a characteristic homeostasis pattern in patients after refractive surgery. There are transient retinal neurovasculature fluctuations after SMILE. Changes in the GCIPL thickness were positively correlated with changes in CIOP. Changes in the vasculature of the SVP and DVP were negatively correlated with changes in CIOP.

Comparison of the corrected intraocular pressure by tonopachy with that of Goldmann applanation tonometry in normal and glaucomatous patients

Purpose:To compare corrected intraocular pressure (IOP) by tonopachy with that of Goldmann applanation tonometry (GAT) in normal and glaucomatous patients.Methods:In this cross-sectional study, IOP and central corneal thickness (CCT) were measured in 426 eyes (213 normal eyes and 213 glaucomatous eyes) of 426 patients by tonopachy followed by GAT and ultrasound pachymetry. IOP was corrected for CCT by in-built formula in tonopachy and Ehlers correction factor for Goldmann tonometer. Limits of agreements were assessed using Bland–Altman plots. Intraclass correlation coefficient was calculated to estimate the absolute agreement between single and average measurements of IOP and CCT of tonopachy with that of Goldmann tonometer and ultrasound pachymetry respectively.Results:Mean corrected IOP measured with tonopachy and GAT in glaucomatous eyes was 17.63 ± 5.04 mmHg and 19.42 ± 5.83 mmHg, and in controls it was 13.4 ± 2.5 mmHg and 16.2 ± 3.1 mmHg, respectively. Limits of agreement ranged from –4.63 to +9.25 mmHg for total population (mean = 2.31), ˗6.01 to +9.59 mmHg (mean = 1.79) for glaucoma group and ˗2.99 to +8.65 mmHg (mean = 2.83) for controls. Intraclass correlation coefficient for IOP measurement between tonopachy and Goldmann tonometer was 0.84 for total population, 0.85 for glaucoma group, and 0.63 for controls, respectively.Conclusion:Corrected IOP obtained by tonopachy showed moderate agreement with GAT and it is more in glaucoma patients than controls. Thus, tonopachy can be used as a screening tool, but cannot replace GAT.

Comparison of Corrected Intraocular Pressure Methods after Corneal Refractive Surgery according to Corneal Ablation Amounts

Purpose : The purpose of this study was to evaluate the intraocular pressure (IOP) that would be underestimated after corneal refractive surgery according to corneal ablation amounts, and was to suggest the most appropriate corrected IOP method for each group. Methods : The subjects were 1,002 eyes of 501 people (237 men, 264 women) who underwent corneal refractive surgery. The mean age was 26.89±5.18 years. IOP was measured with a non-contact tonometer and 4 correction methods, and was used to correct the underestimated IOP. IOP in three groups with low, moderate and high myopia according to ablation amounts was analyzed postoperative corrected IOP to compare correction methods. Results : The preoperative IOP was 15.67±2.39 mmHg and postoperative IOP was 10.12±2.11 mmHg, which was significantly lower than the mean 5.55±2.09 mmHg. The postoperative IOP calculated by Ehlers' correction method was 14.53±2.47 mmHg, which was 1.14±2.83 mmHg different from the preoperative IOP, showing the most similar to preoperative IOP. In addition, the IOP corrected by the Ehlers equation showed the smallest difference from preoperative IOP in all groups. Conclusion : The Ehlers correction method is shown the most accurate among the four correction methods in low, moderate, and high myopia groups after corneal refractive surgery. It would be a useful method for preventing the late diagnosis and treatment of glaucoma.

Repeatability and comparison of new Corvis ST parameters in normal and keratoconus eyes

To evaluate the repeatability of corneal biomechanical parameters in normal and keratoconus eyes, and explore factors that affects the repeatability, and further assess the diagnostic ability of new parameters. Seventy-seven keratoconus eyes of 47 patients and 77 right eyes of 77 normal subjects were recruited in current study. All participants received three repeated measurements with 2 to 5 minutes interval. The interclass correlation coefficient (ICC), Cronbach’ α and repeatability coefficient (RC) were evaluated. The liner regression analysis was used to identify factors that affect the repeatability, and linear mixed effects model was performed to compare the parameters differences. The receiver operating characteristic (ROC) curve was used to evaluate the diagnostic ability of new parameters. Eighteen parameters in normal eyes and twenty-two parameters in keratoconus eyes showed excellent repeatability (ICC ≥ 0.90). Age, axial measurement (AL), spherical equivalent, astigmatism, gender, mean keratometry (Kmean), intraocular pressure (IOP) and central corneal thickness (CCT) could affect the repeatability of new Corvis ST parameters. Compared with normal eyes, the Ambrósio’s Relational Thickness horizontal (ARTh), biomechanical corrected IOP (bIOP), stiffness parameter at first applanation (SP A1) were low and the Max Inverse Radius, deformation amplitude (DA) Ratio Max [2 mm], Pachy Slope, DA Ratio Max [1 mm], Integrated Radius and Corvis Biomechanical Index (CBI) were high in keratoconus eyes (All P < 0.05). Both ARTh and CBI had high Youden index (0.870), and the corresponding cut-off values were 379.29 and 0.44. The repeatability of Corvis ST parameters was acceptable both in normal and keratoconus eyes, and new parameters could effectively diagnose keratoconus eyes from normal eyes.

Intraocular Pressure Measurement Using Ocular Response Analyzer, Dynamic Contour Tonometer, and Scheimpflug Analyzer Corvis ST.

Purpose To compare intraocular pressure (IOP) measurements with Goldmann applanation tonometry (GAT), ocular response analyzer (ORA), dynamic contour tonometer (DCT), and Corvis ST (CST) in healthy subjects. Methods In a prospective, observational study, IOP measurements with GAT (GAT-IOPc), ORA (IOPcc), DCT (DCT-IOP), and CST (bIOP) were performed and analyzed in 94 healthy subjects. Results Mean age of the participants was 45.6 ± 17.2 years (range 18 to 81 years). Mean GAT-IOPc was 12.9 ± 2.4 mmHg, mean DCT-IOP was 16.1 ± 2.6 mmHg, and mean IOPcc was 15.6 ± 3.3 mmHg. DCT-IOP and IOPcc were significantly higher than GAT-IOPc (P < 0.001). Mean bIOP was 13.5 ± 2.4 mmHg that was slightly higher but not significantly different from GAT-IOPc (P=0.146). Correlation analysis of IOP values and central corneal thickness (CCT) revealed a negative correlation between GAT-IOPc and CCT (r = −0.347; P=0.001). However, IOPcc, DCT-IOP, and bIOP showed no significant correlation to CCT. Only bIOP revealed a weak but significant age dependency (r = 0.321, P=0.002). Conclusion All tonometry devices showed a good agreement of biomechanical corrected IOP values with GAT-IOPc. As no influence of CCT on IOPcc, DCT-IOP, and bIOP was detectable, the used correction algorithms appear to be appropriate in these tonometers in the clinical setting. The highest agreement was found between GAT-IOPc and bIOP. However, bIOP weakly correlated with participants' age. Further studies are needed to elucidate the role of bIOP for IOP measurement.

Relationship between novel intraocular pressure measurement from Corvis ST and central corneal thickness and corneal hysteresis

AimsCorvis ST (CST) yields biomechanical corrected IOP (bIOP) which is purported to be less dependent on biomechanical properties. In our accompanied paper, it was suggested that the repeatability of bIOP...

Repeatability of the Novel Intraocular Pressure Measurement From Corvis ST.

PurposeTo assess the repeatability of intraocular pressure (IOP) measured with the Corvis ST (CST) and the Ocular Response Analyzer (ORA).MethodsA total of 141 eyes from 141 subjects were studied, including 35 healthy eyes and 106 glaucomatous eyes. All subjects underwent IOP evaluations with Goldmann applanation tonometer, CST, and ORA. With CST, biomechanical corrected IOP (bIOP) was calculated; bIOP is purported to be less dependent on biomechanical properties. For ORA, corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated IOP (IOPg) were derived. The repeatability of the various IOP values was assessed using the coefficient of variance (CV) and the intraclass correlation coefficient (ICC).ResultsThe CV with bIOP (5.5 ± 3.1: mean ± standard deviation) was significantly smaller than the CVs measured with IOPg (7.3 ± 4.3) and IOPcc (7.2 ± 4.4). ICC values were 0.90, 0.80, and 0.86 with IOPg, IOPcc, and bIOP, respectively.ConclusionsThe bIOP showed a better prevision and repeatability for IOP measurement.Translational RelevanceThe bIOP measurement from CST had a better reproducible than IOPcc measurement from ORA.

Non-contact tonometry using Corvis ST: analysis of corneal vibrations and their relation with intraocular pressure.

The aim of this study was to determine characteristic frequencies of corneal vibrations occurring during air-puff intraocular pressure (IOP) measurement using the Corvis ST tonometer. Relations of frequency of the corneal vibrations with IOP were examined. Two selected vibration frequencies-frequency with maximum amplitude, and mass center of the frequency distribution area, for which the amplitude was higher than 50% (CM50)-present significant correlations with non-corrected IOP and biomechanical corrected IOP (bIOP). The highest correlation was found between the mean values of CM50 and bIOP (r=0.91). Based on the results obtained, it can be stated that the vibration frequencies of corneal peaks are closely related to the measured non-corrected and biomechanical corrected IOPs.

Comparison between corrected intraocular pressure using contact versus noncontact methods in glaucoma patients

Background To determine the difference between corrected intraocular pressure (IOP), based on the central corneal thickness (CCT), measured by the noncontact anterior segment anterior segment optical coherence tomography (AS-OCT), versus contact ultrasound pachymetry (USP) in the management of glaucoma patients. Patients and methods Ophthalmology Department, Ain Shams University, Cairo, Egypt. The study is a prospective, nonrandomized case series. Fifty patients were diagnosed with open-angle glaucoma and controlled with medical treatment with prostaglandin analogs and β-blockers fixed combination, controlled under medical treatment. CCT is measured by two methods, the AS-OCT and by the USP of ocular response analyzer. IOP was measured by applanation tonometry. Corrected IOP was calculated adjustment factor using Ehler’s correction nomogram, statistical analysis of the adjusted IOP with the contact and noncontact methods was done in relation to the CCT measurements. Results The mean age was 60.5±5.24 years, 54% of the studied patients were men while 46% were women. The mean CCT using AS-OCT for the right eye was 529.86±43.52 μm and for the left eye was 530.28±43.57 μm, while CCT using USP for the right eye was 534.88±43.59 μm and for the left eye was 533.34±44.33 μm. Highly significant correlation between CCT was measured by AS-OCT and ultrasound; 0.94 (P Conclusion Although USP has slightly higher measurements of CCT in comparison with measurements with anterior segment OCT, it has no significance on the adjusted IOP in controlled glaucoma patients, making the two methods equally accurate in the management and follow-up of these patients.

The comparison of three different correction formulas and the modified Ehler's algorithm in the evaluation of intraocular pressure after lasik

Aim: The aim of this study is to assess the correlation between the preoperative intraocular pressure (IOP) and the postoperative corrected IOP values calculated by using the modified Ehler’s algorithm and the three formulas after laser asisted in situ keratomileusis (LASIK) surgery.Material and Methods: The medical records of the patients to whom LASIK was performed to correct myopia and/or astigmatism between June 2018 and December 2018 were analyzed. The corrected preoperative and postoperative IOP values calculated with modified Ehler’s correction factor algorithm were compared. In addition, the corrected postoperative IOP values were calculated with Formula 1, Formula 2 and Formula 3 and the corrected postoperative IOP values were compared with the uncorrected preoperative IOP. Paired t-test was performed to compare the preoperative and postoperative IOP values. The Pearson correlation coefficients were calculated to analyze the correlation between preoperative IOP values and postoperative corrected IOP values.Results: The statistically significant difference was not observed between preoperative IOP and postoperative corrected IOP for formula two and formula 3 (p=0.42 and 0.80, respectively). There was significant difference between preoperative and postoperative IOP corrected with modified Ehler’s algorithm (p=0.03). In addition, a significant difference between preoperative IOP and postoperative IOP corrected with formula 1 was observed (p0.01). The mean of the difference between preoperative IOP and postoperative IOP corrected with formula was 3.1±1.4 mmHg (ranging 1.99 to 4.35 mmHg) and the mean of the difference between preoperative and postoperative IOP corrected with modified Ehler’s algorithm was 1.4±1.5 mmHg (ranging 0.1 to 2.6 mmHg). There was no correlation between preoperative IOP and postoperative corrected IOP values for Ehler algorithm and three formulas.Conclusion: Formulas 2 and 3 could be used to acquire a hint about the increased IOP, but none of them is the exact way to assess IOP correctly following LASIK. There is need for new solutions in this field. Keywords: LASIK; intraocular pressure; correction formula; the modified Ehler’s algorithm.

Glaucoma Progression and its Relationship with Corrected and Uncorrected Intraocular Pressure in Eyes with History of Refractive Corneal Surgery

ABSTRACTPurpose: To investigate glaucoma progression and its relationship with corrected and uncorrected intraocular pressure (IOP) in patients with a history of refractive corneal surgery (RCS).Methods: Totally, 56 eyes of 56 primary open-angle glaucoma patients who had a history of RCS were included. Mean keratometry and central corneal thickness were measured at the time of glaucoma diagnosis. Three IOP measurements, i.e., uncorrected IOP (UCIOP) and corrected IOP calculated by applying the Kohlhaas (CKIOP) and Ehlers (CEIOP) formulas, were used. Participants were categorized into two groups (low-teen [<15 mmHg] and high-teen [≥15 mmHg] groups) according to the mean follow-up IOP, in each of the three IOP measurements. Glaucoma progression was determined based on either structurally or functionally by stereoscopic optic disc/retinal nerve fiber layer photographs or visual field tests. Kaplan–Meier survival curves were compared between the low-teens group and high-teens group for each IOP measurement. Risk factors for glaucoma progression, including uncorrected and corrected IOP measurements, were analyzed using a Cox proportional-hazards model.Results: Among total eyes, glaucoma progression was found in 19 (34%) eyes during 4.3 years of mean follow-up period. Individual values of uncorrected IOP and corrected IOP showed significant differences (p < 0.001). Incidence of glaucoma progression was higher in high-teens group than in low-teens group by corrected IOP values (both Kohlhaas and Ehlers, p = 0.006, 0.003), but not by uncorrected IOP values (p = 0.749). The cumulative probability of glaucoma progression was significantly greater in the high-teens group than in the low-teens group using the Elhers formula determined by Kaplan–Meier analysis (p = 0.030).Conclusions: For glaucoma eyes with history of RCS, high-teen group by corrected mean follow-up IOP showed more glaucoma progression than low-teen group. More intensive IOP-lowering treatment will be required for patient with high-teen follow-up corrected IOP to prevent glaucoma progression.

Effects of hemodialysis on corneal and anterior chamber morphometry and intraocular pressure in patients with end-stage renal disease.

To evaluate the effects of hemodialysis (HD) on corneal and anterior chamber morphometry, as well as intraocular pressure (IOP) in patients with end-stage renal disease. Fifty right eyes were examined 30 minutes before and after HD. IOP was measured with a Goldmann applanation tonometer, and Ehlers' formula was used to calculate the corrected IOP values. The central corneal thickness (CCT), corneal volume (CV), keratometric values, anterior chamber depth (ACD), aqueous depth (AQD), anterior chamber volume (ACV), and anterior chamber angle (ACA) in the nasal and temporal quadrants were measured with a Sirius anterior segment analysis system. Blood urea nitrogen levels, body mass, and systolic and diastolic arterial pressure were also measured before and after HD. The mean age was 60.80 ± 13.38 (range: 35-80) years. The mean uncorrected and corrected IOP values decreased from 18.06 ± 3.91 and 18.31 ± 4.83 mmHg to 16.94 ± 3.87 and 16.95 ± 4.74 mmHg after HD, respectively (p=0.011 and p=0.003, respectively). The mean CCT decreased from 536.38 ± 24.73 to 533.18 ± 27.25 µm (p=0.002), and the mean CV decreased from 57.52 ± 3.15 to 55.68 ± 3.55 mm³ (p<0.001) after HD. There were no significant changes in ACD, AQD, ACV, ACA, or the keratometric values (p>0.05 for all values). There were no significant correlations between the ocular and systemic parameters (p>0.05 for all correlations). Uncorrected IOP, corrected IOP, CCT, and CV values decreased after HD, whereas the anterior chamber morphometry values remained similar between the measurements performed before and after HD.