Intraocular pressure evaluation in healthy eyes and diseased ones using contact and non contact devices

Comparative Analysis of Keratometric and Pachymetry Values From Corneal Topography Scans: A Comparison Between Pentacam and Galilei

Objective The objective of this study was to compare K1, K2, Kmax, and pachymetry values from Pentacam and Galilei scans of corneal topography in order to assess their correlation and interchangeability in clinical practice. Methodology A total of 34 patients (68 eyes) were enrolled in the study. Corneal topography was performed using Pentacam and Galilei devices on the same day. K1, K2, Kmax, and pachymetry readings were obtained from the scans and analyzed using paired t-tests and Bland-Altman plots. Results There were minimal differences in clinical settings between Pentacam and Galilei for K1, K2, Kmax (>0.75 D), and pachymetry values (>15 um). However, there was a statistically significant difference found between Kmax and pachymetry, making their interchangeability questionable. Conclusion Pentacam and Galilei demonstrate a good correlation between corneal keratometric values (K1, K2, and Kmax) and pachymetry values in clinical settings, and they should be used interchangeably with caution.

Analysis of Corneal Deformation in Paediatric Patients Affected by Maturity Onset Diabetes of the Young Type 2

BACKGROUND

To evaluate corneal deformation in Maturity Onset Diabetes of the Young type 2 (MODY2), paediatric subjects were analysed using a Scheimpflug-based device. The purpose of this analysis was to find new biomarkers for MODY2 disease and to gain a better understanding of the pathogenesis of the disease.

METHODS

A total of 15 patients with genetic and metabolic diagnoses of MODY2 (mean age 12.8 ± 5.66 years) and 15 age-matched healthy subjects were included. The biochemical and anthropometric data of MODY2 patients were collected from clinical records, and a complete ophthalmic check with a Pentacam HR EM-3000 Specular Microscope and Corvis ST devices was performed in both groups.

RESULTS

Highest concavity (HC) deflection length, Applanation 1 (A1) deflection amplitude, and A1 deflection area showed significantly lower values in MODY2 patients compared to healthy subjects. A significant positive correlation was observed between Body Mass Index (BMI) and HC deflection area and between waist circumference (WC) and the following parameters: maximum deformation amplitude, HC deformation amplitude, and HC deflection area. The glycosylated hemoglobin level (HbA1c) showed a significant positive correlation with Applanation 2 time and HC time.

CONCLUSIONS

The obtained results show, for the first time, differences regarding corneal distortion features in the MODY2 population compared with healthy eyes.

Evaluating Intraocular Pressure After Myopic Photorefractive Keratectomy: A Comparison of Different Tonometers

PRCIS

All devices evaluated in this study showed a significant underestimation in intraocular pressure (IOP) measurement after myopic photorefractive keratectomy (PRK), Goldmann tonometer more than others. Corneal biomechanics indicated a different influence on the different kinds of tonometry.

PURPOSE

The aim was to investigate the reliability of Goldmann applanation tonometry (GAT), rebound tonometry (RT), ocular response analyzer (ORA), Corvis ST (CST), and dynamic contour tonometry (DCT) in IOP evaluation after myopic PRK.

MATERIALS AND METHODS

One eye of 145 patients who underwent myopic PRK for a refractive defect ranging from -10.25 to -0.50 D (mean -4.69±2.00 D) was included in this retrospective comparative study. A complete eye visit with corneal tomography and IOP measurement with GAT, DCT, ORA, RT, and CST was performed before surgery and at 1, 3, and 6 months follow-up. Values provided by each device were tested and compared at each follow-up. Correlation analyses were run between changes in IOP and the corneal, morphologic and biomechanical parameters were measured after PRK.

RESULTS

GAT, DCT, ORA, RT, and CST showed a significant (P<0.01) underestimation of IOP at 6 months follow-up. GAT showed the greatest underestimation (-14.1%) and stronger correlations with corneal deformation parameter changes, whereas ORA, DCT, and RT appeared to be less conditioned by these variations. At 6 months follow-up DCT, ORA, RT, and CST provided IOP values with nonsignificant differences compared with GAT before PRK.

CONCLUSIONS

Each tested tonometer showed a significant IOP underestimation after myopic PRK. As this was most observed with GAT compared with all devices, we suggest DCT, ORA, RT, or CST to evaluate IOP in these patients following surgery.

Analysis of Corneal Distortion after Myopic PRK

The purpose of the study is to evaluate the corneal biomechanical properties (CBP) and their behaviors after myopic refractive surgery both with Ocular Response Analyzer (ORA) and Corvis ST (CST). This retrospective study included 145 eyes of 145 patients with a mean age of 33.13 ± 9.24 years, who underwent myopic photorefractive keratectomy (PRK) for a refractive defect, measured as spherical equivalent, of mean −4.69 ± 2.04 D and have been evaluated before surgery and at 1, 3 and 6 months follow-up. Corneal hysteresis (CH) and corneal resistance factor (CRF) values significantly decreased after 1 month and remained statistically stable during further follow-ups. CST parameters had a different evolution: only second applanation time (AT2) differences showed a significant variation after 1 month that did not statistically change over time. Highest concavity deformation amplitude (HCDA), highest concavity peak distance (HCPD), first applanation time (AT1) and velocity (AV1) showed continuous significant differences both after 3 and after 6 months. This study suggests that after central surface ablation surgery, such as myopic PRK, corneal shape is remodeling, and its deformation parameters are going to change even at 6 months follow-up. This indicates that it should be important to evaluate refractive surgery patients during a longer follow-up because this could allow earlier diagnosis and better management of late-onset complications.

A Review on Different Tonometers for Intraocular Pressure Measurement After Photorefractive Keratectomy or Small Incision Lenticule Extraction

This paper aims to review different tonometers for intraocular pressure measurement in eyes after photorefractive keratectomy or small incision lenticule extraction. An Entrez Pubmed search was performed on July 19th, 2020. There were 32 eligible articles investigated in the use of tonometers or biomechanical properties of cornea in post photorefractive keratectomy eyes and 11 articles investigated in post small incision lenticule extraction eyes. Corvis ST and dynamic contour tonometry were found to be accurate for intraocular pressure measurement in post photorefractive keratectomy eyes. For post small incision lenticule extraction eyes, Corvis ST was found to be more accurate than other tonometers. Other tonometers such as Goldmann applanation tonometer, noncontact tonometry, Tonopen, ocular response analyzer can also be used in post photorefractive keratectomy or small incision lenticule extraction eyes in clinical practice; however, it is important for ophthalmologists to take note of the chances of discrepancies.

Comparative analysis of biomechanically corrected intraocular pressure with corneal visualization Scheimpflug technology versus conventional noncontact intraocular pressure

PURPOSE

To compare the difference between biomechanically corrected intraocular pressure (bIOP) and noncontact IOP measurement (IOP_NCT) and to investigate the effect of corneal biomechanical properties on IOP.

METHODS

IOP was evaluated in 1046 myopic eyes (544 subjects) using a conventional noncontact tonometer and a novel corneal visualization Scheimpflug technology (Corvis ST). Corneal biomechanical parameters were measured using the Corvis ST.

RESULTS

The mean IOP_NCT and bIOP values were significantly different (15.59 ± 2.56 mmHg and 15.89 ± 1.75 mmHg, respectively; P < 0.001). The bIOP showed a less correlation with central corneal thickness (CCT), compared with IOP_NCT (P < 0.01). The IOP_NCT was lower than the bIOP when the thickness of cornea was ≤ 550 μm but higher than bIOP when it was ≥ 550 μm (P < 0.01). A strong association was found between IOP_NCT and deflection amplitude and deflection area at the highest concavity (HC DefA and HC DefArea), stiff parameter, maximum deformation amplitude (DAmax), and maximum deflection amplitude (DefAmax), as well as for bIOP (r > 0.500, P < 0.001). The bIOP could be calculated based on IOP_NCT according to different values of CCT (P < 0.01).

CONCLUSIONS

The bIOP was less affected by CCT as compared to IOP_NCT. IOP_NCT may be underestimated when the cornea is thinner and overestimated when the cornea is thicker because of the difference in corneal biomechanics.

Analysis of differences in intraocular pressure evaluation performed with contact and non-contact devices

Background

To evaluate differences of intraocular pressure (IOP) measurements performed with Goldmann applanation tonometer (GAT), dynamic contour tonometer (DCT), rebound tonometry (RT), Ocular Response Analyzer (ORA) and Corvis ST (CST) in eyes screened for refractive surgery.

Methods

One eye, only the right one, of 146 patients was included in this study. Each participant was submitted to a corneal analysis with Scheimpflug camera and IOP evaluation with GAT, DCT, RT, ORA and CST. Differences in IOP values obtained thanks to each instruments were compared and then correlations between these discrepancies and morphological features such as mean keratometry (MK) and central corneal thickness (CCT) provided by Pentacam were studied. Software used to run statistical evaluations was SPSS, version 18.0.

Results

Study participants had a mean age of 33.1 ± 9.2 years old. IOP values observed in this study were 15.97 ± 2.47 mmHg (GAT), 17.55 ± 2.42 mmHg (DCT), 17.49 ± 2.08 mmHg (RT), 18.51 ± 2.59 mmHg (ORA) and 18.33 ± 2.31 mmHg (CST). The mean CCT was 560.23 ± 31.00 μm, and the mean MK was 43.33 ± 1.35 D. GAT provided significant lower values in comparison to all other devices. DCT and RT gave significantly lower intermediate IOP values than those measured with ORA and CST. All the IOP measures and the differences between devices were significantly correlated with CCT.

Conclusions

According to our data, although our findings should be confirmed in further studies, GAT tonometer cannot be used interchangeably with DCT, RT, ORA and CST.

Comparison among Ocular Response Analyzer, Corvis ST and Goldmann applanation tonometry in healthy children

AIM

To explore the relationship between different parameters of Ocular Response Analyzer (ORA) and Corvis ST (CST) in a sample of healthy Iranian school-aged children and the relationship between parameters of these 2 instruments against intraocular pressure (IOP), measured by the Goldmann applanation tonometer (GAT-IOP), age and gender, and find possible correlation between ORA and CST with GAT.

METHODS

This cross-sectional study included 90 healthy children. A general interview and complete eye examination were performed. Following successful GAT-IOP measurement, ORA and CST were conducted. The CST parameters were A 1/2 length (A1L, A2L), A 1/2 velocity (A1V, A2V), highest concavity deformation amplitude (HCDA), radius of curvature (RoC), peak distance (PD), central corneal thickness (CCT) and IOP. The ORA parameters were corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated IOP (IOP-G) and corneal compensated IOP (IOP-CC). Extracted data was analyzed using the Statistical Package for Social Science software.

RESULTS

Totally 39 males with age of 9.08±1.60 (6-12)y and 51 females with age of 8.96±1.55 (6-13)y were included. Many CST parameters were significantly correlated with CH, CRF, IOP-G and IOP-CC. Some CST parameters had a significant correlation with GAT-IOP, including IOP-CST in both eyes and HCDA, A2L, PD, and RoC in the left eye, but none with age, except A2L in the right eye. The CRF measurement showed a significant correlation with GAT-IOP in both eyes and CH in the right eye, yet, none with age. Among all CST and ORA parameters, CCT-CST in both eyes and A1L in right eye had a significant correlation with gender, although this was a negligible negative correlation. Comparison of mean IOP values by different devices showed a significantly highest IOP overestimation by CST and lowest by IOP-CC compared with GAT. Also, IOP-G versus IOP-CST significantly had the lowest IOP overestimation among others. Overall, either low positive correlation or negligible correlation was found between IOP measurements by 3 instruments.

CONCLUSION

The study finds the highest IOP overestimation by CST and lowest by IOP-CC compared with GAT. Overall, either low positive correlation or negligible correlation is found between IOP measurements by the 3 instruments.

Estimation of the Corneal Young's Modulus In Vivo Based on a Fluid-Filled Spherical-Shell Model with Scheimpflug Imaging

Current intraocular pressure (IOP) measurement using air puff could be erroneous without applying proper corrections. Although noncontact tonometry is not considered to be accurate, it is still popularly used by eye clinics. It is thus necessary to extract the correct information from their results. This study proposes a practical approach to correctly measure IOP in vivo. By embedding a new model-based correction to the Corvis® ST, we can extract the corneal Young's modulus from the patient data. This Young's modulus can be used to correct the IOP readings. The tests were applied to 536 right eyes of 536 healthy subjects (228 male and 308 female) between March of 2012 and April of 2016. The tests were applied to patients at the Department of Ophthalmology, National Taiwan University Hospital and the Hung-Chuo Eye Clinics. The statistical analysis showed that the value for the Young's modulus was independent of all the other parameters collected from the Corvis ST, including the corneal thickness and the intraocular pressure. Therefore, it is important to independently measure the Young's modulus instead of depending on the correlation with the other parameters. This study adds the methodology of measuring corneal stiffness in vivo for ophthalmologists' reference in diagnosis.

Therapeutic potential of AAV-mediated MMP-3 secretion from corneal endothelium in treating glaucoma

Intraocular pressure (IOP) is maintained as a result of the balance between production of aqueous humour (AH) by the ciliary processes and hydrodynamic resistance to its outflow through the conventional outflow pathway comprising the trabecular meshwork (TM) and Schlemm's canal (SC). Elevated IOP, which can be caused by increased resistance to AH outflow, is a major risk factor for open-angle glaucoma. Matrix metalloproteinases (MMPs) contribute to conventional aqueous outflow homeostasis in their capacity to remodel extracellular matrices, which has a direct impact on aqueous outflow resistance and IOP. We observed decreased MMP-3 activity in human glaucomatous AH compared to age-matched normotensive control AH. Treatment with glaucomatous AH resulted in significantly increased transendothelial resistance of SC endothelial and TM cell monolayers and reduced monolayer permeability when compared to control AH, or supplemented treatment with exogenous MMP-3.Intracameral inoculation of AAV-2/9 containing a CMV-driven MMP-3 gene (AAV-MMP-3) into wild type mice resulted in efficient transduction of corneal endothelium and an increase in aqueous concentration and activity of MMP-3. Most importantly, AAV-mediated expression of MMP-3 increased outflow facility and decreased IOP, and controlled expression using an inducible promoter activated by topical administration of doxycycline achieved the same effect. Ultrastructural analysis of MMP-3 treated matrices by transmission electron microscopy revealed remodelling and degradation of core extracellular matrix components. These results indicate that periodic induction, via use of an eye drop, of AAV-mediated secretion of MMP-3 into AH could have therapeutic potential for those cases of glaucoma that are sub-optimally responsive to conventional pressure-reducing medications.