Factors Associated With Corneal Deformation Responses Measured With a Dynamic Scheimpflug Analyzer

Potential dynamic corneal response parameters for myopia: relationships between axial length with whole eye movement at the first and second applanations and the highest concavity

PURPOSE

To investigate the correlation between whole eye movement (WEM) parameters measured using Corvis ST and axial length (AL) to explore whether AL affects WEMs.

METHODS

This single-center, cross-sectional study included data from healthy subjects and patients preparing for refractive surgery at the Qingdao Eye Hospital of Shandong First Medical University. Data were collected from July 2021 to April 2022. We first determined the correlations of WEMs at the time of corneal first applanation (A1_WEM), highest concavity (HC_WEM), and second applanation (A2_WEM), as well as the maximum value of WEM (WEM_Max) with AL. Subsequently, we established a series of regression models to analyze the relationships between different WEM values and AL.

RESULTS

AL was negatively correlated with HC_WEM, A2_WEM, and WEM_Max (r = - 0.28, - 0.23, and - 0.22, respectively; P < 0.001). The correlation between AL and A1_WEM was not significant (P = 0.77). According to the adjusted regression models, AL was negatively associated with HC_WEM (Model 2: β = -7.39, P < 0.001) and WEM_Max (Model 4: β = -3.52, P = 0.02), while the associations of AL with A1_WEM (Model 1: P = 0.61) and A2_WEM (Model 3: P = 0.23) were not significant.

CONCLUSIONS

AL is an independent negative influencing factor for HC_WEM. WEM is a potentially useful parameter that reflects the biomechanical properties of the eye behind the cornea in myopia.

Biomechanical changes of the cornea after orbital decompression in thyroid-associated orbitopathy measured by corvis ST

This study aims to investigate the changes in ocular biomechanical factors in patients with inactive thyroid eye disease (TED) who undergo orbital decompression surgery. This observational prospective study include 46 eyes of 31 patients with inactive TED undergoing orbital decompression at a tertiary university hospital from October 2021 to September 2023. All participants underwent a full ophthalmic examination, and a biomechanical examination was performed using corvis ST at baseline, 1 month, and 3 months postoperatively. The study participants had a mean age of 45 ± 11.6 years, and 58.1% of them were female. The second applanation time (A2T) increased from baseline to postoperative month 1 and continued to increase to postoperative month 3 (P < 0.001). The first applanation velocity (A1V), highest concavity (HC) peak distance, and pachymetry parameters also increased from postoperative month 1 to postoperative month 3 (P = 0.035, P = 0.005, and P = 0.031, respectively). The HC time increased from baseline to postoperative month 3 (P = 0.027). Other changes were statistically insignificant. The P-values were adjusted according to biomechanically corrected intraocular pressure (bIOP). Baseline Hertel significantly influenced A2 time (P < 0.001). Our findings suggest that ocular biomechanical parameters may change following decompression surgery in patients with inactive TED. Specifically, an increase in A2T, A1V, and HC peak distance suggests a decrease in corneal stiffness, although the increased HC time contradicts this. It is recommended to postpone keratorefractive or intraocular lens implantation surgeries until corneal biomechanics stabilize after decompression surgery for optimal results.

Biomechanical properties measured with dynamic Scheimpflug analyzer in central serous chorioretinopathy

PURPOSE

Recent evidence suggests that venous congestion at the vortex vein significantly contributes to the development of central serous chorioretinopathy (CSCR), and sclera is observed to be thicker in affected eyes. This study aims to investigate whether eyes with CSCR exhibit stiff corneas, measured using Corneal Visualization Scheimflug Technology (Corvis ST), which may serve as an indicator of scleral stiffness.

METHODS

This retrospective case-control study comprises 52 eyes from 33 patients diagnosed with CSCR and 52 eyes from 32 normal controls without CSCR. We compared biomechanical parameters measured with Corvis ST and anterior scleral thickness measured using anterior segment swept-source optical coherence tomography between the two groups.

RESULTS

Age, sex, axial length, intraocular pressure, and central corneal thickness showed no significant differences between the two groups (p > 0.05, linear mixed model). Three biomechanical parameters-peak distance, maximum deflection amplitude, and integrated inverse radius-indicated less deformability in CSCR eyes compared to control eyes. The stress-strain index (SSI), a measure of stiffness, and anterior scleral thickness (AST) at temporal and nasal points were significantly higher in the CSCR eyes. SSI and AST were not correlated, yet both were significantly and independently associated with CSCR in a multivariate logistic regression model.

CONCLUSIONS

Eyes affected by CSCR have stiffer corneas, irrespective of thicker scleral thickness. This suggests that stiffer sclera may play a role in the pathogenesis of CSCR.

Analyzing the changing trend of corneal biomechanical properties under different influencing factors in T2DM patients

To analyze the changing trend of CH and CRF values under different influencing factors in T2DM patients. A total of 650 patients with T2DM were included. We discovered that the course of T2DM, smoking history, BMI, and FBG, DR, HbA1c, TC, TG, and LDL-C levels were common risk factors for T2DM, while HDL-C levels were a protective factor. Analyzing the CH and CRF values according to the course of diabetes, we discovered that as T2DM continued to persist, the values of CH and CRF gradually decreased. Moreover, with the increase in FBG levels and the accumulation of HbA1c, the values of CH and CRF gradually decreased. In addition, in patients with HbA1c (%) > 12, the values of CH and CRF decreased the most, falling by 1.85 ± 0.33 mmHg and 1.28 ± 0.69 mmHg, respectively. Compared with the non-DR group, the CH and CRF values gradually decreased in the mild-NPDR, moderate-NPDR, severe-NPDR and PDR groups, with the lowest CH and CRF values in the PDR group. In patients with T2DM, early measurement of corneal biomechanical properties to evaluate the change trend of CH and CRF values in different situations will help to identify and prevent diabetic keratopathy in a timely manner.

Corneal biomechanics and their association with severity of lens dislocation in Marfan syndrome

PURPOSE

To investigate corneal biomechanical properties and its associations with the severity of lens dislocation in patients with Marfan syndrome.

METHODS

A total of 30 patients with Marfan syndrome and 30 age-, sex- and axial length (AL)-matched controls were recruited. Corneal biomechanical parameters of both groups were measured by CorVis ST and were compared between groups. Potential associations between corneal biomechanical parameters and severity of lens dislocation were also investigated.

RESULTS

Lower applanation 1 velocity (A1V) (0.13 ± 0.004 vs. 0.15 ± 0.003, P = 0.016), shorter applanation 2 time (A2T)(22.64 ± 0.11 vs. 22.94 ± 0.11, P = 0.013), longer peak distance (PD) (5.03 ± 0.07 vs. 4.81 ± 0.05, P = 0.008), longer radius (R) of highest concavity (7.44 ± 0.16 vs. 6.93 ± 0.14, P = 0.012), greater Ambrosio relational thickness horizontal (ARTh) (603 ± 20 vs. 498 ± 12, P < 0.001), and integrated radius (IR) (8.32 ± 0.25 vs. 8.95 ± 0.21, P = 0.033) were detected among Marfan eyes compared with controls (all P < 0.05). Marfan individuals with more severe lens dislocation tended to have increased stiffness parameter as longer A1T, slower A1V, shorter A2T, slower application 2 velocity (A2V), smaller PD and smaller Distance Amplitude (DA) (P < 0.05).

CONCLUSION

Marfan patients were detected to have increased corneal stiffness compared with normal subjects. Corneal biomechanical parameters were significantly associated with the severity of lens dislocation in Marfan patients.

Comparison of different corneal residual bed thickness after small incision lenticule extraction (SMILE)

PURPOSE

To evaluate the corneal biological parameters stability between the different corneal residual bed thickness (RBT) after Small Incision Lenticule Extraction (SMILE).

METHODS

In this prospective clinical trial, 127 eyes of 64 patients underwent SMILE. According to the corneal RBT, the patients were divided into the 250-270 µm, 270-290 µm and 290-310 µm groups. Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Scheimpflug camera (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) measurements were performed preoperatively, 1 day, 1week, 1month and 3 months after surgery.

RESULTS

The keratometer values among the three groups were no significant differences in postoperative periods (each P > 0.05), except the corneal thickness values (each P < 0.05). In the 250-270 µm and 270-290 µm groups, the keratometer and corneal thickness values were decreased at postoperative 1 week and increased at 1 and 3 months. The 290-310 µm group significantly higher posterior maximum elevation (PME) than the 250-270 µm group at 1 and 3 months (P = 0.022, 0.022, respectively), and higher preoperative thinnest point (PTE) at 1 week and 1 month (P = 0.013, 0.035, respectively). The PME of the 290-310 µm group was higher than the 270-290 µm group at 3 months (P = 0.045), and higher PTE at 1 week and 3 months (P = 0.022, 0.02, respectively). In all three groups, the maximal deformation amplitude (DA) was significantly higher at 1 and 3 months compared to postoperative 1 day and 1 week, and the IOP was decreased at 1 month then recovered at 3 months (each P < 0.05).The DA of the 250-270 µm group was significantly higher than the 290-310 µm group at postoperative 1 week, 1 and 3 months (P = 0.001, 0.01, 0.02, respectively). The change of the posterior corneal elevation and biomechanical parameters values were no significant differences among the three groups in postoperative periods (each P > 0.05).

CONCLUSIONS

The range of 250-310 µm RBT was safe and stable at the early postoperative of SMILE. The RBT may be positively correlated with the posterior corneal elevation.

Refractive Associations With Whole Eye Movement Distance and Time Among Chinese University Students: A Corvis ST Study

Purpose

Eye movement has been frequently studied in clinical conditions, but the association with myopia has been less explored, especially in population-based samples. The purpose of this study was to assess the associations of eye movement measured by the Corvis ST with refractive status in healthy university students.

Methods

A total of 1640 healthy students were included in the study (19.0 ± 0.9 years). Eye movement parameters (whole eye movement [WEM]; whole eye movement time [WEMT]) were measured by the Corvis ST. Spherical equivalent (SE) was measured using an autorefractor without cycloplegia. IOL Master was used to assess axial length (AL).

Results

AL was negatively correlated with WEM and WEMT (rWEM = -0.28, rWEMT = -0.08), and SE was positively correlated with WEM and WEMT (rWEM = 0.21, rWEMT = 0.14). For the risk of high myopia, breakpoint analysis and restricted cubic spline model showed that the knots of the significant steep downward trend of WEM and WEMT were 0.27 mm and 20.4 ms, respectively. The piecewise linear regression model revealed a significant correlation between AL, SE, and WEM when the value of WEM was below 0.27 mm. Additionally, when WEMT exceeded 20.4 ms, a significant decrease in AL and an increase in SE were observed with increasing WEMT.

Conclusions

A larger distance and longer duration of eye movement were correlated with a lower degree of myopia and shorter AL, and there was a threshold effect.

Translational Relevance

The findings might aid in understanding the pathogenesis of myopia and provide a theoretical foundation for clinical diagnosis and prediction.

Comparing corneal biomechanic changes among solo cataract surgery, microhook ab interno trabeculotomy and iStent implantation

Minimally invasive glaucoma surgery has expanded the surgical treatment options in glaucoma, particularly when combined with cataract surgery. It is clinically relevant to understand the associated postoperative changes in biomechanical properties because they are influential on the measurement of intraocular pressure (IOP) and play an important role in the pathogenesis of open-angle glaucoma (OAG). This retrospective case-control study included OAG patients who underwent cataract surgery combined with microhook ab interno trabeculotomy (µLOT group: 53 eyes of 36 patients) or iStent implantation (iStent group: 59 eyes of 37 patients) and 62 eyes of 42 solo cataract patients without glaucoma as a control group. Changes in ten biomechanical parameters measured with the Ocular Response Analyzer and Corneal Visualization Scheimpflug Technology (Corvis ST) at 3 and 6 months postoperatively relative to baseline were compared among the 3 groups. In all the groups, IOP significantly decreased postoperatively. In the µLOT and control groups, significant changes in Corvis ST-related parameters, including stiffness parameter A1 and stress‒strain index, indicated that the cornea became softer postoperatively. In contrast, these parameters were unchanged in the iStent group. Apart from IOP reduction, the results show variations in corneal biomechanical changes from minimally invasive glaucoma surgery combined with cataract surgery.

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.

Comparison of Corvis ST Parameters between Primary Open-Angle Glaucoma and Primary Angle-Closure Glaucoma

BACKGROUND

We compared corneal visualization Scheimpflug technology (CST) parameters between eyes with primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

METHODS

A retrospective analysis was performed on data from 89 eyes with POAG and 83 eyes with PACG that had CST examinations. CST parameters were compared between eyes with POAG and those with PACG using a linear mixed model (LMM).

RESULTS

No differences were observed in age, central corneal thickness, intraocular pressure, or use of antiglaucoma eye drops between the two groups. Patients with PACG had a significantly shorter axial length (AL), a higher proportion of females, CST parameters, longer applanation 2 (A2) time, deeper A2 deformation amplitude, shorter peak distance, longer whole eye movement, and longer whole eye movement time than patients with POAG. The highest concavity (HC) length and PD showed a significant positive correlation with AL. However, A1 length, A1 deformation amplitude, A2 time, A2 velocity, A2 length, A2 deformation amplitude, HC time, whole eye movement, and whole eye movement time were negatively correlated with AL.

CONCLUSIONS

The biomechanical properties of the cornea differed between POAG and PACG. In some parts, AL differences between the POAG and PACG groups might contribute to the variation in CST parameters.

Changes in aberrations and biomechanics after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in eyes with high astigmatism: a retrospective case control study

BACKGROUND

To compare the 6-month changes in aberration and biomechanics after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for high astigmatism.

METHODS

In this retrospective case control study, 47 eyes with high astigmatism (≥ 2.5 D, HA group) and 47 eyes with low astigmatism (≤ 1.0 D, LA group) underwent FS-LASIK. Preoperative and follow-up examinations included visual outcomes, higher order aberrations (HOAs) and biomechanics. Biomechanical parameters include a deformation amplitude ratio of 2 mm (DA ratio 2 mm), integrated inverse radius (IIR), stiffness parameter at first applanation (SP-A1), and ambrosio relational thickness through the horizontal meridian (ARTh).

RESULTS

Six months postoperatively, there was no significant difference in the efficacy and safety index (both P > 0.05) between the two groups, but the cylinder was higher in the HA group. The HOAs increased significantly after surgery in both groups (all P < 0.05). Six months postoperatively, the changes in spherical aberration and HOAs were larger in the HA group (both P < 0.005), but there was no significant difference between the changes in coma (P > 0.05). Significant decreases in SP-A1 and ARTh and significant increases in the IIR and DA ratio of 2 mm (all P < 0.05) were observed after surgery in both groups. The changes in the DA ratio 2 mm, IIR, SP-A1, and ARTh were not significantly different between the groups.

CONCLUSION

FS-LASIK had relative comparable efficacy and safety in correcting high and low myopic astigmatism, with higher astigmatic under-correction in eyes with high astigmatism. High astigmatism in eyes after FS-LASIK could introduce larger corneal aberrations, but the impact on corneal stiffness was the same as that in eyes with low astigmatism.

Comparison of two analyzer measurements focusing on material stiffness among normal, treatment-naïve, and treated glaucoma eyes

To investigate differences in biomechanical properties focusing on stiffness parameters between normal, treatment-naïve primary open-angle glaucoma (POAG), and treated POAG eyes. Retrospective case-control study, This study included 46 treatment-naïve POAG eyes, 46 POAG eyes treated with prostaglandin analogues, and 49 normal eyes used as controls; matched in terms of age and axial length. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using an ocular response analyzer (ORA). Fifteen biomechanical parameters were measured with the Corneal Visualization Scheimpflug Technology (Corvis ST), including biomechanical glaucoma factor (BGF) and two stiffness parameters of 'SP A1' and 'stress-strain index (SSI)', which were compared among the three groups. Additionally, the area under the curve (AUC) values of the receiver-operating curve to discriminate control and treatment-naïve POAG eyes were calculated for BGF and CH. Treatment-naïve POAG eyes had higher 'SSI' than normal eyes even after controlling for IOP (p < 0.05, Tukey-Cramer test). Treated POAG eyes had significantly lower CRF, and higher BGF than treatment-naïve POAG eyes. There were also significant differences in CH or SP A1 among the three groups. BGF and CH had similar AUC values (0.61 and 0.59). Treatment-naïve POAG eyes had stiffer corneas compared to normal eyes, which seemed to result from the material/structure of the cornea rather than higher intraocular pressure. Antiglaucoma topical medication alters biomechanical properties measured with Corvis ST. These results are important for understanding the pathogenesis and improving the management of POAG.

Changes in Stress-Strain Index and Corneal Biomechanics in Granular Corneal Dystrophy

Background: The aim of this study was to assess stress-strain index (SSI) and corneal biomechanical parameters in eyes with granular corneal dystrophy (GCD). Methods: This case-control study included 12 eyes of 12 patients with GCD (mean age 45.2 ± 18.7 years) and 20 eyes of 20 healthy individuals (mean age 54.4 ± 3.8 years). In addition to SSI, dynamic corneal response (DCR) parameters were assessed at the first and second applanation, including length (AL1, AL2), velocity (AV1, AV2), time (AT1, AT2), and deformation amplitude (DA A1, DA A2), and at the highest concavity (HC) phase, including DA, peak distance (PD), radius (HCR), and DA ratio (DAR 1 and 2 mm), by Corvis ST. Central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered covariates in comparing DCR parameters between the two groups. Results: SSI was statistically significantly lower in eyes with GCD than in normal eyes (p = 0.04). The corneal velocity towards the first applanation was 0.02 m/s faster in the GCD eyes AV1 (0.15 ± 0.02 vs. 0.13 ± 0.02 m/s, p < 0.001) and IR (7.48 ± 1.01 vs. 6.80 ± 1.22 mm, p = 0.003) parameters were significantly higher in the GDC group, while AT1 (7.33 ± 0.66 vs. 7.47 ± 0.36 ms, p = 0.002) and HCR (7.42 ± 0.76 vs. 8.20 ± 1.08 mm, p = 0.014) were significantly lower in the normal group. Conclusions: GCD led to a change in biomechanical properties of the cornea. SSI refers to fewer stiff corneas in GDC than normal.

The short-term effects of wearing swimming goggles on corneal biomechanics

PURPOSE

This study aimed to assess the impact of wearing swimming goggles (SG) on corneal biomechanics.

METHODS

Corneal deformation response, central corneal thickness (CCT), intraocular pressure (IOP) and biomechanically corrected intraocular pressure (bIOP) were measured with the Corvis system (Oculus Optikgeräte GmbH, Wetzlar, Germany) in thirty-one healthy young adults while wearing a drilled SG. All measurements were obtained before, at 30 s, 2 min, 3.5 min and 5 min of wearing SG, just after SG removal and after 2 min of SG removal.

RESULTS

The corneal biomechanics is sensitive to SG wear, observing lower corneal deformability during SG use. Specifically, wearing SG caused an increase in the time and length of the first applanation and radius curvature at the highest concavity, as well as a decrease and in the velocity of the first applanation and time and deformation amplitude of the second applanation (p < 0.001 in all cases). After SG removal, corneal biomechanical parameters showed a rebound-effect, obtaining a higher corneal deformability in comparison with baseline reading (p-corrected < 0.05 in all cases). Additionally, IOP and bIOP significantly increased while wearing SG (p < 0.001 in both cases), whereas CCT remained stable (p = 0.850).

CONCLUSIONS

Wearing SG modifies the biomechanical properties of the cornea, with reduced corneal deformability during SG wear. The outcomes of this study should be taken into consideration when making clinical decisions in subjects at high risk of developing corneal ectasias or glaucoma, as well as in the post-surgical management of these ocular conditions.

Differences of Corneal Biomechanics Among Thin Normal Cornea, Forme-Fruste Keratoconus, and Cornea After SMILE

Background: To compare the corneal biomechanics of thin normal cornea (TNC) with thinnest corneal thickness (TCT) (≤500 µm), forme-fruste keratoconus (FFKC) and cornea after small incision lenticule extraction (Post-SMILE) had their central corneal thickness (CCT) matched by Corneal Visualization Scheimpflug Technology (Corvis ST).

Methods: CCT were matched in 23 eyes with FFKC, 23 eyes by SMILE in 3 months post-operatively, and 23 TNC eyes. The differences in corneal biomechanics by Corvis ST among the three groups were compared.

Results: There was no significant difference in CCT among the three groups, and the biomechanically corrected intraocular pressure (bIOP) did not differ significantly among the three groups (all p &gt; 0.05). There were significant differences in most DCR parameters between pre- and post-operatively (all p &lt; 0.05). Compared with TNC, the values of corneal deflection amplitude during the first applanation (A1DA), length at the first applanation (A1L), corneal deflection amplitude during the second applanation (A2DA), and maximum deformation amplitude (DA) decreased in 3 months after SMILE (all p &lt; 0.05), these values increased in the FFKC (all p &lt; 0.05).

Conclusion: The majority of the DCR parameters were different among the three groups. The parameters A1DA, A1L, A2DA, and DA may be different between TNC and Post-SMILE, TNC and FFKC, and Post-SMILE and FFKC.

Biomechanical Effects of tPRK, FS-LASIK, and SMILE on the Cornea

Purpose: The objective of this study is to evaluate the in vivo corneal biomechanical response to three laser refractive surgeries.

Methods: Two hundred and twenty-seven patients who submitted to transepithelial photorefractive keratectomy (tPRK), femtosecond laser-assisted in-situ keratomileusis (FS-LASIK), or small-incision lenticule extraction (SMILE) were included in this study. All cases were examined with the Corvis ST preoperatively (up to 3 months) and postoperatively at 1, 3, and 6 months, and the differences in the main device parameters were assessed. The three groups were matched in age, gender ratio, corneal thickness, refractive error corrections, optical zone diameter, and intraocular pressure. They were also matched in the preoperative biomechanical metrics provided by the Corvis ST including stiffness parameter at first applanation (SP-A1), integrated inverse radius (IIR), deformation amplitude (DA), and deformation amplitude 2 mm away from apex and the apical deformation (DARatio2mm).

Results: The results demonstrated a significant decrease post-operation in SP-A1 and significant increases in IIR, DA, and DARatio2mm (p < 0.05), all of which indicated reductions in overall corneal stiffness. Inter-procedure comparisons provided evidence that the smallest overall stiffness reduction was in the tPRK group, followed by the SMILE, and then the FS-LASIK group (p < 0.05). These results remained valid after correction for the change in CCT between pre and 6 months post-operation and for the percentage tissue altered. In all three surgery groups, higher degrees of refractive correction resulted in larger overall stiffness losses based on most of the biomechanical metrics.

Conclusion: The corneal biomechanical response to the three surgery procedures varied significantly. With similar corneal thickness loss, the reductions in overall corneal stiffness were the highest in FS-LASIK and the lowest in tPRK.

Association of Corneal Biomechanics Properties with Myopia in a Child and a Parent Cohort: Hong Kong Children Eye Study

Associations between corneal biomechanics, axial elongation and myopia are important but previous results are conflicting. Our population-based study aimed to investigate factors associated with corneal biomechanics, and their relationships with myopia in children and adults. Data from 3643 children and 1994 parents showed that children had smaller deformation amplitudes (DA) than parents (p < 0.001). A larger DA was significantly associated with elongated axial length (AL; children: ß = 0.011; adults: ß = 0.0013), higher corneal curvature (children: ß = 0.0086; adults: ß = 0.0096), older age (children: ß = 0.010; adults: ß = 0.0013), and lower intraocular pressure (IOP; children: ß = −0.029; adults: ß = −0.031) in both cohorts. The coefficient of age for DA in children was larger than in adults (p < 0.001), indicating that the DA change with age in children is faster than in adults. DA was significantly associated with spherical equivalent (p < 0.001) resulting from its correlation with AL and corneal curvature. In conclusion, the cornea is more deformable in adults than in children, whereas corneal deformation amplitude increases faster with age in children than that in adults, along with AL elongation. Longer AL, steeper corneal curvature, older age and smaller IOP correspond to a more deformable cornea. The association between corneal deformation amplitude and refraction was mediated via AL and corneal curvature.

Time-varying regularity of changes in biomechanical properties of the corneas after removal of anterior corneal tissue

Background

The corneal biomechanical properties with the prolongation of time after corneal refractive surgery are important for providing a mechanical basis for the occurrence of clinical phenomena such as iatrogenic keratectasia and refractive regression. The aim of this study was to explore the changes of corneal elastic modulus, and stress relaxation properties from the 6-month follow-up observations of rabbits after a removal of anterior corneal tissue in simulation to corneal refractive surgery.

Methods

The anterior corneal tissue, 6 mm in diameter and 30–50% of the original corneal thickness, the left eye of the rabbit was removed, and the right eye was kept as the control. The rabbits were normally raised and nursed for 6 months, during which corneal morphology data, and both of corneal hysteresis (CH) and corneal resistance factor (CRF) were gathered. Uniaxial tensile tests of corneal strips were performed at months 1, 3, and 6 from 7 animals, and corneal collagen fibrils were observed at months 1, 3, and 6 from 1 rabbit, respectively.

Results

Compared with the control group, there were statistical differences in the curvature radius at week 2 and month 3, and both CH and CRF at months 1, 2, and 6 in experiment group; there were statistical differences in elastic modulus at 1, 3, and month 6, and stress relaxation degree at month 3 in experiment group. The differences in corneal elastic modulus, stress relaxation degree and the total number of collagen fibrils between experiment and control groups varied gradually with time, and showed significant changes at the 3rd month after the treatment.

Conclusions

Corneas after a removal of anterior corneal tissue undergo dynamic changes in corneal morphology and biomechanical properties. The first 3 months after treatment could be a critical period. The variation of corneal biomechanical properties is worth considering in predicting corneal deformation after a removal of anterior corneal tissue.

Effect of Prostaglandin Analogues on Corneal Biomechanical Parameters Measured With a Dynamic Scheimpflug Analyzer

PRCIS

Treatment with topical prostaglandin analogues (PGAs) induces increased corneal compliance in glaucoma eyes measured with a dynamic Scheimpflug analyzer.

PURPOSE

The purpose of this study was to evaluate the effect of topical PGAs on the corneal biomechanical properties.

METHODS

We retrospectively studied the biomechanical parameters of 31 eyes of 19 consecutive patients with glaucoma measured using a dynamic Scheimpflug analyzer (Corvis ST) before and after initiation of treatment with topical PGAs. No patients had a history of glaucoma treatment before the study and no other antiglaucoma medication was used during the study period. Nine biomechanical parameters were evaluated before and 61.6±28.5 days (range: 21 to 105 d) after initiation of the treatment. The changes in the corneal biomechanical parameters before and after treatment were analyzed using multivariable models adjusting for intraocular pressure and central corneal thickness. The Benjamini-Hochberg method was used to correct for multiple comparison.

RESULTS

In multivariable models, PGA treatment resulted in shorter inward applanation time (P=0.016, coefficient=-0.151) and larger deflection amplitude (P=0.023, coefficient=0.055), peak distance (P=0.042, coefficient=0.131), and deformation amplitude ratio at 1 mm (P=0.018, coefficient=0.028). These associations consistently indicated increased corneal compliance (deformability) after PGA treatment.

CONCLUSION

Topical PGAs resulted in greater corneal compliance, suggesting that the changes in the corneal biomechanical properties may lead to overestimation of the intraocular pressure-lowering effects.

Influence of corneal shape parameters on corneal deformation responses measured with a Scheimpflug camera

PURPOSE

To investigate the effect of corneal shape parameters on corneal deformation responses measured with a Scheimpflug camera.

METHODS

A total of 241 eyes of 241 participants were enrolled in this study. The anterior and posterior corneal curvature radii (CCR), anterior and posterior corneal Q-values, and corneal diameters of the participants were measured using the Pentacam HR. A total of 17 corneal deformation parameters including time, velocity, deflection amplitude, length, and area during ingoing applanation, highest concavity, and outgoing applanation were recorded by corneal visualization using Scheimpflug technology (Corvis ST). The effect of corneal shape parameters on corneal deformation responses was evaluated using multivariate regression models.

RESULTS

Multivariate regression analyses showed that six, five, four, and three corneal deformation parameters were significantly correlated with anterior CCR, posterior CCR, anterior Q-value, and posterior Q-value, respectively. Steeper anterior corneal curvature was associated with faster velocity during ingoing applanation and greater deformation during outgoing applanation. Steeper posterior corneal curvature was correlated with faster velocity during outgoing applanation and greater deformation during ingoing applanation. Eyes that had steeper corneal curvatures were associated with less stiff corneas. More negative anterior Q-value corresponded with faster velocity and greater deformation during ingoing applanation. Eyes that had more prolate posterior corneal surfaces showed more resistance to corneal deformation at the highest concavity. However, corneal diameter was not selected in any corneal deformation parameters models.

CONCLUSION

Corneal deformation response is significantly influenced by anterior and posterior corneal curvature and corneal asphericity, but not corneal diameter.

Clinical Characteristics of Highly Myopic Patients With Asymmetric Myopic Atrophic Maculopathy-Analysis Using Multimodal Imaging

Purpose

To evaluate the factors associated with asymmetric myopic atrophic maculopathy (MAM) in highly myopic patients.

Methods

We enrolled highly myopic patients with asymmetric MAM according to the atrophy, traction, and neovascularization (ATN) classification. The results of color fundus photography, optical coherence tomography (OCT), OCT angiography, and corneal visualization Scheimpflug technology (Corvis ST tonometry) were reviewed. The association between inter-eye differences in clinical features and MAM grading was analyzed using logistic regression analysis.

Results

Among the 72 eyes of 36 patients 61.0 ± 9.3 years of age, 9, 33, 17, and 13 eyes had A1, A2, A3, and A4, respectively. The mean axial length was 30.44 ± 1.92 mm, and there was no significant difference between eyes with less severe and more severe MAM. The inter-eye differences in MAM grading were associated with the inter-eye differences in the presence of Bruch's membrane defects (P = 0.014), ellipsoid zone disruption (P = 0.013), vessel density of the deep retinal layer (P = 0.022), foveal avascular zone circularity (P = 0.012), foveal avascular zone area (P = 0.049), flow area of the choriocapillaris (P = 0.013), vessel diameter (P = 0.045), and fractal dimension (P = 0.015). No Corvis ST parameter was statistically significant. A higher difference in the choriocapillaris flow area (P = 0.013; adjusted odds ratio = 1.10 [1.02–1.18]) remained associated with higher inter-eye differences in MAM grading in the multivariable regression.

Conclusions

A smaller choriocapillaris flow area was associated with more severe MAM, suggesting that vascular factors play pivotal roles in MAM.

Changes in ocular biomechanics after treatment for active Graves' orbitopathy

PURPOSE

To evaluate the changes in ocular biomechanical properties in active moderate-to-severe Graves' orbitopathy (GO) after intravenous glucocorticoids (IVGCs), and to clarify correlations between clinical findings and ocular biomechanical properties.

METHODS

A prospective study. A total of 20 consecutive GO patients and 20 age- and sex-matched healthy control subjects were included. GO was diagnosed on the basis of the recommendation by the European Group on Graves' Orbitopathy (EUGOGO), and disease activity was assessed by the clinical activity score (CAS). Patients were assigned to receive once weekly IVGCs (0.5 g, then 0.25 g, 6 weeks each). All participants received a full ophthalmic examination and biomechanical evaluation was performed with dynamic Scheimpflug analyzer (Corvis ST) at baseline and 12th weeks after therapy.

RESULTS

The biomechanically corrected intraocular pressure (bIOP) in GO patients was significantly higher than that in healthy subjects. In contrast, the whole eye movement (WEM) in GO patients was significantly lower than in healthy subjects after adjusting for bIOP. The CAS, NOSPECS score, and exophthalmos were significantly positively correlated with the bIOP and negatively correlated with the WEM after adjusting for bIOP, CCT and age. The WEM significantly increased, whereas bIOP significantly decreased after IVGCs (P < 0.001, P = 0.001 respectively). The overall response rate at the 12th week was 85% (17 of 20).

CONCLUSIONS

The changes of ocular biomechanical properties measured by Corvis ST were an objective indicator of inflammatory activity and severity of GO. Combining CAS and ocular biomechanical properties could better evaluate the therapeutic outcome of active moderate-to-severe GO.

Factors Influencing Corneal Biomechanics in Diabetes Mellitus

PURPOSE

Diabetes mellitus (DM) induces changes in corneal biomechanical properties. The influence of disease-specific factors was evaluated, and a novel DM index was created.

METHODS

Eighty-one patients with DM and 75 healthy subjects were matched according to age, intraocular pressure, and central corneal thickness. Information on the disease was collected, and measurements with the Ocular Response Analyzer and the Corvis ST were taken. Results were compared between the groups, and the influence of disease-specific factors was evaluated. From dynamic corneal response parameters, a DM index was calculated.

RESULTS

In DM, corneal hysteresis was higher than in healthy subjects (10.5 ± 1.9 vs. 9.7 ± 1.9 mm Hg, P = 0.008). In addition, dynamic corneal response parameters showed significant differences. Among others, highest concavity (HC) (17.212 ± 0.444 vs. 16.632 ± 0.794 ms, P < 0.001) and A2 time (21.85 ± 0.459 vs. 21.674 ± 0.447 ms, P = 0.017) as well as A1 (0.108 ± 0.008 vs. 0.104 ± 0.011 mm, P = 0.019) and A2 deflection amplitudes (0.127 ± 0.014 vs. 0.119 ± 0.014 mm, P < 0.001) were increased in DM. In DM type 1, HC deformation amplitude (1.14 ± 0.19 vs. 1.095 ± 0.114 mm, P = 0.035) was higher than in type 2. The time of deflection amplitude max correlated with the severity of retinopathy (R = 0.254, P= 0.023). In case of diabetic maculopathy, A1 velocity (0.155 ± 0.018 vs. 0.144 ± 0.019 ms, P = 0.043) and A2 time (22.052 ± 0.395 vs. 21.79 ± 0.46 ms, P = 0.04) were increased. Deformation amplitude max (R = 0.297, P = 0.024), HC time (R = 0.26, P = 0.049), HC deformation amplitude (R = 0.297, P = 0.024), and A2 deformation amplitude (R = 0.276, P = 0.036) were associated to disease duration. The DM index revealed a sensitivity of 0.773 and a specificity of 0.808 (area under the curve of receiver operating characteristic = 0.833).

CONCLUSIONS

In DM, changes in corneal biomechanics were correlated with disease-specific factors. The DM index achieved reliable sensitivity and specificity values.

Advances in Imaging Technology of Anterior Segment of the Eye

Advances in imaging technology and computer science have allowed the development of newer assessment of the anterior segment, including Corvis ST, Brillouin microscopy, ultrahigh-resolution optical coherence tomography, and artificial intelligence. They enable accurate and precise assessment of structural and biomechanical alterations associated with anterior segment disorders. This review will focus on these 4 new techniques, and a brief overview of these modalities will be introduced. The authors will also discuss the recent advances in research regarding these techniques and potential application of these techniques in clinical practice. Many studies on these modalities have reported promising results, indicating the potential for more detailed comprehensive understanding of the anterior segment tissues.

Dynamic Scheimpflug Ocular Biomechanical Parameters in Untreated Primary Open Angle Glaucoma Eyes

Purpose

To characterize the corneal biomechanical properties of glaucoma eyes by comparing the dynamic Scheimpflug biomechanical parameters between untreated glaucoma and control eyes.

Methods

Cross-sectional observational data of dynamic Scheimpflug analyzer (Corvis ST) examinations were retrospectively collected from 35 eyes of 35 consecutive patients with untreated normal tension glaucoma and 35 eyes of 35 healthy patients matched on age and IOP. Ten biomechanical parameters were compared between the two groups using multivariable models adjusting for IOP, central corneal thickness, age, and axial length. The Benjamini-Hochberg method was used to correct for multiple comparison.

Results

In multivariable models, glaucoma was associated with smaller applanation 1 time (P < 0.001, coefficient = −0.5865), applanation 2 time (P = 0.012, coefficient = −0.1702), radius (P = 0.006, coefficient = −0.5447), larger peak distance (P = 0.011, coefficient = 0.1023), deformation amplitude ratio at 1 mm (P < 0.001, coefficient = 0.072), and integrated radius (P < 0.001, coefficient = 1.094). These associations consistently indicate greater compliance of the cornea in glaucoma eyes.

Conclusions

Untreated normal tension glaucoma eyes were more compliant than healthy eyes. The greater compliance (smaller stiffness) of normal tension glaucoma eyes may increase the risk of optic nerve damage. These results suggest the relevance of measuring biomechanical properties of glaucoma eyes.

Corneal biomechanical properties in myopic eyes evaluated via Scheimpflug imaging

BACKGROUND

To investigate the biomechanical properties of the cornea in myopic eyes using corneal visualization Scheimpflug technology (Corvis ST). The relationships between the biomechanical properties of the cornea and the degree of myopia were also investigated.

METHODS

265 eyes of 265 subjects were included. Based on spherical equivalent (SE) in diopters (D), participants were divided into four groups: low myopia/control (SE: - 0.50 to - 3.00D), moderate myopia (SE: - 3.00 to - 6.00D), high myopia (SE: - 6.00 to - 10.00D) and severe myopia (SE greater than - 10.00D). Axial length (AL), anterior segment parameters, and corneal biomechanical properties were obtained with the Lenstar LS900, Pentacam HR and Corvis ST, respectively.

RESULTS

Mean (±SD) SE was - 7.29 ± 4.31D (range: - 0.63 to - 25.75D). Mean AL was 26.31 ± 1.82 mm (range: 21.87 to 31.94 mm). Significant differences were detected within the four groups in terms of six corneal biomechanical parameters: deformation amplitude (DA), time from start until second applanation (A2-time), length of flattened cornea at the second applanation (A2-length), corneal velocity during the first and second applanation (A2-velocity), time from start to highest concavity (HC-time), and central curvature at highest concavity (HC radius). AL was positively associated with DA whereas negatively associated with A1-velocity and A2-length. SE was positively associated with A2-time, HC-time and A2-velocity, whereas negatively associated with DA. IOP was positively associated with four corneal biomechanical parameters and negatively associated with three parameters.

CONCLUSIONS

Eyes with severe myopia showed greater DA, lesser A2 time, HC time, and faster A2-velocity compared to low to high myopia. This suggests the cornea becomes weaker and more deformable with elongation of axial length with corresponding increases in myopia. DA, A2-time and A2-velocity could be useful corneal biomechanical indicators in patients with myopia.

Comparison of waveform-derived corneal stiffness and stress-strain extensometry-derived corneal stiffness using different cross-linking irradiances: an experimental study with air-puff applanation of ex vivo porcine eyes

Purpose

To assess corneal stiffening of standard (S-CXL) and accelerated (A-CXL) cross-linking protocols by dynamic corneal response parameters and corneal bending stiffness (Kc[mean/linear]) derived from Corvis (CVS) Scheimpflug-based tonometry. These investigations were validated by corneal tensile stiffness (K[ts]), derived from stress-strain extensometry in ex vivo porcine eyes.

Methods

Seventy-two fresh-enucleated and de-epithelized porcine eyes were soaked in 0.1% riboflavin solution including 10% dextran for 10 min. The eyes were separated into four groups: controls (n = 18), S-CXL (intensity in mW/cm²*time in min; 3*30) (n = 18), A-CXL (9*10) (n = 18), and A-CXL (18*5) (n = 18), respectively. CXL was performed using CCL Vario. CVS measurements were performed on all eyes. Subsequently, corneal strips were extracted by a double-bladed scalpel and used for stress-strain measurements. K[ts] was calculated from a force-displacement curve. Mean corneal stiffness (Kc[mean]) and constant corneal stiffness (Kc[linear]) were calculated from raw CVS data.

Results

In CVS, biomechanical effects of cross-linking were shown to have a significantly decreased deflection amplitude as well as integrated radius, an increased IOP, and SP A1 (P < 0.05). Kc[mean]/Kc[linear] were significantly increased after CXL (P < 0.05). In the range from 2 to 6% strain, K[ts] was significantly higher in S-CXL (3*30) compared to A-CXL (9*10), A-CXL (18*5), and controls (P < 0.05). At 8% to 10% strain, all protocols induced a higher stiffness than controls (P < 0.05).

Conclusion

Several CVS parameters and Kc[mean] as well as Kc[linear] verify corneal stiffening effect after CXL on porcine eyes. S-CXL seems to have a higher tendency of stiffening than A-CXL protocols have, which was demonstrated by Scheimpflug-based tonometry and stress-strain extensometry.

Is the Corneal Thickness Profile Altered in Diabetes Mellitus?

Purpose: To investigate the influence of chronic hyperglycemia in diabetes mellitus (DM) on spatial corneal thickness distribution and to analyze the influence of disease-specific factors. Methods: DM patients and healthy subjects were matched according to age and intraocular pressure (IOP). In diabetics, disease duration, DM type, and HbA_1c value were assessed. Spatially resolved corneal thickness was measured by Pentacam HR. Thinnest corneal thickness (TCT) and peripheral pachymetry of concentric circles around TCT were determined. The Dynamic Scheimpflug Analyzer Corvis ST (CST) was used to measure the parameter pachy slope, which is an indicator of the change of corneal thickness from the apex to the periphery. Results: 59 DM patients and 57 healthy subjects were included. Age (P = .486) and IOP (P = .154) were not different between the groups. In DM, pachy slope was significantly higher than in healthy subjects (41.1 ± 9.87 vs. 35.18 ± 10.64 μm, P = .004). Also, the differences between TCT and the average of peripheral corneal thickness of concentric circles with a diameter of 2 mm (10.3 ± 1.7 vs. 9.3 ± 3.8 μm, P < .001) to 6 mm (82.2 ± 12.4 vs. 76.8 ± 12.6 μm, P = .011) were increased in patients. Changes in thickness profile were associated with HbA_1c value and presence of diabetic retinopathy or maculopathy. Conclusion: In DM, a stronger peripheral corneal thickness increase was detectable. This change was shown using the novel CST parameter pachy slope and confirmed by Pentacam readings. These alterations might affect IOP and biomechanical measurements, and influence refractive procedures.

Characteristics of Corneal Biomechanics in Chinese Preschool Children With Different Refractive Status

PURPOSE

To investigate the characteristics of corneal biomechanics in Chinese preschool children with different refractive status.

METHODS

Study participants were 108 Chinese children (216 eyes) aged 4 to 6 years with a spherical equivalent refraction between -9.00 and +9.00 diopters (D). Cycloplegic refraction was measured using an autorefractor, axial length using an IOL Master (Zeiss, Oberkochen, Germany), and corneal biomechanical metrics and corneal power using an ultra-high-speed camera (Corvis ST; Oculus, Wetzlar, Germany) and Pentacam (Oculus; Menlo Park, CA). Differences in corneal biometry and biomechanical characteristics among myopia, emmetropia, and hyperopia eyes were analyzed by SPSS 17.0.

RESULTS

The spherical equivalent refraction was significantly positively correlated with the stiffness parameter at the first applanation (SP-A1, r = 0.22, P < 0.01) and corneal velocity at the second applanation (A2 velocity, r = 0.25, P < 0.001), whereas it was negatively correlated with the peak distance (r = -0.32, P < 0.001) and deformation amplitude ratio (DA ratio, r = -0.34, P < 0.001). In the hyperopia, emmetropia, and myopia groups, the SP-A1 successively decreased (108.70 ± 22.93 vs. 100.50 ± 18.98 vs. 97.97 ± 18.91, P < 0.01), whereas the peak distance progressively increased (4.39 ± 0.32 vs. 4.56 ± 0.30 vs. 4.63 ± 0.34 mm, P < 0.001). In the same order of groups, an increasing trend was found for the axial length (21.11 ± 0.76 vs. 22.39 ± 0.72 vs. 24.09 ± 1.37 mm, P < 0.001), central anterior chamber depth (CACD, 3.04 ± 0.41 vs. 3.21 ± 0.33 vs. 3.37 ± 0.40 mm, P < 0.001) and flat meridian keratometry (K1, 41.92 ± 1.59 vs. 42.73 ± 1.39 vs. 42.98 ± 1.60 D, P < 0.001). Central corneal thickness significantly decreased in the same order of groups (565.46 ± 33.22 vs. 551.97 ± 24.66 vs. 543.36 ± 37.74 µm, P < 0.001).

CONCLUSIONS

Corneal stiffness is reduced in myopia and increased in hyperopia compared with emmetropia in children aged 4 to 6 years. Corneal biometry and biomechanical characteristics in preschool children seem to depend on refractive status.

Clinical Evaluation and Validation of the Dutch Crosslinking for Keratoconus Score

Importance

Defining keratoconus progression is fundamental in clinical decision making because crosslinking treatments are indicated when the disease is considered progressive. Currently, there is no consensus which parameters should be used to define progression.

Objective

To assess and validate a novel clinical scoring system as an easy-to-use assessment tool for crosslinking treatment in patients with keratoconus.

Design, Setting, and Participants

Prospective cohort study at 2 academic treatment centers. Patients with keratoconus referred between January 1, 2012, and June 30, 2014, with 2-year follow-up were included. Analysis began March 2017.

Interventions

The Dutch Crosslinking for Keratoconus (DUCK) score is based on changes in 5 clinical parameters that are routinely assessed: age, visual acuity, refraction error, keratometry, and subjective patient experience. The DUCK score is derived by scoring 0 to 2 points per item, and cutoffs were determined by clinical experience. We compared the DUCK scores to the conventional 1.0-diopter increase in maximum keratometry criterion, within the last 12 months, in a longitudinal discovery and a validation cohort. Sensitivity analyses and intraitem correlations were performed.

Main Outcomes and Measures

Overall treatment rate reduction and the duly withheld treatment rate.

Results

A total of 504 eyes of 388 patients were available for analysis on disease progression in the course of 12 and 24 months. Baseline patient characteristics of the discovery cohort and the validation cohort were comparable in terms of age (mean [SD], 26.8 [8.3] years vs 26.3 [9.1]), sex (216 of 332 [65%] vs 123 of 172 [72%] men), and maximum keratometry (mean [SD], 53.5 [7.1] vs 52.7 [6.3]). Adhering to the DUCK score, rather than maximum keratometry, was associated with a reduction in overall treatment rate by 23% (95% CI, 18%-30%), without increasing the risk of disease progression (ie, the rate of progression for both groups was equal; ±0%). The DUCK score appears to better identify eyes that were duly withheld treatment by 35% (95% CI, 22%-49%).

Conclusions and Relevance

These results provide validation of the DUCK score as a tool to determine whether a crosslinking treatment might be warranted. Compared with the conventional maximum keratometry criterion of more than 1.0 diopter, the DUCK score may better select patients who might benefit from crosslinking treatment. Potentially, it may prevent unnecessary treatments, reduce exposure to treatment risks, and improve the cost effectiveness of crosslinking.

Intraocular pressure measurements in diabetes mellitus

PURPOSE

To investigate the impact of diabetes mellitus-induced changes on intraocular pressure measurements using Goldmann applanation tonometry, Ocular Response Analyzer, and Corvis ST.

METHODS

Measurements were done using Goldmann applanation tonometry, Ocular Response Analyzer, and Corvis ST in 69 diabetic patients. Biomechanical-corrected intraocular pressure values by Ocular Response Analyzer (IOPcc) and Corvis ST (bIOP) were used. In addition, biometry and tomography were performed and information on diabetes mellitus specific factors was collected. Results were compared to an age-matched group of 68 healthy subjects.

RESULTS

In diabetes mellitus, Goldmann applanation tonometry intraocular pressure (P = 0.193) and central corneal thickness (P = 0.184) were slightly increased. Also, IOPcc (P = 0.075) and bIOP (P = 0.542) showed no significant group difference. In both groups, IOPcc was higher than Goldmann applanation tonometry intraocular pressure (P = 0.002, P < 0.001), while bIOP was nearly equal to Goldmann applanation tonometry intraocular pressure (P = 0.795, P = 0.323). Central corneal thickness showed a tendency to higher values in poorly controlled than in controlled diabetes mellitus (P = 0.059). Goldmann applanation tonometry intraocular pressure correlated to central corneal thickness, while IOPcc and bIOP were independent from central corneal thickness in both groups. All intraocular pressure values showed significant associations to corneal biomechanical parameters. Only in diabetes mellitus, bIOP was correlated to Pachy slope (P = 0.023).

CONCLUSION

In diabetes mellitus, Goldmann applanation tonometry intraocular pressure was slightly, but not significantly, increased, which might be caused by a higher central corneal thickness and changes in corneal biomechanical properties. However, intraocular pressure values measured by Ocular Response Analyzer and Corvis ST were not significantly different between diabetes mellitus patients and healthy subjects. The bIOP showed a higher agreement with Goldmann applanation tonometry than IOPcc and was independent from central corneal thickness.

Correlation Between the Myopic Retinal Deformation and Corneal Biomechanical Characteristics Measured With the Corvis ST Tonometry

Purpose

We previously reported that the retinal deformation due to myopia was represented by the peripapillary retinal arteries angle (PRAA). In this study, we investigated the relationship between the PRAA and biomechanical properties measured with Corvis ST (CST) tonometry.

Methods

Thirty-four normative eyes of 34 subjects who underwent CST measurement were enrolled. The PRAA was calculated from a fundus photograph. Variables related to the PRAA were identified from age, axial length, spherical equivalent refractive error, and 10 CST parameters using model selection with the second-order bias-corrected Akaike information criterion index.

Results

The PRAA was best described with axial length (coefficient = −5.66, P < 0.0001), maximum deflection amplitude (mm; coefficient = 130.5, P = 0.0004), and deflection amplitude ratio (DA ratio) 2 mm (coefficient = −25.8, P = 0.0032), where mm was the amount of the maximum corneal apex movement and DA ratio 2 mm was the ratio between the deformation amplitudes at the apex and 2 mm away from the apex. The optimal model was significantly better than the model only with axial length (P = 0.0014, analysis of variance).

Conclusions

The PRAA was significantly better described with the CST parameters compared to the axial length model only; eyes with small PRAA (larger myopic retinal deformation) showed narrow and shallow maximum corneal deflection.

Translational Relevance

The Corvis ST parameters, which represents corneal biomechanical characteristics, were associated with myopic retinal deformation.

Assessment of corneal biomechanical parameters in healthy and keratoconic eyes using dynamic bidirectional applanation device and dynamic Scheimpflug analyzer

PURPOSE

To investigate corneal biomechanical parameters in healthy and keratoconic eyes using the Ocular Response Analyzer dynamic bidirectional applanation device (ORA) and the Corvis ST dynamic Scheimpflug analyzer (CST).

SETTING

Department of Ophthalmology, Carl Gustav Carus University Hospital Dresden, Germany.

DESIGN

Prospective, monocentric, case-control study.

METHODS

Corneal biomechanical parameters were obtained in 60 eyes of 60 healthy participants (Group I) and 60 eyes of 60 keratoconus patients (Group II) with different grades of severity using the ORA and the CST. Participants were matched by age (Group I: 38.3 years ± 12.8 [SD], Group II: 37.3 ± 11.2 years) and intraocular pressure (Group I: 13.7 ± 1.7 mm Hg, Group II: 13.6 ± 1.5 mm Hg).

RESULTS

For the ORA, the receiver operating characteristic curve analysis showed an area under the curve (AUC) of 0.950 for the keratoconus score, a sensitivity of 87% and a specificity of 93%. The AUC for the corneal resistant factor and corneal hysteresis was 0.930 and 0.868 with a sensitivity of 87% and a specificity of 87%, and sensitivity of 80% and a specificity of 80%, respectively. For the CST, the corneal biomechanical index showed the highest AUC (0.977) with a sensitivity of 97% and a specificity of 98%. The AUC of integrated radius (0.974; 90% sensitivity, 93% specificity) was followed by maximum inverse radius (0.962; 92% sensitivity, 93% specificity). Most parameters were able to discriminate healthy eyes from different keratoconus stages and early stages of keratoconus from moderate stages.

CONCLUSION

Both devices allowed for good differentiation between healthy eyes and keratoconic eyes and between different severity grades of keratoconus. Several parameters of ORA and CST revealed high sensitivity and specificity values for keratoconus detection.

Novel dynamic corneal response parameters in a practice use: a critical review

Background

Non-contact tonometers based on the method using air puff and Scheimpflug’s fast camera are one of the latest devices allowing the measurement of intraocular pressure and additional biomechanical parameters of the cornea. Biomechanical features significantly affect changes in intraocular pressure values, as well as their changes, may indicate the possibility of corneal ectasia. This work presents the latest and already known biomechanical parameters available in the new offered software. The authors focused on their practical application and the diagnostic credibility indicated in the literature.

Discussion

An overview of available literature indicates the importance of new dynamic corneal parameters. The latest parameters developed on the basis of biomechanics analysis of corneal deformation process, available in non-contact tonometers using Scheimpflug’s fast camera, are used in the evaluation of laser refractive surgery procedures, e.g. LASIK procedure. In addition, the assessment of changes in biomechanically corrected intraocular pressure confirms its independence from changes in the corneal biomechanics which may allow an intraocular pressure real assessment. The newly developed Corvis Biomechanical Index combined with the corneal tomography and topography assessment is an important aid in the classification of patients with keratoconus.

Conclusion

New parameters characterising corneal deformation, including Corvis Biomechanical Index and biomechanical compensated intraocular pressure, significantly extend the diagnostic capabilities of this device and may be helpful in assessing corneal diseases of the eye. Nevertheless, further research is needed to confirm their diagnostic pertinence.

Evaluation of corneal biomechanics in patients with keratectasia following LASIK using dynamic Scheimpflug analyzer

PURPOSE

To investigate the corneal biomechanics in eyes with keratectasia following LASIK using a dynamic Scheimpflug analyzer.

DESIGN

Case-Control study.

METHOD

The subjects in the study included 12 eyes with keratectasia after LASIK (KE), 24 eyes with keratoconus (KC), 17 eyes without keratectasia after LASIK (LASIK), and 34 eyes with normal corneas (Normal). Corneal biomechanics of the four groups were evaluated using a dynamic Scheimpflug analyzer.

RESULTS

Compared with Normal (7.06 ± 0.54), the radius at the highest concavity (radius, mm) of LASIK (5.96 ± 0.76), KE (4.93 ± 0.61) and KC (5.39 ± 1.02) were significantly small. The Deflection Amplitude (HCDLA, mm) of Normal (0.94 ± 0.07) was significantly lower than those of KE (1.11 ± 0.10) and KC (1.06 ± 0.16), and was not significantly different from that of LASIK (0.98 ± 0.07). There were significant differences between LASIK and KE in radius and HCDLA (P < 0.05), whereas KE and KC had no differences in these parameters.

CONCLUSIONS

Corneal biomechanical features evaluated using the dynamic Scheimpflug analyzer suggest that biomechanical properties in eyes with keratectasia, keratoconus, and LASIK are different from those of normal eyes. Although the biomechanics in eyes with keratectasia differs from that in eyes with LASIK, it is similar to that in eyes with keratoconus.