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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.

Cornea transplant involving applanation results in a deformation of the cornea. This deformation combined with a mismatch of dimensional and mechanical properties between donor and recipient corneas gives rise to tension on the transplanted cornea, astigmatism and vision difficulties. Therefore, accurate prediction of deformation of the incision plant during such operations is necessary to minimize complications. In this work, we employed a finite element simulation on a cornea with measured geometry and hyperelastic Mooney–Rivlin mechanical properties to analyze the intended incision plane’s change during corneal applanation. A simulation of the cornea transplant procedure assuming two different geometries to be the same was performed, and the transplanted cornea showed a 5.1% change in the exterior radius. When the proposed method was applied, no change in the radius after transplant was observed. Moreover, a precise matching of the incision plane can be selected for the corneas, and the corneal deformation after an IntraLase-Enabled Keratoplasty (ILEK) corneal transplant procedure is expected to be minimal.

Purpose of review This study was conducted to demonstrate the importance of the environment in keratoconus (KC) genesis. Recent findings Genetic-related connective tissue disorders demonstrate the inconsistency of theories regarding KC pathogenesis since no corneal steepening was observed in the majority of these patients. Despite recent advances and decades of research into the genetics of KC, the identification of disease-causing KC genes has been frustrating. Variants found based on genome-wide and next-generation sequencing only seem to account for a small number of cases or play a limited role in KC pathogenesis. Summary The literature shows that mechanical manipulation may be the common underlying factor or the indispensable act precipitating the cascade of events leading to permanent corneal deformation. Hence, ophthalmologists have the opportunity to increase patient awareness about eye manipulation repercussions and treatment for ocular surface disorders. Video abstract http://links.lww.com/COOP/A42.

To investigate the effect of corneal shape parameters on corneal deformation responses measured with a Scheimpflug camera. 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. 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. Corneal deformation response is significantly influenced by anterior and posterior corneal curvature and corneal asphericity, but not corneal diameter.

Funding for open access charge: Universidad de Granada/CBUA. The authors have no financial or proprietary interest in a product, method or material described herein. The article has not been presented in a meeting., 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 thirtyone 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., Universidad de Granada/CBUA

We report on a 13-year-old girl undergoing changes in the refraction of her OS associated with eye rubbing. Corneal topography showed a corneal deformation in OS, classified as stage 1 keratoconus according to the Krumeich classification. A significant reduction in eye rubbing led to a normal corneal shape at the 1-year follow-up. Transient and fully reversible corneal ectasia can be caused by eye rubbing in pediatric age. This may have implications when counseling very young patients with eye rubbing.

There are many ways to measure the intraocular pressure (IOP) and all are influenced to some degree by the individual characteristics of the eye. Ocular rigidity (OR) is a familiar concept used in ophthalmology to describe the relationship between pressure and volume changes in the eyeball. This concept partly explains why IOP measurements vary between different types of tonometers. Some tonometers are more heavily influenced by OR than others, due to different amounts of corneal deformation, and volume of fluid displaced during tonometry. More recent tonometers either produce less corneal deformation and less fluid displacement or, attempt to compensate for variations in the biomechanical characteristics of the cornea. Surgical intervention can influence the true IOP but, additionally modify the OR and therefore differentially influence the results from different tonometers. Clinicians should be aware of these effects when interpreting IOP measurements, especially in eyes that have had surgery or have other characteristics that may affect OR. A deeper understanding of the factors that influence OR might lead to the development ofmore accurate instrumentation that is less influenced by OR.

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 &plusmn, 9.24 years, who underwent myopic photorefractive keratectomy (PRK) for a refractive defect, measured as spherical equivalent, of mean &minus, 4.69 &plusmn, 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.

Objective This case report aims to highlight the corneal deformation induced by soft contact lens (SCL) wear, which is accompanied by changes in not only the anterior but also the posterior surface of cornea. Case Report Cases are presented of two patients who wore non- planned replacement SCL for more than 15 years fabricated from materials with low oxygen permeability, sought a consultation with complaints of visual acuity loss in the both eyes. Anterior segment optical coherence tomography imaging demonstrated corneal deformation in the posterior as well as the anterior surface in both eyes of two patients, resulting in the diagnosis of corneal deformation induced by SCL wear. After the cessation of lens wear, there were improvements in visual acuity, anterior and posterior corneal higher-order aberrations, and changes in the anterior corneal shape, whereas the posterior corneal shape was improved in one case and remained mildly deformed in the other case. Conclusion Wearing SCLs with low oxygen permeability for long time periods, could induce corneal deformation in patients, indicating the need for careful observation of changes in not only the anterior but also the posterior corneal surface.

Background: KC is a bilateral, progressive, non-inflammatory corneal degeneration. Corneal deformation and thinning causes irregular astigmatism and leads to visual impairment. Aim of the work: this study aimed to evaluate simultaneous topography-guided partial PRK and CXL as a therapeutic intervention in patients with KC. Methodology: the present study was designed to evaluate simultaneous topography-guided partial PRK and CXL as a therapeutic intervention in patients with KC. It included 25 keratoconic eyes of 17 patients; 8 cases were bilateral and 9 cases were unilateral. All included cases underwent full history taking and ophthalmologic examinations for preoperative evaluation and postoperative assessment. Follow up was carried out at first postoperative day and at 1, 3 and 6 months post-operatively. Results: when comparing K1, K2, thinnest location and BCVA at 1, 3 and 6 months postoperatively to the corresponding values at first postoperative day, there was non-significant difference at any point of time. Conclusion: simultaneous topography-guided partial PRK and CXL as a therapeutic intervention in patients with keratoconus is an effective without significant complications; thus, it had a good efficacy, stability over time and safety.

Background: The aim of the study is to model the corneal dynamic deformation under an air puff excitation. The deformation response of the cornea was modeled by using linear and nonlinear viscoelastic models. The corneal deformation responses generated from the linear and nonlinear viscoelastic model were correlated with the clinical results, which were obtained from Corneal Visualization Scheimpflug Tonometer (Corvis ST) to evaluate the comparable biomechanical parameters of the cornea. Methods: A prompt deformation occurs when the external force applied to the cornea. Then a continuous deformation follows. A simple mass, spring and dashpot system were used to model human eyeball. Results: In linear viscoelastic model, the corneal elastic stiffness commanded behavior of the corneal deformation and its maximum, when the viscous component affected for its lateral shifting and marginally alter the magnitude.Whereas, in the nonlinear viscoelastic model, the corneal material nonlinearity commanded the behavior and maximum of the corneal deformation, while the viscous component marginally contributed for its lateral shifting and demonstrated the minimum affect on the magnitude and form. A multi-objective genetic algorithm-based optimization procedure was used to identify the material properties in the nonlinear viscoelastic model for 29 eyes of 20 normal people. Conclusion: The corneal deformation response model with nonlinear viscoelastic model showed to have a better fit with the corneal dynamic deformation behavior under an air pulse excitation. The biomechanical properties of the cornea in vivo can be evaluated by using and analysing dynamic deformation of the cornea under an air puff excitation model.

This paper proposed an improved point based method to simulate the deformation and cutting of cornea, realized the real-time interaction between the force feedback device and the model in virtual surgery. We construct a hybrid deformable model, the model consists of two parts: the interior of the cornea consists of some particles, and the boundary consists of some meshes which are formed by surfaces nodes, calculate the stress tensor of particle can simulate corneal deformation. In this process, in order to ensure the stability of the deformation, a volume constraint is added to our model. By sampling on the surface of the model to form some meshes, the model could support the changes of topology. Using a node replication method for surface cutting and subdivide the cutting triangles in the cutting process, so that it can generate relatively smooth incision. Experiments show that the model provides a real and efficient deformation simulation, with good stability and scalability.

AimsTo examine corneal biomechanics in healthy and keratoconic eyes, with or without crosslinking obtained by ultrahigh-speed Scheimpflug measurements (Corvis ST).MethodsOne hundred and seventeen eyes were studied in three groups: group 1 (n=39) contained keratoconic eyes without crosslinking. Group 2 (CXL; n=28) comprised keratoconic eyes after crosslinking. These were compared with a control group (n=50 matched healthy eyes). In addition, 10 keratoconus patients, before and after CXL treatment, respectively, were examined.ResultsThe novel parameter A1L–A2L demonstrated highly significant differences between crosslinked corneas and untreated keratoconic or healthy corneas. Velocity during second applanation (A2V) and deformation amplitude (DA) were significantly increased in crosslinked keratoconic eyes both compared with untreated keratoconic eyes and with healthy controls. Radius at highest curvature also was significant among all groups. Inward applanation length (A1L) was significantly increased in controls, whereas outward applanation length (A2L) was significantly reduced in crosslinked keratoconic eyes compared with both other groups. The follow-up analysis revealed statistically significant changes in pachymetry and intraocular pressure and showed tendencies towards significance in applanation times 1 and 2 and in DA.ConclusionsBoth A2V and A2L are viable parameters to discriminate healthy from keratoconic but also crosslinked from non-crosslinked keratoconic corneas. The difference of A1L−A2L could reliably discriminate crosslinked from non-crosslinked and healthy corneas. Follow-up examination in a small cohort allows distinction between crosslinked and untreated keratoconus in follow-up examinations. The difference of A1L-A2L could reliably discriminate crosslinked from non-crosslinked and healthy corneas. Measurements of corneal deformation using dynamic ultrahigh-speed Scheimpflug technology are reproducible and provide useful information about keratoconus assessment and biomechanics. Therefore, the Corvis ST seems to provide useful technology to monitor therapeutic success of crosslinking treatment.

PURPOSE To investigate corneal stiffness and analyze its possible influence on other corneal biomechanical and nonbiomechanical parameters in myopic eyes of Chinese patients. METHODS A total of 387 healthy (right) myopic eyes were included in this study. Corneal visualization Scheimpflug technology was used to measure the corneal stiffness parameter at the first applanation (SP-A1), deformation amplitude ratio at 1.0 and at 2.0 mm, biomechanically corrected intraocular pressure (bIOP), and corneal deformation parameters during the first applanation (A1: A1-time, A1-length, and A1-velocity), second applanation (A2; A2-time, A2-length, and A2-velocity), and highest concavity (HC; HC-time, HC-radius, HC deformation amplitude, and HC peak distance). The Pentacam was used to evaluate central corneal thickness, mean corneal curvature (Km), anterior corneal central elevation, and corneal asphericity (Q value) of the anterior cornea. RESULTS The mean SP-A1 and bIOP values were 90.46 ± 15.39 mm Hg/mm and 13.5 ± 1.85 mm Hg, respectively. The SP-A1 increased with age (β = 0.41 [95% CI, 0.28%-0.54%]; P < 0.0001). Corneal stiffness was positively correlated with central corneal thickness, uncorrected intraocular pressure, and bIOP and was also significantly correlated with all corneal deformation parameters (P < 0.05), except A1-length, HC-time, and HC peak distance. Corneal stiffness was negatively correlated with central corneal elevation of the anterior surface (r = -0.124, P = 0.014) and mean corneal curvature (r = -0.114, P = 0.025) and positively correlated with the Q value of the anterior surface (r = 0.109, P = 0.032). CONCLUSIONS Corneal stiffness increased with age. Stronger corneal stiffness may be related to flattening of the cornea and higher intraocular pressure.

Biomechanical properties are important for the cornea to maintain its normal shape and function. There is still a need to develop better methods for accurate measurement of corneal mechanical properties. In this study, we propose to introduce the optical coherence tomography (OCT) in inflation test for the imaging of corneal deformation in order to measure its biomechanical properties. Ten cornea-mimicking silicone phantoms with different stiffness and five fresh porcine corneas were tested using the proposed method. Intra-ocular pressure was changed from 10 to 90 mmHg using two different loading rates to observe the pressure-apex displacement relationship and calculate the apparent stiffness of the corneas. Stiffness of the corneal phantoms obtained by the inflation test ranged from 0.2 to 1 MPa, which was highly consistent with the results from the mechanical tensile test (y = 0.70x, p

Air-puff induced corneal deformation imaging reveals information highlighting normal and pathological corneal response to a non-contact mechanical excitation. Here, we present a novel customized swept-source optical coherence tomography system coupled with a collinear air-puff excitation. We acquired unobstructed dynamic corneal deformation on multiple meridians with two custom scan patterns over a field of view of up to 15 mm x 15 mm and selected puff profiles at unprecedented scan rates, both ex vivo and in vivo. We show that our system can detect corneal deformation profiles and deformation asymmetries that are useful for corneal biomechanics diagnostics and pathology screening.

The purpose of this study was to ascertain the relationships between the amplitude of the corneal pulse (CP) signal and the parameters of corneal biomechanics during ex-vivo intraocular pressure (IOP) elevation experiments on porcine eyes with artificially induced ocular pulse cycles. Two experiments were carried out using porcine eyes. In the first one, a selected eye globe was subjected to three IOP levels (15, 30 and 45 mmHg), where changes in physical ocular pulse amplitude were controlled by infusion/withdrawal volumes (ΔV). In the second experiment, six eyes were subjected to IOP from 15 mmHg to 45 mmHg in steps of 5 mmHg with a constant ΔV, where corneal deformation parameters were measured using Corvis ST. In both experiments, at each IOP, the CP and IOP signals were acquired synchronically using a non-contact ultrasonic distance sensor and a pressure transmitter, respectively. Based on the amplitudes of the CP and IOP signals ocular pulse based corneal rigidity index (OPCRI) was calculated. Results indicate positive correlations between ΔV and the physical ocular pulse amplitude, and between ΔV and the corneal pulse amplitude (both p < 0.001). OPCRI was found to increase with elevated IOP. Furthermore, IOP statistically significantly differentiated changes in OPCRI, the amplitudes of CP and IOP signals and in most of the corneal deformation parameters (p < 0.05). The partial correlation analysis, with IOP as a control variable, revealed a significant correlation between the length of the flattened cornea during the first applanation (A1L) and the corneal pulse amplitude (p = 0.002), and between A1L and OPCRI (p = 0.003). In conclusion, this study proved that natural corneal pulsations, detected with a non-contact ultrasonic technique, reflect pressure-volume dynamics and can potentially be utilized to assess stiffness of the cornea. The proposed new rigidity index could be a simple approach to estimating corneal rigidity.

Purpose. To compare corneal deformation characteristics using ultra-high-speed Scheimpflug camera (Corvis ST) in patients with nonmyopic (NM), mild-to-moderate nonaxial myopic (MM), and high axial myopic (HM) eyes. Methods. In this cross-sectional study, normal subjects aged >40 years with no history of ocular laser/surgery were classified according to axial length (AL) and spherical equivalence (SE) into three groups: (1) NM (SE > −0.50 D and AL Results. A total of 180 eyes were recruited. 98 eyes were NM, 30 eyes were MM, and 52 eyes were HM. There were significant correlations of OCV to the degree of refractive error (r = 0.203, p<0.001) and AL (r = −0.242, p<0.001). After adjusting for age, sex, intraocular pressure, and corneal thickness, there was significantly higher CDA (β = 0.07, p<0.001), faster OCV (β = −0.08, p<0.001), and smaller radius (β = −0.39, p=0.01) in the HM group compared to the NM group. Conclusion. The higher CDA, faster OCV, and smaller radius found in the HM may suggest that these eyes have reduced ocular stiffness and may be less stable and more prone to stress.

Importance Keratoplasty is a surgical procedure to create a more regular optical surface following biomechanical weakening of the cornea in keratoconus. The ideal keratoplasty procedure should also restore corneal biomechanics to that of the healthy cornea. Background This study aimed to evaluate and compare the biomechanical properties of corneas following penetrating keratoplasty (PKP) and predescematic deep anterior lamellar keratoplasty (DALK) to those of healthy eyes. Design Prospective cross-sectional study. Participants Two cohorts of post-keratoplasty eyes (42 eyes with PKP and 27 eyes with DALK) with each other, and with a cohort of 152 healthy eyes. Methods All eyes were examined by slit-lamp biomicroscopy, tomography, anterior segment-OCT and non-contact tonometry CorVis ST (CST). Main outcome measures CST biomechanical parameters, maximum corneal deformation (MCD) and corneal energy dissipation were compared between keratoplasty techniques, and with healthy eyes. Results The mean age of participants with PKP and DALK were 35 ± 13.7 and 36.1 ± 12.6 years, respectively. None of the CST parameters were significantly different between PKP and DALK eyes. However, when compared to healthy corneas, numerous parameters were significantly different for both keratoplasty techniques. Of note, MCD was significantly higher in PKP compared to DALK and healthy corneas, after controlling for co-factors. Conclusions and relevance Neither type of keratoplasty technique utilized in keratoconus completely restored corneal biomechanical properties to that of healthy corneas. However, PKP resulted in a greater number of parameters significantly different to healthy corneas, compared to DALK.

We demonstrate a swept source OCT-based ocular biometer integrated with an air-puff stimulus to study the reaction of the eye to mechanical stimulation in vivo. The system enables simultaneous measurement of the stimulus strength and high-speed imaging of the eye dynamics along the visual axis. We characterize the stimulus and perform optimization of the data acquisition for a proper interpretation of the results. Access to the dynamics of axial eye length allows for a determination of the eye retraction, which is used to correct the air-puff induced displacement of ocular structures. We define the parameters to quantify the reaction of the eye to the air puff and determine their reproducibility in a group of healthy subjects. We observe the corneal deformation process and axial wobbling of the crystalline lens. OCT biometer combined with the air puff is the first instrument with the potential to provide comprehensive information on the biomechanics of ocular components.

To report a case of a 20-year-old woman who developed massive and progressive corneal remodeling in both eyes after bilateral PRK with mitomycin and CXL as an elective refractive procedure for mild keratoconus. The patient had 6 years of follow up, initially presenting with focal steepening of up to 20 diopters on both eyes one-and-a-half- years postoperatively that spontaneously reversed over the next five years while the high order aberrations worsened. At the present time, the patient depends on bilateral scleral contact lenses for her day-to-day activities. The use of combined elective PRK with mitomycin and prophylactic CXL could lead to progressive corneal deformation. Additional reports would help to establish the role of this combination procedure among the armamentarium to visually rehabilitate patients with keratoconus.

Purpose The aims of this study were to evaluate how the corneal deformation parameters provided by the Corvis ST tonometer (CST) were influenced by pressure-lowering ocular surgery, and to determine the correlations of intraocular pressure (IOP) and axial length (AL) with CST corneal deformation parameters. Methods This prospective 1-month study enrolled 22 subjects (22 eyes) who underwent trabeculectomy combined with mitomycin C. The corneal deformation parameters were measured using the CST. IOP was measured before and after surgery by a Goldmann applanation tonometer and the CST. The central corneal thickness and AL were also recorded. The correlations of the corneal deformation parameters with central corneal thickness, AL, and IOP changes were determined by linear regression analysis. Results IOP decreased significantly after surgery. AL was significantly shorter at 1 week after surgery. There were significant changes in the CST parameters time 1, velocity 1, velocity 2, peak distance highest concavity, and deformation amplitude highest concavity at 1 week and 1 month after surgery and in time highest concavity at 1 week after surgery. The change in time 1 was significantly correlated with preoperative IOP and the IOP reductions, and was positively correlated with the decrease in AL at 1 week. The increase in velocity 1 was negatively correlated with preoperative IOP, and IOP reductions. The change in time highest concavity was negatively correlated with IOP before surgery and the decrease in IOP at 1 week. Conclusion CST is a good choice for measuring IOP, especially when aiming for normalization of IOP after glaucoma surgery.

The purpose of this study is to report the preliminary findings and the retrospective clinical impressions of the integrated corneal tomography and corneal deformation parameters with a dynamic ultra-high-speed Scheimpflug camera equipped with a noncontact tonometer. Twelve eyes of six patients were evaluated by the Scheimpflug imaging system of the Pentacam HR and Corvis ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany) devices. The parameters used were the Belin/Ambrósio deviation (BAD-D) and Corvis biomechanical index (CBI), as well as the recently published tomographic and biomechanical index (TBI), combined with a detailed clinical data and evaluation of normal eyes and patients with different stages of corneal ectasia. How to cite this article Haddad JS, Barnwell E, Rocha KM, Waring IV GO, Ambrosio Jr R. First Clinical Impressions on the Integrated Corneal Tomography and Corneal Deformation with Scheimpflug Imaging. Int J Kerat Ect Cor Dis 2017;6(2):101-109.

Background. Blood pulsation affects the results obtained using various medical devices in many different ways. Method. The paper proves the effect of blood pulsation on intraocular pressure measurements. Six measurements for each of the 10 healthy subjects were performed in various phases of blood pulsation. A total of 8400 corneal deformation images were recorded. The results of intraocular pressure measurements were related to the results of heartbeat phases measured with a pulse oximeter placed on the index finger of the subject’s left hand. Results. The correlation between the heartbeat phase measured with a pulse oximeter and intraocular pressure is 0.69±0.26 (p<0.05). The phase shift calculated for the maximum correlation is equal to 60±40° (p<0.05). When the moment of measuring intraocular pressure with an air-puff tonometer is not synchronized, the changes in IOP for the analysed group of subjects can vary in the range of ±2.31 mmHg (p<0.3). Conclusions. Blood pulsation has a statistically significant effect on the results of intraocular pressure measurement. For this reason, in modern ophthalmic devices, the measurement should be synchronized with the heartbeat phases. The paper proposes an additional method for synchronizing the time of pressure measurement with the blood pulsation phase.

Purpose We evaluated the impact of myopia on corneal biomechanical properties in primary open-angle glaucoma (POAG) and nonglaucoma patients, and the effect of modification of glaucoma on myopic eyes. Methods This cross-sectional study included 66 POAG eyes (33 myopia, 33 nonmyopia) and 66 normal eyes (33 myopia, 33 nonmyopia). Seven corneal biomechanical parameters were measured by ultra-high-speed Scheimpflug imaging, including corneal deformation amplitude (CDA), inward/outward corneal applanation length (ICA, OCA), inward/outward corneal velocity (ICV, OCV), radius, and peak distance (PD). Results Mean age (SD) of the 65 male (49%) and 67 female (51%) patients was 59 (9.82) years. Myopia was associated with significantly higher CDA (adjusted effect = 0.104, P = 0.001) and lower OCV (adjusted effect = -0.105, P < 0.001) in the POAG group. Within the nonglaucoma group, myopic eyes had a significantly lower OCV (adjusted effect = -0.086, P < 0.001) and higher CDA (adjusted effect = 0.079, P = 0.001). All parameters except PD suggested that glaucoma modified the effect of myopia on corneal biomechanics. Percentage differences in the adjusted myopic effect between POAG and nonglaucoma patients was 31.65, 27.27, 31.65, 50.00, 22.09, and 60.49 for CDA, ICA, OCA, ICV, OCV, and radius, respectively. Conclusions Myopia had a significant impact on corneal biomechanical properties in the POAG and nonglaucoma groups. The differences in corneal biomechanical parameters suggest that myopia is correlated with significantly lower ocular rigidity. POAG may enhance the effects of myopia on most of these parameters.

To identify novel corneal biomechanical parameters differentiating glaucomatous from normal eyes.Sixty subjects with varying degrees of glaucoma severity and 61 normal controls underwent corneal biomechanical measurements including corneal deformation amplitude, inward and outward applanation length and velocity, and highest concavity time in 1 eye per subject at Queen Mary Hospital, Hong Kong. Measurements were taken with the Corvis ST device, a noncontact tonometer coupled with a high-speed Scheimpflug camera. The intraocular pressure (IOP) and central corneal thickness (CCT) were also measured.Significant findings included differences in outward applanation velocity (glaucoma: -0.37±0.01 m/s; control: -0.32±0.01 m/s; P=0.001), peak distance (glaucoma: 2.37±0.03 mm; control: 2.30±0.02 mm; P=0.005), and highest concavity time (glaucoma: 16.75±0.08 ms; control: 17.05±0.07 ms; P=0.002) between the 2 groups, after correcting for IOP, CCT, and age. Both outward applanation velocity and peak distance were moderately correlated with IOP and CCT. However, highest concavity time was not correlated with either IOP or CCT (R(2)=0.0140 and 0.000055, respectively). Age was not correlated with any of the 3 parameters.Glaucomatous eyes have a greater mean outward applanation velocity and peak distance, but shorter time to highest concavity than eyes without glaucoma. The difference in time to highest concavity does not correlate with age, IOP, or CCT, suggesting that this parameter may be a marker of increased pressure susceptibility that is independently associated with glaucoma risk.

Traumatic iris sphincter tear has been thought to occur secondary to anteroposterior compression of the globe with defined forces lead to equatorial expansion and active pull along the corneoscleral junction and sphincter tear. However, here in this report, we elaborate the additional forces involved in the traumatic rupture of the sphincter pupillae muscle. During the anteroposterior compressive forces along the globe, the corneal deformation beyond certain limits leads to the development of sudden displacement forces within the anterior chamber. Aqueous within it which is incontinuous circulation with a posterior narrow pupillary aperture as its entrance, find the path of least resistance that is along the pupillary orifices leading to anexpulsive drive to displace the fluid through this small aperture. During this process, the horizontally oriented mechanical stretching forces appear to be the main cause ofpupillary sphincter tear.

Purpose: To quantify biomechanical change associated with autoimmune diseases using Corvis ST deformation data. Methods: Cross-sectional, observational, case control study of 76 patients with systemic autoimmune disease and 21 control subjects. All patients underwent detailed ophthalmic examination with Corvis-ST (Oculus Optikgerate Gmbh, Germany) measurements for biomechanical properties of the eye. Corneal deformation and also deformation caused by the extracorneal tissue were recorded. Using a mathematical formula, the three parameters, namely, corneal stiffness (kc), extracorneal tissue stiffness (kg), and extracorneal tissue viscosity (μg), were defined. Results: The biomechanical analysis showed that kc and μg were significantly lower in patients with systemic autoimmune disease with eye manifestations than control group. However statistically, it was significant in rheumatoid arthritis (RA) patients only. Conclusion: The new parameters, namely, kc, kg, and μg, can provide a sensitive marker of the ocular activity of the collagen vascular diseases.

Keratoconus (KC) is a complex disease whose pathophysiology is only partially understood. The priority in management is to halt the progression of corneal deformation as soon as possible in the course of KC disease. Corneal cross-linking (CXL) is at present the only dedicated treatment for this purpose. Its biochemical mechanism of action leads to changes in the viscoelastic properties of the cornea induced by matrix bonding and renewal of keratocytes. The effect of CXL is difficult to quantify when measured in in-vivo conditions because of a lack of consistent tools adapted for clinical practice. Nevertheless, a large amount of evidence has been collected so far confirming the positive action of CXL on corneal structural reinforcement, and numerous studies have demonstrated significant efficacy in halting progression of KC with long-term follow-up. Published studies, however, are of relatively low scientific power given the great heterogeneity of the disease and the numerous associated biases in evaluation. The purpose of this paper is to summarize the consistent evidence of efficacy of CXL and to justify its role in our therapeutic armamentarium for management of progressive KC.

Purpose To test the ability of metrics derived from corneal response to noncontact tonometry (NCT) to distinguish between normal and ectatic cases. Materials and methods The prototype of CorVis ST (Oculus, Wetzlar, Germany) was used for assessing corneal biomechanical response using ultra-high-speed 8 mm horizontal Scheimpflug photography, taking 4,330 frames per second during NCT. Patients were stratified based on clinical data, including rotating Scheimpflug corneal tomography (Oculus Pentacam HR). Biomechanical data from one eye randomly selected of 177 patients with normal corneas (N) and from 79 patients with bilateral keratoconus (KC) were investigated. Group forme fruste keratoconus (FFKC) was composed of 20 eyes with normal topographic patterns from cases with ectasia detected in the fellow eye. Group keratoconus suspect (KCS) had 16 eyes from 16 patients with topographic patterns suspicious of KC but documented stability over 3 years and normal tomographic findings. A combination of deformation parameters using linear regression analysis (Prototype Factor 1, pF1) was created by the BrAIn (Brazilian Artificial Intelligence on Corneal Tomography and Biomechanics) study group in order to provide the best possible separation of KC and normals. Results Statistical significant differences were found for N × KC for several parameters, including first and second applanation times, deformation amplitude, and maximal concavity radius (Mann–Whitney, p < 0.001). However, the areas under the receiver operating characteristic curves (AUC) were lower than 0.90. The pF1 had AUC of 0.945 (IC 0.909–0.97; sensitivity = 87.3% and specificity = 89.3%). The pF1 had statistically significant differences between the ectatic (KC and FFKC) and nonectatic groups (N and KCS) (p < 0.05, Kruskall–Wallis Test with post hoc Dunn's test). Conclusion Corneal deformation response analysis by ultra- high-speed 8 mm horizontal Scheimpflug photography provides relevant data for distinguishing ectatic and nonectatic corneas but cannot be used independently to detect KC. This data may be integrated with corneal tomography data for enhancing sensitivity and specificity for screening ectasia. How to cite this article Salomão MQ, Correia FF, Ramos I, Luz A, Ambrósio R Jr. Corneal Deformation Response with Dynamic Ultra-high-speed Scheimpflug Imaging for Detecting Ectatic Corneas. Int J Kerat Ect Cor Dis 2016;5(1):1-5.

PURPOSE To evaluate the difference in corneal biomechanical waveform parameters between manifest keratoconus, forme fruste keratoconus, and healthy eyes with a second-generation biomechanical waveform analyzer (Ocular Response Analyzer 2). SETTING Jules Stein Eye Institute, University of California, Los Angeles, California, USA. DESIGN Retrospective chart review. METHODS The biomechanical waveform analyzer was used to obtain corneal hysteresis (CH), corneal resistance factor (CRF), and 37 biomechanical waveform parameters in manifest keratoconus eyes, forme fruste keratoconus eyes, and healthy eyes. Useful distinguishing parameters were found using t tests and a multivariable logistic regression model with stepwise variable selection. Potential confounders were controlled for. RESULTS The study included 68 manifest keratoconus eyes, 64 forme fruste keratoconus eyes, and 249 healthy eyes. There was a statistical difference in the mean CRF between the normal group (10.2 mm Hg ± 1.7 [SD]) and keratoconus group (6.3 ± 1.9 mm Hg) (P = .003), and between the normal group and the forme fruste keratoconus group (7.8 ± 1.4 mm Hg) (P < .0001). There was no statistical difference in the mean CH between the normal group and the keratoconus group or the forme fruste keratoconus group. The CRF, height of peak 1 (P1) (P = .001), downslope of P1 (dslope1) (P = .027), upslope of peak 2 (P2) (P = .004), and downslope of P2 (P = .006) distinguished the normal group from the keratoconus groups. The CRF, downslope of P2 derived from upper 50% of applanation peak (P = .035), dslope1 (P = .014), and upslope of P1 (P = .008) distinguished the normal group from the forme fruste keratoconus group. CONCLUSION Differences in multiple biomechanical waveform parameters can differentiate between healthy and diseased conditions and might improve early diagnosis of keratoconus and forme fruste keratoconus. FINANCIAL DISCLOSURE No author has a financial or proprietary interest in any material or method mentioned.

Purpose To study the association between corneal deformation (CD) and ease of lenticule separation from the stroma in small incision lenticule extraction. Methods Thirty-six myopic eyes of 36 patients underwent small incision lenticule extraction. Preoperative refraction, intraocular pressure, central corneal thickness, and CD were evaluated with Scheimpflug imaging and air-puff applanation. Fourier transform of CD waveform was also performed. The surgeon also graded the ease of separation of lenticule surfaces from the residual stroma intraoperatively as grades 1 (low effort), 2 (moderate effort), and 3 (high effort). All the procedures were performed by the same surgeon. CD values were concealed from the surgeon. Differences between the grades were assessed with 1-way analysis of variance and analysis of covariance. Results Mean preoperative refraction, intraocular pressure, central corneal thickness, lenticule thickness, and incision width were similar among the grades (P > 0.05). A total of 5 of the 10 analyzed CD variables were significantly different among the grades. Among them, deformation amplitude (1.20 vs. 1.13 vs. 1.07 mm in the order of increasing grades, P = 0.001), velocity of the corneal apex at the second applanation point (-0.47 vs. -0.43 vs. -0.40 m/s, P = 0.02), peak distance (5.33 vs. 5.25 vs. 5.07 mm, P = 0.006), area under the deformation amplitude (13.40 vs. 12.84 vs. 12.06, P = 0.04), and root mean square of Fourier coefficients (0.12 vs. 0.12 vs. 0.11 mm, P = 0.005) decreased from grades 1 to 3. Conclusions CD was inversely correlated with the ease of lenticule separation from the residual stroma and may assist in customization of the energy parameters of the laser.

The elasticity of cornea was investigated with and without dextran content in the 0.1% Riboflavin solutions including salt and glucose, respectively. These five different solutions were studied for keratoconus treatment alternatively. The elasticity of the treated and untreated cornea was characterized by using compressive technique. The cornea can be modeled by the mass–spring–damping system. It is understood that the compressive elastic modulus of the cornea changes before and after treatment by the alternative solutions. The mechanical behavior of cornea likes composite anisotropic material due to the structure of cornea which consists of collagen fibrils. The sheep cornea was used as a pilot study before the application of treatment to human cornea. In the cornea, the nonlinear pressure deformation was observed as the behavior of elastomer materials. We found a significant increase in biomechanical rigidity after the cross-linking processes. The observed elasticity properties are consistent with the suggested values in the literature. This study is one of the alternative solutions studies for the treatment of corneal deformation illness after our spectroscopic and mechanical investigations.

Primary objectiveThis study uses numerical analysis and validation against clinical data to develop a method to correct intraocular pressure (IOP) measurements obtained using the Corvis Tonometer for the effects of central corneal thickness (CCT), and age.Materials and methodsFinite element analysis was conducted to simulate the effect of tonometric air pressure on the intact eye globe. The analyses considered eyes with wide variations in IOP (10-30 mm Hg), CCT (445-645 microns), R (7.2-8.4 mm), shape factor, P (0.6-1) and age (30-90 years). In each case, corneal deformation was predicted and used to estimate the IOP measurement by Corvis (CVS-IOP). Analysis of the results led to an algorithm relating estimates of true IOP as a function of CVS-IOP, CCT and age. All other parameters had negligible effect on CVS-IOP and have therefore been omitted from the algorithm. Predictions of corrected CVS-IOP, as obtained by applying the algorithm to a clinical data-set involving 634 eyes, were assessed for their association with the cornea stiffness parameters; CCT and age.ResultsAnalysis of CVS-IOP measurements within the 634-large clinical data-set showed strong correlation with CCT (3.06 mm Hg/100 microns, r(2) = 0.204) and weaker correlation with age (0.24 mm Hg/decade, r(2) = 0.009). Applying the algorithm to IOP measurements resulted in IOP estimations that became less correlated with both CCT (0.04 mm Hg/100 microns, r(2) = 0.005) and age (0.09 mm Hg/decade, r(2) = 0.002).ConclusionsThe IOP correction process developed in this study was successful in reducing reliance of IOP measurements on both corneal thickness and age in a healthy European population.