Refractive associations with corneal biomechanical properties among young adults: a population-based Corvis ST study.

PURPOSE: To assess the associations of corneal biomechanical properties as measured by the Corvis ST with refractive errors and ocular biometry in an unselected sample of young adults. METHODS: A total of 1645 healthy university students underwent corneal biomechanical parameters measurement by the Corvis ST. The refractive status of the participants was measured using an autorefractor without cycloplegia. Ocular biometric parameters were measured using the IOL Master. RESULTS: After adjusting for the effect of age, sex, biomechanical-corrected intraocular pressure and central corneal thickness, axial length was significantly associated with A1 velocity (A1v, ß = -10.47), A2 velocity (A2v, ß = 4.66), A2 deflection amplitude (A2DeflA, ß = -6.02), HC deflection amplitude (HC-DeflA, ß = 5.95), HC peak distance (HC-PD, ß = 2.57), deformation amplitude ratio max (DA Rmax, ß = -0.36), Ambrósio's relational thickness to the horizontal profile (ARTh, ß = 0.002). For axial length / corneal radius ratio, only A1v (ß = -2.01), A1 deflection amplitude (A1DeflA, ß = 2.30), HC-DeflA (ß = 1.49), HC-PD (ß = -0.21), DA Rmax (ß = 0.07), stress-strain index (SSI, ß = -0.29), ARTh (ß < 0.001) were significant associates. A1v (ß = 23.18), HC-DeflA (ß = -15.36), HC-PD (ß = 1.27), DA Rmax (ß = -0.66), SSI (ß = 3.53), ARTh (ß = -0.02) were significantly associated with spherical equivalent. CONCLUSION: Myopic eyes were more likely to have more deformable corneas and corneas in high myopia were easier to deform and were even softer compared with those in the mild/moderate myopia.

Biomechanical changes following corneal crosslinking in keratoconus patients.

PURPOSE: To evaluate the biomechanical and tomographic outcomes of keratoconus patients up to four years after corneal crosslinking (CXL). METHODS: In this longitudinal retrospective-prospective single-center case series, the preoperative tomographic and biomechanical results from 200 keratoconus eyes of 161 patients undergoing CXL were compared to follow-up examinations at three-months, six-months, one-year, two-years, three-years, and four-years after CXL. Primary outcomes included the Corvis Biomechanical Factor (CBiF) and five biomechanical response parameters obtained from the Corvis ST. Tomographically, the Belin-Ambrósio deviation index (BAD-D) and the maximal keratometry (Kmax) measured by the Pentacam were analyzed. Additionally, Corvis E-staging, the thinnest corneal thickness (TCT), and the best-corrected visual acuity (BCVA) were obtained. Primary outcomes were compared using a paired t-test. RESULTS: The CBiF decreased significantly at the six-month (p < 0.001) and one-year (p < 0.001) follow-ups when compared to preoperative values. E-staging behaved accordingly to the CBiF. Within the two- to four-year follow-ups, the biomechanical outcomes showed no significant differences when compared to preoperative. Tomographically, the BAD-D increased significantly during the first year after CXL with a maximum at six-months (p < 0.001), while Kmax decreased significantly (p < 0.001) and continuously up to four years after CXL. The TCT was lower at all postoperative follow-up visits compared to preoperative, and the BCVA improved. CONCLUSION: In the first year after CXL, there was a temporary progression in both the biomechanical CBiF and E-staging, as well as in the tomographic analysis. CXL contributes to the stabilization of both the tomographic and biomechanical properties of the cornea up to four years postoperatively.

Early elastic and viscoelastic corneal biomechanical changes after photorefractive keratectomy and small incision lenticule extraction.

PURPOSE: To compare early changes in the corneal biomechanical parameters after photorefractive keratectomy (PRK) and small incision lenticule extraction (SMILE) and their correlations with corneal shape parameters. METHODS: One hundred twenty four eyes received myopic PRK and SMILE for similar amounts of myopia. Corneal tomography with Pentacam HR, biomechanical parameters using Corvis ST, and Ocular Response Analyzer (ORA) were evaluated before and 2 weeks after surgery. The change in each parameter was compared between groups, while the difference in central corneal thickness and cornea-compensated intraocular pressure measured before and after surgery were considered as covariates. RESULTS: A significant reduction was seen in the corneal stiffness parameter at first applanation, and an increase in deformation amplitude ratio (DAR), and integrated inverse radius (IIR) in both groups after surgery (p < 0.001) Changes in DAR, and IIR were significantly greater in the SMILE than in the PRK group (p < 0.001) Corneal hysteresis (CH) and corneal resistance factor (CRF) decreased in both SMILE and PRK groups after surgery, (p < 0.001) with no statistically significant difference between groups (p > 0.05) Among new Corvis ST parameters, DAR showed a significant correlation with changes in Ambrosio relational thickness in both groups (p < 0.05). CONCLUSIONS: Both techniques caused significant changes in corneal biomechanics in the early postoperative period, with greater elastic changes in the SMILE group compared to the PRK group, likely due to lower tension in the SMILE cap and thinner residual stromal bed in SMILE. There were no differences in viscoelastic changes between them, so the lower CH may reflect the volume of tissue removed.

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.

Assessment of the corneal biomechanical features of granular corneal dystrophy type 2 using dynamic ultra-high-speed Scheimpflug imaging.

PURPOSE: To evaluate the corneal biomechanical features of eyes with granular corneal dystrophy type 2 (GCD2) by analyzing corneal biomechanical indices obtained using a Corvis ST (CST) dynamic ultra-high-speed Scheimpflug imaging device. METHODS: In this retrospective case-control study, 35 CST parameters were compared in normal eyes (control) and eyes of patients with GCD2 treated at Osaka University Hospital, Osaka, Japan. The parameters included the Corvis Biomechanical Index (CBI), which is important in differentiating eyes with keratoconus from normal eyes. We measured the deposition rates of lesions in the central 7-mm region of the eye and assessed the correlation between the deposition rate and the CBI. RESULTS: Twenty-one eyes with GCD2 and 23 control eyes were analyzed. Eyes with GCD2 showed significantly less corneal stiffness in 15 CST parameters than did control eyes. In particular, the CBI was remarkably higher in eyes with GCD2 than in control eyes (P = 0.000006). Additionally, the deposition rate and the CBI were positively correlated. CONCLUSIONS: GCD2 eyes had softer corneas than did control eyes in most biomechanical CST parameters, and one of the parameters (the CBI) was linked to the rate of deposited lesions. Since IOP may be underestimated in GCD2 eyes, management should be especially careful in GCD2 cases complicated by glaucoma.

Corneal biomechanics in normal and subclinical keratoconus eyes.

BACKGROUND: The diagnosis of keratoconus, as the most prevalent corneal ectatic disorder, at the subclinical stage gained great attention due to the increased acceptance of refractive surgeries. This study aimed to assess the pattern of the corneal biomechanical properties derived from Corneal Visualization Scheimpflug Technology (Corvis ST) and evaluate the diagnostic value of these parameters in distinguishing subclinical keratoconus (SKC) from normal eyes. METHODS: This prospective study was conducted on 73 SKC and 69 normal eyes. Subclinical keratoconus eyes were defined as corneas with no clinical evidence of keratoconus and suspicious topographic and tomographic features. Following a complete ophthalmic examination, topographic and tomographic corneal assessment via Pentacam HR, and corneal biomechanical evaluation utilizing Corvis ST were done. RESULTS: Subclinical keratoconus eyes presented significantly higher Deformation Amplitude (DA) ratio, Tomographic Biomechanical Index (TBI), and Corvis Biomechanical Index (CBI) rates than the control group. Conversely, Ambrósio Relational Thickness to the Horizontal profile (ARTh), and Stiffness Parameter at the first Applanation (SPA1) showed significantly lower rates in SKC eyes. In diagnosing SKC from normal eyes, TBI (AUC: 0.858, Cut-off value: > 0.33, Youden index: 0.55), ARTh (AUC: 0.813, Cut-off value: ≤ 488.1, Youden index: 0.58), and CBI (AUC: 0.804, Cut-off value: > 0.47, Youden index: 0.49) appeared as good indicators. CONCLUSIONS: TBI, CBI, and ARTh parameters could be valuable in distinguishing SKC eyes from normal ones.

Effect of ocular biometric factors on corneal biomechanical properties.

PURPOSE: To evaluate the effects of ocular biometric variables on corneal biomechanical properties. METHODS: A total of 102 eyes of 102 participants were enrolled in this cross-sectional study. The axial length (AL) was determined by an IOL master 500 and measurements of corneal biomechanical properties were performed using Corvis ST, integrated with pentacam results. RESULTS: Aging and corneal steepening were associated with less corneal deformability and higher movement of the entire eye. Longer AL corresponded with greater deformability and lower corneal viscous damping properties and less whole eye movement (all P-values < 0.05). In contrast to mean keratometry (Mean K) and corneal diameter, anterior chamber depth (ACD) and AL have a significant effect on corneal biomechanical parameters. Corneal biomechanical index (CBI) was not significantly correlated with any of biometric parameters. Stress-strain index (SSI) was significantly correlated with age (r = 0.470), spherical equivalent (SE) (r = 0.537), AL (r = -0.534) and ACD (r = -0.316) (all P-values < 0.001). CONCLUSIONS: In normal individuals, several parameters such as age, ACD, AL and Mean K have a great impact on corneal biomechanical properties; thereby, these effects should be taken into account prior to interpretation of corneal biomechanics, particularly in older ages and eyes with longer AL and steeper cornea.

Corneal biomechanical properties in vernal keratoconjunctivitis and its subtypes: a preliminary study.

PURPOSE: To explore the corneal biomechanical properties (CBPs) of patients with vernal keratoconjunctivitis (VKC) and the discrepancies among three subtypes of VKC including palpebral, limbal, and mixed forms. METHODS: Forty eyes of 20 VKC patients and twenty eyes of ten non-VKC patients were included in this case-control study. Patients with VKC were further divided into three subtypes (six patients in Palpebral form, five patients in limbal form, and nine patients in mixed form). The CBPs of all patients were obtained from the Corneal Visualization Scheimpflug Technology (Corvis ST). RESULTS: First applanation (A1) length, Ambrosio relational thickness in horizontal (ARTh), and stiffness parameter at first applanation (SP-A1) were significantly lower in the VKC group while A1 velocity was significantly higher in the VKC group (p < 0.05), compared to the non-VKC group. Furthermore, A1 velocity presented a positive correlation with disease course (p < 0.05). In addition, VKC patients of limbal form had lower central corneal thickness (CCT), SP-A1, and higher deformation amplitude ratio (DA ratio), compared to the other two subtypes (p < 0.05). Besides, patients in limbal form had higher A1 velocity, integrated radius, and corneal biomechanical index (CBI) compared with mixed form, and lower A1 length than palpebral form (p < 0.05). CONCLUSIONS: The corneas of VKC patients were softer and more protruded compared with the control group, and the property of steepness was closely related to disease course. VKC patients in limbal form were more inclined to be keratoconus than the other two subtypes due to their CBPs` discrepancies.

Comparison of intraocular pressure measurements between Easyton transpalpebral tonometry and Perkins, iCare iC100 and Corvis ST, and the influence of corneal and anterior scleral thickness.

PURPOSE: To compare intraocular pressure (IOP) measurements between Easyton transpalpebral tonometry and Perkins, iCare iC100 and Corvis ST. Also, to assess the influence of corneal characteristics and anterior scleral thickness (AST) on the IOP measurements. METHODS: Sixty-nine eyes from 69 healthy subjects were included. IOP was measured by Easyton, Perkins, iC100 and Corvis ST (corrected IOP, bIOP; and non-corrected IOP, IOPnct). Other variables studied were AST, axial length (AL), and Corvis parameters: Length 1, velocity 1, length 2, velocity 2, peak distance, radius, deformation amplitude, and central corneal thickness (CCT). Pearson correlation, limits of agreement (LoA), and multiple regression analysis were calculated. RESULTS: No significant differences in IOP between Easyton and Perkins, iC100, and bIOP were observed (all p > 0.05), being significant only between Perkins and IOPnct ( - 1.49 mmHg, p < 0.001). Bland-Altman graphs showed that the mean difference between Perkins and Easyton was 0.07 mmHg (p < 0.001), and LoA - 7.49 to + 7.39 mmHg. Significant correlations were found between the measurements of Perkins and iC100, IOPnct, bIOP (r = 0.710, 0.628, 0.539; p < 0.001 respectively), iC100 and IOPnct, bIOP (r = 0.627, 0.513; p < 0.001, respectively). The multivariate regression analysis revealed that differences between Perkins and Easyton (adjusted R2 = 0.25) were influenced by AL (B = 1.28, p < 0.008), length 1 (B = 3.13, p < 0.018), and the radius (B = 1.26, p < 0.010). Differences between Perkins and bIOP (adjusted R2 = 0.21) were affected by the CCT (B = 0.029, p < 0.003). CONCLUSIONS: There are no significant differences in the IOP measurements between Perkins and Easyton, iC100 or bIOP. Length 1, radius, and CCT have limited influence on these differences, while AST did not show any effect.

Evaluation of orbital soft tissue biomechanical parameters in patients with thyroid eye disease using the non-contact Corvis ST.

INTRODUCTION: In thyroid eye disease (TED), all ocular components and adnexa such as extraocular muscles, orbital adipose tissues, eyelids, and tear glands could be affected. This study aimed to study the orbital biomechanical parameters in patients with TED, in terms of differences with healthy individuals and correlation with clinical findings, using Corvis ST (CST, Oculus Wetzlar). MATERIALS AND METHODS: In this study, 26 consecutive patients with TED were recruited. Demographic data were collected, and patients with TED were assessed for exophthalmos, intraocular pressure, and clinical activity score. Biomechanical response parameters of one randomly-chosen eye of each patient, including whole eye movement length (WEMl) and time (WEMt), were evaluated by the CST, and data were compared between patients and age- and gender-matched healthy controls. RESULTS: The mean age was 39.88 ± 11.61 years old for patients with TED and 34.38 ± 8.57 years old for the healthy subjects. Nine out of 26 patients with TED and nine of 26 healthy individuals were male. The median duration of thyroid disease was 36 (IQR 54) months and the median duration of thyroid ophthalmopathy was 27 (IQR 27) months. Four out of 26 patients (7.7%) had active disease. The mean WEMl was 206.15 ± 61.58 µm in the TED group and 254.23 ± 64.01 µm in the healthy group, the difference of which was statistically significant (p = 0.008). The median of WEMt was 20.90 (1.15) msec in the TED group and 21.45 (0.93) msec in the healthy group (p < 0.001). Also, the mean of WEMl and WEMt were lower in patients with active disease compared to patients with quiescent disease. CONCLUSION: The CST-derived WEMl was significantly smaller in patients with thyroid eye disease compared to normal subjects. The WEMl and WEMt were relatively shorter in the patients with active TED compared to the patients with quiescent TED, although small numbers of patients with active TED limits took a statistically significant conclusion. WEMl and WEMt might be useful in evaluating the compliance of the orbit in patients with TED.

Analysis of the diagnostic accuracy of Belin/Ambrósio Enhanced Ectasia and Corvis ST parameters for subclinical keratoconus.

OBJECTIVE: To investigate the diagnostic accuracy of the parameters in the Belin/Ambrósio Enhanced Ectasia Display built in Pentacam, which is designed for the screening of subclinical keratoconus (SKC) built in Pentacam, and the parameters in Corneal visualization Scheimpflug technology (Corvis ST). METHODS: A retrospective study: The fellow eyes of unilateral keratoconus cases were diagnosed with SKC. Patients presented to Shanxi Eye Hospital with SKC from October 2020 to November 2021 were included as the SKC group, and myopic patients undergoing corneal refractive surgery at the Refractive Surgery Department in our hospital within the same period were included as the control group. The Belin/Ambrósio and Corvis ST parameters were extracted from the system and analyzed using independent samples t test. Receiver operating curves (ROCs) were also created to test the diagnostic accuracy of each parameter. RESULTS: There were 70 patients (70 eyes) in the SKC group and 137 patients (137 eyes) in the control group. For Corvis ST parameters, Radius (P = 0.021), PachySlope (P = 0.040), SP-A1 (P = 0.002), A2 Deformation Amp. (P = 0.028), A2 Deflection Length (P < 0.001), Max ICR (P = 0.005), DA Ratio Max (1 mm) (P = 0.023), IR (P = 0.016), CBI (P = 0.003) and TBI (P < 0.001) were statistically different between the two groups. For Belin/Ambrósio parameters, PPI min. Axis, ART min, ART max, ART avg, Pachy min, Front K2, Astig, BAD-Df, BAD-Db, BAD-Dp, BAD-Dt, BAD-Da, BAD-D, PPI min, PPI max, PPI max. Axis, PPI avg and Dist.Apex-Thin.Loc. were significantly different between the two groups (all p < 0.001). TBI and BAD-D showed the best diagnostic accuracy, with AUCs of 0.944 and 0.965, respectively. CONCLUSIONS: Some Belin/Ambrósio and Corvis ST parameters differed between SKC eyes and eyes with normal cornea. TBI and BAD-D showed the ideal diagnostic performance for SKC. In clinical practice, conventional corneal topography could not be replaced by Corvis ST.

Analysis of corneal biomechanical properties 25 years after myopic photorefractive keratectomy.

PURPOSE: To evaluate corneal biomechanical changes using Corvis ST in patients treated with photorefractive keratectomy (PRK) 25 years ago. METHODS: In this study, 32 post-PRK and 38 normal eyes underwent Corvis ST (CST) assessments. The measured CST factors were: time of highest concavity (HC), time of applanation 1 (AT1), time of applanation 2 (AT2), length of applanation 1 (AL1), length of applanation 2 (AL2), velocity of applanation 1 (AV1), velocity of applanation 2 (AV2), deformation amplitude (DA), peak distance (PD), integrated radius (IR), Ambrosio relational thickness horizontal (ARTh), stiffness parameter at first applanation (SP-A1), DA ratio (2 mm), Belin/Ambrosio enhanced ectasia display (BAD) and corneal biomechanical index (CBI). RESULTS: The mean [± standard deviation (SD)] age was 51.4 ± 7.36 years in PRK, 51.4 ± 3.62 in control group. PRK was performed 24.69 ± 1.78 years ago. ARTh, SP-A1, AT1, AL1, and AL2 were lower in PRK. PD, AT2, DA ratio (2 mm), and IR were statistically higher in PRK (P < 0.01). In PRK and control group the mean value of CBI was 0.91 ± 0.11 and 0.50 ± 0.27 (P < 0.001), and mean value of BAD was 3.34 ± 1.53 and 1.1 ± 0.70 (P < 0.001). In PRK 71.9% of eyes were classed "high risk CBI plus diseased BAD" and 25% remained in the "high risk CBI and normal BAD" group. CONCLUSIONS: In this study, most of the post-PRK eyes which were clinically and topographically normal were classified as "high risk CBI plus diseased BAD" and had significantly worse CBI and BAD values than the control group. This leads to the conclusion that CBI and BAD alone are not appropriate to evaluate post-PRK ectasia.

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

BACKGROUND: To compare the accuracy of non-contact tonometry, Pentacam, and corneal visualization Scheimpflug technology (Corvis ST) for the measurement of intraocular pressure (IOP) after small incision lenticule extraction (SMILE) or femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery. METHODS: A total of 49 patients (98 eyes) undergoing FS-LASIK or SMILE surgery at West China Hospital, Sichuan University from January to March 2021 were enrolled in this prospective, comparative, self-controlled study. IOP values were measured with non-contact tonometer, Pentacam, and Corvis ST before surgery and 1 month after surgery. Pentacam-derived postoperative IOP values were corrected using five correction formulas (Ehlers, Shah, Dresden, Orssengo-Pye, and Kohlhaas), while Corvis ST-derived values were corrected using a single formula. RESULTS: In the SMILE group, no significant differences were observed between the IOP values corrected with the Shah formula before and after surgery (t = 0.17, P = 0.869), whereas postoperative IOP values corrected with the other formulas were significantly different from the corresponding preoperative measurements (P < 0.05). In the FS-LASIK group, postoperative IOP values corrected with the Ehlers, Shah, or Corvis ST formulas were significantly different from the corresponding preoperative IOP measurements (P < 0.05), but no significant differences were observed between pre- and postoperative IOP values corrected with the Dresden (t = - 0.08, P = 0.941), Orssengo-Pye (t = - 0.52, P = 0.604), or Kohlhaas (t = 1.22, P = 0.231) formulas. CONCLUSIONS: Pentacam's Shah correction formula seemed to be the most appropriate method for accurately measuring postoperative IOP in patients undergoing SMILE surgery, while the Dresden, Orssengo-Pye, and Kohlhaas correction formulas of Pentacam were identified as the most reliable methods for estimating IOP in patients after FS-LASIK surgery.

Effect of white-to-white corneal diameter on biomechanical indices assessed by Pentacam Scheimpflug corneal tomography and corneal visualization Scheimpflug technology.

PURPOSE: To provide evidence for more accurate evaluation of refractive surgery candidates in clinics, this retrospective study investigated the effect of corneal diameter on the biomechanical indices assessed by Pentacam Scheimpflug cornea tomography (Pentacam) and corneal visualization Scheimpflug technology (Corvis ST). METHODS: The relevant data were collected of 132 eyes from 132 participants with moderate myopia who were candidates for refractive surgery. Eligible participants were apportioned to 2 groups based on the white-to-white (WTW) corneal diameter: Group A, ≤ 11.5 mm, and Group B, ≥ 11.6 mm. A single clinician performed Pentacam and Corvis ST imaging on each subject for 3 consecutive measurements, and the means were used for statistical analyses. RESULTS: Each group comprised 66 eyes. As measured by Pentacam, the 2 groups were comparable regarding Df and Da. For other measurements, Group A had significantly higher K1, K2, Db, Dp, Dt, Do, PPImin, PPImax, PPIavg, while Group B had significantly higher CCT, BFSf, BFSb, and ARTmax. Corvis ST data included DA ratio, SPA1, CBI, TBI, and ARTh. Only the latter showed a significant difference, with ARTh of group A (437.04 ± 76.60) larger than group B (470.46 ± 103.36, p = 0.04). CONCLUSION: In a Chinese population, WTW corneal diameter showed effect on biomechanical indices assessed by Pentacam and Corvis ST. Personalized evaluation of these measurements based on corneal diameter should improve the sensitivity and specificity for screening of keratoconus by these devices.

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.

[Effects of SMILE with different residual stromal thicknesses on corneal biomechanical properties of rabbits in vivo].

Femtosecond laser small incision lenticule extraction (SMILE) with different residual stromal thicknesses (RST) is set to investigate its effect on corneal biomechanical properties of rabbits in vivo. In this study, 24 healthy adult Japanese rabbits were randomly divided into group A and B. The RST of group A was set 30% of the corneal central thickness (CCT), and the RST of group B was 50% of the CCT. The thickness of the corneal cap in both groups was set one third of CCT. Corneal visualization Scheimpflug technology (Corvis ST) and Pentacam three-dimensional anterior segment analyzer were used to determine corneal biomechanical and morphological parameters before surgery, and 1 week, 1 month and 3 months after surgery. Pearson correlation analysis was used to analyze factors affecting corneal biomechanical parameters after SMILE. The results showed that the corneal stiffness of group A was significantly higher than that of group B at 1 week and 1 month after surgery, and most biomechanical parameters returned to preoperative levels at 3 months postoperatively. The results of correlation analysis showed that postoperative CCT and RST were the main factors affecting corneal biomechanical parameters after SMILE. There was no significant difference in corneal posterior surface height (PE) between 3 months after surgery and before surgery in both two groups. It indicates that although the ability to resist deformation of cornea decreases in SMILE with thicker corneal cap and less RST, there is no tendency to keratoconus, which may be related to the preservation of more anterior stromal layer.

Corneal Stiffness Parameters Are Predictive of Structural and Functional Progression in Glaucoma Suspect Eyes.

PURPOSE: To investigate corneal stiffness parameters (SPs) as predictors of future progression risk in glaucoma suspect eyes. DESIGN: Prospective, longitudinal study. PARTICIPANTS: Three hundred seventy-one eyes from 228 primary open-angle glaucoma suspects, based on optic disc appearance, with normal baseline Humphrey Visual Field (HVF; Carl Zeiss Meditec) results. METHODS: Baseline corneal SPs were measured using Corvis ST (Oculus Optikgeräte GmbH). Participants were followed up every 6 months with clinical examination, HVF testing, and OCT. The baseline SP at first applanation (SP-A1) and highest concavity predicted the prospective outcome measures. MAIN OUTCOME MEASURES: Structural progression was measured by the OCT rate of thinning of the retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GCIPL). Functional progression was assessed by permutation analysis of pointwise linear regression criteria on HVF testing. RESULTS: Stiffness parameters correlated positively with central corneal thickness (CCT), which was adjusted for in all analyses. A higher SP-A1, suggestive of a stiffer cornea, was associated with a faster rate of RNFL thinning (P < 0.001), synergistic with thinner CCT (P = 0.004) over a mean follow-up of 4.2 years. Eyes with higher SP-A1 and thinner CCT (thin and stiff corneas) showed accelerated RNFL thinning by 0.72 µm/year relative to eyes with lower SP-A1 and thicker CCT (95% confidence interval [CI], 0.17-1.28; P = 0.011) and were at 2.9-fold higher likelihood of fast RNFL progression of more than 1 µm/year (95% CI, 1.4-6.1; P = 0.006). Consistent results also were observed with GCIPL thinning. Furthermore, a higher SP-A1 was associated with a greater risk of visual field progression (P = 0.002), synergistic with thinner CCT (P = 0.010). Eyes with higher SP-A1 and thinner CCT were at 3.7-fold greater risk of visual field progression relative to eyes with thicker CCT and lower SP-A1 (95% CI, 1.3-10.5; P = 0.014). CONCLUSIONS: Glaucoma suspect eyes with higher corneal SPs and lower CCT, suggestive of thin and stiff corneas, are at greater risk of progression. Corneal SPs seem to act synergistically with CCT as risk factors for glaucoma progression.

Corneal biomechanics: Measurement and structural correlations.

The characterization of corneal biomechanical properties has important implications for the management of ocular disease and prediction of surgical responses. Corneal refractive surgery outcomes, progression or stabilization of ectatic disease, and intraocular pressure determination are just examples of the many key clinical problems that depend highly upon corneal biomechanical characteristics. However, to date there is no gold standard measurement technique. Since the advent of a 1-dimensional (1D) air-puff based technique for measuring the corneal surface response in 2005, advances in clinical imaging technology have yielded increasingly sophisticated approaches to characterizing the biomechanical properties of the cornea. Novel analyses of 1D responses are expanding the clinical utility of commercially-available air-puff-based instruments, and other imaging modalities-including optical coherence elastography (OCE), Brillouin microscopy and phase-decorrelation ocular coherence tomography (PhD-OCT)-offer new opportunities for probing local biomechanical behavior in 3-dimensional space and drawing new inferences about the relationships between corneal structure, mechanical behavior, and corneal refractive function. These advances are likely to drive greater clinical adoption of in vivo biomechanical analysis and to support more personalized medical and surgical decision-making.

The use of infrared thermal imaging in tonometry with a Scheimpflug camera.

Infrared thermal imaging is currently used in almost every field of medicine. This paper presents the novel use of thermography in ophthalmology - using a thermal camera to assess correct intraocular pressure measurement depending on the position of the patient's head during non-contact tonometry. For the analysed group of 10 healthy subjects, thermographic images of the face were recorded before and after intraocular pressure testing. Pressure was tested with a non-contact tonometer with a Scheimpflug camera. For the acquired 20: 2D images (thermograms), an analysis of the characteristic areas of the face determined temperature changes of the patient's face in contact with the tonometer frame. Analysis and processing of the acquired thermograms was carried out in MATLAB® with the Image Processing Toolbox. The results clearly showed a decrease in the patient's face temperature where the face was in contact with tonometer supports. Temperature changes in the patient's face provide valuable information about the correct position of their head in the device, which directly translates into measurement quality. Therefore, the analysis of changes in the patient's face temperature both before and after the examination can be a tool for assessing correct patient positioning in the tonometer supports.

Effects of caffeine intake on the biomechanical properties of the cornea: a placebo-controlled, double-blind, crossover pilot study in low caffeine consumers.

PURPOSE: To assess the short-term effects of caffeine intake on the biomechanical properties of the cornea, as well as its possible association with the intraocular pressure (IOP), as measured by corneal visualization Scheimpflug technology (CorVis ST) in healthy subjects. METHODS: Twenty-two low caffeine consumers ingested either a caffeine (4 mg/Kg) or placebo capsule in two separate sessions. IOP and corneal biomechanics parameters, including time, velocity, length, and deformation amplitude at the first applanation (A1T, A1V, A1L, and A1D, respectively); time, velocity, length, and deformation amplitude at the second applanation (A2T, A2V, A2L, and A2D, respectively); time at the highest concavity (HCT), radius curvature at the highest concavity (HCR), deformation amplitude at the highest concavity (HCDA), and peak distance (PD), were measured with the Corvis ST before and after 30 min, 60 min, and 90 min of caffeine/placebo intake. RESULTS: Caffeine intake reduced the corneal deformability, inducing significant changes in A1T, A2V, A2T, HCDA, HCT, and PD (all p values < 0.05). Non-corrected and biomechanically corrected IOP values were higher after caffeine intake (p = 0.001 and 0.033, respectively). Also, the changes in IOP after caffeine intake were positively associated with A1T (r = 0.790 to 0.962), and negatively associated with A2T (r = - 0.230 to - 0.722) and PD (r = - 0.506 to - 0.644). CONCLUSIONS: Caffeine intake reduces the corneal deformability, with these changes being partially associated with the IOP rise. These findings evidence that exogenous factors such as caffeine intake should be taken into consideration when making clinical decisions that are based on the biomechanical properties of the cornea.