Corneal Biomechanics Research Articles

Spatial Assessment of Heterogeneous Tissue Natural Frequency Using Micro-Force Optical Coherence Elastography.

Analysis of corneal tissue natural frequency was recently proposed as a biomarker for corneal biomechanics and has been performed using high-resolution optical coherence tomography (OCT)-based elastography (OCE). However, it remains unknown whether natural frequency analysis can resolve local variations in tissue structure. We measured heterogeneous samples to evaluate the correspondence between natural frequency distributions and regional structural variations. Sub-micrometer sample oscillations were induced point-wise by microliter air pulses (60–85 Pa, 3 ms) and detected correspondingly at each point using a 1,300 nm spectral domain common path OCT system with 0.44 nm phase detection sensitivity. The resulting oscillation frequency features were analyzed via fast Fourier transform and natural frequency was characterized using a single degree of freedom (SDOF) model. Oscillation features at each measurement point showed a complex frequency response with multiple frequency components that corresponded with global structural features; while the variation of frequency magnitude at each location reflected the local sample features. Silicone blocks (255.1 ± 11.0 Hz and 249.0 ± 4.6 Hz) embedded in an agar base (355.6 ± 0.8 Hz and 361.3 ± 5.5 Hz) were clearly distinguishable by natural frequency. In a beef shank sample, central fat and connective tissues had lower natural frequencies (91.7 ± 58.2 Hz) than muscle tissue (left side: 252.6 ± 52.3 Hz; right side: 161.5 ± 35.8 Hz). As a first step, we have shown the possibility of natural frequency OCE methods to characterize global and local features of heterogeneous samples. This method can provide additional information on corneal properties, complementary to current clinical biomechanical assessments, and could become a useful tool for clinical detection of ocular disease and evaluation of medical or surgical treatment outcomes.

An exploratory analysis of forme fruste keratoconus sensitivity diagnostic parameters.

To secondary statistical analysis of the Pentacam or Corvis ST parameters from literatures, and to obtain more sensitive diagnostic parameters for clinical keratoconus (CKC) and forme fruste keratoconus (FFKC), respectively. The parameters and the corresponding area of ROC curve (AUC) in previous studies were extracted and screened to obtain the database of CKC (Data-CKC) and FFKC (Data-FFKC), respectively. Two different importance evaluation methods (%IncMSE and IncNodePurity) of random forest were used to preliminary select the important parameters. Then, based on the partial dependency analysis, the sensitive diagnostic parameters that had promotion to the diagnostic performance were obtained. Data-FFKC was analyzed in the same way. Finally, a diagnostic test meta-analysis on the sensitive parameter of interest was conducted to verify the reliability of the above analysis methods. There were 88 parameters with 766 records in Data-CKC, 57 parameters with 346 records in Data-FFKC. Based on two importance evaluation methods, 60 important parameters were obtained, of which 20 were further screened as sensitive parameters of keratoconus, and most of these parameters were related to the thinnest point of cornea. The stiffness parameter at first applanation (SPA1) was the only Corvis ST output parameter sensitive to FFKC except the Tomographic and Biomechanical Index and the Corvis Biomechanical Parameter (CBI). A total of 4 records were included in the meta-analysis of diagnostic tests on SPA1. The results showed that there was threshold effect, but no significant heterogeneity (I2 = 33%), and the area under the SROC curve was 0.87 (95% CI, 0.84-0.90). For the diagnosis of FFKC, the sensitivity of SPA1 is not inferior to the well-known CBI, and may be the earliest Corvis ST output parameter to reflect the changes of corneal biomechanics during keratoconus progression. The elevation parameters based on the typical position of the thinnest point of corneal thickness are of great significance for the diagnosis of keratoconus.

Corneal Biomechanics Differences Between Chinese and Caucasian Healthy Subjects.

PurposeThe aim of this study was to evaluate the difference between Caucasian and Chinese healthy subjects with regards to Corvis ST dynamic corneal response parameters (DCRs).MethodsTwo thousand eight hundred and eighty-nine healthy Caucasian and Chinese subjects were included in this multicenter retrospective study. Subsequently, Chinese eyes were matched to Caucasians by age, intraocular pressure (IOP), and Corneal Thickness (CCT) using a case-control matching algorithm. The DCRs assessed were Deformation Amplitude (DA) Applanation 1 velocity (A1v), integrated radius (1/R), deformation amplitude ratio (DAratio), stiffness parameter at applanation 1 (SPA1), ARTh (Ambrósio's Relational Thickness to the horizontal profile), and the novel Stress Strain Index (SSI).ResultsAfter age-, CCT-, and IOP- matching, 503 Chinese were assigned to 452 Caucasians participants. Statistical analysis showed a statistical significant difference between Chinese and Caucasian Healthy subjects in the values of SPA1 (p = 0.008), Arth (p = 0.008), and SSI (p < 0.001). Conversely, DA, A1v, DAratio, and 1/R were not significantly different between the two ethnical groups (p > 0.05).ConclusionWe found significant differences in the values of the DCRs provided by the Corvis ST between Chinese and Caucasian healthy subjects.

Modification of Corneal Biomechanics and Intraocular Pressure Following Non-Penetrating Deep Sclerectomy.

Changes in the cornea can influence outcomes in patients with primary open-angle glaucoma (POAG). We aimed to evaluate the relevance of changes in corneal biomechanics and intraocular pressure (IOP) in patients undergoing non-penetrating deep sclerectomy (NPDS) with the Esnoper V2000 implant® (AJL Ophthalmic S.A., Gasteiz, Spain). We included 42 eyes of 42 patients with POAG scheduled for NPDS with the Esnoper V2000 implant. Biomechanical properties were measured by Ocular Response Analyzer® G3 (ORA; Reichert Inc., Depew, NY, USA). Corneal hysteresis (CH), corneal resistance factor (CRF), corneal compensated IOP (IOPcc), and Goldmann-correlated IOP (IOPg) were measured the day before surgery and on day 1, 7, and 30 and 2 and 3 months after surgery. CH initially increased, fell below the presurgical value at 30 days after the surgery, and increased again at 2 and 3 months. CRF, IOPcc, and IOPg decreased on the first day after surgery, then followed a trend of increasing but stayed below pre-surgery levels. All values reached statistical significance. While observed changes in corneal biomechanics after NPDS and Esnoper V2000 implant were significant, more studies are needed if we are to understand their influence on corneal biomechanics and their clinical relevance in POAG.

The Protective Effects of Soft Contact Lenses for Contact Sports: A Novel Porcine Model for Corneal Abrasion Biomechanics.

The aim of this study was to determine whether soft contact lenses provide protection for the corneal surface. Fresh porcine eyes were inflated to intraocular pressures of 11 to 22 mm Hg and secured to a Styrofoam head. Newton meters affixed with artificial acrylic nails were placed at angles of 0°, 45°, and 90° from a porcine corneal surface. The force of impact was recorded at which corneal abrasions were induced. The experiment was repeated with Senofilcon A and Lotrafilcon A soft contact lenses placed upon porcine eyes. The mean forces required to induce a corneal abrasion with force at 0°, 45°, and 90° from corneal surface were 11±5.09, 9.18±2.76, and 7.72±2.61 Newtons, respectively. With soft contact lens barrier, the maximum measurable force of 50 Newtons could not produce a corneal abrasion. The force required to create corneal abrasions varies depending on the angle of the force vector. The use of contact lenses can withstand a minimum of five times the average force needed to create corneal abrasions.

Trends in research on corneal cross linking from 2001 to 2020: a bibliometric analysis

ABSTRACT Clinical relevance The research status and hotspots in the field of corneal cross linking (CXL) can benefit clinicians, researchers and the general public. Background The purpose of this study was to map the publishing trend on CXL research and explore the research hotspots. Methods A bibliometric analysis was performed using the Web of Science Core Collection to investigate the publishing trend on CXL research. VOSviewer was used to build the knowledge map to visualise the number of annual publications, distribution of countries and institutions, international cooperation, author productivity, source journals and research hotspots in the field of CXL. Results A total of 2061 peer-reviewed articles on CXL research were collected from 2001 to 2020, and the annual research production increased over time. The United States was the country with the largest number of published articles, and the University of Zurich was the most active institution. Hafezi F published the largest number of articles on CXL, while Cornea was the journal with the largest number of studies on CXL. The most frequently cited references mainly focus on CXL in the treatment of keratoconus. The keywords were divided in 5 categories: 1) CXL mechanism, 2) ectasia diseases and refractive surgery, 3) corneal biomechanics, 4) efficacy evaluation, 5) treatment of infectious keratitis. Conclusion The quantity and quality of articles on CXL were evaluated using bibliometric techniques by extracting the data from the Web of Science Core Collection. The research hotspots could provide insights on CXL research, providing valuable information for clinicians to perform research in this field and find potential partners.

The alterations of corneal biomechanics in adult patients with corneal dystrophy.

To evaluate the changes of corneal biomechanics in granular, lattice and macular corneal dystrophy (GCD, LCD and MCD), and to assess the agreement of intraocular pressure (IOP) between Corvis ST tonometer (CST) and Goldmann applanation tonometer (GAT) and the agreement of central corneal thickness (CCT) between CST and ultrasound pachymeter (USP) in patients with corneal dystrophy. Fifty-nine eyes with corneal dystrophy (26 eyes with GCD, 18 eyes with LCD and 15 eyes with MCD) and 48 eyes from healthy subjects were included in this study. All subjects received ocular examination and anterior segment photography under slit-lamp microscope. Corneal biomechanical parameters were obtained using CST. IOP and CCT were obtained using GAT and USP, respectively. Mixed-effects models were fitted for group comparisons and Bland-Altman analyses were applied for assessing the agreement of IOP or CCT between devices. GCD, LCD and MCD showed higher First Applanation Deformation Amplitude (A1DA) and Corvis Biomechanical Index (CBI), and a lower Stiffness Parameter at First Applanation (SPA1), compared to controls. After CCT adjustment, MCD group showed a higher A1DA compared to GCD or LCD. The IOP measured by CST demonstrated an overestimated bias to the one obtained by GAT in all groups. The CCT measured by CST and USP showed good agreement in healthy eyes but not in those with corneal dystrophy. Corneal biomechanical alterations were observed in GCD, LCD and MCD. IOP and CCT measured by CST should be interpreted carefully in eyes with corneal dystrophy.

Correlation of the Corvis Biomechanical Factor with tomographic parameters in keratoconus.

To investigate the relationship between corneal biomechanics and keratoconus (KC) severity as described by tomographic parameters. University-based German ophthalmology department. Retrospective cross-sectional study. A total of 448 KC corneas of the Homburg Keratoconus Center and 112 healthy corneas (448+112 patients) were examined by Pentacam high-resolution and Corneal Visualization Scheimpflug Technology (Pentacam HR and Corvis ST). The KC population included a wide spectrum of disease severity based on Belin's ABCD classification. Linear regression analysis was performed between the linear term of the Corvis Biomechanical Index (CBI) (CBI beta) and the tomographic values anterior radius of curvature (ARC), posterior radius of curvature (PRC), and thinnest corneal thickness (TCT). A linear transformation of the CBI beta was performed to provide an intuitive scaling, which was referred to as the Corvis Biomechanical Factor (CBiF = -0.24294226 × CBI beta + 6.02). This scaling adjusted the CBI beta to the same scale as posterior corneal curvature (PRC). There was a high correlation of the CBI beta and its modification, the CBiF, with TCT (Pearson, r = -0.775), ARC (r = -0.835), and PRC (r = -0.839) in the KC population (P < .001). In the control corneas, the correlation between the CBI beta and ARC was weak (r = -0.216, P = .022), not significant (PRC, r = -0.146, P = .125), or moderate (TCT, r = -0.628, P < .001). The linear term of the CBI was highly associated with KC severity as defined by corneal tomography. The CBiF represents a new scale based on biomechanical characteristics in KC, which could serve as a basis for a biomechanical KC classification in the future.

Long-term Outcomes of Bowman's Membrane Relaxation for Enhancement of Femtosecond Intrastromal Lenticule Implantation Performed for the Management of High Hyperopia.

To evaluate the feasibility and report long-term outcomes with Bowman's membrane relaxation (BMR) for enhancing the residual refractive error following femtosecond intrastromal lenticule implantation (FILI). BMR was performed using a Hessburg-Barron trephine to create a circular incision into the Bowman's membrane and anterior corneal fibers up to the depth of approximately 120 to 130 µm. After enhancement, clinical outcomes were analyzed for a mean period of 36 months (range: 14 to 57 months). Four eyes of 3 patients (mean age: 29 years) underwent enhancement with BMR for a significant residual refractive error of +2.25 diopters (D) spherical equivalent following FILI for high hyperopia (mean spherical equivalent: +7.00 D). After BMR, the residual refraction reduced to +0.31 D, resulting in improvement in uncorrected distance visual acuity from 0.55 to 0.33 logMAR. The mean front keratometry values increased from 46.20 to 49.30 D, and the mean back keratometry values increased from -5.90 to -6.30 D following BMR, the latter returning to the baseline (pre-FILI) value of -6.30 D. An increase in Q-value with a corresponding increase in higher order aberrations was observed. Corneal biomechanics indicated reduction of stiffness and other parameters after enhancement. No intraoperative or postoperative complications were noted. BMR may be an effective technique for enhancement of residual hyperopia following tissue addition techniques such as FILI. BMR may reverse the posterior curvature changes, negating the steepening effect of the anterior cornea following tissue addition, potentially aiding in the enhancement. [J Refract Surg. 2022;38(2):134-141.].

Comparison of the Clinical Outcomes between Combined Femtosecond Laser-Assisted In Situ Keratomileusis and Corneal Cross Linking versus Combined Small-Incision Lenticule Extraction and Corneal Cross Linking.

Purpose The purpose of this study was to compare femtosecond laser-assisted in situ keratomileusis with prophylactic cross linking (FS-LASIK Xtra) and small-incision lenticule extraction with prophylactic cross linking (SMILE Xtra) in terms of their postoperative clinical outcomes. Methods In this retrospective study, 24 patients (48 eyes) with myopia and myopia astigmatism were recruited from 2017 to 2018. All patients underwent comprehensive ophthalmic examinations preoperatively and follow-up visits at one and three months. Four patients (eight eyes) in each group were followed up for 12 months. The following were assessed at each visit: uncorrected distance visual acuity (UDVA), manifest refractive spherical equivalent (MRSE), keratometry values, biomechanical properties, anterior and posterior curvature, and corneal pachymetry. Results The FS-LASIK Xtra and SMILE Xtra groups both included 24 eyes of 12 patients. At 1, 3, and 12 months after surgery, a UDVA of 20/20 or better was achieved for 91.7%, 91.7%, and 87.5% of individuals, respectively, in the FS-LASIK group and 95.8%, 100%, and 100% in the SMILE group, respectively. For 75% of eyes in the FS-LASIK Xtra group and 100% of eyes in the SMILE Xtra group, the achieved MRSE was within ±1.00D of attempted correction. The LASIK Xtra group had a significantly higher mean MRSE than the SMILE Xtra group at 3 and 12 months after surgery (P=0.006, 0.01), and the SMILE Xtra group had significantly higher K1 and K2 values than the FS-LASIK group at one month after surgery (P=0.024, 0.023). Corneal thickness decreased significantly at one month postoperatively and started to increase over the next 12 months in both groups (P=0.001). The biomechanical properties showed no significant intergroup differences at the 12-month follow-up. Conclusions FS-LASIK Xtra and SMILE Xtra are safe and effective in the correction of myopia and myopia astigmatism, and both procedures have the same effect on postoperative corneal morphology and biomechanics.

Investigation of the effect of solution pH value on rabbit corneal stroma biomechanics.

To facilitate the protection of corneal stability during corneal epithelium defects by determining the effect of solution pH on corneal stroma biomechanics. Thirty rabbit corneas were extracted, and the epithelium was scraped off. The samples were immediately subjected to inflation tests with pressures ranging from 0.3 to 6kPa at baseline and in three subsequent test cycles. During a 10-min interval between cycles, specimens were randomly divided into four groups; in three of these groups, phosphate-buffered saline (PBS) drops with pH values of 6.9, 7.4, or 7.9 were applied to the surface once per minute, whereas the fourth group did not receive drops. The corneal thickness significantly increased following the administration of PBS, while the corneal tangent modulus significantly decreased. At 2.5 and 4.5kPa, the modulus reduction was significantly smaller in the specimens treated with pH 6.9 PBS than in those treated with pH 7.4 or 7.9 PBS, adjusted for changes in corneal thickness. Linear fitting of the pressure-modulus plot revealed that the regression coefficient significantly decreased over time. The reduction in the coefficient was most prominent in the PBS-treated groups, and the administration of pH 6.9 PBS elicited the smallest reduction among those three groups, adjusted for corneal thickness changes. The study demonstrated that the administration of PBS drops with various pH values affected corneal biomechanics independent of corneal stromal swelling, and the impact of slightly acidic PBS was minimal. The effect became more prominent as posterior pressure increased. The research provides the basis for mediating the pH value of tear film and drops to maintain biomechanical stability of epithelium defects corneal stroma.

Effect of photorefractive keratectomy versus laser in situ keratomileusis on corneal hysteresis in moderate myopic eyes

IntroductionAblation procedures used for vision correction such as photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) flap creation produce massive changes within the corneal structure and biomechanical properties. These changes are due to thinning of the central cornea and disruption of continuity of the collagen lamellae. Several approaches to assessment of the biomechanical properties have been proposed. Refractive photoablation procedures that decrease corneal hysteresis (CH) and corneal resistance factor (CRF) have been shown by several studies; therefore, here in our study we are going to discuss the effect of PRK versus LASIK on the corneal biomechanics and stability over time.AimTo compare the postoperative biomechanical properties of the cornea after PRK and after LASIK in eyes with moderate myopia.Patients and methodsThe study is 'prospective, controlled, and randomized.' In all, 40 eyes with moderate myopia (−2.0 to − 5.0 D) underwent refractive correction of myopia; 20 of them (group A) were enrolled for PRK while the other 20 of them (group B) were enrolled for LASIK surgery. CH and CRF were measured with an ocular response analyzer preoperatively and 1and 3 months postoperatively. All eyes were subjected to corneal topography preoperatively and 1 and 3 months postoperatively ocular response analyzer was used preoperatively and 1 and 3 months postoperatively.ResultsAll patients were followed up postoperatively at 1 and 3 months. The CH and CRF were measured in both groups preoperatively and postoperatively. In group A, the mean preoperative CH was 10.7 ± 0.4 (range: 10–11.1) and CRF was 10.2 ± 0.11 (range: 10.1–10.5), whereas in group B it was 10.57 ± 0.38 (range: 10–11.2) and the CRF was 10.21 ± 0.1 (range: 10–10.5), respectively, with no significant difference (P = 0.43 and 0.25, respectively).After 1 month, CH and CRF were 8.4 ± 0.27 (range: 7.9–9.1) and 8.2 ± 0.23 (range: 7.8–8.6) in group A and 8.3 ± 0.25 (range: 8.0–9.0) and 8.17 ± 0.19 (range: 7.9–8.5) in group B, respectively, with no significant difference (P = 0.28 and 0.45, respectively). At 3 months, CH and CRF were 8.6 ± 0.28 (range: 8.1–9.2) and 8.3 ± 0.21 (range: 7.8–8.6) in group A and 8.55 ± 0.26 (range: 8.2–9.1) and 8.28 ± 0.18 (range: 7.9–8.6) in group B, respectively, with no significant difference (P = 0.56 and 0.32, respectively). The corneal biomechanical parameters decreased after both PRK and LASIK procedures. The corneal biomechanical parameters decreased after both PRK and LASIK procedures. The postoperative measurements of CH and CRF at 3 months were lower than the preoperative values in both groups with a significant amount (P < 0.001).ConclusionBoth PRK and LASIK substantially weaken the biomechanical strength of the cornea, the greater the amount of myopic correction, the more the change in corneal biomechanics.

ET‐1 plasma levels and scleral rigidity as risk factors in neovascular age‐related macular degeneration

AbstractPurposeTo study the ocular blood flow, the corneal biomechanics, the scleral rigidity and the endothelin‐1 (ET‐1) plasma levels in patients with neovascular age‐related macular degeneration (ARMD).MethodsWe enrolled 20 patients with ARMD and 20 age‐matched control patients. Retrobulbar blood flow was examined by Colour Doppler Aplio 500 (Toshiba Medical System, Tokyo, Japan). Peak systolic velocity (PSV) and resistivity index (RI) was measured from ophthalmic artery (OA), central retinal artery (CRA) and posterior ciliary arteries (PCA’s). The corneal hysteresis CH and the corneal resistance force (CRF) values were achieved by Ocular Response Analyzer (ORA). Scleral rigidity (E) was determined by using Friedenwald nomograms. ET‐1 plasma levels were determined using a specific radioimmunoassay (Sigma‐Aldrich, Merck, Germany).ResultsWe found a statistically significant difference in the CRF between patients with ARMD and control subjects (ARMD 11.23 ± 1.30 vs. Controls 9.82 ± 1.37; p&lt;0.0025) was found. The CH index between patients with ARMD and control subjects was not statistically significant (ARMD 10.15 ± 1.25 vs. Controls 10.02 ± 1.70; p&lt;0.617). With CDI in PCA’s we found PSV (ARMD 12.37 ± 2.80 cm/sec vs. Controls 15.44 ± 3.59 cm/sec; p&lt;0.0063); RI (ARMD 0.80 ± 0.03 vs Controls 0.74 ± 0.02; p&lt;0.0001). The E had a significant increase in ARMD group (ARMD 0.0358 ± 0.004 vs. Controls 0.0328 ± 0.004; p&lt;0.008) as well as ET‐1 plasma levels (ARMD 2.060 ± 0.276 vs. Controls 1.492 ± 0.0.560; p&lt;0.001). Finally, in ARMD we found that the decrease of PSV and the increase of RI in PCA’s was correlated with the ET‐1 plasma levels (PSV r‐0.615; p&lt;0.0039 and r 0.764; p&lt;0.0001) and not with the values of E, CH and CRF.ConclusionsOur data indicate that patients with neovascular ARMD had a significant increase of RI in all vessels examined with increased corneal CRF index, scleral rigidity values and ET‐1 plasma levels. The decreased blood flow in APC’s was correlated to the increase of ET‐1 plasma levels. These data indicate that elevated plasma ET‐1 and not the scleral rigidity may be an important risk factor in the development of neovascular ARMD.

Corneal Biomechanics for Ocular Hypertension, Primary Open-Angle Glaucoma, and Amyloidotic Glaucoma: A Comparative Study by Corvis ST.

BackgroundTo evaluate biomechanical parameters of the cornea provided by Corvis ST in patients with ocular hypertension, primary open-angle glaucoma, and amyloidotic glaucoma and to compare with healthy controls.MethodsThis was a cross-sectional study of patients with ocular hypertension, primary open-angle glaucoma, and amyloidotic glaucoma that underwent Corvis ST imaging. Primary outcome was the comparison of corneal biomechanical parameters between study groups after adjusting for age, gender, Goldmann intraocular pressure (GAT-IOP), and prostaglandin analogues medication. Secondary outcome was the comparison of different IOP measurements in each group.ResultsOne hundred and eighty-three eyes from 115 patients were included: 61 with primary open-angle glaucoma, 32 with amyloidotic glaucoma, 37 with ocular hypertension and 53 were healthy controls. Amyloidotic glaucoma group had smaller radius (p=0.025), lower deflection amplitude at highest concavity (p=0.019), and higher integrated radius (p=0.014) than controls. Ocular hypertension group had higher stiffness parameter at first applanation (p=0.043) than those with primary open-angle glaucoma, and higher stress–strain index (p=0.049) than those with amyloidotic glaucoma. Biomechanically corrected intraocular pressure was significantly lower than Goldmann intraocular pressure in group with primary open-angle glaucoma (p=0.005) and control group (p=0.013), and Goldmann intraocular pressure adjusted for pachymetry in group with primary open-angle glaucoma (p=0.01).ConclusionEyes with amyloidotic glaucoma have more deformable corneas, while eyes with ocular hypertension have less deformable corneas. These findings may be linked to the susceptibility to glaucomatous damage and progression. There were significant differences between Goldmann applanation tonometry and biomechanically corrected intraocular ocular pressure provided by Corvis ST.

Suspect glaucoma detection from corneal densitometry supported by machine learning

PurposeTo discriminate suspect glaucomatous from control eyes using corneal densitometry based on the statistical modeling of the pixel intensity distribution of Scheimpflug images. MethodsTwenty-four participants (10 suspect glaucomatous and 14 control eyes) were included in this retrospective study. Corneal biomechanics was assessed with the commercial Scheimpflug camera Corvis ST (Oculus). Sets of 140 images acquired per measurement were exported for further analysis. After corneal segmentation, pixel intensities corresponding to different corneal depths were statistically modeled for each image, from which corneal densitometry in the form of parameters α (brightness) and β (homogeneity) was derived. After data pre-processing, parameters α and β were input to six supervised machine learning algorithms that were trained, tested, and compared. ResultsThere exists a statistically significant difference in α and β parameters between suspect glaucomatous and control eyes (both, P < 0.05/N, Bonferroni). From the implemented supervised machine learning algorithms, the K-nearest neighbors (K-NN) algorithm reached 83.93% accuracy to discriminate between groups only using corneal densitometry parameters (α and β). ConclusionDensitometry of the anterior cornea including epithelium on its own has the potential to serve as a clinical tool for early glaucoma risk assessment.

Corneal biomechanics for corneal ectasia: Update.

Knowledge of biomechanical principles has been applied in several clinical conditions, including correcting intraocular pressure measurements, planning and following corneal treatments, and even allowing an enhanced ectasia risk evaluation in refractive procedures. The investigation of corneal biomechanics in keratoconus (KC) and other ectatic diseases takes place in several steps, including screening ectasia susceptibility, the diagnostic confirmation and staging of the disease, and also clinical characterization. More recently, investigators have found that the integration of biomechanical and tomographic data through artificial intelligence algorithms helps to elucidate the etiology of KC and ectatic corneal diseases, which may open the door for individualized or personalized medical treatments in the near future. The aim of this article is to provide an update on corneal biomechanics in the screening, diagnosis, staging, prognosis, and treatment of KC.

Understanding Corneal Epithelial Thickness Mapping.

Corneal epithelial thickness (CET) and the regional variations in response to changes in corneal architecture and biomechanics have recently drawn the interest of corneal surgeons. Corneal epithelium possesses the tremendous capability of remodeling and changing its thickness. This remodeling of corneal epithelium takes place in response to underlying stromal irregularities which can result from a variety of corneal disorders including corneal ectasia. Measurement of CET can reveal the underlying stromal abnormalities and supplement in early diagnosis of corneal disorders especially corneal ectasia which has been one of the leading challenges in planning corneal refractive surgery. A significant number of patients ends up in ectasia after refractive surgery and the most common cause of this complication is the presence of preoperative subclinical keratoconus. Furthermore, postoperative complications of corneal refractive surgery are partly masked by epithelial remodeling and make the diagnosis and management difficult and extremely challenging. This leads not only to unpredictable visual and refractive outcome but also the need of multiple interventions to treat these complications. Although corneal tomography is considered as gold standard in the detection and diagnosis of corneal ectasia, a small number of subclinical cases may still go undetected. In this review, we have highlighted the underlying mechanism of epithelial remodeling, the devices and imaging modalities used to measure CET, and application of epithelial mapping in the diagnosis and management of various corneal disorders.

The Link between Anterior Scleral Thickness, Corneal Biomechanical Response, and Ocular Parameters

Introduction: This study aimed to assess anterior scleral thickness (AST) across diverse scleral meridians and to evaluate the relationship with corneal biomechanical response and several ocular parameters. Methods: This prospective nonrandomized study comprised 50 eyes of 50 patients (mean age, 29.02 ± 9.48 years). AST was measured meridionally at three scleral locations (1, 2, and 3 mm posterior to the scleral spur) using swept-source optical coherence tomography. A multivariate model was created to associate AST with several ocular parameters. Principal component analysis (PCA) was used to reduce linearly the dimensionality of seven biomechanical input metrics to two significant components, C1 and C2. Two multivariate analyses were performed to associate C1 and C2 with AST and ocular parameters. Results: AST was thickest in the inferior (581 ± 52 µm) and thinnest in the superior meridian (441 ± 42 µm) when compared to all meridians (p < 0.001) and similar in the nasal (529 ± 53 µm) and temporal (511 ± 59 µm) meridians (p > 0.05). The sclera exhibited the thinnest point 2 mm posterior to the scleral spur (p < 0.001). The AST was significantly linked with axial length, central corneal thickness, and intraocular pressure (p < 0.001). The PCA showed that C1 accounts for 53.84%, whereas C2 for the 16.51% of the total variance in the original variables. The C1 model was significantly associated with AST along all meridians (p < 0.001). The partial correlation was moderate in the nasal (r = −0.36, p < 0.001) and inferior (r = −0.26, p = 0.004) meridians, whereas weak in the temporal (r = −0.14, p = 0.05) and superior (r = −0.15, p = 0.05) meridians. Conclusions: The relationship between the new biomechanical component and the AST provides the first evidence of the association of AST with the corneal response parameters which should be considered in corneal response interpretation. Tissue thickness varied significantly among meridians supporting the asymmetrical expansion of the ocular globe. The AST was associated with several ocular parameters.

Corneal biomechanics in a pediatric population

AbstractPurposeThe purpose of the study is to explore the relationship between biomechanical corneal parameters and axial length in a pediatric population.MethodsWe conducted a prospective study that included 82 eyes from 41 pediatric patients. All patients were submitted to a complete ophthalmologic examination that included autorefractometry (before and after pharmacological cycloplegia), slit lamp and fundus examination, ocular tonometry. Additionally, the patients underwent examination with Ocular Response Analyzer (Reichert Ophthalmic Instruments Inc., Depew, NY) to determine corneal hysteresis (CH), corneal resistance factor (CRF) and with Aladdin biometer (Topcon, Tokyo, Japan) to determine axial length (AL) and central corneal thickness (CCT). Statistical analysis was performed using IBMSPSS Statistics 26.ResultsOur study included 82 eyes, from 41 patients (63.41% female, 36.59% male). The average age was 13.29 years old (12.92 in females, 13.93 in males). Average CH, CRF, and spherical power, respectively, were similar between sexes: 12.30 mmHg, 12.47 mmHg, −0.70 D respectively in females, 12.89 mmHg, 13.31 mmHg and −1.27 D respectively in males. Mean AL and CCT are larger in males than in females, in a statistically significantmanner. Average AL is 23.69 mm in females, 24.52 mm in males (p = 0.007) and average CCT is 0.558 mm in females and 0.583 mm in males (p = 0.003). We also found a statistically significant moderate negative correlation between CH and AL in the pediatric population (Pearson’s r of −0.350, p = 0.001), and also in both sexes (Pearson’s r of −0.419, p = 0.002 in females and −0.437, p = 0.016 in males).ConclusionsOur study reveals that in the pediatric population, at similar age, males have a thicker central cornea and longer axial length. Furthermore, in these patients, a high axial length is correlated to a low corneal hysteresis. Further studies are needed to explore these data and to confirm these findings in adults.

On refraction shift after trabeculectomy

To determine the factors affecting the shift of refraction after trabeculectomy. The study included 42 patients who were examined prior to trabeculectomy and at the following timepoints: 1 week, 1 month and 3 months after surgery. Examination included tonometry with assessment of corneal biomechanical properties, keratorefractometry with vector analysis, and biometry. The obtained data was processed for regression analysis and to find the possible correlations. All significant correlations between the measured parameters only occur on week 1. Postoperative spherical component of refraction (sphere) correlates negatively both with preoperative axial length (AL) and anterior chamber depth (ACD) (r=-0.699 and r=-0.458, p<0.05) and postoperative AL and ACD (r= -0.767 and r= -0.415, p<0.011). Dependence of sphere on AL is also expressed as a regression model. The magnitude of AL change depends on the magnitude of intraocular pressure (IOP) change (r=0.729, p<0.0001) and correlates negatively with postoperative IOP (r=-0.454, p=0.009) and baseline corneal hysteresis (CH; r= -0.482, p=0.009). Dependence of AL on IOP is also expressed as a regression model. The magnitudes of sphere and cylinder shifts correlate negatively with each other (r=-0.416, p=0.038). Keratometry reveals that the overall cylinder value correlates with the corneal cylinder, and so do the magnitudes of their shifts (r=0.589 and r=0.574, p<0.0001). Dependence of corneal hysteresis on IOP is expressed as a regression model; however, neither tonometric nor biomechanical corneal properties correlate with refraction. Sphere correlates negatively with AL and ACD. In turn, AL is related to the reduction in IOP. This dependence is likely the most important one for the refraction shift after trabeculectomy. No correlations were found for the change of astigmatism.