Abstract
Purpose
Corneal biomechanics is an emerging field and the interest into physical and biological interrelations in the anterior part of the eye has significantly increased during the past years. There are many factors that determine corneal biomechanics such as hormonal fluctuations, hydration and environmental factors. Other factors that can affect the corneas are the age, the intraocular pressure and the central corneal thickness. The purpose of this review is to evaluate the factors affecting corneal biomechanics and the recent advancements in non-destructive, in vivo measurement techniques for early detection and improved management of corneal diseases.
Methods
Until recently, corneal biomechanics could not be directly assessed in humans and were instead inferred from geometrical cornea analysis and ex vivo biomechanical testing. The current research has made strides in studying and creating non-destructive and contactless techniques to measure the biomechanical properties of the cornea in vivo.
Results
Research has indicated that altered corneal biomechanics contribute to diseases such as keratoconus and glaucoma. The identification of pathological corneas through the new measurement techniques is imperative for preventing postoperative complications.
Conclusions
Identification of pathological corneas is crucial for the prevention of postoperative complications. Therefore, a better understanding of corneal biomechanics will lead to earlier diagnosis of ectatic disorders, improve current refractive surgeries and allow for a better postoperative treatment.
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Background
Corneal biomechanics refers to the mechanical properties and behavior of the cornea, which is the clear, dome-shaped front surface of the eye. It involves the study of how the cornea responds to applied forces, deforms, and recovers its shape [1, 2]. The corneal tissue is composed of five basic layers. The cornea’s outermost layer is the epithelium, comprising around 10 percent of the whole tissue’s thickness [3]. It blocks the entrance of foreign materials like water, dust and bacteria into the other layers of the cornea but also the whole eye. Moreover, it provides an ideal surface that absorbs cell nutrients and oxygen and distributes them to the rest of the cornea but is also filled with nerve endings making it sensitive to rubbing or scratching [4]. Basement membrane is the part of the epithelium where the epithelial cells are organized. Below the basement membrane, a transparent sheet of tissue named Bowman’s layer is situated. It forms scars when healing after an injury. However, when the formed scars are centrally located and/or large they can lead to vision loss [5]. Beneath Bowman’s layer the stroma is located, comprising 90 percent of cornea’s thickness [6]. It consists of collagen, that provides the strength, form and elasticity to the cornea, and water [7], but does not contain any blood vessels [8]. In detail, it is composed of dense, regularly packed collagen fibrils shaped in orthogonal layers or lamellae. Limbal epithelial stem cells (LESCs) located in the limbus at the corneoscleral junction are responsible for regenerating and renewing the corneal epithelium [9]. The Descemet’s membrane can be considered as the basement membrane of corneal endothelium [10], helps keep the endothelial monolayer in place to maintain corneal clarity [11] and is located under the stroma [12]. It accounts for the stiffest layer of the cornea and is, thus, critical for corneal integrity, which contributes in protecting the eye from penetrating injury and in guaranteeing its refractive function [13]. It is composed of collagen fibers and therefore acts as a natural barrier against microorganisms and trauma [14]. The innermost part of the cornea is the endothelium. It is an extremely thin layer that pumps the excess fluid leaking slowly from inside the eye to the stroma, keeping the balance between fluid moving to and from the cornea. The cornea is thinner at the center, presenting a gradual increase towards the periphery [15, 16]. Given the fact that the cornea is smooth and transparent, but also strong and durable, it supports the eyes in two ways. It helps to shield the eye from germs, dust, and other harmful matter by sharing this task with the eyelids, the eye socket, tears, and the white part of the eye (sclera) but it also acts as the eye's outermost lens. It functions like a window that controls the entry of light into the eye. The biomechanical properties that characterize the cornea play an important role in maintaining its shape and transparency [17]. These properties are dependent on biochemical and physical components such hydration, elasticity, viscosity, and the thickness of corneal stroma [18].
Basic biomechanical concepts
It is important to be aware of the meaning of the basic corneal properties such as elastic and viscous response, stiffness and hysteresis in order to better understand the results of corneal biomechanical evaluations. Therefore, here is the general definition of the main terms in this regard:
Biomechanical stress is a reaction of any material under a load that tries to separate atoms within a solid. Assuming that the load is uniformly distributed within a homogeneous material the sum of all these stresses (σ) must be equal with the force F (either tension or compression) acting perpendicular to an imaginary plane surface passing through a piece of material divided by the cross-section area (A) in N/m2 [19].
In order to characterize the magnitude of deformation in response to stress another property called strain (ε) is defined:
Typically, it is the fractional amount of elongation (increase in length) or contraction (decrease in length) in a material caused by a stress.
The elastic response of a material is attributed to the instantaneous and reversible deformation under an external load therefore an elastic material has a linear relationship between stress and strain [20]. The constant of proportionality between stress and strain is known as elastic modulus, also called Young’s modulus (E), defined as the ratio of the stress (load per unit area) and the strain (deformation/displacement per unit length) [21].
Note that since ε is dimensionless, E also has units of s, that is, force per unit area. Being measured in vitro, corneal Young’s modulus varies from 0.1 to 57 MPa, due to variations in testing conditions and methods used [22,23,24]. The higher the Young’s modulus, the stiffer the tissue leading to lesser deformation and faster recovery.
However, there is another category of materials, including almost all biological materials and polymer plastics, that displays gradual deformation and recovery when they are subjected to loading and unloading [25]. The response of this kind of materials is dependent upon how quickly the load is applied or removed. This time-dependent behavior is called viscoelasticity. A viscoelastic material possesses both fluid and solid properties since viscosity, a fluid property, is considered as measure of resistance to flow and elasticity is a solid material property [26].
Finally, corneal hysteresis (CH) can be described as the portion of input energy dissipated during mechanical strain due to viscosity of the corneal tissue and corneal resistance factor (CRF) is a measurement of corneal resistance that is relatively independent of intraocular pressure (IOP) that is useful diagnosis and prognosis after refractive surgery [27,28,29].
Factors determining corneal biomechanical properties
Extracellular matrix components
In the biology field, the extracellular matrix (ECM) is a three-dimensional (3D) network of extracellular macromolecules including glycoproteins, collagen and enzymes, providing biochemical and structural support to the surrounding cells [30, 31]. In corneal biomechanics, it plays an important role in the function of the corneal epithelium (development, growth, differentiation, and migration). The right assembly of the ECM is crucial for corneal function since it regulates transparency, shape, avascularity and wound healing, as well as for mechanical stability required for corneal shape and curve [32,33,34]. Corneal transparency is the major refractive element of the eye that is caused by regular arrangement of collagen fibers and interfibrillar space, which appears in the cornea during embryonic development [35].
Collagen fibrillogenesis starts with the interactions between molecules, matrix components and keratocytes [8]. Collagen V regulates the nucleation of protofibril assembly in the stroma [36]. It is also enriched in small leucine-rich proteoglycans (SLRPs) that regulate linear and lateral collagen fibril growth. Collagen XII and XIV, also known as fibril-associated collagens (FACITs) play an important role in the regulation of inter-lamellar interactions and fibril packing [37].
Hydration
Hydration not only affects corneal transparency, but also its elastic modulus. The more hydrated the corneal tissue, the lower the elastic modulus. It potentially arises from an altered collagen attachment to the proteoglycans and/or glycosaminoglycans based on their ionic interaction [38, 39].
Environmental factors
The influence of environmental factors on corneal biomechanics has been poorly investigated. However, it is already known that mechanical disturbance (e.g., eye rubbing) is strongly associated to keratoconus [40]. Another study showed higher CH values in smokers than in non-smokers [41]. Furthermore, exposure to a higher ambient UV radiation over a 65-year period decreased CH values, indicating a viscoelastic change of the cornea [42].
Hormonal fluctuations
Fluctuations of estrogen levels in blood through the menstrual cycle and pregnancy lead to changes and specifically increase in corneal thickness, decreases corneal hysteresis and corneal resistance factor [43,44,45]. Furthermore, pregnancy and disturbed levels of thyroid hormones are reported in corneal ectasia, a pathologic forward bulging and thinning of the cornea [46]. Estrogen administration has been shown to reduce biomechanical stiffness in ex vivo corneas [47].
Factors leading to alterations of biomechanical properties
Age
It is widely known that biomechanical properties of the cornea vary with age. For instance, young age is a risk factor for both keratoconus progression and iatrogenic ectasia whereas the incidence of keratoconus decreases with age [48,49,50]. Many human tissues, usually becoming less flexible by age. It has been demonstrated that the main changes refer to structure, composition, and mechanical properties [51]. In general, corneal stiffness increases because of gain in ocular rigidity coefficient, Young's modulus and cohesive tensile strength [52,53,54], while decreasing in viscous behavior like hysteresis decreases with age [55].
Intraocular pressure (IOP)
Intraocular pressure is the fluid pressure of the eye and accounts for a measure of force per area. IOP is a measurement including the magnitude of the force exerted by the aqueous humor on the internal surface area of the anterior eye [56]. IOP is considered as the key parameter to determine the health of the eye since it could be increased due to anatomical problems, genetic factors, inflammation of the eye, or as a side-effect from medication [57] but is also a major risk factor for glaucoma [58]. The normal intraocular pressure is varies between 12 and 22 mm Hg, with cyclic fluctuations of 2–3 mm Hg throughout the day with the lowest being at night due to circadian regulation of aqueous humor secretion [59] and peaking in the early morning [60]. Levels above 22 mm Hg are considered pathologic [61].
Contact lens wear
While soft contact lenses and scleral lenses are effective tools for visual correction, they could potentially both negatively impact corneal biomechanics in several ways. Soft contact lenses can inhibit the oxygen supply to the cornea, leading to corneal edema or swelling and changes in corneal thickness [61]. Long-term use may also cause corneal warpage or remodeling, leading to increased corneal surface asymmetry and irregularity. On the other hand, scleral lenses, due to their large size and rigid design, can potentially cause hypoxia and physiological changes in the cornea and underlying tissues [62, 63]. The lens-cornea clearance, along with lens fitting and wearing time, may induce stress and potential changes to the corneal structure. Additionally, the pressure exerted by these lenses on the sclera may influence intraocular pressure, thereby affecting corneal biomechanics. Therefore, although both types of lenses have their unique benefits, their potential effects on corneal biomechanics necessitate regular ophthalmological examinations for lens wearers [64].
Central corneal thickness (CCT)
Central corneal thickness is considered as a biometric entity [65, 66], and can be altered by age, ethnicity or genetics [67] but also experiences circadian changes. It is affected by prostaglandins, topical dorzolamide, topical beta-blockers, estrogen levels during ovulation and pregnancy and diabetes [68]. It is a measure of tissue mass and a possible estimator for corneal rigidity and is correlated to biomechanics and an important parameter for the assessment of different ocular diseases such as glaucoma [69]. Corneal thickness can affect the measurements of CH and CRF due to the mechanical properties of the cornea. Thicker corneas generally tend to have higher CH and CRF values, while thinner corneas typically have lower values. This relationship is because corneal thickness is related to corneal rigidity and its ability to absorb and dissipate energy. Thicker corneas have a greater structural integrity and stiffness, which leads to a higher resistance to deformation. As a result, thicker corneas exhibit higher CH and CRF values. Conversely, thinner corneas have a lower capacity to absorb and dissipate energy, resulting in lower CH and CRF values [70, 71].
Tools for evaluation of corneal biomechanics
As mentioned above, evaluation of corneal biomechanics is crucial in order to assess changes in the corneal tissue. Up to date, several techniques have been developed and used in an attempt to quantify the biomechanical properties of the cornea. These techniques can be divided into two groups. The first one is ex vivo destructive testing and the second one is in vivo non-destructive testing [72, 73] (Table 1).
Ex vivo destructive testing
Strip extensometry
Strip testing (also known as coupon testing) is the most common ex vivo technique used experimentally to determine the stress-strain behavior of corneas. The lack of human tissue specimens made it necessary in some cases to rely on animal models, primarily porcine and rabbit tissue [74]. When measuring—a strip of corneal tissue with a specific width is dissected and attached to the grips of a slow rate tension machine while monitoring its behavior under stress. The applied stress on the tissue is plotted against the strain to derive Young's modulus [75].
Limitations: the variation in sample length leads to a non-uniform stress distribution across its width. The flattening of the originally curved specimen produces tensile and compressive strains on the posterior and anterior sides respectively, could be considerable even though the CT might be small in relation to the other dimensions [74].
Inflation tests
Inflation test measures the biomechanical properties by expanding the entire cornea, based on IOP change, while keeping the integrity of the tissue. This testing has been successfully applied to detect the increase of corneal stiffness after collagen cross-linking, a minimally invasive technique to treat progressive keratoconus [76] and has also been used to demonstrate that corneal behavior is affected by age and test loading rate. However, it lacks the ability to monitor the different expansions of the cornea at different locations [77] and the results vary between using an artificial anterior chamber or whole globe mounts [78].
Speckle pattern interferometry
Electronic Speckle Pattern Interferometry (ESPI) and Radial Shearing Speckle Pattern Interferometry (RSSPI) are both optical techniques used in corneal biomechanics to measure the deformation and mechanical properties of the cornea.
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ESPI is an interferometric technique that utilizes laser light to measure the deformation of an object's surface. In corneal biomechanics, ESPI can be used to assess the response of the cornea to external stimuli or forces. The basic principle involves splitting a laser beam into two separate beams. One beam is directed towards the cornea, while the other is directed towards a reference mirror [79]. The two beams are then recombined, creating an interference pattern on a detector. As the cornea deforms, the interference pattern changes, allowing for the measurement of corneal displacement and strain. ESPI has been used in corneal biomechanics studies to investigate the effects of intraocular pressure, external loading, and surgical procedures on corneal deformation. By analyzing the interference patterns, researchers can quantify corneal stiffness, elasticity, and other mechanical properties [80].
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RSSPI is another interferometric technique used in corneal biomechanics research. It is based on the principle of shearing interferometry, where a shearing plate is used to introduce a known displacement gradient between two points on the cornea [81]. This displacement gradient results in a shearing of the speckle pattern created by the laser light reflected from the cornea. By analyzing the changes in the sheared speckle pattern, researchers can determine corneal displacements and strain.
Limitations: ESPI and RSSPI are valuable techniques for studying corneal biomechanics but have limitations. They are sensitive to environmental conditions, requiring controlled environments to ensure accuracy. Both techniques have a limited field of view, hindering comprehensive corneal deformation analysis and the data analysis process is complex and time-consuming, limiting real-time applicability. Additionally, the invasive nature of applying coatings or markers on the cornea can affect natural corneal behavior.
In vivo non-destructive testing
Several non-destructive methods have also been developed and tested for measuring corneal biomechanics in vivo, minimizing the effect of removing the cornea from its native environment. This opens the possibility of different clinical applications of these devices. However, there is a limitation when it comes to the scope of investigation since all measurements have to be performed without affecting the function of the eye. The current available devices include Ocular Response Analyzer (ORA), Corvis ST, Tonometry and Dynamic corneal imaging using Placido, Scheimpflug, or optical coherence tomography devices. Some other devices that have been used in research but are not widely introduced in clinics include Brillouin spectroscopy and supersonic shear imaging surface wave elastometry [80, 82, 83].
Ocular response analyzer (ORA)
The ocular response analyzer (ORA; Reichert Technologies, Depew, NY), a newer type of tonometer, is a non-invasive device that analyses corneal biomechanical properties fast and effective. ORA main function is based on the principles of non-contact tonometry, in which the IOP is determined by the air pressure required to applanate the central cornea. As described by Lau and Pye [84] an air pulse of increasing force lasting approximately 20 ms is directed onto the eye, leading to progressive corneal deformation. The deformation is recorded by using infrared corneal reflex [85]. The measured values are:
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1.
the IOPcc: Corneal compensated IOP, which is less affected by corneal thickness and properties and can be empirically determined by linear combination of applanation pressure 1 (P1) and pressure 2 (P2),
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2.
the IOPg or Goldmann correlated IOP, which is analogous to Goldmann Tonometry and can be considered as the average of applanation P1 and P2,
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3.
the corneal hysteresis (CH), which is the viscoelastic response (difference of P1 and P2) and corneal resistance factor (CRF), viscoelastic response weighted for central corneal thickness (empirically determined linear combination of P1 and P2) but also.
It is used by surgeons to detect corneal diseases such as keratoconus, to predict the risk of ectasia after refractive surgeries and glaucoma progression as CH of glaucomatous eyes is lower than that of their healthy counterparts [86].
Limitations: Deviations from the expected results between CH and CRF have been observed. ORA analysis is not adequate to analyze the cornea after cross-linking and biomechanical modeling is usually needed. Further exploration of the morphology of the ORA’s corneal signal (Bio-corneagram analysis) could add to the robustness of this technique [87, 88].
Oculus CORVIS ST
CORVIS ST non-contact tonometer (OCULUS Optikgeräte GmbH, Wetzlar, Germany) was placed on the global market back in 2010. It provides biomechanical parameters of the cornea [89, 90] and corneal deformation that is influenced by IOP, thickness, and innate biomechanical properties [91]. Furthermore, it allows ectatic diseases such as keratoconus to be detected at a very early stage. In short, the instrument’s camera records a sequence of images, capturing corneal deformation following a rapid air puff. This camera is capable of capturing 4,330 images per second that are analyzed to quantify central corneal thickness (CCT), deformation amplitude (DA), applanation length, corneal velocity and the concave radius of curvature (R) at the point of highest concavity, biomechanical corrected IOP (bIOP), Ambrósio’s Relational Thickness horizontal (ARTh), stiffness parameter at first applanation (SP A1) and Corvis Biomechanical Index (CBI) [92,93,94,95].
Limitations: In some diseases, such as keratoconus, lateral motion of the cornea might not be captured by Corvis ST as it records only 2D images of the corneas.
Goldmann applanation tonometry
Applanation tonometry is based on the Imbert-Fick principle [96], which indicates that the pressure inside an ideal thin-walled sphere equals the force necessary to flatten the surface divided by the area of flattening (P = F/A, P = pressure, F = force and A = area). With this method, by changing the applanating force, the cornea is flattened and the IOP can be determined. Goldmann applanation tonometry is influenced by corneal properties, including thickness, curvature, and Young’s Modulus [97, 98]. The similar Perkins applanation tonometer yields IOP measurements that are closely comparable with GAT [99].
Limitations: the eye under examination has to be numbed with local anesthesia, includes a high level of skill to operate, there is lack of ability to measure in supine patients and decreased accuracy on an irregular or scarred cornea [100].
Brillouin spectroscopy
Currently, there is no way to assess corneal biomechanics in humans with high spatial resolution and clinical conclusions can only be drawn by geometrical analysis of the cornea. Most of the current knowledge has been obtained from ex vivo destructive biomechanical testing described above. Brillouin spectroscopy might be a possible way to assess in vivo corneal biomechanics. It is an emerging technique based on Brillouin light scattering from acoustic waves providing a non-destructive contactless probe of the mechanics on a microscale. The light photons interact with natural acoustic photons in the cornea and lead to Brillouin shift, which is related to elastic modulus [101,102,103]. The shift in frequency of the Brillouin spectrum of the scattered light, caused by the photon interaction leading to loss or gain of energy, is related to the elastic modulus (M′) of the material, as shown in this equation (ρ = mass density, λ = wavelength, Ω = frequency shift, and n = the refractive index): M′ = ρλ2Ω2/4n2.
Limitations: the system is sensitive to temperature, vibration and alignment. The transition into an accurate and reproducible commercially available clinical device is a hurdle that has yet to be overcome [104].
Corneal transient elastography (CTE)
Corneal transient elastography is a non-invasive imaging technique that measures corneal stiffness or elasticity by generating and analyzing shear waves in the cornea [105, 106]. It provides information about corneal biomechanics and has potential applications in assessing corneal diseases and monitoring treatment response and had been primarily used in breast tissue imaging [107]. It uses two different types of energy to measure the corneal properties, the generation of a remote palpation in the cornea and ultrafast (20 000 frames/s) ultrasonic images. The shear wave propagation that is created is linked to local elasticity. With this technique, high-resolution images can be achieved.
Biomechanical models
Biomechanical models are being developed and tested at multiple clinical sites. These models use mathematical expressions to describe the response of a material to disturbance [108]. Finite elements is the best known method for modeling and studying complex structures that depends on the availability and quality of the input values. Providing accurate models, improvement in outcomes of corneal surgery and individualized analysis and simulations of refractive surgery for each patient could be achieved [109].
Clinical applications of corneal biomechanics
As it was mentioned before, corneal biomechanics is a diagnostic modality that could allow the early detection of weaker corneas even at a subclinical stage and pathological conditions in the anterior part of the eye leading to more effective treatments. Clinical applications of biomechanics are envisioned for the following corneal diseases:
Cataract
Cataract, characterized by clouding of the lens, is a prevalent eye condition affecting the elderly and is a leading cause of global blindness [110,111,112]. It can result in faded colors, halos around light, and blurry or double vision. Cataract development is primarily associated with age-related changes in the crystalline lens [113]. Other factors, such as malnutrition, exposure to excessive ultraviolet rays, trauma, atopic disorders, diabetes, and congenital disorders, can also contribute to its occurrence [114]. Mild cataract symptoms can be managed with glasses, but in severe cases, the only effective treatment is cataract surgery. During cataract surgery, the cloudy lens is removed and replaced with an artificial one. It is noteworthy that corneal biomechanical changes have been observed following cataract surgery, including alterations in corneal thickness and hysteresis, which can impact intraocular pressure (IOP) measurements and corneal stability post-surgery [115]. Understanding corneal biomechanics is crucial in planning the surgical approach and determining the optimal location for the incision during cataract surgery. By considering corneal biomechanics, surgeons can optimize surgical outcomes and promote corneal stability during the healing process since their proper understanding helps in choosing an incision location that minimizes induced astigmatism and maximizes wound integrity [116,117,118]. Ensuring a stable and properly sealed incision, promoting optimal visual outcomes and reducing the risk of complications such as corneal edema, wound leakage, or induced corneal irregularities can enhance surgical outcomes, promote faster healing, and improve overall patient satisfaction after cataract surgery.
Glaucoma
Corneal biomechanics, specifically corneal hysteresis (CH), is a crucial parameter in the diagnosis and management of glaucoma [119]. Glaucoma is a prevalent eye disease that can lead to irreversible blindness if left untreated. Early detection of glaucoma is challenging as initial stages often lack noticeable symptoms. It involves the progressive degeneration of retinal ganglion cells and can manifest as primary or secondary, open-angle or angle-closure glaucoma [120, 121]. Although the underlying mechanisms are not fully understood [122, 123], lower CH has been strongly associated with glaucoma-related structural and functional changes, such as optic nerve damage and visual field loss [124]. Assessing corneal biomechanics, especially CH, provides valuable insights into corneal properties, aiding in glaucoma diagnosis, monitoring disease progression, and making informed treatment decisions. Additionally, corneal structure and thickness, mainly represented by CH, serve as useful parameters for diagnosing and monitoring glaucoma. Eyes with lower CH, particularly in advanced disease cases, exhibit structural weakness, indicating that CH and corneal characteristics can be considered independent risk factors for glaucoma [125].
Keratoconus
Keratoconus is a progressive eye disease where instead of having a round cornea it turns into a cone-like shape due to thinning. This altered shape refracts light as it enters the eye on its way to the light-sensitive retina, causing distorted vision. Keratoconic eyes show a weaker stress-strain response alongside with a more disorganized collagen network [23, 126], but also reduced CH [127]. Corneal crosslinking (CXL) [128], a minimally invasive technique designed to treat progressive keratoconus, has been introduced into clinical routine to artificially stiffen pathologically weak corneas and prevent a further progression of the disease. This procedure consists of application of riboflavin, a vitamin B, clinically used in humans and its activation by means of UVA-light. The stiffening effect is achieved by generating reactive oxygen species (ROS), which are responsible for the formation of new bonds within the collagen fiber between the proteoglycans. Although very important, the knowledge about the role of oxygen in this process is very limited and needs to be further investigated [129]. Understanding corneal biomechanics plays a crucial role in the comprehensive management of keratoconus. Assessing corneal biomechanics, such as corneal hysteresis, allows clinicians to objectively evaluate the altered mechanical behavior of the cornea in keratoconus [130]. The reduced corneal hysteresis observed in keratoconic eyes indicates a diminished ability to absorb and dissipate energy, contributing to the weakened stress-strain response and progressive corneal thinning. In the context of treatment, corneal crosslinking (CXL) has become a widely used intervention for progressive keratoconus [131]. The success of CXL relies on the creation of additional cross-links between collagen fibers, which helps strengthen the cornea and halt the disease progression. Monitoring corneal biomechanics is essential in assessing the effectiveness of CXL treatment and evaluating the cornea's response to the intervention. Regular assessment of corneal biomechanics allows for long-term monitoring, enabling early detection of corneal destabilization and guiding appropriate management strategies. Overall, incorporating corneal biomechanics into clinical practice enhances personalized care for keratoconus patients [132, 133].
Iatrogenic corneal ectasia
Iatrogenic corneal ectasia is a rare complication of refractive surgery with an incidence of 0.2–0.66%, but also one of the most feared situations that can occur after corneal laser surgery [134, 135]. The progression of the disease weakens the cornea leading to biomechanical degeneration from delamination and interfibrillar fracture causing severe loss of corrected visual acuity [136]. Corneal biomechanics assessment is crucial since it helps quantify corneal weakening and assess its severity, guiding treatment decisions [137]. Corneal hysteresis reflects the cornea's ability to absorb and dissipate energy, providing valuable insights into corneal mechanical changes. Corneal crosslinking (CXL) is a treatment option that strengthens the cornea by inducing collagen cross-linking, and corneal biomechanics assessment aids in evaluating the effectiveness of CXL and monitoring the cornea's response. In severe cases, where visual impairment is significant, corneal biomechanics assessment assists in identifying the need for more invasive interventions like grafting to restore corneal integrity and improve visual function.
Conclusions
Corneal biomechanics is a rapidly evolving field with significant implications for the diagnosis and treatment of various corneal diseases. The understanding of corneal biomechanics has advanced through ex vivo biomechanical testing and the development of non-destructive, in vivo measurement techniques. These advancements have provided valuable insights into the mechanical properties of the cornea and their relationship to ocular health. Alterations in corneal biomechanics have been identified as important factors in the development and progression of corneal diseases such as keratoconus and glaucoma. Therefore, the ability to accurately assess corneal biomechanics in vivo has become crucial for early detection, diagnosis, and monitoring of these conditions. Non-destructive techniques such as Ocular Response Analyzer (ORA), Corvis ST, and Brillouin spectroscopy offer promising tools for assessing corneal biomechanical properties in a clinical setting. The extracellular matrix (ECM) components, hydration, environmental factors, hormonal fluctuations, age, intraocular pressure (IOP), contact lens wear, and central corneal thickness (CCT) are among the factors that influence corneal biomechanics. Understanding the role of these factors and their impact on corneal properties can aid in the identification of individuals at risk for corneal diseases and help guide treatment strategies. The clinical applications of corneal biomechanics are wide-ranging. In cataract surgery, knowledge of corneal biomechanics can assist in surgical planning and incision placement to optimize outcomes and promote corneal stability during the healing process. For glaucoma management, corneal biomechanics, particularly corneal hysteresis (CH), provides valuable information for diagnosis, disease progression monitoring, and treatment decision-making. In the case of keratoconus, understanding corneal biomechanics is essential for early detection, prognosis, and treatment planning, such as the application of corneal cross-linking. Additionally, the assessment of corneal biomechanics is crucial in addressing iatrogenic corneal ectasia, a rare but serious complication of refractive surgery. In conclusion, advancements in corneal biomechanics research have paved the way for improved understanding, diagnosis, and treatment of corneal diseases. Further research and technological advancements are needed to refine measurement techniques, develop comprehensive biomechanical models, and explore additional clinical applications. The continued exploration of corneal biomechanics will undoubtedly contribute to earlier disease detection, improved surgical outcomes, and enhanced postoperative care, ultimately leading to better visual health and quality of life for patients.
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References
Luce DA (2005) Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J Cataract Refract Surg 31(1):156–162. https://doi.org/10.1016/j.jcrs.2004.10.044
Bao F, Chen W, Wang Y, Elsheikh A (2023) Editorial: How can corneal biomechanics help with clinical applications? Front Bioeng Biotechnol. https://doi.org/10.3389/fbioe.2023.1184840
King-Smith PE, Fink BA, Fogt N, Nichols KK, Hill RM, Wilson GS (2000) The thickness of the human precorneal tear film: evidence from reflection spectra. Invest Ophthalmol Vis Sci 41(11):3348–3359
Masterton S, Ahearne M (2018) Mechanobiology of the corneal epithelium. Exp Eye Res 177:122–129. https://doi.org/10.1016/j.exer.2018.08.001
Lagali N, Germundsson J, Fagerholm P (2009) The role of Bowman’s layer in corneal regeneration after phototherapeutic keratectomy: a prospective study using in vivo confocal microscopy. Invest Ophthalmol Vis Sci 50(9):4192–4198. https://doi.org/10.1167/iovs.09-3781
Wilson SE (2020) Bowman’s layer in the cornea- structure and function and regeneration. Exp Eye Res 195:108033. https://doi.org/10.1016/j.exer.2020.108033
Zhang L, Anderson MC, Liu CY (2017) The role of corneal stroma: a potential nutritional source for the cornea. J Nat Sci 3(8):e428
Bron AJ (2001) The architecture of the corneal stroma. Br J Ophthalmol 85(4):379–381. https://doi.org/10.1136/bjo.85.4.379
Li X, Cheng Y-H, Roman J, Mao H-Q (2017) Chapter 26. Biomimetic nanofibers as artificial stem cell niche. In: Biology and engineering of stem cell niches: 411–927. Academic Press. https://doi.org/10.1016/B978-0-12-802734-9.00026-3
Bourne WM (2003) Biology of the corneal endothelium in health and disease. Eye (Lond) 17(8):912–918. https://doi.org/10.1038/sj.eye.6700559
Chow VWS, Agarwal T, Vajpayee RB, Jhanji V (2013) Update on diagnosis and management of Descemet’s membrane detachment. Curr Opin Ophthalmol 24(4):356–361. https://doi.org/10.1097/ICU.0b013e3283622873
Arnalich-Montiel F (2019) Corneal endothelium: applied anatomy BT—corneal regeneration: therapy and surgery. In: Alió JL, Alió del Barrio JL, Arnalich-Montiel F (eds) Springer, Cham, pp 419–424
Halfter W et al (2020) The human Descemet’s membrane and lens capsule: Protein composition and biomechanical properties. Exp Eye Res 201:108326. https://doi.org/10.1016/j.exer.2020.108326
Dupps WJJ, Wilson SE (2006) Biomechanics and wound healing in the cornea. Exp Eye Res 83(4):709–720. https://doi.org/10.1016/j.exer.2006.03.015
Esporcatte LPG et al (2020) Biomechanical diagnostics of the cornea. Eye Vis (London, England) 7:9. https://doi.org/10.1186/s40662-020-0174-x
Ambrósio RJ, Alonso RS, Luz A, Coca Velarde LG (2006) Corneal-thickness spatial profile and corneal-volume distribution: tomographic indices to detect keratoconus. J Cataract Refract Surg 32(11):1851–1859. https://doi.org/10.1016/j.jcrs.2006.06.025
Ahmed SM et al (2023) Corneal elevation topographic maps assessing different diseases detection: a review. Ain Shams Eng J. https://doi.org/10.1016/j.asej.2023.102292
Hatami-Marbini H (2014) Hydration dependent viscoelastic tensile behavior of cornea. Ann Biomed Eng 42(8):1740–1748. https://doi.org/10.1007/s10439-014-0996-6
Gustafson J, Takenaga T, Debski R (2018) Basic concepts in functional biomechanics, pp 3–15. https://doi.org/10.1007/978-3-662-55713-6_1
Ambrosio L, Netti PA, Nicolais L (2002) Soft tissue BT—integrated biomaterials science. In: Barbucci R (ed) Springer, Boston, pp 347–365. https://doi.org/10.1007/0-306-47583-9_10
Liu J, Roberts CJ (2005) Influence of corneal biomechanical properties on intraocular pressure measurement: quantitative analysis. J Cataract Refract Surg 31(1):146–155. https://doi.org/10.1016/j.jcrs.2004.09.031
Jue B, Maurice DM (1986) The mechanical properties of the rabbit and human cornea. J Biomech 19(10):847–853. https://doi.org/10.1016/0021-9290(86)90135-1
Nash IS, Greene PR, Foster CS (1982) Comparison of mechanical properties of keratoconus and normal corneas. Exp Eye Res 35(5):413–424. https://doi.org/10.1016/0014-4835(82)90040-9
Hjortdal JO (1998) On the biomechanical properties of the cornea with particular reference to refractive surgery. Acta Ophthalmol Scand Suppl 225:1–23
Ciniello AP, Bavastri CA, Pereira JT (2017) Identifying mechanical properties of viscoelastic materials in time domain using the fractional zener model. Latin Am J Solids Struct 14(1):131–152. https://doi.org/10.1590/1679-78252814
Özkaya N, Goldsheyder D, Nordin M, Leger D (2016) Fundamentals of biomechanics: equilibrium, motion, and deformation, 4th edn. https://doi.org/10.1590/1679-78252814
Lam AKC, Chen D, Tse J (2010) The usefulness of waveform score from the ocular response analyzer. Optom Vis Sci Off Publ Am Acad Optom 87(3):195–199. https://doi.org/10.1097/OPX.0b013e3181d1d940
Glass DH, Roberts CJ, Litsky AS, Weber PA (2008) A viscoelastic biomechanical model of the cornea describing the effect of viscosity and elasticity on hysteresis. Invest Ophthalmol Vis Sci 49(9):3919–3926. https://doi.org/10.1167/iovs.07-1321
Kerautret J, Colin J, Touboul D, Roberts C (2008) Biomechanical characteristics of the ectatic cornea. J Cataract Refract Surg 34(3):510–513. https://doi.org/10.1016/j.jcrs.2007.11.018
Theocharis AD, Skandalis SS, Gialeli C, Karamanos NK (2016) Extracellular matrix structure. Adv Drug Deliv Rev 97:4–27. https://doi.org/10.1016/j.addr.2015.11.001
Bonnans C, Chou J, Werb Z (2014) Remodelling the extracellular matrix in development and disease. Nat Rev Mol Cell Biol 15(12):786–801. https://doi.org/10.1038/nrm3904
Espana EM, Birk DE (2020) Composition, structure and function of the corneal stroma. Exp Eye Res 198:108137. https://doi.org/10.1016/j.exer.2020.108137
Bard JB, Bansal MK, Ross AS (1988) The extracellular matrix of the developing cornea: diversity, deposition and function. Development 103(Suppl):195–205. https://doi.org/10.1242/dev.103.Supplement.195
Meier S, Hay ED (1974) Stimulation of extracellular matrix synthesis in the developing cornea by glycosaminoglycans. Proc Natl Acad Sci USA 71(6):2310–2313. https://doi.org/10.1073/pnas.71.6.2310
Michelacci YM (2003) Collagens and proteoglycans of the corneal extracellular matrix. Braz J Med Biol Res = Rev Bras Pesqu. medicas Biol 36(8):1037–1046. https://doi.org/10.1590/s0100-879x2003000800009
Chen S, Mienaltowski MJ, Birk DE (2015) Regulation of corneal stroma extracellular matrix assembly. Exp Eye Res 133:69–80. https://doi.org/10.1016/j.exer.2014.08.001
Kimura K et al (2010) Quantitative analysis of the effects of extracellular matrix proteins on membrane dynamics associated with corneal epithelial cell motility. Invest Ophthalmol Vis Sci 51(9):4492–4499. https://doi.org/10.1167/iovs.09-4380
Hatami-Marbini H, Etebu E (2013) Hydration dependent biomechanical properties of the corneal stroma. Exp Eye Res 116:47–54. https://doi.org/10.1016/j.exer.2013.07.016
Kling S, Marcos S (2013) Effect of hydration state and storage media on corneal biomechanical response from in vitro inflation tests. J Refract Surg 29(7):490–497. https://doi.org/10.3928/1081597X-20130617-08
Sugar J, Macsai MS (2012) What causes keratoconus? Cornea 31(6):716–719. https://doi.org/10.1097/ICO.0b013e31823f8c72
Kilavuzoglu AE, Celebi ARC, Altiparmak UE, Cosar CB (2017) The effect of smoking on corneal biomechanics. Curr Eye Res 42(1):16–20. https://doi.org/10.3109/02713683.2016.1145233
Schweitzer C et al (2016) Associations of biomechanical properties of the cornea with environmental and metabolic factors in an elderly population: the ALIENOR study. Invest Ophthalmol Vis Sci 57(4):2003–2011. https://doi.org/10.1167/iovs.16-19226
Kiely PM, Carney LG, Smith G (1983) Menstrual cycle variations of corneal topography and thickness. Am J Optom Physiol Opt 60(10):822–829. https://doi.org/10.1097/00006324-198310000-00003
Weinreb RN, Lu A, Beeson C (1988) Maternal corneal thickness during pregnancy. Am J Ophthalmol 105(3):258–260. https://doi.org/10.1016/0002-9394(88)90006-2
Giuffrè G, Di Rosa L, Fiorino F, Bubella DM, Lodato G (2007) Variations in central corneal thickness during the menstrual cycle in women. Cornea 26(2):144–146. https://doi.org/10.1097/01.ico.0000244873.08127.3c
Gatzioufas Z, Thanos S (2008) Acute keratoconus induced by hypothyroxinemia during pregnancy. J Endocrinol Invest 31(3):262–266. https://doi.org/10.1007/BF03345600
Spoerl E, Zubaty V, Raiskup-Wolf F, Pillunat LE (2007) Oestrogen-induced changes in biomechanics in the cornea as a possible reason for keratectasia. Br J Ophthalmol 91(11):1547–1550. https://doi.org/10.1136/bjo.2007.124388
Randleman JB, Khandelwal SS, Hafezi F (2015) Corneal cross-linking. Surv Ophthalmol 60(6):509–523. https://doi.org/10.1016/j.survophthal.2015.04.002
McMahon TT, Edrington TB, Szczotka-Flynn L, Olafsson HE, Davis LJ, Schechtman KB (2006) Longitudinal changes in corneal curvature in keratoconus. Cornea 25(3):296–305. https://doi.org/10.1097/01.ico.0000178728.57435.df
Ertan A, Muftuoglu O (2008) Keratoconus clinical findings according to different age and gender groups. Cornea 27(10):1109–1113. https://doi.org/10.1097/ICO.0b013e31817f815a
Geraghty B, Whitford C, Boote C, Akhtar R, Elsheikh A (2015) Age-related variation in the biomechanical and structural properties of the corneo-scleral tunic BT—mechanical properties of aging soft tissues. In: Derby B, Akhtar R (eds) Springer, Cham, pp 207–235
Elsheikh A, Geraghty B, Rama P, Campanelli M, Meek KM (2010) Characterization of age-related variation in corneal biomechanical properties. J R Soc Interface 7(51):1475–1485. https://doi.org/10.1098/rsif.2010.0108
Elsheikh A, Wang D, Brown M, Rama P, Campanelli M, Pye D (2007) Assessment of corneal biomechanical properties and their variation with age. Curr Eye Res 32(1):11–19. https://doi.org/10.1080/02713680601077145
Pallikaris IG, Kymionis GD, Ginis HS, Kounis GA, Tsilimbaris MK (2005) Ocular rigidity in living human eyes. Invest Ophthalmol Vis Sci 46(2):409–414. https://doi.org/10.1167/iovs.04-0162
Kamiya K, Shimizu K, Ohmoto F (2009) Effect of aging on corneal biomechanical parameters using the ocular response analyzer. J Refract Surg 25(10):888–893. https://doi.org/10.3928/1081597X-20090917-10
Stamper R, Lieberman M, Drake M (2009) Becker-Shaffer’s diagnosis and therapy of the glaucomas. Becker-Shaffer’s Diagn Ther Glaucomas. https://doi.org/10.1016/B978-0-323-02394-8.00025-5
Cheng X, Petsche SJ, Pinsky PM (2015) A structural model for the in vivo human cornea including collagen-swelling interaction. J R Soc Interface 12(109):20150241. https://doi.org/10.1098/rsif.2015.0241
Hučko B et al (2021) Measurement and evaluation of biomechanical properties of cornea ‘in vivo.’ Meas Sensors 18:100281. https://doi.org/10.1016/j.measen.2021.100281
Forrester JV, Dick AD, McMenamin PG, Roberts F, Pearlman E (2016) Chapter 4—biochemistry and cell biology. In: Pearlman E (ed) Fourth, W.B. Saunders, pp 157–268.e4. https://doi.org/10.1016/B978-0-7020-5554-6.00004-6
David R, Zangwill L, Briscoe D, Dagan M, Yagev R, Yassur Y (1992) Diurnal intraocular pressure variations: an analysis of 690 diurnal curves. Br J Ophthalmol 76(5):280–283. https://doi.org/10.1136/bjo.76.5.280
DennysonSavariraj A et al (2021) Ophthalmic sensors and drug delivery. ACS Sensors 6(6):2046–2076. https://doi.org/10.1021/acssensors.1c00370
Kumar M, Shetty R, Lalgudi VG, Roy AS, Khamar P, Vincent SJ (2022) Corneal biomechanics and intraocular pressure following scleral lens wear in penetrating keratoplasty and keratoconus. Eye Contact Lens 48(5):206–209. https://doi.org/10.1097/ICL.0000000000000886
Lu W et al (2023) Repeatability and correlation of corneal biomechanical measurements obtained by Corvis ST in orthokeratology patients. Cont Lens Anter Eye 46(3):101793. https://doi.org/10.1016/j.clae.2022.101793
Sah R, Paudel N, Chaudhary M, Adhikari P, Mishra S (2014) The effects of soft contact lens wear on corneal thickness, curvature, and surface regularity. J Chitwan Med Coll 4:35–39. https://doi.org/10.3126/jcmc.v4i2.10861
Khachikian SS, Belin MW, Ciolino JB (2008) Intrasubject corneal thickness asymmetry. J Refract Surg 24(6):606–609. https://doi.org/10.3928/1081597X-20080601-09
Doughty MJ, Zaman ML (2000) Human corneal thickness and its impact on intraocular pressure measures: a review and meta-analysis approach. Surv Ophthalmol 44(5):367–408. https://doi.org/10.1016/s0039-6257(00)00110-7
Belovay GW, Goldberg I (2018) The thick and thin of the central corneal thickness in glaucoma. Eye (Lond) 32(5):915–923. https://doi.org/10.1038/s41433-018-0033-3
Park SJK, Ang GS, Nicholas S, Wells AP (2012) The effect of thin, thick, and normal corneas on Goldmann intraocular pressure measurements and correction formulae in individual eyes. Ophthalmology 119(3):443–449. https://doi.org/10.1016/j.ophtha.2011.07.058
Ehlers N, Hjortdal J (2004) Corneal thickness: measurement and implications. Exp Eye Res 78(3):543–548. https://doi.org/10.1016/j.exer.2003.09.017
Du Y, Zhang Y, Zhang Y, Li T, Wang J, Du Z (2023) Analysis of potential impact factors of corneal biomechanics in myopia. BMC Ophthalmol 23(1):143. https://doi.org/10.1186/s12886-023-02891-8
Zhang Y et al (2023) Corneal biomechanical properties of various types of glaucoma and their impact on measurement of intraocular pressure. Ophthalmic Res 66(1):753–760. https://doi.org/10.1159/000530291
Kotecha A (2007) What biomechanical properties of the cornea are relevant for the clinician? Surv Ophthalmol 52(Suppl 2):S109–S114. https://doi.org/10.1016/j.survophthal.2007.08.004
Nyquist GW (1968) Rheology of the cornea: experimental techniques and results. Exp Eye Res 7(2):183–188. https://doi.org/10.1016/s0014-4835(68)80064-8
Elsheikh A, Anderson K (2005) Comparative study of corneal strip extensometry and inflation tests. J R Soc Interface 2(3):177–185. https://doi.org/10.1098/rsif.2005.0034
Vellara HR, Patel DV (2015) Biomechanical properties of the keratoconic cornea: a review. Clin Exp Optom 98(1):31–38. https://doi.org/10.1111/cxo.12211
Yu J et al (2013) Assessment of corneal biomechanical behavior under posterior and anterior pressure. J Refract Surg 29(1):64–70. https://doi.org/10.3928/1081597X-20121228-05
Elsheikh A, Alhasso D, Rama P (2008) Biomechanical properties of human and porcine corneas. Exp Eye Res 86(5):783–790. https://doi.org/10.1016/j.exer.2008.02.006
Metzler KM, Mahmoud AM, Liu J, Roberts CJ (2014) Deformation response of paired donor corneas to an air puff: intact whole globe versus mounted corneoscleral rim. J Cataract Refract Surg 40(6):888–896. https://doi.org/10.1016/j.jcrs.2014.02.032
Jaycock PD, Lobo L, Ibrahim J, Tyrer J, Marshall J (2005) Interferometric technique to measure biomechanical changes in the cornea induced by refractive surgery. J Cataract Refract Surg 31(1) (online). https://journals.lww.com/jcrs/Fulltext/2005/01000/Interferometric_technique_to_measure_biomechanical.45.aspx
Wang H, Diop M, Carson JJL (2023) Double exposure ESPI for non-contact photoacoustic tomography. Proc SPIE 12574:1257411. https://doi.org/10.1117/12.2665758
Knox Cartwright NE, Tyrer JR, Marshall J (2012) In vitro quantification of the stiffening effect of corneal cross-linking in the human cornea using radial shearing speckle pattern interferometry. J Refract Surg 28(7):503–507. https://doi.org/10.3928/1081597X-20120613-01
Li F, Wang K, Liu Z (2023) In vivo biomechanical measurements of the cornea. Bioengineering. https://doi.org/10.3390/bioengineering10010120
Reyes JL, Pineda R (2023) Chapter 20—other diagnostic imaging tools for keratoconus. In: Izquierdo L, Henriquez M, Mannis M (eds) Keratoconus. Elsevier, New Delhi, pp 287–300
Lau W, Pye D (2011) A clinical description of Ocular Response Analyzer measurements. Invest Ophthalmol Vis Sci 52(6):2911–2916. https://doi.org/10.1167/iovs.10-6763
Luz A, Fontes BM, Lopes B, Ramos I, Schor P, Ambrósio RJ (2013) ORA waveform-derived biomechanical parameters to distinguish normal from keratoconic eyes. Arq Bras Oftalmol 76(2):111–117. https://doi.org/10.1590/s0004-27492013000200011
Congdon NG, Broman AT, Bandeen-Roche K, Grover D, Quigley HA (2006) Central corneal thickness and corneal hysteresis associated with glaucoma damage. Am J Ophthalmol 141(5):868–875. https://doi.org/10.1016/j.ajo.2005.12.007
Qin X, Yu M, Zhang H, Chen X, Li L (2019) The mechanical interpretation of ocular response analyzer parameters. Biomed Res Int 2019:5701236. https://doi.org/10.1155/2019/5701236
Kaushik S, Pandav SS (2012) Ocular response analyzer. J Curr Glaucoma Pract 6(1):17–19. https://doi.org/10.5005/jp-journals-10008-1103
Cheng AM, Hsia Y, Wei Y-H, Liao S-L (Jun.2023) Evaluation of changes in ocular biomechanical properties and intraocular pressure using Corvis ST after orbital decompression and anterior blepharotomy for thyroid eye disease. Invest Ophthalmol Vis Sci 64(8):3411
Fabregas-Sanchez-Woodworth D et al (2023) Corneal biomechanical metrics by Corvis ST in a healthy mexican population. Invest Ophthalmol Vis Sci 64(8):1699
Sedaghat M-R et al (2020) Corneal biomechanical properties in varying severities of myopia. Front Bioeng Biotechnol 8:595330. https://doi.org/10.3389/fbioe.2020.595330
Valbon BF, Ambrósio RJ, Fontes BM, Luz A, Roberts CJ, Alves MR (2014) Ocular biomechanical metrics by CorVis ST in healthy Brazilian patients. J Refract Surg 30(7):468–473. https://doi.org/10.3928/1081597X-20140521-01
Serbecic N, Beutelspacher S, Markovic L, Roy AS, Shetty R (2020) Repeatability and reproducibility of corneal biomechanical parameters derived from Corvis ST. Eur J Ophthalmol 30(6):1287–1294. https://doi.org/10.1177/1120672119864554
Chan TC, Wang YM, Yu M, Jhanji V (2018) Comparison of corneal dynamic parameters and tomographic measurements using Scheimpflug imaging in keratoconus. Br J Ophthalmol 102(1):42–47. https://doi.org/10.1136/bjophthalmol-2017-310355
Vinciguerra R et al (2016) Detection of keratoconus with a new biomechanical index. J Refract Surg 32(12):803–810. https://doi.org/10.3928/1081597X-20160629-01
Gloster J, Perkins ES (1963) The validity of the Imbert-Fick law as applied to applanation tonometry. Exp Eye Res 2(3):274–283. https://doi.org/10.1016/s0014-4835(63)80048-2
Bamdad S, Vatan Y (2017) Goldmann applanation tonometry: using a red-free filter for mass screening. Med. Hypothesis, Discov Innov Ophthalmol J 6(1):22–23
Stevens S, Gilbert C, Astbury N (2012) How to measure intraocular pressure: applanation tonometry. Commun Eye Heal 25(79–80):60
Arora R, Bellamy H, Austin M (2014) Applanation tonometry: a comparison of the Perkins handheld and Goldmann slit lamp-mounted methods. Clin Ophthalmol 8:605–610. https://doi.org/10.2147/OPTH.S53544
Aziz K, Friedman DS (2018) Tonometers-which one should I use? Eye (Lond) 32(5):931–937. https://doi.org/10.1038/s41433-018-0040-4
Remer I, Shaashoua R, Shemesh N, Ben-Zvi A, Bilenca A (2020) High-sensitivity and high-specificity biomechanical imaging by stimulated Brillouin scattering microscopy. Nat Methods 17(9):913–916. https://doi.org/10.1038/s41592-020-0882-0
Lepert G, Gouveia RM, Connon CJ, Paterson C (2016) Assessing corneal biomechanics with Brillouin spectro-microscopy. Faraday Discuss 187:415–428. https://doi.org/10.1039/C5FD00152H
Scarcelli G, Pineda R, Yun SH (2012) Brillouin optical microscopy for corneal biomechanics. Invest Ophthalmol Vis Sci 53(1):185–190. https://doi.org/10.1167/iovs.11-8281
Seiler TG, Shao P, Eltony A, Seiler T, Yun S-H (2019) Brillouin spectroscopy of normal and keratoconus corneas. Am J Ophthalmol 202:118–125. https://doi.org/10.1016/j.ajo.2019.02.010
Li R et al (2023) Simultaneous assessment of the whole eye biomechanics using ultrasonic elastography. IEEE Trans Biomed Eng 70(4):1310–1317. https://doi.org/10.1109/TBME.2022.3215498
Lan G et al (2023) In vivo corneal elastography: a topical review of challenges and opportunities. Comput Struct Biotechnol J 21:2664–2687. https://doi.org/10.1016/j.csbj.2023.04.009
Tanter M et al (2008) Quantitative assessment of breast lesion viscoelasticity: initial clinical results using supersonic shear imaging. Ultrasound Med Biol 34(9):1373–1386. https://doi.org/10.1016/j.ultrasmedbio.2008.02.002
Sinha Roy A, Dupps WJJ (2011) Patient-specific computational modeling of keratoconus progression and differential responses to collagen cross-linking. Invest Ophthalmol Vis Sci 52(12):9174–9187. https://doi.org/10.1167/iovs.11-7395
Seven I, Vahdati A, De Stefano VS, Krueger RR, Dupps WJJ (2016) Comparison of patient-specific computational modeling predictions and clinical outcomes of LASIK for myopia. Invest Ophthalmol Vis Sci 57(14):6287–6297. https://doi.org/10.1167/iovs.16-19948
Resnikoff S et al (2004) Global data on visual impairment in the year 2002. Bull World Health Organ 82(11):844–851
Resnikoff S, Pascolini D, Mariotti SP, Pokharel GP (2008) Global magnitude of visual impairment caused by uncorrected refractive errors in 2004. Bull World Health Organ 86(1):63–70. https://doi.org/10.2471/blt.07.041210
Abraham AG, Condon NG, West Gower E (2006) The new epidemiology of cataract. Ophthalmol Clin North Am 19(4):415–425. https://doi.org/10.1016/j.ohc.2006.07.008
Asbell PA, Dualan I, Mindel J, Brocks D, Ahmad M, Epstein S (2005) Age-related cataract. Lancet (London, England) 365(9459):599–609. https://doi.org/10.1016/S0140-6736(05)17911-2
Allen D, Vasavada A (2006) Cataract and surgery for cataract. BMJ 333(7559):128–132. https://doi.org/10.1136/bmj.333.7559.128
Kato Y, Nakakura S, Asaoka R, Matsuya K, Fujio Y, Kiuchi Y (2017) Cataract surgery causes biomechanical alterations to the eye detectable by Corvis ST tonometry. PLoS ONE 12(2):e0171941. https://doi.org/10.1371/journal.pone.0171941
das Neves NT, Boianovsky C, Lake JC (2023) Functional profile of a customized wound parameter in femtosecond laser-assisted corneal incision for cataract surgery. Clin Ophthalmol 17:175–181. https://doi.org/10.2147/OPTH.S384660
Hammer A, Heeren TFC, Angunawela R, Marshall J, Saha K (2023) A novel role for corneal pachymetry in planning cataract surgery by determining changes in spherical equivalent resulting from a previous LASIK treatment. J Ophthalmol 2023:2261831. https://doi.org/10.1155/2023/2261831
Hirnschall N (2023) Surgically induced corneal astigmatism BT—cataract and lens surgery. In: Shajari M, Priglinger S, Kohnen T, Kreutzer TC, Mayer WJ (eds) Springer, Cham, pp 185–190
Dascalescu D et al (2015) Correlations between corneal biomechanics and glaucoma severity in patients with primary open angle glaucoma. Maedica (Buchar) 10(4):331–335
Day AC et al (2012) The prevalence of primary angle closure glaucoma in European derived populations: a systematic review. Br J Ophthalmol 96(9):1162–1167. https://doi.org/10.1136/bjophthalmol-2011-301189
Friedman DS et al (2004) (2004) Prevalence of open-angle glaucoma among adults in the United States. Arch Ophthalmol (Chicago, Ill. 1960) 122(4):532–538. https://doi.org/10.1001/archopht.122.4.532
Weinreb RN, Khaw PT (2004) Primary open-angle glaucoma. Lancet (London, England) 363(9422):1711–1720. https://doi.org/10.1016/S0140-6736(04)16257-0
Nickells RW, Howell GR, Soto I, John SWM (2012) Under pressure: cellular and molecular responses during glaucoma, a common neurodegeneration with axonopathy. Annu Rev Neurosci 35:153–179. https://doi.org/10.1146/annurev.neuro.051508.135728
Deol M, Taylor DA, Radcliffe NM (2015) Corneal hysteresis and its relevance to glaucoma. Curr Opin Ophthalmol 26(2):96–102. https://doi.org/10.1097/ICU.0000000000000130
Brazuna R, Alonso RS, Salomão MQ, Fernandes BF, Ambrósio R (2023) Ocular biomechanics and glaucoma. Vision. https://doi.org/10.3390/vision7020036
Meek KM et al (2005) Changes in collagen orientation and distribution in keratoconus corneas. Invest Ophthalmol Vis Sci 46(6):1948–1956. https://doi.org/10.1167/iovs.04-1253
Mikielewicz M, Kotliar K, Barraquer RI, Michael R (2011) Air-pulse corneal applanation signal curve parameters for the characterisation of keratoconus. Br J Ophthalmol 95(6):793–798. https://doi.org/10.1136/bjo.2010.188300
Perez-Straziota C, Gaster RN, Rabinowitz YS (2018) Corneal cross-linking for pediatric keratcoconus review. Cornea 37(6):802–809. https://doi.org/10.1097/ICO.0000000000001579
Seiler TG, Komninou MA, Nambiar MH, Schuerch K, Frueh BE, Büchler P (2021) Oxygen kinetics during corneal cross-linking with and without supplementary oxygen. Am J Ophthalmol 223:368–376. https://doi.org/10.1016/j.ajo.2020.11.001
Cavas F, Piñero D, Velázquez JS, Mira J, Alió JL (2020) Relationship between corneal morphogeometrical properties and biomechanical parameters derived from dynamic bidirectional air applanation measurement procedure in keratoconus. Diagnostics (Basel, Switzerland). https://doi.org/10.3390/diagnostics10090640
Viswanathan D, Kumar NL, Males JJ, Graham SL (2015) Relationship of structural characteristics to biomechanical profile in normal, keratoconic, and crosslinked eyes. Cornea [Online]. https://journals.lww.com/corneajrnl/Fulltext/2015/07000/Relationship_of_Structural_Characteristics_to.12.aspx
Esporcatte LPG et al (2023) Biomechanics in keratoconus diagnosis. Curr Eye Res 48(2):130–136. https://doi.org/10.1080/02713683.2022.2041042
Ambrósio R, Esporcatte LPG, Salomão M, Sena NB, Roberts CJ (2023) Chapter 6—biomechanics of keratoconus. In: Izquierdo L, Henriquez M, Mannis MBT-K (eds) Elsevier, New Delhi, pp 65–82
Rad AS, Jabbarvand M, Saifi N (2004) Progressive keratectasia after laser in situ keratomileusis. J Refract Surg 20(5 Suppl):S718–S722. https://doi.org/10.3928/1081-597X-20040903-18
Pallikaris IG, Kymionis GD, Astyrakakis NI (2001) Corneal ectasia induced by laser in situ keratomileusis. J Cataract Refract Surg 27(11):1796–1802. https://doi.org/10.1016/s0886-3350(01)01090-2
Moshirfar M, Edmonds JN, Behunin NL, Christiansen SM (2013) Corneal biomechanics in iatrogenic ectasia and keratoconus: a review of the literature. Oman J Ophthalmol 6(1):12–17. https://doi.org/10.4103/0974-620X.111895
Lopes BT, Elsheikh A (2023) In vivo corneal stiffness mapping by the stress-strain index maps and Brillouin microscopy. Curr Eye Res 48(2):114–120. https://doi.org/10.1080/02713683.2022.2081979
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Komninou, M.A., Seiler, T.G. & Enzmann, V. Corneal biomechanics and diagnostics: a review. Int Ophthalmol 44, 132 (2024). https://doi.org/10.1007/s10792-024-03057-1
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DOI: https://doi.org/10.1007/s10792-024-03057-1