What is the sclera?

The sclera is the white part of the eye and is believed to play a key role in the development of myopia. Myopia is the most common vision defect, affecting approximately 22% of the world’s population. Furthermore, this percentage has been increasing in recent years, reaching 90% in some Asian populations.

The sclera is a connective tissue whose cells are immersed in a material formed mainly by bundles of collagen fibers that intertwine to form a more or less firm structure. In very myopic eyes, the posterior part of the sclera is thinner than in eyes that see without defects (emmetropes).

This interweaving of collagen fibers is essential for the rigidity of the sclera, so its biomechanical behavior could depend on the degree of intertwining of the fibers, which in turn could affect the deformation or non-deformation of the eye.

Myopia

Myopia is the result of a mismatch between the focal length of the ocular components and the depth of the eye, whereby the images are focused in front of the retina, rather than right on the retina. Excessive axial growth of the eye is responsible for 95% of myopia cases.
It has been suggested that the ocular components (the cornea and lens) also undergo changes in myopic patients, although to a lesser degree. Myopic patients exhibit, for example, a thinner lens and lower lens power compared to flawless eyes, presumably to compensate for axial elongation of the eye. The sequence of events leading to axial elongation leads to remodeling of the scleral tissue, hence the importance of investigating its biomechanical properties.

The study

In the study, the researchers have published a method to estimate the biomechanical properties of porcine sclera in intact eyeballs previously extracted from the animal. They have used the technique of optical coherence tomography to record the vibrations caused by an air blast source, and have isolated interesting mechanical properties of tissue from the data using inverse optimization mathematical techniques based on finite element modeling.
In the same way that the method, previously developed by the authors to evaluate the cornea, is applied in vivo to determine the corneal mechanical properties, it is expected that in the future the developed technique can also be applied in vivo to obtain information from the scleral tissue.

Optical coherence tomography

Scanning source optical coherence tomography is a non-invasive tomographic (section imaging) imaging technique that uses a wavelength scanning light source to obtain information from the different layers in depth in a tissue.

Applications

The use of scleral air puff imaging holds promise for non-invasive investigation of structural changes in the eye associated with myopia and glaucoma, and for monitoring changes in scleral stiffness during disease or treatment.

The application of this technique in vivo has the potential to identify patients at risk of developing myopia or other diseases involving scleral biomechanics (for example, glaucoma), and to verify the efficacy of new myopia treatments such as cross- Scleral linking and other pharmacological methods.

Air puff stimulation is standard practice in corneal clinical evaluation, and may be applicable in vivo in the sclera by eccentric fixation or ocular rotation, at least in regions around the limbus.

For this technique to be applied, more studies are needed in animal models and in human eyes to establish the relationship between the mechanical properties of the anterior and posterior regions, depending on the myopia suffered and age.

Scleral Crosslinking

There are already techniques to strengthen the sclera and thus prevent the development of myopia, through crosslinking.
These techniques help to form new bonds between the collagen fibers, which although they do not prevent the reduction of the number of collagen fiber bundles, they do make the fiber bundles appear denser and more evenly distributed.

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