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Gene Therapy for Retina and Eye Diseases
Published in Yashwant V. Pathak, Gene Delivery Systems, 2022
Keratoconus gives rise to visual impairment due to gradual corneal thinning and steepening. The cornea becomes cone-shaped, which leads to refractive abnormalities, blurry vision, diplopia, impaired night vision, and visual acuity and can lead to myopia (49).
Corrections in highly aberrated eyes
Published in Pablo Artal, Handbook of Visual Optics, 2017
Jason D. Marsack, Raymond A. Applegate
In the context of contact lens correction, there are several conditions of the eye that tend to be frequently associated with high levels of optical aberration. Ocular disease processes (e.g., keratoconus and pellucid marginal degeneration) lead to rotationally asymmetric morphological changes in the cornea. Due to the fact that the refractive power of the eye is directly related to the shape of the eye and the fact that the anterior surface of the cornea is responsible for roughly 66% of the refracting power of the eye (Smith and Atchison, 1997), these rotationally asymmetric changes in shape induce rotationally asymmetric optical properties in the cornea, leading to an increased level of higher-order optical aberration in the eye. For example, keratoconus is a disease that is classically defined as resulting in an inferior steepening of the cornea, leading to an inferior displacement of the corneal apex. In the uncorrected eye, Pantanelli et al. showed that higher-order aberration in keratoconus was approximately 5.5 times higher than levels found in a normal population and that 53% of the HOA variance in the KC population can be accounted for by vertical coma (term C3−1 in the Zernike polynomial) (Pantanelli et al., 2007). This result is optically consistent with the downward displacement of the corneal apex mentioned earlier. Along with disease processes, prior ocular surgery, in particular, corneal transplantation (Pantanelli et al., 2012), and early corneal refractive procedures (Applegate and Howland, 1997) can lead to morphological asymmetry in the cornea and the induction of higher-order aberration. While the root cause of the change in corneal shape may differ, the presence of elevated levels of non-sphero-cylindrical errors poses challenges for the patient as well as the clinician attempting to provide the patient with a traditional refractive correction.
Two lamellar tissues: cornea and annulus fibrosus. Active transport
Published in Benjamin Loret, Fernando M. F. Simões, Biomechanical Aspects of Soft Tissues, 2017
Benjamin Loret, Fernando M. F. Simões
Keratoconus is the most common dystrophy of the cornea with an incidence of 1 over 2000. It is characterized by a thinning and ectasia of the central cornea, inducing severe astigmatism, Fig. 19.1.8.
Effects of corneal preservation on the mechanical response of porcine corneas measured by nano-indentation
Published in Soft Materials, 2022
Shima Bahramizadeh-Sajadi, Hamid Reza Katoozian, Jiri Nohava, Miguel Angel Ariza-Gracia, Philippe Büchler
The biomechanics of the cornea plays an essential role in our vision because the shape of the cornea is determined by the mechanical balance between the intraocular pressure and its mechanical response. Since the cornea is responsible for about two-thirds of the refractive power of the eye, any change in this balance can have a significant impact on the shape of the cornea and thus on the patient’s visual acuity. Several surgical procedures affect the biomechanics of the cornea by making incisions, as in cataract surgery,[1] by removing tissue, as in refractive surgery,[2,3] or by altering the mechanical properties of the cornea, as in chemical cross-linking.[4] Corneal biomechanics have also been implicated in the underlying mechanism of keratoconus (KC), a severe ocular disease characterized by localized alteration of corneal mechanical properties. The locally decreased corneal stiffness causes the cornea to bulge under the intraocular pressure, resulting in catastrophic deterioration of the patient’s visual acuity. Corneal biomechanics is not only essential for understanding keratoconus but also plays an important role in current treatment procedures[5]. The current intracorneal ring segments implanted into the cornea to control the progression of this disease have a significant impact on the stress and strain distribution within the cornea.
Biomechanical analysis of corneal keratoconic disease
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
N. Falgayrettes, E. Patoor, F. Cleymand, J-M. Perone
The cornea is the outermost transparent tissue of the eye composed of five distinct layers. The keratoconus disease is described as a progressive and non-inflammatory corneal ectasia caused by decrease in the biomechanical strength of the tissue. As the cornea becomes thinner and softer, it cannot support the inner eye pressure anymore and assumes a conical shape which leads to increasingly blurred vision (Ferrari and Rama 2020).