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Conducting Polymers for Ophthalmic Applications
Published in Ram K. Gupta, Conducting Polymers, 2022
The posterior segment has three layers as sclera, choroid, and retina, as well as a vitreous cavity filled with vitreous humor. The sclera is the external white shell of the eye and serves as a protective layer with the eyelids as well as helps in the preservation of the eye's form by giving mechanical support. The hydrophobicity and charge of the molecules are critical parameters for drug molecule penetration through the sclera. The high surface area and relatively permeable nature of the sclera make it suitable for researches in drug delivery to the posterior segment [6]. The choroid is the middle layer of the eyeball, with a dense vascular system and maintains the temperature of the eye medium and feeds the inner layer. The retina is the innermost layer of the eye and is primarily responsible for vision. The incoming light is transformed into an electrical signal by specialized neurons called photoreceptors in the retina (i.e., rods and cones) then delivered to the brain for image formation.
Lasers in Medicine: Healing with Light
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
The anatomy of the eye is shown in Figure 3.30a. The white of the eye is called the sclera. Light enters the eye through the cornea and the pupil, the opening of the iris. It then passes through the lens and the vitreous humor, a jellylike substance that fills the eyeball, and falls upon the inner lining of the eyeball, called the retina. Both the cornea and the lens refract entering rays of light in such a way as to project tiny images of the outside world onto the retina, which plays a role analogous to the image sensor in a camera. The retina is a complex structure consisting of many specialized layers, including the pigment epithelium, which contains specialized cells for sensing light, and choroid, which contains blood vessels and dark blue pigments to absorb stray light. Some layers hold the rod and cone cells that actually sense light, some provide circulation and support. In the regions of the retina known as the fovea and the macula, or yellow spot, visual acuity is highest because of a high concentration of light-sensing cells. The optic disc, or blind spot, is where the optic nerve enters the retina. Preserving the functioning of these regions is of especial concern during laser surgery.
Development of Ophthalmic Formulations
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Paramita Sarkar, Martin Coffey, Mohannad Shawer
The sclera covers five-sixths of the eyeball surface and has a mean surface area of 16.3 cm2 [22]. It connects to the cornea anteriorly at the limbus. The sclera is mainly composed of collagen fibers with varying sizes and orientation that are embedded in a glycosaminoglycan matrix. Scleral thickness varies by location; the mean thickness is 0.53 mm near the limbus, is 0.39 mm near the equator, and is about 0.9–1.0 mm near the optic nerve [23]. The sclera is composed of three main components: Episclera—the outermost layer made up of loosely arranged collagen fibers and connected to the eyeball sheath (Tenon’s capsule)Stroma—composed of larger collagen fibers and elastic tissueLamina fusca—the innermost layer of sclera that forms the uveal tract with the choroids. It is composed of loosely coherent collagen bundles and melanocytes.
Eye Tracking, Usability, and User Experience: A Systematic Review
Published in International Journal of Human–Computer Interaction, 2023
Jakub Štěpán Novák, Jan Masner, Petr Benda, Pavel Šimek, Vojtěch Merunka
Eye tracking is a technology of tracking a person’s eye movement to determine where they are looking, for how long, and how the eye got there. Eye tracking systems analyze the user’s eye location, movement, and pupil size at a specified moment to determine areas of interest (Hasse & Bruder, 2015). Many studies involve eye trackers, including visual systems, psychology, neurology, and virtual reality (McNamara & Mehta, 2020). Essential usable components of the human eye for eye tracking technology are the retina, pupil, cornea, sclera, and iris (Hansen & Ji, 2010). The activity of these components can be recorded as signals and utilized in many applications (Annerer-Walcher et al., 2021). Eye detection is the process of locating the eye and measuring the eye gaze. Several methods are used for gaze tracking, such as shape, feature, appearance, and hybrid-based methods (Hansen & Ji, 2010). There are numerous eye tracking devices on the market—from glasses to specialized bars that can be mounted to monitors and other devices or placements. The primary mechanism of these devices is based on an infrared non-visible light beam pointing to subjects’ face and eyes. This approach aims to recognize two core reference elements. The first is the reflection of retinal light, and the second is the reflection of light in the cornea (Chivu et al., 2018).
Wavefront aberrations caused by biomechanical effects after Small Incision Lenticule Extraction (SMILE) based on finite element analysis
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Yinyu Song, Lihua Fang, Qianwei Liu, Jiahui Gong, Binhui Guo
The same structural data and material parameters were used for the 3D human eye model, avoiding the influence of personalized eyeball parameters on experimental data. Then the method of quantitative analysis was used to explore the effects of diopter, IOP, and the incision size on wavefront aberrations. In addition, the factors of influencing residual wavefront aberrations may include decentration, corneal ablating depth, etc. Therefore, the same method was used to carry out the exploration of refractive surgery, which not only saved costs, but also provided specific theoretical support for SMILE refractive surgery. However, there are some limitations in our study. First, the cornea and sclera of the human eye were considered, but the influence of other components were not considered. Second, the material properties of the sclera and corneal tissues were fundamental to the induced wavefront aberrations. Our model used the Ogden function to represent the nonlinear material properties of the models. In clinical practice, the eye material parameters have significant individual differences. The influence of these aspects was worth further exploration.
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 cornea was excised with a scalpel blade and Castroviejo curved corneal scissors, while the eyeball was held in place with large Colibri corneal forceps. The cornea was cut at the exact border connecting the cornea to the sclera. Then, the harvested corneas (n = 21) were divided into three groups: a) fresh corneas that were mechanically tested within 10 hours of eyeball harvesting (Fsh), b) corneas that were placed in the freezer at −20°C and stored for six days (Frz), and c) corneas that were in culture medium for six days (TiC). The weight of all specimens was measured immediately after dissection (w0). For specimens stored for six days (Frz and TiC), weight was also measured immediately before mechanical characterization (w1). Relative weight change was then calculated as the difference between the weight of the specimen after and before six days in the preservation media, divided by its initial weight: