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Long-term contact lens use can lead to alterations in corneal thickness, stromal thickness, curvature, corneal sensitivity, cell density, and epithelial oxygen uptake, etc. Other changes may include the formation of epithelial vacuoles and microcysts (containing cellular debris) as well as the emergence of polymegethism in the corneal endothelium.
Computer vision syndrome. Computer vision syndrome ( CVS) is a condition resulting from focusing the eyes on a computer or other display device for protracted, uninterrupted periods of time and the eye's muscles being unable to recover from the constant tension required to maintain focus on a close object.
Refractive surgery. Refractive surgery is an optional eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea ( keratomileusis ), lens implantation or lens replacement.
The lens of the eye is the most obvious example of gradient-index optics in nature. In the human eye, the refractive index of the lens varies from approximately 1.406 in the central layers down to 1.386 in less dense layers of the lens. [1] This allows the eye to image with good resolution and low aberration at both short and long distances. [2]
Chromatic aberration. Focal length of lens varies with the color of light. In optics, chromatic aberration ( CA ), also called chromatic distortion, color aberration, color fringing, or purple fringing, is a failure of a lens to focus all colors to the same point. [ 1][ 2] It is caused by dispersion: the refractive index of the lens elements ...
Presbyopia: When the flexibility of the lens declines, typically due to age. The individual would experience difficulty in near vision, often relieved by reading glasses, bifocal, or progressive lenses. Astigmatism is when the refractive power of the eye is not uniform across the surface of the cornea because of asymmetry. In other words, the ...
Orthokeratology lens. Orthokeratology, also referred to as Night lenses, Ortho-K, OK, Overnight Vision Correction, Corneal Refractive Therapy (CRT), Accelerated Orthokeretology, Cornea Corrective Contacts, Eccentricity Zero Molding, and Gentle Vision Shaping System (GVSS), is the use of gas-permeable contact lenses that temporarily reshape the cornea to reduce refractive errors such as myopia ...
The gradient starts at the wearer's distance prescription at the top of the lens and reaches a maximum addition power, or the full reading addition, at the bottom of the lens. The length of the progressive power gradient on the lens surface depends on the design of the lens, with a final addition power between 0.75 and 3.50 dioptres.
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