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Vision
Published in Anne McLaughlin, Richard Pak, Designing Displays for Older Adults, 2020
Although many visual changes are normative, some are pathological or can be brought on by surgery on the eye. Surgery to correct vision became popular in the late 1990s, and the early adopters are now reaching older age, pairing their normative changes with those related to their surgeries. LASIK (laser-assisted in situ keratomileusis) is the most popular surgery to correct vision, where the cornea is reshaped through burning with a laser until it correctly focuses light on the retina. Common side effects include dry eyes, seeing “halos” around light sources (particularly at night), and reduced night vision. The long-term effects of LASIK are not yet known, but it can be assumed that they will relate to the commonly experienced side effects: the need to blink or clear the eyes due to dryness, difficulty reading road signs at night, and clutter when multiple light sources are present.
The Human Eye and Its Aberrations
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Correction of higher-order aberrations is also commonly performed in refractive surgery. Laser in situ keratomileusis (LASIK) is a surgical technique originally developed for correcting myopia, hyperopia and axial astigmatism. The surgery involves forming a thin flap in the anterior surface of the cornea and using an excimer laser to ablate or sculpt the underlying tissue to a new shape. Once the flap is replaced, the shape of the cornea has been modified to correct the patient's refractive error [72]. This procedure has been extended to create custom ablation patterns to correct for an individual's aberrations. Again the patient's wavefront error is measured with aberrometry. The compensating phase profile is then ablated into the cornea providing enhanced vision over conventional procedures, which just correct spherical and cylindrical refractive error. Customized LASIK is now a routine option for patient's seeking vision correction.
Recent developments in imaging and surgical vision technologies currently available for improving vitreoretinal surgery: a narrative review
Published in Expert Review of Medical Devices, 2023
Elham Sadeghi, Sashwanthi Mohan, Danilo Iannetta, Jay Chhablani
The contact lenses are attached to the cornea and are held by an assistant to correct the corneal aberrations to improve stereopsis, axial depth, and image resolution. They provide a wider field of view than non-contact lenses, but inverted images need a microscope inverter. For the best image quality, complete contact with the cornea with viscoelastic material is necessary, so it should be used cautiously for post-LASIK (laser in situ keratomileusis) cases. The small pupillary size may be a limiting factor. These lenses are designed with different magnifying power and angle of view for various surgeries. Depending on the design, they may provide up to a 155-degree field of view. Lenses such as the Central Retinal Vitrectomy lens (Volk) and Clarivit lens (HOYA), with their narrow surgical field but excellent resolution, are suitable for macular surgeries. However, the MiniQuad XL lens provides a broad fundus view with less image resolution, which is ideal for other types of procedures [127,127].
Quantification for biomechanical properties of human cornea by using acoustic radiation force optical coherence elastography
Published in Journal of Modern Optics, 2022
Yanzhi Zhao, Yongbo Wang, Yueyuan Xu, Yunjiang Zhang, Hongwei Yang, Xiao Han, Yirui Zhu, Yubao Zhang, Guofu Huang
The cornea, lying in front of the iris and pupil, is a totally transparent avascular connective tissue which provides three-fourths of the total refractive power of the human eye along with the tear film on the ocular surface [1,2]. Most refractive errors, such as myopia, hyperopia and astigmatism can be attributed to the altered biomechanical properties of the cornea [3]. Corneal refractive surgeries such as laser-assisted in-situ keratomileusis (LASIK) and small incision lenticule extraction (SMILE) have gained considerable popularity in recent years, offering a long-term solution to refractive errors. However, these surgeries are always accompanied by the alteration of cornea elasticity between pre- and post-operation, and there is a lack of good characterization of this change [4–7]. In addition to the above-mentioned factors, other ocular diseases like keratoconus and keratomalacia are also associated with the biomechanical properties of cornea [8,9]. Therefore, assessment of cornea elasticity is important for better understanding corneal pathologies, accurate diagnosing the related diseases, as well as improving the safety and efficacy of current refractive surgeries.
Correlation of accommodation and lens location with higher-order aberrations and axial length elongation during orthokeratology lens wear
Published in International Journal of Optomechatronics, 2021
Jy-Been Liang, Wen-Pin Lin, Richard Wu, Connie Chen
Orthokeratology (OK) can correct up to moderate myopia and slow progression by overnight wearing of rigid gas permeable (RGP) contact lenses with a “reverse geometry” design, that is, a central flat curve and a very steep reverse curve.[1–4] Wearing overnight OK lenses results in an increase in the corneal surface, central corneal flattening, thinning of the central corneal epithelium, and thickening of the mid-peripheral cornea; the lenses flatten the apical radius of the cornea and restructure it toward an oblate-like ellipse as a result of their shape.[5] Flattening of the central cornea reduces corneal power, and thus corrects the myopic refractive error, and with the removal of the lenses on awakening, satisfactory unaided vision is achieved during the daytime.[1] The effect is similar to that of laser refractive surgery, such as photorefractive keratectomy (PRK) or laser in-situ keratomileusis (LASIK).