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The Visual Environment: Measurement and Design
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
In myopia, light rays entering parallel to the optic axis are brought into focus at a point some distance in front of the retina. This can be caused by the eye being too long anteroposteriorly or due to excessive power of the refractive system. Myopia is sometimes referred to as nearsightedness because the near point is closer to the eye in myopic people (for an equal amount of accommodation) than it is to a healthy eye. Myopic individuals cannot bring distant objects into focus. Temporary myopia often occurs after a near object has been viewed for a period of time—accommodation is not instantaneous because the lens requires time to change to a flatter shape when the ciliary muscle relaxes. Myopic individuals can often carry out close tasks such as VDT work or sewing with ease but experience difficulties with tasks such as driving where target objects are more than 5–10 m away.
Descriptive Statistics
Published in William M. Mendenhall, Terry L. Sincich, Statistics for Engineering and the Sciences, 2016
William M. Mendenhall, Terry L. Sincich
Contact lenses for myopia. Myopia (i.e., nearsightedness) is a visual condition that affects over 100 million Americans. Two treatments that may slow myopia progression is the use of (1) corneal reshaping contact lenses and (2) bifocal soft contact lenses. In Optometry and Vision Science (Jan., 2013), university optometry professors compared the two methods for treating myopia. A sample of 14 myopia patients participated in the study. Each patient was fitted with a contact lens of each type for the right eye, and the peripheral refraction was measured for each type of lens. The differences (bifocal soft minus corneal reshaping) are shown in the following table. (These data, simulated based on information provided in the journal article, are saved in the MYOPIA file.) Find measures of central tendency for the difference measurements and interpret their values.Note that the data contains one unusually large (negative) difference relative to the other difference measurements. Find this difference. (In Section 2.7, we call this value an outlier.)The large negative difference of -8.11 is actually a typographical error. The actual difference for this patient is -0.11. Rerun the analysis, part a, using the corrected difference. Which measure of central tendency is most affected by the correcting of the outlier?
Corneal onlays and inlays
Published in Pablo Artal, Handbook of Visual Optics, 2017
Myopia is a condition of the eye where the optics of the eye are too strong or the axial length of the eye is too long for light to come into focus on the retina. Light from a distant object focuses in front of the retina in a myopic eye, necessitating a decrease in power in order to “push” the focus back to the retina. Negative (minus) powered spectacle or contact lenses are used to decrease the power of the eye. For myopia, a change in the power of the eye can be achieved by either decreasing the curvature of the cornea or introducing a negative powered implant.
EVO/EVO+ Visian Implantable Collamer Lenses for the correction of myopia and myopia with astigmatism
Published in Expert Review of Medical Devices, 2023
Elena Martínez-Plaza, Alberto López-de la Rosa, Alberto López-Miguel, Alfredo Holgueras, Miguel J. Maldonado
Myopia occurs when the images are focused in front of the retina. It is defined as a spherical equivalent (SE) equal or below -0.50 dioptres (D) and is currently the most common refractive error worldwide [1]. It represents the main cause of distance impairment worldwide, involving a high socioeconomic impact [2]. When the refractive error is equal or below -6.00 D, it is considered as high myopia. It represents a considerably higher risk of associated ocular anomalies, such as retinal detachment and myopic maculopathy [3,4]. Thus, high myopia can lead to irreversible ocular damage and, even, blindness [5]. Regrettably, the prevalence of both, myopia and high myopia, is dramatically increasing. In fact, it has been estimated that in 2050 the 50% of the world population will be myopic and the 10% will be high myopic [6].
Buildings, Lighting, and the Myopia Epidemic
Published in LEUKOS, 2023
Kevin W. Houser, Lisa Heschong, Richard Lang
Myopia, also known as nearsightedness, is an eye disease that most often begins in early childhood and progresses through late adolescence. It was once relatively rare, but within a few generations it has grown in prevalence (Morgan et al. 2018; Williams et al. 2015), and is now a global epidemic of astonishing proportions (WHO 2016). Holden et al. (2016) predict that 50% of the world’s population will be afflicted by 2050, up from 34% today and 23% in 2000. A severe form of myopia (high myopia) is associated with increased risk of vision loss through glaucoma and retinal detachment (Williams and Hammond 2019). Current myopia interventions emphasize clinical treatments rather than prevention and focus on medications and refractive correction (Cooper and Tkatchenko 2018). Uncorrected refractive error has been estimated to cost more than $200 billion annually in global GDP (Naidoo et al. 2019).
Liquid crystal technology for vergence-accommodation conflicts in augmented reality and virtual reality systems: a review
Published in Liquid Crystals Reviews, 2021
The second major challenge, vision correction (the so-called prescription problem), originates from the need for eyes to see objects and virtual images clearly when the eyes have refractive errors. Currently, a pair of personal prescription eyeglasses is one of the solutions to correct refractive errors of eyes, but this solution is incompatible with the AR and VR systems. The AR and VR optical systems are usually designed for people with 20/20 vision without considering the refractive errors in the eye [3]. Therefore, vision correction function should be designed into AR and VR optical systems with tunable optical elements. For a normal eye, light from infinity can converge at the surface of the retina, which means that the eye can clearly see objects that are far away, as shown in Figure 4(a). When the eyes have refractive errors (e.g. the cornea is curved more than required), light from infinity does not converge at the surface of the retina, as shown in Figure 4(b). When the light converges between the crystalline lens and retina, the eye can only see an object close to the eye. This condition is called near-sightedness or myopia. Similarly, when the convergent light is located outside the eyeball, the eye sees a blurry image when an object is near the eye; this condition is called far-sightedness or hyperopia. Myopia requires prescription lenses with negative focal lengths (or negative lenses, f < 0), while hyperopic condition require positive lenses (f > 0) for eye corrections. Both myopic and hyperopic eyes may have normal accommodation abilities. Another eye condition, presbyopia, mainly results from the weak accommodation ability of crystalline lenses of the eyes. From statistical results [13], the accommodation ability of crystalline lenses decreases with age, and people start to have presbyopia after 40 years of age and may eventually lose accommodation ability. People with myopia and presbyopia usually need two pairs of eyeglasses: one with positive lenses and the other with negative lenses. It is estimated that half of the world population will suffer from myopia by 2050 [14]. Based on other statistical results [15–17], the range of lens powers of prescription lenses should be from −2 diopters (D) to +2 D (i.e. 4 D in total) in order to cover the prescription lens requirements of ∼80% of the population. To cover a larger population, the range of the lens power must be larger. Thus, implementing tunable lenses in AR and VR systems to provide an appropriate lens power is one of the solutions to the prescription problem.