China 
Africa 
Explore chapters and articles related to this topic
Visual Perception
Published in Robert W. Proctor, Van Zandt Trisha, Human Factors in Simple and Complex Systems, 2018
Robert W. Proctor, Van Zandt Trisha
For nearsightedness, or myopia, the eye is too long, resulting in a focal point that is in front of the receptors when the lens is relaxed. For farsightedness, or hyperopia, the eye is too short, resulting in a focal point that is behind the receptors when the lens is fully flexed. As people become older, the speed and extent of their accommodation decrease continually. With age, the lens becomes harder and less responsive to the pulls of the muscles in the eye, so accommodative ability decreases and essentially all people become hyperopic. This condition is called presbyopia, or old-sightedness. The near point can increase from as close as 10 cm for 20-year-olds to as far as 100 cm by age 60. Presbyopia can be corrected with reading glasses or bifoc als, which typically are not prescribed until age 45 years or older. A person can have perfect vision in all other respects but still need reading glasses to compensate for the decreased accommodative ability of the lens.
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.
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.