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Conducting Polymers for Ophthalmic Applications
Published in Ram K. Gupta, Conducting Polymers, 2022
The eye can be split into two parts, called the anterior and posterior segments. The anterior segment includes the cornea, the iris, the ciliary body, the conjunctiva, the crystalline lens, and a chamber filled with aqueous humor [5]. The cornea is the outermost surface of the eye and consists of five layers, transparent to allow light refraction and transmission to the retina. In addition, it covers the eye surface to provide a protective layer. The iris is the colored circular part surrounding the pupil. The pupil changes its size in response to light levels, allowing the proper amount of light to reach the retina through muscular contraction and relaxation. The ciliary body produces the aqueous humor that has immunological and nutritional tasks as well as maintaining a 10–21 mmHg intraocular pressure (IOP) in a healthy eye. The conjunctiva is a clear mucous membrane that covers the front of the eye up to the cornea and the inner surfaces of the eyelids, responsible for tear production and preservation of the tear film. The human crystalline lens has a clear and biconvex shape that helps in focusing light onto the retina. The lens is flexible and can vary its shape and focusing power based on the distance between the object and the eye thanks to muscles called zonules.
Exhibition Ergonomics
Published in Prabir Mukhopadhyay, Ergonomics for the Layman, 2019
The amount of light entering the eye is controlled by the pupil or aperture in the human eye. In intense light the pupil becomes small to permit less light and in low illumination or dark environments the pupil dilates to facilitate more light so that one is able to see clearly. When a person enters from a brightly lit area to a relatively dimly lit area it takes time for the pupil to dilate (called dark adaptation). When the same person moves from a dark area to a brightly lit area the pupil takes much less time to constrict (called light adaptation). These adaptations are also facilitated by an adaptation by the nerve cells in the eyes and the brain. Along with this there are certain chemical conversions of photo chemicals of the eyes which also aid in this process of light and dark adaptation. This phenomenon has a design connect in that when you are designing exhibits in enclosed spaces, which need to be artificially illuminated, then one has to keep in mind that a person who enters the space suddenly from bright sunlight will not be able to see things properly for at least 20–25 minutes, so you need to give time for the eyes to adapt. At many venues, graded foot lighting is provided, the intensity of which gradually increases as the person walks into the space. This is to compensate for the dark adaptation of the eyes (Figure 6.4).
Optics and optical instruments
Published in Andrew Norton, Dynamic Fields and Waves, 2019
When people talk colloquially about another person’s beautiful, or piercing, or limpid eyes, they are really referring, of course, to the iris. This is the coloured diaphragm just in front of the crystalline lens that gives the eye its characteristic hue — blue, green, brown, hazel or grey, for instance. The hole at the centre of this diaphragm, which is the hole through which light enters the eye, is called the pupil. In humans, it is roughly circular; it looks black because the inside of the eye is normally dark. The amount of light entering the eye can be altered (again on instructions from the brain) by retracting or advancing the iris across the lens. The typical eye can change its pupil size from a diameter of about 2 mm in bright light, to about 8 mm in very dim light.
Capturing Luminous Flux Entering Human Eyes with a Camera, Part 1: Fundamentals
Published in LEUKOS, 2022
Siqi He, Hankun Li, Yonghong Yan, Hongyi Cai
The pupil dilates or constricts as controlled by the iris to allow more light to enter human eyes under dim ambient light conditions but prevent too much light exposure of eyes in bright light conditions. The effective pupil size in reaction to the ambient light level is determined by the corneal flux density in a non-linear relationship (Atchison et al. 2011), as shown in Fig. 6a. Corneal flux density reflects the light level at the corneal position () coming from the entire visible environment without cosine correction, which can be calculated using Equation (1), as the summation of the product of the luminance (Li) across the entire visual field and its solid angle () subtense to the eye’ nodal point. In the field measurement, a binocular luminance HDR map of the observer’s luminous environment can be used to retrieve the luminance and solid angle subtense of every pixel (as target point), to calculate the corneal flux density () value accordingly.
Bodies in mind: using peripheral psychophysiology to probe emotional and social processes
Published in Journal of the Royal Society of New Zealand, 2021
Gina M. Grimshaw, Michael C. Philipp
The pupil is the opening in the eye through which light passes to the retina. The size of the pupil is controlled by two sets of muscles in the iris. Contraction of the sphincter muscle (under parasympathetic control) constricts the pupil, while contraction of the dilator muscle (under sympathetic control) widens it (see Wang and Munoz 2015, for further review of pupil physiology). Changes in pupil diameter affect vision: constricted pupils are optimised for visual acuity (i.e. sharp visual focus) whereas dilated pupils are optimised for visual sensitivity (i.e. detection of faint stimuli). The parasympathetic pathway mediates the light reflex, a rapid constriction of the pupil that occurs when light levels suddenly increase. The sympathetic pathway, in contrast, acts more slowly to dilate the pupil when people engage with important, interesting, or emotional stimuli (Hess and Polt 1964; Bradley et al. 2008). This pathway is under control of the locus coeruleus, a neural structure that plays an important role in alertness and waking via modulation of norepinephrine (Aston-Jones and Cohen 2005). In different experimental contexts, pupil dilation can be a physiological outcome of both cognitive effort (Kahneman and Beatty 1966; Einhauser 2017) and emotional arousal (Hess and Polt 1964; Bradley et al. 2008). Relative changes in pupil dilation can be measured with most eye-trackers, meaning that pupillometry can be easily integrated into lab-based experiments of visual perception (Sirois and Brisson 2014; Mathôt 2018).
A computational model of pupil dilation
Published in Connection Science, 2018
Birger Johansson, Christian Balkenius
The largest change in pupil dimeter is caused by light changes that elicit the pupil light reflex (Ellis, 1981; Hess & Polt, 1960; Heller, Perry, Jewett, & Levine, 1990; Hess & Polt, 1964; Woodhouse & Campbell, 1975). Although the pupil diameter can vary between 2 and 8 mm (Pamplona et al., 2009; Watson & Yellott, 2012), in normal light conditions it is around 3 mm (Wyatt, 1995), and a flashing bright light will give a contraction of 0.2–2.5 mm depending of the light intensity (Ellis, 1981). Ellis (1981) reported a latency of the light reflex at a minimum 220 ms and suggested that this was mainly due to slow muscle constriction. After constriction is complete, the pupil will dilate again and return to its initial size. Interestingly, the contraction of the pupil is approximately three times faster than the subsequent dilation. A higher light intensity reduces the latency of pupil contraction and the maximum constriction velocity increases with increasing stimulus intensity (Ellis, 1981; Pamplona et al., 2009).