Image, eye, and retina (invited review)

Recent trends and advances in fundus image analysis: A review

Automated retinal image analysis holds prime significance in the accurate diagnosis of various critical eye diseases that include diabetic retinopathy (DR), age-related macular degeneration (AMD), atherosclerosis, and glaucoma. Manual diagnosis of retinal diseases by ophthalmologists takes time, effort, and financial resources, and is prone to error, in comparison to computer-aided diagnosis systems. In this context, robust classification and segmentation of retinal images are primary operations that aid clinicians in the early screening of patients to ensure the prevention and/or treatment of these diseases. This paper conducts an extensive review of the state-of-the-art methods for the detection and segmentation of retinal image features. Existing notable techniques for the detection of retinal features are categorized into essential groups and compared in depth. Additionally, a summary of quantifiable performance measures for various important stages of retinal image analysis, such as image acquisition and preprocessing, is provided. Finally, the widely used in the literature datasets for analyzing retinal images are described and their significance is emphasized.

Visual Adaptation to Scattering in Myopes

Myopes exhibit a larger capability of adaptation to defocus. Adaptation produces a boost in visual performance that can be characterized through different metrics. The ability of myopes to adapt to other sources of blur, such as diffusion, has not been studied so far. In this work, a group of 20 myopes with normal vision underwent high-contrast visual acuity (VA) measurements under different viewing conditions, wearing their refractive correction with or without a diffuser (Bangerter filter, BF). VA decreased immediately after wearing the BF of density 0.6, showing a significant relationship with the ocular refraction. After 40 minutes of binocular vision through the BF, a statistically significant increase (p = 0.02) in VA from 0.54 to 0.62 in decimal scale (from 0.3 to 0.2 logMAR) was obtained. No correlation with the refraction was observed. After removing the diffuser, VA returned to baseline. A control group (17 subjects) underwent the same experimental protocol but without diffuser filters. No significant changes in VA were found in this group. We describe a new type of contrast adaptation to blur in myopes caused by scattering, rather than by defocus. The effects of low scattering levels in vision might be relevant in the analysis of early stage of cataract, amblyopia treatments, and myopia understanding.

Microscopic anatomy of sensory receptors

Experiences following stimulation of the senses have been recorded for millennia, and they could be related to the gross anatomy of the sense organs. Examination of their microanatomy was to await the development of achromatic microscopes in the early nineteenth century. Among the microscopic structures that were isolated and described were specialized sensory cells, called receptors, and they could be related to the stimuli that excited them. Those located in well-defined sense organs (like the eyes, ears, nose, and tongue) were named on the basis of their morphology, whereas the receptors in or beneath the surface of the skin were generally named after those who first described them. Illustrations of early representations of sensory receptors are combined with "perceptual portraits" of the microanatomists who described them.

Head-mounted eye gaze tracking devices: An overview of modern devices and recent advances

An increasing number of wearable devices performing eye gaze tracking have been released in recent years. Such devices can lead to unprecedented opportunities in many applications. However, staying updated regarding the continuous advances and gathering the technical features that allow to choose the best device for a specific application is not trivial. The last eye gaze tracker overview was written more than 10 years ago, while more recent devices are substantially improved both in hardware and software. Thus, an overview of current eye gaze trackers is needed. This review fills the gap by providing an overview of the current level of advancement for both techniques and devices, leading finally to the analysis of 20 essential features in six head-mounted eye gaze trackers commercially available. The analyzed characteristics represent a useful selection providing an overview of the technology currently implemented. The results show that many technical advances were made in this field since the last survey. Current wearable devices allow to capture and exploit visual information unobtrusively and in real time, leading to new applications in wearable technologies that can also be used to improve rehabilitation and enable a more active living for impaired persons.

Receptor Visionaries

Sensory receptors were described and illustrated after they had been observed with the aid of microscopes. Most descriptions were made in the 19th century after the introduction of achromatic lenses in microscopes. In some senses (like vision), receptors were named according to their morphology whereas in others (like touch), they are known by the names of those who initially described them. Illustrations of the receptors from original sources are here combined with portraits of their originators.

Dancing letters'and ticks that buzz around aimlessly: on the origin of crowding

When we see an object, we know where it is. Or do we? Perhaps not in indirect vision, as was observed by the gestalt psychologist Korte in 1923. Objects and object parts appear to 'dance around', and these phenomena may underlie a part of what is called the crowding effect today. From Korte's account of pattern recognition in indirect vision, I select two phenomena: a loss of the positional code for letter parts and a loss of the same for whole letters. Using these examples, I present a novel, speculative explanation for a contradiction in the literature: patterns located more peripherally than a target show more interference than do more centrally located patterns, yet for whole-letter confusions the asymmetry is the other way round. The inward, not the outward, flanker is increasingly confused with a target at increasing target eccentricities. I propose that feature-binding decreases with eccentricity such that free-floating letter parts more often intrude from the periphery and whole letters from the centre. I conclude with a few remarks on computational modelling as, hopefully, a challenge to neural computationalists.

Does print size matter for reading? A review of findings from vision science and typography

The size and shape of printed symbols determine the legibility of text. In this paper, we focus on print size because of its crucial role in understanding reading performance and its significance in the history and contemporary practice of typography. We present evidence supporting the hypothesis that the distribution of print sizes in historical and contemporary publications falls within the psychophysically defined range of fluent print size--the range over which text can be read at maximum speed. The fluent range extends over a factor of 10 in angular print size (x-height) from approximately 0.2° to 2°. Assuming a standard reading distance of 40 cm (16 inches), the corresponding physical x-heights are 1.4 mm (4 points) and 14 mm (40 points). We provide new data on the distributions of print sizes in published books and newspapers and in typefounders' specimens, and consider factors influencing these distributions. We discuss theoretical concepts from vision science concerning visual size coding that help inform our understanding of historical and modern typographical practices. While economic, social, technological, and artistic factors influence type design and selection, we conclude that properties of human visual processing play a dominant role in constraining the distribution of print sizes in common use.

Optics of human eye: 400 years of exploration from Galileo's time

We present a brief historical background and a description of the main features of the eye's optical properties: the eye is a simple, but rather optimized, optical instrument. It is only since Galileo's time that the importance of the eye as a part of different optical instruments has driven a continuous scientific exploration of ocular optics. In the past decade, the use of wavefront sensing technology allowed us to complete our understating of eye optics as a robust aplanatic system.

Binocular Vision: Defining the Historical Directions

Ever since Kepler described the image-forming properties of the eye (400 years ago) there has been a widespread belief, which remains to this day, that an object seen with one eye is always seen where it is. Predictions made by Ptolemy in the first century, Alhazen in the eleventh, and Wells in the eighteenth, and supported by Towne, Hering, and LeConte in the nineteenth century, however, are contrary to this claimed veridicality. We discuss how among eighteenth-and nineteenth-century British researchers, particularly Porterfield, Brewster, and Wheatstone, the erroneous idea continued and also why observations made by Wells were neither understood nor appreciated. Finally, we discuss recent data, obtained with a new method, that further support Wells's predictions and which show that a distinction between headcentric and relative direction tasks is needed to appreciate the predictions.

Galileo's eye: a new vision of the senses in the work of Galileo Galilei

Reflections on the senses, and particularly on vision, permeate the writings of Galileo Galilei, one of the main protagonists of the scientific revolution. This aspect of his work has received scant attention by historians, in spite of its importance for his achievements in astronomy, and also for the significance in the innovative scientific methodology he fostered. Galileo's vision pursued a different path from the main stream of the then contemporary studies in the field; these were concerned with the dioptrics and anatomy of the eye, as elaborated mainly by Johannes Kepler and Christoph Scheiner. Galileo was more concerned with the phenomenology rather than with the mechanisms of the visual process. His general interest in the senses was psychological and philosophical; it reflected the fallacies and limits of the senses and the ways in which scientific knowledge of the world could be gathered from potentially deceptive appearances. Galileo's innovative conception of the relation between the senses and external reality contrasted with the classical tradition dominated by Aristotle; it paved the way for the modern understanding of sensory processing, culminating two centuries later in Johannes Müller's elaboration of the doctrine of specific nerve energies and in Helmholtz's general theory of perception.

An ancient eye test--using the stars

Vision testing in ancient times was as important as it is today. The predominant vision testing in some cultures was the recognition and identification of constellations and celestial bodies of the night sky. A common ancient naked eye test used the double star of the Big Dipper in the constellation Ursa Major or the Big Bear. The second star from the end of the handle of the Big Dipper is an optical double star. The ability to perceive this separation of these two stars, Mizar and Alcor, was considered a test of good vision and was called the "test" or presently the Arab Eye Test. This article is the first report of the correlation of this ancient eye test to the 20/20 line in the current Snellen visual acuity test. This article describes the astronomy, origin, history, and the practicality of this test and how it correlates with the present day Snellen visual acuity test.

Vision and visualization

The art of visual communication is not restricted to the fine arts. Scientists also apply art in communicating their ideas graphically. Diagrams of anatomical structures, like the eye and visual pathways, and figures displaying specific visual phenomena have assisted in the communication of visual ideas for centuries. It is often the case that the development of a discipline can be traced through graphical representations and this is explored here in the context of concepts of visual science. As with any science, vision can be subdivided in a variety of ways. The classification adopted is in terms of optics, anatomy, and visual phenomena; each of these can in turn be further subdivided. Optics can be considered in terms of the nature of light and its transmission through the eye. Understanding of the gross anatomy of the eye and visual pathways was initially dependent upon the skills of the anatomist whereas microanatomy relied to a large extent on the instruments that could resolve cellular detail, allied to the observational skills of the microscopist. Visual phenomena could often be displayed on the printed page, although novel instruments expanded the scope of seeing, particularly in the nineteenth century.