Visual fatigue caused by viewing stereoscopic motion images: Background, theories, and observations

Abstract

The background, theories, and observations on visual stress possibly caused by viewing stereoscopic motion images are reviewed. Visual fatigue caused by stereoscopic images is a safety issue. Fatigue is possible caused by the discrepancy between accommodative and convergence stimuli that are included in the image. Studies on accommodation and convergence are surveyed and an explanation regarding the characteristics of these functions is offered. Studies in the literature on changes in oculomotor function after viewing stereoscopic images, including changes in pupillary responses, are discussed. Evaluation of visual fatigue, particularly in relation to different methods of viewing stereoscopic displays is described.

Introduction

Visual fatigue is a wide range of visual symptoms, including tiredness, headaches, and soreness of the eyes [1]. Visual fatigue can be caused by demands on early visual functions such as focusing and converging the eyes on a near object and may also involve central cortical structures, for example, those involved in viewing a wide-field, high-contrast, geometric pattern [2]. Most visual tasks in everyday life can contribute in some way to visual fatigue, especially when the eyes are used for long periods. Visual fatigue may occur for example when doing fine work, when reading poorly printed texts and low-quality computer images, when reading in inadequate or intense lighting, and when exposed to flickering lights or to geometric patterns, as well as when a person has uncorrected ametropia. Visual fatigue can also arise when people are viewing stereoscopic motion images. Stereoscopic images used for entertainment must be particularly free of visual fatigue because they are not essential for our lives.

Visual fatigue as a topic of study came to the fore after the 1970s with the introduction of visual display units (VDUs) in the office environment [3]. As a result, international and domestic organizations such as ISO (International Organization for Standardizing) published recommendations for working environments using VDU, in order to reduce fatigue symptoms [4]. In spite of these measures, many people suffer from visual fatigue even today, although it is often said that the number of people reporting visual fatigue in the office environment has decreased since the recommendations were implemented.

Visual fatigue or asthenopia is sometimes referred to as eyestrain. Generally “strain” indicates the elastic distortion caused by “stress”. If the stress is too high, or if the stress continues for a long time, irreversible changes may result. A number of studies on myopia [5], [6], [7] has suggested that similar to mental strain, eyestrain is also a warning of possible irreversible health damage.

Symptoms of visual fatigue generally include eyestrain, dried mucus or tears around the eyelids, feeling of pressure in the eyes, ache around the eyes, discomfort when the eyes are open, hot eyes, difficulty in focusing or blurred vision, stiff shoulders, and headaches [1]. Very little is known about the mechanisms of fatigue, this is partly attributed to the fact that fatigue, and its symptoms are generally assessed subjectively. Although many studies have attempted to measure human stress/strain objectively as described below. Among the known studies on visual fatigue, Wilkins has published a book on visual stress [2]. He has proposed that when a person looks at a specific pattern (such as fine stripes), a part of the brain is strongly stimulated, resulting in migraine and/or fatigue. Wilkins has suggested that people who easily develop migraine also tend to be affected by eyestrain.

In this review, firstly, differences between natural depth perception and depth perception in stereoscopic images are described. Then, types of visual stress resulting from different instruments used for viewing stereoscopic images are identified. After that, methods of evaluating visual fatigue are discussed. Next, accommodation and convergence functions and their discrepancies are reviewed. Finally, the literature on changes in oculomotor balance and pupillary responses caused by viewing images are discussed.