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CHAPTER ONE

INTRODUCTION

  • Background of the Study

Computer Vision Syndrome (CVS) is characterized by visual symptoms which result from interaction with computer display or work environment. In most cases, symptoms occur because the visual demands of the task exceed the visual abilities of the individual to comfortably perform the task, the visual problems occur frequently among users of digital devices. Vision problems are pervasive among computer operators and are the source of operator discomfort and decrease work performance. There appears to be a communication gap regarding the nature and extent of vision problems related to users of digital devices. The vision experienced by users of digital devices is varied and are difficult to grasp and understand by those who do not specialize in vision.

The awareness of tear film stability and its effects on the public’s health will aid in proper management and prevention which most definitely will foster economic growth. The economic significance of this is that, users of digital devices will have increase in service productivity as a result of the preventive measure taken against tear film instability. It is therefore against this background that the vast majority of digital devices users have eye symptoms and thus seek eye examinations in order to improve upon their work output and achieve a more comfortable work environment. In addition, there is a large percentage of the prevalence of ocular symptoms in computer users, forming the bulk of computer vision syndrome.

Worth mentioning is the fact that, previous researches have affirmed that there is the association of physiological dysfunction with the use of the computer technology. Hence, for the everyday users of digital devices, the presence and indeed prevalence of tear film instability is not farfetched. Treatment and management of tear film instability involves management of dry eye syndrome alongside other complications of the condition.

The eye should be protected with adequate eye wears in cases not revealing adverse symptomatic conditions. Glasses and low aids are also indicated in cases of refractive errors and low vision. Consequently, presbyopia (an eye condition prevalent in the elderly) should be managed adequately with bifocals and single vision in non-presbyopes as the case may imply. Some other simple practices that can reduce, or even prevent the effects of computer vision syndrome are; Making sure the lighting in the room is comfortable on the eyes to prevent you from staring into glare on the computer screen, positioning the computer screen so that your head is in a naturally comfortable position while working, taking breaks that is looking away from the computer for a few minutes can go a long way when it comes to the eyes. Also, making sure your seat is comfortable. A comfortable chair with support for the neck and back will help the operator avoid neck and shoulder strain commonly associated with computer vision syndrome.

The Precorneal Tear Film

This is the liquid layer bathing the cornea and conjunctiva. It creates a perfectly smooth liquid outer layer that polishes the corneal surface, mechanically traps and flushes out foreign bodies and chemicals, contains bacterio-static substances that inhibit the growth of microorganisms and reduces the surface friction associated with blinking and eye movement.

The tear film itself serves as the anterior refracting surface of the eye in conjunction with the corneal epithelial membrane which it baths (i.e. the anterior corneal surface), providing the first interface between air and liquid medium. It also plays a role in maintaining hydration of the cornea by means of changes in the toxicity of the tear film secondary to the evaporation of the tear layer.

The tear film also serves as the primary source of oxygen for the cornea. Oxygen from the atmosphere is dissolved within tears and is available for uptake by the corneal cells to support the normal aerobic metabolism of the corneal epithelium.

The tear contains at least three (3) anti-bacterial substances; lysozyme and lactoferrin that helps protect the ocular surface against infection. Among its protective function, it lubricates the lids and the corneal surface and also plays an important role in the healing of central wounds of the vascular cornea, providing a pathway for white blood cell from the corneal-conjunctival circulation to reach the central cornea (Albarran et al, 1997).

The Tear Film Structure and Function

          The tear film is a dynamic structure that serves multiple functions to maintain the health of the ocular surface, protect it against noxious influences, repair damage and create an optically clear and stable anterior-refracting surface of the eye to sub-serve clear vision.

This structure of the tear film is thought to be that of a meta-stable film between blinks consisting of three major components; an innermost membrane-spanning mucin layer contributing to the structure of the epithelial cell surface and anchoring the overlying aqueous gel are produced by the goblet cells of the conjunctiva and stabilize the tear film, interact with the outermost lipid layer and serve to cleanse the surface by wiping away debris, exfoliating cells and microbial contaminants. The lipid layer produced by the meibomiam glands of the eyelids retards evaporative tear loss and with the gel forming mucins provides lubrication between lids and the ocular surface.

The aqueous component of the tears produced by the main accessory lacrimal glands contains all the water-solube elements of the tears including electrolytes and hundreds of proteins and peptides. Although there is a resident population of a few relatively stable proteins, for example, – albumin, lipocalin, lysozyme, lactoferrin etc, many represent cytokines, growth factors and other groups of agents normally present in only nanogram quantities or absent and can increase in response to disease, injury, or environmental stress; for example IgE in ocular allergy. This exquisitely balanced and responsive system is referred to as the Lacrimal Functional Unit (LFU) – (Pflugfelder & Stern 2010) and is linked by a neural network consisting of several sensory receptors, afferent nerve fibres to the central nervous system, and efferent fibres to the lacrimal and meibomian glands. The communication between the structure of the ocular surface and glandular structures regulate secretory activity in response to disease, injury and environmental stress. Breakdown in one or more of these elements can lead to mild-to-severe dysfunction of the tear film and ocular surface, which is the hallmark of dry eye disease (Craig, Tomlinson & McCam, 2010).

Tear Production

The lacrimal gland is located in the superolateral aspect of the eyelid below the eyebrow(s). It secretes watery (aqueous) tears and produces about 0.2 ml of tears in 24 hours. Aqueous tears flow downward and inward toward the tear drainage system at the inner canthus. In addition to aqueous tears, several glands located in the conjunctiva and eyelid margins secrete oily and sticky (mucous) tears. The meibomian glands are located within the tarsal plate of the eyelid and secrete oily tears. The glands of Zeiss, Moll, Wolfing, and Krause secrete sticky tears. These three types of tears provide moisture and protection to the surface of the eye(s). With each blink, tears are pushed across the eye toward the puncta located at the medial junction of the upper and lower eyelids. From the puncta, tears are pushed into the canaliculi and then into the lacrimal sac. They are drained from the lacrimal sac and nasolacrimal duct to the inside of the nose and down the throat.

 

 

Tear Breakup Time

Tear breakup time (TBUT) is a clinical test used to assess for evaporative dry eye disease.  To measure TBUT, fluorescein is instilled into the patient’s tear film and the patient is asked not to blink while the tear film is observed under a broad beam of cobalt blue illumination.  The TBUT is recorded as the number of seconds that elapse between the last blink and the appearance of the first dry spot in the tear film, as seen in this progression of these slit lamps photos over time.  A TBUT under 10 seconds is considered abnormal.  This patient also has punctate epithelial erosions (PEE) that stain positively with fluorescein, another sign of ocular surface dryness.

Schirmer Test

A Schirmer’s test is used to assess how quickly the eyes produce tears. The test is most commonly used to diagnose dry eyes. Dry eye occurs when the tear glands are unable to produce enough tears to keep the eyes moist and healthy. The results of the Schirmer’s test help the eye doctor to determine whether the eyes are producing too much tears or too few tears (Scot et al., 2004).

The eye doctor will order a Schirmer’s test if he suspects that the eyes are producing too many or too few tears. The test may be done on one eye or both eyes, but it is typically done on both. Abnormal test results will prompt the eye doctor to look for the underlying cause of the condition (Lemp, 1995). The low cost and simplicity of Schirmer test makes itself the most commonly used screening test for assessment of tear production, named after Schirmer who brought the test forward for the first time in 1903.

Schirmer test was divided into Schirmer I test and Schirmer II test. Schirmer II test is performed by irritating the nasal mucosa with a cotton-tipped applicator prior to measuring tear production, which is mainly used for measuring the reflex tear secretion of main lacrimal gland. S I t has two branches: S I t without anesthesia and with topical anesthesia. When performed without anesthesia, the S I t measures the basal tear secretion and the function of the main lacrimal gland whose secretory activity is stimulated by the irritating nature of the filter paper. S I t performed after topical anesthesia measures the function of the basal lacrimal secretion (Lemp, 1995). The critical value for diagnosis has not yet been unified. Lemp et al. (2010) defined anomaly area of S per 5 minutes t without anesthesia to be <10mm per 5 minutes and ≤5.5mm per 5 minutes respectively and a cutoff ≤5.0mm per 5 minutes is always recommended currently (Lemp, 1995). Vitali (1994) presented that the cut-point of basal S I t should be set at 10mm per 5 minutes.

The Effects of the Tear Film destabilization

The tear film has three distinct layers. The outermost layer is secreted by the meibomian glands. This lipid layer prevents evaporation of the underlying tear layers, keeping the cornea continually moist. The middle layer consists of aqueous tears from the lacrimal gland. These tears provide nutrients that help sustain the health of the cornea. The innermost layer is composed of mucous, which provides stability to the tear film as well as lubrication and also functions to trap and remove debris.

Quality of vision is affected by the stability of the tear film (Igwe, 1999). “Crocodile tears syndrome”, also known as Bogorad’s syndrome, is an uncommon consequence of nerve regeneration subsequent to Bell’s palsy or other damage to the facial nerve in which efferent fibers from the superior salivary nucleus become improperly connected to nerve axons projecting to the lacrimal glands, causing one to shed tears (lacrimate) during salivation while smelling foods or eating. It is presumed that one would also salivate while crying due to the inverse improper connection of the lacrimal nucleus to the salivary glands, but this would be less noticeable (Strughold, 2003).

Keratoconjunctivitis sicca, known as dry eye, is a very common disorder of the tear film. However, sufferers can experience watering of the eyes, which is in fact a response to irritation caused by the original tear film deficiency. Lack of Meibomian gland secretion can mean the tears are not enveloped in a hydrophobic film coat, leading to tears spilling onto the face. Familial dysautonomia is a genetic condition that can be associated with a lack of overflow tears (alacrima) during emotional crying (Prydal et al., 2006).

Obstruction of the punctum, nasolacrimal canal, or nasolacrimal duct can cause even normal levels of basal tear to overflow onto the face (epiphora), giving the appearance of constant psychic tearing. This can have significant social consequences.

Socially, in nearly all cultures, crying is seen as a specific act associated with tears trickling down the cheeks and accompanied by characteristic sobbing sounds. Emotional triggers are most often sadness and grief but crying can also be triggered by anger, happiness, fear, laughter or humor, frustration, remorse, or other strong, intense emotions. In many cultures, crying is associated with babies and children.

Some cultures consider crying to be undignified and infantile, casting aspersions on those who cry publicly except if it is due to the death of a close friend or relative. In most cultures, it is more socially acceptable for women and children to cry than men. In some Latin regions, crying among men is acceptable (Prydal et al., 2006).

Some modern therapy movements such as Re-evaluation Counseling teach that crying is beneficial to health and mental well-being, encouraging it positively (Lemp et al., 2000). An insincere display of grief or dishonest remorse is sometimes called crocodile tears in reference to an Ancient Greek anecdote that crocodiles would pretend to weep while luring or devouring their prey (Prydal et al., 2006). In addition, in medical terms, someone is said to have crocodile tears syndrome as an uncommon consequence of recovery from Bell’s palsy, in which faulty regeneration of the facial nerve causes sufferers to shed tears while eating.

1.2     Statement of the Problem

Viewing a digital device screen is different from viewing a typewritten or printed page. Often, the output on the digital device screen is not as precise or sharply defined, as the level of contrast of the letters to the background is reduced and the presence of the glare and the reflections on the screen may make viewing difficult. Computer screens cause a great amount of constant focus for eyes. Focusing a monitor for too long can cause the muscles in the eyes to become fatigued (Caldwell, 2010). Constant computer usage has been recorded to significantly decrease rate of blinking among workers (Caldwell, 2010). While this may not seem like a major complication, regular blinking protects the eyes by keeping them moist and functioning properly. Overuse and dryness can cause damage to the eye itself and muscles within, leading to strain or may reduce vision permanently (Caldwell, 2010). In the light of this, this study tends to evaluate the tear film stability amongst users of digital devices.

1.3     Objectives of the Study

  1. To determine the effect of digital devices on tear secretion
  2. To determine the effect of digital devices on tear stability

1.4     Research Questions

  1. What is the effect of digital devices on tear secretion?
  2. What is the effect of digital devices on tear stability?

1.5     Research Hypotheses

  1. H0: There is no significant effect of digital devices on tear secretion

H1: There is a significant effect of digital devices on tear secretion

  1. H0: There is no significant effect of digital devices on tear stability

H1: There is a significant effect of digital devices on tear stability

1.6     Significance of the Study

This study will help Digital devices users to understand the relevance of good vision and ergonomics as it relates to the unique demands of digital device use. Consequently, this study will serve as a tool for subsequent research and improvement in the healthcare sector. This study will also provide and disseminate information to policy makers in order to monitor and offer its guidelines in the development of policies or legislation related to the regulation of digital use.

1.7     Scope and Limitation of the Study

The scope of the study is limited to randomly selected volunteers of Imo State University vicinity aged 18-50 years.

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