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DISTRIBUTION OF HABITUAL LATERAL PHORIA AMONG UNDERGRADUATES WITHIN THE AGE BRACKET OF 18-30 YEARS IN MADONNA UNIVERSITY NIGERIA, ELELE CAMPUS, RIVERS STATE. 

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                                                   ABSTRACT

This descriptive cross sectional study was to determine the distribution of habitual lateral phoria among undergraduates in Madonna University Nigeria, Elele campus, Rivers state. Subjects were screened and ascertained pathologically free and their lateral habitual phoria status was determined using Von Graefe technique. A total of 350 students participated in the study within the age range of 18-30years and mean age (22.04) and Standard Deviation of (±2.74). Male were 171 (48.9%) and Females were 179 (51.1%) of the population. Out of 350 students, 22 (6.3%) were emmetropes, 210 (60.0%) were myopes, 100 (28.6%) were hyperopes and 18 (5.1%) were astigmats. It was found that vast majorities of the students were exophoric 179 (51.1%) at distance, followed by esophoria 111 (31.7%) and then orthophoria 60 (17.1%), At near most of the students had exophoria 224 (64.0%), followed by esophoria 95 (27.1%) and then orthophoria 31 (3.9%).The participants’ refractive errors (simple myopia, simple hyperopia and astigmatism) showed significant difference in the habitual lateral phoria of students both at far and at near (p ˂ 0.05). The correlation of participants’ ages with habitual lateral phorias both at far and near respectively revealed significant relationship (p ˂ 0.05). Statistical analysis revealed no significant relationship between habitual lateral phorias both at far and near with participant’s gender (p ˃ 0.05). A vast majority of the subjects were exophoric both at distance and near in this study. Therefore, there is a need to perform heterophoria measurements on every patient (symptomatic or asymptomatic) because in some asymptomatic patients, symptoms may occur after extended near work especially if the relevant compensatory mechanism is not adequate.

CHAPTER ONE

• INTRODUCTION

Heterophoria often simply called phoria has been defined in many ways by researchers. Heterophoria also known as ‘latent strabismus’ is a condition in which the tendency of the eyes to deviate is kept latent by fusion. Therefore, when the influence of fusion is removed the visual axis of one eye deviates away (Khurana, 2012).

Phoria is also defined as a non-primarily existing ocular deviation but a reaction to an interruption of the sensory-motor-feedback control system (Kommerel & Kromeier, 2002).

Heterophoria can be vertical, horizontal or cyclophoria. A small heterophoria is present in 70-80% of the population (Kommerel & Kromeier, 2002).

• LATERAL PHORIA

Lateral phoria is the tendency of the eyes to want to turn more inward or outward than necessary when an individual is viewing an object at near or at distance which may cause the individual to experience eyestrain and other symptoms (Garin, 2017). Lateral phoria can be classified as follows:

• ESOPHORIA:

It is tendency of the eyes to want to turn more inward than necessary when an individual is viewing an object at near or at distance which may cause the individual to experience eyestrain and other symptoms (Garin, 2017). It is usually due to an excess of convergence, divergence insufficiency more marked for distant vision (Ahmed, 2011). It is also usually associated with excessive accommodation and hence common in hypermetropia (Ahmed, 2011). Other causes include high (accommodative convergence/ accommodation) AC/A ratio, weak negative fusional reserves, narrow interpupillary distance and extrinsic muscle weakness (Ahmed, 2011).

Types of esophoria

1. Convergence excess type (esophoria greater for near than distance).
2. Divergence weakness type (esophoria greater for distance than near).
3. Non- specific type; esophoria which does not vary significantly in degree for any distance (Khurana, 2012).
4. EXOPHORIA:

It is tendency of the eyes to want to turn more outward than necessary when an individual is viewing an object at near or at distance which may cause the individual to experience eyestrain and other symptoms (Garin, 2017). It is more common in myopes and occasionally in presbyopes and anisometropes (Ahmed, 2011). It is usually due to divergence excess more marked for distant vision and may be due to convergence insufficiency. It may also be caused by weak positive fusional reserves, wide interpupillary distance and extrinsic muscle weakness (Ahmed, 2011).

Types of exophoria

Convergence weakness type (exophoria greater for near than distance).

1. Divergence excess type (exophoria greater on distant fixation than the near).
2. Non- specific type; exophoria which does not vary significantly in degree for any distance (Khurana, 2012).
   • Measurement of Lateral Phoria

Lateral phoria measurement is very vital during binocular vision assessment as its values are used in the diagnosis of binocular vision anomalies such as divergence excess and convergence insufficiency. There are several methods used clinically to evaluate lateral phorias. In all of these methods fusion must first be broken to achieve dissociation of the eyes, allowing evaluation of lateral phoria (Goss, 1995). The methods may differ in the ability to control accommodation adequately in the level of proximal convergence induced and in the method by which lateral phoria is quantified. The duration and the degree of dissociation when fusion is disrupted will also affect the measurements in that a longer duration of dissociation will increase vergence adaptation (Rainley et al., 1998). Therefore lateral phoria values may vary from one procedure to another.

Decompensated lateral phoria is associated with several symptoms such as photophobia, eyestrain, headaches, decreased stereopsis, pain in the eyes, diplopia, poor visual performance (Kaimbo & Missotten, 2003). Hasebe et al. (2001) reported that fatigue reduces tonic accommodation; therefore individuals such as students who are exposed to a lot of near work are likely to have decompensated lateral phorias which may result in symptoms.

1.1 Statement of Problem

Phoria is a physiological function rather than being pathological and is present in every human eye arising from malformation of the fusion mechanism and so may vary with different refractive status. Decompensated lateral phorias may become significant after a working day and they can result in ocular symptoms and visual discomfort. Clinically, significant lateral phorias are symptomatically manifested as asthenopia (Eye strain) pain in eyes, headache, blurred vision, diplopia, decreased stereopsis and poor reading performance. Lateral phoria is common even amongst individuals who have normal visual mechanisms and will not be a source of discomfort unless fusional reserves are inadequate. This study estimated the distribution of lateral phoria status among undergraduates in Madonna University Nigeria, Elele Campus, Rivers State.