COMPARATIVE ANALYSIS OF AMPLITUDE OF ACCOMMODATION AND BINOCULAR CROSS CYLINDER METHOD IN DETERMINATION OF READING ADD

ABSTRACT

This study was carried out to compare the amplitude of accommodation and binocular cross cylinder methods in determination of reading Add. A total of sixty two (62) presbyopic subjects where used and thirty were males and thirty were females. Amplitude of accommodation and binocular cross cylinder test were performed and the reading add were determined using amplitude of accommodation and binocular cross cylinder methods. The mean add determined through the amplitude of accommodation were 1.39 ± 0.57 and the mean add determined through the binocular cross cylinder were 1.89 ± 0.59. statistically software using pared sample T-test at 0.05 level of confidence and 95% confidence interval showed that there was a significantdifference (P<0.05) in obtaining the reading add using the amplitude of accommodation and binocular cross cylinder method. Reading add determined through binocular cross cylinder method provides a tentative reading add closer to the final reading add than the reading add determined through the amplitude of accommodation method. Binocular cross cylinder method should be used when determining reading Addition for presbyopes since it gives a tentative reading Addition closer to the final reading Addition for presbyopic subjects.

TABLE OF CONTENTS

Cover Page                                                                                                                           i

Title Page                                                                                                                              ii

Certification                                                                                                                         iii

Dedication                                                                                                                            iv

Acknowledgement                                                                                                            v

Table of contents                                                                                                               vi

List of Tables                                                                                                                        x

Abstract                                                                                                                                xi

CHAPTER ONE: INTRODUCTION                                                                                  

• Background of Study 2
• Statement of Problem 14

1.3        Objective of Study                                                                                              15

1.4        Research Questions                                                                                            15

1.5        Research Hypothesis                                                                                          16

1.6        Significance of Study                                                                                          16

1.7        Scope of Study                                                                                                     16

1.8        Limitation of Study                                                                                              17

CHAPTER TWO

Literature Review                                                                                                               18

CHAPTER THREE: MATERIALS AND METHOD                                                         

3.1        Area of Study                                                                                                        23

3.2        Research Design                                                                                                   23

3.3        Population of Study                                                                                            24

3.3.1     Inclusion Criteria                                                                                                  24

3.3.2     Exclusion Criteria                                                                                                 24

3.4        Sample Size Determination                                                                              24

3.5        Sampling Technique                                                                                           26

3.6        Instruments for Data Collection                                                                      26

3.6.1     Validation of Instrument                                                                                   26

3.7        Procedure for Data Collection                                                                         27

3.8        Procedures for Data Analysis                                                                           27

3.9        Ethical Consent                                                                                                     28

CHAPTER FOUR: RESULTS                                                                                                              

4.1        Presentation of Data                                                                                          29

4.2        Testing of Hypothesis                                                                                         41

CHAPTER FIVE: DISCUSSION                                                                                         

5.1        Contribution of knowledge                                                                              44

CHAPTER SIX: CONCLUSION AND RECOMMENDATION                                     

6.1        Conclusion                                                                                                             45

6.2        Recommendation                                                                                                45

REFERENCE                                                                                                                          46

APPENDICES                                                                                                                        49

LIST OF TABLES

Table 4.1:     Age Distribution of subjects                                                                         29

Table 4.2:     Age and gender distribution of subjects.                                                 30

Table 4.3:     Statistical data on Age of subjects                                                              31

Table 4.4:     Statistical data on AA and BCC of subjects                                               32

Table 4.5:     Statistical data on Add with AA and BCC of subjects                            33

Table 4.6:     Distribution of reading add using amplitude of accommodation     34

Table 4.7:     Gender distribution of amplitude of accommodation values            35

Table 4.8:     Gender distribution of binocular cross cylinder values                        36

Table 4.9:     Distribution of reading add using amplitude of accommodation     37

Table 4.10:   Gender distribution of reading add using binocular cross cylinder  38

Table 4.11:   Statistical data on AA and BCC of subjects                                               39

Table 4.12:   Statistical data on Add with AA and BCC of subjects                            40

CHAPTER ONE

INTRODUCTION

Aging is a normal physiological process, which is associated with changes in the functional capacity of the body. All vital organs of the body begin to lose function as one gets older. And therefore, the effect of aging on vision (the eye) cannot be over emphasized. The most distressing challenge an emmetropic aging adult (mostly from 42 years) has is difficulty in continuing to read tiny prints at hitherto, normal range of near distances (25cm – 60cm). This condition is known as presbyopia.

Caring for patients with presbyopia requires appropriate eye examination and management procedures to reduce the potential visual disabilities associated with presbyopia.Optometrists play an important role in evaluating patients with symptoms or functional disability resulting from presbyopia, an expected vision change that,in some way, affects everyone at some point in adult life.

Vision is the ability to see and the eye is the sense organ responsible for vision. Clinically, it is classified as far and near vision. It is termed far when an object of regard is at 6m and beyond, near when an object is at 40cm. near vision task may include reading, writing, needle work, computing etc. which are all performed at 40cm distance. To achieve clear retina image at 40cm, the mechanism of accommodation must come into play and this is necessary to enable an individual do near work comfortably (Nwala et al., 2015).

Accommodation has been define as the process whereby changes in the dioptric power of the crystalline lens occurs so that an in-focus retinal image of an object of regard at near (40cm) is obtained and maintained at the eyes high resolution area (Nwala et al., 2015). Accommodation is achieved by fine adjustment brought about by a change in the shape of crystalline lens. The cilliary muscle is the active element which facilitates the anatomical changes that occur during accommodation. During accommodation, the cilliary muscle contracts pulling the cilliary ring forward and inward, relaxing the tension on the zonule of zinn while the shape of the crystalline lens (especially of its anterior surface) changes, rounding up and becoming more convex. As a result, the power of the crystalline lens increases bringing about a clearer near vision (Millodot, 2004).

Presbyopia is an age-related progressive loss of crystalline lens power of accommodation resulting in the inability to focus at near distance (Emerole et al., 2014). The ability of the eye to focus clearly for objects at various distances is called accommodation (Grosvenor, 2007). Presbyopia is an aging alteration causing a gradual reduction in near vision which is initially noticed at the age of 45-45 years.

1.1   BACKGROUND OF STUDY

Presbyopia is an age-related progressive crystalline lens power of accommodation resulting in the inability to focus at near distances (Emerole et al; 2014). It is a slow, normal naturally occurring age-related irreversible reduction in maximal accommodative amplitude (recession of near point) sufficient to cause symptoms of blurred vision and eye discomfort or asthenopia at customary near working distance (Nwala et al., 2005), clinically, presbyopia can be defined as a condition whereby the amplitude of accommodation diminishes with increasing age to a point where comfortable or clear vision at near is no longer achieved by mechanism of accommodation (Nwala et al., 2015). The term presbyopia mean “old eye” and is a vision condition involving loss of the eyes ability to focus on close objects. It is a condition that occurs as a part of normal aging and is not considered to be an eye disease. Presbyopia is characterized by long sightedness caused as a result of aging. Presbyopia involves the normal decreasing elasticity of the crystalline lens causing loss of accommodation, and far sightedness. There is a reduced ability to form a clear image of a near object due to this loss of elasticity of the crystalline lens thus, bringing about asthenopic systems such as headache and fatique (Donnell, 2007). The human lens (crystalline lens) makes the fine adjustment which brings the image into sharp focus on the retina. This is done by a change in the thickness of the lens when focusing on a distance objects, the lens become thinner and when focusing on near object, the lens bulges or become falter (More convex). This changes in the shape of the lens are brought about by the cilliary muscles (Benjamin, 2006). Presbyopia a condition of physiological insufficiency of accommodation leading to a progressive fall in near vision, it is not a refractive error (Ametropia), but is now increasingly recognized as an aspect of refractive error that needs to be addressed, it is also called eye sight of old age. The cause is as a result of decrease in the accommodative power of the crystalline lens with increasing age, which occurs due to:

1. Age-related changes in the lens which includes decrease in the elasticity of the lens capsule, and progressive increase in size and hardening (Sclerosis) of the lens substance.
2. Age-related decline in cilliary muscle, power may also contribute to presbyopia.

(Khurana, 2012). Good near vision is important even among population who use it for task other than reading and working. The age of onset of presbyopia is usually between 38 and 45 years and prevalence is 100% by age 55 (Benjamin, 2006). For most people, doing close work becomes difficult when the amplitude of accommodation is less than 5.000 (corresponding to a near point of accommodation while wearing lenses to correct any distance refractive error) (Grosvenor, 2007). The use of convey lenses (plus lens) to compensate for the reduction in the range of accommodation associated with presbyopia, brings the near point of accommodation to a comfortable distance for a near visual task.

The prevalence of presbyopia in 68 years has been estimated to be 58.15% (Hashemi et al; 2012). Presbyopia affect the patients and also created economic burden if it is left untreated. Factors which can lead to presbyopia include a gradual reduction of zonular tension to increase lens power (Glasser et al., 1998) gradually altered anterior segment geometry and increased lens thickness. Changes in crystalline materials due to the ageing process and the accommodation mechanics by which the alteration in the ciliary muscle position leads to the flattening of crystalline lens decreasing its power (Mancil, 2011). The initial progression depend on several factors and environmental elements such as illumination and temperature (Macmillan et al; 2011).

1.2 CAUSES/SIGNS AND SYMPTOMS/MANAGEMENT

Age is the main risk factor in presbyopia; however, other factors such as trauma, cardiovaslar diseases, systemic diseases (Diabetes mellitus, multiple sclerosis, anemia, influenza, myasthenia gravis, etc. (Mancil et al., 2011). Environmental issues have been proposed to play a role in the development of presbyopia (Mancil, et al., 2011). Blur vision and disability to detect details in near taking are the main presentation, however, headache, asthenopia, drowsiness, diplopia and increased working distance are frequently complained by the patients as well (Mancil et al., 2011).

Amplitude of accommodation is a unique measurement for each eye, therefore, it is necessary to provide the weakest and most proper addition measured for each eye separately, in order to establish a correlation between accommodation and convergence (Bittencourt,et al., 2013). Patient habitual working distance is a fundamental factor to determine distance a precise and suitable correction (Bittencourt,et al., 2013). According to a classic rule for optical correction of presbyopia, patient should use up to half of their amplitude of accommodation (Bittencourt,et al., 2013). Calculation based on the amplitude of accommodation is more accurate compared with subjective refraction (Leffler, et al., 2008). Age-related near addition values show a difference compared with the amplitude of accommodation measurements due to inter-individual difference (Milder, 2005). However, some studies proved that eye-expected addition might be more precise compared with ones estimated by amplitude of accommodation (Antona, et al., 2008), several method have been used to determine addition which includes; increasing plus lens (IPL), Balanced Range of Accommodation (NRA/PRA), Amplitude of Accommodation (AA), addition, Dynamic Retinoscopy and Near Duochrome Subject Retiniscopy Preference are most commonly used method for determining addition in presbyopia (Antona, et al., 2008). Bittencourt, et al; compared four methods for determining addition, one-half amplitude of accommodation with minus lenses: one third accommodative demand with positive lenses; balanced range of accommodation with minus and positive lenses; and cross cylinder test with initial myopization. All the methods estimated the comparable and almost similar near addition.

The clinical consequence of presbyopia is that without optical correction the amplitude of accommodation is insufficient to meet the near vision demand of the patient (Grosvenor, 2007).

Presbyopia may be classified into;

Incipient Presbyopia: This represent the earliest stage at which symptoms of blurring of small prints at early, also referred to as borderline, reading small prints requires extra effort.

Premature Presbyopia: In premature presbyopia, accommodation ability become insufficient for the patients usual near vision task at an earlier age than expected, due to environment, disease- related, or ding induced causes.

Nocturnal Presbyopia: Nocturnal presbyopia is a condition in which near vision difficulties result from an apparent decrease in the amplitude of accommodation in dim light. Increased pupil size and decreased depth of field are usually responsible for the reduction in the range of clear vision in dim light (Glasser and Kaufman 2003).

Functional Presbyopia: With gradually declining accommodation amplitude and continued near task demand, adult patient eventually report visual difficulties that clinical findings confirm as functional presbyopia.

Absolute Presbyopia: With continuous gradual decline in accommodation, functional presbyopia progresses to absolute presbyopia. Absolute presbyopia is the condition in which virtually no accommodation ability remains.

Amplitude of accommodation: The amplitude of accommodation is the maximum amount of accommodation or focusing ability that the patient can exert in response to a near target. The near target is moved closer to the patient’s eyes until it first blurs (the push-up amplitude) and then moved away from the eyes until it becomes clear (push-down amplitude). An average of these two threshold values provides an indication of the amplitude of accommodation (Elliott, 2007).

Risk Factors: Age is the major risk factor for development of presbyopia although the condition may occur prematurely as the result of factors such as trauma, systemic disease, cadiiovascular disease, or a dry side effect.

Hyperopia: additional accommodative demand (if not corrected).

Occupation: Near vision demands

Gender: Early onset in females (short stature, menopause etc.) and

Poor nutrition.

Common signs and symptoms: The onset of presbyopia is gradual. Although blurred near vision signals the onset of presbyopia, the symptoms reach significance only when the patients’ accommodative amplitude becomes inadequate for his or her visual needs. The patients’ difficulty in performing vocational or avocational activities largely determines when the symptoms of impairment are manifest.

Blurred vision and the inability to see fine details at the customary near working distance are the hallmarks of presbyopia. Other common symptoms are, delays in focusing at near or distance, ocular discomfort, headache, asthenopia, squinting, fatigue, or drowsiness from near work, increased working distance, need for brighter light for reading and diplopia (Wemer, 2002).

Management of Presbyopia:

A variety of options are available for optical correction of presbyopia, which include;

1. Bifocal lenses: These lenses incorporate the distant vision and the near vision prescription into a single lens.
2. Trifocal lenses: These multifocal lenses incorporate distant, intermediate and near lens prescription which is often important for patients who have advanced or absolute presbyopia.
3. Occupational lenses: Spectacle lens design that incorporate double or triple segments may be indicated for patients who has special vision needs or whose work involves near vision tasks when the objects of regards are above eye level (e.g. postal workers, librarians, painters, and electricians).
4. Single vision lenses: The use of spectacles containing single vision lenses in an appropriate option for some patients with presbyopia. Typical candidates for this treatment are patients with emmetropia or patients with a low degree of ametropia (who do not require distant prescription). Single vision spectacles with the near correction provide a wide field of view unmatched any other form of spectacle correction for presbyopia, but they cause blurring of distant vision.
5. Progressive Addition Lenses: By means of a corridor of progressively changing power that connects the distance portion with the near portion of the lens, progressive addition lenses (PALs) can provide clear vision for a range of distances. Because of the limited number of powers in bifocals and trifocals, your depth of focus with these lenses are limited. Objects must be within a specific range of distances. Objects that are outside the distances covered by the bifocals trifocal lens powers will be blurred. Progressive lenses, on the other hand, have a smooth, seamless progression of lens powers for clear vision at all distances. Progressive lenses provide a more natural depth of focus, meaning there is no “image jump”.

Because of their advantages over bifocals and trifocals such as wider zone of clear vision, more comfort for active wear, progressive lenses have become the most popular multifocal lenses for presbyopes who wear eyeglasses. (Grosvenor, 2007 and Sheedy, 2005).

Correction with Contact Lenses:

There are two types of contact lenses available for presbyopia;

1. Monovision lenses
2. Multifocal lenses
3. Monovision contact lenses: These type of contact lenses correct one eye for distance vision and the other eye for close-up vision. Because you need to train your brain to use one eye for distance and the other eye for near vision, it usually takes some time to adjust to monovision. Some depth perception may also be lost with monovision. The dominant eye is usually the eye that wears the distant prescription while the non-dominant eye wears the near prescription in monovision therefore test need to be performed to determine which eye is dominant.
4. Multifocal contact lenses: As the name implies, multifocal contact lenses are lenses that have more than one focal point allowing for both near and distance vision.
5. Concentric bifocal design: In this bifocal design, the near correction is in the small circle at the centre of the lens surrounded by a much larger circle containing the distance prescription. The distant prescription can also be placed in the centre with the near correction in the outer ring.
6. Alternating image design: The alternating image design which has distinct zone for distance and near vision. Just like bifocal glasses, the top part is for distant vision while the bottom part is for near vision and they are separated by a nearly invisible line which helps the eyecare practitioner determine if the lens is fitted properly.

• Simultaneous image design: In this design, both the distant and the near portions of the lens are in front of the pupil at the same time and your brain has to determine which area of the lens to emphasize and which area to ignore to provide the best image resolution (Bennett, et al., 2001).

CORNEAL INLAYS: They are one of the options for correction of decreased near vision in presbyopic people who desire spectacle-independent good vision at all distances.They  do not restore ability to accommodate as they have no effect on ciliary muscle of the lens.They work by increasing the depth of focus or the refractive power of the central or paracentral part of cornea.The central 1.8mm diameter is plano and has no refractive power,it allows light rays from distant source to focus on the retina preserving distant vision,and the inlay power ranges from +1.25 to +3.0 D in 0.25D increments.

Currently,three corneal inlays are in various stages of development. The Flexivue Microlens(presbia) is a refractive inlay that alters the index of refraction by using a bifocal optic.The Raindrop(ReVision Optics)  is a reshaping inlay that changes corneal curvature, and the Kamra (Acufocus) inlay that was recently approved by the Food and Drug Administration,employs small –aperture optics to increase the depth of focus.

All are implanted in the nondominant eye and are all considered modified monovision,because they are all intended to be done in a single eye.

PEARL (PRESBYOPIC ALLOGENIC REFRACTIVE LENTICLE):

It is a procedure that places a small piece of tissue from one part of the cornea into another part improving near vision. It is a procedure that uses laser to make a small cut in the cornea. A small disc of corneal tissue called a lenticle is removed through this  cut. The lenticle is reshaped and sculpted with a laser then placed into a small pocket made in the patient’s corneautilizes less complications than Corneal Inlay because the inlay is made of the patients’s own tissue , it is biologically compatible,making it less likely to cause complications.The corneal tissue inlay is expected to allow oxygen and nutrients to flow through the patient’s cornea better than synthetic inlay, helping to keep the cornea healthier.

EVO6(Encore Vision) eyedrop : It is a novel topical modality for restoring near vision in presbyopic patients, it contains topical administration of lipoic acid choline ester 1.5%, it acts via an anti – crosslinking mechanism, the treatment increases lens elasticity through reduction of lens protein disulfides, and was associated with impressive improvements in accommodative amplitude and near vision in an initial randomized , double- masked phase I-II clinical trial.

However, this topical treatment is the first agent that has been shown in a clinical trial to restore natural accommodation , and it has exciting potential, by Dr Lindstrom,founder,Minnesota Eye Consultants,Minnepolis.

PRESBYOPIC ADD: Presbyopic add is simply, the plus lens placed over the distant prescription, for near work. In some individuals who does not require distant prescription, this presbyopic add may be given as reading glasses.

Table 1.1: Standard Notation Table for Presbyopia

Source (Bhattacharyya, 2009)

The amplitude of accommodation measures the full range of accommodation from far point, where accommodation is fully relaxed, to the near point with maximum accommodation exerted (Elliott, 2007). If the far point is at infinity (as in the case of emmetropes and those wearing optimal refractive correction for distance vision), then measurement of the near point allows the amplitude of accommodation to be determined with ease. The amplitude is calculated by taking the inverse of the near point of accommodation which is expressed in meters. The amplitude of accommodation gradually falls with age, and causes patients over the age of about 45 years to have difficulty with near work and required reading glasses. Measurement of the amplitude of accommodation can help to identify the appropriate reading add required to alleviate the patient’s near vision problem.

• STATEMENT OF PROBLEM

Presbyopia is an age-related visual condition characterized by the depletion of functional amplitude of accommodation, which affects adult population above 37 years. Ordinarily, presbyopia is not classified as a refractive error, but a physiological age-related visual change, coupled with increased visual demand for near work. It is usually problematic when left uncorrected or under corrected. Uncorrected, under corrected or over corrected presbyopia will affect the ability to focus near work effectively due to the effect on the accommodative, phoria and AC/A ratio faculties, which may be accompanied by decompensated symptoms of blurry near vision, fatigue, headache, drowsiness, diplopia, et cetera. Due to the problems associated with it, it is paramount that adequate management is done by providing the appropriate reading add that will compensate the failing accommodative power and provide a comfortable near vision.

Ultimately, the success of treatment depends on the lens power, the optical correction,the specific visual tasks,characteristics of the individual patient, and the appropriate patient education given by the practitioner.

1.4     SIGNIFICANCE OF THE STUDY

1. Inthis technologically-driven society, the results obtained will help to address the issue of visual deficit experienced by presbyopes by providing the necessary optical correction needed to compensate for the compromised near vision, thereby enhancing productivity at work, and promote social interaction.
2. It will make them to be aware of the implications of uncorrected and under corrected compromised near vision on their visual demand and sensitize them on when to seek optometric care .
3. It will serve as a literature for furtherstudy in the same or related field, which will also help in the management of presbyopia.
4. It will help our literate adults to know the expectant age of presbyopia, in order not to be taken unaware.
5. It will provide a better and more convenient choice of the method to adopt in effective handling of presbyopic problems.
6. It will inform policy makers on the burden of presbyopia, and help in designing an eye-care programmes and incentives, which will help in reducing eye fatigue due to near work and absenteeism due to ill-health associated with excessive strain on the accommodative faculty, thus increasing productivity and raising the profit margin of an organization.

1.5      OBJECTIVES OF STUDY

General Objective

To compare the reading add of presbyopes using amplitude of accommodation method and binocular cross cylinder method.

Specific Objective

1. To determine any difference in the results of the two methods with reference to age.
2. To determine any difference in the results of the two methods with reference to gender.

• To compare the effect of the tentative add by the two methods on lateral phoria at near .

1.6     RESEARCH QUESTIONS

1. Is there anysignificant difference in the results of the two methods with reference to age?
2. Is there any significant difference in the results of the two methods with reference to gender?

• Is there anysignificant difference of the effect of the tentative add by the two methods on lateral phoria at near ?

 1.7    RESEARCH HYPOTHESIS

1. NULL HYPOTHESIS: There is no significant difference in the results of the two methods with reference to age.

ALTERNATIVE HYPOTHESIS: There is no  significant  difference in the results of the two methods with reference to age

2.NULL HYPOTHESIS: There is no significant difference in the results of the two methods with reference to gender

ALTERNATIVE HYPOTHESIS: There issignificant difference in the results of the two methods with reference to gender

3. NULL HYPOTHESIS: There is no significant difference of the effect of the tentative add by the two methods on lateral phoria at near.

ALTERNATIVE HYPOTHESIS:  There is significant difference of the effect of the tentative add by the two methods on lateral phoria at near .

1.8SCOPE OF STUDY

This involves the measurement of amplitude of accommodation and binocular cross cylinder methodsin determination of reading adds for presbyopes.

1.9   LIMITATION OF STUDY

Success itself is not achieved without some pitfalls. In this research,there were some limitations encountered in the course of carrying out this study. These include:

1. Falsification of age by some subjects which affects some of the results of sex comparison of the two methods of determining ADD.
2. Time factor : most of the subjects will like to go to their working places or some places first and come to the clinic before the scheduled time thereby affecting the scheduled time allocation of procedures on each subject which will result in hurrying of the procedures hence affecting measurements.
3. Some subjects on drugs will not admit or don’t know the name of drugs being taken to rule it out of the ones that will affect accommodation hence affecting the results of the methods.
4. Inability to report or identify blur during AA method measurement affecting results.
5. Inability to detect which lines of cross grid of binocular cross cylinder method is more distinct or clearly thereby affecting result.

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