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Archives of Ophthalmology and Optometry ISSN 2638-5120 Volume 3, Issue 1, 2020, PP: 01-10 Comparative Study of the Effect of Experimentally Induced Anisometropia on the Stereoacuity of Teenagers Ihesiulor Grand Chikezie*1, Amaugo Victoria Chidinma2, Eleazar UchennaIkonne3 *Corresponding Author:Department Ihesiulor ofGrand Optometry, Chikezie, Abia Department State University, of Optometry, Uturu, Nigeria. Abia State University, Uturu, Nigeria. Abstract Purpose: To examine the effect of experimental anisometropia on steroacuity in teenagers using Titmus Stereo Fly Test. Methods: Fifty-six teenage volunteers (ages ranging from 16-19 years) participated in the present study. Placing trial lenses over the dominant eye (from -3.50D to +1D), two different anisometropia types (including myopia and hyperopia), were induced. Steroacuity was measured using the Titmus Stereo Fly Test. Results: In all the anisometropia types, there was a decline in stereopsis as anisometropia increased (p<0.05). The greatest impairment in stereoacuity was due to compound myopic anisometropia, -1.00DS and -3.50DS, +1.00DS and +3.50DS, and +2.00Ds and -2.00DS giving 3552 arc seconds in Titmus circles. Conclusion: Anisometropia reduces stereopsis and compound myopic anisometropia gives the most noticeable change. The impairment had no gender correlation. Keywords: Stereoacuity, anisometropia, stereopsis. INTRODUCTION objects and a phenomenal sense of realism. These visual characteristics are conventionally thought to Stereoacuity can be defined as the discrimination of be a result of the different views of an object afforded differences in depth on the basis of binocular disparity. by binocular vision (disparity) or self-motion (motion In other words, stereoacuity can be defined as the parallax) (1). measurement of stereopsis. Essentially, stereoacuity is the smallest detectable disparity of retinal images The perception of depth depends on the combination (1). It could be as low as three seconds of arc with a of- several factors such as: high contrast and sharp-edgedstimuli in the central - Retinal disparity zone, but conventionally in a normal person with good binocular vision, stereoacuity is forty seconds - Motion parallax of arc. Stereopsis is the perception of depth based - Shading cues on horizontal, relative and retinal disparity. Retinal disparity is the difference in position of images on the - Inter-position cues (overlap of objects) left and right retina measured in visual angle units of - Size or perspective degree, minutes or seconds of arc (1,2,3). Blur Stereopsis, which is the third grade of vision, could be the characteristically vivid qualitative impression Anisometropia is a condition in which the two eyes of a 3D structure that is observed when real (or have unequal refractive power; that are in different stimulated 3D) scenes are viewed binocularly. It is states of myopia (near-sightedness) or hyperopia associated with a compelling perception of solidity (far-sightedness). The unequal refractive state Archives of Ophthalmology and Optometry V3 . I1 . 2020 1 or 3-dimensionality, a clear sense of space between causes unequal rotations thus leading to diplopia and Comparative Study of the Effect of Experimentally Induced Anisometropia on the Stereoacuity of Teenagers asthenopia. The higher the amount of ametropia, the anisometropia, simple myopic anisometropia and more often anisometropia occurs. The name is from antimetropia. Since both eyes are not accommodating the Greek components: an – “not”, so – “same”, metro – equally, an uncorrected anisometrope has the problem “measure”, and ops – “eye”. of never having sharply focused images on both retinas Very few people are born with identical power in the at the same time (1,5). two eyes, but the brain manages to compensate the Blum et al. (1959) and Hirsch, (1967) found the differences, thereby making it unnoticed. However, prevalence of anisometropia of 1.00D or more to when a person has anisometropia, the difference in vary from 2-6 percent, being lowest at age 5 and vision between the two eyes is significant and will increasing during the school year. In Hirsch’s study, interfere with normal binocular vision (about 1D some of the children who had equal refraction in both difference or more). Sometimes anisometropia can be eyes (isometropia) on entering school developed present at birth, although it won’t become apparent anisometropia during the school years, whereas until later in life most times. others had anisometropia when entering school but There- are three types of anisometropia namely: eventually became isometropic and still some were found to be anisometropic on entering school and Simple anisometropia: This is when one eye is remained anisometropic (2,6,7). affected while the other eye has no refractive - error. Majority of patients in school children population are affiliated with the disturbance of binocular vision due Compound anisometropia: This is when both eyes to anisometropia. Lack of information on where this are myopic or hyperopic both with a significant problem occurs most frequently results to a difficult - difference of about 1diopter between both eyes. diagnosis of the problem. An example is a complaint Mixed anisometropia: This is when both eyes have of diplopia by a patient. If this symptom is elicited by appreciable refractive errors with one eye being a patient who belongs to a target population where myopic and the other hyperopic. This can also be the anisometropia is high, the clinic will immediately called Antimetropia. think about the ruling out of anisometropia before Symptoms- of anisometropia are: going further for another diagnosis(1,2,3). - Amblyopia Anisometropia is one of the etiological factors in the pathogenesis of amblyopia as well as a contributing - Strabismus (crossed eyes) factor to decrease stereoacuity. The precise - Diplopia mechanism by which anisometropia causes a decrease in stereoacuity is not clear. It has been suggested that - Eyestrain foveal suppression in the defocused eye is the cause - Headaches of decreased stereopsis. This decreased stereopsis - Nausea whether it is secondary to loss of visual acuity or loss of bifoveal fixation is not known (1,2). According to - Light sensitivity Von Noordeen and Campos (2002), anisometropia - Tiredness can result in the defocus of retinal images in one eye, including reduction of retinal image size (aniseikonia), Dizziness contrast and clarity (1). So, for a person who is Anisometropia could result from defects in the eye anisometropic, the signal from one eye which is sent at birth as well as uneven size of the two eyes (axial to the brain to be analyzed cannot be harmonized length). Anisometropia present at birth could be with that of the other. transient and may disappear as the eyes emmetropize There may be active suppression of the fovea to (1,2,3). Ogle, (1950), reported that clinically significant overcome the secondary interaction between the eye degrees of anisometropia are axial in nature (4). with the better vision and that with lesser vision. It Schapero et al. (1968), classified anisometropia has been suggested that an onset of blurred vision Archives of Ophthalmology and Optometry V3 . I1 . 2020 into2 anisometropic astigmatism, simple hyperopic early in life as a result of anisometropia may provoke Comparative Study of the Effect of Experimentally Induced Anisometropia on the Stereoacuity of Teenagers a particular pattern of functional loss. However, the University,- Uturu which involved: quantitative relationship between the degree of - Case history anisometropia and functional loss has not been fully explored(1,2,3). Anisometropia is clinically important - Visual acuity testing (both at far and near) because it is one of the most frequent cases of vision - Penlight examination loss in infants and children. Poor stereoacuity causes - impairment particularly in visual feedback control of Ophthalmoscopy movements leading to significantly longer and less Refraction (when necessary) accurate movements (8). The Stereoacuity of the subjects was then measured Buckley et al. (2010) and Helbostad et al. (2009) both before and after induction of anisometropia and suggested that the effect of losing stereopsis extends recorded respectively.A total of 56 subjects were used beyond hand movements. In addition, adaptation to for this study. These subjects were emmetropes or changes in terrain (e.g. steps) are significantly less artificial emmetropes who had no significant existing accurate without stereopsis in normal sighted people pathological condition.A Randomized sampling viewing monocularly, people with amblyopia and technique was used. The following criteria were people with reduced stereoacuity. Impaired stereopsis considered to determine the eligibility of the subjects may also negatively affect the everyday activity in used for this study: children (9,10). The aim of this study is to determine the effect of anisometropia on the stereoacuity of 1. Subjects were in good ocular and systemic health teenagers.Objectives condition. - 2. Subjects were emmetropes or artificial emmetropes. To determine if anisometropia has a significant effect on loss in stereoacuity so as to bring it to 3.Materials/Instruments Subjects were teenagers (i.e. 16-19 years of age). the awareness of optometrists and the general public that persons with anisometropia are likely - to have an impaired stereopsis. - Snellen’s Visual Acuity Chart To determine the nature of effect of anisometropia - Pen torch
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