PROBLEMS vision is decreased despite normal appearance of the

    PROBLEMS ASSOCIATED WITH AMBLYOPIA    TYPE OF MANUSCRIPT:-   Review  RUNNING TITLE:-   PROBLEMS ASSOCIATED WITH AMBLYOPIA.  AUTHOR NAME :-  Inchara.RUndergraduate student Saveetha dental college Saveetha university, Chennai, India Telephone number:- +917019291359Email:- [email protected]   CORRESPONDING AUTHOR :- K. Yuvaraj Babu Department of anatomy Saveetha dental college Saveetha university Telephone number:- +919840210597Email:-     YEAR OF STUDY:-    I- BDS 2017-2018            ABSTRACT:-  AIM :- To determine the problems related with Amblyopia  OBJECTIVE :-To review and establish the problems of Amblyopia.   INTRODUCTION:-   Amblyopia is reduced visual acuity in one or both eyes in the absence of any demonstrable abnormality of the visual pathway. With Amblyopia,the brain suppress one of these images and this negatively impacts a person’s binocular vision .It is not immediately resolved by the correction of refractive error. The amblyopia eye must have the most accurate optical correction possible . Due to high amounts of nearsightedness,farsightedness,astigmatism and the presence of a constant eye turn,the brain has suppressed the information in that eye and this suppression negatively impacts the development of clear vision. Amblyopia is a reduction in best-corrected visual acuity that cannot be accounted for by any structural abnormality, either in the eye or in the visual pathways (i.e., a pathway or tract of optic nerves and fibbers that transmits a visual image from the eye to the brain). A commonly-used term for this condition is “lazy eye.” A “lazy eye” refers to an amblyopic eye, not an eye that is misaligned (i.e., an eye that does not point or look in the same direction as the other eye). In some cases, however, amblyopia may be the result of a misaligned eye, or severe amblyopia may cause a misaligned eye.In addition to a reduction in visual acuity in one or both eyes, individuals with amblyopia do not learn to use both eyes together well. As a result, they can have poor depth perception.Normal vision develops during the first few years of life. At birth infants, have very poor vision, however as they use their eyes the vision improves because the vision centres in the brain are developing. If infants are not able to use their eyes for various reasons the vision centres do not develop properly and the vision is decreased despite normal appearance of the structures of the eyes.The most common cause is refractive error in one or both eyes that is not corrected early in childhood resulting in poor development of the visual function in the affected eye or eyes. This is called refractive amblyopia.Another common cause is strabismus or eye misalignment. This is called strabismic.Rarely there is a structural anomaly that impairs the visual function like a droopy eyelid or opacity in the visual axis like cataract or corneal scar. This is called deprivation amblyopia.    MATERIALS AND METHODS:-A total of 180 articles were identified through the database searches. An additional 10 articles were identified through a recent HTA publication and two systematic reviews on amblyopia screening and treatment. These articles were not identified because the publication was in a journal that was not included in the search engines used (ie, articles were published in journals not found on Medline). After the removal of duplicates, a total of 632 articles were applicable for this review. Every article identified was checked by one reviewer (JC) and subjected to a pre-determine inclusion/exclusion criteria. Articles were rejected at title if they were not related to the subject area  and rejected at abstract if they were in a non-English publication or not pertinent to the research question  Letters, reviews, and editorials describing other studies reporting  implications of amblyopia were excluded. Where abstracts were ambiguous, the article was obtained. A further seven articles were rejected at full paper stage. These were found to be review papers, summaries of other studies, or contained no data to inform the research question.A total of 35 articles were included in the review.   RESULTS AND DISCUSSION;- Amblyopia  is a childhood problem that happens when one eye is weaker than the other. The brain chooses to take in images from the stronger eye and ignore images from the weaker eye. This means that your child uses the strong eye more than the weak eye. If the weak eye doesn’t have to work, it isn’t able to develop good vision. This leads to poor vision  in the weaker eye. Amblyopia  usually affects only one eye.The problem starts between birth and about age 7. Your child may not even know that he or she is using only one eye. Ignoring the images from the weak eye is an automatic response.Amblyopia can result from any condition that prevents the eye from focusing clearly. Amblyopia can be caused by the misalignment of the two eyes—a condition called strabismus. With strabismus, the eyes can cross in (esotropia) or turn out (exotropia). Occasionally, amblyopia is caused by a clouding of the front part of the eye, a condition called cataract.A common cause of amblyopia is the inability of one eye to focus as well as the other one. Amblyopia can occur when one eye is more nearsighted, more farsighted, or has more astigmatism. These terms refer to the ability of the eye to focus light on the retina. Farsightedness, or hyperopia, occurs when the distance from the front to the back of the eye is too short. Eyes that are farsighted tend to focus better at a distance but have more difficulty focusing on near objects. Nearsightedness, or myopia, occurs when the eye is too long from front to back. Eyes with nearsightedness tend to focus better on near objects. Eyes with astigmatism have difficulty focusing on far and near objects because of their irregular shape. Amblyopia is derived from the Greek word for “blunt or dull sight.” The loss of sight can occur in childhood. The brain depends on receiving simultaneous clear focused images from both eyes for the visual pathways to develop properly.137 Because of difficulty in producing a single image when looking with both eyes, the person with amblyopia elects to see with only one eye to see one image. The lazy eye, if deprived of visual input for sufficient time, will lose sight, and the child will become functionally blind because of a lack of visual cortex development. This problem may be associated with an eye that is deviated in any direction–in, out, up, or down–a condition known as strabismus. However, strabismus is not necessarily a cause of amblyopia. In addition, the use of only one eye may not be apparent unless screening is conducted.In 2002, the American Academy of Pediatrics (AAP) issued a statement regarding the use of photoscreening, a vision screening technique, as a method of identification of children with visual problems.138 The AAP reaffirmed this position in August 2008. All children should be screened for risk factors associated with amblyopia. The prevalence of amblyopia is thought to be 1% to 4%.13 However, almost 80% of children in preschool never get screened.140 With only 21% of children being screened, there is a very real possibility that a lot of children with visual problems are not being identified. The difficult to screen population such as the very young and developmentally delayed are at even greater risk for not being screened for preventable visual loss or treatable visual conditions. The AAP138recommends use of a photoscreening method that would facilitate screening in all children. Salcido and colleagues141 found photoscreening more efficient than traditional screening in a group of 3- and 4-year-old children. A U.S. preventive task force142 recommended that photoscreening was able to identify amblyogenic factors, such as significant refractory error, strabismus, and media opacities but not amblyopia. Amblyopia can occur in children when there is aberrant or contradictory information coming from a retina. The brain will selectively inhibit development of the cortical cells receiving the aberrant input. Just like cells everywhere else in the nervous system, the cells of the occipital lobe need to be stimulated to function. If the cells are not stimulated, the connections and organization of the cells will be affected. This may occur if a child has a strabismus severe enough that a double image is created. The brain will shut off the signal from the deviant eye. Cells in the occipital cortex receiving signals from this eye will be deprived of stimulation and will not develop. Although the globe, the retina and the nerve pathways may be functional, the occipital lobe cannot interpret the signal they carry.  Symptoms• Decreased vision in one or both eyes• Strabismus (misaligned eyes)• Poor depth perception               • Misaligned eyes (strabismus)Eye misalignment is the most common cause of amblyopia. When both eyes are not aimed in the same direction, the developing brain “turns off” the image from the misaligned eye to avoid double vision and the child uses only the better, or dominant, eye. If this persists for any period of time, even as short as a few weeks, the eye will not connect properly to the visual cortex of the brain and amblyopia will result.• Unequal refractive error (anisometropia)If the refractive error of each eye is not the same then both eyes cannot be in focus at the same time. Amblyopia occurs when one eye (usually the eye with the greater refractive error) remains out of focus because it is more nearsighted, farsighted, or astigmatic than the other, which becomes the dominant seeing eye. This results in disuse of the unfocused eye, which fails to connect properly to the brain and will not develop normal vision. Because both eyes in children with anisometropia often look normal, this can be the most difficult type of amblyopia to detect. It requires careful evaluation of visual acuity and ocular preference in infants and young children by a primary care physician or ophthalmologist as part of a vision screening evaluation at 6 months and 3 years of age and preschool. Treatment with glasses or contact lenses to properly correct the refractive error of each eye, sometimes with part-time patching of the better-seeing eye, is necessary in early childhood to correct the problem.• Obstruction or cloudiness of the visual system (deprivation)Obstruction or cloudiness in the normally clear eye tissues also may lead to amblyopia. Any disorder that prevents a clear image from being focused inside the eye can block the formation of a clear image on the retina and lead to the development of amblyopia in a child. This often results in the most severe form of amblyopia. Examples of disorders that can interfere with projecting a clear image on the retina are a cataract or cloudy lens inside the eye, a cloudy cornea at the front of the eye, a droopy eyelid (ptosis) or eyelid tumour.It is not easy to recognize amblyopia. Unlike adults, a child is usually unaware if one of his or her eyes has reduced vision. Unless the child has a misaligned eye or other obvious external abnormality, there is often no way for parents to tell that something is wrong. In addition, it is difficult to measure vision in very young children at an age in which treatment is most effective. A positive family history of strabismus, amblyopia, or media opacities would increase the risk of amblyopia in the child. Children who have conditions that increase the risk of strabismus, anisometropia, or media opacities (ex. Down syndrome) would also be at increased risk for the development of amblyopia. The risk of developing amblyopia, from a condition that is known to cause amblyopia, diminshes as the child approaches 8-10 years of age. As a corollary to this, the depth of amblyopia is typically less severe the older the child is at the time of onset of the amblyogenic factor. Amblyopia is a developmental problem in the brain, not any intrinsic, organic neurological problem in the eyeball (although organic problems can lead to amblyopia which can continue to exist after the organic problem has resolved by medical intervention) The part of the brain receiving images from the affected eye is not stimulated properly and does not develop to its full visual potential. This has been confirmed by direct brain examination.”The maximum “critical period” in humans is from birth to two years old.  Reliance on parental history for some information and on assessments by general medical examiners (rather than ophthalmologists) raises the possibility of misclassification of amblyopia. However, visually impairing disease is rare in childhood,12 and amblyopia is the most likely cause of unilateral reduced acuity despite optical correction. Thus, most people with amblyopia were probably correctly classified, and they also probably account for most “cases.” This is supported by our prevalence of 1.2% for residual amblyopia at a threshold of 6/18 or worse, which is consistent with previous reports.13 14 The 1958 birth cohort is a representative population, studied longitudinally, ensuring that visual status was known before measurement of a range of important outcomes. This confers important advantages for studying the functional consequences of amblyopia; the size of the population studied was sufficient to detect even modest associations, for key outcomes, where they exist. No directly comparable previous work in this area exists, but indirect comparisons are made below.   Extensive psychophysical and neurophysiological work has elegantly delineated clear deficits in specific components of vision, such as contrast sensitivity, that occur in amblyopia.2 Our findings fail to identify their “real life” functional correlates. For example, the reading speed of people with amblyopia may be measurably slower but may nevertheless, on average, be adequate for educational or occupational purposes. 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