Introduction of visual acuity after birth. The most

Introduction

Amblyopia
consider disorder a neuro-development of the visual cortex which appear from
abnormal visual acuity early in life, influencing 1%-4% of the general
population (Ciuffreda, Levi, & Selenow, 1991; McKean-Cowdin
et al., 2013; MEPEDS, 2009). It is having onsets during the first 3 years
of life and the alterations can be effect on properties of neurons in early
cortical areas (V1 and V2), may be even as early as the LGN (Bi et al., 2011;
Hess et al., 2009; Kiorpes, 2006). The deficit of sensory involve reduction or
loss visual acuity and stereopsis, position acuity and contrast sensitivity,
particularly at high spatial frequencies (Levi, 2006). Recently, some studies suggest
amblyopic deficit is then amplified downstream (Levi, 2006; Muckli et al.,
2006). Amblyopeic patients not only suffer from sensory deficits, thus also suffer
from second-order processing, contour integration, and temporal, spatial and/or
capacity limits of attention. Diagnosis of amblyopia is clinically important
because is most cause of vision loss in infants and young children aside
refractive error (Sachsenweger, 1968). Also, it is basic interest which reflect
neural impairment can be occur during disruption of normal visual development
and provide understanding how brain plasticity may be harnessed for recovery of
function ((Bavelier et al., 2010).

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Definition

Amblyopia
is unilateral or bilateral reduction of best corrected visual acuity to less
than 6/9 in or at least two-line difference in LogMAR between the eyes caused
by depravation of pattern vision or abnormal binocular interaction. Amblyopia
is disorder a neuro-development of the visual cortex that induced by abnormal
visual experience early in life (von Noorden, G. K,1996). There is no manifest
ocular disease underling decrease visual acuity but some condition predispose
that influences the development of visual acuity after birth. The most common
condition that predispose to amblyopia are strabismus, refractive error or,
more rarely, media opacification causing reduction in image quality (such as
congenital cataract) (Simons K, 2005).

Incidence
and Prevalence

 The prevalence of amblyopia in general
population estimated 2 to 4% (Donnelly et al., 2005; Williams et al., 2008). Moreover,
prevalence of amblyopia reported 4.4% in New Delhi and 1.9 in South China
children 5-15 years-old (Murthy GV et al.,2002). In Europe, the prevalence
amblyopia in children range between 1% to 2.5% (Newman, 2000). However, Amblyopia
affects about 29% unilateral blindness in Copenhagen and as much as 8.3% of
bilateral blindness for childhood cataract surgery in India (Buchet al., 2001).
Amblyopia also influence on about 50% of the children that have strabismus and
18% anisometropic children (Birch and Holmes, 2010). However, this ratio revers
in adult s, which Attebo et al. (1998) reported 50% of the patients with amblyopia
suffering from anisometropia whereas strabismus was induced only 19% of cases. Also,
strabismus was caused 24% of preschool children untreated for amblyopia. Moreover,
amblyopia prevalence in preschool and school-age population in different region
in Iran has been reported to vary from 0.2% to 3%( Rezvan F et al., 2012). Thampson
et al. reported both anisometropia and strabismus about 21% of cases and Show
et al, found these causes in 35% of cases of amblyopia.   

In Saudi
Arabia, several studies conducted in different regions before 1994 found
prevalence of amblyopia in preschool children was 2.6% in Riyadh and among
school age children was 1.9% in Abha and 1.6% in Al Baha City (Al-Faran MF et
al.,1994). Aldebasi YH (2015) reported prevalence in primary school children in
Qassim was 3,9% and unilateral amblyopia more than bilateral amblyopia. The
most causes of amblyopia in children are refractive error has high frequent was
ratio 94.56%, then anisometropic amblyopia was estimated 77.72%, isoametropic
amblyopia in 16.84% and strabismus in 5.44%.

 

 

 

Classification
of amblyopia

 Amblyopia classified into two types organic
and functional which each type can be further subdivided. Organic amblyopia induced
from some pathological or anatomical abnormalities of the retina where
including four situations from retinal eye disease (e.g. receptor dystrophy,
neonatal macular), nutritional amblyopia (from nutritional deficiencies), toxic
amblyopia (from poisoning e.g. arsenic, lead or quinine), and idiopathic or
congenital amblyopia of unknown aetiology. Alcohol and tobacco amblyopia mostly
are classified as toxic amblyopias and sometimes classified as nutritional
amblyopias. Currently, modern electrophysiological testing and imaging techniques,
will be found to have subtle pathological causes for different cases unknown.
Some cases may be pathological causes could be cortical or subcortical (Spalton
et al., 1984).   

Other type
of amblyopia is functional amblyopia, in which no organic lesion exists. Functional
amblyopia contains of four subtypes stimulus (or visual) deprivation amblyopia,
strabismic amblyopia, anisometropic amblyopia, refractive amblyopia
(isometropic amblyopia), and psychogenic amblyopia (hysterical amblyopia). Stimulus
deprivation amblyopia result from opacities or occlusion of the ocular media
(e.g. congenital cataracts or ptosis). Strabismic amblyopia induced by neural
changes in the deviated eye or visual pathway in strabismus. Strabismic
amblyopia and stimulus deprivation amblyopia both used to be called amblyopia
ex anopsia. Anisometropic amblyopia result from a blurred image in in
uncorrected anisometropia hypermetropia is common anisometropia. It is
association with microtropia. Refractive amblyopia often caused by bilateral
uncorrected refractive errors, usually hypermetropia. Psychogenic amblyopia is psychological
which includes meridional amblyopia which occurs in the principal meridian(s)
of high uncorrected astigmatism (Hardman Lea et al 1991).

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