الفهرس 
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Abstract
SUMMARY AND CONCLUSION
The choroid is the vascular layer of the eye, containing connective tissue, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm. The choroid provides oxygen and nourishment to the outer layers of the retina. Along with the ciliary body and iris, the choroid forms the uveal tract. The primary role of the choroid is nourishment and thermoregulation of the retina; however, it also is thought to have a role in emmetropization and refractive error development.
The structure of the choroid is generally divided into four layers (classified in order of furthest away from the retina to closest): Haller’s layer which is the outermost layer of the choroid consisting of larger diameter blood vessels, Sattler’s layer which is layer of medium diameter blood vessels, Choriocapillaris which is layer of capillaries and Bruch’s membrane innermost layer of the choroid.
Myopia is a condition of the eye where light focuses in front of the retina. This causes distant objects to be blurry while close objects appear normal. Other symptoms may include headaches and eye strain. Severe near-sightedness increases the risk of retinal detachment, cataracts, and glaucoma. Myopia is generally classified into two groups: non-pathologic and pathologic myopia. Both groups have separate disease processes, clinical features, and prognoses. Non-pathological myopia is also commonly referred to as physiological, simple or school myopia. In non-pathologic myopia the refractive structures of the eye develop within normal limits. Axial myopia is attributed to an increase in the eye’s axial length. Refractive myopia is attributed to the condition of the refractive elements of the eye.
Myopia presents with blurry distance vision, but generally gives good near vision. In high myopia, even near vision is affected as objects must be extremely close to the eyes to see clearly, and people with myopia cannot read without their glasses prescribed for distance. On fundoscopic examination of the eye, the optic nerve appears to be tilted and an area of white sclera could be seen on next to the disc with a line of hyperpigmentation separating this area from normal retina.Optical correction using glasses or contact lenses is the most common approach in management of myopia other approaches include drugs (mostly atropine), vision therapy, orthokeratology, and refractive surgery.
Our study suggest that the choroid may have a role in human eye growth and refractive error development.Choroidal thickness could be an important parameter to study the pathogenesis of macular vision loss in high myopia (Spaide et al., 2008). Pathological myopia is one of the leading causes of visual impairment in the world (Fredrick, 2002; Hayashi et al., 2010). In myopia, axial elongation of globe can cause biomechanical stretching and thinning of choroid and retinal pigmented epithelium layers, leading to increased risk of chorioretinal complications such as choroidal neovascularization, posterior staphyloma, lacquer cracks in Bruch’s membrane and myopic foveoschisis, which may lead to visual loss.
We conclude that the SFCT is thinner in myopes (84.54 ±31.93) than emmetropes(92.94 ± 28.52).in parafoveal and perifoveal area the nasal CT is the most thin and the temporal CT is the most thick in both groups (emmetropes and myope) except in emmetropic group the lower parafoveal CT is the most thick.The difference between CT measurements between four quadrants (upper, lower, nasal and temporal) in parafoveal and perifoveal area between myopic and emmetropic group is non significant.
In emmetropic group the temporal perifoveal CT is the most thick and the nasal perifoveal CT is the most thin and these differences were statistically highly significant (P <0.001). in myopic group the temporal perifoveal CT is the most thick and the nasal perifoveal CT is the most thin and these differences were statistically highly significant (P<0.001) but in parafoveal area no significant difference was detected.
In our study the difference between CMCT, mean total parafoveal and perifoveal CT in both groups is significant. CMCT is the most thin and perifoveal choroidal thickness is the most thick in both groups.
We found correlation between CT and refraction.in emmtropic group there was negative correlation between refraction and both upper parafoveal CT and upper perifoveal CT which is significant.in myopic group there was negative (reverse) correlation between refraction and SFCT, upper parafoveal and upper perifoveal CT which is also significant and positive correlation between refraction and nasal perifoveal CT which is also statistically significant.