الفهرس 
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Abstract
Myopia, or nearsightedness, is a common refractive error in which near objects are seen clearly, but far objects are blurry. It occurs when the light rays entering the eye don’t focus on the retina but focus in front of the retina. Myopia is due to either an elongation of the axial length more than normal (axial length is the distance between the anterior surface of the cornea and the fovea) or an increase in the curvature of the cornea. The mechanism of axial length elongation is unknown, but several studies have found that the process is slow and stable, except in myopia, where the rate of axial length change is rapid. There are a number of high myopia-related complications brought on by excessive axial length elongation, including foveoschisis, macular holes, choroidal neovascularization, lacquer crack formation, peripheral retinal degenerations, and rhegmatogenous retinal detachment. According to histologic studies, Chorioretinal atrophy is assumed to be caused by big and small artery obstruction and replacement with fibrous tissue. Choroidal atrophy leads to photoreceptor cellular death and subsequent loss of central vision because of an interruption of the oxygen and nutrition supply to the outer retina. In recent years, advances in optical coherence tomography (OCT) technology have improved our ability to image and measure the choroid in the human eye. Research using this technology over the past decade has dramatically improved our knowledge of the normal choroid, and its potential role in the regulation of eye growth and refractive error development. Optical coherence tomography (OCT) can obtain high-resolution and high-speed ophthalmic images of the posterior pole of the eye, one of the biggest contributions of OCT is the noninvasive visualization of the choroid. Swept-source optical coherence tomography (SS-OCT) can noninvasively provide high-resolution structural images of the choroid in a depth-resolved manner. This study aimed to find a correlation between axial length and choroidal changes in high myopia using swept-source optical coherence tomography (SS-OCT). This Prospective cross-sectional controlled study was conducted on sixty eyes with high myopia and 30 emmetropic, nirh (25-35 years old). High myopic patients with spherical equivalents equal to or more than -6.00 diopters (D) and axial lengths equal to or more than 26.5 mm were included. All patients were subjected to a complete medical history check, visual acuity testing, slit lamp examinations, and SS-OCT imaging studies. Summary of our results: • The participants’ baseline characteristics as the study group A1 included 14(46.7%) males and 16 (53.3 %) females, their ages ranged from 25 to 35 years with a mean of 30.0 ± 3.59. Study group A2 included 18(56.7 %) males and 12 (40.0%) females, their ages ranged from 25 to 35 years with a mean of 30.33 ± 3.55 years. The control group B included 30 emmetropic eyes [17 (56.7 %) males and 13 (43.3%) females]. Their ages ranged from 25 to 35 years old. There was no statistically significant difference between the study groups • The studied eyes of group A1 had a mean refraction of -10.13 ± 2.16 D with a range from -7.62: -14.75 D, and group A2 had a mean refraction of -18.52 ± 1.65 D with a range from -15.12: -21.12 D. As regard BCVA (decimal) in group A1 ranged from 0.50 – 1.0 with a mean of 0.71 ± 0.19 and group A2 ranged from 0.10 – 0.33 with a mean of 0.21 ± 0.08. • Axial length in group A1 with a mean of 27.49 ± 0.75mm ranged from 26.59 – 28.88mm, in group A2 with a mean of 30.28 ± 0.62mm ranged from 29.10 – 31.11 mm, and in group B with a mean of24.01 ± 0.33mm ranged from 23.50 – 24.50 mm. Axial length was significantly higher in eyes with high myopia in groups A1, A2 in compared to group B. There was significant difference between the studied groups. • Sub foveal choroidal thickness, choroidal thickness (CT) 1 mm nasal, 1 mm inferior, 1 mm temporal, and 1 mm superior to the fovea in group A1 were significantly lower as compared to group A2 (P values <0.001) and in group A1 and A2 were significantly lower as compared to group B (P values <0.001). • There was statically significant difference between the studied groups • By studying different choroidal thickness measurements, the choroid 1mm nasal to the fovea was found thinner when compared to other measurements with mean 218.7 ± 19.96 μm and ranged from189.0 – 247.0 μm in group A1 and with mean of 127.0 ± 25.60 μm ranged from 86.0 – 179.0 μm in group A2 . • group A axial length in total sample group had significant negative correlation with choroidal thickness sub foveal (r=-0.986, P<0.001), sub foveal choroidal thickness 1 mm nasal to the fovea (r=-0.989, P<0.001), ,1mm inferior to the fovea (r=-0.979, P<0.001),1 mm temporal to the fovea (r=-0.984, P<0.001), and 1 mm superior to the fovea (r=-0.991, P<0.001). • Eyes with group A total sample group refraction show significant positive correlation with axial length (r =0.997, P <0.001 ) , and significant negative correlation with sub foveal choroidal thickness (r=0.981,P<0.001),1mm nasal to the fovea (r=-0.988,P P<0.001),1mm inferior to the fovea(r=-0.977 , P <0.001) , 1mm temporal to the fovea (r= -0.981,P<0.001) and 1 mm superior to the fovea (r=- 0.991,P<0.001). • There was statistically significant difference between the studied groups. • Best corrected visual acuity (BCVA)in group A total sample group had significant negative correlation with refraction (r=-0.986, P<0.001), significant negative correlation with axial length (r -0.985, P<0.001). Best corrected visual acuity (BCVA) shows significant positive correlation with sub foveal choroidal thickness (r=-0.985, P<0.001),1mm nasal to the fovea (r= 0.985, P<0.001),1mm inferior to the fovea (r=0.986, P<0.001),1mm temporal to the fovea (r=0.986, P<0.001), and 1 mm superior to the fovea (r=0.984, <0.001). • There was statistically significant difference between the studied groups.