الفهرس 
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Abstract
OCT is a non- invasive method that have the ability of in situ visualization of tissue, It became of particular importance in ophthalmology because of the key information provided by them regarding the physiology and the diseases related to the eye .The structures of the anterior segment can be analyzed using OCT .It became used increasingly due to its ability for providing a non -contact scans to the anterior segment of the eye. This makes the examination comfortable, safe and fast.
This includes the option to determine central corneal thickness and also corneal epithelial thickness in addition to anterior corneal radius of curvature.
The cornea is considered the most important structure of refraction for the eye. Corneal parameters measurements are very important in both diagnosis and management of many ocular pathological conditions that may cause bad visual outcome.
CCT is an important indicator of cornea health. Interest in CCT measurement has greatly increased because its effect on IOP measurement. CCT itself affects the accuracy of measurement of IOP.
In addition to all that in the era of refractive surgery, CCT values became marvelously important to evaluate the patients pre-operatively because they affect the decision whether not or to do the operation, type of the recommended procedure and rate of the complications that might occur postoperatively.
The human corneal surface is covered by the corneal epithelium, where it plays an important role in protecting and maintaining the optimum optical quality. It cannot be ignored that the corneal epithelium contributes greatly to the corneal refractive power and hence to the ocular refraction. Some diseases like keratoconus alter the thickness of the epithelium to reduce the irregularity of the corneal surface.
Anterior corneal curvature (ACC) is related to the frontal surface of the cornea and is one of the valuable measurements used to make optical properties of the cornea more characteristic. In clinical practice, vertical and horizontal anterior corneal curvatures are both measured.
Anterior curvature expressed in radii (millimeters typically) is of importance for fitting and management of contact lens, analysis of ocular aberration, refractive surgery of cornea in addition to diagnoses and treatment of corneal pathological cases like keratoconus.
Aim of the study is to make a biometric study for the anterior segment of the eyes of healthy individuals using Spectral-Domain AS-OCT. Anterior segment spectral domain OCT was used to determine range of distribution, correlation of ocular parameters (CCT, CET, horizontal and vertical corneal radii of curvature) in a number of individuals with abroad range of refractive error and IOP.
Subjects and methods : The study was designed as a cross-sectional, highly selective study, the participants were chosen by simple random sampling. The study was conducted from February 2017 to September 2017. This study was conducted on 100 eyes of 100 volunteers 52 males and 48 females ranging from (20-60) year-old. The study will include healthy individuals including 34 myopic, 34 emmetropic and 32 hypermetropic individuals.
IOP was measured using Goldman applanation tonometer.
Measurements of refractive status were detected by autorefractor (Nidek AR-310 Auto refractometer) and then confirmed by retinoscopy and spherical equivalent was calculated of astigmatic patients.
Using anterior segment spectral domain optical coherence tomography (SD-OCT) (3D OCT-2000 (Topcon Corp., Tokyo, Japan)); central corneal thickness, Corneal epithelial thickness and corneal radii of curvature both horizontally and vertically were measured. .The subject was asked to look at the internal fixation target and. Three scans were obtained for each tested eye and the mean of these scans was used for the analysis.
The results of the current study can be summarized as follow: This study including 100 eyes of 100 subjects from which age range between (20-60) years old and males (52%) were more than females (48%).
The mean IOP was 15.65 ± 1.56 mm Hg.
Considering all eyes together, mean CCT was 541.62 ± 21.11μm . (mean SD In males it was 541.94 ± 22.53 and in females 541.27 ± 19.68) . This study showed no statistically difference in myopic (542.79 ± 20.02), emmetropic (540.09 ± 22.29) or hypermetropic (542.0 ± 21.52) (f=0.145, p=0.865) (Table 2). The study also showed positive correlation between CCT and IOP (r = 0.867, p<0.001) and also positive correlation between CCT and CET (r= 0.516, p<0.001).
Regarding CET; average was 54.80 ± 2.68μm. (mean SD was 54.75 ± 2.44 in males and 54.85 ± 2.94 in females (Table 4)). The study showed no correlation between CET and refractive error (f= 0.165, p=0.848) (Table 2). IT showed that there is also positive correlation between CET and IOP (r=0,490, p<0,001).
About corneal radii of curvature the study showed that average horizontal corneal radius of curvature was 7.61 ± 0.25mm while mean vertical corneal radius of curvature was 7.61 ± 0.27mm . This study has showed the correlation between the corneal radius of curvature and refractive state of the eye (p<0.001) (Table 2) as it was found that myopes (H 7.53 ± 0.19 mm – V 7.50 ± 0.18mm) tend to have steeper corneas meaning shorter radius of curvature followed by the emmetropes (H 7.52 ± 0.23mm - V 7.50 ± 0.21mm) and lastly the hypermetropes (H 7.80 ± 0.23mm - V 7.84 ± 0.28mm) whose corneas tend to be flatter with longer radius of curvature. On the other hand there was no correlation between corneal radius of curvature and IOP (H r= -0.094, p=0.351 – V r= -0.060, p= 0.556).
This study showed what no association between corneal radius of curvature and CCT or CET.
Regarding anthropometric characteristics of the study sample, age and gender were not associated with CCT, CET or corneal radii of curvature .