الفهرس 
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Abstract
Keratoconus is a progressive, non-inflammatory, ectatic corneal disorder, characterized in most cases by progressive corneal thinning that results in corneal protrusion, astigmatism, and decreased vision. The aetiology of keratoconus is still uncertain, although many pathological, biomechanical and biochemical changes at the structural and cellular level of the cornea have been suggested. There are several classifications of keratoconus depending on the severity of the clinical and topographic signs. The Amsler-Krumeich grading system was applied to grade the cases involved in this study. With the developments in refractive surgery and contact lens fitting, corneal topography has become a widely used diagnostic tool. Various types of topographers have been introduced for assessment of the corneal parameters that can aid diagnosis, facilitate monitoring and intervention for corneal diseases such as keratoconus. Pentacam and Orbscan are valuable noncontact diagnostic tools which are able to analyze both qualitatively and quantitatively the morphology of the cornea and represent data about the corneal topographic pattern, corneal thickness & corneal elevation, which are then displayed on color maps to facilitate interpretation. [eyes of 22 keratoconus patients (8 male and 14 female eyes) of different clinical stages were enrolled in this study which was aimed to compare the corneal measurements, obtained by rotating scheimpflug camera (Pentacam) and scanning-slit topography (Orbscan IIz), in keratoconic eyes. The mean age of the patients was 25.833 ± 5.590 years (range: 17 - 40y). All patients in this study were subjected to a thorough ophthalmological examination including visual acuity assessment, manifest refraction, and slit lamp biomicroscopy which was followed by corneal imaging using Pentacam HR and Orbscan IIz. The average K value in the studied sample was 49.31 ± 3.449 D. Considering Amsler–Krumeich classification, 13 eyes were in stage I, 11 in stage II, and 6 in stage III of keratoconus severity. According to this study, there was no significant difference noticed between the two devices for CCT measurements (456.01 and 451.92 μm). In addition, ICC was high 0.980 (95% CI: -2.27 to 10.476, P=0.198) and there was a significant positive correlation between both assessment techniques (r = 0.963 – p < 0.001). In the current study, the two instruments made similar measurements for TCT (442.58 and 441.29 μm) with high ICC of 0.971 (95% CI: -6.81 to 9.39, P=0.746). Additionally, a significant positive correlation was present between Pentacam and Orbscan (r = 0.942 – p < 0.001). [ In terms of the ACD, Pentacam reported significantly lower values compared to the Orbscan (3.14 vs. 3.28 mm respectively). Despite that difference, there was a significant positive correlation between both devices (p < 0.001) together with a high ICC of 0.985 (95% CI: -0.18 to -0.09, P<0.001). Similarly, regarding PD, there was a significant difference between Pentacam and Orbscan (3.77 vs. 4.30 mm respectively – p < 0.001). However, a significant positive correlation was detected between the two techniques (r = 0.699 – p < 0.001) together with a moderate strength ICC of 0.638 (95% CI: -0.69 to -0.37, P<0.001).