الفهرس 
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Abstract
Keratoconus is a bilateral and asymmetrical progressive disease characterized by non-inflammatory localized thinning of the corneal stroma, most commonly in the inferior temporal as well as the central cornea and results in a conical corneal shape, irregular astigmatism and myopic shift. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 1.3 - 50 per 100,000, but it varies in relation to environmental, genetic, and ethnic factors. Theories have suggested causes of keratoconus including genetic, biomechanical and biochemical causes.
Different systems for classificationof keratoconus have been proposed based on; morphology, disease evolution, ocular signs and index-based systems including; Corneal Topography, Optical Coherence Tomography and Corneal Aberrometer. Recently, relatively new instruments like Ocular Response Analyzer and Pentacam have included built-in software for detection and monitoring keratoconus.
Keratoconus management varies according toits severity. Traditionally, spectacles are used to manage the incipient cases, contact lenses for mild to moderate cases and keratoplasty for severe cases. New surgical options have been developed such as, corneal ring segments implantation and cross-linking procedures to treat moderate to severe cases.
This study was conducted on 60 eyes of 44 patients from both sexes with age ranging from 18 to 36 years diagnosed as progressive keratoconic patients and divided into 2 groups; group 1 involved 30 eyes were treated with corneal collagen cross-linking (CXL) and group 2 involved also 30 eyes treated by combined corneal cross linking and femtosecond laser-assisted intra-stromal corneal ring segment (ICRS). Our aim was to compare both groups for visual, refractive, and topographic outcomes, contrast sensitivity measurements, and high order aberrations (by Pentacam).
A complete history from all cases was taken and a full ophthalmological examination including visual acuity, manifest refraction, and anterior and posterior segments examination was done. Pentacam and contrast sensitivity measurement were performed as well to all patients at the pre-operative and 3 months, 6 months and one year post-operative follow-up visits. Obtained data was compared to the pre-operative data and between both groups.
In our study, during the postoperative first year follow-up, both treatment options were safe and effective in treatment and stabilization of progressive keratoconus. Furthermore, no postoperative complications were observed with the ICRS orwith the CXL procedures.
Both groups showed obvious changes between the preoperative and the postoperative values, with a significant increase in UAVA, and contrast sensitivity; both lower frequency (6cpd)with an early effect in group 2 and higher frequencies (12cpd, 18cpd) at 6 months and one year postoperatively.
Both groups also showed significant decrease in spherical equivalent refraction at 6 months and one year follow-ups. group 2, in addition, showed significant increase in the BCVA at one year, and significant decrease in the following: the steepest K at 6 monthsand one year, the refractiveand keratometric astigmatism at all follow-up visits, and the corneal thickness at 3 months follow-up.
The combined CXL with ICRS group showed an additional improvement over CXL group for UDVA at 3 months, BCVA at one year, in refractive and keratometric astigmatism at all follow-up visits, and in corneal ashericity at 3 months and 6 months follow-up visits. Despite its added effect, the combined group was not significantly different from CXL group for other parameters.
As a result, we found that cross linking procedure is a safe and effective method for halting the progression of keratoconus. However, visual improvement is generally started after 6 months from treatment and may be due to decreased SE and improvement in contrast sensitivity. Hence, ICRS implantation enhances the flattening effect of CXL on the cornea, improves corneal asherisity and contrast sensitivity, and augments the CXL effect on SE and astigmatism, resulting in early improvement in visual acuity and patient satisfaction.