الفهرس 
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Abstract
SUMMARY
N
oninflammatory corneal ectasias is a group of diseases including keratoconus, pellucid marginal degeneration (PMD) and keratoglobus. Keratoconus is the most common form of corneal ectasia characterized by progressive thinning of the central or inferior cornea, causing corneal steepening and cone formation. The disease typically presents during the second decade of life and is bilateral, but often one eye precedes the other. Pellucid marginal degeneration is a second cause of irregular steep cornea but less common than keratoconus characterized by a flattened cornea centrally and peripheral inferior ectasia running from 4 o’clock to 8 o’clock. The disease is bilateral; occurring in patients aged 20–40, in both males and females.
Keratoconus, pellucid marginal degeneration, and keratoglobus share a basic treatment algorithm. Visual correction for mild cases begins with glasses, followed by contact lens fitting. Other treatment modalities that allow stabilizing progression of the disease include Intrastromal rings and cross linking can also improve vision and facilitate contact lens fitting. Failing of these modalities and in more advanced cases, a surgical approach, designed to restore a more normal corneal contour like penetrating keratoplasty or DALK, is to be planned.
Ectatic corneal disorders are considered absolute contraindication for laser refractive surgeries due to the high risk of developing post lasik ectasia, thus meticulous screening of refractive surgery candidates prior to surgery is mandatory as most patients with corneal ectasia may not be aware of their disease and seek refractive surgery for the progressive diminution of vision and discomfort with glasses or soft contact lenses due to frequent change in their refractive error.
Detecting the cases of subclinical keratoconus had always been a challenge for refractive surgeons especially when the suggestive clinical signs and symptoms to differentiate subclinical keratoconus from the normal are not observed.
The evolution and expansion of refractive surgeries together with the development of new imaging modalities had its interest in discovering and early diagnosing different corneal disorders that could be hard to be detected clinically like forme fruste keratoconus or subclinical KC.
Our study was conducted on patients seeking consultation for refractive surgery at Al Mashreq Eye Centre during the period from June 2017 to December 2017.
We used the Pentacam device to screen 1439 refractive surgery candidates after being subjected to precise ocular examination and full general and ocular history taking, a total of 42 patients (84 eyes) showed topographic signs of manifest and subclinical keratoconus making a total prevalence of (3.0%), no cases with PMD or KG were found, but cases with KC having a topographic pattern mimicking PMD called pellucid like KC ”PLK” were found in 5 eyes (3 patients).
In our study males showed a higher prevalence than females (54.76 %) and (45.24%) respectively.
Subclinical KC cases, those who showed suspicious topographic signs with no clinical signs of KC, or had manifest KC in one eye and other eye showed normal topography those patients represented the majority of cases (51.2 %).
KC stage 1 was the most common compared to other stages (22.6 %) followed by stage 2 (20.2 %) and stage 3 (6.0 %).
Compound myopic astigmatism was the commonest refractive error in keratoconic patients (71.4 %) followed by simple myopic astigmatism (14.3 %) and mixed astigmatism (10.7 %), 2 eyes of 2 patients had myopia (2.4 %) and one eye had no error of refraction (1.2 %).
In conclusion, prevalence of KC accidently discovered in refractive population may reflect an approximate idea of its prevalence in general population, meticulous examination of refractive surgery candidates can forbidden bad consequences in patients at high risk of developing post lasik ectasia, and may save patients discovered at mild or moderate stages from the ultimate fate of keratoplasty by introducing alternative safer treatment modalities like CXL and ICRs, also surgeons should be aware that hypermetropia doesn’t eliminate the possibility of an associated ectatic corneal disease, although corneal ectasia induce index myopia and irregular astigmatism, it has been proven that cases of mixed astigmatism can also exist