|Year : 2018 | Volume
| Issue : 1 | Page : 19-23
Screening for keratoconus in a refractive surgery population of Upper Egypt
Adham S Saro1, Gamal A Radwan2, Usama A Mohammed2, Mortada A Abozaid MD 2
1 Department of Ophthalmology, Sohag University Hospital, Sohag, Egypt
2 Department of Ophthalmology, Faculty of Medicine, Sohag University, Sohag, Egypt
|Date of Submission||25-May-2017|
|Date of Acceptance||10-Sep-2017|
|Date of Web Publication||1-Feb-2018|
Mortada A Abozaid
Department of Ophthalmology, Faculty of Medicine, Sohag University, Sohag 82524
Source of Support: None, Conflict of Interest: None
The purpose of this study was to evaluate the prevalence of keratoconus among candidates of refractive surgery in Upper Egypt.
The study was conducted in Sohag University Hospital and Future Center (a private center) for laser in-situ keratomiluesis and refractive surgery in Sohag Governorate, Egypt.
This is an observational cross-sectional study.
Patients and methods
Refractive surgery candidates referred for preoperative evaluation before laser in-situ keratomiluesis, photorefractive keratectomy, and phakic intraocular lens implantation in the period from April 2015 to September 2015 were screened for keratoconus using Sirrus Scheimpflug camera.
The study included 1202 patients, 623 male and 579 female. Keratoconus was detected in 210 (17.5%) patients.
Prevalence of keratoconus among refractive surgery candidates in Upper Egypt is relatively high, which may reflect an underlying high prevalence in the general population.
Keywords: keratoconus screening, laser in-situ keratomiluesis, photorefractive keratectomy, refractive surgery, Upper Egypt
|How to cite this article:|
Saro AS, Radwan GA, Mohammed UA, Abozaid MA. Screening for keratoconus in a refractive surgery population of Upper Egypt. Delta J Ophthalmol 2018;19:19-23
|How to cite this URL:|
Saro AS, Radwan GA, Mohammed UA, Abozaid MA. Screening for keratoconus in a refractive surgery population of Upper Egypt. Delta J Ophthalmol [serial online] 2018 [cited 2018 May 22];19:19-23. Available from: http://www.djo.eg.net/text.asp?2018/19/1/19/224564
| Introduction|| |
Keratoconus (KC) is a noninflammatory condition in which the inferior or central portion of the cornea bulges forward in a cone-shaped manner as a result of thinning of the corneal stroma. Such corneal thinning induces a variable degree of myopia and irregular astigmatism, causing mild to severe visual impairment ,.
KC is bilateral in the vast majority of cases, although usually asymmetric in severity and progression. In many cases, the disorder may start unilaterally, but eventually the other eye becomes involved . Although unilateral cases do exist, their frequency might be even lower than reported, if appropriate diagnostic criteria and examination techniques that detect very early KC are used . The disease has its usual onset at puberty and, in many cases, progresses until the third to the fourth decade of life, when it usually arrests.
KC is a relatively common disorder with a reported prevalence ranging from 50 to 2300 per 100 000 and affects all races and both sexes equally . The reported prevalence of KC varies widely depending upon the geographic location, diagnostic criteria used, and the cohort of patients selected. The first population-based study was conducted by Hofstetter  using a Placido disc, and he reported an incidence of 600 per 100 000. The most commonly cited prevalence is 0.054% in Minnesota by Kennedy et al.  who used scissors movement in retinoscopy and keratometry for diagnosis. In Central India, the prevalence of KC was studied based only on the anterior corneal power obtained by keratometry. Prevalence of KC, defined as a corneal refractive power of at least 48 diopters, was 2.3%. However, the prevalence dropped to 0.6% using a cutoff power of at least 49 diopters and 0.1% using a cutoff value of at least 50 diopters . Environmental factors may contribute to the wide variation in prevalence. Geographical locations with plenty of sunshine and hot weather such as India  and the Middle East  have higher prevalence than locations with cooler climates and less sunshine such as Denmark  and Russia .
Family history of KC varies between 6 and 10% in most studies . KC affects both men and women. However, it remains unclear whether men or women have higher prevalence. A higher prevalence of KC has been found in patients with eye rubbing associated with atopy, ocular allergies, Down’s syndrome, and tapetoretinal degenerations . The prevalence of KC among refractive surgery candidates has been reported to vary from 0.9 to 5.8% ,,,,,.
To the best of our knowledge, no studies have been conducted to detect incidence or prevalence of KC in the general population, nor the refractive surgery candidates in Upper Egypt. In this study, the authors planned to detect the prevalence of KC in a refractive surgery population, which may represent an indirect indicator of the prevalence in the general population and to study the characteristics of the disease in such population.
| Patients and methods|| |
This observational cross-sectional study was held in the Ophthalmology Department of Sohag University Hospital in association with the Future Center [a private center for laser in-situ keratomiluesis (LASIK) and refractive surgery in Sohag Governorate, Egypt, where all cases were seen]. The study was performed in accordance with the Declaration of Helsinki guidelines for human research, and an approval was obtained from the Ethics Committee of Sohag Faculty of Medicine and an informed written consent was obtained from all participants in this study.
All patients referred for preoperative evaluation before refractive surgery, LASIK, photorefractive keratectomy, and phakic intraocular lens implantation in the period from 1 April 2015 to 30 September 2015 were included in this study. Patients younger than 18 years who were included in this study were anisometropic. Patients known to have KC and referred for intrastromal corneal ring segments and/or cross-linking were excluded from the study.
Preoperative valuation of the patients for refractive surgery was done as usual with stress upon the following:
- Complete history taking including age, sex, medical ophthalmic problems such as allergic conjunctivitis, last spectacle prescription, contact lens wear, and previous eye surgery. Patients with history or signs of allergic conjunctivitis were asked about the approximate number of attacks of eye allergy per year.
- Slit-lamp examination.
- Manifest and cycloplegic refraction.
- Scheimpflug corneal imaging (Sirrus; CSO, Florence, Italy) of both eyes with special attention to the saggital curvature map, corneal thickness map, and thinnest location, maximum anterior elevation in 4 mm central circle, maximum posterior elevation in 4 mm central circle, corneal volume, mean and maximum keratometry in 4 mm central circle, Q value, and KC screening class ([Figure 1]).
|Figure 1: Four-map image of a case of keratoconus (grade I) showing central steepening in the sagittal map with corresponding high anterior and posterior surface elevation and corneal thinning.|
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Cases diagnosed as KC with the sirrus camera were graded according to the Amsler_Krumeich classification  as follows:
Stage 1: Eccentric steepening, myopia, induced astigmatism, or both less than 5.00 D, mean central K readings of less than 48 D.
Stage 2: Myopia, induced astigmatism, or both from 5.00 to 8.00 D, mean central K readings of less than 53.00 D, absence of scarring, corneal thickness of more than 400 µm.
Stage 3: Myopia, induced astigmatism, or both from 8.00 to 10.00 D, mean central K readings of more than 53.00 D, absence of scarring, corneal thickness 200–400 µm.
Stage 4: Refraction not measurable, mean central K readings of more than 55.00 D, central corneal scarring, corneal thickness of less than 200 µm.
| Results|| |
This study included 1202 patients (623 male and 579 female). KC was detected in 210 patients, representing 17.5% of all screened patients. Of these patients, 117 (56.25%) were male and 93 (43.75%) were female. KC patients were subdivided into seven age groups ([Table 1] and [Figure 2]). The mean number of attacks of eye allergy per year in patients with KC were 2.77±2.17 times. The median number was three times per year. It ranged from 0 to 12 attacks per year. Eye allergy attacks were classified into two groups; the first group had two or less attacks per year, and this was associated with older patients and lower stages of KC, whereas the second group who had three or more attacks per year was associated with younger patients and higher stages of KC ([Table 2] and [Table 3]).
|Figure 2: A pie chart representing percentage of keratoconus in different age groups.|
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|Table 3: Distribution of the stage of keratoconus in relation to number of attacks of eye allergy per year|
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The mean thinnest location in KC cases was 450.71±54.06 µm, and the median was 454 µm. It ranged from 269 to 585 µm. The mean keratometry for KC patients was 48.23±6.17 D and the median was 46.78 D, ranging from 40.78 to 73.21 D. The mean posterior surface elevation in KC patients was 36.94±27.31 µm, and the median was 28 µm, and it ranged from 7 to 120 µm ([Table 4]).
|Table 4: Mean, median, and range values of thinnest location, keratometry, and posterior surface elevation|
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As regards the stage of KC; 99 (47.1%) patients had stage 1, 74 (35.2%) had stage 2, 16 (7.7%) had stage 3, and 21 (10%) had stage 4 ([Figure 3]).
|Figure 3: A pie chart representing percentage of different stages of keratoconus.|
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| Discussion|| |
Recently, KC has been dealt with as a serious potentially blinding corneal disease with higher frequency than reported before. However, this is not an actual increase in the number of cases; rather, it is due to introduction of better methods of diagnosis in addition to the role of refractive surgery in the early diagnosis of the disease, even the subclinical cases with minimal refractive error and no clinical signs.
The aim of this study was to assess the epidemiology of KC detected in patients who were seeking refractive surgery, and to have an approximate idea about the general distribution of the disease in Upper Egypt as regards prevalence, age and sex distribution, and associated factors.
It is well known that the prevalence of KC in the general population differs markedly according to the geographical location. For example, Gorskova  described that the prevalence was 0.3 per 100.000 in Russia, whereas Jonas  documented a prevalence of 2300 per 100.000 in central India.
However, the prevalence of KC in refractive surgery candidates shows less variation probably because KC patients tend to select themselves into the refractive surgery population because of their moderate to high myopia and the less than optimal optical quality with spectacles and contact lenses.
Wilson and Klyce  evaluated patients expressing an interest in refractive surgery for myopia in a clinic at the University of Texas during a 2-year interval using computed corneal topographic analysis and found that five eyes of three patients out of 53 (5.7%) were diagnosed as definite KC. Using video-keratography, Nesburn et al.  screened 146 apparently normal myopic eyes of 91 candidates for photorefractive keratectomy and found that five (5.49%) patients were having KC in addition to one patient with early pellucid marginal degeneration. Ambrosio et al.  used Atlas anterior topography, biomicroscopy, and ultrasonic pachymetry to screen 1392 candidates for refractive surgery, and 12 (0.9%) were found to have KC. Hori-Komai et al.  screened 2784 patients requesting refractive surgery and found that 1.62% have KC using TMS-2 topography and the Klyce-Maeda KC index to detect early KC. Xu et al.  used ultrasonic pachymetry and Orbscan IIz to screen 552 patients seeking refractive surgery and found that 13 (2.3%) patients have forme fruste or manifest KC. Bamashmus et al.  screened 2091 candidates for refractive surgery using pachymetry, biomicroscopy, and topography (TMS-2) and found that 5.8% were poor candidates because of forme fruste or manifest KC. A summary of these six studies is provided in [Table 5].
|Table 5: Summary of studies that investigated the prevalence of keratoconus in refractive surgery population|
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In the present study, using the Sirrus Scheimpflug system, the prevalence of KC in patients seeking refractive surgery was 210 out of 1202 (17.5%) patients. Such unexpected high prevalence may suggest an underlying high prevalence in the general population, which may be due to the hot dry weather and the increased prevalence of allergic conjunctivitis and eye rubbing in Upper Egypt.
In the current study, a higher prevalence of KC was found in males (56%) than in females (44%), and a strong relationship between age and stage of KC was noted with higher percentage of stage 4 KC in younger age groups. In addition, it has been noticed that increased number of attacks of eye allergy per year was associated with younger age groups and higher stage of KC, which corresponds to previous studies that found a strong relationship between frequent eye rubbing and the development and upgrading of KC ,.
Financial support and sponsorship
Conflicts of interests
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]