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KERATOCONUS UPDATE
Year : 2022  |  Volume : 36  |  Issue : 1  |  Page : 3-6

Keratoconus epidemiology: A review


Department of Ophthalmology and Visual Sciences, Paulista Medical School/Federal University of São Paulo (EPM/UNIFESP), Sao Paulo, Brazil

Date of Submission28-Aug-2021
Date of Decision05-Sep-2021
Date of Acceptance20-Dec-2021
Date of Web Publication08-Jul-2022

Correspondence Address:
Prof. José A P. Gomes
Department of Ophthalmology and Visual Sciences, Paulista School of Medicine/Federal University of São Paulo
Brazil
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sjopt.sjopt_204_21

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  Abstract 


Keratoconus is an ectatic corneal disease that affects both men and women, usually at a young age. Risk factors such as eye rubbing, environmental and genetic factors contribute to its pathogenesis. Keratoconus presents a variable prevalence, being as high as 5% of the population in the Middle East. In this review, an English-language search for keratoconus epidemiology was undertaken using the PubMed database. We present and discuss the findings of the most relevant epidemiological studies on keratoconus and describe its characteristics and risk factors, correlating them with its pathogenesis.

Keywords: Corneal ectasia, epidemiology, keratoconus, prevalence, risk factors


How to cite this article:
P. Gomes JA, Rodrigues PF, Lamazales LL. Keratoconus epidemiology: A review. Saudi J Ophthalmol 2022;36:3-6

How to cite this URL:
P. Gomes JA, Rodrigues PF, Lamazales LL. Keratoconus epidemiology: A review. Saudi J Ophthalmol [serial online] 2022 [cited 2022 Aug 14];36:3-6. Available from: https://www.saudijophthalmol.org/text.asp?2022/36/1/3/350222




  Introduction Top


Over the last years, researchers have found that the prevalence and incidence of keratoconus cases in the population presented a high variability.[1],[2],[3] There are different explanations for this variability, including the heterogeneity of epidemiological studies and the lack of well-defined criteria for the definition and classification of keratoconus.[4] These criteria have been mainly affected using new diagnostic imaging devices to assess different cornea parameters and by artificial intelligence algorithms.[1],[3]

A great majority of the prevalence studies are performed with patients in hospitals or medical clinics - when it is easier to collect data, leading to an underestimated prevalence as patients are commonly symptomatic, and the early and more subtle forms can be missed.[4],[5],[6],[]7,[8],[9],[10],[11],[12],[13],[14],[15] One of the first publications on keratoconus epidemiology is the study performed by Kennedy et al.[5] in Minnesota, USA, who found a prevalence of 0.054% based on the clinical findings of scissors movement in retinoscopy and keratometry. This number was similar to those reported in Finland[6] or in Denmark[7] but higher than those reported in Russia, 0.0004%,[8] or 0.0068% in Macedonia.[4] More recently, a large-scale study from the Netherlands showed a much higher prevalence of keratoconus, 0.27%.[9]

The true prevalence of the disease can be determined more accurately by population-based screening studies. Cross-sectional surveys enroll people who volunteer to participate in the investigation, creating selection bias.[4],[16] The first population-based screening study for keratoconus was published in the USA in 1959[17] when 0.6% of examined eyes had the ectasia diagnosis confirmed by finding the typical oval pattern images on a Placido disc.[17]

Another study in India using keratometry values of more than 48D as a cutoff found a prevalence of 2.3% of keratoconus.[18] A similar study conducted in China found a prevalence of 1% of corneas with more than 48D[19] using optical low coherence reflectometry biometry. An investigation of French army recruits using corneal topography reported a prevalence of keratoconus of 1.2%.[4] Using corneal topographic and tomographic values, other population-based surveys from Asia, the Middle East, and Oceania found a higher prevalence of keratoconus ranging from 0.9% to 3.3% [Table 1].[4] In 2018, Torres-Netto et al. used the Scheimpflug corneal tomography to determine the prevalence of keratoconus in a pediatric population in Saudi Arabia: 4.79% or 1:21, the highest reported so far.[24] A recent meta-analysis that included more than 50 million individuals from 15 countries determined that the global prevalence of keratoconus was 138/100,000.[25]
Table 1: Population-based epidemiological studies of keratoconus*,**

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Characteristics and risk factors for keratoconus

Age

Keratoconus has its most significant incidence in the age of 20 and 30 years, and progression occurs up to 35 years of age.[26],[27] New imaging technology, including corneal tomography, has provided an early diagnosis of keratoconus, even before the decrease of visual quality.[4] Corneal tomography has allowed an early therapeutic intervention and more efficient control of the ectasia progression. It is postulated that the rate of progression of keratoconus in children is higher than in adults.[28],[29] The most likely reason is the association of young patients with ocular allergy and eye friction.

The prevalence of keratoconus in patients older than 50 years is not very significant, ranging from 7.4% to 15%.[30],[31],[32] There is an inverse relationship between the severity of keratoconus and age. The corneal collagen interfibrillar space decreases with age, and the collagen bundles' fibers thicken, which increases the corneal rigidity. This change might explain the decrease in keratoconus incidence with increasing age.

Sex

Some authors reported a higher prevalence of keratoconus in men, with values ranging from 53% to 62%.[15],[32],[33],[34],[35] Others found a preponderance of women, with rates ranging from 53% to 66%.[15],[33],[36] The Collaborative Longitudinal Assessment of Keratoconus (CLEK) study showed the most significant functional discomfort in women, not evidenced in the clinical examination.[37]

A possible relationship between sex hormones and corneal biomechanical properties at different stages of life was raised after discovering that there are estrogen, progesterone, and androgen receptors on corneal epithelial cells and keratocytes.[38] High estrogen levels during pregnancy impair corneal biomechanics and thickness.[39],[40] Several studies have shown that serum levels of MMPs increase and serum levels of TIMPs decrease during pregnancy.[41],[42] The increase in proteolytic enzymes and the decrease in their inhibitors during pregnancy must be correlated with the progression of keratoconus. Another example of this correlation is the report of rapid progression of keratoconus in a 49-year-old woman on selective tissue estrogen regulator (STEAR) therapy for endometriosis.[30],[43]

Genetics

The pathogenesis of keratoconus seems to have the contribution of genetics and heredity. Familial keratoconus is primarily autosomal dominant.[44] Furthermore, monozygotic twins show a greater concordance in the topography of keratoconus than dizygotic twins.[44] On the other hand, family-based linkage studies have identified 19 likely genetic loci with mutations for keratoconus, indicating genetic heterogeneity. Keratoconus can show itself in different degrees of involvement, even in the same individual.[45],[46] These characteristics reveal the influence of cofactors in the phenotypic presentation of this corneal ectasia.

Keratoconus association with predisposing family history has also been investigated, presenting a wide variability.[15],[29],[46],[47] The CLEK study found a positive family history of keratoconus in 13.5% of the patients.[37] The Dundee University Scottish Keratoconus Study[48] reported a keratoconus rate of 5% for Caucasians and 25% for the Asian subgroup. This difference confirms a higher level of positive family history in populations with a higher prevalence of keratoconus. Similar results were observed in studies involving patients with keratoconus in families with many children.[6] Lapeyre et al. collected data from 94 unrelated patients already diagnosed with keratoconus and at least 2 of their first-degree relatives. Among the 221 relatives, 20 (9.05%) were diagnosed with keratoconus and 31 (14.03%) with subclinical keratoconus. The prevalence was estimated to be 0.14 among their parents, 0.03 among their children, and 0.10 among their siblings.[35] In the Iranian rural study, there was a higher odds ratio for the sibling pairs than parent-offspring pairs.[32] In communities with consanguineous relationships, the genetic influence for keratoconus is also strongly present.[49]

Environment

Keratoconus prevalence is not the same throughout the different parts of the world. Northern Europe, the Urals, northern USA, and Japan have low numbers,[5],[6],[8],[13],[42],[50] whereas in countries of the Middle East,[14],[15],[16],[18],[22],[23] India,[18] and China,[19] keratoconus is relatively common. A characteristic shared by the Middle East countries and some areas in India is the hot and dry climate, where oxidative damage due to excessive ultraviolet light exposure and ethnic background and nutrition seem to facilitate the manifestation of keratoconus[51] [Table 1]. Rabinowitz analyzed the main environmental factors associated with 218 patients with keratoconus were allergy in 44%, joint hypermobility in 34%, eye rubbing in 80%, and positive family history 10% compared with 183 regular patients (35%, 12%, 58%, and 0.05%, respectively).[47]

Eye rubbing and atopy

Allergy and syndromic conditions, such as Down's,[52] stimulate eye rubbing.[31] This action induces biomechanical alterations and inflammation of the cornea. Approximately 70% of keratoconus patients report rubbing their eyes. There are some variations in this association, whether the eye rubbing is gentle or vigorous[48] and the rubbing length. The CLEK study reported that 48% of keratoconus patients rubbed both eyes vigorously, and 2.2% rubbed only one eye.[37] Asymmetric keratoconus has also been correlated with eye rubbing. The mechanism behind this association includes the trauma on the ocular surface[53] that induces epithelial and stromal cells to secrete matrix metalloproteinases, which together with the release of inflammatory mediators lead to apoptosis of keratocytes and progressive loss of the stromal collagen and corneal thinning.[53]

There are some conflicting reports in the literature regarding the association between keratoconus and atopy.[53] A positive association has been reported,[35],[54],[55],[56] but many reports did not find a significant association when compared to a control group.[57],[58],[59] A multivariate logistic regression analysis confirmed that atopy was not truly associated with keratoconus but with eye rubbing.[6],[31],[35],[48],[52],[54],[55],[60]

Other factors

The association between diabetes and keratoconus has been reported.[61] Diabetes can exert a protective against keratoconus by enhancing nonenzymatic glycosylation, which increases protein crosslink.[62],[63]

Other genetic conditions have been linked to keratoconus such as mitral valve prolapse,[64] floppy eyelid syndrome,[65] obstructive sleep apnea,[30],[66] and connective tissue disorders as Ehlers-Danlos, Marfan syndrome, and Osteogenesis Imperfecta.[67]


  Conclusion Top


The prevalence of keratoconus is variable and affects up to 5% of the population in some regions of the world, as the Middle East. Both sexes are affected, reaching different ethnic groups. Environmental factors such as sunlight exposure and dry weather, eye rubbing, and genetic factors contribute to its pathogenesis. The combination of new imaging technologies and artificial intelligence algorithms has allowed earlier diagnosis and more efficient therapy, improving the visual prognosis and quality of life of patients with keratoconus.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Salomão MQ, Esposito A, Dupps WJ Jr. Advances in anterior segment imaging and analysis. Curr Opin Ophthalmol 2009;20:324-32.  Back to cited text no. 1
    
2.
Stapleton F, Alves M, Bunya VY, Jalbert I, Lekhanont K, Malet F, et al. TFOS DEWS II epidemiology report. Ocul Surf 2017;15:334-65.  Back to cited text no. 2
    
3.
Galvis V, Sherwin T, Tello A, Merayo J, Barrera R, Acera A. Keratoconus: An inflammatory disorder? Eye (Lond) 2015;29:843-59.  Back to cited text no. 3
    
4.
Gordon-Shaag A, Millodot M, Kaiserman I, Sela T, Barnett Itzhaki G, Zerbib Y, et al. Risk factors for keratoconus in Israel: A case-control study. Ophthalmic Physiol Opt 2015;35:673-81.  Back to cited text no. 4
    
5.
Kennedy RH, Bourne WM, Dyer JA. A 48-year clinical and epidemiologic study of keratoconus. Am J Ophthalmol 1986;101:267-73.  Back to cited text no. 5
    
6.
Ihalainen A. Clinical and epidemiological features of keratoconus genetic and external factors in the pathogenesis of the disease. Acta Ophthalmol Suppl 1986;178:1-64.  Back to cited text no. 6
    
7.
Nielsen K, Hjortdal J, Aagaard Nohr E, Ehlers N. Incidence and prevalence of keratoconus in Denmark. Acta Ophthalmol Scand 2007;85:890-2.  Back to cited text no. 7
    
8.
Gorskova EN, Sevost'ianov EN. Epidemiology of keratoconus in the Urals. Vestn Oftalmol 1998;114:38-40.  Back to cited text no. 8
    
9.
Godefrooij DA, de Wit GA, Uiterwaal CS, Imhof SM, Wisse RP. Age-specific incidence and prevalence of keratoconus: A nationwide registration study. Am J Ophthalmol 2017;175:169-72.  Back to cited text no. 9
    
10.
Tanabe U, Fujiki K, Ogawa A, Ueda S, Kanai A. Prevalence of keratoconus patients in Japan. Nippon Ganka Gakkai Zasshi 1985;89:407-11.  Back to cited text no. 10
    
11.
Santiago PY, Assouline M, Ducoussau F, Bazin S, Ballion JC, Mezraoui A, et al. Epidemiology of keratoconus and corneal topography in normal young male subjects. Invest Ophthalmol Vis Sci 1995;36:p. S307.  Back to cited text no. 11
    
12.
Barbara R, Gordon-Shaag A, Millodot M, Shneor E, Essa M, Anton M Prevalence of Keratoconus amoung young Arab students in Israel. Int J Keratoconus Ectatic Corneal Dis 2014;3:9-14.  Back to cited text no. 12
    
13.
Georgiou T, Funnell CL, Cassels-Brown A, O'Conor R. Influence of ethnic origin on the incidence of keratoconus and associated atopic disease in Asians and white patients. Eye (Lond) 2004;18:379-83.  Back to cited text no. 13
    
14.
Assiri AA, Yousuf BI, Quantock AJ, Murphy PJ. Incidence and severity of keratoconus in Asir province, Saudi Arabia. Br J Ophthalmol 2005;89:1403-6.  Back to cited text no. 14
    
15.
Ziaei H, Jafarinasab MR, Javadi MA, Karimian F, Poorsalman H, Mahdavi M, et al. Epidemiology of keratoconus in an Iranian population. Cornea 2012;31:1044-7.  Back to cited text no. 15
    
16.
Millodot M, Shneor E, Albou S, Atlani E, Gordon-Shaag A. Prevalence and associated factors of keratoconus in Jerusalem: A cross-sectional study. Ophthalmic Epidemiol 2011;18:91-7.  Back to cited text no. 16
    
17.
Hofstetter HW. A keratoscopic survey of 13, 395 eyes. Am J Optom Arch Am Acad Optom 1959;36:3-11.  Back to cited text no. 17
    
18.
Jonas JB, Nangia V, Matin A, Kulkarni M, Bhojwani K. Prevalence and associations of keratoconus in rural maharashtra in central India: The central India eye and medical study. Am J Ophthalmol 2009;148:760-5.  Back to cited text no. 18
    
19.
Xu L, Wang YX, Guo Y, You QS, Jonas JB, Beijing Eye Study Group. Prevalence and associations of steep cornea/keratoconus in Greater Beijing. The Beijing Eye Study. PLoS One 2012;7:e39313.  Back to cited text no. 19
    
20.
Waked N, Fayad AM, Fadlallah A, El Rami H. Keratoconus screening in a Lebanese students' population. J Fr Ophtalmol 2012;35:23-9.  Back to cited text no. 20
    
21.
Hashemi H, Beiranvand A, Khabazkhoob M, Asgari S, Emamian MH, Shariati M, et al. Prevalence of keratoconus in a population-based study in Shahroud. Cornea 2013;32:1441-5.  Back to cited text no. 21
    
22.
Hashemi H, Khabazkhoob M, Fotouhi A. Topographic keratoconus is not rare in an Iranian population: The tehran eye study. Ophthalmic Epidemiol 2013;20:385-91.  Back to cited text no. 22
    
23.
Hashemi H, Khabazkhoob M, Yazdani N, Ostadimoghaddam H, Norouzirad R, Amanzadeh K, et al. The prevalence of keratoconus in a young population in Mashhad, Iran. Ophthalmic Physiol Opt 2014;34:519-27.  Back to cited text no. 23
    
24.
Torres Netto EA, Al-Otaibi WM, Hafezi NL, Kling S, Al-Farhan HM, Randleman JB, et al. Prevalence of keratoconus in paediatric patients in Riyadh, Saudi Arabia. Br J Ophthalmol 2018;102:1436-41.  Back to cited text no. 24
    
25.
Lucas SE, Burdon KP. Genetic and environmental risk factors for keratoconus. Annu Rev Vis Sci 2020;6:25-46.  Back to cited text no. 25
    
26.
Krachmer JH, Feder RS, Belin MW. Keratoconus and related noninflammatory corneal thinning disorders. Surv Ophthalmol 1984;28:293-322.  Back to cited text no. 26
    
27.
Bilgin LK, Yilmaz S, Araz B, Yüksel SB, Sezen T. 30 years of contact lens prescribing for keratoconic patients in Turkey. Cont Lens Anterior Eye 2009;32:16-21.  Back to cited text no. 27
    
28.
Chatzis N, Hafezi F. Progression of keratoconus and efficacy of pediatric [corrected] corneal collagen cross-linking in children and adolescents. J Refract Surg 2012;28:753-8.  Back to cited text no. 28
    
29.
Léoni-Mesplié S, Mortemousque B, Touboul D, Malet F, Praud D, Mesplié N, et al. Scalability and severity of keratoconus in children. Am J Ophthalmol 2012;154:56-62.e1.  Back to cited text no. 29
    
30.
Pobelle-Frasson C, Velou S, Huslin V, Massicault B, Colin J. Keratoconus: What happens with older patients?. J Fr Ophtalmol 2004;27:779-82.  Back to cited text no. 30
    
31.
Zadnik K, Barr JT, Edrington TB, Everett DF, Jameson M, McMahon TT, et al. Baseline findings in the collaborative longitudinal evaluation of keratoconus (CLEK) study. Invest Ophthalmol Vis Sci 1998;39:2537-46.  Back to cited text no. 31
    
32.
Hashemi H, Heydarian S, Yekta A, Ostadimoghaddam H, Aghamirsalim M, Derakhshan A, et al. High prevalence and familial aggregation of keratoconus in an Iranian rural population: A population-based study. Ophthalmic Physiol Opt 2018;38:447-55.  Back to cited text no. 32
    
33.
Amsler M. The “forme fruste” of keratoconus. Wien Klin Wochenschr 1961;73:842-3.  Back to cited text no. 33
    
34.
Ertan A, Muftuoglu O. Keratoconus clinical findings according to different age and gender groups. Cornea 2008;27:1109-13.  Back to cited text no. 34
    
35.
Lapeyre G, Fournie P, Vernet R, Roseng S, Malecaze F, Bouzigon E, et al. Keratoconus prevalence in families: A french study. Cornea 2020;39:1473-9.  Back to cited text no. 35
    
36.
Laqua H. Hereditary diseases in keratoconus. Klin Monbl Augenheilkd 1971;159:609-18.  Back to cited text no. 36
    
37.
Wagner H, Barr JT, Zadnik K. Collaborative longitudinal evaluation of keratoconus (CLEK) study: Methods and findings to date. Cont Lens Anterior Eye 2007;30:223-32.  Back to cited text no. 37
    
38.
Khaled ML, Helwa I, Drewry M, Seremwe M, Estes A, Liu Y. Molecular and histopathological changes associated with keratoconus. Biomed Res Int 2017;2017:7803029.  Back to cited text no. 38
    
39.
Spoerl E, Zubaty V, Raiskup-Wolf F, Pillunat LE. Oestrogen-induced changes in biomechanics in the cornea as a possible reason for keratectasia. Br J Ophthalmol 2007;91:1547-50.  Back to cited text no. 39
    
40.
Gupta PD, Johar K Sr., Nagpal K, Vasavada AR. Sex hormone receptors in the human eye. Surv Ophthalmol 2005;50:274-84.  Back to cited text no. 40
    
41.
Wang C, Li AL, Pang Y, Lei YQ, Yu L. Changes in intraocular pressure and central corneal thickness during pregnancy: A systematic review and Meta-analysis. Int J Ophthalmol 2017;10:1573-9.  Back to cited text no. 41
    
42.
Pizzarello LD. Refractive changes in pregnancy. Graefes Arch Clin Exp Ophthalmol 2003;241:484-8.  Back to cited text no. 42
    
43.
Torres-Netto EA, Randleman JB, Hafezi NL, Hafezi F. Late-onset progression of keratoconus after therapy with selective tissue estrogenic activity regulator. J Cataract Refract Surg 2019;45:101-4.  Back to cited text no. 43
    
44.
Tuft SJ, Hassan H, George S, Frazer DG, Willoughby CE, Liskova P. Keratoconus in 18 pairs of twins. Acta Ophthalmol 2012;90:e482-6.  Back to cited text no. 44
    
45.
Ambrósio R Jr. Heritability of corneal shape in twin study. Invest Ophthalmol Vis Sci 2014;55:8365.  Back to cited text no. 45
    
46.
McMahon TT, Shin JA, Newlin A, Edrington TB, Sugar J, Zadnik K. Discordance for keratoconus in two pairs of monozygotic twins. Cornea 1999;18:444-51.  Back to cited text no. 46
    
47.
Rabinowitz YS. The genetics of keratoconus. Ophthalmol Clin North Am 2003;16:607-20, 27.  Back to cited text no. 47
    
48.
Weed KH, MacEwen CJ, Giles T, Low J, McGhee CN. The Dundee University Scottish Keratoconus study: Demographics, corneal signs, associated diseases, and eye rubbing. Eye (Lond) 2008;22:534-41.  Back to cited text no. 48
    
49.
Gordon-Shaag A, Millodot M, Essa M, Garth J, Ghara M, Shneor E. Is consanguinity a risk factor for keratoconus? Optom Vis Sci 2013;90:448-54.  Back to cited text no. 49
    
50.
Nielsen K, Hjortdal J, Pihlmann M, Corydon TJ. Update on the keratoconus genetics. Acta Ophthalmol 2013;91:106-13.  Back to cited text no. 50
    
51.
Davidson AE, Hayes S, Hardcastle AJ, Tuft SJ. The pathogenesis of keratoconus. Eye (Lond) 2014;28:189-95.  Back to cited text no. 51
    
52.
McMonnies CW. Mechanisms of rubbing-related corneal trauma in keratoconus. Cornea 2009;28:607-15.  Back to cited text no. 52
    
53.
Gordon-Shaag A, Millodot M, Shneor E, Liu Y. The genetic and environmental factors for keratoconus. Biomed Res Int 2015;2015:795738.  Back to cited text no. 53
    
54.
Nemet AY, Vinker S, Bahar I, Kaiserman I. The association of keratoconus with immune disorders. Cornea 2010;29:1261-4.  Back to cited text no. 54
    
55.
Shneor E, Millodot M, Blumberg S, Ortenberg I, Behrman S, Gordon-Shaag A. Characteristics of 244 patients with keratoconus seen in an optometric contact lens practice. Clin Exp Optom 2013;96:219-24.  Back to cited text no. 55
    
56.
Kaya V, Karakaya M, Utine CA, Albayrak S, Oge OF, Yilmaz OF. Evaluation of the corneal topographic characteristics of keratoconus with orbscan II in patients with and without atopy. Cornea 2007;26:945-8.  Back to cited text no. 56
    
57.
Lowell FC, Carroll JM. A study of the occurrence of atopic traits in patients with keratoconus. J Allergy 1970;46:32-9.  Back to cited text no. 57
    
58.
Gasset AR, Hinson WA, Frias JL. Keratoconus and atopic diseases. Ann Ophthalmol 1978;10:991-4.  Back to cited text no. 58
    
59.
Chan E, Chong EW, Lingham G, Stevenson LJ, Sanfilippo PG, Hewitt AW, et al. Prevalence of keratoconus based on scheimpflug imaging: The raine study. Ophthalmology 2021;128:515-21.  Back to cited text no. 59
    
60.
Jordan CA, Zamri A, Wheeldon C, Patel DV, Johnson R, McGhee CN. Computerized corneal tomography and associated features in a large New Zealand keratoconic population. J Cataract Refract Surg 2011;37:1493-501.  Back to cited text no. 60
    
61.
Seiler T, Huhle S, Spoerl E, Kunath H. Manifest diabetes and keratoconus: A retrospective case-control study. Graefes Arch Clin Exp Ophthalmol 2000;238:822-5.  Back to cited text no. 61
    
62.
Kuo IC, Broman A, Pirouzmanesh A, Melia M. Is there an association between diabetes and keratoconus? Ophthalmology 2006;113:184-90.  Back to cited text no. 62
    
63.
Kosker M, Suri K, Hammersmith KM, Nassef AH, Nagra PK, Rapuano CJ. Another look at the association between diabetes and keratoconus. Cornea 2014;33:774-9.  Back to cited text no. 63
    
64.
Gomes JA, Rapuano CJ, Belin MW, Ambrosio R Jr., Group of Panelists for the Global Delphi Panel of Keratoconus and Ectatic Diseases. Global consensus on keratoconus diagnosis. Cornea 2015;34:e38-9.  Back to cited text no. 64
    
65.
Donnenfeld ED, Perry HD, Gibralter RP, Ingraham HJ, Udell IJ. Keratoconus associated with floppy eyelid syndrome. Ophthalmology 1991;98:1674-8.  Back to cited text no. 65
    
66.
Gokhale NS. Epidemiology of keratoconus. Indian J Ophthalmol 2013;61:382-3.  Back to cited text no. 66
  [Full text]  
67.
Skoumal M, Haberhauer G, Mayr H. Concomitant diseases in primary joint hypermobility syndrome. Med Klin (Munich) 2004;99:585-90.  Back to cited text no. 67
    



 
 
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