**5. Gender differences**

*Ocular Surface Diseases - Some Current Date on Tear Film Problem and Keratoconic Diagnosis*

based study in Saudi Arabia, the incidence was 20 per 100,000 in young patients age ranged from 8 to 24 years, with more than half (54%) of patients classified as advanced keratoconus [48]. In India, onset of disease has been reported to happen at a younger age and progresses more rapidly [49]. In a study totaling 5200 Indian patients, the average age of presentation was 21.5 years with 1970 patients (37.9%) having an onset of disease before 20 years of age. The overall prevalence was very high at 5200/100,000 (5.2%) [50]. In a rural population in central India, a slightly lower prevalence of 2300/100,000 was recorded [51]. In huge contrast, the prevalence in Japanese was low: 12 in 100,000 males and 5.6 in 100,000 females [52]. In Chinese, a population based study in Beijing for an elder population of 3468 individuals aged 50–93 years, steep cornea/keratoconus occurred in 33 persons, giving a prevalence of 950 in 100,000 [53]. In this study steep cornea/keratoconus was defined as corneal refractive power equal to or greater than 48 diopters according to optical low-coherence reflectometry. In a study 2 years later in Singapore in people older than 40 years, the prevalence of steep cornea was comparable in Malays (606 in 100,000), Indians (1000 in 100,000), and Chinese (500 in 100,000)

A summary of reported studies (**Table 1**) shows in general higher prevalence in Asians than Caucasians, with disease started earlier and severe. But occurrence at Japanese is low. There are also vast differences in the same ethnic group. Environmental factors and investigative criteria other than genetics would affect the reported occurrence of keratoconus. The very wide range of keratoconus prevalence and incidence may be a result of non-uniform diagnostic criteria applied in different studies. Another cause may be genetic variations among different ethnic populations. There is a significant role of ethnicity. Hence rigorous, multiethnic, well-organized, and population-based epidemiological studies with large sample sizes for keratoconus are needed. Nevertheless, in addition to ethnicity, currently reported epidemiologic studies indicate that potential causes underlying higher prevalence of keratoconus could be due to a host of factors including geographic locations, ultraviolet irradiation exposure, consanguinity, persistent eye rubbing and atopy. The etiology of keratoconus is complex, involving multi-factorial inter-

(0.5%) (95% CI 0.3–0.8%) [54].

**4.2 Basis for ethnic diversities**

actions of genetic, personal, and environmental factors.

*Geographical and ethnical diversities in reported prevalence of keratoconus.*

**58**

**Table 1.**

Whether males and females have different prevalence is unclear as inconsistent results have been reported [55]. Disease onset in males tend to be earlier and disease progression faster than female patients in both Asian and Western studies, while gender bias has not been consistent [40, 50, 56, 57]. Male and female sex, did not show difference in prevalence, while gender bias have not been consistent in previous reports. In a Japanese cohort of 90 patients, men were diagnosed younger than women [58]. A questionnaire survey of 670 patients in New Zealand also showed male patients were detected at younger ages than females [59]. In a Turkish cohort of 248 patients, there was no gender difference in cornea properties including central cornea thickness and keratometry parameters [56]. In a study in the USA of 1209 patients from 16 clinics, while there was no difference in disease severity according to keratometry or scarring, less women were had have Vogt striae [57]. Female patients in this study had higher mean age than the males. Overall, there was indication that men developed keratoconus earlier, progressed faster and required more serious treatment.
