Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
ACTA OPHTHALMOLOGICA SCANDINAVICA 2004 Risk factors for pterygium in an adult Jordanian population Muawyah D. Al-Bdour and Mo’tasem M. Al-Latayfeh Department of Ophthalmology, School of Medicine, Jordan University of Science and Technology, Irbid, Jordan ABSTRACT. Purpose: To evaluate the risk factors for the development of pterygium in a Middle Eastern country (Jordan) and to compare our findings with those from other countries. Methods: This study was conducted in Irbid District, in northern Jordan, a region located 31 degrees north of the equator, with a stable, subtropical climate. In this case control study, 96 adult subjects presenting with pterygium were interviewed and compared to 192 control subjects who were group-matched for age and sex. A standard questionnaire and eye examination were completed for both groups. Results: There was a strong positive association between pterygium and environmental factors. The most striking increase in the risk of pterygium occurred in subjects who worked outdoors compared to those who worked indoors, with an odds ratio of 5.47. Current and previous sunlight exposures were associated with a higher risk of developing pterygium, with odds ratios of 3.54 and 4.52, respectively. Previous use of sunglasses represented a protective element, but the protective role of recent use of sunglasses was not statistically significant. Conclusion: There is a statistically significant association between outdoor work, sunlight exposure and pterygium formation. Efforts should be made to educate outdoor workers to wear sunglasses and brimmed hats. Public education should focus on avoidance of unnecessary sunlight exposure. Key words: Jordan – pterygium – sunlight exposure – sunglasses Acta Ophthalmol. Scand. 2004: 82: 64–67 Copyright # Acta Ophthalmol Scand 2003. Several modalities of surgical treatment have been advocated, but the recurrence rate remains high (Lewallen 1989; Sebban & Hirst 1991; Sugar 1992; Dan et al. 1997). Although a proportion of cases appear to be inherited (Faraldi & Gracis 1976; Booth 1985; Hecht & Shoptaugh 1990), pterygium formation has been linked to corneal and conjunctival microtrauma caused by exposure to sunlight and particulate matter such as dust particles (Dimitry 1937; Dhir et al. 1967; Moran & Hollows 1984; Mackenzie et al. 1992; Threlfall & English 1999). Risk factors for the development of pterygium have been evaluated in different parts of the world (Rojas & Malaga 1986; Khoo et al. 1998; Saw & Tan 1999), including the Middle East (Youngson 1972; Hosni 1977; Norn 1982). This study was designed to evaluate the potential risk factors for the development of pterygium in Jordan and to compare our findings with those from other countries. doi: 10.1046/j.1600-0420.2003.00213.x Material and Methods Introduction The term ‘pterygium’ describes a fleshy, triangular or wing-shaped growth of the conjunctiva that encroaches onto the cornea. It is not simply a degenerative process arising from pinguecula, as has been previously thought (Wong 1978; Hill & Maske 1989). More recent reports have suggested that pterygium is an active, invasive, inflammatory 64 process associated with cellular proliferation, connective tissue remodelling and angiogenesis leading to fibrovascular proliferation (Kwok & Coroneo 1994; Coroneo et al. 1999). Pterygia are usually small and relatively benign, but they are common (Luthra et al. 2001; Wong et al. 2001). They cause considerable discomfort and tearing, and may progress to involve the central part of the cornea. The study was conducted at the Princess Basma Teaching Hospital, which is affiliated to the Jordan University of Science and Technology, from July 1999 to April 2002. This hospital serves the district of Irbid in the north of Jordan, which is located 31 degrees north of the equator and has a stable, subtropical climate. A total of 96 adult patients presenting with problems related to pterygia were included in ACTA OPHTHALMOLOGICA SCANDINAVICA 2004 the study. The next two consecutive patients to present after each pterygium patient in the same outpatient clinic were selected as controls. All subjects were group-matched for age and sex. All subjects agreed to be included in the study after the nature of the study had been explained and they had been interviewed by the ophthalmologist. The same questionnaire was given to all subjects in both groups. Each subject’s main occupation during the previous 7 years was classified as either predominantly ‘indoor’ (such as office workers, clerks, teachers, etc.) or ‘outdoor’ (such as taxi drivers, construction workers, etc.) based on the nature, location and circumstances of their work. Each subject was questioned about their current level of sunlight exposure in average hours per day and their exposure level 7 years previously. In addition, their use of protective sunglasses at the time of the study and 7 years previously was recorded. Data including age, gender, smoking and previous surgical treatment were collected. All subjects were examined using slit-lamp biomicroscopy. When present, the size of the pterygium was measured in millimetres from its apex to limbus, using the slit-lamp beam. Odds ratios (ORs) and 95% confidence intervals (95% CI) were calculated to obtain the relative risk of developing pterygium for each risk factor. Results A total of 96 pterygium subjects and 192 control subjects were included in the study. The mean age of the pterygium subjects at interview was 49.1 years (range 22–72 years), while that of the control subjects was 48.2 years (range 25–70 years). In all, 83% of pterygium subjects were male, as were 77.6% of control subjects. As shown in Fig. 1, 54 pterygium subjects (56%) had unilateral disease almost equally distributed between the two eyes, while 42 (44%) had bilateral disease. The average size of pterygium was 2.1 mm in the right eye and 1.9 mm in the left eye. Twelve patients out of 96 had had previous surgical treatment for pterygium. The results shown in Table 1 demonstrate that those who worked predominantly outdoors were 5.74 times more at risk of developing pterygium than Fig. 1. Comparison between unilateral and bilateral disease among case subjects. those who worked indoors. Current and previous sunlight exposures (on an average of 1 hour or more daily) were strongly associated with a higher risk of developing pterygium, with ORs of 3.54 and 4.52, respectively. Previous use of sunglasses was shown to be protective against pterygium formation. However, the protective role of current use of sunglasses was not statistically significant. In addition, smoking did not represent a statistically significant risk factor for pterygium formation. Bilaterality of the disease was independent of the studied risk factors, in that the studied risk factors were not found to increase the risk of bilateral involvement. Discussion The most striking increase in the risk of developing pterygium occurred in subjects who worked in an outdoor environment compared with those who worked indoors. This finding is comparable to that of similar studies evaluating the relationship between outdoor work and pterygium conducted in different parts of the world (Rosenthal et al. 1988; Mackenzie et al. 1992; Nakaishi et al. 1997; Wong et al. 2001). In a study conducted in Japan, the OR for the prevalence of pterygium among outdoor workers as compared to indoor workers was 2.1 (95% CI 1.68–2.45) (Nakaishi et al. 1997). This Table 1. Comparison between pterygium subjects (cases) and control subjects. Cases Controls Total OR 95% CI p-value n (%) n (%) No. of subjects 96 (100) 192 (100) 288 Sex Males Females 80 16 (83) (17) 149 43 (77.6) (22.4) 229 59 Work Outdoors Indoors 62 34 (64.6) (35.4) 48 144 (25) (75) 110 178 5.47 3.3–9.1 < <0.005 Sun exposure 7 years previously 1 hour/day 78 (81) < 1 hour/day 18 (19) 94 98 (49) (51) 172 116 4.52 2.6–7.9 <0.005 Sunglasses 7 years previously Absent 76 (79) Present 20 (21) 87 105 (45) (55) 163 125 4.59 2.7–7.9 <0.005 Current sun exposure 1 hour/day 70 < 1 hour/day 26 (73) (27) 83 109 (43) (57) 153 135 3.54 2.1–5.9 <0.005 Current sunglasses Absent 56 Present 40 (58) (42) 90 102 (47) (53) 146 142 1.59 NS NS Smoking Smoker Non-smoker (46) (54) 102 90 (53) (47) 146 142 0.75 NS NS 44 52 OR ¼ odds ratio; 95% CI ¼ 95% confidence interval; NS ¼ not significant. 65 ACTA OPHTHALMOLOGICA SCANDINAVICA 2004 association may be related to a higher level of exposure to sunlight (Rojas & Malaga 1986; Mackenzie et al. 1992; Nakaishi et al. 1997; Threlfall & English 1999) and possibly to a higher level of exposure to dust (Dimitry 1937; Mackenzie et al. 1992; Nakaishi et al. 1997) in outdoor workers. In our study, outdoor workers were more likely to be male, because outdoor occupations are predominantly male vocations in Jordan. This explains why the majority of pterygium subjects were male. Current and previous sunlight exposures were associated with a higher risk of developing pterygium. The association was stronger for previous exposure than for current exposure. This might reflect the cumulative effect of exposure, whereby solar radiation may initiate ocular tissue changes that later promote the development of pterygium so that sunlight exposure is reflected in later years of life by development of pterygium. Our finding is consistent with other findings in Singapore (Khoo et al. 1998) and Australia (Threlfall & English 1999). Several surveys have consistently shown that countries near the equator have higher rates of pterygia (Taylor 1981; Moran & Hollows 1984; Saw & Tan 1999). The theory that chronic exposure to sunlight causes pterygium seems to be beyond any debate. The effect of solar radiation on the eye was studied thoroughly by Taylor et al. (1992). The effects of visible radiation as well as ultraviolet-A and ultraviolet-B were evaluated. A positive association was found between ocular exposure to each band of radiation (bands of visible radiation, UV-A, UV-B) and the development of pterygium. Most plastic lenses in sunglasses block substantial amounts of UV-A and UV-B radiation (Rosenthal et al. 1988). Glass is slightly less effective in blocking UV-B radiation (Rosenthal et al. 1986). In our study, previous use of sunglasses was shown to be protective against pterygium formation while current use was not. In a study by Khoo et al. (1998), neither previous nor current use of sunglasses were shown to have a protective role. Most other studies have demonstrated that the use of sunglasses has a protective role to varying extents (Rosenthal et al. 1986, 1988; Mackenzie et al. 1992; Threlfall & English 1999). One possible explanation for the variation in the pro- 66 tective role of sunglasses may be that different types of sunglasses have been used by both case subjects and control subjects. Genetic attributes (Tan et al. 1997) and variable lifestyle behaviour may also contribute to this variation. A possible explanation for the nonprotective effect of recent use of sunglasses is that subjects start wearing sunglasses once the pterygium has already formed. Although some previous studies found a positive correlation between smoking and pterygium formation (Khoo et al. 1998), smoking was not found to be a statistically significant risk factor in our study. As a method of recruiting subjects with pterygium, the hospital-based study design represents a practical alternative to a large scale, community-based survey. We incorporated several features into our study design to reduce bias. For instance, both pterygium and control subjects were selected from the same clinic population and interviewed using a standard questionnaire. Diagnosis was made by an ophthalmologist using a slit-lamp. The subjects were group-matched for age and sex. Although the possibility of investigator bias was minimized by the similarity of the study procedure for both groups, it could not be completely eliminated because it was impossible to mask the interviewer to a patient with grossly visible pterygium during a face-to-face interview. Another limitation in our study is that data on the average daily ocular radiation dose were not available, and therefore a dose–response relationship between sunlight exposure and development of pterygium could not be described. In addition, the relatively small sample size might have made some factors, such as smoking, insignificant, in contrast to some previous studies. Conclusion This study shows that outdoor work and sunlight exposure are positively associated with the development of pterygium. Public education should focus on encouraging people to take appropriate protective measures, such as wearing sunglasses and brimmed hats when outdoors, and to avoid unnecessary sunlight exposure. Meanwhile, further research is required to enable us to better understand the relative contributions of different risk factors. References Booth F (1985): Heredity in one hundred patients admitted for excision of pterygia. Aust N Z J Ophthalmol 13: 59–64. Coroneo MT, DiGirolamo N & Wakefield D (1999): The pathogenesis of pterygia. Curr Opin Ophthalmol 10: 282–288. Dan DTH, Chee SP, Dear KBG & Lim ASM (1997): Effect of pterygium morphology on pterygium recurrence in a controlled trial comparing conjunctival autografting with bare sclera excision. Arch Ophthalmol 115: 1235–1240. Dhir SP, Detels R & Alexander ER (1967): The role of environmental factors in cataract, pterygium and trachoma. Am J Ophthalmol 64: 128–135. Dimitry TJ (1937): Dust factor in production of pterygium. Am J Ophthalmol 20: 40. Faraldi NC & Gracis GP (1976): Pterygium in twins. Ophthalmologica 172: 361–366. Hecht F & Shoptaugh MG (1990): Winglets of the eye: dominant transmission of early adult pterygium of the conjunctiva. J Med Genet 27: 361–366. Hill JC & Maske R (1989): Pathogenesis of pterygium. Eye 3: 218–226. Hosni FA (1977): Pterygium in Qatar. Ophthalmologica 174: 81–87. Khoo J, Saw SM, Banerjee K, Chia SE & Tan D (1998): Outdoor work and the risk of pterygia: a case control study. Int Ophthalmol 22: 293–298. Kwok SL & Coroneo MT (1994): A model for pterygium formation. Cornea 13: 219–224. Lewallen S (1989): A randomized trial of conjunctival autografting for pterygium in the tropics. Ophthalmology 96: 1612–1614. Luthra R, Nemesure RR, Wu SY, Xic SH & Leake MC (2001): Frequency and risk factors for pterygium in the Barbados Eye Study. Arch Ophthalmol 119: 1827–1832. Mackenzie FD, Hirst LW, Battistuta D & Green A (1992): Risk analysis in the development of pterygia. Ophthalmology 99: 1056–1061. Moran DJ & Hollows FC (1984): Pterygium and ultraviolet radiation: a positive correlation. Br J Ophthalmol 68: 343–346. Nakaishi H, Yamamoto M, Ishida M, Someya I & Yamada Y (1997): Pingueculae and pterygium in motorcycle policemen. Ind Health 35: 325–329. Norn MS (1982): Spheroid degeneration, pinguecula and pterygium among Arabs in the Red Sea territory, Jordan. Acta Ophthalmol Scand 60: 949–954. Rojas JR & Malaga H (1986): Pterygium in Lima, Peru. Ann Ophthalmol 18: 147– 149. Rosenthal FS, Bakalian AE, Lou CQ & Taylor HR (1988): The effect of sunglasses on ocular exposure to ultraviolet radiation. Am J Public Health 78: 72–74. Rosenthal FS, Bakalian AE & Taylor HR (1986): The effect of prescription eyewear on ocular exposure to ultraviolet radiation. Am J Public Health 76: 1216–1220. ACTA OPHTHALMOLOGICA SCANDINAVICA 2004 Saw SM & Tan D (1999): Pterygium: prevalence, demography and risk factors. Ophthalmic Epidemiol 6: 219–228. Sebban A & Hirst LW (1991): Treatment of pterygia in Queensland. Aust N Z J Ophthalmol 19: 123–127. Sugar A (1992): Who should receive Mitomycin C after pterygium surgery? Ophthalmology 99: 1645–1646. Tan D, Lim ASM, Goh HS & Smith DR (1997): Abnormal expression of the P53 tumour suppression gene in the conjunctiva of patients with pterygium. Am J Ophthalmol 3: 404–405. Taylor HR (1981): Climatic droplet keratopathy and pterygium. Aust J Ophthalmol 9: 199–206. Taylor HR, West S, Munoz B, Rosenthal FS, Bressler SB, & Bressler NM (1992): The longterm effects of visible light on the eye. Arch Ophthalmol 110: 99–104. Threlfall TJ & English DR (1999): Sun exposure and pterygium of the eye: a dose–response curve. Am J Ophthalmol 128: 280–287. Wong WW (1978): A hypothesis on pathogenesis of pterygium. Ann Ophthalmol 10: 303–8. Wong TY, Foster PJ, Johnson GJ, Seah SK, & Tan DT (2001): The prevalence and risk factors for pterygium in an adult Chinese population in Singapore. The Tanjong Pagar Survey. Am J Ophthalmol 131: 176–183. Youngson RM (1972): Pterygium in Israel. Am J Ophthalmol 74: 954–959. Received on December 27th, 2002. Accepted on October 18th, 2003. Correspondence: Muawyah D. Al-Bdour FRCSI (Ophth) PO Box 141461 Amman 11814 Jordan Tel: þ 962 6 535 3399 Fax: þ 962 6 535 3399 Email: [email protected] 67