Table 4

HRs and 95% CIs for pterygium according to duration and frequency of smoking

Smoking status	No. of cases	Crude %	HR	95% CI	P Value
Duration of smoking (n=181 094)
Never smoked	5389/90 547	5.93	1 (reference)
≤9 years	503/10 835	4.68	0.81	0.74 to 0.89	<0.001
10–19 years	837/22 625	3.69	0.69	0.64 to 0.74	<0.001
20–29 years	1133/28 937	3.78	0.70	0.65 to 0.74	<0.001
≥30 years	1425/28 150	5.05	0.75	0.71 to 0.80	<0.001
Daily consumption of cigarette (n=154 942)
Never smoked	5389/90 547	5.98	1 (reference)
<10 cigarettes	670/15 791	4.73	0.69	0.64 to 0.75	<0.001
10–19 cigarettes	1342/34 533	3.68	0.67	0.63 to 0.71	<0.001
≥20 cigarettes	544/14 071	3.65	0.68	0.62 to 0.74	<0.001

We performed age-stratified analyses for the duration of smoking and pterygium as well as age-adjusted analyses for daily consumption of cigarettes and pterygium. Persons with missing data regarding daily cigarette consumption were excluded.