According to World Health Organization data, smoking has become a serious global public health problem. Among the approximately 1.3 billion smokers in the world, over 6 million die annually due to tobacco exposure, especially in
. Cigarette smoking is related to many eye diseases such as cataract, age-related macular degeneration
[11–13]. Existing studies on the relationship between cigarette smoking and POAG remain controversial. Findings vary among ethnic groups and study design. And most of these studies focused on AOAG. There are limited data of these studies in the Chinese population. Recently in a cohort of African-American women, Wise L. A. et al. reported that smoking might be associated with increased risk of early-onset POAG
. Kang, J. H. et al. also reported cigarette smoking conferring risk to POAG
. Similar findings were also reported in other independent studies
[16–18]. But some other studies reported no association between smoking and POAG. In a prospective follow-up study from 1980 and 1986, respectively, to 1996, the results showed neither current smokers nor ex-smokers were at greater risk for POAG than those who had never smoked, and heavier smoking did not increase the risk of POAG
. And in a systematic review, Richard et al. also reported that there was little evidence for the association between smoking and POAG
. Other independent studies also reported lack of such association
[9, 20]. In our Chinese cohort, smoking was not found to confer risk to disease onset in either JOAG or AOAG. Our study thus did not support cigarette smoking as a risk factor of POAG onset.
Apart from disease onset, it remains to be elucidated whether cigarette smoking is related to IOP, CCT and VCDR, which are glaucoma risk factors. In 2003, Yoshida M. et al. reported that cigarette smoking had a significantly positive association with the IOP in Japanese male individuals
. Lee A. J. et al. also reported similar association
. In the current study, although no significant association with IOP was observed, we found evidence that smoking could be correlated with decreased CCT in AOAG. As reported by previous studies, in individuals with thinner cornea, their IOP tends to be lower estimated
[23–25]. In AOAG smokers, their IOP could possibly be lower estimated due to thinner CCT. In addition, the change of CCT in POAG may affect the disease course. A previous study on corneal thickness and functional damage in patients with ocular hypertension showed that patients with ocular hypertension plus thinner cornea had a greater risk of developing functional damage over time
The exact reason for decreased corneal thickness in POAG smokers remains unclear. However, cigarette smoking may exert this effect through hypoxia and collagen in the cornea. Smoking has been reported to decrease oxygen and collagen production in tissues during wound healing
[27, 28]. Ocular hypertension causes damage to the cornea
. Smoking probably deteriorates ocular hypoxia caused by ocular hypertension
, and consequently affects the biosynthesis of collagen and extracellular matrix turnover
, which could be an explanation to the decreased corneal thickness.
In the current study, cigarette smoking was not found to be associated with disease onset of POAG. However, the association of smoking with decreased CCT in POAG suggested that more attention should be paid on CCT in the early stage of POAG in smokers to estimate more correct target IOP in order to better reduce the early lesion of optic nerve. Current findings thus warranted further study.