Introduction
Psychoactive substance abuse in India continues to be a substantive problem for the individual as well as for the society. Of the various substances, alcohol and tobacco are most commonly abused substances with majority of the people being dependent on them. The current prevalence of alcohol usage in India ranges from 65.84% to 67.4%.1 2 It varies in urban and rural areas with estimates being 7.3 per 1000 in urban areas to 5.8 per 1000 in rural areas.2 It is also common among the poorer sections of the society. Alcohol use in India is reported exclusively in males. Owing to its large population, India is the third largest market for alcoholic beverages in the world.1
Overall, tobacco use currently causes about six million deaths worldwide.3 Nearly one million deaths in a year in our country are attributable to smoking.4 According to the National Family Health Survey-3, tobacco usage is more prevalent among men, rural population, illiterates and poorer sections of the society.5 Tobacco usage inflicts high direct and indirect costs on the society due to mortality and morbidity resulting from their consumption. According to Indian Council of Medical Research, the total losses in 1999 due to tobacco-related diseases were almost 277.6 billion rupees. Morbidity due to these substance usage produce indirect costs on the society that includes the cost of caregivers and value of work loss due to illness.6
International Agency for Research on Cancer monograph shows that chronic tobacco smoking causes cancers like that of oral cavity, nasopharynx, oropharynx and hypopharynx, nasal cavity and paranasal sinuses, larynx, oesophagus, stomach, pancreas, liver, kidney, ureter, urinary bladder, uterine cervix and bone marrow (myeloid leukaemia).7 Tobacco use also causes toxic amblyopia. Abundant scientific evidences exist to establish that exposure to tobacco smoke can cause disease, disability and death.3 Tobacco smoking is a powerful risk factor conducive to various eye diseases, including the development of cataract, glaucoma, retinal vascular disorders and age-related macular degeneration. Tobacco amblyopia is the most common ocular disease related to its use.8
Review of literature revealed a small case series establishing retinal nerve fibre layer (RNFL) thinning in chronic alcohol and tobacco users.9 Hence, a large case–control study was undertaken to report the changes in RNFL thickness in patients of chronic alcohol and tobacco use. Since the patients were recruited from the deaddiction clinic from a tertiary care hospital, the RNFL thickness may vary in patients with acute intoxication.
Toxic optic neuropathy refers to a group of medical disorders defined by visual impairment due to optic nerve damage resulting from exposure to a toxin. The exact pathogenesis of toxic optic neuropathy resulting from tobacco and alcohol is not established and is probably multifactorial, but cyanide in tobacco smoke and malnutrition due to alcohol intake appear to be the most important causative factors.10 Toxic optic neuropathy is usually an underdiagnosed disease entity and a large proportion of patients present at a stage when recovery of vision is not possible. The mechanism is the primary insult to mitochondria that disrupts the process of oxidative phosphorylation causing axonal loss, which preferentially affects the parvocellular neurons in papillomacular bundle, thus resulting in thinning of RNFL.10 11
Optical coherence tomography (OCT) is a non-contact imaging technology that provides live histopathological images of the retinal layers. An early diagnosis of decreased RNFL thickness goes a long way in preventing blindness due to toxic optic neuropathy and can also guide the treating physician about the severity of the condition.