Smoking and Eye Health

Helping a patient to quit smoking is the most important health intervention a pharmacist can make as it can contribute towards reducing the risk of COPD, cancers and early mortality. Yet smoking is also a major risk factor in eye conditions – from dry, gritty eye irritation to chronic disease and potential blindness.

Tobacco smoke is composed of as many as 4,000 active compounds. Most of these are toxic and can affect the eyes, mainly through ischaemic or oxidative mechanisms. Most chronic ocular diseases (except diabetic retinopathy and primary open-angle glaucoma) appear to be associated with smoking and both cataract development and age-related macular degeneration, the leading causes of severe visual impairment and blindness, are directly accelerated by smoking.

Dry eyes

Dry eyes may occur for a number of reasons, including environmental (computer users, air conditioning), auto immune disease and ocular diseases, contact lenses or medication. However, given one in five people smoke, pharmacists should be aware that patients presenting for dry eyes could be smokers or ex-smokers; studies have found smokers suffer twice as much from dry eyes. 

Symptoms Healthy comfortable tears are composed of layers of mucin (adhere tears to the eye), antimicrobials and a lipid outer layer (to reduce evaporation), all suspended in an aqueous media. However, smoker's tears lose lactoferrin and lysozyme, risking infection, and smokers have fewer conjunctival goblet cells.

The lower skin temperature of smokers along with the increase in ocular inflammatory cell causes inflammatory episodes, damaging the meibomian glands and making tears less comforting. Without these glands tears evaporate quickly, and reduced ocular sensitivity means fewer tears can be produced, causing less reflex tearing. This causes increased evaporation of the aqueous part of the tear, which can lead to increased incidence of blepharitis and conjunctivitis and ‘toxic' tears.

In clinical settings, smokers who smoke 10 or more cigarettes a day (with five or more ‘pack-years' – see below) will report a diurnal variation of symptoms, with dry, gritty eyes in the morning, and  ocular irritations and wetness in the evening. This contrasts with non-smokers who often wake up without irritation, only to get evaporative dry eye in the afternoons.

This is because the ‘toxic' tears cause the gritty sensation in the morning, which slowly improves as nicotine levels rise (although microinflammation at the lid margin will cause stinging and sensitivity for many smokers by the afternoon). However, as nicotine is a cholinergic drug, it causes activation of the lacrimal gland, producing more tears and causing wet eyes in the evenings; these tears are less comfortable as they have less meibum (which adds comfort). 

After 25 pack years the dry eye symptoms become less problematic, possibly because of neural sensitivity damage. 

Destruction of the meibomian glands also causes blepharitis; this is indicated by eyelid margin notching and dimpling – visible signs that and signal a gland 'drop-out'.

Treatment Treatment is based on managing symptoms until the patient stops smoking. This includes the use of ‘spray on' lipid supplements to reduce tear evaporation, and lid wipes to maintain good lid hygiene, which will help meibomian lipid production.

On smoking cessation, neural sensitivity recovers more quickly than damage to glands; this often means the patient's eyes feel worse. This can be ameliorated by using a compress such as an eye bag three mornings a week to unplug any blocked meibomian oils, and a tear substitute product.

It takes more than six months for neural sensitivity to stabilise and up to two years abstinence to a gain stable tear film. Patients should be advised to used crops for comfort(eg hypromellose 0.3 per cent eye drops) during this time and maintain careful lid cleansing to reduce inflammations.

Pack years

Pack years are a means of calculating the amount a patient has smoked.

Number of pack years = number of packs per day x number of years as a smoker

Most packs have 20 cigarettes in them. Therefore a smoker who has smoked 10 cigarettes per day for five years would have a pack year total of 0.5 x 5 = 2.5 pack years

Cataracts

Studies have found that smoking accelerates cataract formation by a factor of more than two, in addition to any pre-existing cataract risk (such as high myopia, trauma, intra-ocular injury or diabetes). It is speculated that the oxygen radicals in smoke damage crystalline proteins.

Smoking is associated with a higher prevalence of nuclear and posterior sub-capsular cataracts, and people who smoke and drink heavily have been found to have an increased prevalence of nuclear cataract in studies. Patients with more than 14 pack years have a risk of cataracts at even a young age.

Cataracts are diagnosed by examinations and tonometry tests. Treatment often means following a surgical procedure such as phacoemulsification, followed by lens replacement. Smoking cessation can slow cataract progression.

Uveitis

Cigarette smoking is a risk factor for uveitis, inflammation within the eye usually associated with auto immune diseases and infections. This is a serious and painful condition that causes blurred vision and requires urgent referral and assessment, as it may result in permanent loss of vision if left untreated. Smokers have 2.2 times the risk of developing the condition than non-smokers. 

In developing  countries like India, viruses are the most common cause of infectious uveitis. Infectious uveitis (eg herpes simplex virus) responds well to treatment with antiviral medications or antibiotics. Non-infectious uveitis is treated by corticosteroids drops (eg dexamethasone).

Age-related macular degeneration (AMD)

The macula is rich in antioxidants, which replenish the central visual cones. Smoking depletes this, causing the build-up of waste products called drusen. These can disrupt the visual cones and cause vessels to grow within the macula, causing wet macular degeneration. 

Smoking is known to treble the risk of developing AMD and can result in early-onset wet macular degeneration; smoking cessation can slow progression and is vital.

by

Akshaya Srikanth, Dr.Sunil Kumar Jain*

Pharm.D Intern, Clinical Pharmacist, AIIMS

India