Eye Health

SMOKING IS INJURIOUS TO EYE HEALTH

August 3, 2022January 11, 2023By

WHO estimates that tobacco kills over 8 million people every year, including over 1.2 million from second-hand smoke exposure.

The second-hand tobacco smoke is the smoke from burning end of cigarettes, bidis, and water pipes and the smoke that people exhale when they smoke.

The inhalation of tobacco smoke exposes the body to more than 4000 chemicals. Ocular damage from these chemicals may even result in blindness.

Numerous effects of tobacco smoke can be seen on ocular structures. This may result from oxidative damage, vascular changes, and inflammation.

There is an increased incidence of the following eye conditions associated with smoking:

CATARACT:

WHAT IS CATARACT?

Cataract is the clouding of the natural lens. 

Cataract is the leading cause of blindness worldwide and therefore, timely diagnosis and intervention are crucial to help restore vision.

HOW DOES SMOKING CAUSE CATARACT?

  1. Due to the high level of free radical activity caused by smoking, there is a great deal of oxidation. As a result of this oxidative damage to the lens, cataracts can develop
  2. Furthermore, smoking depletes endogenous antioxidants such as vitamin C, E, and beta carotene, which exacerbates oxidative stress.
  3. Tobacco by-products contain heavy metals, such as cadmium, lead, and copper, which accumulate in the lens and cause direct damage.
  4. The blood of smokers contains higher levels of cyanide and aldehyde, which can modify lens protein and cause opacification.

GLAUCOMA

Glaucoma is a group of diseases causing progressive damage to the sight which finally leads to irreversible blindness. 

In many cases it is painless and affects the peripheral vision first, therefore people having glaucoma may not even realize that they have it until it’s too late. 

Glaucoma is the leading cause of blindness in patients more than 60 years of age. 

In glaucoma, the nerve in the eye called the optic nerve, which connects the back of the eye to the brain, is damaged, usually due to increased pressure in the eyes. 

Primary open-angle glaucoma or POAG: This is the most common type of glaucoma. Here the trabecular meshwork gradually becomes less effective at draining the fluid hence there is a build-up of fluid in the eyes, causing the  IOP to rise, which puts pressure on the optic nerve. 

HOW DOES SMOKING CAUSE POAG?

The evidence of causal relationship between tobacco smoking and POAG is  limited

Researchers found no significant association between smoking and IOP in the study, but they did find evidence that smoking may decrease CCT, or central corneal thickness. CCT is an important factor to consider when measuring IOP. 

The IOP measurement depends on corneal rigidity or how rigid the outer layer of the eye is, some patients with thicker corneas show falsely high IOP, and patients with thin corneas can show falsely low IOP. 

Therefore patients with thin corneas or lesser CCT can still have glaucoma even if the IOP measurement is normal. 

According to this study, smoking is associated with decreased CCT in POAG, suggesting that CCT should be more closely monitored in smokers to estimate a more accurate target IOP to reduce the early optic nerve lesions.

DIABETIC RETINOPATHY

When diabetes affects the retina (the inner sensitive layer of the eye where light is perceived), it is known as diabetic retinopathy. This is a progressive condition and can lead to irreversible vision loss and even blindness. 

WHAT IS DIABETIC RETINOPATHY? 

The increased glucose in diabetes damages retinal arteries and weakens their walls. As a result, the vessels start leaking, which leads to bleeding (hemorrhages) and swelling (hard exudates, edema) within the retinal layers. This is called diabetic retinopathy. 

Diabetic Macular Edema (DME) is when the retinal vessels leak around the central part of the retina called the macula, which is responsible for the sharp central vision, causing significant vision loss. 

HOW DOES SMOKING CAUSE DR

Smoking does not cause diabetic retinopathy, but it can impede healing and also create bleeding in the eyes for those who already have diabetic retinopathy.

Even though smoking’s role in microvascular complications remains unclarified, stopping smoking should remain the primary goal of people with diabetes to lower their risk for macrovascular complications.

In patients with diabetes, quitting smoking has specific benefits. Patients with diabetes are advised to stop smoking in order to improve quality of life and delay the onset and progression of diabetes complications.

Age-related macular degeneration or AMD is seen most commonly among people in the older age group, over 50 years, in which there is damage to the macula or the central part of the retina where a straight-ahead image is formed. Therefore, it leads to central vision loss while the peripheral or side vision remains fine. 

This is the third leading cause of blindness worldwide and the first in the developed world, affecting 1 in 7 people.

HOW Does SMOKING CAUSE AMD

Cigarette smoke contain compounds that are toxic or mutagenic.

The mechanism of AMD due to smoking :

1. Growth of new blood vessels in macula:

As nicotine has vasculogenic properties, cigarette smoke can stimulate the formation of new blood vessels in the retina. Because it retards wound healing, smokers’ eyes bleed more and take longer to heal.

2. Cigarette smoke also contains dioxins which promotes VEGF (Vascular Endothelial Growth Factor), another vasculogenic factor.

3. Nornicotine which is a metabolite of nicotine contribute to the formation of yellow deposits called drusens in the retina.

4. In the RPE layer of the retina, cadmium accumulates, which leads to increased free radicals and oxidative damage, as well as drusen formation.

5. Oxidative damage and cell death in macula causes central vision loss

6. High level of carboxyhemoglobin in smokers hampers the oxygen delivery to macula causing hypoxia. This lack of oxygen can lead to macular degeneration.

7. Macular pigments are crucial to keep the macula healthy. People naturally lose these pigments with time, but smoking accelerates the loss of macular pigments.

8. Vitamins are crucial in AMD according to AREDS 2 for macular health and smoking interferes with the absorption of most of these vitamins.

DRY EYE SYNDROME:

Dry eye syndrome is a multifactorial disease affecting the production or normal functioning of tears. Tears are important to moisten, protect and cleanse our eyes, therefore its dysfunction can make eyes susceptible to infections. 

There are mainly two types of dry eye disease,

1. Evaporative due to poor quality of tear film

2. Secretary due to poor secretion of tears.

HOW DOES SMOKING CAUSE DRY EYE

  1. Smoke from the cigarette causes burning and eye discomfort: this occurs in primary smokers and passive smokers alike. 
  2. Tear film instability: the toxins in smoke interfere with the normal functioning of the tear film
  3. Foreign body sensation 
  4. Noxious particles present in tobacco smoke act as irritants to the conjunctiva
  5. Some studies found that smoking reduces tear stability and corneal and conjunctival sensitivity, which also lowers TBUT.

UVEITIS:

Uveitis refers to ocular inflammation or swelling inside the eye. It typically impacts the uvea, middle layer of the eye, but it can also affect other crucial eye structures which could result in permanent vision loss. 

Smoking cigarettes causes the release of chemicals that cause blood vessel inflammation, which can affect the immune system and cause uveitis. All anatomic subtypes of uveitis and infectious uveitis are substantially related to a history of smoking.

THYROID EYE DISEASE (TED)

The general population and patients with Graves disease should be informed about the dangers of smoking and TED.

Unknown biological processes may be at play when smoking leads to the onset of TED. Numerous hypotheses have been put forth.

  1. Smoking might directly irritate the eye.
  2. The hypoxia caused by smoking may affect the release and activity of inflammatory mediators, which is thought to play a significant role in the pathogenesis of TED.
  3. Smoking can alter TSH (Thyroid stimulating hormone).
  4. Smoking also affects the immunological reactions involved in the pathogenesis of eye disease.

OPTIC NERVE

Heavy smokers are believed to experience vision impairment due to nicotine interfering with the transmission of these visual signals. 

A study of patients recovering from optic neuritis found a significant red-green color defect in the affected eye of heavy smokers as compared to non-smokers. 

Read our article to know how to take care of your eyes.

QUICK SUMMARY

The effects of smoking extend not only to our own health but also to the health of those around us. There is also evidence linking this harmful habit to other ocular disorders, such as retinal ischemia, anterior ischemic optic neuropathy, and Graves’ ophthalmopathy. A healthy lifestyle begins with reducing smoking and eventually quitting for good.