Effects of Smoking on Ocular Health

Cigarettes contain many toxic components, such as heavy metals (e.g., cadmium, arsenic, chromium, lead, and nickel). In addition, burning cigarettes leads to the production of many toxic materials, such as nicotine, carbon monoxide, tar, volatiles, heavy hydrocarbons, amines, acids, and aldehydes. The accumulation of toxicants inside the human body leads to serious damage and illnesses. These toxicants cause cancer, damage the renal and cardiovascular systems, and negatively affect the central nervous system. Smoking shortens the human lifespan by at least 10 years and increases the risk of death threefold compared with nonsmokers.

Smoking has a negative effect on the ocular tear film as it leads to damage to the corneal epithelial layer and ocular surface. It is also responsible for various ocular disorders, such as:

• Cataracts
• Glaucoma
• Thyroid eye
• Conjunctival intraepithelial neoplasia
• Dry eye

In addition, smoking is associated with dyslipidaemia and increases blood cholesterol levels, which are risk factors for dry eye.

Dry eye is the result of a high evaporation rate and/or low tear volume. Dysfunction of the meibomian gland is one of the most common causes of dry eye and is a result of lipid secretion shortage. The methods used to detect dry eye include:

• Schirmer’s test
• The phenol red thread (PRT) test
• Tear break-up time (TBUT)
• Tear evaporation rate
• Tear ferning
• The tear osmolarity test

In addition to questionnaires, such as the ocular surface disease index (OSDI).

Excessive tear evaporation leads to hyperosmolarity. Osmolarity measurement in vivo is a reliable tool to diagnose dry eye, especially since the introduction of the TearLab and I-Pen osmometers. These osmometers do not induce reflux tears and require a very small volume of tears. In addition, the measurement procedure is simple, fast, repeatable, and accurate.

The current prospective, nonrandomized comparative study investigated the correlation between the TearLab and I-Pen osmolarity scores in smokers and compares them with those of non-smoking healthy males.

Thirty male smokers (25.3 ± 2.2 years) participated in the study. An age-matched (22.9 ± 2.0 years) control group of non-smoking healthy males (N = 30) was also recruited for comparison purposes. The ocular surface disease index (OSDI) was completed first, followed by the TearLab and I-Pen osmolarity measurements.

The median TearLab osmolarity score was lower (P < 0.001) than that obtained using the I-Pen in both the study and the control groups. The OSDI scores and osmolality measurements were higher (P < 0.001) in smokers than in the control subjects. In the smoker group, there were moderate correlations between the OSDI scores and the measurements obtained using the TearLab (Spearman’s correlation coefficient, r = 0.463; P = 0.010) and I-Pen (r = 0.449; P = 0.013) systems. In addition, there was a strong correlation between the osmolarity scores obtained from the TearLab and I-Pen systems in smokers (r = 0.911; P < 0.001).

Smoking has a significant negative effect on the ocular tear film. Smoking reduces tear film stability and increases corneal staining. In addition, eye irritation and dryness are common symptoms in smokers and passive smokers. Tear osmolarity scores can be used to detect the signs and severity of dry eye. High tear osmolality is an indication of dry eye symptoms. In this study, osmolarity scores were significantly higher in smokers compared to individuals in the control group. In smokers, significant changes occur within the lipid layer, possibly due to a peroxidation process. These changes lead to an abnormal lipid spread. As a result, the TBUT has been shown to be lower (5.4 s; P < 0.05) in smokers compared to control subjects (11.2 s). In addition, smoking leads to a high concentration of carbon monoxide in serum haemoglobin. The level of carbon monoxide has been found to be 4.8% ± 0.4% in smokers and 0.5% ± 0.5% in control subjects. Goblet cells have been found to be lower and the tear evaporation rate has been found to be higher in smokers, compared with normal eye subjects. Moreover, smoking affects tear protein patterns, leading to tear film instability.

The I-Pen scores in smokers were significantly higher than those obtained using TearLab. The TearLab scores showed small variations compared with those obtained using I-Pen. A strong correlation was found between the TearLab and I-Pen scores in smokers. The osmolarity TearLab and I-Pen scores were significantly higher in smokers compared with normal eye subjects.

Source: Mana A. Alanazi, Gamal A. El-Hiti, Osamah A. Alturki; Hindawi Journal of Ophthalmology Volume 2022, Article ID 9970388, 6 pages https://doi.org/10.1155/2022/9970388