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ORIGINAL ARTICLE
Year : 2016  |  Volume : 29  |  Issue : 3  |  Page : 606-611

The effect of smoking on choroidal thickness measured by optical coherence tomography


Department of Ophthalmology, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission01-Mar-2016
Date of Acceptance05-Jun-2016
Date of Web Publication23-Jan-2017

Correspondence Address:
Al-Shimaa Hussein Maklad
Etaei Elbarod Hospital, Itay Elbarod Behera? Government, Behera, 22511
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-2098.198727

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  Abstract 

Objective
The objective of this study was to investigate the effect of smoking on choroidal thickness using the enhanced-depth imaging mode of Spectralis Heidelberg optical coherence tomography (OCT).
Background
Cigarette smoking is an important risk factor for the development of systemic vascular disease and ocular vascular disease. The effect of smoking on the retina and deeper retinal tissues is now a topic of great interest besides being a risk factor for ocular vascular disease. Recently, optical coherence tomography has been shown to be effective in evaluating the choroidal thickness.
Patients and methods
The right eyes of 100 participants (50 healthy smokers and 50 healthy nonsmokers) were included in this study. We measured the choroidal thicknesses of the never-smoking individuals as a control group. The choroidal thicknesses of the smoking participants were measured at 1 and 8 h after smoking. Choroidal thickness measurements were taken at the fovea and at five more points, which are located at, respectively, 500 μm nasal to the fovea, 1000 μm nasal to the fovea, 500 μm temporal to the fovea, 1000 μm temporal to the fovea, and 1500 μm temporal to the fovea.
Results
A significant difference was found for the choroidal thickness, as the choroidal thickness was decreased after 1 h in comparison of smokers and nonsmokers, and there was an increase in choroidal thickness after 8 h in smokers compared with nonsmokers at all measurements points.
Conclusion
Smoking caused an acutely significant decrease in choroidal thickness that returned to increase after 8 h. The choroidal thickness significantly differs between the healthy young smokers and nonsmokers.

Keywords: choroidal thickness, enhanced-depth imaging, smoking


How to cite this article:
Sarhan AE, Elgouhary SM, Ibrahim AM, Maklad ASH. The effect of smoking on choroidal thickness measured by optical coherence tomography. Menoufia Med J 2016;29:606-11

How to cite this URL:
Sarhan AE, Elgouhary SM, Ibrahim AM, Maklad ASH. The effect of smoking on choroidal thickness measured by optical coherence tomography. Menoufia Med J [serial online] 2016 [cited 2020 Apr 2];29:606-11. Available from: http://www.mmj.eg.net/text.asp?2016/29/3/606/198727


  Introduction Top


Cigarette smoking is an important risk factor for the development of systemic vascular disease and ocular vascular  disease [1] .

In particular, smoking is known to be associated with anatomical alterations in both the microvasculature and macrovasculature. These alterations include an increase in arterial wall thickness [2] and atherosclerosis.

The  negative effect of smoking on human circulatory tissue is well documented in the literature because of the highly vascularized nature of the eye; the effect of smoking on the retina and deeper retinal tissues is now a topic of great interest besides being a risk factor for ocular vascular diseases such as hypertensive retinopathy, age-related macular degeneration, and anterior ischemic optic neuropathy. Smoking directly causes a decrease in retinal blood flow; however, the pathogenesis of this decrease is not fully understood yet, and several studies have reported various results with different techniques to evaluate blood flow [3] .

To date, color duplex imaging, laser speckle method, and laser Doppler flowmetry have been reported to be used to assess the ocular blood flow in smokers and nonsmokers [4] .

The peripheral vasoconstriction effect of nicotine is proposed to cause an increase in the peripheral resistance to blood flow [5] .

Recently , optical coherence tomography (OCT) has been shown to be effective in evaluating the choroidal thickness. With current technological developments, new-generation spectral domain OCT devices with enhanced scanning speed and special software programs such as enhanced-depth imaging (EDI) give the opportunity to achieve high-resolution images, and thus evaluation of deeper ocular tissues beyond the retina became possible, which could not be defined by time domain OCT [6] .

As the choroid is an important moderator of ocular physiology in the current study, we aimed to analyze the effect of smoking on choroidal thickness with spectral domain OCT.


  Patients and methods Top


This was a prospective, observational, clinical study carried out on 100 participants (50 smokers and 50 healthy nonsmokers) at the Ophthalmology Department in Menoufia University in the period between May 2014 and May 2015.

Informed consent was obtained from all of the study participants.

Inclusion criteria

Inclusion  criteria were patients aged 25-45 years, having less than 3 D of spherical and less than 1 D of cylindrical refractive error, best-corrected visual acuity of 20/20 or better, normal blood pressure (<140/90 mmHg), normal blood parameters including complete blood count and clinical chemistry (glucose, sodium, potassium, creatinine, uric acid, total cholesterol, triglycerides, alanine aminotransferase, aspartate aminotransferase, g-glutamyl transferase, total bilirubin, and total protein), normal thyroid function test (thyro tropin, free T4 and total T3), and smokers who had a minimum 10-year smoking history with at least one pack of cigarettes per day for 1 year.

Exclusion criteria

Exclusion criteria included the presence of ocular disease preventing the examination of the cornea, having laser surgery or any ocular surgery, history of chronic ocular disease (e.g. glaucoma, cataract, and uveitis), history of smoking or alcohol intake in the control group, history of alcohol intake in the smoking group, any systemic disease (e.g. cardiac, diabetes mellitus or hypertension), and a history of taking any medication within the past 3 months, including systemic vasoactive drugs.


  Methods Top


All participants were subjected to the following examinations: best-corrected visual acuity measurement using Snellen eye chart, anterior segment examination using slit lamp, intraocular pressure using Goldmann applanation tonometer, posterior segment examination after pupillary dilatation using slit-lamp biomicroscopy with +90 D volk lens, and indirect ophthalmoscopy.

Choroidal thickness was assessed using Spectralis SD OCT (Heidelberg Engineering, Heidelberg, Germany). All OCT scans and measurements were acquired by the same experienced operator.

The choroidal thickness was measured manually from the outer portion of the hyper-reflective line corresponding to the retina pigment epithelium to the inner surface of sclera using the manual calipers provided with the OCT software, at the fovea and at five more points, which are located, respectively, 500 μm nasal to the fovea, 1000 μm nasal to the fovea, 500 μm temporal to the fovea, 1000 μm temporal to the fovea, and 1500 μm temporal to the fovea.

SD-OCT (Spectralis HRA+OCT; Heidelberg Engineering, Heidelberg, Germany) (specralis software version 4.0) with the horizontal 30-line-scan EDI mode through the fovea was used. All basal OCT scans were performed at the same time of the day, in the morning, to avoid diurnal fluctuations. This was immediately followed by smoking one standard cigarette for the smoking group. The OCT measurements were repeated at 1 and 8 h after smoking. The participants in the nonsmoking group also underwent OCT examination after at least 8 h of being free from caffeine-containing drinks as the control group of the  study. The first OCT measurement in the morning was followed by two further examinations at the first and eighth hour, respectively. Participants in both groups were instructed not to take any medications, not to consume caffeine-containing products, and not to smoke until the end of the measurements.

Statistical analysis

Results were collected, tabulated, and statistically analyzed by an IBM personal computer compatible with SPSS statistical package version 20 (SPSS Inc.,   released 2011, IBM SPSS statistics for Windows, version 20.0; IBM Corp., Armonk, New York, USA).

Two types of statistical analyses were performed.

  1. Descriptive statistics were expressed in number (N) and percentage (%).
  2. Analytic statistics included the following:
    1. Student's t-test is a test of significance used for comparison of quantitative variables between two groups of normally distributed data.
    2. Analysis of variance test was used for comparison of quantitative variables between more than two groups of normally distributed data with least significant difference test as post-hoc test.
    3. Pearson's correlation was used to study the correlation between two quantitative variables.
    4. P value of less than 0.05 was considered statistically significant.



  Results Top


This was a prospective, observational, clinical study carried out on 100 participants (50 smokers and 50 healthy nonsmokers) at the Ophthalmology Department in Menoufia University in the period between May 2014 and May 2015.

The selected participants were divided into two groups:

Group 1 included 50 healthy smokers.

Group 2 included 50 healthy nonsmokers as a control group.

Patient characteristics of the studied groups

The smokers had smoked an average of 24.25 ± 4. 87 cigarettes per day for 10 years (range = 20-40 years).

The mean age, among the study groups, was 33.83 ± 6.23 years for the smoking group (range = 26-45 years) and 32.51 ± 5.07 for the nonsmoking group (range = 23-45 years), which was not statistically significant as the P value was greater than 0.05.

There was no statistical difference between the studied participants regarding sex, as all the participants are men.

  1. There was a statistically significant reduction in all OCT measures after 1 h of smoking in the smoker group in comparison with the baseline [Table 1].
    Table 1 Choroidal thickness measurements of smokers at baseline and at first hour


    Click here to view
  2. Choroidal thickness decreased after 1 h of smoking in comparison of smokers and nonsmokers, and there was an increase in choroidal thickness after 8 h in the smoking group compared with the nonsmoking group at all measurement points [Table 2].
    Table 2 Choroidal thickness measurements by optical coherence tomography (enhanced-depth imaging) in smokers and nonsmokers at first hour and eighth hour


    Click here to view



  Discussion Top


We investigated the acute and the chronic effects of smoking on choroidal thickness in healthy young smokers. We included healthy participants with normal blood parameters, including complete blood count, clinical chemistry, and thyroid function test.

At present, there is no gold-standard method for evaluating choroidal thickness [7] . Since the introduction of Fourier spectral domain, OCT high scanning speeds and high resolution have enabled accurate imaging and investigation of the choroid [8] . As a highly vascular ocular structure, the choroid is directly influenced by intraocular and perfusion pressure.

Therefore, real-time high-definition images of the choroid are more likely to demonstrate the real-time vascular status of this tissue in vivo. Choroidal function and structure are known to play a role in the pathogenesis of several ocular disorders [9] . Spectral-domain OCT is a noninvasive noncontact transpupillary imaging modality used to diagnose, make treatment decisions, and monitor many retinal diseases [10] .

Obtaining choroidal thickness measurements is useful for evaluating choroidal thickening and thinning diseases. A new method for visualizing the choroid, EDI OCT, has been reported [11] .

The current study was conducted on 100 participants (50 healthy smokers and 50 healthy nonsmokers) to evaluate the effect of smoking on the choroidal thickness by OCT (EDI) mode as one of the recommendations of the research conducted by Sizmaz et al. [12] .

We included healthy individuals with normal blood parameters, including complete blood count, clinical chemistry, and thyroid function test.

In the current  study, the baseline choroidal thicknesses of smokers and nonsmokers were similar according to the results of our study; smoking one cigarette revealed a significant decrease in choroidal thickness after 1 h, and this result was in agreement with Sizmaz et al. [12] , who found a significant decrease in choroidal thickness after 1 h and tended to persist for at least 3 h.

In addition, our result was in agreement with Mehmet [13] , who found that  chewing 4 mg of nicotine gum decreased choroidal thickness after 1 h compared with placebo. Nicotine causes a significant decrease in choroidal thickness following oral intake, and this acute decrease might be a result of reduced ocular blood flow due to the vasoconstrictive effect of nicotine.

Rojanapongpun and Drance [14] studied the effect of nicotine on the ophthalmic artery flow velocity using transcranial Doppler ultrasound. They observed that small doses of nicotine (nicotine gum) increase blood flow velocities in the ophthalmic artery.

In addition, Tamaki et al. [6] reported a decrease in choroidal blood flow 30 min after smoking. The results of this study depend on indirect findings obtained by color duplex scan or laser speckle; our study demonstrated a reduction in choroidal thickness, and this study has demonstrated a reduction in choroidal blood flow after smoking. This confirms the hypothesis that the choroidal thickness correlates with blood flow.

Kool et al. [15] reported that smoking causes acute hemodynamic and vascular changes, and chronic smoking leads to vascular dysfunction in the eye [16] .

Steigerwalt et al. [5] found a reduction in blood flow velocity in the posterior ciliary artery after acute smoking, which the authors suggested to be a good indicator of peripapillary choroidal blood flow, with color duplex scanning. They proposed that this decrease was due to the increase in the vascular resistance of the vessels using laser speckle method.

The current study does not seem to agree with the study by UlaΊ et al . [17] , which evaluated the acute and chronic effects of cigarette smoking on the choroidal thickness of young male smokers with smoking histories exceeding 10 years using spectral domain OCT. He found that smoking caused an acute, significant increase in choroidal thickness that returned to baseline levels after 1 h. This increase, which is due to the production of endothelium-derived substances, such as nitric oxide, angiotensin-converting enzyme, or tissue type plasminogen activator, is altered after cigarette smoking [18] .

Several previous reports studied the effect of cigarette smoking on the ocular circulation in habitual smokers. Using the laser speckle method, it was found that smoking increases tissue blood velocity in the optic nerve head and possibly in the choroids of habitual smokers with smoking histories of 10 years on average [19] .

Choroidal blood flow is strongly dependent on blood gas concentrations, which change during smoking [20] .

Our study showed that smoking one cigarette revealed a significant increase in choroidal thickness after 8 h; as this duration was long enough to reveal the enhanced effect of smoking on choroidal thickness, our data confirm our hypothesis that there is an increase in choroidal thickness by an increase in choroidal blood flow by inflammatory markers including erythrocyte sedementation rate, interleukin-6, monocytes, and tumor necrosis factor-α in both male and female smokers, and this seems to agree with the study by Tracy et al. [21] .

Similarly, Resch et al. [22] reported that retinal and choroidal blood flow increased during inhalation of carbon monoxide (CO), which is a major component of cigarette smoke, and it seems to accumulate more in chronic smokers. The mechanism for the CO-induced increase in tissue blood flow is still a matter of controversy. The classical theory introduced hypoxia as an explanation. As the affinity of hemoglobin for CO is 200-fold greater than that for oxygen, the presence of COHb reduces the number of oxygen carriers.

COHb levels as low as 5% have been shown to cause a considerable loss in the oxygen-carrying capacity of blood [23] .

High COHb levels may lead to impaired visual discrimination and motor coordination, [24] , especially affecting organs with high oxygen demand, such as the eye or the brain. Given that the oxygenation of the photoreceptors is barely adequate under normal conditions [25] , one could hypothesize that the vasodilation effect of CO can be mainly attributed to local tissue hypoxia, which in turn leads to retinal and choroid vasodilatation.

Our study was in agreement with Wimpissinger et al. [3] who found a significant increase in choroidal blood flow in smokers than in nonsmokers by laser Doppler flowmetry, and they found that choroidal thickness correlates directly with choroidal blood flow.

There are several limitations to our study. One is that we have no quantification of nicotine levels for our subjects. However, based on the investigation reported by Russell et al. [26] on blood nicotine levels after cigarette smoking and nicotine gum, we can estimate that nicotine might reach the maximum level. The study revealed maximum blood plasma nicotine levels 1 h after smoking one cigarette. In addition, the study by Sizmaz et al. [12] , which showed significant choroidal thickness reduction at 1 h after smoking, supports these findings.

Other limitations of the current study are the relatively limited number of cases and the potential interobserver and intraobserver bias while measuring choroidal thickness manually. However, this bias is an issue to be solved in all studies regarding choroidal thickness measurements. Including more than one measurement point and using two independent observers may overcome the problem in this preliminary study, may generate valuable hypotheses, and provide a basis for future  studies.

In conclusion, we found a significant decrease in choroidal thickness due to smoking after 1 h. We consider that this decrease could be associated with decreased blood flow to the choroid following smoking; we also found an increase in choroidal thickness after 8 h, and we hypothesize that this is because of congestion of the choroid as a result of inflammation or hypoxia.

To the best of our knowledge, our study is the first to investigate the effect of smoking on choroidal thickness after 8 h by OCT. We believe that the results of this preliminary study will be useful in future studies about this  topic ([Figure 1], [Figure 2], [Figure 3], [Figure 4]).
Figure 1: Choroidal thickness measurements by OCT (EDI) in smokers and nonsmokers at 1 and 8 h at all measurements points. EDI, enhanced-depth imaging; OCT, optical coherence tomography.

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Figure 2: Choroidal thickness was normal by OCT (case 1). OCT, optical coherence tomography.

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Figure 3: Choroidal thickness measurements at 1 h (case 2).

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Figure 4: Choroidal thickness measurements at 8 h.

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  Conclusion and recommendations Top


We found a significant decrease in choroidal thickness due to smoking after 1 h. We consider that this decrease could be associated with decreased blood flow to the choroid following smoking; we also found an increase in choroidal thickness after 8 h, and we hypothesize that this is because of congestion of the choroid as a result of inflammation or hypoxia.

Further larger studies to investigate more long-term effects of smoking on choroidal thickness may help to explain the role of smoking as a risk factor in ocular diseases such as age-related macular degeneration.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2]


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