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   Table of Contents      
ORIGINAL ARTICLE
Year : 2018  |  Volume : 5  |  Issue : 1  |  Page : 12-18

Effect of prolonged and chronic occupational exposure to lead (Pb) poison metal on anterior segments of the eye


1 Department of Binocular Vision, Faculty of Optometry and Visual Sciences, Al-Neelain University, Khartoum, Sudan
2 Department of Binocular Vision, Faculty of Optometry and Visual Sciences, Al-Neelain University, Khartoum, Sudan; Department of Optometry, College of Applied Medical Sciences, Qassim University, Saudi Arabia

Date of Submission27-May-2018
Date of Acceptance14-Apr-2020
Date of Web Publication11-Jul-2020

Correspondence Address:
Dr. Saif Hassan Alrasheed
Department of Binocular Vision, Faculty of Optometry and Visual Sciences, Alneelain University, Khartoum

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DOI: 10.4103/bijo.bijo_4_18

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  Abstract 


Background: Lead is a naturally occurring toxic metal found in the earth's crust. Its widespread use has resulted in extensive environmental contamination, human exposure, and significant public health problems in many parts of the world.
Aim: This study aimed to assess the effect of prolonged occupational lead exposure and the outer eye abnormalities among workers of military industrial factory as well as to assess the knowledge and practice of the workers toward lead exposure and hazards of lead poisoning.
Materials and Methods: This is a comparative cross-sectional study of 100 workers selected randomly from the lead factory, and their ages ranged from 21 to 67 years, with a mean age of 39.1 ± 10.3 years. They were divided into two groups according to their duration of work (duration of exposure) group of short duration (<10 years) and group of long duration (more than 10 years). Investigations included vision and visual acuity (VA) measurements using Snellen tumbling E-chart and refraction using retinoscopy, and a cover test was conducted to find if phoria or tropia existed, as well as examinations of the external eye, anterior segment, and media using torchlight with low-power magnifier.
Results: The finding revealed that 8% of the workers of long duration had VA < 6/12 after best correction in place compared to 1% among workers of short duration, and this difference was statistically significant (P < 0.001). About 66% of the long duration group presented with symptoms of irritated eye (foreign body sensation and tearing, itching and burning sensation, and periodic redness) compared to 18% among the group of short duration with a significant association (P = 0.038). Almost 36% of the workers of long duration had an ocular sign of conjunctival discoloration (gray-bluish conjunctiva) compared to 10% among workers of short duration with a significant association (P = 0.004). Anterior segment examination revealed that the majority (83%) of the workers in the group of long duration had conjunctival disorders of (pterygium, 77%, and allergic conjunctivitis, 6%) compared only to 25% among the group of short duration (pterygium, 23%, and allergic conjunctivitis, 2%), which was significantly associated (P = 0.01). The media examination showed that 14% of the long duration workers had cataract, 2% had corneal opacity, and 2% were pseudophakic, whereas surprisingly, none of the workers in the group of short duration had any of those media abnormalities, which was statistically significant (P = 0.04). With regard to knowledge of the workers about the effect of the lead poison on the eye, only 30% of the respondents were knew that the lead poison had effect on ocular health; therefore, the most of them not use the protection tools.
Conclusion: Lead poison has a great effect on vision and eye health of the workers, its lead to decrease of vision result in development amblyopia, it also has influence on ocular media and causes severe allergic reaction Thus, all the workers in this field should wear the protection tools provided in the factory, and there is a critical need for examining their ocular health annually.

Keywords: Allergic conjunctivitis, cataract, gray-bluish conjunctiva, lead poisoning on the eye, pterygium


How to cite this article:
Elsir IT, Alrasheed SH. Effect of prolonged and chronic occupational exposure to lead (Pb) poison metal on anterior segments of the eye. Albasar Int J Ophthalmol 2018;5:12-8

How to cite this URL:
Elsir IT, Alrasheed SH. Effect of prolonged and chronic occupational exposure to lead (Pb) poison metal on anterior segments of the eye. Albasar Int J Ophthalmol [serial online] 2018 [cited 2021 Jul 29];5:12-8. Available from: https://www.bijojournal.org/text.asp?2018/5/1/12/289595




  Introduction Top


The eyeball is a cystic structure kept distended by the pressure inside it. Although generally referred to as a globe, the eyeball is not a sphere but an ablate spheroid, consisting of two modified spheres fused together,[1] which houses the structures responsible for vision. It lies in a bony cavity within the facial skeleton, known as the bony orbit.[2] Anatomically, the eyeball can be divided into three parts: the outer fibrous coat (which is a dense strong wall which protects the intraocular contents) – it consists of the sclera and cornea; the middle vascular coat (which supplies nutrition to the various structures of the eyeball) – it consists of the iris, ciliary body, and choroid; and the inner nervous coat (which concerned with visual function) – it consists of the retina, the light detecting part of the eye in addition to the neural layer, pigmented layer, and the visual pathway.[1]

It is assumed that the incidence of visual disorders in industrial workers may result in visual loss, anguish, reduced manpower, man-hours, and economic loss. Most of these hazards are preventable if adequate precautionary measures are taken. Workers' eyes may be exposed to a variety of dangerous agents depending on the type of industry, which may constitute an occupational hazard.[3] Workers in certain occupations such as auto repair, mining, painting, manufacture of ammunition, batteries, sheet lead, and military equipment and construction are known to have a high risk for lead exposure.[4]

Lead (Pb) is a heavy and highly toxic[5] metal that found widely around the world's surface and is used in many products.[6] It occurs naturally in the earth's crust, but human activity – mining, burning fossil fuels, and manufacturing – has caused it to become more widespread.[7] It is denser than most common materials and one of the earliest metals discovered by the human. It has unique properties such as softness, odorless, high malleability,[8] ductility, low melting point, and resistance to corrosion.[9] It has a blue-gray lustrous solid appearance.[10]

Lead exposure occurs when lead dust or fumes are inhaled, or when lead is ingested through contaminated hands, food, water, cigarettes, or clothing[11] and also by skin contact and eye contact to lead compounds originating from lead paints, dust, occupational exposure, ceramics, and other compounds.[8],[9]

Lead entering the respiratory and digestive systems is released to the blood and distributed throughout the body. More than 90% of the total body burden of lead is accumulated in the bones, where it is stored. Lead in bones may be released into the blood, re-exposing organ systems long after the original exposure.[11] Lead exposure is known to disturb a myriad of body process due to its toxicity to our vital organs[12] and functions of the body to a varying degree. The frequency and severity of symptoms among exposed individuals depend on the amount of exposure.[11]

Lead poisoning has effects on central nervous system (CNS), renal system, cardiovascular system and reproductive system, it also has effects on bone and hemoglobin formation.[9],[13] Although the eye itself is not a part of the nervous system, it is connected to the brain by the optic nerve, and all the information that the eye receives are transferred to the brain for processing. Accordingly, human vision a mental process that can be impaired by lead poisoning in different ways as well as directly exposure to the lead toxic from the anterior eye segment.[14] Therefore, the present study conducted to assess the effect of prolonged occupational lead exposure on the outer eye abnormalities among workers of military industrial factory as well as to assess the knowledge and practice of the workers toward lead exposure.


  Materials and Methods Top


Study design and population

This was a comparative cross-sectional study of anterior segment abnormalities among workers of military manufacturing in Al-Shagara Industrial Complex in Khartoum state. The research focused on workers who were directly dealing with or exposed to lead dust or fume during their work. The study was carried out in Al-Shagara Industrial Complex for military manufacturing and ammunition in Khartoum state in the period from November 2017 to March 2018.

Inclusion criteria

Workers who were directly dealing with or directly exposed to lead fume or dust during their occupation were included in the study.

Exclusion criteria

Workers who did not directly deal with or exposed to lead fume or dust during their work were excluded from the study.

Sample selection

The study sample required workers who were in dealing with lead metal for different durations were selected from two workshops randomly. The total of the study sample was 100 workers who were accepted and volunteered to participate in this study.

Clinical examinations

After gathering the demographic information, direct questions were asked to workers to assess their knowledge and practices toward lead exposures and hazards of lead poisoning. Then, clinical investigations included presenting distance vision, and visual acuity (VA) was assessed using Snellen Tumbling E-chart with E's of standard size at a 6-m distance. All the workers underwent a torchlight and lower power hand magnifier examination to rule out any anterior segment abnormalities in the following parts of the eye: eyelids, conjunctiva, cornea, the pupil and pupillary reflex reaction, and lens. A cover test was conducted to find if ocular deviation (phoria or tropia) existed; then, it was classified into orthophoria, heterophoria (eso and exo), and heterotropia (eso and exo). Objective refraction was performed using retinoscope (Neitz RX, Japan) to rule out refractive errors, and finally, the refractive error was further classified into myopia, hypermetropia, and astigmatism.

Data analysis

Data forms were reviewed for accuracy and completeness before data capture. The data for each subject were analyzed using the Statistical Package for the Social Sciences (SPSS Version 22.0, Inc., Chicago, IL, USA). Standard deviation and percentages were used to determine the descriptive statistics. The Chi-squared tests were used to determine statistical significance. For all statistical determinations, the significance level was established at P = 0.05.


  Results Top


Study population

A total of 100 workers' eyes (200) were examined in this study from Al-Shagara Industrial Complex; all the participants who were included in this study exposed to lead poison during their occupation by direct ways and different amounts.

Sociodemographic characteristics of participants

A total of 100 workers were included in the study. All of them were males, and their ages range from 21 to 67 years, with a mean of 39.1 ± 10.3 years. Their duration of the exposure to lead poison range was <1–36 years, with a mean of 15.3 ± 10 years; then, participants were divided into two groups according to the duration of lead toxic exposure, about 38 (38%) of short duration (less than 10 years' workers) and 62 (62%) were of long duration (more than 10 workers) as shown in [Table 1] and [Figure 1].
Table 1: Distribution of ocular signs and symptoms according to the duration of exposure

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Figure 1: Comparison between vision and visual acuity means according to duration

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Distribution of ocular signs and symptoms among workers according to the duration of exposure

A total of 11 (11%) workers did not complain of any ocular symptoms, in whom 8 (8%) were of short duration and 3 (3%) were of long duration. In all, the majority (78, 78%) of the participants complained of blurred vision at distance, in whom near 14 (14%) were of short duration and 64 (64%) of long duration. Almost 41 (41%) workers had foreign body sensation and tearing, in whom 8 (8%) were of short duration and 33 (33%) were of long duration, whereas 37 (37%) participants had photophobia and pain, in whom 15 (15%) were of short duration and 22 (22%) were of long duration. About 30 (30%) participants complained of itching, in whom 8 (8%) were of short duration and 22 (22%) were of long duration. Almost 26 (26%) participants had redness, in whom 10 (10%) were of short duration and 16 (16%) were of long duration, 13 (13%) participants had burning and dryness sensation, in whom 2 (2%) were of short duration and 11 (11%) of long duration, whereas only 12 (12%) complained of headache, in whom 8 (8%) were of short duration and 4 (4%) of long duration. About 46 (46%) participants present with gray-bluish conjunctiva, in whom 10 (10%) were of short duration and 36 (36%) of long duration, and the ocular signs and symptoms among the workers were significantly associated with the duration of lead exposure (P = 0.038), as presented in [Table 1].

Distribution of visual acuity after best correction according to the duration of lead exposure

A total of 183 (91%) eyes presented with normal VA (6/6–6/12), in whom 75 (37.5%) were of short duration and 108 (54%) were of long duration, whereas about 17 (8.5%) had visual impairment (VI) (moderate, severe, and blindness) or amblyopia (shown corrected VA <6/12), in whom 1 (0.5%) was of short duration and 16 (8%) were of long duration. The prevalence of amblyopia or VI after best correction was high among workers of long duration of exposure; however, it was significantly associated with the duration of lead exposure (P < 0.001), as presented in [Table 2].
Table 2: Distribution of visual acuity after best correction according to the duration of exposure

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Distribution of visual impairment according to duration of exposure before best correction

The findings of VI among 200 workers' eyes are shown in [Table 2]. A total of 161 (80.5%) eyes presented with normal unaided vision (6/6–6/12), in whom 67 (33.5%) were of short duration and 94 (47%) were of long duration, whereas 34 (17%) had a moderate VI (6/18–6/60), in whom 7 (3.5%) were of short duration and 27 (13.5%) were of long duration. About 2 (1%) had severe VI (5/60–3/60), in whom 1 (0.5%) was of short duration and 1 (0.5%) was of long duration, whereas 3 (1.5) were legally blind (<2/60), in whom 1 (0.5%) was of short duration and 2 (1%) were of long duration. The prevalence of VI was associated with the subject of long duration of lead exposure, which was statistically significant (P < 0.001), as presented in [Table 3].
Table 3: Distribution of visual impairment before best correction according to duration of exposure

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Distribution of refractive errors according to the duration

The distribution of refractive errors among short exposure participants as the following: about 23.5% were emmetropic, 5.5% were myopic and 9% were astigmatic. On the other hand, the distribution of refractive errors among long exposure participants about (24) % were emmetropic, 5% were myopic, 7.5% were hypermetropic and 19% were astigmatic. The prevalence of refractive errors was not significantly associated with duration of lead exposure (P = 0.147), as presented in [Table 4].
Table 4: Distribution of refractive errors according to the duration

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Distribution of ocular deviation at near fixation according to the duration

Almost (37%) of workers with short duration of lead exposure presented with exophoria (latent squint) at near fixation only 1% presented with exotropia (manifest squint) while the workers of long exposed majority of them (54%) had exophoria (latent squint) and (4%) had exotropia (manifest squint). However, the prevalence of ocular deviation at near fixation was not significantly associated with duration of lead exposure (P = 0.628), as presented in [Table 5].
Table 5: Distribution of ocular deviation at near fixation according to the duration

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Distribution of anterior segment abnormalities according to the duration

About 41 (41%) of short exposure workers present with normal eyes, followed by 23 (23%) with pterygium and 2 (2%) with allergic conjunctivitis. However, majority 77 (77%) of long exposure workers had pterygium, followed by cataract 14 (14%), allergic conjunctivitis 6 (6%), Pseudophakia, 2 (2%), and corneal opacity 2 (2%). However, the prevalence of anterior segment abnormalities among workers was significantly associated with the duration of lead exposure (P = 0.004), as presented in [Table 6].
Table 6: Distribution of anterior segment abnormalities according to the duration

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Finally, according to the knowledge of lead poisoning, a few workers (30%) were aware of the risk of the lead poisoning and other heavy metals on the eye health, so the level of awareness about the risks of lead poisoning on eye health among workers was low and that interpreted the lake of using the protective tools among them.


  Discussion Top


The fact is that exposure to lead could greatly affect vision including the development of the eye, and lead poisoning is known to have severe effects on the human nervous system and brain processing. Although the eye itself is not part of the nervous system, it is connected to the brain by the optic nerve, and all the information that the eye receives are transferred to the brain for processing. This makes vision a cognitive process that can be impaired by lead poisoning. Studies of lead exposure and eye health have revealed that when a person has lead poisoning, they may experience problems with vision including difficulty seeing in low light, blurred vision, and chronic eye irritation. An increasing risk of suffering cataracts has also been identified in some studies.[14]

The current study was conducted to assess the effect of prolonged occupational lead exposure on the anterior segment of the eye. In the present study, the majority of the participants (84%) with symptoms of eyes discomfort which included (foreign body sensation and tearing, itching and burning and dryness sensation), most of the participants 66% of long duration of exposure compared to 18% participants with short duration of exposure; the association between the duration of exposure and the complaints of irritated eye was statistically significant (P = 0.038). This could be due to direct exposure of anterior surface of the eye to lead toxic which result in eye dryness and discomfort symptoms and this is agreed with Shu and Roberts[12] and Mulak, et al.[15] they reported that chronic lead exposure is major cause of eye discomfort. In our study, 36% of the workers of long duration had a sign of discoloration of conjunctiva (gray-bluish conjunctiva) or called argyrosis, compared to 10% among workers of short duration, which was statistically associated with the duration of lead exposure at P = 0.004. This is may be due to the nature of the lead which contains silver compounds which is major cause of argyrosis. In study conducted by the American academy of ophthalmology[16] revealed that ocular argyrosis has been reported by several of participants after frequent exposure to silver- containing compounds.

The current study revealed that 15% of the workers of long duration had blurred or defective vision <6/12 in the best eye before correction, whereas 7% of them their vision was improved to normal and 8% still had blurred vision or had amblyopia, the association between prolonged exposure and blurring of vision was statistically significant (P < 0.001). This is may be due to consequence of lead toxicity on the visual system and optic nerve which might be cause toxic amblyopia, this agreed with Roberts[12] he reported that deteriorating of vision that cause by optic neuritis which is inflammatory condition may be due toxic effect.

In this study, the high percentage of refractive errors was 28% of astigmatism, 9% on workers of short duration, and 19% among workers of long duration, but it revealed that there was no significant association between the duration of exposure and astigmatic refractive errors, and also, there was no previous study that was used to compare with it. Furthermore, the study revealed that there was no significant association between duration of exposure and the ocular deviation at distance and near fixation. This was disagreed with Shu and Roberts,[12] who suggested that the increased intracranial pressure induced by lead exposure can cause paralysis of the extended recti muscles involved in eye movement which may contribute to strabismus and consequently double vision due to the lack of fixation of both eyes on a target.

This study indicated that the most anterior segment abnormalities among workers were pterygium and allergic conjunctivitis which were 77% and 6%, respectively, compared to 23% and 2%, respectively, among workers of short duration, which was statistically associated with the duration of exposure (P = 0.01). This might be due to exposure to lead dust and hot smoke or vapor which may lead to allergic conjunctivitis and pterygium formation. This was compatible with Mulak et al.[15] and Wingate et al.,[14] who reported that periodical conjunctival inflammatory states are caused by irritative dust and smoke during lead exposure and a person may experience chronic eye irritation and pterygium formation. Furthermore, in our study, 14% of the workers of long duration had cataracts with different grades, whereas surprisingly, no workers of short duration had cataract, and the association between the duration of exposure and lenticular changes (cataract) was statistically significant (P = 0.04). This could be due to the deposition of lead dust on crystalline lens and the effects of lead smoke and vapor after prolonged exposure. This is agreed with the studies conducted by Davis,[17] Phelps,[18] and The Doctors Health Press,[19] who reported that lead exposure could cause age-related cataracts the leading cause of blindness and VI worldwide. Meanwhile lead toxic cause damage in human cells may also lead to protein build up on the lens of the eye and interfering with calcium absorption, which keeps the lens unclear and decrease lens transparency result in cataract formation.

The present study had some limitations: first, the sample included in this study was small because of the lack of lead industrial factories in our country, and second, lack of previous studies performed on the effect of prolonged occupational lead exposure on the anterior segment of the eye worldwide as well as no previous studies performed in Sudan to compare our study findings with them.


  Conclusion Top


To our knowledge, no similar study has been conducted in our country; thus, the data obtained make a valuable contribution to the understanding of occupational hazard especially of lead substance and its challenges to threaten the eye health of the workers. The study concluded that prolonged occupational lead exposure affect on the outer eye health of the workers. The study concluded that the lead exposure has major effect on the vision and anterior eye segment. Therefore, it is very important to increase the awareness and knowledge of the workers about the effect of lead toxic on the eye and the importance of using the protective tools such as (face mask, gloves, and boots in addition to the full protective suit and protective eye goggles), also following a special type of a healthy diet containing calcium and potassium can help to absorb lead substance from blood. Finally, this study was limited on assessing the effects of lead exposure just on the outer eye of workers, so we recommend the coming searchers after us to extend and expand this study by doing examinations on the inner eye and fundus as whole to complete the picture for us.

Acknowledgment

After Almighty Allah, We would like to express our sincere thanks and gratitude to all the members and staff of Al-Shagara Industrial Complex beginning from the managers and engineers ending by workers for their great help in data collection and completing this study. We would also like to thanks all the people who participated in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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