Impact of environmental pollution on the eye - Wiley Online Library

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Due to the constant contact of the preocular tear film, cornea and conjunc- tiva with the surrounding air, toxins have direct access to these ocular structures and.

ACTA OPHTHALMOLOGICA SCANDINAVICA 2003

Impact of environmental pollution on the eye Rohit Saxena,1 Sushma Srivastava,2 Deepa Trivedi,2 Eswaraiah Anand,2 Sujata Joshi2 and Suresh Kumar Gupta2 1

Dr Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India 2 Department of Pharmacology, All India Institute of Medical Sciences, New Delhi, India

ABSTRACT. Purpose: To study the effect of environmental toxins on the ocular surface in persons travelling through highly polluted areas of the metropolis of Delhi. Methods: A total of 500 apparently healthy volunteers recruited from the metropolis of Delhi were examined to establish the frequency of ocular surface disorders. All subjects underwent a slit-lamp examination, tear break-up time (BUT) test, Rose Bengal test, Schirmer’s test and tear lysozyme level test. Results: Subjects in the study group had significantly higher levels of ophthalmic symptoms compared to the control group. In all, 105 (42%) and 125 (50%) subjects in the study group compared to 50 (20%) and 65 (26%) in the control group complained of redness and irritation (p < 0.05). There was no significant difference in visual acuity (VA) between the two groups, with best corrected VA being 6/9 or better in 92% of the study group and 96% of the control group. The average (±standard deviation) Schirmer’s test result was 13.42±6.67 mm in the study group compared to 15.95±6.14 mm in the control group. This difference was statistically significant. The BUT was also significantly lower in the study group (12.97±6.12 seconds) compared to the control group (19.23±5.70 seconds) (p < 0.001). The Rose Bengal test and tear lysozyme activity did not show any significant difference between the two groups. Conclusion: According to our study, environmental conditions appear to have a very significant effect on the ocular surface. There were very high levels of subclinical ocular surface changes among persons travelling in highly polluted areas. Key words: environmental toxins – ocular surface disorder – tear break-up time – lysozyme activity

Acta Ophthalmol. Scand. 2003: 81: 491–494 Copyright # Acta Ophthalmol Scand 2003. ISSN 1395-3907

Introduction Progressive industrialization and the increase in the number of motorized vehicles have resulted in high levels of air and water pollution. This environmental pollution can have marked detrimental effects on human health. Although illeffects on the skin and oropharyngeal

and respiratory systems are well documented, the harmful effects of increased air pollution on the eye have not been well defined (Kjaergaard & Pedersen 1989; Paschides et al. 1998; Versura et al. 1999). Due to the constant contact of the preocular tear film, cornea and conjunctiva with the surrounding air, toxins have

direct access to these ocular structures and can abnormally change them. A previous study (Frank & Skov 1991) suggested that the quality of environmental air can result in premature break-up of the preocular tear film and corneal epithelial damage. This can lead to significant ocular irritation and discomfort. The aim of the current study was to study the impact of environmental pollution and toxins on the eyes of people who commuted daily on routes with documented high levels of pollution.

Material and Methods Study population

The study was conducted among healthy, adult volunteers working at the All India Institute of Medical Sciences hospital. The subjects were informed and enrolled after written consent regarding the nature and purpose of the study had been obtained. The subjects were divided into two groups. The study group comprised people who had commuted daily to the hospital using open vehicles (e.g. scooter, motorcycle and cycle) for more than 10 years via areas identified as highly polluted. The control group comprised people who had resided on the campus of the All India Institute of Medical Sciences for more than 10 years and who were not routinely involved in long distance travel or significant exposure to vehicular or industrial pollution.

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ACTA OPHTHALMOLOGICA SCANDINAVICA 2003 All subjects enrolled in the study and control groups were healthy, non-smoking adults aged 35–65 years who had been employed at the hospital for 10 or more years. All subjects were engaged in related activities at the hospital and worked in similar environments. None of the subjects had any history of ocular surface disease, lid abnormalities or contact lens use and none were being treated by any systemic or topical drugs that might affect the ocular surface. All the subjects were employed in sedentary office jobs in the hospital. They were examined by a single observer, who was masked to their history. A detailed history was recorded for each subject. It included information on the subject’s age, sex, the distance they travelled in kilometres per day, their commuting time, mode of transport, period of travelling in years and the geographic area travelled through while commuting. A history of ocular morbidity that induced redness, irritation, foreign body sensation, lacrimation, blurred vision, photophobia and eye strain was also taken. The duration of any of the symptoms was recorded. All the patients underwent a best corrected Snellen’s visual acuity (VA) assessment as well as lid, cornea and conjunctiva examination with slit-lamp. The tear film was examined using the slitlamp for the presence of mucus, debris or particulate matter. The height of the tear film was measured in mm using the graduated slit-beam height. All the subjects enrolled in the study underwent the following tests in the given order. There was a half-hour interval between each of the tests conducted. Schirmer’s test

Standardized strips of filter paper (Sno strips; Smith and Nephew Pharmaceuticals Ltd, Romford, UK) were hooked on the rim of the lower eyelid at the junction of the middle and lateral one-third of the lower eyelid margin, with the head of the strip in the lower conjunctival fornix (Schirmer 1903). The strips did not touch the cornea. No topical anaesthesia was used and the patients remained relaxed with open eyelids for 5 min. After 5 min the strips were removed and the length of the wetted part was measured from the fold of the strip. Wetting of the strip greater than 10 mm was considered as the normal value.

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Results

Break-up time

A dose of 10 ml of 1% fluorescein solution without any preservative or anaesthetics was applied in each eye (Norn 1969; Lemp 1973). The interval between the last complete blink and the appearance of the first black spot in the fluorescein stained tear film without touching the eyelid was measured. Break-up time (BUT) was estimated three times in each eye and the mean value was calculated. Values over 15 seconds were considered as normal. Values between 10 and 15 seconds were taken to be indicative of a definite abnormality. Rose Bengal score

The Rose Bengal score (RBs) was calculated by application of 10 ml of 1% Rose Bengal solution without preservatives or anaesthetics in each eye (Norn 1983). The patients were examined after a waiting period of 2 min, allowing the excess stain to wash out. The degree of staining was estimated using the method described by Van Bijsterveld (1969). Lysozyme activity

Lysozyme activity in tears was measured using the method described by Mackie & Seal (1976). Normal values are reported as 70 units/ml at 20 years of age to 40 units/ml at 85 years of age. The cut-off point used in the study was 50 units/ml. Any value below this level was taken to imply a deficiency of lysozyme activity. Statistical analysis

Each of the tests between the two groups was compared using Chi-square and Fisher’s exact tests. Data were also analysed to study the possible effects of mode of transport and number of miles travelled daily.

A total of 500 subjects were enrolled in the study, with 250 patients in each group. The study group consisted of 160 males and 90 females with a mean age of 47.7  14.9 years. The control group included 145 males and 105 females with a mean age of 50.2  12.2 years. The age and sex distribution was comparable between the two groups (p ¼ NS). Subjects in the study group had a significantly higher degree of ophthalmic symptoms compared to the control group (Table 1). Direct questioning established occasional ocular redness, irritation and lacrimation to be present in nearly half of the study group, with 105 (42%) and 125 (50%) of subjects complaining of redness and irritation, respectively, compared to 50 (20%) and 65 (26%) of subjects in the control group (p < 0.05). However, none of these symptoms were severe enough to result in the subjects seeking any treatment for them. There was no significant difference in VA between the two groups. Best corrected VA was 6/9 or better in 92% of the study group and 96% of the control group. The average Schirmer’s test result was 13.42  6.67 mm in the study group compared to 15.95  6.14 mm in the control group. This difference was statistically significant (Table 2). Less than 10 mm wetting of the strip was considered an abnormal value. In all, 28 (11.2%) subjects in the study group and 10 (4%) in the control group had an abnormal Schirmer’s test result (p < 0.001). The BUT was also significantly lower in the study group (12.97 þ 6.12 seconds) compared to the control group (19.23  5.70 seconds; p < 0.01). The Rose Bengal test and tear lysozyme activity did not show

Table 1. Ocular subjective complaints in the control and study groups. Parameters

Redness Irritation Lacrimation Blurred vision Photophobia Eye strain Burning Dryness

Control group n (%)

Study group n

(%)

50 65 45 10 5 35 0 0

105 125 95 40 10 60 70 20

(42) (50) (38) (16) (4) (24) (28) (8)

(20) (26) (18) (4) (2) (14) (0) (0)

n ¼ number of persons; NS ¼ non-significant.

p-value

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