|ORIGINAL RESEARCH REPORT
|Year : 2021 | Volume
| Issue : 2 | Page : 81-89
Prevalence and pattern of dry eye symptoms among “okada” riders in Southwest Nigeria using the ocular surface disease index: A cross sectional study
Adetunji Olusesan Adenekan1, Olubanke Theodora Ilo1, Adegboyega Sunday Alabi2, Olufisayo Temitayo Aribaba1, Folasade Bolanle Akinsola1
1 Department of Ophthalmology, College of Medicine, University of Lagos; Guinness Eye Centre, Lagos University Teaching Hospital, Lagos, Nigeria
2 Department of Ophthalmology, College of Medicine, University of Lagos; MeCure Eye Center, Me Cure Healthcare Limited, Lagos, Nigeria
|Date of Submission||03-May-2020|
|Date of Acceptance||28-Jan-2021|
|Date of Web Publication||24-Apr-2021|
Dr. Adetunji Olusesan Adenekan
Department of Ophthalmology, Guinness Eye Center, Lagos University Teaching Hospital, Lagos
Source of Support: None, Conflict of Interest: None
Background: Dry eye is a common disorder of the tear film that results in epithelial damage and the disruption of normal homeostasis at the ocular surface. It is a common ocular condition that is often missed in clinical diagnosis. The objectives of this study were to determine the prevalence and pattern of dry eye symptoms using the Ocular Surface Disease Index (OSDI) among commercial motorcyclists and also identify factors that may be responsible for dry eye symptoms in this population. Methods: This was a descriptive, cross-sectional, population-based study. Using a multistage random sampling technique, 422 commercial motorcyclists were surveyed from 10 units of registered commercial motorcyclists. Interviewer-administered OSDI questionnaires (face to face) were used, and visual acuity (VA) measurement was done. Results: The prevalence of dry eye symptoms in this study was 83.42%. Using the OSDI, the pattern of dry eye symptoms in this study showed that 21.56% had mild dry eye, 54% had moderate dry eye, and 7.82% had severe dry eye. Riders aged >50 years (86.90%), P < 0.05, 95% confidence interval: 0.012–0.021; nonuse of protective spectacles (87.46%), P < 0.05, 95% confidence interval: −0.235–−0.087; and use of helmets with face shields while riding (92.89%), P < 0.05, 95% confidence interval: −0.160–−0.062, were risk factors for dry eye symptoms. All respondents who had diabetes mellitus (P < 0.05, 95% confidence interval: 0.084–0.429) and a larger proportion (84.86%) of those not on topical medications (P < 0.05, 95% confidence interval: −0.365–−0.066) had dry eye. Visual impairment (VA <6/18) was observed in three respondents, with uncorrected refractive errors as the cause. Multivariate analysis showed that respondents aged <50 years, nonuse of protective spectacles, use of crash helmets with face shield, medical conditions, particularly diabetes mellitus, and nonuse of topical medications were significantly associated with dry eye symptoms. Conclusion: The prevalence of dry eye symptoms was high, and majority had moderate dry eyes based on OSDI grading. Furthermore, public health awareness program should be commenced to educate motorcyclists on the importance of using protective goggles in preventing dry eye disease.
Keywords: Dry eye symptoms, dry eyes, Ocular Surface Disease Index
|How to cite this article:|
Adenekan AO, Ilo OT, Alabi AS, Aribaba OT, Akinsola FB. Prevalence and pattern of dry eye symptoms among “okada” riders in Southwest Nigeria using the ocular surface disease index: A cross sectional study. J Clin Sci 2021;18:81-9
|How to cite this URL:|
Adenekan AO, Ilo OT, Alabi AS, Aribaba OT, Akinsola FB. Prevalence and pattern of dry eye symptoms among “okada” riders in Southwest Nigeria using the ocular surface disease index: A cross sectional study. J Clin Sci [serial online] 2021 [cited 2022 Aug 18];18:81-9. Available from: https://www.jcsjournal.org/text.asp?2021/18/2/81/314447
| Introduction|| |
Dry eye is a common disorder of the tear film that results in epithelial damage and the disruption of normal homeostasis at the ocular surface. It is a common ocular condition that is often missed in clinical diagnosis. Dry eye symptoms are frequently encountered by ophthalmologists in their daily practice and are often seen in association with ocular and systemic conditions.
Dry eye is a highly prevalent, yet largely underdiagnosed condition that can substantially affect the quality of life. If untreated, dry eye is associated with chronic eye pain and increased risk of ocular surface disease. Current demographic changes and lifestyle factors indicate that dry eye patient's population will increase significantly; this means that general practitioners and ophthalmic clinicians alike will experience a surge in number of patients presenting with dry eye symptoms. Greater public and practitioners' awareness of emerging research, technologies, and therapies is crucial to ensuring appropriate interventions to meet the specific needs of patients, thereby resulting in clinically favorable outcomes.
Accordingly, accurate diagnosis and appropriate treatment are critical because outcomes depend on the therapy applied. Mild dry eye has been estimated to affect up to 20% of the United States population and moderate dry eye affects 15% of those aged >65 years. Moderate-to-severe dry eye is more common in women than men aged >50 years, with an estimated prevalence of 7.8% and 3.5%, respectively, in the United States. The prevalence of lid margin disease also varies among populations and age groups and can approach 50% with increasing age and contact lens use, although in one study, it was also reported in 39% of normal healthy controls.
Based on data from the largest studies of dry eyes to date, the Women's Health Study (WHS), and the Physicians' Health Study (PHS), it has been estimated that about 3.23 million women and 1.68 million men, a total of 4.91 million Americans 50 years and older, have dry eye., Epidemiological studies from the large WHS and PHS indicate that the prevalence of symptomatic dry eye in the United States is about 7% in women and 4% in men over the age of 50 years.
In a population-based study in Indonesia, the prevalence of one or more of the six dry eye symptoms often or all the time adjusted for age was reported to be 27.5%, and the dry eye was associated with age, cigarette smoking, and pterygium. In a hospital-based study conducted in Bangkok, it was found that 34% reported significant symptoms of dry eye which were defined as having one or more symptoms often or all of the time. Women are most susceptible to dry eyes, especially those receiving estrogen replacement therapy alone or in combination with progesterone. Dry eye is widespread with as many as 25% of patients visiting ophthalmologists reporting dry eye symptoms. The prevalence of dry eye is estimated to be 7.4%–33.7% depending on which study is cited, how the disease is diagnosed, and which population is surveyed. The Beaver Dam population-based study found the prevalence rate to be 14% in adults aged 48–91 years that it affected more women than men (16.7% vs. 11.4%, respectively).
These numbers translate into approximately 3.2 million women and 1.05 million men with dry eyes in the United States. It is worth noting that the prevalence and incidence of dry eye in the clinical setting may also be underreported as patients may fail to recognize the symptoms of dry eye or do not report the problem to a physician.
In a panel study in São Paulo, Brazil, it was detected that there were a significant association between nitrogen dioxide (NO2) quartiles and reported ocular irritation (Chi-square = 9.2, P < 0.05) and a significant negative association between tear breakup time (TBUT) and NO2 exposure (P < 0.05). Individuals exposed to higher levels of traffic-derived air pollution reported more ocular discomfort symptoms and presented greater tear film instability, suggesting that the ocular discomfort symptoms and TBUT could be used as convenient bioindicators of the adverse health effects of traffic-derived air pollution exposure.
Several factors have been found to increase the likelihood of having ocular surface disorders, one of them, being exposure to traffic-derived air pollution, primarily due to exposure to NO2. Commercial motorcycling, popularly called “okada” riding, is a common occupation in Ogun State. These commercial motorcyclists are exposed to air pollution during their daily economic activities which may predispose them dry eye symptoms.
The Ocular Surface Disease Index
The impact of dry eye on the quality of life is mediated through a variety of mechanisms including pain, effect on general well-being, effect on visual function, and impact on visual performance. Common activities such as driving, riding, reading, working at the computer, or watching television are affected as well as social interaction giving the necessity of frequent lubricant instillation. The Ocular Surface Disease Index (OSDI), developed by the Outcomes Research Group at Allergan Group at Allergan Inc. (Irvine, California), is a 12-item questionnaire designed to provide a rapid assessment of the symptoms of ocular irritation consistent with dry eye disease and their impact on vision-related functioning. The OSDI is assessed on a scale of 0–100 with higher scores representing greater disability. The index demonstrates sensitivity and specificity in distinguishing between normal controls and patients with dry eye disease. The OSDI is a valid and reliable instrument for measuring dry eye disease (normal, mild to moderate, and severe) and effect on vision-related function.
This study was, therefore, conducted among commercial motorcyclists in Ifo Local Government Area, Ogun State, to determine the prevalence and pattern of dry eye symptoms among them and also identify factors that may be responsible for dry eye symptoms in this population using the OSDI.
| Methods|| |
This was a population-based descriptive, cross-sectional study that used a quantitative method of data collection and was carried out over a 3-week period from May 17 to June 7, 2013. The study was conducted among commercial motorcycle riders registered with the Amalgamated Commercial Motorcycle Owners and Riders Association of Nigeria (ACOMORAN) in Ifo Township, Ifo Local Government Area of Ogun State. Ethical approval was obtained from the Health Research Ethics Committee (HREC) of Lagos University Teaching Hospital, Idi-Araba, Lagos State, with protocol number ADM/DCST/HREC/971 and approval dated from May 16, 2013, to May 16, 2014. Clearance was also obtained from the ACOMORAN executives and head of units in Ifo Local Government Area (LGA). Informed consent was obtained from each of the participants included in the study. Informed consent was obtained from each of the participants included in the study.
There were 10 units with different numerical strengths comprising of 950 registered members in total. The sample size for this study was determined using the Leslie Kish formula, with the standard normal deviate at 95% confidence level set at 1.96, the prevalence of an attribute present in the population, P was taken as 50% = 0.5, as the authors could not get data on the prevalence of dry eye symptoms in Nigeria. The desired level of precision, d, was set at 5%. Thus, the minimum sample size(n) calculated when the population is >10,000 with the above parameters was 384, and following the inclusion of attrition rate of 10%, the sample size came to 422. A pilot survey that provided the opportunity for the study team to have practical field experience and allowed pretesting of the questionnaire was conducted separately among riders that were not selected for the study.
All the 10 units of registered commercial motorcycle riders within Ifo Township, Ifo LGA, were used as the sampling frame.
A multistage random sampling method – Stage 1: Probability proportional to size was used to allocate sample to each unit because of the differences in the numerical strength of all the units. This was to allow for relatively equal representation of each unit in the overall sample size.
Stage 2: Systematic random sampling was used. The population of each unit was divided by the allocated sample size to determine the sampling interval. The starting point was randomly selected by balloting.
Data were collected over a period of 3 weeks (May 17 to June 7, 2013), using structured interviewer-administered questionnaires, OSDI questionnaire (as shown below), and visual acuity (VA) assessment with Snellen's chart or tumbling “E” chart placed 6 m from the respondent at his eye level in a well-lit area. Respondents with simple treatable ocular infections were treated at no cost to them with guttae chloramphenicol. Those with mild-to-moderate dry eye symptoms had guttae hypotears gel given to them, and those requiring further ophthalmic evaluation, refraction and glasses, and medical or surgical treatment were referred to the Lagos University Teaching Hospital with a referral form.
The OSDI questionnaire was used to assess the reporting of dry eye symptoms by respondents, and each number in the box that represented each answer was circled indicating chosen response This score is then read on the OSDI score scale to determine the grading of dry eye as either Normal, mild, moderate or severe.
Data were analyzed with Epi Info 188.8.131.52 Statistical Software For Epidemiology developed by Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia (US). Univariate analysis was conducted, and frequencies were reported in tables, graphs, and charts. Multivariate analysis was also conducted to test the association between the dependent variables and independent variables. P value was set at 0.05. Fisher's exact P value was used when the expected value of any cell was <5.
| Results|| |
A total of 422 motorcyclists were studied, and the response rate of this study was 100%. The mean age of the sample population was 32.64 ± 8.64 years. The sociodemographic characteristics of the respondents are shown in [Table 1].
Majority, 339 (80.33%), of the respondents were full-time owner-riders, part-time owner-rider 62 (14.69%), full-time hire-riders 15 (3.55%), while only 6 (1.42%) were part-time hire-riders. The duration of riding was indicated to be <5 years 257 (60.9%), 5–9 years 109 (25.83%), 10–14 years 34 (8.06%), 14–19 years 18 (4.27%), and 20 years and above 4 (0.95%). The mean years of riding were 5.01 ± 3.74 years. Majority of the respondents got their drivers'/riders' license at age 18 years or older 411 (97.39%) while the others got theirs below 18 years 11 (2.61%). Most of the riders did not have any medical test conducted on them before obtaining their license 404 (95.73%). Only 24 (5.69%) riders had eye test before they were issued their riders' license. Respondents spent >12 h 218 (51.66%), 6–12 h 178 (42.18%), and <6 h 26 (6.16%) riding daily, and the time of day spent riding was mostly morning–evening 345 (81.75%).
About a quarter of the respondents 103 (24.41%) used protective spectacles while riding, and of these, 94 (91.26%) cited protection from dust and particles as the reason they use protective spectacles. Other reasons include to prevent germs 4 (3.88%), to protect the eyes 3 (2.91%), and for safety 2 (1.94%). Among the majority who did not use protective spectacles while riding, 203 (63.64%) said that they had no reason for not using it and 52 (16.30%) felt uncomfortable with it. Other reasons include not liking it 29 (9.09%), no need for it 19 (5.96%), inability to afford purchasing a protective spectacle 9 (2.82%), while misplaced/lost spectacles were in 7 (2.19%) as the reason for not using it. The majority of the respondents used protective helmets while riding 357 (84.6%), which had face shield attached to it 239 (66.95%) and no attached face shields 118 (33.05%). In the proportion of riders who did not use helmets while riding, 24 (36.92%) indicated that using the helmet made them uncomfortable, 15 (23.08%) feel that they do not need it and 2 (3.08%) did not like it.
Only 56 (13.27%) respondents had a medical condition which was reported to be diabetes mellitus 32 (57.14%), hypertension 13 (23.2%), depression 6 (10.71%), and asthma 5 (8.93%). Of these respondents with medical conditions, 27 (48.21%) were on medication for their medical conditions.
Only 48 (11.37%) respondents had any eye problem, with both eyes being the problem among 38 (79.17%) of them. The problem with their eyes, according to 15 (31.25%) respondents, was blurred vision, as shown in [Table 2]. Only 13 (3.08%) respondents, however, wore recommended eyeglasses or contact lens which was recommended by an optometrist 6 (46.15%), ophthalmologist 5 (38.46%), or self-purchased over the counter 2 (15.38%). The glasses recommended were for seeing distant objects only 6 (46.15%), reading only 3 (23.08%), both seeing distant objects and reading 2 (15.38%), and dust protection 2 (15.38%).
A proportion of respondents indicated that they had had eye injury in the past 101 (23.93%), however, only a minority of them indicated consulting an ophthalmologist with their eye complaints 6 (5.94%), whereas others consulted nurses 59 (58.42%), chemists 30 (29.70%), optometrists/opticians 3 (2.97%), and self 3 (2.97%). Majority did not know the name of the treatment given 88 (87.13%), while other treatments known included herbs 5 (4.95%), glasses (2.97%), operation 3 (2.97%), and chloramphenicol 2 (1.98%).
Only 19 (4.5%) respondents were using eye drops that were recommended, in which the largest proportion 11 (57.89%) were on eye drops recommended by a chemist while equal proportions 2 (10.53%) each used eye drops recommended by ophthalmologists and pharmacists, respectively.
In this study, of the 422 respondents, 352 had dry eye symptoms using the OSDI. This translated to a prevalence of 83.42%. The distribution of the pattern of dry eye symptoms using the OSDI is shown in [Figure 1].
|Figure 1: Pattern of dry eye symptoms among respondents using Ocular Surface Disease Index|
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Using the World Health Organization classification, the presenting VA test results of almost all, 419 (99.3%) respondents were normal (≥6/18 in the better eye), while only 3 (0.7%) had visual impairment of <6/18 in the better eye. Refractive error was noted in 115 (27.2%) riders in this study [Table 3].
|Table 3: Presenting visual acuity in better eye using the World Health Organization classification|
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There was a statistically significant association between age of respondents and dry eye symptoms. A larger proportion (86.9%) of those aged <50 years had dry eye symptoms compared to 28% of those aged 50 years and above (P < 0.05, 95% confidence interval: 0.012–0.021).
A statistically significant association exists between years of riding and dry eye symptoms. A larger proportion, 226 (87.94%), of riders who have been riding for <5 years have dry eye symptoms compared to 14 (77.78%) of those who had been riding for 15–19 years had no dry eye symptoms (P < 0.05) [Table 4].
|Table 4: Association between age group, years of riding, and dry eye symptoms|
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There was a statistically significant association between using protective spectacles and dry eye symptoms most 279 (87.46%) of respondents who did not use protective spectacles when riding had dry eye symptoms (P < 0.05, 95% confidence interval: −0.235–−0.087). There was a statistically significant association between respondents' crash helmet having a face shield and dry eye symptoms. A larger proportion, 222 (92.89%), of respondents whose helmets have face shields had dry eye symptoms compared to 95 (80.51%) who were without face shield (P < 0.05, 95% confidence interval: −0.160–−0.062) [Table 5].
|Table 5: Association between using protective spectacles when riding, crash helmet having a face shield, and dry eye symptoms|
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There was a statistically significant association between having a medical condition and dry eye symptoms A majority, 54 (96.43%), of respondents with medical condition had dry eye symptoms (P < 0.05). There was a statistically significant association between having diabetes mellitus and dry eye symptoms (P < 0.05, 95% confidence interval: 0.084–0.429). All the respondents (100%) who had diabetes mellitus had dry eye symptoms [Table 4]. There was a statistically significant association between nonuse of eye drops and dry eye symptoms. Most of the respondents, 342 (84.86%), who did not use eye drops had dry eye symptoms (P < 0.05, 95% confidence interval: −0.365–−0.066) [Table 6].
|Table 6: Association between having a medical condition, diabetes mellitus, and dry eye symptoms|
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Multiple regression analysis of dry eye symptoms on statistically significant variable showed that respondents aged <50 years, nonuse of protective spectacles, use of crash helmets with face shield, diabetes mellitus, and nonuse of eye drops still had a relationship with the occurrence of dry eye symptoms [Table 7].
|Table 7: Multiple regression (multivariate analysis) of dry eye symptoms on statistically significant variables|
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All the riders with dry eye symptoms had artificial tears preservative free eye drops given to them. Those with moderate to severe forms had additional anti-inflammatory eye drops with subsequent referral to the Lagos University Teaching Hospital Annex, Pakoto, Ogun State, due to its proximity to the study area.
| Discussion|| |
The mean age of respondents in this study was 32.64 (standard deviation ± 8.64). Most of the riders (81.28%) were between the ages of 20 and 49 years [Table 1]. However, it is important to note that 5.92% of the riders above 50 years were still actively riding motorcycle for commercial purposes in this study; this may not be unconnected to the economic gain derived from riding. Most of the riders, 297 (70.38%), were married. It also could mean quite a number of them might have engaged in commercial motorcycling business due to the responsibilities of having to cater for their families. All the respondents (100%) were males, and this may be as a result of gender role as influenced by cultural beliefs and the society. Almost all, 393 (93.13%) had some form of education while the largest proportion of them did complete secondary school education. These riders may have been inspired into commercial cycling business as a means of generating or supplementary income in order to survive since oftentimes money is earned daily once a rider is able to ply the road. It was also discovered that a significant number of motorcyclists obtained riders' card/driving license without prior medical or visual test which is one of the requirements laid down for the job.
The prevalence of dry eye symptoms in this study was 83.42% in wide contrast with other studies where the prevalence of dry eye symptoms was far less.,,,,,, This may not be surprising, considering the difference in the study population, possible disparity in diagnosis criteria, and difference in geographic location.
The US study that employed the same OSDI grading criteria had 20% of respondents with mild dry eye symptoms, which is quite similar to 21.56% in our study. However, while our study recorded 54.03% of respondents with moderate symptoms, only 15% of respondents in the US study had moderate dry eye symptoms. Possible explanation would be the difference in the study population in terms of age group and occupation.
One of the factors that have been found to increase the likelihood of having dry eye symptoms is exposure to traffic-derived air pollution (NO2). There is a statistically significant association between years of riding <5 years and dry eye symptoms (P < 0.05); this study showed that report of symptoms of dry eye symptoms decreased as the years of riding increased; a possible reason may be that those who have been riding for more than 15 years may have challenge with recall bias and may have become more adaptable to those dry eye symptoms as compared to those riding for less years (≥15 years). A more precise indicator would be to measure the amount of the gas (NO2) exposure and riding history (in years) and compare with OSDI scores just like in the study in Sao Paulo, Brazil.
In this study, there is a statistically significant association between respondents' crash helmet having a face shield and dry eye symptoms (P < 0.05). The majority, 222 (92.89%), of the respondents whose helmets have face shields had dry eye symptoms. Furthermore, in this study, one-quarter, 103 (24.41%), of the respondents used protective spectacle when riding, majority (91.26%) of whom cited protection from dust and particles as the reason they use protective spectacles, though very few riders were operating their motorcycle with vision below the requirements laid down for the job.
However, there is a statistically significant association between nonuse of protective spectacles and dry eye symptoms (P < 0.05). Majority of those who do not use protective spectacle, 279 (87.46), had dry eye symptoms. This means that the use of protective spectacle may confer some protection against the development of dry eye symptoms.
Poor metabolic control of diabetes, treatments with photocoagulation, and proliferative diabetic retinopathy had been found to increase the risk of development of dry eye symptoms. In this study, a statistically significant association between having diabetes mellitus and dry eye symptoms (P < 0.05) was found as all the 32 respondents (100%) who had diabetes mellitus had dry eye symptoms. Although the blood glucose values was not part of data obtained in this study for possible analysis of its relationship with dry eyes. Having a medical condition was also shown to have a statistically significant association with dry eye symptoms. Surprisingly, the use of medications for these medical conditions has no association with dry eye symptoms.
This study showed a statistically significant association between nonuse of eye drops and dry eye symptoms (P < 0.05). Very few, 19 (4.50%), riders were on topical medications; more than half, 10 (52.63%), of them had dry eye symptoms. Whereas information on the indications and types of medications being used as regards preservatives composition which may be a confounder was not obtained in this study owing to recall bias. Furthermore, the prevalence of dry eye found in this study is high, and most riders had moderate dry eye symptoms.
All the riders who had dry eye symptoms irrespective of the pattern had artificial tears preservative free eye drops given to them while those with moderate and severe pattern had additional anti inflammatory eye drops with subsequent referral to the Lagos University Teaching Hospital Annex, Pakoto, Ogun State, due to its proximity to the study area.
Limitation in this study included the rider's ability to understand, recall, and report symptoms accurately which may have led to underreporting or exaggeration of responses. This study only demonstrated associations because of its descriptive study design but not actual cause of dry eyes because a statistical association does not necessarily mean causal association.
| Conclusion|| |
The prevalence of dry eye found in this study was high, and most riders had moderate pattern of dry eye symptoms as assessed by the OSDI grading system. Furthermore, there was a statistically significant association between medical condition and dry eye, particularly in riders with diabetes. There was also a statistically significant association between <50 years, nonuse of protective spectacles, crash helmets with face shield, and nonuse of topical medications and dry eye.
This study, therefore, recommends that commercial motorcyclists be visually assessed before issuance or renewal of rider's license as a few of the respondents were noted to have skipped this important requirement for commercial riding. Furthermore, public health awareness program should be commenced to educate motorcyclists on the importance of using protective goggles in preventing dry eye disease.
The authors wish to acknowledge the support of the commercial motor owners and riders' Association of Ifo Township in Ifo LGA, Ogun State.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| Questionnaire 1|| |
Ocular Surface Disesase Index.
Add subtotals A, B, and C to obtain D
D = Sum of scores for all questions answered divided by the
Total number of questions answered (Do not include questions answered N/A) E
OSDI score is D/E
This score is then read on the OSDI score scale to determine the grading of dry eye as either Normal, mild, moderate, or severe.
| References|| |
Asbell PA. Increasing importance of dry eye syndrome and the ideal artificial tear: Consensus views from a roundtable discussion. Curr Med Res Opin 2006;22:2149-57.
Ong BL. Relation between contact lens wear and Meibomian gland dysfunction. Optom Vis Sci 1996;73:208-10.
Schaumberg DA, Sullivan DA, Buring JE, Dana MR. Prevalence of dry eye syndrome among US women. Am J Ophthalmol 2003;136:318-26.
Lee AJ, Lee J, Saw SM, Gazzard G, Koh D, Widjaja D, et al
. Prevalence and risk factors associated with dry eye symptoms: A population based study in Indonesia. Br J Ophthalmol 2002;86:1347-51.
Williams K, Watsky M. Gap junctional communication in the human corneal endothelium and epithelium. Curr Eye Res 2002;25:29-36.
Doughty MJ, Fonn D, Richter D, Simpson T, Caffery B, Gordon K. A patient questionnaire approach to estimating the prevalence of dry eye symptoms in patients presenting to optometric practices across Canada. Optom Vis Sci 1997;74:624-31.
Lin PY, Tsai SY, Cheng CY, Liu JH, Chou P, Hsu WM. Prevalence of dry eye among an elderly Chinese population in Taiwan: The Shihpai Eye Study. Ophthalmology 2003;110:1096-101.
Moss SE, Klein R, Klein BE. Prevalence of and risk factors for dry eye syndrome. Arch Ophthalmol 2000;118:1264-8.
Schaumberg DA, Sullivan DA, Dana MR. Epidemiology of dry eye syndrome. Adv Exp Biol Med 2002;506:989-98.
Novaes P, Saldiva PH, Matsuda M, Macchione M, Rangel MP, Kara-José N, et al
. The effects of chronic exposure to traffic derived air pollution on the ocular surface. Environ Res 2010;110:372-4.
Schiffman RM, Christianson MD, Jacobsen G, Hirsch JD, Reis BL. Reliability and validity of the Ocular Surface Disease Index. Arch Ophthalmol 2000;118:615-21.
Araoye MO. Research Methodology with Statistics for Health and Social Sciences. Ilorin, Nigeria: Nathadex Publishers; 2003, p. 128.
Walt JG, Rowe MM, Stern KL. Evaluating the functional impact of dry eye: The Ocular Surface Disesase Index. Drug Inf J 1997;311-436.
Brujic M. Ocular surface strategies are a must for treating patients with glaucoma. Ophthalmology Times Europe.2011; 7.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]