The impact of smoking on age-related macular degeneration among tea garden workers of Southern Assam

INTRODUCTION

Age-related macular degeneration (AMD) is a chronic, progressive retinal disease and a leading cause of irreversible vision loss and blindness among the elderly population worldwide.^[1] The pathogenesis of AMD is multifactorial, involving genetics, age, and environmental and lifestyle risk factors.^[2] Among these, tobacco smoking remains the most consistently documented and potent modifiable factor, with studies demonstrating a two- to four-fold increased risk of AMD among smokers.^[3,4]

The global burden of AMD is substantial and rising, particularly in developing nations like India.^[5] Certain Indian populations face a disproportionately higher risk due to socioeconomic disadvantage, occupational hazards, and poor healthcare access. Tea garden workers of Assam represent one such vulnerable group.^[6,7]

The rationale for selecting this cohort lies in their unique combination of occupational exposure, nutritional deprivation, and exceptionally high prevalence of tobacco use. The physically demanding labor, chronic sunlight exposure, and low intake of antioxidant-rich foods make this group especially prone to oxidative retinal damage. Furthermore, undernourishment and malnutrition, common among tea garden workers, may act synergistically with smoking to accelerate the disease process. This study was prompted by the need to evaluate these interlinked factors in this distinct socio-occupational cohort within Assam.

A prominent feature of this community is the high prevalence of tobacco use, particularly hand-rolled filterless cigarettes (“beedis”), which are often more harmful than conventional cigarettes.^[8,9] Initiation occurs early and persists lifelong, driven by social and occupational factors.^[10] Despite this high exposure, awareness of the smoking-AMD link remains low.

While the smoking-AMD relationship is well-established in Western populations,^[3,4] there is limited data from socio-occupational cohorts in India, especially quantifying exposure in pack-years. Hence, this study aims to assess the impact of smoking on AMD prevalence, severity, and visual outcomes among tea garden workers in Southern Assam.

MATERIAL AND METHODS

This was a cross-sectional, analytical study conducted in the tea garden estates of Southern Assam. The study protocol was reviewed and approved by the Institutional Ethics Committee (Reference No: SMC/ETHICS/M4/2024/21). The study was conducted in accordance with the tenets of the Declaration of Helsinki. Written informed consent was obtained from every participant after explaining the nature and possible consequences of the study in their local language. For illiterate participants, the consent form was read aloud in the presence of an impartial witness, and a thumb impression was obtained.

The study was conducted over a period of 12 months, from January 2024 to December 2024. The study area comprised five major tea estates of Southern Assam, which were selected through a random sampling method from a list of all registered estates in the region.

The study population consisted of permanent tea garden laborers aged 50 years and above. The sample size was calculated using the formula for comparing two proportions. Assuming a prevalence of AMD of 30% among smokers and 15% among non-smokers^[11,12] with a power of 80% and a significance level (α) of 0.05, the minimum required sample size was 364. After accounting for a 10% non-response rate, the final sample size was 400.

A stratified random sampling technique was employed. The strata were formed based on the tea estate (to ensure proportional representation) and gender. Within each estate, a complete list of eligible workers was obtained from the estate management. Participants were then selected from these lists using a computer-generated random number sequence.

Participants were included if they were aged 50 years or older, had been a resident of the tea estate for a minimum of 10 years, and provided informed consent. Participants were excluded if they had hazy media (e.g., significant corneal opacity, mature cataract, or vitreous hemorrhage) that precluded adequate fundus visualization, a history of retinal surgery, high myopia (spherical equivalent ≥−6.0 diopters), or known genetic macular disorders (e.g., Stargardt’s disease).

RESULTS

A total of 400 tea garden laborers participated in the study. The mean age of the participants was 59.7 years (±6.3 SD), with an age range of 50-82 years. The cohort comprised 184 (46%) males and 216 (54%) females [Figure 1].

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Figure 1:

Gender distribution.

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Regarding smoking history, 168 participants (42%) were identified as current smokers and 70 (17.5%) were former smokers [Figure 2], making a total of 238 (59.5%) participants with a history of smoking. The majority of smokers (89.1%) consumed beedis exclusively. The mean pack-year history among ever-smokers was 24.7 ± 11.2. Among former smokers, the mean duration of smoking before cessation was 21.3 ± 9.8 years, and the average time since quitting was 6.2 ± 3.4 years.

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Figure 2:

Smoking status distribution.

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The overall prevalence of AMD in the study population was 41% (n = 164) [Figure 3]. Early AMD was diagnosed in 106 participants, accounting for 26.5% of the total sample and 64.6% of all AMD cases. Late AMD was present in 58 participants (14.5% of total; 35.4% of AMD cases). Among those with late AMD, 36 (62.1%) had neovascular AMD and 22 (37.9%) had GA. Figure 4 shows representative OCT images of dry and wet AMD.

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Figure 3:

Prevalence of age-related macular degeneration (AMD).

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Figure 4:

(a) Fundus photo and OCT (optical coherence tomography) macula images of dry age-related macular degeneration (AMD), (b) Fundus photo and OCT macula images of wet AMD.

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A highly significant association was observed between smoking status and AMD prevalence [Figure 5]. Among the 238 ever-smokers, 139 were diagnosed with AMD (58.4%). In stark contrast, only 25 of the 162 non-smokers (15.4%) had AMD (χ² = 72.4, P < 0.001). The prevalence of both early and late AMD was significantly higher in smokers compared to non-smokers (P < 0.001 for both). Furthermore, a dose-response relationship was evident. Participants with a higher cumulative smoking exposure (≥20 pack-years) had a markedly higher prevalence of late AMD compared to those with lower pack-year exposure (<20 pack-years) and non-smokers.

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Figure 5:

Correlation between smoking and age-related macular degeneration (AMD).

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Multivariate logistic regression analysis was performed to adjust for potential confounders, including age, gender, hypertension, and diabetes. The model confirmed that smoking was the strongest independent risk factor for AMD. As detailed in Table 1, smoking with an exposure of ≥20 pack-years was associated with a nearly four-fold increased odds of developing late AMD (OR = 3.92; 95% CI: 2.10-7.33; P < 0.001). Age >60 years was also a significant independent risk factor (OR = 1.67; 95% CI: 1.14-2.45; P = 0.002). Hypertension showed a modest but statistically significant association with AMD risk (OR = 1.43; 95% CI: 1.03-2.83; P = 0.03). Gender and diabetes were not found to be significant independent risk factors in this model.

A statistically significant correlation was noted between BCVA and AMD severity. Participants with early AMD had mild visual impairment, while those with late AMD showed a marked reduction in vision. The mean BCVA for eyes with no AMD was approximately 6/9, for early AMD, it was 6/12, and for late AMD, it declined to 6/36 or worse (P < 0.001).

DISCUSSION

This study provides compelling evidence of a strong and independent association between smoking and AMD among tea garden workers in Southern Assam, a population characterized by high tobacco consumption and significant health disparities. The key finding is that a cumulative smoking exposure of ≥20 pack-years increases the odds of developing late AMD nearly fourfold, even after adjusting for age and other comorbidities.

The overall AMD prevalence of 41% in our cohort is notably higher than the reported rates in many general population studies from India and other parts of the world,^[5,15] but aligns with studies focusing on high-risk groups with significant smoking exposure.^[16] This elevated prevalence underscores the extreme vulnerability of this population. It is likely attributable to the synergistic effect of high rates of smoking, prolonged outdoor occupational exposure to sunlight (a potential risk factor),^[17] and possible nutritional deficiencies - a common concern in economically disadvantaged communities.^[18]

The decision to conduct this study among tea garden workers was prompted by their unique combination of occupational, lifestyle, and nutritional risk factors. Tea garden laborers represent a distinct socio-occupational cohort within Assam, often suffering from chronic undernourishment and limited access to healthcare. Such nutritional deficiencies - especially reduced intake of antioxidant-rich fruits, vegetables, and fish - may accentuate oxidative retinal injury induced by smoking. Hence, undernutrition combined with chronic tobacco exposure may accelerate the disease process in this group.

The dose-response relationship between pack-years of smoking and AMD risk observed in our study is a critical finding. It reinforces the causal nature of the association, consistent with the established biological plausibility. The toxins in tobacco smoke are known to induce oxidative stress, promote inflammation, compromise the choroidal circulation, and directly damage RPE cells - all key pathways in AMD pathogenesis.^[19,20] The predominance of beedi smoking in our population is of particular concern, as beedis may deliver higher concentrations of harmful toxins such as nicotine, carbon monoxide, and tar, compared to conventional cigarettes.^[9,21]

While smoking was the dominant risk factor, our analysis also confirmed the role of advancing age, which is the strongest non-modifiable risk factor for AMD due to cumulative oxidative damage and physiological changes in the retina.^[1] The association with hypertension, though modest, is supported by some studies suggesting that vascular factors may contribute to AMD development and progression by affecting choroidal blood flow.^[22]

A noteworthy observation was the high prevalence of AMD among females, a majority of whom were non-smokers. This can likely be explained by exposure to passive smoking and indoor air pollution from biomass fuel used for cooking, which has been implicated as a risk factor for AMD in other studies involving women in South Asia.^[23] This highlights an important environmental risk factor beyond active smoking.

Visual acuity correlation with AMD type revealed a clear functional decline in vision as disease severity increased [Table 2]. Early AMD cases showed mild visual impairment, whereas late AMD was associated with severe visual loss. This reinforces the importance of early identification and intervention before irreversible macular damage occurs.

The strengths of our study include its community-based design, use of stratified random sampling to enhance representativeness, detailed quantification of smoking exposure, adherence to standardized AREDS classification for AMD grading, and the use of OCT for accurate diagnosis. However, certain limitations must be acknowledged. The cross-sectional design allows for the establishment of association but not causality. Recall bias in reporting smoking history, especially among older participants, is possible. We did not adjust for dietary factors such as intake of antioxidants or genetic predispositions (e.g., Complement factor H (CFH), age-related maculopathy susceptibility 2 (ARMS2) genes), which are known to influence AMD risk.^[24] We did not adjust for other possible confounders, such as alcohol use or occupational ultraviolet exposure, quantitatively. Future longitudinal and interventional studies incorporating nutritional assessment, genetic profiling, and follow-up data would help confirm and expand these findings.

CONCLUSION

This study unequivocally identifies heavy smoking (≥20 pack-years) as the most significant modifiable risk factor for AMD among tea garden workers in Southern Assam. The alarmingly high prevalence of AMD in this community signals a pressing public health concern.

These findings necessitate a multi-pronged approach:

• Targeted anti-smoking interventions: Intensive, culturally sensitive health education campaigns must be implemented within tea gardens to raise awareness about the ocular risks of smoking and to promote cessation.

• Nutritional and dietary reinforcement: Programs promoting a balanced diet rich in antioxidants, fruits, vegetables, and fish should be encouraged, as nutritional support may mitigate AMD risk.

• Enhanced access to eye care: Regular, community-based retinal screening programs are essential for early detection of AMD, enabling timely intervention to prevent blindness.

• Policy integration: National eye health programs and non-communicable disease initiatives must specifically include and address the needs of high-risk, marginalized populations like tea garden workers.

Addressing AMD in this vulnerable group requires combined efforts from ophthalmologists, public health authorities, and community organizations to implement smoking cessation, dietary modification, and regular retinal health monitoring as part of comprehensive preventive care.