Optic and Auditory Nerve Dysfunction in Glaucoma Patients with Tobacco and Neurotoxin Exposure: A Hidden Barrier to Cataract Surgery Outcomes

Cataract surgery usually restores vision very successfully, but the results are often less impressive in people who also live with glaucoma. While glaucoma itself damages the optic nerve, other hidden factors may be quietly shaping how much vision a patient actually regains after surgery. One of these important but often overlooked factors is exposure to tobacco and other neurotoxins. Smoking and chewing tobacco are known to put additional stress on the optic nerve. Studies have shown that smokers with glaucoma lose optic nerve vessel density faster than non-smokers, and this is linked to further thinning of the retinal nerve fiber layer¹˒². Beyond the eyes, tobacco also harms the ears: people who smoke are more likely to develop sensorineural hearing loss, and even second-hand smoke can affect the delicate structures of the inner ear³. Systemic toxins such as methanol are another major concern. Methanol poisoning leads to accumulation of toxic metabolites like formic acid, which can severely damage the retina and optic nerve, sometimes leaving patients with permanent vision loss⁴. Even smokeless forms of tobacco are not safe—there are reports of young people developing toxic optic neuropathy from gutka and other chewing products, often presenting with central scotomas and optic disc swelling⁵. When these toxic exposures combine with pre-existing glaucoma, the potential for visual recovery after cataract surgery may be limited. On top of that, hidden hearing loss can affect quality of life and the ability to adapt after surgery. For these reasons, it becomes essential to look beyond just the eye and consider broader neuro-sensory health when planning cataract surgery in glaucoma patients.

AIM AND OBJECTIVES

AIM
To evaluate optic and auditory nerve dysfunction in glaucoma patients with exposure to tobacco and systemic neurotoxins, and its impact on visual rehabilitation following cataract surgery.

OBJECTIVES

• To study the pattern of optic nerve changes (RNFL thinning, visual field defects) in exposed vs. non-exposed glaucoma patients.
• To assess the prevalence and severity of auditory dysfunction in the study groups.
• To analyse the relationship between exposure duration and severity of optic/auditory deficits.
• To identify the role of these factors in predicting post-cataract surgery outcomes.

MATERIALS AND METHODS

Study Design and Setting

This was a hospital-based, cross-sectional observational study conducted in the Department of Ophthalmology, Rajshree Medical and Research Institute, Bareilly (U.P., India).

Study Population

A total of 100 patients diagnosed with chronic glaucoma (duration ≥1 year) and scheduled for cataract extraction were enrolled in the study. All participants provided informed consent prior to inclusion.

Inclusion Criteria

Patients aged ≥40 years with a clinical diagnosis of glaucoma for at least one year. Presence of visually significant cataract requiring surgery. Willingness to undergo ocular, auditory, and biochemical evaluation.

Exclusion Criteria

Patients with pre-existing middle ear pathology, history of ear surgery, or chronic otitis media.

History of systemic or neurological conditions affecting the optic or auditory nerve (e.g., multiple sclerosis, uncontrolled diabetes, stroke). Patients already on long-term vitamin B12 supplementation. Unwillingness to participate in the study.

Grouping of Patients

Patients were divided into five groups based on their exposure history:

• Group A: Tobacco chewers
• Group B: Smokers
• Group C: Mixed users (both smoking and chewing)
• Group D: Other systemic neurotoxin exposure (e.g., methanol, industrial toxins)
• Group E: Controls (non-users)

Clinical Assessment

Ocular Evaluation

Best Corrected Visual Acuity (BCVA): Measured using Snellen’s chart and converted to logMAR values for analysis.

Visual Field Testing: Humphrey Visual Field Analyzer (HVF) 10-2 program was used to assess central and paracentral field defects.

Optical Coherence Tomography (OCT): Retinal Nerve Fiber Layer (RNFL) thickness was measured, with emphasis on temporal quadrant thinning.

Auditory Evaluation

Pure Tone Audiometry (PTA): Performed in a soundproof room to record air- and bone-conduction thresholds across 0.5–8 kHz frequencies.

Tuning Fork Tests: Rinne, Weber, and Absolute Bone Conduction (ABC) tests were performed to qualitatively confirm PTA findings.

Biochemical Investigations

Serum Vitamin B12 levels were measured to rule out nutritional optic neuropathy. Mean Corpuscular Volume (MCV) was derived from complete blood count to evaluate macrocytosis as an indirect marker of B12 deficiency or chronic toxin exposure.

Data Collection and Analysis

All data were recorded in a structured proforma. Continuous variables (e.g., RNFL thickness, hearing thresholds, serum B12 levels) were expressed as mean ± standard deviation and compared across groups using one-way ANOVA. Categorical variables (e.g., presence of centrocecal scotomas, SNHL grades) were analysed using Chi-square test. Pearson’s correlation test was applied to determine the relationship between duration of exposure and severity of optic/auditory dysfunction.

A p value <0.05 was considered statistically significant.

Statistical analysis was performed using SPSS (version 29).

RESULTS

Demographic Details and Baseline Clinical Characteristics

A total of 100 chronic glaucoma patients scheduled for cataract surgery were enrolled: Group A (tobacco chewers, n=20), Group B (smokers, n=20), Group C (mixed users, n=20), Group D (other neurotoxin exposure, n=20), and Group E (controls, n=20). The mean age was 58.4 ± 9.2 years, with a male predominance (62%). There were no significant differences in age, sex distribution, or glaucoma duration across groups (p>0.05). Baseline BCVA was comparable among groups (Table 1).

Table 1. Demographic and Baseline Clinical Characteristics

Optic Nerve Assessment

RNFL Thickness

Temporal RNFL thinning was most pronounced in Groups C and D, while controls exhibited minimal changes. Superior, nasal, and inferior quadrants showed no statistically significant differences. Duration of toxic exposure negatively correlated with temporal RNFL thickness (r = -0.52, p<0.01) (Table 2).

Table 2. RNFL Thickness by Quadrant (µm)

Visual Field Defects

Centrocecal scotomas were most frequent in Groups C (60%) and D (55%), while Groups A and B had lower prevalence (25–30%), and only 5% of controls showed such defects. Paracentral scotomas were similarly more common in exposed groups (Table 3).

Table 3. Visual Field Defects (HVF 10-2)

AUDITORY ASSESSMENT

Pure Tone Audiometry

Mild-to-moderate SNHL was most prevalent in Groups C (50%) and D (45%). High-frequency thresholds (4–8 kHz) were significantly higher in these groups compared to controls (Table 4).

Table 4. Mean Hearing Thresholds (dB HL) at Key Frequencies