Hypothyroidism and primary open-angle glaucoma (POAG) represent major public health problems due to their substantial global prevalence and long-term morbidity [1]. Overt hypothyroidism affects approximately 0.3–0.4% of the general population, while subclinical hypothyroidism is observed in nearly 4–10% of individuals [1]. The burden of hypothyroidism is disproportionately higher in iodine-deficient regions and is more commonly reported among women and the elderly population [1]. In the Indian context, the prevalence of hypothyroidism has been reported to range from 3.9% to 11%, with variability attributable to differences in study populations and diagnostic criteria employed [2,3]. Primary open-angle glaucoma, the most prevalent form of glaucoma, affects nearly 3% of the global population aged above 40 years [4,5]. In India, POAG accounts for approximately 4.0% of visual impairment and 5.5% of blindness among individuals older than 50 years, underscoring its significant contribution to the national burden of visual morbidity [6]. Both hypothyroidism and primary open-angle glaucoma (POAG) exert substantial but distinct adverse effects on patients’ quality of life. Chronic, untreated hypothyroidism may result in serious systemic complications, including cardiovascular disease, myxedema coma, and infertility, thereby contributing to significant morbidity [7,8]. POAG, in contrast, predominantly compromises quality of life through its characteristic insidious and progressive visual loss. The gradual deterioration of peripheral vision, with eventual involvement of central vision, can significantly impair daily activities such as reading, driving, and facial recognition [9,10]. In addition to visual disability, the psychological consequences of POAG—including fear of blindness, anxiety, and depression—further intensify the overall disease burden. Primary open-angle glaucoma is the most common subtype of glaucoma and is typically characterized by an open anterior chamber angle accompanied by elevated intraocular pressure (IOP) [11]. The underlying pathophysiology of POAG is multifactorial, involving a complex interaction between mechanical and vascular mechanisms. Elevated IOP remains a key risk factor and arises primarily from impaired aqueous humor outflow through the trabecular meshwork and Schlemm’s canal [12]. The coexistence of hypothyroidism and primary open-angle glaucoma (POAG) may present additional diagnostic and therapeutic challenges. The association between hypothyroidism and POAG has been debated for several decades, with existing literature yielding inconsistent findings. While certain studies have reported a possible link between the two conditions, others have not demonstrated a clear or independent association. These divergent results underscore the need for further investigation to determine whether hypothyroidism constitutes an independent risk factor for the development of POAG. Furthermore, the majority of available studies have been conducted in Western populations, resulting in a paucity of data from other ethnic and geographical settings, including India. This lack of uniform evidence and region-specific data represents a significant gap in understanding the potential role of hypothyroidism in the pathogenesis of POAG. India bears a substantial share of the global burden of both hypothyroidism and POAG. Hypothyroidism affects approximately 11% of the Indian population, particularly among older adults, and is recognized as one of the most prevalent endocrine disorders in the country [2]. Concurrently, POAG remains a leading cause of irreversible blindness, contributing significantly to visual morbidity nationwide. Establishing a definitive association between hypothyroidism and POAG could have meaningful clinical implications for the management of both conditions. Early identification of POAG among patients with hypothyroidism may facilitate timely intervention, potentially slowing or preventing the progression of glaucomatous optic neuropathy and reducing the burden of blindness. Additionally, elucidating this relationship could support the development of more individualized management strategies. With this frame of mind we aimed to evaluate ophthalmologic findings in patients with hypothyroidism and determine the hospital-based prevalence of primary open-angle glaucoma (POAG) among them.

This was a single-centre, hospital-based, cross-sectional observational study conducted in the Department of Ophthalmology at Maharishi Markandeshwar Medical College and Hospital, Kumarhatti, Solan, over a period of 18 months, following approval from the Institutional Ethics Committee. Adult patients aged ≥40 years with biochemically confirmed hypothyroidism (elevated TSH >4.20 µIU/mL with normal or low T3/T4 levels) attending the ophthalmology outpatient department were included after obtaining written informed consent. Patients with a history of glaucoma, intraocular surgery, ocular trauma, pseudoexfoliation syndrome, high myopia, dense cataract precluding fundus examination, systemic comorbidities (diabetes, hypertension, cardiovascular disease), corticosteroid or thyroid medication use, and pregnant women were excluded. The minimum sample size was calculated as 80, based on an assumed POAG prevalence of 4.6%, a confidence level of 96.7%, and a margin of error of 5%. Participants were recruited using convenience sampling. All participants underwent a comprehensive ophthalmologic evaluation, including best-corrected visual acuity assessment, intraocular pressure measurement using non-contact tonometry, gonioscopy with a three-mirror lens, slit-lamp biomicroscopic fundus examination using a +90D lens, and standard automated perimetry (Humphrey Field Analyzer, 30–2 SITA standard). Visual fields were interpreted using the modified Hodapp–Anderson–Parrish criteria. POAG was diagnosed based on characteristic optic disc changes with corresponding visual field defects in the presence of an open anterior chamber angle. Data were entered into Microsoft Excel and analyzed using Stata version 17.0. Descriptive statistics were used to summarize demographic and clinical variables, and appropriate inferential tests were applied to assess associations. The study received no external funding, and the authors declare no conflicts of interest.

A total of 80 hypothyroid patients aged 40 years and above were included in the study. Among these, 9 patients (11.25%) were diagnosed with Primary Open-Angle Glaucoma (POAG), while the remaining 71 (88.75%) had normal intraocular pressure and no signs of glaucoma. Table 1 presents the distribution of participants based on gender, age group, BMI category, and family history. The majority of participants were female in both groups—70.4% in the normal IOP group and 88.9% among POAG patients. Most POAG cases (44.4%) were in the 51–60 year age group. The mean age was 58.4 ± 8.74 years in the normal group and 55.7 ± 9.15 years in the POAG group. No POAG cases were found in participants with normal BMI. Most POAG patients were overweight (55.6%) or obese (44.4%). None of the POAG patients had a family history of thyroid disorders, but a positive family history of glaucoma was present in 77.8% of POAG cases compared to 23.9% in the normal group. Table 1: Characteristics of Participants Subjects with normal IOP (n=71) Subjects with POAG (n=9) n % n % Gender Female 50 70.4 8 88.9 Male 21 29.6 1 11.1 Age Group 41-50 16 22.5 3 33.3 51-60 24 33.8 4 44.4 61-70 25 35.2 1 11.1 71-80 6 8.45 1 11.1 Mean, SD 58.4 8.74 55.7 9.15 BMI Category Normal 10 14.1 0 0 Overweight 36 50.7 5 55.6 Obese 25 35.2 4 44.4 Family History of Thyroid Disorders No 57 80.3 9 100 Yes 14 19.7 0 0 Family History of Glaucoma No 54 76.1 2 22.2 Yes 17 23.9 7 77.8 Table 2 shows the hospital-based prevalence of POAG among hypothyroid patients. Out of 80 participants, 9 were diagnosed with POAG, yielding a prevalence of 11.25% (95% CI: 5.3% – 20.3%). Table 2: Prevalence of POAG among participants (n=80) Primary Open-Angle Glaucoma (POAG) Freq. Percent No 71 88.75 Yes 9 11.25 Total 80 100.00 Table 3 presents data on visual field changes. Visual field defects were significantly more common in POAG patients. In the right eye, 77.8% of POAG patients had a defect compared to 7.04% in the normal group (p < 0.001). In the left eye, 66.7% of POAG patients had a defect compared to 8.45% in the normal group (p < 0.001). All POAG patients (100%) had some form of visual field damage, while none was found in the non-POAG group. Similarly, optic nerve damage was present in 77.8% of POAG patients and absent in all others. These findings were statistically significant (p < 0.001). Table 3: Distribution of Participants based on Visual Field Changes Subjects with normal IOP (n=71) Subjects with POAG (n=9) P-value n % n % Visual Field Defect (Right Eye) No 66 93 2 22.2 < 0.001 Yes 5 7.04 7 77.8 Visual Field Defect (Left Eye) No 65 91.5 3 33.3 < 0.001 Yes 6 8.45 6 66.7 Visual Field Damage No 71 100 0 0 < 0.001 Yes 0 0 9 100 Optic Nerve Damage No 71 100 2 22.2 < 0.001 Yes 0 0 7 77.8 Table 4 compares thyroid hormone levels between the two groups. POAG patients had significantly higher mean TSH levels (14.4 ± 2.87 µIU/mL) than those without POAG (10.5 ± 3.71 µIU/mL), with a p-value of 0.0036. T3 levels were significantly lower in POAG patients (71.4 ± 31 ng/dL) compared to the normal group (88.1 ± 29.6 ng/dL), with a p-value of 0.0116. There was no significant difference in T4 levels between the two groups (p = 0.7881). Table 4: Distribution of Participants based on Thyroid Hormone Level Subjects with normal IOP (n=71) Subjects with POAG (n=9) P-value n % n % TSH Level (micro-IU/mL) 10.5 3.71 14.4 2.87 0.0036 T3 Level 88.1 29.6 71.4 31 0.0116 T4 Level 5.87 1.24 5.74 1.49 0.7881

In the present study, the prevalence of primary open-angle glaucoma (POAG) among patients with hypothyroidism was observed to be 11.25%. Previous investigations exploring the association between hypothyroidism and POAG have reported heterogeneous findings. The results of this study are consistent with those reported by Smith et al. (1993), who demonstrated a significantly higher prevalence of hypothyroidism among POAG patients (23.4%) compared to controls (4.7%) [5]. Similarly, Unnikrishnan et al. (2024) reported that subclinical hypothyroidism was present in 20.6% of POAG patients, compared to 4.8% in the control group (P < 0.01), with an odds ratio of 5.2 (95% CI: 1.7–22), suggesting a strong association between thyroid dysfunction and glaucoma development [13]. A meta-analysis by Wang et al. (2017) further corroborated this relationship, reporting a significantly increased risk of POAG among individuals with hypothyroidism (OR = 1.64, 95% CI: 1.27–2.13) [1]. This meta-analysis synthesized data from multiple observational studies and demonstrated a statistically significant association between hypothyroidism and POAG. In addition, Cross et al. (2008), in a large population-based study, found a higher prevalence of glaucoma among individuals with thyroid disorders (6.5%) compared to those without thyroid disease (4.4%; P = 0.0003) [10]. Importantly, this association remained significant after adjusting for confounding variables such as age, sex, race, and smoking status (OR = 1.38, 95% CI: 1.08–1.76), indicating that thyroid disorders may independently contribute to glaucoma risk [10]. However, not all studies have demonstrated a consistent association. Thvilum et al. (2018), in a nationwide cohort study, reported a slightly higher prevalence of glaucoma among hypothyroid individuals prior to diagnosis (4.6% vs. 4.3%; P < 0.001), but found no increased risk of glaucoma following the diagnosis and treatment of hypothyroidism [14]. Their Cox regression analysis revealed a hazard ratio of 1.00 (95% CI: 0.96–1.06), which further decreased after adjusting for comorbidities (HR = 0.88, 95% CI: 0.84–0.93). Similarly, Munoz-Negrete et al. (2000) and Gillow et al. (1997) found no significant association between POAG and hypothyroidism. Munoz-Negrete et al. reported hypothyroidism in only 2.67% of POAG patients and 4% of controls, leading to the conclusion that routine thyroid screening in POAG patients was not warranted [15]. Gillow et al. also reported a low prevalence of hypothyroidism among POAG patients (4%, 95% CI: 1.1–9.4%), with no significant difference compared to population-based controls [16]. The variability in prevalence estimates across studies may be explained by differences in study design, sample size, geographic and ethnic characteristics, and diagnostic criteria for both hypothyroidism and POAG. The findings of the present study align more closely with case-control studies and meta-analyses suggesting a positive association, rather than large population-based cohort studies that have failed to establish a definitive link. These findings suggest a potential role for routine ophthalmologic screening for POAG among patients with hypothyroidism, particularly those at higher risk. Nonetheless, large-scale prospective longitudinal studies with standardized diagnostic criteria are required to establish causality and to clarify the contribution of thyroid dysfunction to the pathophysiology of glaucoma. Thyroid Hormone Levels (TSH, T3, T4) The present study demonstrated a significant association between thyroid hormone levels and POAG among hypothyroid patients. Mean TSH levels were significantly higher in patients with POAG (14.4 ± 2.87 µIU/mL) compared to those without POAG (10.5 ± 3.71 µIU/mL; P = 0.0036). Additionally, mean T3 levels were significantly lower in the POAG group (71.4 ± 31.0 ng/dL) compared to the non-POAG group (88.1 ± 29.6 ng/dL; P = 0.0116), while T4 levels did not differ significantly between the two groups (P = 0.7881). These findings indicate that elevated TSH and reduced T3 levels may be associated with an increased risk of POAG in hypothyroid individuals. These observations are supported by Unnikrishnan et al. (2024), who reported significantly higher TSH levels and a greater prevalence of subclinical hypothyroidism among POAG patients [13]. Similarly, the meta-analysis by Wang et al. (2017) demonstrated an increased risk of POAG among individuals with hypothyroidism (OR = 1.64, 95% CI: 1.27–2.13), reinforcing the link between thyroid dysfunction and glaucoma risk [1]. Ulas et al. (2015) examined ocular parameters in hypothyroid patients and found significantly higher intraocular pressure and increased choroidal thickness compared to healthy controls (P = 0.021 and P = 0.013, respectively) [17]. They also observed that patients with overt hypothyroidism, characterized by elevated TSH levels, exhibited greater susceptibility to glaucoma-like changes. Babic Leko et al. (2022) further demonstrated that TSH levels negatively correlated with corneal thickness, while T4 levels were inversely associated with intraocular lens power, suggesting that abnormal thyroid hormone levels may contribute to structural ocular changes relevant to glaucoma development [18]. These findings are consistent with the present study, which demonstrated significantly lower T3 levels among POAG patients. Conversely, Thvilum et al. (2018) found no causal relationship between hypothyroidism and glaucoma, suggesting that thyroid dysfunction alone may not directly cause POAG but may contribute indirectly through mechanisms such as vascular dysregulation or metabolic alterations [14]. Overall, the findings of the present study support the hypothesis that abnormal thyroid hormone levels—particularly elevated TSH and reduced T3—may contribute to the pathogenesis of POAG by influencing intraocular pressure regulation, optic nerve health, and ocular vascular function. These results underscore the importance of monitoring thyroid function in patients with glaucoma, especially those with known hypothyroidism. Future research should focus on longitudinal studies assessing whether early thyroid hormone optimization can modify POAG risk or progression, as well as molecular and genetic studies exploring the interaction between thyroid hormones and glaucomatous neurodegeneration. Family History In the present study, none of the POAG patients reported a family history of thyroid disorders, whereas 19.7% of non-POAG participants had a positive family history of thyroid dysfunction. This difference was not statistically significant (P = 0.142), suggesting that hereditary thyroid disease may not be a direct risk factor for POAG among hypothyroid patients. This finding contrasts with Smith et al. (1993), who reported a higher prevalence of hypothyroidism among POAG patients, with a notable proportion having a positive family history of thyroid disease [5]. Wang et al. (2017), in their meta-analysis, also reported that individuals with a first-degree relative diagnosed with hypothyroidism had a higher likelihood of developing POAG (OR = 1.64, 95% CI: 1.27–2.13), with a stronger association observed in overt hypothyroidism [1]. In contrast, a strong association was observed between POAG and family history of glaucoma. In the present study, 77.8% of POAG patients reported a positive family history of glaucoma, compared to 23.9% among participants with normal intraocular pressure, and this difference was statistically significant (P = 0.001). These findings reinforce the well-established genetic predisposition to POAG and highlight family history as a major risk factor. The present results are consistent with Cross et al. (2008), who reported a significantly higher prevalence of glaucoma among individuals with a family history of the disease (6.5%) compared to those without (4.4%; P = 0.0003) [10]. Similarly, Wang et al. (2017) demonstrated that individuals with a first-degree relative affected by glaucoma had a significantly increased risk of POAG (OR = 2.14, 95% CI: 1.72–2.67) [1]. These findings emphasize the need for regular ophthalmologic screening in individuals with a family history of glaucoma, particularly when coexisting thyroid dysfunction is present. Future studies should explore genetic variants common to both glaucoma and thyroid disorders and evaluate whether early thyroid management can modify glaucoma risk in genetically susceptible individuals.

This study demonstrated a notable prevalence of primary open-angle glaucoma (11.25%) among patients with hypothyroidism. Elevated TSH levels and reduced T3 levels were significantly associated with the presence of POAG, suggesting a potential link between thyroid dysfunction and glaucomatous changes. Most POAG cases occurred in overweight or obese females and in individuals with a positive family history of glaucoma. These findings support the need for routine ophthalmologic screening in hypothyroid patients, particularly those with additional risk factors. Early detection and timely management may help prevent irreversible visual loss and improve clinical outcomes. Further large-scale studies are warranted to clarify the causal relationship between hypothyroidism and POAG.

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