European Journal of Cardiovascular Medicine

Diabetes mellitus is characterized by hyperglycemia, which is usually due to defects in insulin secretion or insulin action [1]. This chronic condition affects millions of people globally and has significant systemic and ocular implications. One of the lesser-known yet impactful complications is its association with increased intraocular pressure (IOP) and the consequent risk of glaucoma. It is also considered to be one of the risk factors for the development of open-angle glaucoma, a leading cause of irreversible blindness worldwide. Various studies have found that chronic hyperglycemia in diabetes is associated with raised intraocular pressure, hence suggesting a close relationship between diabetes and glaucoma [2,3]. Elevated IOP in diabetic patients can contribute to the onset and progression of glaucoma. Glaucoma is identified by raised intraocular pressure along with optic disc cupping and visual field impairment. If not detected and managed in the early stages, it can further lead to low vision, optic atrophy, and permanent loss of vision [4,5,6]. This makes early diagnosis and intervention critical in preventing vision loss among diabetic patients. India faces one of the greatest health challenges regarding diabetic patients and there are approximately over 35 million people with diabetes, which will increase to around 80 million by 2030 [7,8].

This alarming increase underscores the need for comprehensive studies and early interventions to mitigate the risks associated with diabetes. Diabetes mellitus is an important ocular risk factor that requires vigilant monitoring and management. Ophthalmological disorders associated with diabetes are also one of the major concerns of blindness in India and worldwide. These disorders commonly include cataracts, glaucoma, macular edema, retinal vascular changes, and diabetic retinopathy. Among these, diabetic retinopathy is one of the most severe complications, which can lead to significant vision impairment if not managed properly. Early diagnosis and management of these conditions are crucial to prevent the systemic associations as well as the severe ophthalmological conditions related to diabetes mellitus. This study aimed to compare intraocular pressure in diabetic and non-diabetic individuals to better understand the impact of Type 2 Diabetes Mellitus on ocular health. By exploring the relationship between diabetes and elevated IOP, the study seeks to provide insights that can inform more effective strategies for preventing and managing vision loss in diabetic patients. The primary objective was to examine the distribution of intraocular pressure and its association with Type 2 Diabetes Mellitus, contributing to improved clinical practices and patient outcomes.

This case-control, hospital-based study was conducted at the Department of Ophthalmology, Government Medical College and Hospital, Bettiah, Bihar, India. The study was designed to compare intraocular pressure (IOP) between individuals with Type 2 Diabetes Mellitus (T2DM) and non-diabetic individuals. Written informed consent was obtained from all participants, ensuring ethical compliance and voluntary participation. A total of 100 participants were enrolled, comprising 50 cases of T2DM and 50 age- and gender-matched non-diabetic controls. The age range for inclusion was 21 to 80 years, ensuring a broad representation of the adult population.

Inclusion Criteria:

1. Diabetic Group: Patients diagnosed with Type 2 Diabetes Mellitus, confirmed by blood sugar levels (fasting blood sugar [FBS], postprandial blood sugar [PPBS], and glycated hemoglobin [HbA1c]) as per the standard guidelines of the American Diabetic Association [9].
2. Non-Diabetic Group: Age- and gender-matched individuals with no history of diabetes or elevated blood sugar levels.
3. Age range: 21–80 years.
4. Willingness to provide informed consent and comply with the study protocol.

Exclusion Criteria:

1. History of glaucoma, ocular hypertension, or any other condition affecting intraocular pressure.
2. Presence of ocular infections, inflammation, or trauma.
3. History of ocular surgery, including cataract surgery, refractive surgery, or any other intraocular procedures.
4. Use of medications known to affect intraocular pressure, such as corticosteroids or antiglaucoma drugs.
5. Systemic conditions or medications that could influence IOP or blood sugar levels.
6. Inability to cooperate during ocular examinations.

Diagnostic Criteria for Type 2 Diabetes Mellitus:
The diagnosis of T2DM was confirmed using standard diagnostic criteria:

• Fasting blood sugar (FBS) ≥ 126 mg/dL.
• Postprandial blood sugar (PPBS) ≥ 200 mg/dL.
• Glycated hemoglobin (HbA1c) ≥ 6.5%.
  FBS and PPBS were measured at baseline and after one month, while HbA1c was measured only at baseline to assess long-term glycaemic control.

Ocular Examination Protocol:
All participants underwent a comprehensive ocular examination, which included the following:

1. Visual Acuity Assessment: Measured using a Snellen chart.
2. Color Vision Testing: Evaluated using Ishihara charts.
3. Slit-Lamp Examination: Conducted to assess the anterior segment of the eye.
4. Tonometry: Intraocular pressure (IOP) was measured using a Non-Contact Tonometer (NCT). Measurements were taken between 9:00 AM and 11:00 AM to minimize diurnal variations.
5. Dilated Fundus Examination: Performed using an indirect ophthalmoscope with a +20D lens to evaluate the optic disc, retina, and other posterior segment structures.

Data Collection and Analysis:
Detailed demographic and clinical data, including age, gender, duration of diabetes, and systemic comorbidities, were recorded. IOP measurements were compared between the diabetic and non-diabetic groups. Statistical analysis was performed to determine the significance of the observed differences and to assess the relationship between T2DM and intraocular pressure.

Statistical Analysis: The collected data was initially organized into a table using Microsoft Excel 2019. Subsequently, the data was transferred to GraphPad version 8.4.3 for further statistical analysis. Continuous variables were expressed as mean ± standard deviation (SD). Statistical analysis was performed using Student’s t-test. The correlation between HbA1c and intraocular pressure (IOP) was analyzed using Pearson’s correlation coefficient. A P-value of less than 0.05 was considered statistically significant.

Table 1 presents the age distribution and demographic characteristics of patients, comparing those with diabetes to those without. In the age group of 21-40 years, 8% of diabetics were represented, while 7% of non-diabetics fell into the same category. Among the 41-60 years age group, 23% of diabetics and 25% of non-diabetics were observed. For the 61-80 years age group, the distribution included 19% of diabetics and 18% of non-diabetics. The total number of patients in both groups was equal, with 50 patients (50%) in each category. The mean age for diabetics was 59.58 years (±6.86), compared to 58.78 years (±7.45) for non-diabetics.  In terms of gender distribution, males constituted 31% of the diabetic group, while 30% of the non-diabetic group were male. Conversely, females made up 19% of diabetics and 20% of non-diabetics. Overall, the age and gender distributions were relatively similar between the two groups.

Table 1: Showing the age distribution among patients of both groups.

Among males, the mean IOP for diabetics was 17.20 ± 1.80 mm Hg, significantly higher than that of non-diabetics, which was 14.04 ± 1.26 mm Hg (p < 0.0001). Similarly, among females, the mean IOP for diabetics was 18.16 ± 1.37 mm Hg, significantly higher than that of non-diabetics, which was 14.38 ± 1.59 mm Hg (p < 0.0001). Overall, the mean IOP for diabetics was 17.57 ± 1.67 mm Hg, compared to 14.17 ± 1.40 mm Hg in non-diabetics, with the difference being statistically significant (p < 0.0001) (Table 2). The findings indicate that individuals with Type II Diabetes Mellitus have significantly higher intraocular pressure compared to non-diabetic individuals, regardless of gender. This suggests that diabetes may be a contributing factor to elevated IOP, which is a known risk factor for conditions such as glaucoma.

Table 2: Showing the intraocular pressure (IOP) among patients of both groups.

Patients with diabetes for less than 1 year (n=12) had a mean IOP of 17.74 ± 1.66 mm Hg. Those with a diabetes duration of 1-5 years (n=19) had a lower mean IOP of 15.98 ± 2.34 mm Hg. However, patients with diabetes for more than 5 years (n=19) exhibited the highest mean IOP of 18.13 ± 1.54 mm Hg. The findings suggest that the duration of diabetes may influence intraocular pressure. Patients with diabetes for less than 1 year and those with diabetes for more than 5 years had higher IOP levels compared to those with a diabetes duration of 1-5 years. This could indicate that early and long-term diabetes may be associated with elevated IOP, potentially due to progressive changes in ocular structures or metabolic factors over time. The lower IOP in the 1-5 years group may reflect a transitional phase or better management during this period.

Table 3: Showing the distribution of intraocular pressure (IOP) among diabetic patients based on duration of diabetes

Table 4 shows that intraocular pressure (IOP) increases with higher HbA1c levels in both male and female diabetic patients. Males in the HbA1c <7%, 7-8%, and >8% groups had mean IOPs of 16.14 ± 1.78 mm Hg, 17.23 ± 2.76 mm Hg, and 18.65 ± 1.98 mm Hg, respectively. Females had slightly higher IOPs: 16.95 ± 2.86 mm Hg, 17.93 ± 2.34 mm Hg, and 18.96 ± 2.77 mm Hg in the same HbA1c categories. Poor glycaemic control (higher HbA1c) is associated with elevated IOP, indicating a potential risk for ocular complications like glaucoma. Maintaining optimal glycaemic control and regular IOP monitoring is crucial for diabetic patients to prevent such risks.

Table 4: Showing the distribution of intraocular pressure (IOP) among diabetic patients stratified by HbA1c levels and gender

Diabetes mellitus (DM) is a multifaceted metabolic disorder characterized by chronic hyperglycemia, which can lead to a wide array of systemic complications, including microvascular and macrovascular damage. Among the microvascular complications, ocular manifestations such as diabetic retinopathy and glaucoma are particularly concerning due to their potential to cause irreversible vision loss. Elevated intraocular pressure (IOP) is a critical risk factor for glaucoma, a condition that damages the optic nerve and can lead to blindness if left untreated. This study explored the impact of Type II Diabetes Mellitus on intraocular pressure (IOP) and compared it with non-diabetic individuals, while also investigating the influence of glycaemic control and diabetes duration on IOP. The results of this study demonstrate that diabetic patients have significantly higher IOP compared to non-diabetic individuals, irrespective of gender. The mean IOP in diabetic patients was 17.57 ± 1.67 mm Hg, compared to 14.17 ± 1.40 mm Hg in non-diabetics (p < 0.0001). This finding is consistent with previous studies that have reported a strong association between diabetes and elevated IOP, likely due to structural and functional changes in the eye induced by chronic hyperglycemia. For instance, diabetes can impair the autoregulation of blood flow in the retinal and optic nerve vessels, leading to increased IOP [10-14]. However, some studies have suggested that while diabetes is associated with higher IOP, it may not directly contribute to the development of glaucoma [15-18]. This discrepancy underscores the need for further research to elucidate the mechanisms linking diabetes, IOP, and glaucoma. The study also revealed that poor glycaemic control, as indicated by higher HbA1c levels, is associated with elevated IOP. Diabetic patients with HbA1c >8% had the highest mean IOP values (18.65 ± 1.98 mm Hg in males and 18.96 ± 2.77 mm Hg in females), while those with HbA1c <7% had lower IOP values (16.14 ± 1.78 mm Hg in males and 16.95 ± 2.86 mm Hg in females). This finding aligns with the study by Anandalakshmi et al. [1] and Khalaj et al. [4], who also reported a positive correlation between poor glycemic control and elevated IOP. However, some studies, such as those by Kawase et al. [16], Xu et al. [19], and Pimentel et al. [20], found no significant association between blood glucose levels and IOP. These contrasting results may be due to differences in study populations, methodologies, or the duration of diabetes. The duration of diabetes also appeared to influence IOP levels. Patients with diabetes for more than five years had the highest mean IOP (18.13 ± 1.54 mm Hg), while those with a diabetes duration of 1-5 years had lower IOP (15.98 ± 2.34 mm Hg). This suggests that long-standing diabetes may lead to progressive changes in ocular structures, such as increased rigidity of the trabecular meshwork or reduced aqueous humor outflow, resulting in elevated IOP. These findings are supported by Dielemans et al. [12], who reported that newly diagnosed diabetes and poor glycaemic control are associated with elevated IOP and high-tension glaucoma. The clinical significance of these findings lies in the potential implications for diabetic patient management. Elevated IOP is a modifiable risk factor for glaucoma, and early detection and intervention can prevent or delay the onset of vision loss. Regular monitoring of IOP in diabetic patients, particularly those with poor glycaemic control or long-standing diabetes, is essential. Additionally, optimizing glycaemic control through lifestyle modifications, pharmacological interventions, and patient education may help reduce the risk of elevated IOP and its associated complications. These findings underscore the importance of integrating ocular health assessments into the routine care of diabetic patients. Future research should focus on longitudinal studies to better understand the causal relationships between diabetes, IOP, and glaucoma, as well as the impact of glycaemic control interventions on IOP levels.

The study concluded that intra-ocular pressure (IOP) was higher in diabetic subjects compared to controls. Individuals with poor glycaemic control were more likely to experience elevated IOP, and a significant positive correlation was observed between IOP and HbA1c levels in patients with diabetic retinopathy. Therefore, the study suggests that diabetic patients should be routinely screened for both diabetic retinopathy and intra-ocular pressure. This proactive measure would help detect the development of ocular hypertension or early glaucomatous changes. Additionally, further research into the relationship between diabetes and ocular hypertension is recommended to better understand and potentially reduce the incidence of glaucoma among diabetic patients.

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