Primary open angle glaucoma (POAG) is a chronic, progressive optic neuropathy characterized by loss of retinal ganglion cells, optic nerve head cupping, and corresponding visual field defects. It represents one of the leading causes of irreversible blindness worldwide¹. The global prevalence of glaucoma is rising, with recent estimates suggesting that more than 110 million people will be affected by 2040, of whom the majority will have POAG². In India, POAG is a significant public health problem due to delayed diagnosis, poor awareness, and limited access to specialized care³. Traditionally, elevated intraocular pressure (IOP) has been considered the most important risk factor for glaucoma development and progression. However, not all individuals with high IOP develop glaucomatous optic neuropathy, while a subset of patients continues to show progressive optic nerve damage despite having IOP within the statistically normal range. These observations indicate that factors beyond IOP play a critical role in the pathogenesis of glaucoma. Among these, vascular dysregulation and impaired blood flow to the optic nerve head have received increasing attention⁴,⁵. Ocular perfusion pressure (OPP), defined as the difference between mean arterial pressure and intraocular pressure, is an important determinant of ocular blood flow. A reduction in OPP can compromise optic nerve head perfusion, leading to ischemia, axonal injury, and progression of glaucomatous damage¹,². Several population-based studies, such as the Barbados Eye Study and the Los Angeles Latino Eye Study, have demonstrated an association between low OPP and increased risk of glaucoma²,⁵. OPP is influenced by both systemic and ocular factors, making it a potential bridge between vascular health and optic nerve integrity⁴. The cup-to-disc ratio (CDR) is a widely used clinical marker to assess glaucomatous optic nerve damage. Progressive enlargement of the cup relative to the disc reflects structural loss of retinal ganglion cell axons³. Since CDR directly correlates with disease severity, it serves as a valuable clinical parameter for evaluating the extent of glaucomatous neuropathy⁶. Studying the relationship between OPP and CDR is important in understanding the vascular contribution to glaucoma pathogenesis. A strong correlation between reduced OPP and increased CDR would support the hypothesis that compromised ocular blood flow plays a significant role in optic nerve damage independent of IOP¹–³. Such evidence may have clinical implications for comprehensive glaucoma management, emphasizing not only IOP control but also systemic vascular health and blood pressure regulation⁵,⁷. Therefore, this study aims to evaluate the correlation between ocular perfusion pressure and cup-to-disc ratio in patients with primary open angle glaucoma through a cross-sectional design. By doing so, it seeks to provide further insights into the interplay between vascular factors and glaucomatous optic neuropathy.

This was a cross-sectional, observational study conducted at Sree Uthradom Thirunal Academy of Medical Sciences, Thiruvananthapuram, Kerala for a period of 18 months. Inclusion Criteria: Patients aged 40 years and above attending ophthalmology outpatient department with newly detected primary open angle glaucoma. Exclusion Criteria: 1. Presence of any other forms of glaucoma other than primary open angle glaucoma. 2. Patients who underwent surgical treatment for primary open angle glaucoma 3. Progressive Retinal diseases due to any cause other than glaucoma 4. Patients not willing to participate Sampling Method: Consecutive sampling Measurements: • Cup-Disc Ratio (CDR) was assessed by slit-lamp microscopy with a 90D lens and confirmed by OCT-RNFL³. • Intraocular Pressure (IOP) was measured using Goldmann applanation tonometry. • Blood Pressure was recorded in sitting position using a calibrated sphygmomanometer, and Mean Arterial Pressure (MAP) was calculated as: DBP + 1/3 (SBP–DBP). • MOPP was calculated using the formula: MOPP = 2/3 × MAP − IOP¹,². • Risk factor data included: age, sex, presence of diabetes mellitus (DM), and dyslipidaemia (DLP), obtained from patient records and fasting blood work⁴,⁵.

A total of 94 participants were included. The mean (±SD) MOPP was 47.52 ± 5.83 mmHg, while the mean worst-eye CDR was 0.783 ± 0.132 (Table 1). Variable Mean Standard Deviation N Mean Ocular Perfusion Pressure (MOPP) 47.52 mmHg 5.83 94 Worst Cup-Disc Ratio (CDR) 0.783 0.132 94 Table 1. Descriptive Statistics -Mean and standard deviation values of MOPP and worst eye cup-disc ratio in the study population. Correlation between MOPP and CDR: Pearson correlation revealed a modest but statistically significant negative association between MOPP and worst-eye CDR (r = –0.207, P = 0.023). In contrast, Spearman’s rank correlation was not significant (r = –0.094, P = 0.185), suggesting potential sensitivity to outliers or non-linear trends (Table 2, Figure 1). Test Correlation Coefficient (r) Significance (1-tailed) Pearson correlation -0.207* 0.023 Spearman correlation -0.094 0.185 Table 2. Correlation Between MOPP and Worst CDR: Pearson correlation showed a statistically significant negative correlation between MOPP and worst CDR (p = 0.023), while Spearman correlation did not reach statistical significance. *p < 0.05. Linear regression analysis: Simple linear regression confirmed that MOPP was a significant predictor of CDR (β = –0.207, P = 0.046). Specifically, each 1 mmHg decrease in MOPP corresponded to an expected 0.005-unit increase in CDR (R² = 0.043), indicating that MOPP explained approximately 4.3% of the variation in CDR (Table 3). Predictor B (Unstd.) Std. Error Beta (Std.) T p-value Constant 1.006 0.111 – 9.084 <0.001 MOPP -0.005 0.002 -0.207 -2.021 0.046 Model Fit R R² Adj. R² F p-value 0.207 0.043 0.032 4.086 0.046 Table 3. Linear Regression Analysis – Predicting Worst CDR from MOPP -Linear regression showed that MOPP was a statistically significant negative predictor of worst eye CDR (β = -0.207, p = 0.046), with a modest R² = 0.043, indicating MOPP explains approximately 4.3% of CDR variability. Figure 1-A scatter plot demonstrates the association between MOPP and CDR. While the slope indicates lower MOPP relates to higher CDR, the data points are widely dispersed (R² = 0.043)—suggesting that other factors contribute to optic nerve head morphology. Multivariate regression analysis: When adjusted for age, sex, diabetes mellitus, and dyslipidemia, none of these factors—including MOPP—showed independent significance in predicting CDR (all P > 0.05; Table 4). Variable F p-value Age 0.031 0.862 Sex 0.000 1.000 Diabetes Mellitus (DM) 0.393 0.535 Dyslipidemia (DLP) 0.393 0.535 MOPP 0.582 0.451 Table 4. Multiple Linear Regression: Influence of Risk Factors on Worst CDR-None of the included systemic variables (age, sex, DM, DLP) or MOPP were statistically significant independent predictors of CDR when adjusted for in a multivariate model Variable Mean Standard Deviation N Mean Ocular Perfusion Pressure (MOPP) 47.52 mmHg 5.83 94 Worst Cup-Disc Ratio (CDR) 0.783 0.132 94 Table 1. Descriptive Statistics -Mean and standard deviation values of MOPP and worst eye cup-disc ratio in the study population. Test Correlation Coefficient (r) Significance (1-tailed) Pearson correlation -0.207* 0.023 Spearman correlation -0.094 0.185 Table 2. Correlation Between MOPP and Worst CDR: Pearson correlation showed a statistically significant negative correlation between MOPP and worst CDR (p = 0.023), while Spearman correlation did not reach statistical significance. *p < 0.05. Predictor B (Unstd.) Std. Error Beta (Std.) T p-value Constant 1.006 0.111 – 9.084 <0.001 MOPP -0.005 0.002 -0.207 -2.021 0.046 Model Fit R R² Adj. R² F p-value 0.207 0.043 0.032 4.086 0.046 Table 3. Linear Regression Analysis – Predicting Worst CDR from MOPP -Linear regression showed that MOPP was a statistically significant negative predictor of worst eye CDR (β = -0.207, p = 0.046), with a modest R² = 0.043, indicating MOPP explains approximately 4.3% of CDR variability. Variable F p-value Age 0.031 0.862 Sex 0.000 1.000 Diabetes Mellitus (DM) 0.393 0.535 Dyslipidemia (DLP) 0.393 0.535 MOPP 0.582 0.451 Table 4. Multiple Linear Regression: Influence of Risk Factors on Worst CDR-None of the included systemic variables (age, sex, DM, DLP) or MOPP were statistically significant independent predictors of CDR when adjusted for in a multivariate model Figure 1-A scatter plot demonstrates the association between MOPP and CDR. While the slope indicates lower MOPP relates to higher CDR, the data points are widely dispersed (R² = 0.043)—suggesting that other factors contribute to optic nerve head morphology.

This study evaluated the relationship between mean ocular perfusion pressure (MOPP) and worst-eye cup–disc ratio (CDR), along with the influence of systemic risk factors such as age, sex, diabetes mellitus (DM), and dyslipidaemia (DLP). Our findings demonstrate a modest but statistically significant inverse correlation between MOPP and CDR, suggesting that lower ocular perfusion may be associated with greater optic nerve head cupping¹,². The Pearson correlation coefficient (r = –0.207, P = 0.023) and regression analysis confirmed that lower MOPP was a predictor of increased CDR, aligning with previous research highlighting the impact of ocular blood flow on optic nerve health¹–³. Though the explained variance was limited, this association emphasizes the importance of vascular factors in optic disc changes, especially in individuals without established glaucoma⁵. Interestingly, in the multivariate model adjusting for systemic variables, MOPP lost its statistical significance, and none of the included risk factors emerged as independent predictors of CDR. This may reflect the complexity of optic nerve head remodelling, which likely results from an interplay between ocular, systemic, and possibly genetic factors⁴,⁵. Several population-based studies have reported associations between CDR and systemic variables such as age, BMI, and metabolic syndrome components, albeit with variable consistency³,⁶–⁸. Our findings are concordant with prior studies that demonstrated compromised optic disc perfusion in patients with ocular hypertension and systemic diseases like diabetes and hypercholesterolemia⁶,⁷. The inverse relationship we observed reinforces the hypothesis that vascular insufficiency, as reflected by low MOPP, may contribute to optic nerve susceptibility, even in individuals not diagnosed with glaucoma²,⁵. Additionally, our scatterplot visualizes this trend clearly, showing a concentration of higher CDR values at lower MOPP levels. This may have diagnostic implications, suggesting that patients with borderline IOP but low MOPP could be at greater risk of optic nerve damage¹,².

This study demonstrates a significant inverse association between MOPP and worst-eye cup–disc ratio, suggesting that reduced ocular perfusion may be a risk factor for optic nerve head changes¹,². While systemic variables such as age, sex, DM, and DLP were not independently associated with CDR in this cohort, our findings underscore the need to consider vascular factors in optic disc evaluation³–⁵,⁷. Larger, longitudinal studies incorporating OCT-A and functional outcomes are warranted to further elucidate these relationships⁶,⁸.

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