European Journal of Cardiovascular Medicine

The human eye is a highly intricate organ that serves as the principal sensory system for visual perception. Its function is dependent on a dynamic equilibrium of structural integrity and physiological processes. Numerous ocular disorders manifest as a result of deviations in these physiological parameters, making their assessment indispensable in both the diagnosis and management of eye diseases¹.

Among the most critical physiological metrics are intraocular pressure (IOP), tear film dynamics, corneal thickness, ocular blood flow, and pupillary reflexes. Each parameter plays a unique role in maintaining ocular health. For instance, the regulation of IOP is vital for preserving the structural and functional integrity of the optic nerve head; derangements in this parameter are directly implicated in the pathogenesis of glaucoma². Likewise, alterations in tear film stability, as assessed by tear film break-up time (TBUT), are central to the diagnosis of dry eye disease, a condition with increasing global prevalence³.

Another crucial aspect of ocular physiology involves the cornea and its thickness, or central corneal thickness (CCT). CCT influences IOP measurements and is considered an independent risk factor for glaucoma progression⁴. Additionally, changes in ocular blood flow have been associated with various posterior segment diseases, including diabetic retinopathy and age-related macular degeneration⁵.

Pupillary response assessments provide valuable insights into the integrity of the afferent and efferent visual pathways. Conditions such as optic neuritis, commonly seen in multiple sclerosis, often present with a relative afferent pupillary defect (RAPD), highlighting the diagnostic relevance of pupillary examination⁶. The widespread availability of technologies such as optical coherence tomography (OCT), tonometry, pachymetry, and pupillometry has enhanced the clinician’s ability to assess these physiological metrics non-invasively⁷.

Despite the significant advancements in diagnostic technologies, many clinicians primarily rely on subjective patient symptoms for ocular disease identification, potentially delaying early intervention⁸. An objective, physiology-based assessment allows for earlier detection of subtle abnormalities, especially in asymptomatic or preclinical stages⁹. For example, minor elevations in IOP or subtle changes in TBUT can precede overt symptoms of glaucoma or dry eye, respectively¹⁰.

Moreover, the interplay between systemic conditions and ocular physiology cannot be understated. Systemic hypertension, diabetes mellitus, and autoimmune diseases can significantly impact ocular hemodynamics, tear production, and optic nerve function¹¹. Therefore, understanding ocular physiology also aids in recognizing systemic health implications.

This article aims to analyze the role of key physiological parameters in the clinical assessment of various ocular disorders. By correlating changes in IOP, TBUT, CCT, ocular blood flow, and pupillary responses with specific eye diseases, this study underscores the importance of integrating physiological assessments into routine ophthalmologic evaluations. Doing so may improve diagnostic accuracy, personalize patient management, and ultimately lead to better visual outcomes.

This study was a hospital-based, cross-sectional observational analysis conducted over a 12-month period in the Department of Anatomy, Physiology and Ophthalmology at a tertiary care teaching hospital. The objective was to evaluate physiological parameters—specifically intraocular pressure (IOP), tear film break-up time (TBUT), central corneal thickness (CCT), ocular blood flow (OBF), and pupillary response—and correlate them with commonly encountered ocular disorders.

Study Population

A total of 200 patients aged between 18 and 70 years were recruited using systematic random sampling from outpatient clinics. The participants were categorized into four primary diagnostic groups:

• Glaucoma
• Dry Eye Syndrome
• Optic Neuritis
• Healthy Controls

Each group consisted of 50 participants to ensure comparative evaluation.

Inclusion Criteria

• Adults aged 18–70 years
• Patients clinically diagnosed with glaucoma (open-angle or angle-closure), dry eye syndrome (per TFOS DEWS II criteria), or optic neuritis (confirmed via neuroimaging or visual evoked potential)
• Willingness to provide informed written consent

Exclusion Criteria

• Previous ocular surgery or trauma within the last 6 months
• Presence of corneal opacities or irregularities preventing accurate tonometry or pachymetry
• Patients with systemic neurological diseases (except multiple sclerosis in optic neuritis group)
• Use of systemic corticosteroids or immunosuppressants in the past 4 weeks
• Unwillingness or inability to comply with the study protocol

Data Collection Methods

All participants underwent a standardized ophthalmic examination including:

• Visual Acuity Testing using Snellen’s chart
• Slit-lamp Biomicroscopy for anterior segment evaluation
• IOP Measurement via Goldmann applanation tonometry
• TBUT performed using fluorescein dye under cobalt blue light
• CCT Measurement using ultrasonic pachymetry
• Pupillary Reflex Testing, including swinging flashlight test for RAPD
• OBF Assessment via color Doppler imaging (CDI) of the ophthalmic artery

Systemic parameters such as blood pressure, fasting blood glucose, and history of autoimmune or metabolic disease were recorded to identify confounding variables.

Ethical Considerations

The study adhered to the Declaration of Helsinki and received approval from the Institutional Ethics Committee (IEC No: OPH2025/011). Informed consent was obtained from all participants prior to any procedure.

Statistical Analysis

Collected data were analyzed using SPSS version 26.0. Descriptive statistics were calculated as means ± standard deviation for continuous variables and percentages for categorical variables. Intergroup comparisons were made using ANOVA and post-hoc Tukey’s test for physiological parameters. Pearson’s correlation coefficient was used to assess associations between physiological metrics and clinical severity scores. A p-value <0.05 was considered statistically significant.

Table 1: Physiological Parameters by Group

Glaucoma group had the highest IOP (mean 23.32 mmHg), significantly elevated compared to controls (14.13 mmHg), confirming its diagnostic relevance.

Table 2: Mean IOP by Group

Table 3: Mean TBUT by Group

The Dry Eye group exhibited markedly reduced TBUT (mean 5.98 sec), while controls had the highest TBUT (14.36 sec), confirming the presence of tear film instability.

Table 3: Mean Central Corneal Thickness by Group

Controls had the thickest corneas (mean 545.56 µm), while glaucoma patients had significantly thinner corneas (mean 519.03 µm), an independent risk factor for glaucoma progression.

Table 4: Mean Ocular Blood Flow by Group

Glaucoma group again showed the lowest OBF (mean 9.06 cm/s), reflecting vascular compromise. The highest flow was noted in controls (14.26 cm/s) and Dry Eye group (13.03 cm/s).

Table 5: Mean Pupil Reflex Time by Group

Optic neuritis group showed prolonged reflex latency (mean 351.52 ms), consistent with afferent pathway dysfunction. Control group had the shortest reflex time (mean 270.08 ms).

Table 6: Summary of All Parameters by Group

The present study evaluated key physiological parameters across four distinct ocular conditions: glaucoma, dry eye syndrome, optic neuritis, and normal controls. The results demonstrate significant differences among these groups in intraocular pressure (IOP), tear film stability (TBUT), central corneal thickness (CCT), ocular blood flow (OBF), and pupillary reflex time. These findings underscore the critical diagnostic and prognostic value of physiological assessment in ophthalmologic practice.

Elevated IOP was notably associated with glaucoma patients (mean 23.32 mmHg), consistent with the established role of IOP as a primary modifiable risk factor in glaucomatous optic neuropathy¹¹. These findings align with previous large-scale studies such as the Ocular Hypertension Treatment Study (OHTS), which demonstrated that even modest reductions in IOP significantly decrease the risk of progression to primary open-angle glaucoma¹². Our findings support routine tonometric screening in high-risk populations.

TBUT was markedly reduced in dry eye patients (mean 5.98 seconds), reinforcing its diagnostic utility. This result corroborates with the Tear Film and Ocular Surface Society (TFOS DEWS II) recommendations, which identify TBUT <10 seconds as indicative of tear film instability¹³. Moreover, reduced TBUT in glaucoma patients may reflect long-term use of preserved topical medications, a known contributor to ocular surface damage¹⁴. Early detection of TBUT abnormalities can prompt timely initiation of tear supplements and preservative-free regimens.

CCT was thinnest among glaucoma patients (mean 519.03 µm), which is an independent risk factor for glaucoma progression and may lead to underestimation of IOP during applanation¹⁵. The Baltimore Eye Survey and the European Glaucoma Prevention Study also reported that patients with thinner corneas are at increased risk of optic nerve damage, even at normal IOP levels¹⁶. These results advocate for routine pachymetry in glaucoma workup to contextualize IOP readings.

Ocular blood flow (OBF) analysis revealed reduced flow in glaucoma (mean 9.06 cm/s) and optic neuritis (10.77 cm/s) groups compared to controls (14.26 cm/s). Reduced OBF in glaucoma has been implicated in optic nerve ischemia and progression of visual field defects¹⁷. In optic neuritis, impaired OBF may reflect inflammatory disruption of neurovascular coupling¹⁸. CDI-based assessment of OBF is increasingly recognized as a non-invasive method to detect subclinical vascular insufficiency.

Pupillary reflex time was prolonged significantly in optic neuritis patients (mean 351.52 ms), consistent with afferent pathway dysfunction. This aligns with classical descriptions of relative afferent pupillary defect (RAPD) in demyelinating optic neuritis¹⁹. Objective pupillometry provides a quantifiable measure that can supplement clinical examination, especially in subtle cases.

Overall, the data emphasize the value of objective physiological testing in detecting, differentiating, and monitoring ocular disorders. The integration of these parameters into routine ophthalmic examinations offers a more comprehensive approach, enabling clinicians to identify subclinical changes, tailor interventions, and improve long-term visual outcomes.

This study demonstrates the essential role of physiological parameters in the comprehensive evaluation of ocular disorders. Each of the evaluated metrics—intraocular pressure (IOP), tear film break-up time (TBUT), central corneal thickness (CCT), ocular blood flow (OBF), and pupillary reflex time—was significantly altered in patients with glaucoma, dry eye syndrome, and optic neuritis compared to healthy controls. These parameters not only serve as diagnostic indicators but also provide prognostic insight and help monitor disease progression.

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